Early stabilizing alveolar ventilation prevents acute respiratory distress syndrome

Early stabilizing alveolar ventilation prevents acute respiratorydistress syndrome: A novel timing-based ventilatory

intervention to avert lung injury

Shreyas Roy, MD, CM, Benjamin Sadowitz, MD, Penny Andrews, RN, Louis A. Gatto, PhD,William Marx, DO, Lin Ge, PhD, Guirong Wang, PhD, Xin Lin, PhD, David A. Dean, PhD, Michael Kuhn, BA,

Auyon Ghosh, BSc, Joshua Satalin, BA, Kathy Snyder, BA, Yoram Vodovotz, PhD, Gary Nieman, BA,and Nader Habashi, MD, Syracuse, New York

BACKGROUND: Established acute respiratory distress syndrome (ARDS) is often refractory to treatment. Clinical trials have demonstrated modesttreatment effects, and mortality remains high. Ventilator strategies must be developed to prevent ARDS.

HYPOTHESIS: Early ventilatory intervention will block progression to ARDS if the ventilator mode (1) maintains alveolar stability and (2) reducespulmonary edema formation.

METHODS: Yorkshire pigs (38Y45 kg) were anesthetized and subjected to a ‘‘two-hit’’ ischemia-reperfusion and peritoneal sepsis. After injury,animals were randomized into two groups: early preventative ventilation (airway pressure release ventilation [APRV]) versus non-preventative ventilation (NPV) and followed for 48 hours. All animals received anesthesia, antibiotics, and fluid or vasopressor therapyas per the Surviving Sepsis Campaign. Titrated for optimal alveolar stability were the following ventilation parameters: (1) NPVgroupVtidal volume, 10 mL/kg + positive end-expiratory pressurej 5 cm/H2O volume-cycled mode; (2) APRV groupVtidal volume,10 to 15mL/kg; high pressure, low pressure, time duration of inspiration (Thigh), and time duration of release phase (Tlow). Physiologicaldata and plasma were collected throughout the 48-hour study period, followed by BAL and necropsy.

RESULTS: APRV prevented the development of ARDS (p G 0.001 vs. NPV) by PaO2/FIO2 ratio. Quantitative histological scoring showed thatAPRV prevented lung tissue injury (p G 0.001 vs. NPV). Bronchoalveolar lavage fluid showed that APRV lowered total protein andinterleukin 6 while preserving surfactant proteins A and B (p G 0.05 vs. NPV). APRV significantly lowered lung water (p G 0.001 vs.NPV). Plasma interleukin 6 concentrations were similar between groups.

CONCLUSION: Early preventative mechanical ventilation with APRV blocked ARDS development, preserved surfactant proteins, and reduced pul-monary inflammation and edema despite systemic inflammation similar to NPV. These data suggest that early preventative ventilationstrategies stabilizing alveoli and reducing pulmonary edema can attenuate ARDS after ischemia-reperfusion and sepsis. (J TraumaAcute Care Surg. 2012;73:391Y400. Copyright * 2012 by Lippincott Williams & Wilkins)

KEY WORDS: Sepsis; shock; ARDS; acute lung injury; ventilator-induced lung injury.

A cute respiratory distress syndrome (ARDS) is a lung con-dition that can be caused by systemic inflammation or lung

injury, affecting approximately 200,000 critically ill patientsannually.1 Despite 30 years of research, ARDS claims the livesof 40% of affected patients and is associated with costs inexcess of $150,000 per case.1Y3 Low tidal volume ventilation(LTV), the present ‘‘gold standard’’ of management,4 repre-

sents a supportive intervention limiting progression rather thanaltering the underlying pathophysiology of ARDS. LTV im-proves survival by a modest 9%.5 A new approach is thereforeneeded to improve patient outcome and to reduce the gravehuman toll taken by this disease.

The current perception of ARDS pathophysiology islimited by the characterization of ARDS in a binary construct:it is viewed by clinicians as either being present or absent.1,6

Consequently, therapy to treat ARDS is not implemented untilall features of the disease are already present.7 However, recentpopulation data suggest that ARDS is a hospital-acquiredphenomenon in which 67% of ARDS patients develop thedisease in a hospital usually within 30 hours of admission.8

Patients appear to be developing ARDS during those 30 hoursbefore showing signs of respiratory compromise. These studiessuggest that the development of ARDS represents a progres-sion of pathology in the lung between the time of insult and thetime at which ARDS criteria are met. The concept of a gradualprogression frommoderate lung injury to ARDS versus the ‘‘allor none’’ phenomenon is important clinically for several rea-sons. First, fulminant disease is resistant to treatment, and thusthe prevention of ARDS is the key.2,4 Second, ARDS may havepreclinical stages, similar to some cancers, offering a window

EAST 2012 PLENARY PAPER

J Trauma Acute Care SurgVolume 73, Number 2 391

Submitted: December 1, 2011; Revised: April 26, 2012; Accepted: April 26, 2012.From Cardiopulmonary & Critical Care Laboratory, Department of Surgery (S.R.,

B.S., L.G., G.W., M.K., A.G., J.S., K.S., G.N.), SUNY Upstate Medical Uni-versity, Syracuse, New York; Division of Surgical Critical Care (P.A., N.H.), R.Adams Cowley Shock Trauma Center, Baltimore, Maryland; Department ofBiology (L.A.G.), SUNY Cortland, Cortland, New York; Division of GeneralSurgery (W.M.), Veterans Administration Medical Center, Syracuse, New York;University Department of Pediatrics, Neonatology (X.L., D.A.D.), Universityof Rochester Medical Center, Rochester, New York; Department of Surgeryand Department of Immunology (Y.V.), University of Pittsburgh, Pittsburgh,Pennsylvania.

This work was presented at the 25th annual meeting of the Eastern Association forthe Surgery of Trauma, January 10Y14, 2012, in Lake Buena Vista, Florida.

Address for reprints: Shreyas Roy, MD, CM, Department of Surgery, SUNYUpstateMedical University, 750 East Adams Street, Syracuse, NY 13210; email: [email protected].

DOI: 10.1097/TA.0b013e31825c7a82

Copyright © 2012 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.

of opportunity to prevent ARDS before the full disease ex-pression.8,9 Third, patients at risk are hospitalized during thisprocess.8 Clinicians therefore have an opportunity to interveneearlier, potentially reversing disease progression before clinicalmanifestations when ARDS criteria are met.

During the onset of ARDS, there are two processesthat contribute significantly to the development of disease andrepresent potential excellent targets for early preventative ther-apy: high permeability pulmonary edema and alveolar instability(the repetitive expansion and collapse of alveoli with tidalventilation that causes atelectrauma).10Y12 We hypothesized thata preventative ventilatory intervention would be successful inblocking the progression from injury to ARDS if the ventilatormode was capable of (1) maintaining alveolar stability, therebypreventing the injurious process of atelectrauma, and (2) re-ducing pulmonary edema formation, which is the driving forceof disease in ARDS.10,11,13 We refer to this strategy as early,preventative stabilizing alveolar ventilation and edema (SAVE)reduction. Any ventilatory mode that both stabilizes alveoli byminimizing intratidal collapse and reduces edema in the al-veolar space would fall under the SAVE category. The key tothis novel strategy is not the ventilatory mode itself but ratherthe early intervention aimed at preventing the progression ofdisease and targeting the central components of alveolar insta-bility and pulmonary edema.

In this study, we applied SAVE in the form of airwaypressure release ventilation (APRV) immediately after injury, ina translational porcine model of sepsis and ischemia-inducedARDS. In this setting, SAVE dramatically reduced lung diseaseand prevented the development of fulminant ARDS.

MATERIALS AND METHODS

All techniques and procedures described have been fullyapproved by the Committee for the Human Use of Animals atUpstate Medical University.

AnimalsHealthy female Yorkshire pigs (30Y50 kg) were anesthe-

tized using continuous infusion of ketamineYxylazineYpropofolto maintain a surgical plane of anesthesia. Animals were con-tinuously monitored and cared for by the investigators for thefull 48-hour duration of the experiment.

Surgical PreparationUnder sterile conditions, animals underwent tracheos-

tomy, arterial and venous catheterization, and bladder cathe-terization. Baseline measurements were taken after surgicalpreparation and before injury.

InjuryLung injury was induced using a ‘‘two-hit’’ model as

previously described.14,15 Briefly, for (1) ischemia-reperfusion,the superior mesenteric artery was clamped for 30 minutes toinduce intestinal ischemia, and for (2) peritoneal sepsis, stoolwas harvested from a cecotomy and mixed with blood to createa fecal clot, which was implanted in the abdomen before ab-dominal closure. Time zero measurements were taken imme-

diately after the induction of injury (i.e., removal of clamp andplacement of fecal clot) upon closure of the abdomen.

Treatment GroupsOne hour after injury, animals were randomized into

two groups: APRV (n = 3) or nonpreventative ventilation(NPV; n = 5).

NPV GroupAnimals were connected to a Galileoi ventilator

(Hamilton Medical, Reno, Nev) with the following initial set-tings: tidal volume, 10 mL/kg; respiratory rate, 15 breaths perminute; FIO2, 21%; and positive end-expiratory pressure (PEEP),5 cm H2O. FIO2 was adjusted to maintain adequate oxygenationthroughout the study. Respiratory rate was titrated to maintainPaCO2 at 35 to 45 mm Hg.

APRV GroupThe technique of administering APRV has been de-

scribed previously16 and is critical for APRV functioning asa SAVE mode. APRV administered without the specific tech-niques described will not stabilize alveoli or reduce edema andmay actually produce significant lung injury. Animals wereconnected to a Drageri Evita XL ventilator (Drager, Lubeck,Germany) with initial settings during surgical preparationidentical to the NPV group. At 1 hour after injury, the ventilatormodewas switched to APRVwith the following initial settings:high pressure (Phigh) was initially set at the plateau pressurefrom the volume cycled setting (15Y25 cm H2O). Low pressure(Plow) was set at 0 cm H2O to minimize expiratory resistanceand maximize peak expiratory flow rate (PEFR). The durationof Phigh (Thigh) was set at 3.9 to 6 seconds to equal 90% to 95%of the respiratory cycle. The duration of Plow (Tlow) was setat 0.4 to 0.55 seconds to achieve a termination of PEFR thatwas equal to 75% of PEFR. This was calculated on the basisof the angle of deceleration noted on the expiratory flow waveform.16 Release volumes were titrated to a range of 10 mL/kgby adjusting Phigh and Thigh to ensure that the APRV animalswere not inadvertently receiving ‘‘protective’’ LTV. Phigh, Thigh,Tlow, and FIO2 were titrated throughout the study to minimizelung de-recruitment, to limit airway pressures, to optimize theefficiency of CO2 clearance, and to minimize dead space ven-tilation. These adjustments were based on the interpretation ofexpiratory flow wave form, static compliance, calculated resis-tance, and arterial blood gases.

AntibioticsBroad-spectrum antibiotics (ampicillin, 2 g i.v. [Bristol

Myers Squibb, Princeton, NJ]; metronidazole, 500 mg i.v.[Baxter, Deerfield, Ill]) were given after abdominal closure andevery 12 hours until the end of the study.

Resuscitative ProtocolAnimals were treated with intravenous fluid resuscitation

and vasopressors in a protocol adapted from the early goal-directed therapy strategy.17 This strategy is considered thestandard of care for the management of hemodynamic collapsein sepsis. Maintenance intravenous fluid requirements werecalculated by body weight and given via continuous infusion.

J Trauma Acute Care SurgVolume 73, Number 2Roy et al.

392 * 2012 Lippincott Williams & Wilkins


Ringer’s lactate was used for maintenance and resuscitation.Hemodynamic parameters were assessed to determine the needfor resuscitative fluid bolus according to parameters describedby Rivers et al.17 According to the early goal-directed therapyguidelines, continuous infusion of norepinephrine was startedwhen the animal was no longer responsive to fluid bolus.Epinephrine was added when Norepinephrine was no longereffective.

Physiological MeasurementsHemodynamic parameters were measured (Agilent,

CMS-2001i System M1176A, with Monitor M1094BBobingen, Germany) using Edwards transducers (PressureMonitoring Kit [PXMK1183]; Edwards Lifesciences, Irvine,Calif ). Pulmonary parameters were measured or calculatedusing the Drageri ventilator. Blood was drawn every 6 hoursfor the quantification of interleukin 6 (IL-6) levels in systemiccirculation using enzyme-linked immunosorbent assay. Mea-surement of blood gases and chemistries were made withRoche Blood gas analyzer (Cobas b221, Basel, Switzerland)every 3 hours. Clinical pathology and blood cultures were an-alyzed using the Upstate Medical University pathology labo-ratory facility.

NecropsyAt necropsy, lungs, liver, spleen kidney, and small intes-

tine were removed and preserved in formalin. Lungs were in-flated to 25 cm H2O using stepwise increases in PEEP beforesubmersion in formalin.

Bronchoalveolar Lavage FluidAt necropsy, the right middle lobe of the lung was lavaged

with 60 mL of normal saline. The concentration of total proteinin bronchoalveolar lavage fluid (BALF) was determined usingthe bicinchonic acid method. The concentration of IL-6 wasdetermined in the plasma and BALF using enzyme-linkedimmunosorbent assay according to the manufacturer’s recom-mendations. Western blot analysis of surfactant proteins A andB (SP-A and SP-B) expression in the BALF as well assodiumYpotassium adenosine triphosphatase (Na,K-ATPase)in lung tissue were performed as previously described.18,19

Quantitative HistologyThe quantitative histological assessment of the lung was

based on the image analysis of 120 photomicrographs (10 peranimal), made at high-dry magnification following a validated,unbiased, systematic sampling protocol.14,20 Each photomicro-graph was scored using a 4-point scale for each of five para-meters: atelectasis, fibrinous deposits and blood in air space,vessel congestion, alveolar wall thickness, and leukocytes. Thehistologist performing the analysis was blinded to the treatmentgroups and samples.

StatisticsRepeated measures ANOVA with pig number and treat-

ment as random effects was performed to compare differenceswithin and between treatment groups for continuous para-meters; p G 0.001 was considered significant. Post hoc Tukey’stests were performed on continuous data at specific time points

only if significance was found in the group � time effect usingrepeated measures ANOVA. Categorical data were comparedusing an unpaired Student’s t test. Quantitative histology datawere analyzed using the Mann-Whitney U test after testing fornormality; p G 0.05 was considered significant. All analyseswere performed using JMP version 5.1.1 (Cary, NC).

RESULTS

Hemodynamics and Laboratory DataAll animals in both groups developed polymicrobial

bacteremia in blood cultures, as previously described.20 Nodifferences between groups were found in hemoglobin or he-matocrit, white blood cell count, platelets, liver enzymes, cre-atinine, electrolytes, or coagulation parameters. There was asignificant time trend toward anemia, leukopenia, thrombo-cytopenia, and coagulopathy in both groups, consistent withsevere sepsis. Both groups demonstrated a similar degree ofhyperlactatemia and base deficit consistent with shock. PlasmaIL-6 levels increased during the 48-h course of the experimentin both groups, from 0 pg/mL at baseline for both groups tomean (SD) values of 2045 (650) pg/mL for NPV at 48 hoursand 1779 (458) pg/mL for APRV at 48 hours; this differencewas not significant.

All animals demonstrated hemodynamics consistent withsevere septic shock: progressive hypotension, tachycardia, andhigh resuscitative fluid and vasopressor requirements. Meanarterial pressure, central venous pressure, pulmonary arterypressure, and thermodilutional cardiac output were similarbetween groups.

SurvivalThis study was designed and powered to detect a dif-

ference in ARDS incidence between groups as the primaryoutcome and not differences in mortality. Therefore, statisti-cal significance in mortality is not achieved. All APRVanimalssurvived the full 48-hour duration of the experiment. NPVanimals experienced a 40% mortality, with 60% of animalssurviving the full 48-hour experiment. These differences werenot statistically significant.

Sequential Organ Failure AssessmentTo give a sense of shock severity, sequential organ failure

assessment (SOFA) scores were calculated.21 Scores weresimilarly elevated in both groups with no differences betweenAPRVand NPV. The mean (SD) SOFA scores of NPV were 2.2(0.45) versus 4.0 (2.65) for APRV at 24 hours and 7.4 (0.89)versus 6.0 (3.21) for APRV 48 hours. Both groups had anincrease in SOFA score, reflecting the worsening clinical statusover time.

Fluid BalanceAll animals in both groups required aggressive fluid re-

suscitation and had significantly positive fluid balances, mean(SD), 36.54 (1.02) L. There were no differences between groupsin fluids infused, urine output, or fluid balance.

WetYDry Weight RatioTo assess the degree of high permeability edema, we

assessed wetYdry (W/D) weight ratio. In the lung, the NPV

J Trauma Acute Care SurgVolume 73, Number 2 Roy et al.

* 2012 Lippincott Williams & Wilkins 393


group had significantly higher mean (SD) W/D weight ratio,8.82 (0.76), than the APRV group, 6.73 (0.45) (p G 0.0001).There were no differences between groups in W/D weightratios for liver, kidney, intestine, or spleen.

Lung InjuryThe development of lung injury in the present study was

determined by PaO2/FIO2 (P/F) ratio and static compliance(Cstat) (Fig. 1, A and B). The APRV group had normal P/F ratiosand normal Cstat throughout the 48-hour experiment (Fig. 1, Aand B). In contrast, animals in the NPV group developed pro-gressive, severe lung injury with declining P/F ratio and Cstat

over the course of the study (Fig. 1,A and B). The P/F ratio in theNPV animals dropped to meet the acute lung injury criteria(G300) by 30 hours and ARDS criteria (G250) by 39 hours(Fig. 1, A).1 This progression to lung injury in the NPV groupwas corroborated by steadily declining Cstat to less than 50%of baseline by the end of the study, reflecting pulmonary me-chanics characteristic of ARDS.

Pulmonary DataNo significant differences were found in peak pressure,

PEEP, PaCO2 and minute volume between groups. Peak pres-sure rose from 15 to 20 cm H2O for both groups at baseline toapproximately more than 30 cm H2O for both groups by theend of the experiment. Minute volume rose from 4 L/min forboth groups at baseline to 6 L/min for both groups by the endof the experiment. PaCO2 was 35 to 40 mm Hg at baseline forboth groups. In the NPV group, the mean (SD) PaCO2 was54.7 (7.9) mm Hg at 48 hours, whereas in the APRV group, itremained 38.7 (1.7) mm Hg at 48 hours; however, this dif-ference was not statistically significant. Mean airway pressurewas significantly higher in the APRV group than that in the NPVgroup: mean airway pressure began at 7 cmH2O for both groupsat baseline and was 20.7 (2.6) cm H2O at 48 hours for NPVversus 30.0 (4.0) cm H2O at 48 hours for APRV (p 9 0.0001).Tidal volume began at approximately 10 mL/kg for both groups

at baseline and remained 10 mL/kg throughout the 48-hourcourse of the study for both groups.

BALF DataTotal protein concentration in the BALF was lower in the

APRV group (p G 0.05 vs. NPV) (Fig. 2). BALF IL-6 levels atthe end of the study were increased in the NPV group (p G 0.05vs. APRV) (Fig. 2).

Alveolar stability, one of two key components of theSAVE strategy, is dependent on surfactant composition andfunction. Surfactant composition was assessed by measuringSP-A and SP-B in BALF using Western blot. SP-A was sig-nificantly lower in NPV (p G 0.05 vs. APRV; Fig. 3, A). Threeout of five NPV animals showed a fine monomer of SP-Aprotein; the remaining two did not show SP-A monomer band.

Figure 1. (A) P/F ratio of the NPV group, n = 5 (dashed line), and the APRV group n = 3 (bold line). Data are presented as meanTSEM (*p G 0.05). The APRV P/F ratio remained within normal limits (9300) throughout the 48-hour study. The NPV P/F ratiodecreased below the acute lung injury criteria (G300) by 36 hours and subsequently well below ARDS criteria (G200) by 39 hours. (B)Static compliance (Cstat) of the NPV group, n = 5 (dashed line), and the APRV group, n = 3 (bold line). Data are presented as mean(SEM) (*p G 0.05). Both groups begin with normal Cstat at baseline. APRV maintains normal levels throughout the 48-hour study,whereas NPV demonstrates a progressive decline in Cstat, reflecting ‘‘stiffening’’ lungs and worsening lung injury.

Figure 2. Bronchoalveolar lavage data total protein and IL-6.BALF total protein (left-sided vertical axis) and IL-6 (right-sidedvertical axis) concentrations. g, APRV group (n = 3); h, NPVgroup (n = 5). Total protein and IL-6 concentrations aresignificantly higher in the BALF of NPV (*p G 0.05 vs. APRV),reflecting greater pulmonary vascular permeability andlung inflammation.




All of the APRVanimals exhibited SP-A monomer bands withhigher density (p G 0.05) (Fig. 3, A). SP-B protein expression inthe BALF from NPV was markedly lower compared withAPRV but not statistically significant (p = 0.08) (Fig. 3, B).These data suggest that a degradation of both SP-A and SP-Boccurred in the NPV animals.

The difference in the W/D weight ratio of lungs betweengroups shows that APRV significantly alters extravascular fluidhandling in the lung. This occurs at least in part via a greaterexpression of the Na,K-ATPase pump at the alveolar surface,which could facilitate fluid transport and affect a difference inpulmonary edema between groups. Na,K-ATPase was quan-tified in the cryopreserved lung tissue. The mean (SD) betapump/actin expression levels were 1.0 (0.24) in the NPV groupand 1.16 (0.16) in the APRV group. Themean (SD) alpha pump/actin expression levels were 1.0 (0.19) in the NPV group and1.29 (0.21) in the APRV group. Data are relative to the beta-actinloading control. There were no significant differences in therelative abundance of Na,K-ATPase between groups.

Gross PathologyThe lungs of NPV-treated animals demonstrated se-

vere inflammation, heterogeneous atelectasis, airway edemapouring from the bronchial openings, and hemorrhagic areas(Fig. 4, A). By comparison, the APRV-treated animals exhibitednormal, pink, homogenously well-inflated lung tissue with noevidence of inflammation (Fig. 4, B). The cut surface ofthe representative APRV lung specimen shows no bronchialedema (Fig. 4, B).

Quantitative and Descriptive HistologyThe quantitative histological technique described in the

Materials and Methods section allows an unbiased compari-son of degree of tissue injury to the lungs between the twotreatment groups. The histological lesions analyzed are con-sidered pathognomonic for ARDS when the clinical contextis appropriate.1 These lesions are atelectasis, fibrin deposits,capillary congestion, leukocyte infiltration, intra-alveolar hem-

orrhage, and alveolar wall thickness. Significant differenceswere observed between groups in all histological lesions exceptatelectasis. APRV resulted in 78% improvement in fibrinousexudates, 83% improvement in intra-alveolar hemorrhage,61% improvement in capillary congestion, 83% improvement

Figure 3. Western Blot of SP-A and SP-B in BALF. Each animal is labeled by treatment group (APRV vs. NPV). (A) APRV preserved SP-Aabundance relative to NPV (*p G 0.05). (B) SP-B protein expression in the BAL fluid from NPV was markedly lower comparedwith APRV; however, this was not statistically significant (p = 0.08).

Figure 4. Gross pathology cut surface of right lower lobe oflung of representative animals from (A) the NPV group and(B) the APRV group. (A) NPV shows severe inflammation,atelectasis, edema pouring from the bronchial openings, andhemorrhagic areas. (B) APRV shows normal pink, homogenouslywell-inflated lung tissue with no inflammation and nobronchial edema.




in alveolar wall thickness, and 33% improvement in leukocyticinfiltration (p G 0.0001 vs. NPV; SDC Table 1).

The histological section of the lung of a representativeNPV animal (Fig. 5, A) shows classic stigmata of ARDS at-electasis, fibrinous exudates, intra-alveolar hemorrhage, con-gested capillaries, thickened alveolar walls, and leukocyticinfiltrates. A histological section of the lung of a representativeAPRV animal (Fig. 5, B) shows the preservation of normalpulmonary architecture and none of the lesions characteristic ofARDS. Notably, APRV animals exhibit prominent perivascularedema cuffs and dilated lymphatics as compared with NPVanimals. Furthermore, APRVanimals exhibit normal alveolarpatency, whereas NPVanimals exhibit intra-alveolar fibrin aswell as alveolar collapse.

DISCUSSION

The current study demonstrates SAVE ventilation in theform of APRV applied in an early preventative strategy suc-cessfully stops the development of ARDS in our clinicallyapplicable lung injury model. To our knowledge, this is the firststudy in which all ARDS-related lung injury was completely

prevented by early preventative ventilatory intervention. SAVEintervention applied 1 hour after injury preserved oxygenation,lung compliance, and SP-A and SP-B abundance. SAVE alsosignificantly reduced pulmonary edema, pulmonary vascularpermeability (BALF total protein), lung inflammation (BALFIL-6), and histopathologic lung injury score. Lung function andarchitecture were so preserved by APRV they were similar tothe values of our historic naive controls.22 The time frame forthe manifestation of ARDS among NPV animals in this studywas 39 to 42 hours, which is consistent with recent populationdata,7,8 further demonstrating the fidelity of our experimentalmodel to the human disease.

Prevention of ARDSThemost novel aspect of this approach is the concept that

ARDS can be prevented using the mechanical ventilator. Theprevention of any disease depends on a clear understanding ofthe natural history of the disease, the identification of reversibleearly events in the pathogenesis, and the modulation of thoseevents before clinical manifestations.23 A classic example of thisapproach is the management of colorectal cancer. The under-standing that colon cancer progresses from preclinical ade-noma to carcinoma allowed the evolution of routine screening

Figure 5. Histology. Histological comparison of four pigs, two NPV (A and C) versus two APRV (B and D), at low magnification(A and B; bar, 500 Km) and high magnification (C and D; bar, 50 Km). The NPV animals (A and C) show a classic stigmata of ARDSatelectasis, fibrinous exudates, intra-alveolar hemorrhage, congested capillaries, thickened alveolar walls, and leukocytic infiltrates.The APRV animals (B and D) show the preservation of nearly normal pulmonary architecture. The NPV pig at low magnification(A) shows an intrapulmonary airway (IpA) accompanied by a branch of the pulmonary artery (Pa), which exhibits an edematous cuff(star) with conspicuous lymphatic vessels (arrow). The APRV counterpart (B) is marked by amore substantial cuff withmore prominentlymphatic vessels. Alveoli are notably more patent in APRV. The NPV pig at high magnification (C) shows lumina of alveoli (Alv)occupied by fibrin deposits (arrowheads) and wandering cells, whereas alveolar walls show pronounced cellular infiltration (arrow).APRV at high magnification (D) shows comparable cellular infiltration (arrow), although alveoli (Alv) are patent and clear.




colonoscopies in high-risk patients, thereby revolutionizingthe management of colon cancer from treatment to preven-tion.24 Within the intensive care setting, both thromboprophy-laxis for venous thromboembolism and stress ulcer prophylaxisare preventative maneuvers that significantly improved out-comes for these complications of critical illness.25 The presentstudy provides compelling evidence that ARDS, like venousthromboembolism and gastric stress ulceration, may be pre-ventable. Our finding that ARDS is potentially preventableusing an immediate postinjury SAVE strategy suggests that theprogression of this disease can be attenuated in its preclini-cal pathogenesis. To take full therapeutic advantage of thesefindings, we must depart from the binary concept of ARDS aseither present or absent and begin to target the populations atrisk for ARDS with early preventative ventilation strategies.

ARDS is notoriously difficult to treat once the diagnosisis made. The consistently poor clinical performance of varioustreatments for many decades suggests that the timing of in-tervention is too late in the pathogenesis of ARDS to succeed.Three recent reviews of the literature show that nearly allclinical trials in ARDS have had unimpressive outcomesduring the past 30 years.2,4,26 Only LTV received a relativelyhigh recommendation; yet, this standard-of-care interventiononly reducedmortality by 9%.5 Because treatment of establishedARDS is so difficult and has not proven efficacious over theyears, we must investigate approaches that prevent this diseasefrom developing. Recent data suggest that in most cases ARDSdevelops while the patient is in the hospital. This finding offersphysicians the opportunity to intervene earlier and prevent thedisease.8 The present study builds on this compelling clinicaldata by suggesting that ARDS is in fact preventable by the earlyapplication of ventilation techniques that stabilize the alveolusand reduce pulmonary edema.

Alveolar StabilityAlveolar instability is an important driver of lung injury

in the surfactant-depleted lung.10,11,13 Surfactant depletionhappens early in ARDS onset as edema fluid leaks into the al-veolus, disrupting the surfactant layer and deactivating surfac-tant.27 Surfactant depletion-induced alveolar instability causesatelectrauma with tidal ventilation, which is a significant con-tributor to alveolar shear stress and eventual ARDS.13 There-fore, we designed SAVE to target alveolar instability directlybecause blocking alveolar instability and atelectrauma couldhelp prevent progression to ARDS.

The ventilator mode APRV was selected for the earlySAVE strategy in our study. The specific technique of APRVused is critical because not all APRV settings fit the SAVEcategory. We postulate that the mechanisms of APRV’s successin this study are derived from airway pressure (P) sustainedover a period (T), or the pressure-time profile (PTP). Main-taining a prolonged PTP keeps the alveoli stable for a greaterportion of the ventilatory cycle. In fact, the method of APRVused in this study maintains the Phigh for more than 90% ofthe respiratory cycle.16 These pulmonary mechanics supportthat APRV minimizes atelectrauma and stabilizes alveoli. Therelative preservation of SP-A and SP-B in APRV versus NPV(Fig. 3, A and B) further supports that APRV maintains alveolarstability.

Pulmonary Edema ReductionPulmonary edema from increased vascular permeability

is the key pathophysiological event associated with the de-velopment of ARDS.12,27 APRV nearly eliminated the accu-mulation of pulmonary edema as assessed by lung W/D weightratio and also reduced lung vascular permeability as indicatedby BALF total protein (Fig. 2). These data suggest that lungdistending pressure sustained over time (prolonged PTP)changes the dynamics of pulmonary fluid flux and reducesedema formation in the alveolar space. In contrast, pulmonaryedema accumulated in the NPV group (short PTP) as assessedby lung W/D weight ratio and vascular permeability was sig-nificantly elevated (Fig. 2). The mechanisms for APRV-inducedreduction in edema may include increasing interstitial hydro-static pressure, reducing capillary transmural pressure, andreducing permeability surface area.28Y30 A prolonged PTPmay reverse the pressure gradient for edema flowing out ofthe capillaries and into the alveolus. Investigations in high-permeability lung injury have shown that the pressurization ofthe alveolus with PEEP can reduce permeability and therebyreduce extravascular lung water,29,31 which corroborates ourfindings using PTP. Others have shown that a prolonged PEEP,affecting a long PTP, not only reduces extravascular lung waterbut also causes redistribution of edema from alveoli intoperivascular cuffs.29Y31 Qualitative histology in the presentstudy revealed that animals treated with APRV showed nor-mally inflated alveoli with edematous perivascular cuffs andinterlobular septa corroborating the findings of Malo et al30 thatprolonged PTP moves edema from the airways into extravas-cular cuffs.

The present study demonstrated that the APRV-inducedreduction of airspace edema was associated with a reduction inother downstream events associated with ARDS. Withoutairspace edema, there is no disruption of surfactant, whichprevents alveolar instability-induced atelectrauma, a processcritical for the development of fulminant ARDS.10,13,27,32Y34

SAVE ventilation preserved SP-A and SP-B to near normallevels in the BALF of the APRV versus the near-total loss ofSP-A and SP-B in the NPV group, suggesting improved sur-factant function in the APRV animals. Thus, preventing alve-olar flooding with SAVE eliminated the pathologic sequelae ofairspace edema and speaks to the powerful potential of thisnovel strategy to reverse the progression to ARDS. Derailingthe ARDS cascade early reinforces the importance of timing ininterventions such as mechanical ventilation. Once alveolaredema and instability develop, the mechanical ventilator maypropagate rather than prevent lung dysfunction.35

New Understandings of ARDS OnsetIn the current paradigm, ARDS pathogenesis begins

after diagnostic criteria for ARDS have been met and has beencategorized into three phases: (1) exudative, (2) fibroprolifera-tive, and (3) fibrotic repair and recovery.1 The success of earlyintervention in the present study has led us to conceptualize theonset of ARDS as a staged process (Fig. 6). We hypothesizethat there are three distinct pre-ARDS stages based on theposition of edema with respect to the airspace. Stage 1 (occultARDS) is characterized by interstitial edema in alveolar wallsand in vascular cuffs without alveolar flooding or clinical




symptoms; this stage is reversible with SAVE. Stage 2 (pseudo-ARDS) is characterized by alveolar flooding with moderatesurfactant deactivation that causes alveolar instability. All ofthe clinical symptoms of ARDS are present, except that hyp-

oxemia is not refractory if SAVE is applied. Stage 3 (fulminantARDS) is characterized by complete alveolar flooding withedema and total surfactant deactivation, and all the diagnosticcriteria of ARDS are met5,7,26; in this stage, hypoxemia cannot

Figure 6. Hypothetical staging of ARDS onset diagram of ARDS development from normal (N) to fulminant ARDS (3) with clinicalparameters at each stage. Column 1, diagram of alveoli, interstitial space and capillary; column 2, the percent of the entire lungthat these lesions occupy; and column 3, the clinical presentation at each stage. N, normal alveoli, no interstitial or alveolaredema; 1, stage 1 (occult ARDS) interstitial edema in vascular cuffs (gray) without alveolar flooding or serious clinical symptoms;2, stage 2 (pseudo-ARDS) interstitial edema (light gray) and partial flooding of alveoli (dark gray) with moderate surfactantdeactivation (dotted lines) causing alveolar instability and hypoxemia. Pseudo-ARDS has all of the clinical features of fulminant ARDSexcept hypoxemia is not refractory if SAVE ventilation is applied; 3, stage 3 (fulminant ARDS) interstitial edema (light gray) andcomplete alveolar flooding with edema (black) with total surfactant deactivation and all clinical features as defined by theARDS consensus conference including refractory hypoxemia even if SAVE is applied. Stage 3 is the currently the only descriptionof ARDS.




be reversed with SAVE. We are currently investigating thepathophysiology of each stage and the mechanisms of theSAVE-induced prevention of ARDS.

SummaryBecause we were investigating a preventative interven-

tion, this study was designed and powered to detect a differencein ARDS incidence between groups as its primary outcome.Mortality was not an outcome detected by this study; hence,although the APRV animals had a 100% survival comparedwith the NPV 40% survival rate, this difference was not sig-nificant. Only three animals were included in the APRV group.Although this is a small number of animals, all key parametersattained statistical significance as compared with the NPVgroup (0% ARDS incidence for APRV vs. 100% for NPV);therefore, the study was stopped to minimize the number ofanimals used, a key requirement of IACUC. The present studyclearly demonstrates that timing-based early ventilatory inter-vention with SAVE reduction strategy, in the form of APRV,completely prevents ARDS in a clinically relevant animalmodel. There are distinctly attractive aspects to this treatmentstrategy because APRV is readily available onmost commercialventilators and can be implemented with appropriate tech-nique16 as soon as patients are selected based on well-knownrisk factors for developing ARDS.8 Although mechanisticdetails of this type of treatment regimen and of our proposedARDS stages still need to be elucidated, we believe that thefuture of ARDS treatment can be best summed up by a recentquote from Villar and Slutsky,35 ‘‘ARDS is no longer a syn-drome that must be treated, but is a syndrome that should beprevented.’’

AUTHORSHIP

S.R., B.S., P.A., W.M., G.W., D.A.D., K.S., Y.V., G.N., and N.H. designedthis study. S.R., B.S., P.A.,M.K., A.G., J.S., K.S., G.N., andN.H. performedthe experiments and collected data. S.R., L.A.G.,W.M., L.G., G.W.,M.K.,A.G., J.S., K.S., G.N., and N.H. analyzed the data. S.R., B.S., P.A., L.A.G.,L.G., G.W., C.L., D.A.D., J.S., G.N., and N.H. conducted tissue analyses.L.A.G. provided histological analysis and quantification. L.G. and G.W.performed BALF analysis, Western blots of surfactant protein, IL-6 data,and total protein analysis. X.L. and D.A.D. managed the sodium po-tassium adenosine triphosphatase data. J.S. performed statistical anal-yses. S.R., W.M., Y.V., G.N., and N.H. conducted the literature review.S.R., B.S., P.A., G.N., and N.H. wrote the manuscript, for which L.G.,G.W., and J.S. prepared figures. S.R., B.S., P.A., L.A.G., W.M., L.G., G.W.,X.L., D.A.D., J.S., K.S., Y.V., G.N., and N.H. edited the manuscript.

ACKNOWLEDGMENTS

This work was partially funded by the National Institutes of Health (grantnos. R33HL089076 and R21HL092801-01). The authors thank thepatients and Oisin McGinty for teaching what is possible when newthinking is applied to careful observation and Robert Cooney for hispatience and guidance.

DISCLOSURE

The authors declare no conflicts of interest.

REFERENCES1. Ware LB, Matthay MA. The acute respiratory distress syndrome. N Engl J

Med. 2000;342:1334Y1349.2. Cepkova M, Matthay MA. Pharmacotherapy of acute lung injury and the

acute respiratory distress syndrome. J Intensive Care Med. 2006;21:119Y143.

3. Herridge MS, Tansey CM, Matte A, Tomlinson G, Diaz-Granados N,Cooper A, et al. Functional disability 5 years after acute respiratorydistress syndrome. N Engl J Med. 2011;364:1293Y1304.

4. McIntyre RC, Jr, Pulido EJ, Bensard DD, Shames BD, Abraham E. Thirtyyears of clinical trials in acute respiratory distress syndrome. Crit CareMed. 2000;28:3314Y3331.

5. Brower RG, Matthay MA, Morris MDA, Schoenfeld D, Thompson BT,Wheeler A.Ventilation with lower tidal volumes as compared withtraditional tidal volumes for acute lung injury and the acute respiratorydistress syndrome. The Acute Respiratory Distress Syndrome Network. NEngl J Med. 2000;342:1301Y1308.

6. Artigas A, Bernard GR, Carlet J, Dreyfuss D, Gattinoni L, Hudson L, et al.The American-European Consensus Conference on ARDS: part 2.Ventilatory, pharmacologic, supportive therapy, study design strategiesand issues related to recovery and remodeling. Intensive Care Med. 1998;24:378Y398.

7. Sheridan M, Donnelly M, Bailie R, Power M, Seigne P, Austin S, Marsh B,Motherway C, Scully M, Fagan C, et al. Acute lung injury and the acuterespiratory distress syndrome in Ireland: a prospective audit ofepidemiology and management. Crit Care. 2008;12:R30.

8. Shari G, Kojicic M, Li G, Cartin-Ceba R, Alvarez CT, Kashyap R, et al.Timing of the onset of acute respiratory distress syndrome: a population-based study. Respir Care. 2011;56:576Y582.

9. Navarrete-Navarro P, Rivera-Fernandez R, Rincon-Ferrari MD, Garcia-Delgado M, Munoz A, Jimenez JM, et al. Early markers of acuterespiratory distress syndrome development in severe trauma patients. JCrit Care. 2006;21:253Y258.

10. Schiller HJ, McCann UG 2nd, Carney DE, Gatto LA, Steinberg JM,Nieman GF. Altered alveolar mechanics in the acutely injured lung. CritCare Med. 2001;29:1049Y1055.

11. Carney D, DiRocco J, Nieman G. Dynamic alveolar mechanics andventilator-induced lung injury. Crit Care Med. 2005;33:S122YS128.

12. Ware LB. Pathophysiology of acute lung injury and the acute respiratorydistress syndrome. Semin Respir Crit Care Med. 2006;27:337Y349.

13. Otto CM, Markstaller K, Kajikawa O, Karmrodt J, Syring RS, PfeifferB, et al. Spatial and temporal heterogeneity of ventilator-associatedlung injury after surfactant depletion. J Appl Physiol. 2008;104:1485Y1494.

14. Kubiak B, Albert SP, Gatto LA, Vieau CJ, Roy SK, Snyder KP, Maier KG,Nieman GF. A Clinically applicable porcine model of septic and ischemia/reperfusion-induced shock and multiple organ injury. J Surg Res. 2010;166:59Y69.

15. Kubiak B, Roy S, Albert S, Gatto L, Synder K, Vieau C, et al. COL-3prevents histologic intestine damage in a clinically applicable porcinemodel of multiple organ dysfunction syndrome (MODS). Crit Care Med.2009;37.

16. Habashi NM. Other approaches to open-lung ventilation: airway pressurerelease ventilation. Crit Care Med. 2005;33:S228YS240.

17. Rivers E, Nguyen B, Havstad S, Ressler J, Muzzin A, Knoblich B, et al.Early goal-directed therapy in the treatment of severe sepsis and septicshock. N Engl J Med. 2001;345:1368Y1377.

18. Machado-Aranda D, Adir Y, Young JL, Briva A, Budinger GR, YeldandiAV, et al. Gene transfer of the Na+,K+-ATPase beta1 subunit usingelectroporation increases lung liquid clearance. Am J Respir Crit CareMed. 2005;171:204Y211.

19. Wang G, Taneva S, Keough KM, Floros J. Differential effects of humanSP-A1 and SP-A2 variants on phospholipid monolayers containingsurfactant protein B. Biochim Biophys Acta. 2007;1768:2060Y2069.

20. Kubiak BD, Albert SP, Gatto LA, Snyder KP, Maier KG, Vieau CJ, et al.Peritoneal negative pressure therapy prevents multiple organ injury in achronic porcine sepsis and ischemia/reperfusion model. Shock. 2010;34:525Y534.

21. Minne L, Abu-Hanna A, de Jonge E. Evaluation of SOFA-based modelsfor predicting mortality in the ICU: a systematic review. Crit Care. 2008;12:R161.

22. Steinberg J, Halter J, Schiller H, Gatto L, Carney D, Lee HM, et al.Chemically modified tetracycline prevents the development of septicshock and acute respiratory distress syndrome in a clinically applicableporcine model. Shock. 2005;24:348Y356.




23. Gordon RS Jr. An operational classification of disease prevention. PublicHealth Rep. 1983;98:107Y109.

24. Muller AD, Sonnenberg A. Prevention of colorectal cancer by flexibleendoscopy and polypectomy. A case-control study of 32,702 veterans.Ann Intern Med. 1995;123:904Y910.

25. Parrillo J.Critical CareMedicine: Principles of Diagnosis andManagementin the Adult. Philadephia, Pa: Mosby; 2008.

26. Brower RG, Fessler HE. Another ‘‘negative’’ trial of surfactant. Time tobury this idea? Am J Respir Crit Care Med. 2011;183:966Y968.

27. Ware LB,MatthayMA. Alveolar fluid clearance is impaired in the majorityof patients with acute lung injury and the acute respiratory distresssyndrome. Am J Respir Crit Care Med. 2001;163:1376Y1383.

28. Pare PD, Warriner B, Baile EM, Hogg JC. Redistribution of pulmonaryextravascular water with positive end-expiratory pressure in caninepulmonary edema. Am Rev Respir Dis. 1983;127:590Y593.

29. Russell JA, Hoeffel J, Murray JF. Effect of different levels of positive end-expiratory pressure on lung water content. J Appl Physiol. 1982;53:9Y15.

30. Malo J, Ali J, Wood LD. How does positive end-expiratory pressure reduce

intrapulmonary shunt in canine pulmonary edema? J Appl Physiol.1984;57:1002Y1010.

31. Ruiz-BailenM, Fernandez-Mondejar E, Hurtado-Ruiz B, Colmenero-RuizM, Rivera-Fernandez R, Guerrero-Lopez F, et al. Immediate application ofpositive-end expiratory pressure is more effective than delayed positive-end expiratory pressure to reduce extravascular lung water. Crit CareMed. 1999;27:380Y384.

32. Imai Y, Parodo J, Kajikawa O, de Perrot M, Fischer S, Edwards V, et al.Injurious mechanical ventilation and end-organ epithelial cell apoptosisand organ dysfunction in an experimental model of acute respiratorydistress syndrome. JAMA. 2003;289:2104Y2112.

33. Slutsky AS. Lung injury caused by mechanical ventilation. Chest.1999;116:9SY15S.

34. Bredenberg CE, Nieman GF, Paskanik AM, Hart AK. Microvascularmembrane permeability in high surface tension pulmonary edema. JAppl Physiol. 1986;60:253Y259.

35. Villar J, Slutsky AS. Is acute respiratory distress syndrome an iatrogenicdisease? Crit Care. 2010;14:120.




Early stabilizing alveolar ventilation prevents acute respiratory distress syndrome

Documents

Transcript of Early stabilizing alveolar ventilation prevents acute respiratory distress syndrome