Efficacy and side effects of intraoperative analgesia with intrathecal bupivacaine and...

R E S E A R C H P A P E R

Efficacy and side effects of intraoperative analgesia

with intrathecal bupivacaine and levobupivacaine:

a retrospective study in 82 dogs

Diego Sarotti*, Roberto Rabozzi� & Federico Corletto�*Centro Veterinario Fossanese, Fossano, Italy

�Clinica Veterinaria dell’ Adriatico, Vasto, Italy

�Dick White Referrals, Six Mile Bottom, Suffolk, UK

Correspondence: Diego Sarotti, c/o CVF, Via Cuneo 29/E, 12045 – Fossano (CN), Italy. E-mail: [email protected]

Abstract

Objective To evaluate spinal (intrathecal) anaesthe-

sia (SA) in addition to general anaesthesia in dogs,

and report the incidence of side effects and cardio-

vascular response (CR) to surgery.

Study design Retrospective clinical study.

Animals One hundred and fifteen dogs undergoing

general anaesthesia for surgery caudal to the

diaphragm between 2005 and 2008.

Methods Records of anaesthetized dogs that had

received SA with bupivacaine or levobupivacaine

0.5%, together with morphine or fentanyl were

reviewed. Success rate of SA, complication rate and

incidence of CR were recorded and examined in

relation to the dose of local anaesthetic administered

and the type of surgery. Univariate and Cusum

analysis were performed to identify independent

predictors of response to surgical stimulation and

characterize the learning curve for the technique,

respectively.

Results Eighty-two dogs received successful SA. The

Cusum plot suggested that a failure rate of 10% is

achieved when the procedure is performed more

than 66 times. Median local anaesthetic dose

related to weight was 0.40 mg kg)1 (0.3–0.5),

and to spinal cord length 0.1 mg cm)1 (0.07–

0.12). Morphine was added to the local anaesthetic

in 56 and fentanyl in 22 dogs. CR post-stimulus

occurred in 29 cases: 11 of 22 ovariohysterecto-

mies, 14 of 33 hindlimb-surgeries, 2 of 10 caudal-

abdominal-surgeries and 2 of 17 Caesarean sec-

tions. Anaesthetic dose related to weight was not a

predictor of CR. Bradycardia occurred in seven,

hypotension in 24, urinary retention in four and

hypersalivation in 6 of 82 dogs.

Conclusions SA was practicable to apply, but in this

study did not totally block CR, Side effects were

minimal, with an incidence similar to that in

humans.

Clinical relevance SA can be used in clinical cases

with few side effects although monitoring of and

ensuing treatment of hypotension is required.

Comparative prospective studies are required to

establish efficacy and a reliable dose.

Keywords bupivacaine, cardiovascular response,

dog, intrathecal, locoregional anaesthesia, side

effects incidence, spinal.

Introduction

Intrathecal, or more colloquially, spinal anaesthesia

(SA) consists of the administration of a local

anaesthetic (LA), alone or in combination with

other drugs, in the subarachnoid space. It is one of

240

Veterinary Anaesthesia and Analgesia, 2011, 38, 240–251 doi:10.1111/j.1467-2995.2011.00608.x

the oldest and most effective local-regional tech-

niques and has a fast onset of action and predictable

pharmacodynamic (PD) and pharmacokinetic (PK)

characteristics. In 1899, August Bier (1899) per-

formed the first spinal anaesthesia in humans with

cocaine. Cuille & Sendrail (1901) described sub-

arachnoid injection in the dog 2 years later, but it

took several years before spinal anaesthesia was

accepted as safe and became used widely in

humans. The technique gained popularity following

the introduction of thinner and less traumatic nee-

dles, the use of which reduced incidence of post

dural puncture headache (Greene & Barnett 1950;

Sprotte et al. 1987). Over the last 50 years evidence

has been accumulating which demonstrates the low

incidence of side effects and the benefits of spinal

(Dripps & Vandam 1954) and epidural anaesthesia

in humans.

The advantages of central neuraxial anaesthesia

compared to general anaesthesia in human medi-

cine include inhibition of central temporal summa-

tion (Curatolo et al. 1997), easier control of pain

with reduced perioperative use of opioids, better

control of cardiovascular response, abolition of

metabolic and endocrine stress during surgery

(Weissman 1990; Kehlet 1991), smaller intraoper-

ative blood loss (Modig 1988), faster postoperative

recovery and a possible reduction of postoperative

mortality and morbidity, as reported in large meta-

analyses (Rodgers et al. 2000). Spinal anaesthesia

has some significant advantages over epidural

anaesthesia: faster onset and offset of action, and

lower systemic absorption of drugs. However, the

greater sympathetic blockade induced by cranial

spread of LA that may occur in spinal anaesthesia

may also result in an increased risk of cardiovascu-

lar side-effects when compared to epidural anaes-

thesia. Many variables affect cranial spread of LA

after subarachnoid administration including the

dose, the volume and baricity, the injection site,

the direction of the needle, the cerebrospinal fluid

(CSF) density and the position of the patient (Greene

1985).

Local anaesthetics such as lidocaine, mepiva-

caine, tetracaine, bupivacaine, levobupivacaine,

ropivacaine, may be administered in the subarach-

noid space to achieve a sensory and motor block. In

humans, spinal administration of lidocaine recently

has fallen into disuse, because of its potential

neurotoxicity (Freedman et al. 1998; Hogson et al.

1999). Opioids such as morphine, fentanyl and

sufentanil are used commonly as adjuvants to

improve quality and increase duration of the block,

to decrease the risk of cardiovascular response to

surgery (Samii et al. 1981; Ben-David et al. 1997)

and to achieve longer lasting and better postoper-

ative analgesia. Morphine may spread cranially and

cause delayed respiratory depression in humans

(Carpenter et al. 1992), but to our knowledge, this

has never been documented in dogs. Side effects

reported in human patients include cardiovascular

and respiratory depression, urinary retention, nau-

sea, vomiting, headache, pruritus, and transitory or

permanent neurological deficit (Carpenter et al.

1992; Freedman et al. 1998; Brull et al. 2007;

Feliciano et al. 2008). In the veterinary literature

these side effects have not yet been reported in dogs

and cats. Large retrospective or prospective studies

about the true incidence of side effects after spinal

anaesthesia are lacking in veterinary medicine. This

information currently is available only for epidural

anaesthesia in dogs and cats (Troncy et al. 2002).

The only reported descriptions of the technique of

spinal anaesthesia in dogs consist of a few case

reports on elective spinal anaesthesia during ortho-

paedic surgery, Caesarean section or during unin-

tentional spinal injections (Campoy 2004; Sarotti

2005; Novello & Corletto 2006).

The aim of this work is to evaluate the procedural

failure rate of spinal anaesthesia in dogs undergoing

different types of surgery, and to report for the first

time the incidence of side effects and the rate of

cardiovascular response (CR) to surgical stimula-

tion.

Materials and methods

A retrospective analysis was performed reviewing

the medical records of all dogs in which elective

spinal administration of bupivacaine and levo-

bupivacaine was attempted between 2005 and

2008.

Clinical protocol and recording

In the clinic where these cases were collected, it is

standard operating practice to administer spinal

anaesthesia in addition to general anaesthesia for

all patients undergoing surgery caudal to the dia-

phragm unless there are specific contra-indications.

Skin infection at the site of injection, shock or

severe hypovolaemia, pre-existing disease involv-

ing the spinal cord, increased intracranial pressure,

coagulopathy, decompensated cardiac disease, and

Intrathecal bupivacaine in dogs undergoing surgery D Sarotti et al.

� 2011 The Authors. Veterinary Anaesthesia and Analgesia� 2011 Association of Veterinary Anaesthetists and the American College of Veterinary Anesthesiologists, 38, 240–251 241

unknown duration of surgery were considered the

exclusion criteria for this study.

The same person (D.S.) was in charge of all the

anaesthetics and performed the SA. Information on

the drugs and doses used for pre-anaesthetic med-

ication, induction and maintenance of anaesthesia

were recorded. Common aspects of anaesthetic

management, identical in all patients, included:

management of ventilation, pharmacodynamic tar-

get for anaesthetic delivery, positioning of the

patient, technique used for SA, and intraoperative

monitoring and administration of fluids. All patients

were allowed to breathe spontaneously during

anaesthesia, unless end-tidal CO2 was higher than

45 mmHg (6 kPa), in which case intermittent

positive pressure ventilation was imposed (Siare

ALPHA DELTA Lung Ventilator Crespellano, Italy)

to restore and maintain normocapnia. Delivery of

anaesthetic agent in all patients was titrated to

maintain palpebral reflex and allow examination of

the perineal, tibial, patellar and pannicular reflexes.

In order to perform SA, anaesthetized dogs were

positioned in right lateral recumbency and, after

clipping the hair, the skin over L3-S1 vertebrae was

prepared aseptically with chlorexidine 4% and

alcohol. Spinal injection was performed using a

paramedian approach at the level of the interverte-

bral space between L5 and L6. The needle was

advanced until it reached the dorsal sub-arachnoi-

dal space, confirmed by flow of cerebrospinal fluid in

the hub of the needle. When it was not possible to

perform the injection in the L5-6 space, because of

the difficulty in reaching the sub-arachnoid space,

or if there was accidental puncture of a blood vessel,

SA was attempted at the level of an adjacent space.

All solutions of local anaesthetic were injected at

room temperature over a period of 20 seconds.

The bevel of the needle was always facing crani-

ally during administration of the LA. Patients

undergoing orthopedic surgery were positioned

with the operated limb uppermost. The table was

maintained in a horizontal position throughout the

procedure.

Lactated Ringer’s solution was infused intrave-

nously at 5–10 mL kg)1 hour)1 during anaesthesia

in all dogs. Systemic arterial blood pressure was

measured every 2–3 minutes with an oscillometric

technique (HP Viridia C26, Germany) using a cuff of

appropriate size placed on the distal third of the left

forearm, and the reading was confirmed using a

Doppler flow detector (Minidop ES 100 VX; Hadeco,

Japan), while the fraction of inspired oxygen, end-

tidal CO2, electrocardiogram, pulse oximetry, heart

rate (HR), respiratory rate and temperature were

monitored continuously (HP Viridia C26; Ger-

many). During surgery an active heating system

was employed.

Records included body mass, sex, age and phys-

ical status according to the American Society of

Anesthesiology (ASA). For each patient the distance

between the caudal part of the spinous process of L7

and the occipital bone, was recorded as length of the

spine. Every measurement was made in triplicate

and a mean value was noted (and used in the

later analysis). Information regarding presence or

absence of spinal cord reflexes immediately before

and after the procedure noted in the clinical records

of some patients, and the approximate time between

SA and ability to walk with minimal ataxia was

recorded in all.

The following events were recorded, if they

occurred: bradycardia, hypotension, cardiovascular

response to surgical stimulation, urinary retention,

vomiting, hypersalivation, neurological damage,

proprioceptive deficit 24 hours after spinal injection,

perioperative death and 30 day mortality. Bradycar-

dia was defined as a HR lower than 60 beats

minute)1. Hypotension was defined as a mean

arterial pressure (MAP) lower than 60 mmHg or a

systolic arterial pressure (SAP) lower than 90 mmHg

for at least 5 minutes or as any MAP value lower than

55 mmHg or SAP lower than 85 mmHg. An increase

of HR, or MAP or SAP >20% compared to prestimu-

lus values was considered to be a cardiovascular

response (CR) (Wynands et al. 1984; Novello et al.

2008). The prestimulus value was defined as the

mean value of the parameter in the 5 minutes prior to

the stimulus itself. Information regarding the man-

agement of CR was recorded in the anaesthetic

records of the patient. Urinary retention was defined

as the inability to void spontaneously in the presence

of bladder overdistension 12–24 hours postopera-

tively. Abdominal palpation or ultrasonography was

used to assess bladder size in all patients that did not

spontaneously urinate within 8 hours after the end of

surgery. The urinary bladder was catheterised when

over distension was suspected. At the end of surgery

all patients received 0.2 mg kg)1 of meloxicam

(Metacam; Boehringer Ingelheim, Germany) by

intra-muscular injection and the patient without a

complete intraoperative CR block received also a

single 0.2 mg kg)1 of methadone (Eptadone; Molte-

ni, Italy) injection IM. A pain scoring system was used

to evaluate postoperative analgesia every 2 hours


� 2011 The Authors. Veterinary Anaesthesia and Analgesia242 � 2011 Association of Veterinary Anaesthetists and the American College of Veterinary Anesthesiologists, 38, 240–251

until discharge and if necessary a methadone dose of

0.2 mg kg)1 was administrated.

Retrospective analysis

Cases with incomplete clinical records were ex-

cluded from the analysis, but for all others, the data

listed above were obtained from the clinical records

of the patients.

The dose of local anaesthetic and opioid used to

perform the SA was recalculated on the basis of the

body mass (mg kg)1) and spinal length (mg cm)1).

Statistical analysis

Surgical procedures were grouped in four categories

for the purpose of statistical analysis: hindlimb

surgery (HLS), caudal abdominal surgery (CAS),

caesarean section (CS), and ovariohysterectomy

(OV).

Categorical variables are reported as frequencies

and percentage. Continuous variables were checked

for normal distribution with visual inspection of bar

graphs, histograms and Shapiro–Wilk test. Categor-

ical variables were analyzed using a Chi-square test,

and continuous ones using Student’s t-test or, when

applicable, Mann–Whitney U test. Odds ratios and

95% confidence interval (95% CI) for univariate

analysis of independent predictors were calculated

using logistic regression. Significance level was set

to 5%. Learning curve of success rate in performing

spinal anaesthesia (CSF flow in the hub of the

needle) was analysed with Cusum analysis consid-

ering acceptable rate of failure p0 = 0.1 and unac-

ceptable rate of failure p1 = 0.2. Data were analyzed

using SPSS version 16.01 for Windows (SPSS Inc., IL,

USA) and R Software for Statistical Computing

version 2.80 (R Development Core Team, Austria).

Variables with normal distribution are reported as

mean ± standard deviation (SD), whereas those

with non normal distribution are reported as

median and range (minimum–maximum). Percen-

tiles (25th, 75th) are included in the figures.

Results

Spinal anaesthesia was attempted in 115 patients,

CSF flow was evident in 86 of these 115 (74%) and

only in these cases was the local anaesthetic

administered. Between case 1 and case 66 the

Cusum plot repeatedly crossed the unacceptable

control line (H1 = 2.71) from below indicating that

the true failure rate was significantly higher than

the acceptable rate, with a risk of type 1 error equal

to a (0.1), thus the performance should be consid-

ered unacceptable. Between cases 67 and case 115,

the Cusum plot reached but remained just above the

control level (H0 = )2.71) indicating that observa-

tion of performance must be continued to confirm

that the learning curve has improved to an

acceptable failure rate of 10% (Konrad et al. 1998)

(Fig. 1).

Eighty-two out of eighty-six cases (95%) met the

inclusion criteria and were enrolled in this retro-

spective analysis. The demographic data on sex,

age, weight, American Society of Anesthesiologists

(ASA) physical status, spine length and numbers of

dogs categorised in each type of surgery are reported

in Table 1, and the preanaesthetic medication used

in Table 2. Propofol (4–6 mg kg)1, Rapinovet;

Schering Plough, Italy) was used to induce anaes-

thesia in 74 (90%) patients, and thiopental (6–

10 mg kg)1, Pentothal Sodium; Gellini, Italy) was

used in 8 (10%) patients. A median fentanyl bolus

of 3 lg kg)1 (range 2–4 lg kg)1) was used before

induction of anaesthesia to reduce the dose of

induction agent and facilitate endotracheal intuba-

tion. General anaesthesia was maintained with

isoflurane (Isoba; Schering-Plough, Italy) in 71

(88%) patients [median end tidal isoflurane 1%

(0.7–1.3%)] and with a variable rate propofol

infusion (between 15 and 25 mg kg)1 hour)1) in

11 (12%) patients.

A 22-gauge Quincke needle (Terumo, Japan) was

used to perform the spinal injection in 47 (58%), a

25-gauge Quincke needle (Terumo) in 31 (37%)

and a 26-gauge Atraucan needle (B Braun, Ger-

many) in four dogs (5%). The site of spinal injection

was L5-6 in 54 (67%) patients; L4-5 in 15 (18%);

L6-7 in seven (8%) and L7-S1 in six (7%). Bupiva-

caine 0.5% (Bupivacaina Ang; Angelini, Italy) was

used in 73 (89%) cases and levobupivacaine 0.5%

(Chirocaine; Abbot, UK) was used in nine (11%)

cases. Median LA dose related to body mass was

0.40 mg kg)1 (0.3–0.5) while the median dose

related to spinal cord length was 0.1 mg cm)1

(0.07–0.12). Morphine 10 mg mL)1 (Morfina Cl

Molt; Molteni, Italy) was added to LA in 56 (67%)

cases, with a median dose of 0.1 mg kg)1 (0.05–

0.12) or 0.02 mg cm)1 (0.01–0.03) and fentanyl

50 lg mL)1 (Sublimaze; Janseen, Italy) in 22 (27%)

with a median dose of 0.5 lg kg)1 (0.38–0.63), or

0.1 lg cm)1 (0.07–0.15). Five (6%) patients did not

receive any adjuvant. Frequency distribution of



puncture site, median dose of LA in mg kg)1,

median dose in mg cm)1, use of adjuvant and the

premedication used were not different between the

four surgery groups (p > 0.05).

In 35 (43%) dogs spinal reflexes were assessed just

before the spinal injection and about 10 minutes

later. After spinal injection, the patellar reflex was

absent in 33 (94% of those tested), the tibial reflex

in eight (23%), the perineal reflex in five (14%)

patients. A CR post-stimulus was recorded to have

occurred during surgery in 29 (35%) cases: 11 of 22

(50%) in the OV surgery group [11 of 18 (61%) in

animals in which the uterus appeared normal, but

none in the four animals with pyometra]: 14 of 33

(42%) in HLS, 2 of 10 (20%) in CAS, two of 17 (12%)

in CS (Fig. 2). The odds ratio (95% CI) for CR in the

presence of different types of surgery suggested a

significant event risk reduction in CS versus OV (OR

0.133, 95% CI 0.024–0.726, p = 0.019) and CS

versus HLS (OR 0.181, 95% CI 0.035–0.922,

p = 0.020). Although the CAS group should have

been the reference category for the lowest CR

incidence, no significant difference was demon-

strated because of the small sample size and the

small incidence of CR in this group. From the records

it was found that after the occurrence of CR,

anaesthetic depth was increased, and in 18 of the

82 dogs (21%) fentanyl was also administered at a

median dose of 2 lg kg)1 (1–3) followed by an IV

infusion rate between 8–13 lg kg)1 hour)1.

Overall negative CR (NCR) patients (n = 53) had

a median LA dose of 0.41 mg kg)1 (0.28–0.5) and

(a)

(b)

Figure 1 Cumulative sum (Cusum)

analysis of failure rate in spinal

anaesthesia. (a) = Cusum chart in-

creases through seven successive

boundary lines (h0–1: 2.71) in the

first 66 attempts and then changed

the trend. The failure rate for this

series between 1 to 66 is 23/66

(35%), while the total failure rate is

29/115 (25%). (b) = Between case

67 to 115 Cusum has not crossed

any boundary. The null hypothesis

cannot be accept or rejected. The

failure rate for this series is 6/49

(12%).



0.1 mg cm)1 (0.09–0.13), while CR patients

(n = 29) had a median LA dose of 0.4 mg kg)1

(0.32–0.5) and 0.09 (0.06–0.12) mg cm)1. There

was no difference between groups in the median LA

dose based on patient body mass (kg) (Fig. 3) and

spinal length (cm) (Fig. 4) (p > 0.05). Local anaes-

thetic median doses related to body mass (mg kg)1)

and to length (mg cm)1) for CR versus NCR patients

in different types of surgery are reported in Table 3

and Figs 5 & 6. The odds ratio for the dose expressed

in mg cm)1 explored as an independent predictor of

CR risk in the HLS group was 0.963 (95% CI 0.93–

0.99, p = 0.024), but in no other group was it

statistically significant.

Most subjects [67 of the 82 (82%)] were able to

walk with only a residual ataxia 5 hours after spinal

anaesthesia and 12 others (15%) were able to walk

with minimal ataxia between the fifth and the tenth

hour. The remaining three (3%) patients still had a

proprioceptive deficit 18 hours after spinal injec-

tion, but it had completely disappeared at 36 hours.

The body temperature was higher than 36 �C

during the perioperative period in all patients.

We recorded the following side effects in the 82

dogs (Table 4): intraoperatively bradycardia in

seven and A-V block in one; postoperatively urinary

retention in four, postoperative hypersalivation in

six and vomiting in one. Permanent neurologic

injury and mortality at 30 days were not observed

in any patient. Intraoperative hypotension was

recorded in 24 (29%) patients and event frequency

distribution in the different surgery groups was: four

of 10 (40%) CAS, 10 of 33 (30%) in HLS, five of 22

(23%) in OV, and four of 17 (24%) in CS, with no

significant difference between groups (p > 0.05).

From the records, hypotension was treated by

reducing administration of general anaesthetic,

and giving a bolus of fluids (lactated Ringer’s) in

10 minutes (1–3 mL kg)1 over 10 minutes) in 10

of the 24 (42%) dogs. In the other hypotensive dogs,

the following drugs were used: 11 of the 24 (78%)

were treated with a median ephedrine dose of

50 lg kg)1 (25–100); two (16%) with dobutamine

(3 lg kg)1 minute)1 (2–6); one dog (4%) with

hypotension and bradycardia was treated with

atropine (IV) at the dose of 10 lg kg)1. Occurrence

of intraoperative hypotension was not related to the

type of surgery, which was not an independent

predictor of the event (p > 0.05).

Discussion

Pre-emptive spinal anaesthesia caused minimal

side-effects, however at the dose used failed to pro-

vide complete intraoperative analgesia in a propor-

tion of dogs.

We included in this retrospective study dogs that

received intrathecal bupivacaine 0.5% or levobup-

ivacaine 0.5%, as these two anaesthetic agents are

considered equipotent according to the equipotency

studies published in humans (Alley et al. 2002).

The technical failure rate (no CSF flow) of the

Table 1 Demographic and procedures data of anaesthe-

tized dogs that underwent additional spinal anaesthesia

Spinal punctures – number of dogs 115

Failure rate – number of dogs 29 of these 115 (25%)

Animals (number and %) that met

inclusion criteria (successful puncture,

local administered, and completed

records)

82 (95%) of the 86

which received

SA: 26 males,

56 females

Physical Status (n = 82 dogs)

ASA I 19 (23%)

ASA II 52 (63%)

ASA III 11 (14%)

ASA IV and V 0 (0%)

Age in months [median (range)] 72 (6–168)

Body mass in kg [median

(range)]

12 (2–75)

Spinal length L7-occiput in cm

[median (range)]

50 (32–100)

Time between spinal injection and

beginning of surgery in minutes

[median (range)]

10 (5–24)

Duration of surgery in minutes

[median (range)]

50 (30–150)

Classification of Surgery

Hindlimb Surgery (HLS) 33 (40%)

Caudal Abdominal Surgery (CAS) 10 (12%)

Caesarean section (CS) 17 (21%)

Ovariohysteretomy (OV) 22 (27%)

Table 2 Type of preanaesthetic medication used in 82

anaesthetized dogs that underwent successful spinal anal-

gesia

Number of dogs (%) Premedication

47 (57) Methadone 0.25 mg kg)1(0.2–0.3)

7 (9) Medetomidine 2 lg kg)1

5 (6) Methadone 0.1–0.2 mg kg)1 and

Medetomidine 2 lg kg)1

4 (5) Methadone 0.1–0.2 mg kg)1,

Acepromazine 10–20 lg kg)1 and

Medetomidine 2 lg kg)1

19 (23) No preanaesthetic medication



technique was higher than expected. Failure rate

reported in humans is considerably lower in all

types of surgery considered here (Levy et al. 1985;

Brun-Buisson et al. 1988; Tarkkila 1991; Williams

et al. 2006). The reason for this relatively high rate

of technical failures in dogs could be the variable

morphology of subjects, related to breed and to

amount of subcutaneous fat, but it should also be

considered that in our study the technique was not

performed with the aid of fluoroscopic or radio-

graphic guidance, which may have improved suc-

cess rate. In our study it was apparent that failure

rate significantly decreased with time, suggesting

the existence of a learning curve for this technique.

Once the procedure had been performed 66 times,

the learning curve changed and the failure rate

reduced to just above the acceptable level of 10%. It

is therefore likely that success rates similar to those

obtained in humans can be achieved in dogs with

increasing experience of the operator.

The rate of hypotension that we report in dogs

undergoing combined general and spinal anaesthe-

sia is similar to that found in human patients

undergoing spinal anaesthesia alone (Carpenter

Figure 2 Incidence of cardiovascular

response (CR) as % of the number of

dogs in each different surgical cate-

gory. For definitions of the categories

see Table 1. The odds ratio (95% CI)

for CR in the presence of different

types of surgery showed a significant

event risk reduction in CS versus OV

(OR 0.133, 95% CI 0.024–0.726,

p = 0.019) and CS versus HLS (OR

0.181, 95% CI 0.035–0.922, p =

0.020).

Figure 3 Box plot of local anaes-

thetic median dose related to body

mass in dogs which showed a car-

diovascular response to surgery

(group CR) and those that did not

(group NCR). There was no difference

in median local anaesthetic (LA) dose

based on body mass (p > 0.05).



et al. 1992). The individual contribution of spinal

and general anaesthesia to cardiovascular depres-

sion remains undefined in our study, and further

characterisation may be complicated by the fact

that locoregional techniques are very rarely per-

formed in non-anaesthetized animals. Hypotensive

episodes were treated easily by reducing the amount

of anaesthetic delivered, fluid boli and by using

sympathomimetic drugs. The fluid bolus used to

treat hypotension in the cases examined in this

retrospective study was relatively small, so it is

possible that the improvement of arterial blood

pressure after its administration may have been

caused by the concomitant reduction of anaesthetic

agent. Administration of a larger volume of crys-

talloids or colloids may have been effective in

increasing arterial blood pressure without resorting

to administration of vasoactive agents. The most

likely cause of hypotension after SA is sympathetic

blockade and vasodilation (Sevarino 2003), and it

may be argued that the most appropriate interven-

tion to treat this complication is administration of a

vasoconstrictor, because intravenous administra-

tion of large volumes of fluids would impose a

considerable workload on the kidney during the

postoperative period.

Presence of CR as a sign of lack of complete

analgesia was more frequent in our study than


thetic median dose related to spinal

length in CR and NCR group. There

was no difference in median LA dose

based on spinal length (p > 0.05).

For group definitions, see Fig. 3.

Table 3 Local anaesthetic median (interquartile range) dose related to body mass (mg kg)1) and to length of spine

(mg cm)1) given to dogs which demonstrated a cardiovascular response (CR) compared to those that did not (NCR) in

different types of surgery. For group descriptions, see Table 1

Groups

CR dose related

to body mass

NCR dose related

to body mass p-value

CR dose related

to length

NCR dose related

to length p-value

CAS 0.32 mg kg)1

(0.27, 0.37)

0.37 mg kg)1

(0.29, 0.56)

ns 0.1 mg cm)1

(0.07, 0.13)

0.09 mg cm)1

(0.08, 0.13)

ns

OV 0.4 mg kg)1

(0.34, 0.46)

0.37 mg kg)1

(0.25, 0.5)

ns 0.12 mg cm)1

(0.07, 0.15)

0.1 mg cm)1

(0.07, 0.11)

ns

CS 0.28 mg kg)1

(0.19, 0.37)

0.5 mg kg)1

(0.3, 0.62)

ns 0.07 mg cm)1

(0.04, 0.1)

0.1 mg cm)1

(0.06, 0.13)

ns

HLS 0.41 mg kg)1

(0.31, 0.51)

0.42 mg kg)1

(0.25, 0.50)

ns 0.1 mg cm)1

(0.09, 0.11)

0.08 mg cm)1

(0.05, 0.1)

p = 0.022

ns, not significant.



reported in humans for similar types of surgery

(Williams et al. 2006). The risk of CR was smaller in

CS compared to other surgeries, despite a similar

dose per unit of body mass. While CR rate was

acceptable in CS, the incidence of CR in OV was in

our opinion unsatisfactory. The high rate of CR in

OV surgery may have resulted from the extensive

area involved by surgery. A possible reason for the

unexpected high rate of CR may be the individual

variability of CSF volume in dogs, which makes it

difficult to find the minimum effective dose in each

patient.

Morphine or fentanyl was administered also, to

improve postoperative analgesia, and to obtain a

better intraoperative sensory block, respectively.

Spinal administration of opioids may have reduced

the occurrence of CR, and in order to better

characterize the effect of SA on CR a prospective

study in which SA is performed with LA alone

should be carried out.


thetic median dose related to body

mass (mg kg)1) in group CR versus

group NCR for different types of

surgery (CAS, CS, OV, HLS). For

group definitions see Fig. 3, and for

definitions of surgery types, Table 1.

There was no difference in median

LA dose based on body mass

(p > 0.05). NA = not applicable be-

cause of low sample size.


thetic median dose related to spinal

length (cm kg)1) in group CR com-

pared to group NCR for different

types of surgery (CAS, CS, OV, HLS).

For group definitions see Fig. 3, and

for definitions of surgery types,

Table 1. In HLS surgery, median CR

dose related to spinal length was

different between group CR and non

group NCR (p = 0.022). NA = not

applicable because of low sample size.

For group definitions see Fig. 3, and

Table 1.



Other major confounding factors dependent on

the execution of the technique are needle direction,

puncture site and speed of injection. A prospective

study, aimed at evaluating which independent

variables better predict the minimum effective dose,

is needed to reduce the incidence of CR. Because of

the great morphotypic differences in our patients’

population, this prospective study should include a

large sample. Evaluation of spinal reflexes after

intrathecal injection using as site of puncture L5-6

and a needle with a cranial direction, demonstrated

a high incidence of partial caudal motor block

(presence of the tibial reflex and absence of the

patellar reflex). Considering that the canine spinal

cord ends at the caudal lumbar vertebrae (L6 to S1),

in order to reach a higher rate of caudal motor block

it is most likely necessary to consider a more caudal

puncture site, a caudal direction of the needle or the

use of hyperbaric solutions. This finding may

depend on the different location of the dural sac in

dogs compared to humans (McCartney 1997). In

humans the spinal cord ends at the L2 interverte-

bral space and spinal anaesthesia is normally

performed at the level of L3-4 or L2-3, because in

these locations the risk of puncture of the spinal

cord is low. Although the needle is placed more

cranially in humans compared to dogs, the local

anaesthetic is administered in a more caudal

position compared to the end of the spinal cord.

Thus, a caudal block is always performed. In dogs,

we chose to perform the puncture at the level of

L5-6 because, in our experience, this space is

usually easy to identify in most patients, but this

may have resulted in a block more cranial than

planned. Specific anatomic spinal studies are

required to confirm this hypothesis. It has been

shown in humans that palpation alone used to

identify lumbar interspinous spaces is inaccurate,

and the puncture level is usually estimated to be at

least one interspace higher (Schlotterbeck et al.

2008). Since we did not confirm the exact location

of the needle with radiography or fluoroscopy, it is

possible that we encountered a similar problem.

The motor block completely disappeared in the

majority of subjects within 5 hours, but we were

not able to characterise in detail return of spinal

reflexes and motor function, because of the retro-

spective nature of the study. Since in humans it has

been shown that morphine prolongs the duration of

the motor block (McCartney 1997), the possibility of

reducing its dose could be considered to hasten

recovery of motor function. In addition, another

method to increase the extension of the block while

decreasing its duration could be increasing the

volume of local anaesthetic while maintaining the

same dose (Malinovsky et al. 1999).

The use of opioids as adjuvants is common in

spinal anaesthesia to improve the quality of the

block and to achieve a longer lasting analgesia in

the postoperative period. In humans, together with

these advantages, some dose dependent side effects

are also present, including pruritus, urinary reten-

tion, respiratory depression and nausea (Carpenter

et al. 1992). Many studies have investigated the

optimal dose of intrathecal morphine and fentanyl

necessary to reduce these side effects but achieve

the best analgesic effect. In dogs, however, while

the toxicity of a spinal morphine injection after an

accidental overdose is reported (Kona-Boun &

Pibaroty 2003) the incidence of side effects using

the therapeutic dose has not been determined in a

large scale study. Respiratory depression and

pruritus were not identified in our retrospective

study. In humans, postoperative urinary retention

is a common problem that occurs in between 7%

and 52% of patients after SA (Feliciano et al.

2008). It is associated with an increased rate of

urinary tract infections (Carpenter et al. 1992) and

causes additional discomfort and pain for the

patients undergoing surgery. Male gender, increas-

ing age, a history of bladder outflow problems

(Feliciano et al. 2008), postoperative presence of

epidural catheter (Lingaraj et al. 2007) are all

considered risk factors for the development of

urinary retention in humans. The factors that

affect the risk of urinary retention in dogs are

unknown. The low incidence of these events and

Table 4 Incidence of side effects in 82 dogs that received

spinal anaesthesia

Side effect

Number of

dogs (%)

Intraoperative bradycardia 7 (9)

Intraoperative 2nd degree A-V block 1 (1)

Postoperative urinary retention 4 (5)

Postoperative hypersalivation 6 (7)

Postoperative vomiting 1 (1)

Intraoperative hypotension 24 (29)

Postoperative pruritus 0 (0)

Postoperative transitory or permanent

neurologic injury

0 (0)

Mortality (intraoperative and 30 days) 0/82 (0)



the relatively small sample size in our study does

not allow speculation on possible risk factors for

developing urinary retention in dogs after spinal

anaesthesia. However, draining the urinary blad-

der at the end of the surgical procedure, and

careful titration of intraoperative fluid-therapy and

effective pain control are recommended. Even if the

incidence of postoperative urinary retention is

lower in dogs than in humans, it must still be

considered a possible complication and monitoring

is advised.

We cannot exclude the possibility that the differ-

ent premedications and anaesthetic protocols used

in this retrospective study may have affected our

results. In order to investigate their effect in a

clinical trial, a considerably larger sample is

required. That there is a small difference in density

between bupivacaine and levobupivacaine could

have also influenced the distribution of the LA in the

CSF and could be considered a study limitation.

Another limitation of our study is represented by

monitoring arterial blood pressure using an oscillo-

metric technique, which may not guarantee the

same level of accuracy in all patients.

Post-operative analgesia was monitored and as-

sessed in the dogs, but the use of different pain scoring

systems during the time period of the study prevented

the results from being of use for comparison of the

efficacy of spinal analgesia in providing postoperative

analgesia with different groups. The absence of

patients requiring rescue analgesia both in the CR

and NCR group could indicate long acting effects of

spinal morphine or fentanyl, but all dogs received

meloxicam which also has a long duration of action.

In conclusion, spinal anaesthesia represents a

valid alternative to epidural anaesthesia, and in our

series of 82 dogs, appeared safe and had a low

incidence of side effects. Spinal anaesthesia, how-

ever, requires continuous monitoring of haemo-

dynamic parameters in order to rapidly detect

hypotension and assess anaesthetic depth to mini-

mize cardiovascular depression. In our study the

absence of difference in the dose related to body

mass between haemodynamic responders to surgi-

cal stimulation and non responders makes it difficult

to suggest a dose able to predict the presence or

absence of cardiovascular response to surgery,

based on body mass alone. Future studies aimed at

investigating the use of hyperbaric local anaesthetic

solution or higher doses of plain local anaesthetic

solution may allow better characterization and

refinement of this technique.

References

Alley EA, Kopacz DJ, McDonald SB et al. (2002) Hyper-

baric spinal levobupivacaine: a comparison to racemic

bupivacaine in volunteers. Anesth Analg 94, 188–193.

Ben-David B, Solomon E, Levin H et al. (1997) Intrathecal

fentanyl with small-dose diluted bupivacaine: better

anesthesia without prolonging recovery. Anesth Analg

85, 560–565.

Bier A (1899) Versuche uber Kokainisierung des Ruc-

kenmarks. Dtsch Z Chir 51, 361–369.

Brull R, McCartney CJ, El-Beheiry H et al. (2007)

Neurological complications after regional anesthesia:

contemporary estimates of risk. Anesth Analg 104,

965–974.

Brun-Buisson V, Bonnet F, Saada M et al. (1988) Failure of

spinal anaesthesia. Evaluation of the practice at a uni-

versity hospital. Ann Fr Anesth Reanim 7, 383–386.

Campoy L (2004) Epidural and spinal anaesthesia in the

dog. In Pract 26, 262–269.

Carpenter RL, Caplan RA, Wu R et al. (1992) Incidence

and risk factors for side effects for spinal anesthesia.

Anesthesiology 76, 906–916.

Cuille J, Sendrail M (1901) Analgesie cocainique par voie

rachidienne. Rev Vet 26, 98–103.

Curatolo M, Petersen-Felix S, Zbinden AM et al. (1997)

Spinal anaesthesia inhibits central temporal summation.

Br J Anaesth 78, 88–89.

Dripps RD, Vandam LD (1954) Long-term follow-up of

patients who received 10,098 spinal anesthetics: failure

to discover major neurological sequelae. J Am Med

Assoc 156, 1486–1491.

Feliciano T, Montero J, Priester M et al. (2008) A retro-

spective, descriptive, exploratory study evaluating inci-

dence of postoperative urinary retention after spinal

anesthesia and its effect on PACU discharge. J Perianesth

Nurs 23, 394–400.

Freedman J, Li D, Jaskela M et al. (1998) Transient neuro-

logic symptoms after spinal anaesthesia: an epidemiologic

study of 1,863 patients. Anesthesiology 89, 633–641.

Greene NM (1985) Distribution of local anesthetic solu-

tions within the subarachnoid space. Anesth Analg 64,

715–730.

Greene BA, Barnett A (1950) A 26 gauge lumbar punc-

ture needle: its value in the prophylaxis of headache

following spinal analgesia for vaginal delivery. Anes-

thesiology 11, 464–469.

Hogson PS, Neal JM, Liu SS et al. (1999) The neurotoxicity

of drugs given intrathecally (Spinal). Anesth Analg 88,

797–809.

Kehlet H (1991) The surgical stress response: should it be

prevented? Can J Surg 34, 565–567.

Kona-Boun JJ, Pibaroty P (2003) Veterinary myoclonus

and urinary retention following subarachnoid morphine

injection in a dog. Anesth Analg 30, 257–264.

Konrad C, Schupfer G, Wietlisbach M et al. (1998)

Learning manual skills in anesthesiology: is there a



recommended number of cases for anesthetic proce-

dures? Anesth Analg 86, 635–639.

Levy JH, Islas JA, Ghia JN et al. (1985) A retrospective

study of the incidence and causes of failed spinal anes-

thetics in a university hospital. Anesth Analg 64, 705–

710.

Lingaraj K, Ruben M, Das SD et al. (2007) Identification of

risk factors for urinary retention following total knee

arthroplasty: a Singapore hospital experience. Singapore

Med J 48, 213–216.

Malinovsky JM, Renauld G, Pinaud M et al. (1999)

Intrathecal bupivacaine in humans. Influence of volume

and baricity of solutions. Anesthesiology 91, 1260–

1266.

McCartney WT (1997) Lumbar myelography in 79

dogs using different puncture sites. Vet Rec 141, 417–

419.

Modig J (1988) Regional anaesthesia and blood loss. Acta

Anaesthesiol Scand Suppl 89, 44–48.

Novello L, Corletto F (2006) Combined spinal-epidural

anesthesia in a dog. Vet Surg 35, 191–197.

Novello L, Corletto F, Rabozzi R et al. (2008) Sparing

effect of a low dose of intrathecal morphine on fen-

tanyl requirements during spinal surgery: a pre-

liminary clinical investigation in dogs. Vet Surg 37,

153–160.

Rodgers A, Walker N, Schug S et al. (2000) Reduction of

postoperative mortality and morbidity with epidural or

spinal anaesthesia: results from overview of randomized

trials. BMJ 321, 1493–1504.

Samii K, Chauvin M, Viars P (1981) Postoperative spinal

analgesia with morphine. BJA 8, 817–820.

Sarotti D (2005) Elective spinal anaesthesia for caesarean

section in a bull terrier. Vet Reg Anaesth Pain Med 3,

53–54 (abstract). Available from http://www.isvra.org

Schlotterbeck H, Schaeffer R, Diemunsch P et al. (2008)

Ultrasonographic control of the puncture level for lum-

bar neuraxial block in obstetric anaesthesia. Br J Ana-

esth 100, 230–234.

Sevarino F (2003) Management of hypotension in obstet-

ric anesthesia: is it time to rewrite the textbooks? Curr

Opin Anaesthesiol 16, 249–251.

Sprotte G, Schedel R, Pajunk H (1987) An atraumatic

universal needle for single-shot regional anaesthesia:

clinical results and a 6 year trial in over 30000 regional

anaesthesias. Reg Anaesth 10, 104–108.

Tarkkila PJ (1991) Incidence and causes of failed spinal

anesthetics in a university hospital: a prospective study.

Reg Anesth 16, 48–51.

Troncy E, Stephane J, Sophie C et al. (2002) Results of

preemptive epidural administration of morphine with or

without bupivacaine in dogs and cats undergoing sur-

gery: 265 cases (1997–1999). J Am Vet Med Assoc 5,

666–672.

Weissman C (1990) The metabolic response to stress: an

overview and update. Anesthesiology 73, 308–327.

Williams RK, Adams DC, Aladjem EV et al. (2006) The

safety and efficacy of spinal anesthesia for surgery in

infants. Anesth Analg 102, 67–71.

Wynands JE, Wong P, Townsend GE et al. (1984) Narcotic

requirements for intravenous anesthesia. Anesth Analg

63, 101–105.

Received 29 March 2010; accepted 11 August 2010.



Efficacy and side effects of intraoperative analgesia with intrathecal bupivacaine and...

Documents

Transcript of Efficacy and side effects of intraoperative analgesia with intrathecal bupivacaine and...