INTRODUCTION TO THE CARDIAC ROOM

Division of Cardiac Anesthesia, Beth Israel Deaconess Medical Center

REV 3/08 abl

Overview Welcome to the Division of Cardiac Anesthesia and the heart room. Your rotation in cardiac

anesthesia will likely be memorable both because of its high level of demand and greater level of reward. Our Division expects your highest level of commitment. We expect you to know the contents of this handout as well as level appropriate knowledge of cardiovascular physiology and cardiac anesthetic principles when you start.

Review your basic cardiovascular physiology before starting this rotation! All of our

expectations are spelled out in our Resident Expectation outlines included with your syllabus materials. Please play an active role in your own education by reading your provided texts and available peer-reviewed articles. We can only help to build your knowledge base if you provide a foundation for us.

The Cardiac operating rooms require respect – not fear! Good communication is critical.

You must speak clearly and professionally. Repeating requests is a very good idea whether they come from nurses or surgeons. Most importantly, if you are unsure about something ask!

You may be asked to give talks during your rotation. The topic and a mentor will always be

provided. Please attend all Division related talks. They occur every Wednesday, with occasional exception, at 4 pm in the west campus anesthesia library. At the end of your rotation you will be given an oral examination. This exam will cover level appropriate cardiac anesthetic issues. It will serve to give us some objective information on your knowledge base and give you practice for your oral boards. You and the Residency Director will be given feedback on your performance.

We want you to enjoy your experience! We are always available to you for any and all issues – do not hesitate to call on us.

This handout is intended to orient you to some basic principles of cardiac anesthesia and how

we conduct our cases on a daily basis. It is not intended to be a comprehensive manual of cardiac anesthesia and thus should not take the place of suggested textbook readings. Keep in mind that our practice continually evolves and that some of our practices outlined within may have changed. Enjoy!

PREOPERATIVE EVALUATION OF CARDIAC SURGICAL PATIENTS

You should perform your usual history and physical, paying special attention to the following:

1) Exercise tolerance is extremely useful information that gives an overall picture of a patient’s cardiovascular and pulmonary status. Ask patients how far they can walk, flights of stairs that they can navigate, etc.

2) Bleeding history - pursue all abnormal coagulation studies, especially platelet count for patients on heparin as potential evidence for heparin induced thrombocytopenia. Investigate the potential for subclinical liver disease that may predispose the patient to clotting difficulties during and after the procedure. Pay special attention to any and all

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antiplatelet medications the patient may have taken in the past few days. Examples include clopidogrel (Plavix), tirofiban (Aggrestat), eptifibatide (Integrilin), ticlodipine (Ticlid) and abciximab (ReoPro).

3) History of reflux, hiatus hernia, odynophagia, dysphagia, esophageal diverticulum (e.g. Zenker’s), esophageal varices, gastric and/or esophageal surgery, and chest wall radiation (see attached contraindications to TEE).

4) Cerebrovascular disease, including auscultation for carotid bruits. 5) Pulmonary function in smokers and patients with a history of pulmonary disease. Assess

the patient clinically and investigate any studies which have been done including pulmonary function tests, chest x-ray, CT, etc.

6) Evaluate radial pulses. Be sure to check blood pressures in both arms. Some patients may have a significant arterial stenosis in one arm causing falsely low blood pressure readings. Place the arterial line in the arm with the higher blood pressure, or in a femoral artery. If the left arm has a lower pressure, make sure the surgical team is aware, since there may be reduced blood flow in the left internal mammary artery, making it a poor choice as conduit for bypass grafting.

7) Check labs, ECG, and cardiac cath data. When evaluating the ECG pay special attention for the presence of bundle branch blocks, particularly LBBB, which may cause difficulties when placing a pulmonary artery catheter. Standard preoperative laboratory evaluation should include CBC with platelet count, PT (INR), PTT, chemistries for sodium, potassium, chloride, serum bicarbonate, BUN, creatinine, glucose and LFTs. If current data is not available, write an order for the appropriate studies to be drawn.

8) Always discuss your plans with your attending or an available cardiac anesthesiologist after seeing the patient. Present the patient’s history, exam, and relevant lab studies in an orderly and concise fashion.

9) Evaluate the patient’s renal function, noting BUN and creatinine and any episodes of acute renal failure or conditions predisposing the patient to renal disease (e.g. diabetes). If the patient is requiring hemodialysis, note the time of last dialysis, whether the plan is for intraoperative hemodialysis, etc. Note the patient’s electrolyte status.

10) Note all medications the patient was taking at home and in the hospital (if different) and any drug allergies. Specify the specific allergic manifestations.

Your appearance when seeing patients should always be professional.

It is YOUR responsibility to see that the patient is appropriately evaluated

preoperatively regardless of whether you are performing the preop, or someone else is doing the preoperative evaluation for you. You are expected to call the Main operating room desk at (75)4-3000 before going home for the evening to see if any cases have been booked, added to, or changed in your room. Cases that are booked before 5pm are YOUR responsibility to preop. Cases booked after 5pm may be seen by the call team but it remains YOUR responsibility to see that a complete evaluation has been performed and that any additional tests, conversation with the surgical team, etc. has been completed. You are strongly encouraged to see ALL of your own preops. This establishes your role as a member of the perioperative care team, earns respect from the surgical team, and maximizes your educational experience. You will also know your patients better and, as a result, will provide superior care.

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PREMEDICATION

Otherwise healthy patients presenting for cardiac surgery should be premedicated with a benzodiazepine (usually midazolam or lorazepam). Rarely, a narcotic may be required and added to the regimen. A common premedication used in otherwise healthy in-house patients is lorazepam 1-2 mg PO hs on the night preceding surgery and repeated on the morning of surgery. Elderly and debilitated patients receive minimal premedication, as do patients with valvular heart disease, since unmonitored changes in preload and afterload can cause rapid hemodynamic decompensation. “Late Hearts” may benefit from benzodiazepines PO at approximately 7:00 A.M. and then again when “on call” to the OR. There is a trend towards giving less premedication; discuss this with your attending prior to writing the order. Never order a premedication to be given intravenously unless you plan on being with the patient from that point forward or have arranged for appropriate nursing coverage.

Patients who are coming to surgery from an intensive care unit (CCU, MICU, NSICU,

TSICU, or CSRU) should be sedated per ICU protocol, until an anesthesiologist is present, usually on the day of surgery during line placement.

All cardiac medications are continued as usual. Exceptions include diuretics and digoxin

(unless it is being given for rate control of atrial arrhythmias, in which case it should be continued). Preoperative orders should be written clearly and in detail. Specify the cardiac medications to be continued and those medications to be held. IV nitroglycerin and IV heparin should be continued throughout the preoperative period until leaving the prep/holding area at which time the heparin should be discontinued (unless the patient is ischemic). The nitroglycerine should be continued at least until induction of anesthesia since abrupt withdrawal of nitrate therapy may result in myocardial ischemia.

Finally, write an order stating that the patient should be transported to the OR by 6:30 A.M. on Mondays, Tuesdays, Thursdays, and Fridays and 8:00 AM on Wednesdays. The patient should be transported on a stretcher with 6 liters of 02 by face mask. Patients with orthopnea should be transported with their head elevated 30 degrees. Patients should be brought into the operating room between 7:00 and 7:10 AM on all days except. Wednesdays, when they should be brought to the OR at 8:45 AM. The goal is to have anesthetic induction completed by 7:45 AM (9:30 on Wednesday). If a patient is coming from an intensive care unit, it is necessary for the anesthesia team to transport the patient to the operating room. Peripheral lines (IVs and a-line) should be placed prior to transport. Plan accordingly and always leave time for unexpected delays.

ROOM SETUP Machine checkup and airway equipment

Your setup must be completed in timely manner that allows you to get to your patient with enough time to place your preoperative lines. Always defer room setup if there comes a choice between preparing the patient and finishing the room setup. If for some reason this situation occurs, you are expected to notify your attending and inform

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him/her of what aspect of the setup is incomplete so that it can be done. THIS SHOULD NOT HAPPEN OFTEN!

Complete a machine checkup as you would for any other case, including a check of the level of O2 cylinder. Remember to check vaporizers and fill them as needed. Airway equipment should also be set up, including 7.0 and 7.5 styleted ET tubes and auxiliary equipment as required by the procedure, e.g. need for lung isolation, or by the patient.

Medications and drips A cardiac “brown bag” containing many of the necessary vasoactive medications should

be retrieved form the OR pharmacy or Omnicell unit off hours. Please place a patient sticker on this bag and bring it with you to the ICU with the patient so that the nursing staff there can use the remaining medications.

Phenylephrine and nitroglycerine pre-mixed syringes should be placed on infusion pumps, appropriately primed, i.e. purged on the infusion pump using the purge button, and programmed for the correct infusion protocol and patient weight. You can leave the pump on as long as the charging cable is attached. Other vasoactive drips may be required in certain circumstances based on patient condition and preoperative infusions already running.

Every cardiac patient requiring cardiopulmonary bypass will receive an antifibrinolytic medication prophylactically to reduce blood loss. Our current medication is tranexamic acid. This medication is dosed based on patient weight and renal function. A dosing guide is available in every cardiac room and a dosing calculator is available on line through your AIMS links tab. Generally, the cardiac anesthesia technicians prepare this for you but you should know how to set up when necessary.

A typical tray setup should include:

• Induction agent as determined by anesthetic plan

• 20 cc syringe of fentanyl

• 5 mg midazolam diluted to 1 mg/cc

• Pancuronium 10 mgs

• Succinylcholine 100 – 200 mgs *

• Atropine 1 mg *

• Ephedrine 50 mgs, diluted to 5 mg/cc

• Multiple phenylephrine syringes (100 mcg/cc) *

• Calcium chloride 1 gram (100 mg/cc)\

* = medications that are premixed by pharmacy

Some attendings like to have diluted nitroglycerine 40 mcg/cc available for bolus administration. This can be accomplished by removing 1 ml of the nitroglycerine in your large infusion syringe and diluting it with 9 mls of saline. Other medications may be required based on specific patient or case related issues.

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IVs and tubing Every patient will require two IV infusions using the “Y-piece tubing” that allows for transfusion of blood products. One of these infusions will run through the fluid warmer which is located on the base of the left IV pole. Generally lactated ringers is used as infusate although patients with renal issues may require normal saline. Another infusion, using normal saline running through microdrip tubing is set up for eventual connection to the “gang of 5” connector and central access line. This will hang from the left side IV pole. A rapid infusion device, i.e. “level – 1”, may be required for some cases.

Monitors Usually the cardiac anesthesia techs will setup the necessary transducer set. If the transducers are not setup, either talk to the techs or setup a triple transducer appropriately connected to the monitor and zeroed. Please make sure the defibrillator in the room is on and functioning. Some cases, e.g. minimally invasive surgeries and redo sternotomies, require defibrillator pads (R2 pads) to be placed on the patient prior to surgical prep. Please have the tech retrieve them if you can’t find them.

Make sure that all necessary supplies for placing your central access are available and collected neatly near your other supplies. These include:

• Universal introducer kit

• 9 Fr introducer cordis and PA catheter if using

• 2 or 3-lumen CVP line

• Gown

• Appropriate sized sterile gloves

If a continuous cardiac output/oximetric PA catheter is used, the techs will generally perform the necessary setup and calibration. It is important that you learn from the tech or your attending how to perform this setup so that you could do so in a situation where you had to.

An Echo machine should be present in the room, along with the appropriate TEE probe. Once again, the technician will generally take care of this responsibility.

There are several other specialized devices that may be required, e.g. arctic sun warming device, etc. Your attending should discuss this with you during the preoperative planning stage and notify you what you are responsible to prepare.

THE HOLDING AREA

The patient should arrive in the holding area by 6:30 AM. Inform your attending if the patient does not arrive on time. When the patient arrives in the holding area on the morning of surgery, you must initially check the following: 1) Patient identification 2) Level of consciousness

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3) Blood pressure, heart rate and rhythm, oxygen saturation 4) Patient record - be sure that the patient has received his pre-medication as ordered and that

NO PROBLEMS HAVE ARISEN DURING THE EVENING PRIOR to the surgery. If any questions arise, do not hesitate to contact the patient’s floor nurse.

5) Patient’s should always be appropriately sedated for the placement of peripheral lines. Place, preferentially, a 14 or 16 gauge IV in each hand or arm. Be careful not to place IVs in locations where they may be affected by position, e.g., on the dorsum of the hand on the same side where the a-line is placed. If the arterial blood pressures are equal in both arms, place a right radial a-line in the patients who will be receiving a left internal mammary artery grafts (assume this will apply to all patients). A right sided arterial line is necessary in these patients to avoid loss of pressure monitoring which occasionally occurs when the LIMA retractor is used. If the surgeon is planning on using a radial artery for conduit, do not place any lines, including IVs, in that arm (usually the non-dominant hand). You must be absolutely certain that your peripheral lines are properly placed and functioning since the patient’s arms will be tucked at his/her side during the procedure and you will not have the opportunity to manipulate any existing lines, or place new ones.

6) Prophylactic antibiotics should be administered before surgical incision but no more than one hour prior to incision. Patients admitted to the hospital on the day of surgery and without contraindication should receive cefazolin 2 gms as close to the surgical incision as possible but always within 30 minutes of the incision. If it has been greater than 90 minutes since the cefazolin administration and the incision, the cefazolin should be re-dosed. The cefazolin should be re-dosed every 4 hours during the procedure. In cases where cefazolin is not used, vancomycin 1 gm and ciprofloxacin 400 mgs should be given. The vancomycin and ciprofloxacin infusions should finish within 90 minutes of the incision. If over 210 minutes has elapsed since the end of the infusions and the surgical incision the antibiotic should be re-dosed at an appropriate dose based on the renal function of the patient (may require ID/pharmacy consult). Vancomycin and ciprofloxacin should be re-dosed every 8 hours intraoperatively. MOST IMPORTANTLY, MAKE SURE THAT YOUR RECORD ACCURATELY REFLECTS WHEN YOU GAVE THE ANTIBIOTIC. DON'T LET THE DOCUMENTED TIME SIMPLY REFLECT WHEN YOU GOT AROUND TO ENTERING IT INTO YOUR RECORD. If administration occurs in the preop holding area it is imperative that the nurses in that area are made aware and vital signs monitored appropriately to insure an untoward reaction does not go unnoticed. Our standard antibiotic regimen does occasionally change - ask your attending for the current protocol if you are unsure.

7) A baseline arterial blood gas will be drawn in the operating room after induction of anesthesia. However, this may done in the holding area if dictated by specific circumstances. Preoperative cardiac enzymes may be advisable in patients who have been unstable /ischemic.

8) Consider performing a preoperative ECG in the holding area if there has been any change in the patient’s status. Review the ECG paying special attention to differences from previous ECGs.

9) Same day admit (SDA) patients may also need a “clot” drawn and sent to the blood bank so that blood may be typed and crossmatched. Send this off immediately after your initial IV or arterial line placement to minimize any delays.

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10) If a patient is coming to the OR from an intensive care unit, place the peripheral lines (IV and a-line) in the intensive care unit prior to transport. The patient is then taken directly to the operating room from the ICU. These patients must be monitored with at least ECG, blood pressure, and pulse oximetry and transported with a defibrillator and resuscitation drugs. The patient should receive 6 liters of 02 by face mask during transport.

11) In advance of intraoperative TEE monitoring, ask the patient about esophagogastric pathology (e.g.dysphagia, odynophagia, symptoms of Zenker’s diverticulum, chest wall radiation, esophageal surgery, etc.). Ideally, this discussion will take place during the preoperative evaluation so that any issues can be addressed at the appropriate time. Document this discussion on the preoperative anesthesia record. If there is a question regarding a patient’s candidacy for TEE, contact one of the cardiac anesthesia attendings and discuss the problem.

OPERATING ROOM

Upon arrival in the operating room, transfer the oxygen source from the portable tank on the stretcher to a wall source or to the anesthesia machine. Transfer the patient from the stretcher to the operating room table making sure not to tangle any lines. Take special care to ensure that any infusions are not interrupted.

A manual blood pressure cuff may be placed on the arm which has the a-line. The two

readings should be compared. The ECG leads, pulse oximeter, IV lines, and a-line will-usually be connected by the anesthesia technician and attending anesthesiologist while the resident/fellow begins pre-oxygenation. If the central line is to be placed prior to anesthetic induction (unusual), the resident/fellow will proceed to scrub while the monitors are being applied. Always check with the attending anesthesiologist what the plan is regarding timing of central line placement.

We typically monitor three ECG leads simultaneously: II and AVF on the anesthesia

machine monitor, and II and V5 on the auxiliary monitors (refer to cardiac anesthesia technician responsibilities for correct monitor setup). ECG amplitude should be calibrated and ST segment measurement points set immediately after placement of the ECG leads, prior to anesthetic induction. Intra-aortic balloon pump ECG leads (“skin leads”) may be placed preoperatively if IABP placement is anticipated or considered likely.

All patients have central access of some sort – either a 2 or 3 lumen CVP or a pulmonary

artery catheter. You must scrub and wear appropriate sterile attire to place these lines. You are expected to know how to appropriately scrub and don this attire. A no-touch technique will be used for putting on gloves. If you do not know how to do this, inform your attending so that he/she can instruct you. An internal jugular approach is preferred over an external jugular approach as there is a failure rate of approximately 15% in passing the J wire by the external jugular route. Subclavian cannulation is less desirable since our access to the catheter is limited and violation of the sterile surgical field is more likely. Once you have located the internal jugular vein with the 22 gauge finder needle and then with the 18 gauge thin-walled needle, make sure you have not accidentally punctured the carotid artery. Suggested safeguards include:

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• Having your attending or other qualified assistant confirm correct wire placement

by TEE • Checking the color of the venous blood in the finder syringe against a sample of

arterial blood drawn from the a-line. • Checking the oxygen saturation of a sample from the finder needle (i.e. send an

ABG). • Passing an angiocath over the wire, remove the wire and observe for

nonpulsatility of flow. • Transducing the angiocath.

These methods ensure that the wire is in a vessel and that it is in the correct vessel. This

is a reliable means of assuring that a vein has been accessed. Be sure the defibrillator is receiving a signal from the ECG prior to passing the J wire.

Passing the wire into the heart can cause ventricular tachycardia, VPC’s, RBBB, APC’s and/or atrial fibrillation. Special care must be taken when inserting the J wire, and subsequent PA line, into patients with pre-existing LBBB since complete heart block may occur in 1-5% of patients. You should consider what hemodynamic compromise may occur in your patient if complete heart block results and use this as a guide as to the alternate means of pacing you would like to have available. You are expected to know how to use the defibrillator – what energy is necessary, when to synchronize, how energy is delivered. If you are not sure, ask your attending for a tutorial. It is not necessary to pass the J wire more than a few centimeters beyond the tip of the intravenous cannula. A good rule of thumb is to insert the wire only until the proximal end of the wire is level with the top of the patient’s head. A TEE probe can be used to help guide wire depth. The introducer with dilator, or central line, is then inserted over the wire in typical Seldinger fashion. The line is then sutured in place. Make sure that all connections are properly tightened as they are frequently loose when packaged by the manufacturer. In very short patients you may wish to suture the cordis after placement of the PA line in the event it needs to be withdrawn slightly. Remove all air from the line using a syringe. Connect the side port to the carrier tubing through a “gang of 5” connector and begin a slow carrier infusion.

Prior to inserting the PA catheter (PAC), make certain the thermistor is functioning

properly by connecting it to the cardiac output computer and observing a temperature of approximately 21°C (room temperature). The cardiac anesthesia technician or assistant will then connect the CVP, PA, and proximal infusion ports (VIP) to their respective transducers and flush. Inflate the balloon on the distal tip of the PAC and flush the distal port. This assures that the balloon is functioning properly and will not occlude the distal tip of the PAC when inflated. The balloon should inflate symmetrically. Place the pulmonary artery pressure scale on 60mm Hg and shake the catheter tip observing the screen for fluctuations in the pulmonary artery pressure trace. The continuous flush device of the transducer may be tested by occluding the distal port of the PAC and observing a slow rise in the pressure tracing on the screen. This also checks that the PA transducer cable is connected to the distal port of the PAC. Insert the PAC to 20 centimeters, inflate the balloon, and begin advancing the catheter. Observe the characteristic pressure tracing in each cardiac chamber. Consider not wedging the catheter in patients who are

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heparinized or who have severe pulmonary hypertension or severe mitral regurgitation, as rupture of a pulmonary artery could result in catastrophic hemorrhage. After the PAC has been floated into place, deflate the balloon and secure the introducer with a suture, if not already done. Record baseline hemodynamics, cardiac output, and treat as necessary.

INDUCTION OF ANESTHESIA

Immediately prior to induction, observe the patient’s ECG for rate, rhythm, ST segment deviation and any conduction abnormalities. If not already done, calibrate the ST segments and establish measurement points. If a PAC is already in place, note baseline filling pressures including CVP, PA, and, if relevant, pulmonary wedge pressures. Measure and record a baseline cardiac output. Take an average of 3 cardiac outputs measured at end expiration (they should be within 10% of each other). In patients receiving positive pressure ventilation it may be easier to temporarily place the ventilator in the “bag” position while performing the cardiac output measurements. Note the patient’s heart rate and make a mental note of the stroke volume. At this time, it is crucial that any gross derangements in hemodynamic parameters be corrected. For example, a common situation is low intravascular filling pressures due to inadequate replacement of overnight insensible and urinary losses. If induction of anesthesia is allowed to proceed while the patient is relatively hypovolemic, one can expect hypotension to ensue. Optimal hemodynamic function can be determined by serial cardiac output measurements after crystalloid infusion, i.e., the construction of a Starling curve.

Induction of anesthesia is accomplished most easily and safely by a “graded stimulus”

technique. The patient is preoxygenated and a “priming dose” of muscle relaxant (typically 1 mg pancuronium) is injected. “Priming” is necessary to reduce the chest wall rigidity that can result from the use of a higher dose narcotic induction. It is believed that the muscle rigidity is the result of central dopaminergic antagonism by the synthetic opioids fentanyl and sufentanil. Evidence suggests that the nucleus raphe pontis is an integral central site responsible for opioid induced rigidity. Chest wall rigidity may impair the ability to adequately ventilate the patient. Should this occur, succinylcholine will reduce, and eventually eliminate, this problem.

Approximately two minutes after the priming dose, administration of narcotics is initiated

(5-15 ug/kg fentanyl or .5-1.5 ug/kg sufentanil). Administration of narcotics is carried out over a 2 to 5 minute period of time while maintaining verbal contact with the patient to assess the level of consciousness. It is also helpful at this time to keep one hand on the bag of the breathing circuit to judge the depth and rate of respiration. Once confirmation of adequate opioid effect for induction has occurred, an appropriately dosed induction agent is administered. The remainder of the muscle relaxant is injected to facilitate intubation. As the patient loses consciousness and respirations become depressed, the anesthesiologist gently takes over ventilation by hand. Depth of anesthesia is initially assessed by inserting an oropharyngeal airway. If there is no hemodynamic response, the depth of anesthesia is presumed to be adequate and the Foley catheter is inserted. Again, if there is no hemodynamic change, it can be assumed that the depth of anesthesia is adequate and laryngoscopy and endotracheal intubation can be performed. A

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graded stimulus induction technique affords some protection against hazardous increases in blood pressure and heart rate which can occur if depth of anesthesia is inadequate.

The above technique describes the “traditional” technique of anesthetic induction using

graded stimulation and high dose narcotic. Over the past 5-10 years, it has become apparent that cardiac surgical patients can be anesthetized safely using much lower doses of narcotics. Likewise, it has been realized that these patients do not need to stay intubated and sedated for a predetermined length of time. This so-called “fast-track” theory of cardiac surgery and anesthesia was initially applied to only the youngest and healthiest of our patients, but the role of this technique has been expanded over the past few years to include all but the sickest of patients. It is now our practice that all cardiac surgical patients should be considered “fast-track” until proven otherwise. In simple terms, this means that when the surgery is over, so should the anesthetic. Please plan accordingly. A typical “fast-track” anesthetic is described in the section on “Off-pump coronary artery bypass” procedures.

Immediately after induction, tape the eyes and place an orogastric tube and nasal

temperature probe. The tip of the nasal temp probe should be in the posterior pharynx, where it is closest to the base of the brain. An OG tube is placed, suctioned and then removed and the TEE probe is inserted. The probe should not be manipulated during the patient prep. While the patient is being prepped and draped, it is a good time to check the blood in the cooler. All patients having cardiac surgery for the first time (primary procedures) should have four units of PRBCs typed and crossed at the beginning of the procedure (2 units will be in the cooler). Patients who are either having a redo procedure or have a difficult crossmatch should have at least 6 units PRBCs available (4 units in the cooler). If you wish to deviate from this protocol, notification to the blood bank is required and is best dealt with either early on the morning of surgery or the day prior to surgery. A post-induction arterial blood gas should be drawn along with a sample for measurement of baseline ACT. During the pre-bypass period, keep the following times of increased stimulation in mind: skin incision, sternotomy, pericardiotomy, and aortotomy. The ventilator should be turned off during the sternotomy (sawing) to minimize pulmonary injury. When the proximal portion of the internal mammary artery (IMA) is being taken down and/or when right sided cardiac structures are being worked on (atrial cannulation, retrograde (coronary sinus) cannula placement, etc.) you may consider either hand ventilating the patient and/or decreasing tidal volumes so that surgical exposure is maximized.

Remember to draw all ACTs through a port not exposed to heparin, i.e. the side port of

the cordis (if a PA line was inserted), the arterial line, or through one of the CVP ports other than the one that the heparin was given through.

There is a strong correlation between blood glucose levels and the incidence of sternal

wound infections, with a large increase occurring above a serum glucose of 200 mg/dl. Please familiarize yourself with our protocol for treating elevated blood glucose levels. A copy of the protocol is included in your introductory material and is posted in all of the cardiac operating rooms. Please note that patients are classified based on their history of insulin use and their initial blood glucose on the post-induction ABG. Please ask if you have any questions regarding this important topic.

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HEPARINIZATION

The patient is heparinized for bypass when all purse strings have been placed in the aorta. Frequently, the surgical team will ask for a smaller dose, usually 5,000 units, just before the distal IMA is ligated. Heparin dosing for bypass is determined by the Hepcon device operated by the perfusionist. This device determines a heparin dose-response curve for every patient from a blood sample drawn shortly after anesthetic induction. Remember that 1 mg of heparin is equivalent to 100 units. Although we try to talk about heparin dose in units, some practitioners will refer to mgs. Please ask if you are confused about this conversion. Inject heparin into the CVP port of the PA line, or if not using a PA line, inject it into one of the CVP ports. Before injecting, draw back and observe for blood return. Injecting heparin into a central line after you have observed blood return assures that the heparin has not been injected into the subcutaneous space which might occur if a peripheral IV were used. Be sure to flush the port after injecting the heparin. Heparin should be given over approximately one minute to minimize the hypotension associated with its administration (histamine release and calcium chelation). Always communicate with the perfusionist the amount of heparin given, and the time it was given. Draw an ACT after 3 minutes. Please draw your ACT from a different port through which you gave the heparin. The ACT should be greater than 400 seconds before allowing the initiation of bypass. If the ACT is less than 400 seconds, additional boluses of heparin are given and the ACT is repeated. The dose of heparin will be determined by a discussion between the anesthesia and perfusion teams. Heparin resistance is mostly likely due to a diminished amount of circulating antithrombin III (ATIII), which may have to be exogenously supplied. The preferred source of antithrombin III is “liquid plasma” which is FFP that has been thawed for more than 24 hours. Although some of the clotting factors in liquid plasma will be deficient (particularly factor VII), the ATIII levels are preserved. Standard FFP is used if liquid plasma is unavailable. An alternative source of ATIII is “lyophilized ATIII” which is supplied in reconstituted form by the blood bank. Lyophilized ATIII is a recombinant form of ATIII and therefore is not associated with blood borne pathogens. Unfortunately, it also very expensive and not available to us at this time.

GREAT VESSEL CANNULATION

For cardiopulmonary bypass to be established, the patient’s venous blood must be delivered to the bypass circuit and returned to the arterial circulation. The most common way to do this is by cannulating the right atrium for venous return (to the pump) and cannulating the ascending aorta for arterial return (to the patient). Alternatively, femoral vessels may be used for a variety of reasons.

During aortic cannulation, wall stress must be reduced to avoid intimal tearing and vessel

dissection. Reduction of aortic wall tension is achieved by reducing wall pressure and the change in wall pressure with time (dp/ dt). Systolic blood pressure is decreased to approximately 100 mm Hg and tachycardia is avoided. Patients with left main coronary artery disease and/or aortic stenosis are particularly challenging since decreasing perfusion pressures by even this small degree may precipitate ischemia. Systolic blood pressure is allowed to rise slightly after aortic cannulation in anticipation of venous cannulation.

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Venous cannulation is accomplished via either a single 2-stage cannula (typically) or

separate SVC and IVC cannulae. Placement of the cannulae may be associated with arrhythmias such as atrial fibrillation or atrial flutter. Be sure that the defibrillator is operational and in the “sync” mode prior to venous cannulation. Additionally, if venous cannulation is difficult, rapid blood loss may occur through the atriotomy resulting in hypotension. It is therefore important to maintain adequate intravascular volume prior to and during venous cannulation. Remember, the patient may be transfused via the aortic cannula: always check with the surgeon to make sure that all the connections have been secured and the tubing has been de-aired first. The last cannula to be placed prior to CPB is the retrograde cardioplegia catheter. It is placed through the right atrium into the coronary sinus (CS). The surgeon must place his hand under and behind the heart to feel the CS and guide the catheter into position. This frequently results in hemodynamic compromise and may necessitate early institution of CPB. Pay attention!

The surgeon may hand you a monitoring line for cardioplegia pressure monitoring. Most

surgeons monitor only the retrograde pressure (via CS catheter), but some also monitor the pressure while giving antegrade cardioplegia in the aortic root. It should be connected to the PA transducer if you are using only a CVP, or to the CVP transducer (with a male-to-male connector) if you are using a PAC so that you can continue to monitor PA pressures during bypass which will help you determine the adequacy of venous drainage. Do not flush this line unless the surgeon asks you to so that air is not accidentally injected into the patient. Communicate to the surgeon and perfusionist which tracing will be used to monitor this pressure.

CARDIOPULMONARY BYPASS

Upon initiation of cardiopulmonary bypass, check the following:

1) Ensure adequate muscle relaxation. Typically an additional dose of pancuronium is given just prior to, or coincident with, initiation of CPB. This is so that the patient will not shiver when cooled which would result in increased oxygen consumption, or possible muscle breakdown with potential myoblobinuria, renal failure, etc.

2) Venous return - make sure the venous line is draining blood to the pump reservoir. At our institution, CPB flow is nonpulsatile and therefore only a MAP is followed. If the arterial trace is pulsatile, it indicates that blood is entering the left ventricle somehow. There are 3 possibilities:

a) the aortic valve is incompetent and the LV is filling retrograde from the aorta (the PA trace will be nonpulsatile)

b) venous return is not complete to the reservoir and therefore blood is being conducted in antegrade fashion to the LV (the PA trace will be pulsatile)

c) there is significant noncoronary collateral circulation. Assess and treat as appropriate

3) Oxygenation - check the color of blood in the pump arterial line to make sure oxygenation is occurring (compare it to the venous blood) in the reservoir. Check with the perfusionist to be sure he/she feels that bypass is adequate before shutting off the ventilator. Do not shut off the ventilator until you observe oxygenated blood returning to the patient from the bypass circuit.

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4) Communicate to the perfusionist if the patient was requiring an unusual dose of vasopressor, inotrope, or vasodilator during the prebypass period.

5) Check the patient’s head and sclera for swelling. Swelling may occur if superior vena cava blood drainage is inadequate.

6) Decrease ambient room temperature. 7) Continue to check urine output at 30 minute intervals throughout the bypass period. 8) Withdraw the PA catheter 2 0r 3 cm so that if it migrates distally it will not cause

pulmonary artery rupture. While the patient is on CPB observe the construction of the distal and proximal anastomoses.

Anastomotic quality, as judged by the surgeon, has been shown to be a strong predictor of patient outcome in cardiac surgery. Prepare any drugs anticipated for the postbypass period, such as magnesium, calcium and/or inotropes/pressors. Sitting with the perfusionist and discussing CPB management strategies is also a good idea during this time. While on CPB, the perfusionist controls both the fraction of inspired oxygen and the rate of oxygen flow through the circuit, thereby controlling the patient’s arterial oxygen and carbon dioxide levels, respectively. The perfusionist will periodically draw blood gas samples to monitor the patient’s pH, oxygen and carbon dioxide levels, potassium, and glucose. These values should be recorded on the same blood gas sheet that we record our ABGs on. Time and Fi02 should accompany each blood gas. Recording all of the intraoperative blood gasses on a single sheet allows rapid assessment of patient well-being and therapeutic interventions and promotes interdisciplinary dialogue in the management of these complex patients.

Hematocrit is also checked approximately every thirty minutes. Because pump flow (i.e.

cardiac output) is determined by turning a knob and since Fi02 is readily manipulated while on bypass, oxygen delivery is less dependent on hemoglobin levels. Therefore, hematocrits anywhere above 20 are deemed adequate. A set of general policies regarding transfusion of cardiac surgical patients as well as transfusion triggers has been included with your syllabus materials. Your attending must be notified before any blood or blood products are given, even while on CPB!!! When products are given, a notation of why they were given must be made in your record. This can be easily performed by going to the “Transfusion Notes” submenu in your AIMS record.

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AORTIC CROSS CLAMP

After the patient has been placed on CPB, an aortic cross clamp will be applied on the ascending aorta proximal to the aortic cannula. This will separate the systemic circulation from the heart and lungs. The time during which the clamp is on is referred to as “ischemic” time because the coronary arteries will not be perfused. After both the proximal and distal anastomoses have been constructed and the patient has been at least partially rewarmed, the clamp will be removed, restoring perfusion to both the native and newly constructed coronary conduits. Alternatively, some surgeons prefer to do their proximal anastomoses after the aortic cross clamp has been removed, to allow a longer period of myocardial reperfusion prior to separation from bypass. With this technique, a partial aortic occluder (side-biting clamp) is placed on the ascending aorta during construction of the proximal anastomoses.

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Magnesium given postbypass to cardiac surgical patients has been shown to decrease the incidence of both ventricular and atrial arrhythmias. Typically, 5 grams are diluted in 50 or 100 cc NS or DSW and given immediately after the aortic cross clamp has been removed.

REWARMING

At the initiation of rewarming, additional muscle relaxant and benzodiazepines may be given. This helps ensure continued muscle relaxation and amnesia, since rewarming is the most common time for patient awareness. The patient should be warmed gradually since a rapid rise in patient temperature frequently leads to overshooting the goal temperature; this has been associated with adverse neurological outcomes. Feel the difference in temperature between the patient’s forehead and shoulders. Initially a very large gradient will be appreciated. With continued warming, the difference in temperature between the peripheral and central compartments should diminish. When nasopharyngeal temperature is 37oC and a minimal temperature gradient exists between the shoulder and forehead, the patient has been adequately rewarmed.

DEFIBRILLATION

It is not uncommon to have to defibrillate the heart after cross clamp removal. This is usually done with 10-30 Joules of power if the paddles are being placed directly on the heart, or as high as 50 Joules if one or both paddles are placed outside the pericardium. You must make certain you are familiar with how to connect the paddles and operate the unit, both for defibrillation and cardioversion! Ask your attending if you need a demonstration.

INOTROPES AND VASOPRESSORS

Insight into the appropriate drugs to use to terminate cardiopulmonary bypass may be gained from several sources:

1) Preoperative variables including cath data, baseline LV/RV function, etc. 2) Length of CPB and/or aortic cross clamp times 3) Quality of surgical repair as judged by the surgeon 4) Hemodynamic parameters immediately prior to terminating cardiopulmonary bypass 5) Experience

Preoperative studies that reveal low cardiac output or decreased ejection fraction are a strong

indication that a patient may require inotropic support to terminate cardiopulmonary bypass. Additionally, patients demonstrating high ventricular filling pressures during cath and/or the pre-bypass period generally tend to require high ventricular filling pressures to maintain cardiac output in the post- bypass period. The choice of inotrope is generally determined by several factors including:

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1) Mechanism of action (B-receptor agonism or other) 2) Effects on SVR and PVR 3) Side effect profile (tachycardia, etc.) 4) Institutional preferences.

Hemodynamics immediately prior to termination of CPB offers insight into the patient’s

systemic vascular resistance and whether there will be a need for vasopressors or vasodilators. Systemic vascular resistance immediately prior to termination of cardiopulmonary bypass can be calculated by dividing the mean arterial pressure by the cardiac output and multiplying by 80. Systemic vascular resistance should be in the range of 1000-1500 dynes/sec/cm’. Phenylephrine or norepinephrine can be used to increase systemic vascular resistance in the postbypass period. Norepinephrine, although primarily an alpha agent, also has mild beta agonistic properties which may be beneficial for the post ischemic myocardium. In addition, norepinephrine has been shown to improve flow in internal mammary artery grafts when compared with phenylephrine.

TERMINATING CARDIOPULMONARY BYPASS Before terminating bypass, run through the following checklist:

1) Mean arterial blood pressure is between 50 and 70 mm Hg with appropriate flow on the heart-lung machine. Pressors, vasodilators and/or inotropes are infusing as required.

2) An arterial blood gas drawn after the patient has been adequately warmed, demonstrates controlled potassium and glucose.

3) The hematocrit is appropriate for the particular patient. 4) The patient is in an organized rhythm. 5) Pacing capability has been secured. By convention, ventricular wires will be passed off

the field on the patient’s left side and atrial wires will be passed off on the patient’s right side. Assess your ability to A pace, V pace, and AV pace and institute the appropriate mode. A rate of 80-90 beats/min is desired.

6) Suction the orogastric tube if no TEE probe is in place. If a TEE probe is being used, we typically place it in the stomach and monitor the LV short axis view at the midpapillary muscle level while we are weaning from bypass.

7) Initiate ventilation. Hand ventilate at first to check lung compliance. While watching the lungs in the field, fully expand the lungs to eliminate any atelectatic segments while making sure you do not over inflate them which could stretch and tear off the IMA graft. Place the patient on the ventilator.

8) While weaning from the heart-lung machine, observe the PA pressures to confirm that the catheter has not migrated into a wedge position, or been withdrawn into the RV.

9) Check the minimal occlusion pressure in the ETT cuff since warming may have expanded the air and increased cuff pressure.

Once pharmacologic support has been stabilized, CPB may be discontinued. Bypass is

terminated by decreasing venous return to the pump which allows increasing venous return to the heart. Ideally, the patient’s cardiac output should not change much during this process- initially the heart-lung machine is providing the output and then the patient’s heart takes over. Look at the heart!! - see how it’s doing. You can evaluate right ventricular filling and contractility and

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then correlate this with pressure measurements. If a TEE probe is being used (>98% of cases) it is generally placed in the transgastric short axis view to monitor LV preload and systolic function (i.e., contractility).

Watch left atrial pressure and/or pulmonary artery diastolic pressure as the heart is filled and

observe the blood pressure simultaneously. The point where the arterial blood pressure stops increasing but left atrial pressure or pulmonary artery diastolic pressure continues to rise is generally regarded as proper filling pressure and transfusion from the cardiopulmonary bypass pump is then terminated. When in doubt as to the proper filling pressure, serial cardiac output determinations and incremental transfusion from the cardiopulmonary bypass pump will allow determination of optimal cardiac performance.

PROTAMINE ADMINISTRATION

Once bypass has been terminated and hemodynamics are stable, heparin reversal is initiated. The protamine dose will be determined by the perfusion team based on Hepcon testing performed during rewarming. The protamine dose is based on patient size and by a determination of serum heparin concentration. This protamine is given through the cordis side port or “gang of five” via an infusion pump. Do not EVER connect the protamine to the side port until you are ready to give it since accidental administration of protamine could be fatal. Infusion is begun at 60 cc/hr and is increased only after 2 cc’s have been given and no adverse hemodynamic events have occurred. It is a good idea to have your carrier running briskly at this time to dilute the protamine and to allow rapid changes in pressor and inotrope delivery. Observe the PA pressure very closely during protamine infusion and watch for any significant changes, either up or down, which may signal a protamine reaction. An ACT is measured five minutes after the protamine is completed. This sample will be checked for ACT and for the presence of residual heparin. If further dosing of protamine is required, the perfusionist will notify you of the appropriate dose. This should also be given over several minutes.

After the protamine infusion has started and no reaction obvious, the aortic cannula will

be removed. This is also a time when dP/dt and wall stress on the aorta should be minimized by reducing systolic blood pressure to 90-100 mm Hg and avoiding tachycardia.

CHEST CLOSURE

The surgical team may choose to close the pericardium. This can result in hypotension, decreased cardiac output and increased right sided filling pressures, largely from a decrease in preload or impaired RV systolic function. Watch closely and be prepared to give fluids, bolus pressors, and/or have the surgeon reopen the pericardium. Similar events can occur when the sternum is closed so it is a good idea to raise the arterial blood pressure 10 to 15 mm Hg above your closed chest “goal” prior to these events.

After the chest is closed, cardiac output and other hemodynamic measurements are

observed and recorded. An arterial blood gas is drawn and sent to the lab. The TEE probe is kept in place until you are almost ready to move the patient from the OR bed to the transport bed.

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After the TEE probe is removed, an orogastric tube is placed and gastric contents are suctioned. A propofol infusion is generally initiated at this time to provide adequate sedation for transport to the ICU.

TRANSFER AND TRANSPORT OF THE CARDIAC SURGICAL PATIENT

The major prerequisites for transporting the patient from the operating room to the ICU are stable cardiopulmonary status and adequate hemostasis. If the patient’s condition is unstable at the end of the operative procedure, resuscitation should be continued in the OR until stability and hemostasis are achieved. The period from when the drapes come down to arrival in the ICU is a particularly vulnerable time for the patient. The general atmosphere of the OR is relaxed but vigilance must be maintained!

Equipment for transport is collected and checked. The goal of our transport system is

continuous, uninterrupted monitoring of the same quality that is provided during the procedure. Essentially, it is an extension of our intraoperative monitoring. Arterial blood pressure, pulmonary artery pressure and/or central venous pressure, two lead ECG and pulse oximetry are all continued during transport. A portable defibrillator is carried at the foot of the bed and receives an ECG signal from the monitor for synchronization should cardioversion be required. All transport defibrillators also have “quick look” paddle capability.

As the chest dressing is applied, the ECG and pressure modules are switched to the

portable monitor. The pressure transducers along with the flush system and all infusion pumps are transferred to an IV pole on the ICU bed. We transfer the patient from the OR table directly to the ICU bed. The eyes are left closed with tape until the patient is in the ICU to avoid accidental eye damage should the lines or monitoring wires brush the face during transport. The chest and mediastinal tubes function as drains for evacuating air and blood. These drainage systems must always be transferred at a level below the patient’s chest. The underwater seal will allow continued drainage of fluid or air under pressure from the chest such that continuous suction need not be applied during transport. This system should never be clamped during transport. Clamping will prevent drainage and could allow a rapid increase in intrathoracic pressure from accumulating fluid or air leading to cardiac or respiratory compromise. The only time chest and mediastinal systems should be clamped is when it is necessary to briefly elevate the drainage bottle above the chest.

Major physiologic events occurring during transport that require intervention are premature emergence from anesthesia or sedation, hypotension, hypertension, and arrhythmias. The ability to treat each of these occurrences must be readily available.

Hypotension during transport from the OR may be due to hypovolemia, decreased

systemic vascular resistance, inotropy, chronotropy, etc. If the patient has been requiring pressors or inotropes, a quick check to make sure that pumps and carrier lines are functional should be performed. Hypertension during transport should be treated aggressively because of the associated increase in myocardial oxygen demand. Hypertension may also cause hemorrhage at surgical anastomotic sights. Inadequate anesthesia should be suspected first as the etiology of

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acute hypertension during transport. If supplemental anesthesia fails to decrease blood pressure, a vasodilator may be required.

For ventilation during transport, we use a manual self inflating resuscitation bag with an attached oxygen reservoir. Without a reservoir bag, room air will be entrained as the bag reinflates unless very high oxygen flows are used. Oxygen cylinder pressures should be checked to ensure adequate oxygen supply for transport. An oxygen flow rate of 15 liters per minute is used. Hand ventilation allows the anesthesiologist to constantly monitor lung compliance so that endotracheal tube obstruction or malfunction of the chest tubes with resulting tension pneumothorax or hemothorax may be readily diagnosed.

The selection of drugs carried during transport should allow for maintenance of

anesthesia and resuscitation on route to the ICU. Bring the cardiac output syringe, bag, and cooler (if present) for use in the ICU.

On arrival in the ICU, the anesthesiologist should continue to monitor hemodynamics and continue treatment until responsibility for care has been transferred to the ICU team. Complete reports should be given to the ICU team in an unhurried and organized manner. This report should include the following details:

1) Detailed preoperative information including medical history, preop medications,

allergies, cath data, and echo data 2) Details of airway manipulations – i.e. ease of intubation 3) Antibiotic dosing 4) Prebypass events including baseline hemodynamics – i.e. CVP, PAP, CO measurements 5) Bypass and cross clamp times 6) The surgical procedure performed 7) Details of pacing capabilities 8) Inotropes and vasopressors, including doses, used to wean from CPB 9) Postbypass hemodynamics 10) Closed chest hemodynamics 11) Details of hemostasis 12) Totals of relevant medications – e.g. opioids, benzodiazepines 13) Fluid totals (crystalloids, blood products, urine). We do not estimate blood loss – too

complicated in these patients 14) Current doses of medications on arrival to ICU

It is important to make sure that your paperwork is accurate and complete! INACCURATE CHARTING WILL NOT BE TOLERATED!

POSTOPERATIVE PERIOD

Please be sure to complete a cardiac QA form for every patient in a timely fashion. The cardiac QA system is available on the Anesthesia Intranet. Please ask your attending to show you how to access it and complete this data.

It is extremely important and, in fact, mandatory, that every patient be seen

postoperatively. This visit serves at least two important purposes. The first is to assess the

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patients well being and to determine if any anesthetic issues need be addressed. The second is to get feedback from patients and their families as to their satisfaction with our care. This serves to maintain a good patient and family rapport developed from the preoperative period. It also shows our commitment to our patients and reinforces our critical role in their care.

CARDIAC CALL Cardiac call will be distributed amongst senior anesthesia residents and cardiac fellows in an equitable manner as determined by the chief residents and Ms. Joanne Grzybinski. Cardiac call is a “beeper call.” You are absolutely expected to be available at all times and within a reasonable distance from the hospital – i.e. within 40 minutes travel time. If you can not fulfill these criteria you must notify the attending on call with you. On work days, the cardiac call resident/fellow is expected to remain “in-house” until 5 pm. If the resident/fellow needs to leave early, their attending must know so that other arrangements for coverage can be confirmed. It is the responsibility of the resident/fellow to make all reasonable efforts to find coverage for themselves when they can not fulfill their responsibilities. Their chief residents can assist when necessary. It is absolutely expected that the call resident will ensure that the appointed emergency heart room be prepared appropriately (See the “Cardiac Emergency Room Setup” guide in your syllabus or on ADEL). It does not matter if the resident/fellow finds someone to set up the room for them – however it will be the call resident that will be held responsible for any deficiencies in the room! It is also expected that the cardiac call resident/fellow will check in with ongoing cases before they leave to see if it is appropriate for that resident/fellow to relieve their non-call colleague in the room. This decision will be made after respectful discussion between the involved residents/fellows and will be mediated and approved by the supervising attending.

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PART 2: THE ESSENTIALS OF HEMODYNAMIC MONITORING

The true driving force of blood flow between two points is the difference in the total fluid energy between these two points. Total fluid energy is the sum of pressure, positional (gravitational) and kinetic energy expressed by the equation E = P + GH + 1/2 v2. The arterial pressure pulse is very complex, being composed of both a pressure wave (propagated at 5-10 meters per second) and a flow element (conducted at a much slower average velocity of 0.3-0.5 meters per second). The pressure pulse is generated by the mechanical contractions of the heart and sustained by the viscoelastic properties of the arteries. As such, the pressure pulse is markedly changed as it travels distally, undergoing amplification and contour transformation. Also, the flow velocity drops dramatically as the cross sectional area of the vascular system increases from the aorta to the capillaries. This alteration of the pressure pulse from the arch of the aorta to the distal arterioles explains some of the variability in blood pressure obtained by different methods and at different arterial locations. INDIRECT PRESSURE MEASUREMENTS

The blood pressure cuff is wrapped around an extremity and is inflated with air, collapsing the underlying artery. The pressure within the cuff is assumed to equal that of the arterial vessel wall. As the cuff is slowly deflated over a series of pulses, cuff pressure is continually noted. Simultaneously a signal of interest is observed (e.g. arterial line pulsation, Korotkoff sounds).

It is important to recall the importance of cuff size in cuff application. The best cuff width is about 40% of the circumference of the arm. This will allow a uniform pressure to develop around the limb: Narrower cuffs do not produce a uniform pressure increase throughout the underlying extremity segment and cause inaccurate determination of blood pressure. A cuff < 40% of arm circumference will give readings higher than actual arterial wall pressure. It is always better to err on the side of using a cuff which is too large, as the error introduced by too large a cuff is minimal. Wrapping the cuff loosely or eccentrically will allow part of the inflated cuff to lift off the skin and a similar artifact is produced.

DIRECT PRESSURE MEASUREMENT

Transduction is the process of changing energy from one form to another. Pressure transducers are electromechanical devices which change pressure energy into an electric potential. The transducer consists of a transducer membrane and electronic components. The intravascular pressure pulse generates a slight to-and-fro motion in the connecting tubing which deforms the transducer membrane and produces electrical voltage. Prior to interpreting the pressures derived from the pressure pulse, the transducer must be zeroed. Intravascular pressures are not specified as absolute pressures but are referenced or measured as a difference from the atmospheric pressure surrounding the body. Pressures within both the arterial and venous system reflect not just the pressure pulse of cardiac ejection, but also the hydrostatic pressure (gravitational energy) of the vertical offset above or below the heart. By convention, intravascular pressures are referenced to atmosphere at the atrial level. As long as the relative vertical distance between the heart and the transducer remains unchanged, the zeroing of the

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transducer remains valid. Manufacturers of transducers have in general accepted a standard calibration factor of 10 mm Hg pressure = 50 microvolts transducer output for relating pressure to voltage. The physiological monitor assumes this calibration factor to quantify pressures. The physiological monitor amplifies, filters, and processes the transducer signal and displays the pressure waveform. Current physiological monitors (Hewlett Packard, Merlin system) also display in digital form the systolic, mean and diastolic pressures.

The pressure pulse can be considered as a low frequency sound wave. Frequency is measured in Hertz (cycles per second). If the heart rate is 60 beats per minute then the base frequency of the pressure trace is 1 Hertz. In addition, there are higher frequencies or harmonics superimposed on this base frequency. Frequencies up to 10 times the base frequency are thought to be important in recording the pressure pulse. Accurate reproduction of the pressure pulse on the monitor screen requires that the monitoring system faithfully reproduce frequencies up to 20 hertz. At high heart rates during rapid left ventricular ejection, fidelity up to 60 Hertz might be necessary. Most current transducers and monitor systems have a good fidelity even above 60 hertz.

A transducer cannot faithfully reproduce vascular sound if the catheter or connecting tubing inaccurately transmits it. The transmission function of the catheter and connecting tubing (frequency response) can be characterized and divided into two parts: relative natural frequency and damping. The fluid in the catheter and connecting tubing oscillates back and forth as the heart beats. These fluid filled tubes have a so-called “natural frequency”. If the frequency of the fluid vibrations is close to this natural frequency, then the amplitude of the vibrations increases and the peaks and valleys of the pressures pulse will be exaggerated. As long as the natural frequency is above 20 Hertz, there will be little consequence as most of the frequencies of the pressure pulse are less than 20 Hertz. Thus, the higher the natural frequency of the system, the better. The natural frequency of the catheter and connecting tubing is highest for a short, stiff tube of large diameter. As the total length of the catheter and connecting tubing approaches 4 feet, the natural frequency decreases towards 10 hertz. Under such circumstances, the displayed systolic pressure will be 10 or more millimeters less than the true pressure. The fluid oscillations in the catheter and connecting tubing die away with time, much as a bouncing ball bounces less vigorously with each bounce until it stops. This decay in amplitude is called damping. A system is optimally damped when the amplitude dies away quickly. Damping increases with decreased tubing radius, increased tubing length, and increased tubing capacitance. Either high or low damping will distort the pressure pulse. Air bubbles trapped within the connecting tubing or stopcock increase capacitance and thus raise damping with a loss in frequency response. Underdamping is also serious, as the amplitude of fluid vibrations near the resonant frequency will be increased exaggerating the pressure pulse highs and lows. Improper damping and a low natural frequency will not impair measurement of mean arterial pressure. However, systolic and diastolic pressures measurement will be inaccurate. The continuous flush device may be used to determine whether the natural frequency and damping coefficient of a monitoring system are acceptable. The 300 millimeter pressure at which the flush fluid is held may be directed into the connecting tubing and catheter and against the transducer membrane and is almost a square wave pulse by activating and then deactivating the rapid flush mechanism. An optimum wave form is present when flush results in one undershoot on the pressure trace followed by a small overshoot. If the flush test response is not ideal, a search should be made for air bubbles or the connecting tubing should be shortened.

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MONITORING ACCURACY

Arterial catheters are always placed with the catheter tip facing upstream. The measured pressure is thus a summation of both pressure and kinetic energy. Even during tripling of flow, kinetic energy remains low in peripheral arteries. It is important to realize that even the mean arterial pressure measured at the wrist is not always reliable. Immediately following warming and discontinuation of cardio-pulmonary bypass, there can be a large discrepancy (10-30 millimeters mercury) between mean aortic and mean radial artery pressure. Always check arterial catheter pressures against blood pressure obtained by occlusion of the A-line trace using a blood pressure cuff or central aortic pressure.

CARDIAC OUTPUT MEASUREMENT

The evaluation of cardiac output (CO) is useful in the assessment of cardiac function, especially when used in conjunction with ECG, blood pressure, cardiac filling pressures, mixed venous 02 saturation and contractility, as determined by transesophageal echo (TEE). Cardiac output may be measured by the Fick principle, thermodilution (TDCO) or with TEE using a modified Gorlin equation. In the operating room, the most common technique is TDCO.

How to obtain a TDCO 1) A pulmonary artery catheter is placed in the pulmonary artery (PA), usually via the right

internal jugular vein. 2) The PA catheter must be a thermodilution catheter (i.e. must have a thermistor probe at the

distal end and a right atrial (CVP) injection port). Remember that many PA catheters placed via the femoral vein by our cardiologists in the cath lab may not have TDCO capability.

3) There must be at least a 10 degree Celsius temperature difference between the injectate temperature and body temperature for the TDCO computer to work properly. We typically use room temperature D5W injectate for “on-pump” cases and iced solution for “off-pump” cases where the ambient room temperature is often times elevated. From the bag, the D5W passes through a coil of tubing and connects to a stop-cock of which one end is attached to the CVP port of the PA catheter and the other end attaches to a 10cc cardiac output syringe. This stopcock contains a one-way valve so that only D5W (not blood) is drawn into the CO syringe. There is also a connector site for attaching the indicator temperature probe from the CO computer. The injectate temperature will be compared to the temperature measured at the thermistor.

4) The cable from the HP module (the TDCO computer) contains two connectors. The first is for the injectate temperature sensor, which is connected to the 3-way stopcock, and the second is for the thermistor probe, which attaches to the 5-pronged connector on the PA catheter (usually covered by a red cap). Both the indicator temperature probe and thermistor probe connections are extremely fragile and should be handled with care. The thermistor should be connected to the CO cable PRIOR TO INSERTION so that any defects can be detected before insertion.

5) Once both temperature probes are connected to the CO computer, the CO syringe is put in place, and the 3-way stopcock is connected to the CVP port, you’re ready to “shoot” a CO.

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6) You access the CO function by pressing the pad on the front of the HP module. You will then be prompted to confirm the CO constant. The correct constant depends on the brand/type of PA line being used, the volume of injectate (we always use 10cc), and the temperature of the injectate. Constants for each type of catheter are listed on laminated cards attached to the side of the monitors in each heart room. The cardiac techs will be able to help you enter the appropriate number.

7) Press “start” and inject the entire 10cc’s of DSW when the monitor beeps and “inject now” shows on the screen. The measured CO will be displayed on the screen in about 30 seconds.

8) Shoot 3 cardiac outputs and average their values. If conditions are in a steady-state, the measurements should be within 10% of each other. If the patient is receiving positive pressure ventilation, the ventilator should be temporarily turned off at end expiration since changes in preload that occur with mechanical ventilation can alter the cardiac output by up to 60%.

THEORY OF INDICATOR DILUTION TECHNIQUE

The theory of indicator dilution technique is the same whether one is using dye, saline or something else as the injectate. As long as the substance can be identified and quantitatively assessed, it can be used as an indicator solution. In the case of TDCO, the injectate is differentiated by its temperature. By knowing the volume and temperature of the injectate solution and measuring the change in temperature this volume of solution undergoes, one can calculate the degree of “dilution” it has undergone. This dilution is proportional to the flow of blood between the injectate port and the thermistor. In this setting, flow is cardiac output. The formula which is used to calculate the TDCO is called the Stewart-Hamilton equation:

CO = [V( TB - TI )K1K2] / [∫ ∆TB (t) dt]

where: TB= temperature of blood TI = temperature of injectate V = volume of injectate K1= density factor K2= computation constant (catheter dead space, heat transfer, injection rate, unit correction) ∫ ∆TB (t) dt = rate of change of temperature with time (i.e. the area under the thermodilution curve)

SOME HELPFUL HINTS

If your thermodilution CO measurement seems inappropriate, and after considering other parameters, including visual assessment of cardiac function, you should:

1) Make sure that both the thermistor probe and injectate temperature sensor are connected to the CO module

2) Check for leaks at the injectate syringe port (falsely low injectate volume) 3) Confirm computation constant 4) Confirm that iced injectate is used if the room temperature is elevated

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5) Check connections at the CO module 6) Make sure the PA catheter has not advanced into the wedge position or retracted into the

right ventricle 7) Consider anatomic causes (e.g. tricuspid regurgitation, intracardiac shunting) 8) Tricuspid regurgitation - may cause errors in TDCO measurements, but the degree of error

and whether or not the measurement will be falsely high or low is unpredictable.

Falsely elevated CO’s (less injectate sensed by the thermistor) may result from: low injectate volume, right to left intracardiac shunting, less than 10 degree Celsius difference between injectate temp and patient temp, tip of catheter (i.e. thermistor) not in blood flow (e.g. partial wedge, thrombus on tip) Falsely low CO’s (more injectate sensed by thermistor) may result from: temperature sensor not attached when using iced saline, left to right intracardiac shunting, tricuspid regurgitation (effect is unpredictable).

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