European Journal of Cardio-thoracic Surgery 40 (2011) 902—906
www.elsevier.com/locate/ejcts
Intra-operative paravertebral block for postoperative
analgesia in thoracotomy patients: a randomized,
double-blind, placebo-controlled study
Olivier Helms a,*, Juliette Mariano a, Jean-Gustave Hentz a, Nicola Santelmo b,
Pierre-Emmanuel Falcoz b, Gilbert Massard b, Annick Steib a
a
Department of Anaesthesia and Intensive Care Medicine, Strasbourg University Hospital, Strasbourg, France
b
Department of Thoracic Surgery, Strasbourg University Hospital, Strasbourg, France
Received 6 December 2010; received in revised form 17 January 2011; accepted 26 January 2011; Available online 5 March 2011
Abstract
Objective: Epidural analgesia is the gold standard for post-thoracotomy pain relief but is contraindicated in certain patients. An alternative is
paravertebral block. We investigated whether ropivacaine, administered through a paravertebral catheter placed by the surgeon, reduced
postoperative pain. Methods: In a randomized double-blind study, adult patients with a paravertebral catheter placed by the thoracic surgeon
after thoracotomy were randomly assigned to receive through this catheter, either a 0.1 ml kg 1 bolus of 0.5% ropivacaine, followed by a
continuous infusion of 0.1 ml kg 1 h 1 for 48 h, or saline at the same scheme of administration. Patients also benefited from patient-controlled
analgesia with intravenous morphine (bolus 1 mg, lockout time 7 min), paracetamol, and nefopam. The primary endpoint was pain intensity on a
visual analog scale at rest and on coughing. Secondary endpoints were total morphine consumption and side effects during the first 48
postoperative hours. Surgeons, anesthesiologists, and all the nurses and caring staff involved in this study were blinded. Solutions of saline and
ropivacaine were prepared identically by the central pharmacy, without any possible identification of the product. Results: Forty-seven patients
with contraindications to epidural anesthesia were included. There were no significant differences between the groups receiving ropivacaine and
saline in terms of pain severity at rest and on coughing, mean postoperative morphine consumption (45.7 mg for ropivacaine, 43.2 mg in controls),
and incidence of morphine-related side effects (nausea and vomiting, urinary retention, pruritus, respiratory rate, and sedation). Conclusions:
Paravertebral block using a catheter placed by the thoracic surgeon was ineffective on postoperative pain after thoracotomy and did not confirm
the analgesic effect that has been observed after percutaneous catheter placement. A direct comparison of these two placement methods is
required.
# 2011 European Association for Cardio-Thoracic Surgery. Published by Elsevier B.V. All rights reserved.
Keywords: Paravertebral; Analgesia; Thoracic surgery; Thoracotomy
1. Introduction
Morbidity and mortality rates after pulmonary resection
by thoracotomy remain high. Effective analgesia at rest and
on coughing can help reduce postoperative morbidity through
early mobilization and rehabilitation. Thoracic epidural
analgesia is the gold standard not only for pain relief after
thoracotomy because of its efficiency but also for many
beneficial effects (reduction in the intra-operative requirements for opioids, improvement in postoperative ventilatory
function and in cardiac performance, suppression of stress
response, etc.). Unfortunately, it is contraindicated in
* Corresponding author. Address: Pôle d’Anesthésie Réanimation SAMU 67/
SMUR, CHU de Strasbourg-NHC, 1 place de l’Hôpital — BP 426, 67091 Strasbourg
Cedex, France. Tel.: +33 3 69 55 12 72; fax: +33 3 69 55 18 10.
E-mail address: [email protected] (O. Helms).
patients in whom anticoagulant or antiplatelet drugs can
be interrupted peri-operatively only for a very short time and
must be reintroduced quickly after surgery [1—5]. An
alternative to epidural analgesia is thoracic paravertebral
block (PVB) which induces nerve block of multiple contiguous
thoracic dermatomes above and below the infusion site [6].
Two alternatives are used to locate the paravertebral space
for catheter insertion: a blind anesthetic approach (loss of
resistance technique) described by Eason and Wyatt [7] and
de visu during surgery [8].The present placebo-controlled
study in patients with a contraindication to epidural
analgesia investigates whether administering the local
anesthetic ropivacaine through a paravertebral catheter
placed by the thoracic surgeon after thoracotomy, combined
with multimodal intravenous patient-controlled analgesia
(PCA), reduces pain severity during the first 48 h after
surgery.
1010-7940/$ — see front matter # 2011 European Association for Cardio-Thoracic Surgery. Published by Elsevier B.V. All rights reserved.
doi:10.1016/j.ejcts.2011.01.067
O. Helms et al. / European Journal of Cardio-thoracic Surgery 40 (2011) 902—906
2. Materials and methods
2.1. Design and setting
This was a prospective randomized placebo-controlled
study performed between March 2008 and January 2009 at
Strasbourg University Hospital. The Institutional Review
Board approved the study (reference 07/469, January
2008; clinical trial registry number PRI HUS N8 4068). All
subjects provided written and informed consent.
2.2. Inclusion and exclusion criteria
We included consecutive patients aged 18—80 years
scheduled for unilateral thoracotomy with a contraindication
to thoracic epidural analgesia or those who refused such
analgesia. These contraindications included antiplatelet
treatment, therapeutic anticoagulant treatment, hemostasis, and/or coagulation disorders (platelets <100,000 mm 3,
activated partial thromboplastin time >1.5, prothrombin
ratio <75%), local or systemic infection, second- or thirdgrade atrioventricular block without a pacemaker, severe
aortic stenosis, severe scoliokyphosis, and known neuropathy. Exclusion criteria were difficulty in understanding the
study protocol, pregnancy and breast-feeding, epilepsy,
third-grade atrioventricular block without a pacemaker,
severe hepatic insufficiency, anti-arrhythmic treatment,
local infection at insertion site, allergy to local anesthetics,
and surgical contraindications to catheter insertion.
2.3. Catheter insertion procedure
After thoracotomy, a multi-perforated catheter was
inserted as described by Berrisford et al. [9] without raising
of the pleura to avoid endopleural spread of local anesthetic.
Therefore, an 18-G Tuohy needle was advanced perpendicularly through the chest wall until the needle tip was visible
through the parietal pleura. The percutaneous puncture
point was located 10 cm far from the midline, at the same
level than intercostal space chosen for the thoracotomy.
Injection of 20-ml saline created an extrapleural detachment
pocket. The catheter was then inserted 10 cm into the
paravertebral space under direct visual control by the
surgeon who confirmed its correct location. After checking
for the absence of blood reflux by aspiration, 4 ml of 2%
lidocaine containing 5 mg ml 1 epinephrine were injected via
the catheter. Surgery was performed by three senior
surgeons, always in axillary’s position.
2.4. Patient randomization
A list of random numbers was generated by Excel and
patients with a successfully placed catheter were randomly
assigned, according to this list, to receive in a double-blind
manner either 0.9% saline or 0.5% ropivacaine administered
as an initial bolus of 0.1 ml kg 1 and then as a continuous
0.1 ml kg 1 h 1 infusion for 48 h postoperatively. Investigators used a programmable portable, electronic infusion pump
(CADD Prizm PCS PCA pump). All patients received 1 g
paracetamol and 20 mg nefopam 1 h before the end of
surgery followed by 1 g paracetamol every 6 h and 100 mg
903
nefopam every 24 h. Patients also benefited from IV PCA of
morphine (1 mg morphine bolus, lockout time 7 min) with
added droperidol (0.05 mg ml 1) and ketamine (1 mg ml 1).
Investigators were blinded to treatment group. The postoperative care, which included physiotherapy, was the same
for all the patients.
2.5. Endpoints
The primary endpoint was pain at rest and on coughing. It
was evaluated after 1, 3, 6, 12, 24, 36, and 48 h using a visual
analog scale (VAS) from 0 to 10 (0 = no pain, 10 = worst pain
imaginable). Secondary endpoints were total morphine
consumption and morphine-related side effects (nausea
and vomiting, urinary retention, pruritus, and sedation).
Heart rate, arterial blood pressure, and oxygen saturation
rate were recorded. The sensory and motor function of the
arms and the aspect of the catheter site were checked daily
as well as the superior and inferior level of the sensory
function of the chest wall, using an ice cubicle.
2.6. Statistics
The number of intent to treat was 20 per group for an a
risk of 0.05 and a b risk of 0.12 to demonstrate a 30%
difference in VAS score at rest between the two groups. The
two groups were compared by Student’s t-test. A variance
analysis was used for repeated measures. A p-value <0.05
was considered statistically significant. All analyses were
performed with SPSS software (version 13.0).
3. Results
Between March 2008 and January 2009, 283 patients
underwent thoracotomy in our hospital. Of these, 47
presented contraindications to epidural anesthesia and were
enrolled in our study. These contraindications were antiplatelet treatment (35%), therapeutic anticoagulant treatment (31%), patient refusal (12%), hemostasis and/or
coagulation disorders (2%), severe scoliokyphosis (2%), and
other (18%). Seven patients were excluded for the following
reasons: surgical contraindication to catheter insertion
(history of parietal pleurectomy), hemorrhage requiring
revision surgery, prolonged ventilation, myocardial infarction, and logistic reasons. The type of intervention undergone by the 40 remaining patients was lobectomy (74%),
wedge (11%), pneumectomy (7%), segmentectomy (2%),
exploratory thoracotomy (2%), and other (4%).
These 40 included subjects were randomized to receive
either 0.5% ropivacaine (n = 19) or saline (n = 21). There were
no significant differences between the two groups in terms of
demographics (except for the mean age: p = 0.026), morphometric features, American Society of Anesthesiologists (ASA)
score, vital signs, or in the type of contraindication to epidural
anesthesia or surgical procedure (Table 1).
Patients receiving 0.5% ropivacaine or saline experienced
similar pain severity at rest ( p = 0.380) and on coughing
( p = 0.433) (Fig. 1A and B). Their mean morphine consumption during the first 48 postoperative hours was similar:
O. Helms et al. / European Journal of Cardio-thoracic Surgery 40 (2011) 902—906
904
Table 1. Demographics.
Group
Mean
Standard deviation
Standard error
Minimum
Maximum
p value
Age (years)
Ropivacaine
Control
57.74
65.42
13.715
8.782
2.860
1.793
21
44
76
77
0.026 *
Weight (kg)
Ropivacaine
Control
74.65
77.00
15.302
15.010
3.191
3.064
45
54
102
115
0.598
Height (cm)
Ropivacaine
Control
Control
171.17
172.63
16.67
8.711
6.927
2.120
1.816
1.414
0.433
150
160
12
187
186
20
0.530
ASA score
Ropivacaine
Control
2.48
2.68
0.511
0.504
0.106
0.103
2
2
3
3
0.481
Time for surgery (min)
Ropivacaine
Control
155
145
260
300
0.151
*
199
220
38.5
47.3
8.6
10.6
Significative.
45.7 33.9 mg for ropivacaine and 43.2 30.3 mg for saline
(Fig. 2A and B).
The incidence of morphine-related side effects did not
differ significantly between the two groups of patients.
Incidence was as follows: for nausea and vomiting, 8.7% for
ropivacaine versus 0% for saline ( p = 0.219), for urinary
retention, 39.1% versus 29.17% ( p = 0.530), and for sedation
( p = 0.942). There were no cases of pruritus in either group.
The catheter remained clean over 48 h. The motor
function was similar in both groups ( p = 0.739 for the
ropivacaine group and p = 0.761 for the control group). No
patient experienced a motor block of the arms. There was no
significant difference between sensory function of the chest
wall between the two groups at any time.
4. Discussion
[()TD$FIG]
Administration of a 0.1 ml kg 1 bolus of 0.5% ropivacaine
followed by continuous infusion of 0.1 ml kg 1 h 1 via
surgical placed paravertebral catheter combined with PCA
(morphine) was not superior to PCA alone in terms of pain
[()TD$FIG]
Fig. 1. Visual analog scale mean values (standard error) during the first 48 h:
(A) at rest, (B) on coughing.
Fig. 2. Morphine consumption (standard error): (A) validated requests, (B)
total requests.
PVB (percutaneous)
vs systemic analgesia.
RCT
Marret et al.,
2005 [6]
Thoracotomy
PVB (percutaneous)
vs epidural
Thoracotomy
Prospective
RCT
Richardson et al,
1999 [13]
PVB (intra-operative
placement) vs epidural
Thoracotomy
PVB: paravertebral block; RCT: randomized controlled trial; VAS: visual analog scale; DB: double-blind.
40
Lower score for PVB at rest and effort
( p < 0.005)
Not DB
Double bupivacaine
concentration for PVB
Lower score for PVB ( p = 0.02 at rest;
p = 0.0001 on coughing)
100
Not DB
No VAS scores 1st 32 h
50
68 (22 vs 21 vs 20)
Infusion 0.25% bupivacaine vs 1%
lidocaine vs saline
0.1% bupivacaine
(10—15 ml h 1) + 10 mg ml 1
fentanyl
0.5% bupivicaine
(20 ml pre-op bolus) + infusion 0.25%
bupivacaine (0.1 ml kg 1 h 1)
0.5% ropivacaine (0.1 ml kg 1 h 1) vs
multimodal analgesia
PVB (percutaneous)
Thoracotomy
Double-blind
RCT
Prospective DB
RCT
Prospective
RCT
Berrisford et al.,
1990 [9]
Barron et al.,
1999 [17]
Bimston et al.,
1999 [8]
PVB (percutaneous)
Infusion 0.5% bupivacaine vs saline
46 (25 vs 21)
Lower score for PVB over 5 days
( p < 0.01)
Lower score for PVB ( p < 0.05)
over first 72 h
Scores similar over first 8 h but lower
for epidural next 32 h
No objective pain
assessment
No control
Thoracotomy
Pain relief
92.6% patients required no additional
analgesia over 24 h post-operative
81
Patients (n)
Anesthetic
0.5% bupivacaine (5—7 ml h 1)
PVB (percutaneous)
Analgesia
Surgery
Type
Retrospective
Study
Sabanathan et al.,
1988 [21]
Table 2. Review of studies.
Thoracotomy
Comment
O. Helms et al. / European Journal of Cardio-thoracic Surgery 40 (2011) 902—906
905
relief at rest or on coughing during the first 48 h following
thoracotomy raising on the efficiency of this technique.
Ropivacaine is comparable to bupivacaine for its local
anesthetic effects and was chosen in this study for its lower
cardiotoxicity.
Published results on pain relief by PVB after thoracotomy
are reviewed in Table 2 and have been the subject of three
recent reviews [10—12]. PVB is an effective technique with
few adverse effects. However, most studies on PVB have
included small numbers of patients and have tended to
employ percutaneous and not surgical paravertebral catheterization. No study to date has compared the two catheter
placement methods. A large body of evidence has established
the marked superiority of epidural anesthesia over other
types of analgesia after thoracotomy [1—5]. The results of
the Richardson et al. study in Table 2, however, conflict with
this evidence [13]. This team found significantly lower VAS
scores at rest and on coughing for PVB than for epidural
anesthesia probably because they doubled the local
anesthesia doses in PVB patients.
Discrepancies with our results can be noted in Table 2.
Coveney et al. successfully used the percutaneous PVB
technique to perform major breast cancer surgery, whereas
our surgical PVB technique was unable to lower VAS scores
significantly with respect to control [14]. The VAS pain scores
in the Naja et al. study are similar to ours (VAS at rest <3, on
coughing 5) but to achieve such scores we used a daily
ropivacaine dose exceeding 900 mg and combined PVB and
PCA [15].
Our VAS scores at rest and on coughing are also similar to
those of Marret et al. over the first postoperative 12 h but we
administered a much higher mean intra-operative sufentanil
dose (80 mg vs 45 mg) — however, for much lengthier operations
(210 min vs 68 min) [6]. A longer operation might induce more
postoperative pain and impact adversely on PVB efficacy. Marret
et al. recorded significantly lower VAS scores after epidural
analgesia than after PVB using statistical methodology similar to
ours but their assessment of PVB efficacy might be flawed by
subjectivity because of the lack of a control and a double-blind
design. Paradoxically, both their epidural analgesia and PVB
groups had similar total morphine consumption, whereas VAS
pain scores decreased significantly in the PVB group.
VAS pain scores on coughing in the Fibla et al. study were
similar to ours: 3.8 versus 4.26, respectively after 1 h, 7.1
versus 4.05 after 6 h, 6.6 versus 5.11 after 24 h, and 5.2
versus 5.11 at 48 h [16]. However, our daily ropivacaine dose
was 7.6-fold higher (nearly 920 mg for a mean patient weight
of 75.85 kg vs just 120 mg), thus calling into question the
reliability of our intra-operative catheter placement technique. An accidental breach of the parietal pleura might have
led to ropivacaine leaking into the pleural space, thus
lowering PVB efficacy, but our patient numbers make this
unlikely. We could have used a methylene blue test to check
parietal pleura integrity or injected contrast agent before Xray to check correct extrapleural and paravertebral product
diffusion [6]. We did not check the right position of the
catheter with a bolus of local anesthetic, which could have
limited this double-blind study by reducing VAS score in a
patient randomized to the saline group.
In our study, there was a marked increase in pain between
6 and 36 h after surgery. The early increase may have been
906
O. Helms et al. / European Journal of Cardio-thoracic Surgery 40 (2011) 902—906
due to less PCA use at night when the patient was asleep but
the increase on the following day is less easy to explain.
Intense respiratory physiotherapy or patient mobilization by
nurses during care might explain the increase.
Since both our study groups had similar VAS pain scores, it is
not surprising that morphine consumption in both groups was
also similar. Our morphine consumption was higher than that in
the Coveney et al. retrospective study in which only 25% of
patients benefiting from PVB required morphine versus 98% of
patients in the general anesthesia group [14]. However, these
authors did not report morphine doses and used percutaneous
PVB. Our total morphine requirements were also significantly
higher than in the placebo-controlled studies by Berrisford
et al. and Barron et al. using percutaneous PVB [9,17]. Total
consumption over 48 h in our study (intra-operative PVB) was
similar to that in the Marret et al. study (percutaneous PVB)
(43.2 mg vs 57 24 mg for controls, 45.7 mg vs 51 29 mg for
ropicavaine) [6]. However, initial morphine-titrated doses in
their study were higher (9 mg vs 6 mg for saline, 6 vs 4.6 for
ropivacaine). Although the difference was significant in their
study ( p = 0.02), it was not so in ours ( p = 0.637). Despite the
addition of ketamine, the higher morphine doses in our study
may have induced hyperalgesia [18]. Burns et al. (preoperative
percutaneous PVB) observed a 63% lower morphine consumption than Watson et al. (intra-operative PVB), highlighting the
value of early infusion [19,20]. We did not find a lower
incidence of undesirable effects in patients receiving
ropivacaine compared to placebo, but both groups had similar
morphine consumption, and we looked out mainly for
morphine-related side effects.
No patient experienced motor block. PVB is a peripheral
multitrunk block of intercostal nerves, and functional
respiratory tests would have been necessary to reveal a
motor block of the intercostal muscles involved in ventilation. Clinical signs of an upper limb nerve block, for example,
requiring daily neurological surveillance, could have
revealed abnormal PVB extension but no event of this kind
was observed. There were no signs of Claude Bernard—Horner
syndrome from cervical plexus block. The thoracic PVB block
does not reach the cervical nerve roots unless the anesthetic
spreads abnormally. There were no cases of pruritus probably
because morphine, the least liposoluble opiate, was used.
The incidence of postoperative nausea and vomiting did
not differ significantly between groups and was lower than
usually reported after surgery (20—30% during the first 24 h),
particularly when severe pain persists. Lung surgery patients
present few risk factors for nausea and vomiting (male
gender, smokers, and mean age 62 years). We found no
significant difference in the incidence of urinary retention
from morphine action on bladder muscle fibers.
The catheter insertion site did not change in aspect over
the first 48 h. There are no published data on PVB catheter
insertion and removal. In the study by Burns et al., no
complication was recorded despite the catheter being in
place for 3—9 days [19].
In our study, we did not make routine measurements of
serum ropivacaine levels to detect overdosing, but we used
the same ropivacaine doses as Marret et al. [6]. In their study,
serum drug levels were below toxic levels at 24 and 48 h
(2.83 1.31 mg ml 1 and 2.74 1.65 mg ml 1, respectively)
with no clinical signs of toxicity.
5. Conclusion
In conclusion, the results of our study call into question
the reliability of the intra-operative technique for PVB. This
technique needs to be compared to percutaneous PVB in
order to determine their relative efficacy in managing pain
after thoracotomy.
References
[1] Kuhlman G. Analgésie après thoracotomie. Conférences d’actualisation.
48ème Congrès National d’Anesthésie et de Réanimation. Paris: Elsevier;
SFAR 2006. p. 689—98.
[2] Dajczman E, Gordon A, Kreisman H, Wolkove N. Long-term postthoracotomy pain. Chest 1991;99:270—4.
[3] Tiipana E, Nilsson E, Kalso E. Post-thoracotomy pain after thoracic
epidural analgesia: a prospective follow-up study. Acta Anaesthesiol
Scand 2003;47:433—8.
[4] Hentz JG, Helms O, Bauer C. L’analgésie péridurale thoracique: expérience de plus de 2000 cas. Cah Anesthesiol 2004;52(5):349—61.
[5] Soto RG, Fu ES. Acute pain management for patients undergoing thoracotomy. Ann Thorac Surg 2003;75:1349—57.
[6] Marret E, Bazelly B, Taylor G, Lembert N, Deleuze A, Mazoit JX, Bonnet
FJ. Paravertebral block with ropivacaine 0.5% versus systemic analgesia
for pain relief after thoracotomy. Ann Thorac Surg 2005;79(6):2109—13.
[7] Eason MJ, Wyatt R. Paravertebral thoracic block — a reappraisal. Anaesthesia 1979;34(7):638—42.
[8] Bimston DN, McGee JP, Liptay MJ, Fry WA. Continuous paravertebral
extrapleural infusion for post-thoracotomy pain management. Surgery
1999;126(4):650—6. discussion 656—7.
[9] Berrisford RG, Sabanathan SS, Mearns AJ, Bickford-Smith PJ. Pulmonary
complications after lung resection: the effect of continuous extrapleural
intercostal nerve block. Eur J Cardiothorac Surg 1990;4(8):407—10.
[10] Scarci M, Joshi A, Attia R. In patients undergoing thoracic surgery is
paravertebral block as effective as epidural analgesia for pain management? Interact Cardiovasc Thorac Surg 2010;10:92—6.
[11] Joshi GP, Bonnet F, Shah R, Wilkinson RC, Camu F, Fischer B, Neugebauer
EAM, Rawal N, Schug SA, Simanski C, Kehlet H. A systematic review of
randomized trials evaluating regional techniques for postthoracotomy
analgesia. Anesth Analg 2008;107:1026—40.
[12] Kotzé A, Scally A, Howell S. Efficacy and safety of different techniques of
paravertebral block for analgesia after thoracotomy: a systematic review
and metaregression. Br J Anaesthesia 2009;103(5):626—36.
[13] Richardson J, Sabanathan S, Jones J, Shah RD, Cheema S, Mearns AJ. A
prospective, randomized comparison of preoperative and continuous balanced epidural or paravertebral bupivacaine on post-thoracotomy pain,
pulmonary function and stress responses. Br J Anaesth 1999;83(3):387—92.
[14] Coveney E, Weltz CR, Greengrass R, Iglehart JD, Leight GS, Steele SM, Lyerly
HK. Use of paravertebral block anesthesia in the surgical management of
breast cancer: experience in 156 cases. Ann Surg 1998;227:496—501.
[15] Naja Z, Lonnqvist PA. Somatic paravertebral nerve blockade. Incidence of
failed block and complications. Anaesthesia 2001;56(12):1184—8.
[16] Fibla JJ, Molins L, Mier JM, Sierra A, Vidal G. Comparative analysis of
analgesic quality in the postoperative of thoracotomy: paravertebral
block with bupivacaine 0.5% vs ropivacaine 0.2%. Eur J Cardiothorac Surg
2008;33(3):430—4.
[17] Barron DJ, Tolan MJ, Lea RE. A randomized controlled trial of continuous
extra-pleural analgesia post-thoracotomy: efficacy and choice of local
anaesthetic. Eur J Anaesthesiol 1999;16:236—45.
[18] Richebe P, Rivat C, Rivalan B, Maurette P, Simonnet G. Low doses
ketamine: antihyperalgesic drug, non-analgesic. Ann Fr Anesth Reanim
2005;24(11—12):1349—59.
[19] Burns DA, Ben-David B, Chelly JE, Greensmith JE. Intercostally placed
paravertebral catheterization: an alternative approach to continuous
paravertebral blockade. Anesth Analg 2008;107:339—41.
[20] Watson DS, Panian S, Kendall V, Maher DP, Peters G. Pain control after
thoracotomy: bupivacaine versus lidocaine in continuous extrapleural intercostal nerve blockade. Ann Thorac Surg 1999;67:825—8. discussion 828—9.
[21] Sabanathan S, Smith PJ, Pradhan GN, Hashimi H, Eng JB, Mearns AJ.
Continuous intercostal nerve block for pain relief after thoracotomy. Ann
Thorac Surg 1988;46(4):425—6.