Anesth Analg 2005;100:205-209
© 2005 International Anesthesia Research Society
doi: 10.1213/01.ANE.0000140237.96510.E5
REVIEW ARTICLE
A Randomized Comparison of Three Methods of Analgesia for Chest Drain Removal in Postcardiac Surgical Patients
Maria Akrofi, FRCA,
Scott Miller, FRCA,
Steve Colfar,
Peter R. Corry, FRCA,
Brian M. Fabri, FRCS,
Mark D. Pullan, FRCS,
Glenn N. Russell, FRCA, and
Mark A. Fox, FRCA
Cardiothoracic Centre National Health Service Trust, Thomas Drive, Liverpool, United Kingdom
Address correspondence and reprint requests to Mark A. Fox, FRCA, The Cardiothoracic Centre, Thomas Dr., Liverpool, UK L14 3PE. Address e-mail to mark.fox{at}ctc.nhs.uk
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Abstract
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Sixty-six patients scheduled for coronary artery bypass graft and/or valve surgery were recruited in a prospective, randomized study designed to compare the effectiveness of three analgesic regimens for chest drain removal. Patients were randomized to receive 0.1 mg/kg IV morphine, 20 mL of 0.5% bupivacaine infiltrated subcutaneously, or inhaled 50% nitrous oxide in oxygen (Entonox) via a demand valve. We assessed pain by measuring visual analog scale pain scores before and during drain removal. Median (25th, 75th centile) visual analog scale pain scores associated with drain removal in the bupivacaine, Entonox, and morphine groups were 9.5 mm (3, 18 mm), 37.0 mm (13, 56 mm), and 15.0 mm (7, 27 mm), respectively. The pain scores were higher in the Entonox group compared with the bupivacaine group (P = 0.005) and the morphine group (P = 0.047). Differences between baseline and drain-removal scores were –0.5 mm (–13, 7 mm), +10 mm (1, 29 mm), and –3.0 mm (–11, 12 mm), respectively. There was no difference among groups in arterial blood pressure, heart rate, PaCO2, oxygenation, or sedation. Bupivacaine and morphine, unlike Entonox, produce lower pain scores associated with drain removal.
IMPLICATIONS: The efficacy of IV morphine, subcutaneous bupivacaine, and inhaled 50% nitrous oxide in oxygen as analgesia for the removal of mediastinal chest drains after cardiac surgery was compared. All methods afford hemodynamic stability, but Entonox was the least effective in providing analgesia.
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Introduction
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Mediastinal chest drains are a source of pain after cardiac surgery, and their removal is often a very unpleasant aspect of a patient’s hospital experience (1–3), possibly even the worst (4). The choice of analgesic modalities currently described includes propofol (5), isoflurane (6), opiates (7), and local anesthetic infiltration or instillation (2,8).
Surprisingly little research has been published describing effective methods of minimizing patient discomfort. Carson et al. (2) compared morphine with bupivacaine but were unable to demonstrate efficacy. Bryden et al. (6) compared the efficacy of Entonox with that of 0.25% isoflurane in Entonox and demonstrated a difference among groups, but they presented no numerical data indicating a change of sensation from baseline for the intervention.
The aim of this study was to compare the efficacy of subcutaneous bupivacaine infiltration, IV morphine, and inhaled 50% nitrous oxide in oxygen (Entonox) in the setting of a large, rapid-discharge cardiac surgical intensive care unit.
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Methods
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We recruited patients scheduled for coronary artery bypass graft surgery, valve surgery, or both in a prospective randomized study after ethics committee approval and with informed written consent. During the consenting process, patients were coached in the use of the visual analog pain scale (VAS). Patients in whom mediastinal chest drain removal was clinically indicated within 24 h of surgery were subsequently studied. Two drain sizes are in common use in our institution (19F and 28F). The number, size, and position of the drains were determined by surgical requirements. Intraoperative analgesia was fentanyl, and postoperative analgesia was morphine. On the day after surgery, 40 min before chest drain removal, the following baseline measurements were recorded: pain score on a 100-mm VAS, pain score on a verbal rating scale (VRS; Appendix 1), Bloomsbury Sedation Score (9) (Appendix 2), arterial blood pressure, heart rate, and arterial blood gas analysis. Patients were excluded if they required more than 60% oxygen via face mask to maintain PaO2 more than 10 kPa, if PaCO2 was <4.5 kPa or more than 6.5 kPa, or if they were unable to cooperate or unable to communicate. Patients were randomized into three groups by means of sealed envelopes. The morphine group was given 0.1 mg/kg morphine as an IV bolus over 2 min. The bupivacaine group was given a subcutaneous infiltration of 0.5% bupivacaine around the drain-insertion sites with a 23-gauge needle according to a standardized method (Appendix 3). For both of these groups, 20 min was allowed to elapse before drain removal. The Entonox group received inhaled 50% nitrous oxide in oxygen from 12-L cylinders (water volume) filled to 13.7 MPa. A demand valve system (Ohmeda) was used, and Entonox was administered via a face mask held by the patient. Care was taken to ensure that an appropriate seal was formed and that the patient was opening the demand valve with each inspiration. Entonox was inhaled satisfactorily for 2 min before drain removal. In all three groups, arterial blood pressure, heart rate, and Bloomsbury Sedation Score were recorded immediately before chest drain removal.
The drains were removed by two intensive care nurses by following the institutional protocol under direct investigator observation. During drain removal, the maximum heart rate and arterial blood pressure were recorded. Subsequent drains were removed at 2-min intervals; arterial blood pressure and heart rate were recorded at 1-min intervals. The Entonox group continued to inhale Entonox throughout until the final dressing was applied.
Five minutes after completion of the procedure, patients were asked to mark on the VAS the worst pain experienced during the entire procedure. A VRS was recorded in a similar way. Arterial blood pressure, heart rate, and Bloomsbury Sedation Score were recorded, and after another 10 min (15 min after completion), arterial blood gas analysis was performed. Data-collection timings are depicted in Figure 1.
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Figure 1. Time scheme of the protocol. VAS = visual analog scale; VRS = verbal rating scale; BP = arterial blood pressure; HR = heart rate; ABG = arterial blood gas.
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The time that elapsed between the completion of drain removal and the patient’s leaving the intensive care unit was recorded. On the following day, patients were visited and were asked, by using a scripted interview, whether they recalled the drain removal and if so, to record with a VRS the worst pain they recalled. A power calculation based on audit data estimated the need for 22 patients in each group to detect a 25% difference based on a standard deviation of 21 mm ( = 0.05; ß = 0.8). Statistical analysis was performed with Analyze-it for Microsoft Excel. VAS pain scores were compared by using Kruskal-Wallis analyses of variance and Student’s t-tests where appropriate. Proportions were tested with  2 tests, and VRS pain scores were tested with Wilcoxon’s signed rank test. Repeated-measures analysis of variance testing was applied to the hemodynamic data.
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Results
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Patient characteristics, intraoperative fentanyl dosage, postoperative morphine usage, analgesia in the 4 h preceding drain removal, and variables relating to the surgical procedure were similar among the three groups (Table 1). In all cases, the analgesia was tolerated, and no technical problems were experienced during the study. The median number of drains per patient was 2 in all groups. Drains were removed 19.4 h (SD, 2.7 h) after arrival in the intensive care unit (ICU). The median baseline pain score (25th, 75th centile) over all three groups was 19.5 mm (2, 35 mm), and the groups were equivalent (P = 0.759). There were no differences among groups in sedation scores or oxygenation. In no case was discharge from the ICU delayed because of a complication of analgesia.
Within each group, no variation in heart rate or arterial blood pressure was detectable throughout the study period, nor was there a difference among groups (Table 2). The differences between PaCO2 at baseline and after drain removal in the bupivacaine, Entonox, and morphine groups [mean (SD)] were –0.10 kPa (0.31 kPa), –0.06 kPa (0.37 kPa), and +0.19 kPa (0.46 kPa), respectively, indicating a slight increase in the morphine group (P = 0.052). Four patients were excluded because the PaCO2 was >6.5 kPa.
The VAS pain scores [median (interquartile range)] at baseline in the bupivacaine, Entonox, and morphine groups were similar: 19 mm (1–26 mm), 15 mm (2–32 mm), and 21 mm (4–35 mm), respectively. Median (25th, 75th centile) VAS scores in the bupivacaine, Entonox, and morphine groups (Fig. 2) on drain removal were 9.5 mm (3, 18 mm), 37.0 mm (13, 56 mm), and 15.0 mm (7, 27 mm), respectively.
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Figure 2. Visual analog pain scale (VAS) scores at baseline and on drain removal in each of the three groups. B = bupivacaine; E = Entonox; M = morphine. Box and whisker plots: box (25% and 75% values), line in box (median), and whiskers (5%–95% values). *Significant difference versus Entonox, P < 0.05; **significant difference versus Entonox, P < 0.01.
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Paired comparisons revealed the differences between the bupivacaine and Entonox groups (P = 0.005), and between the bupivacaine and morphine groups (P = 0.047) to be significant. The differences within groups between baseline and drain-removal VAS scores were examined separately. The median (25th, 75th centile) differences in the bupivacaine, Entonox, and morphine groups were –0.5 mm (–13, 7 mm), +10 mm (1, 29 mm), and –3.0 mm (–11, 12 mm), respectively, indicating a tendency toward higher scores in the Entonox group (Figure 3; P = 0.062). Pain score results are summarized in Table 3. A separate categorical analysis investigated whether there was an increase or decrease in the VAS pain score on drain removal compared with baseline (Table 4). The percentage of patients who experienced an increase in VAS pain scores in the bupivacaine, Entonox, and morphine groups was 36%, 77%, and 41%, respectively. The observed frequency in the Entonox group was significantly more than that in the other groups (2; P = 0.012).
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Figure 3. Difference between visual analog pain scores (VAS) at baseline and drain removal in each of the three groups. B = bupivacaine; E = Entonox; M = morphine. Box and whisker plots: box (25% and 75% values), line in box (median), and whiskers (5%–95% values). P = 0.062.
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The worst pain during the procedure as recorded on the VRS pain scale was 1 (median) in all three groups immediately after the procedure, with no demonstrable difference among groups (P = 0.139). On the following day, the median VRS referring to the pain the patient remembered experiencing was 0 (P = 0.107), and, again, no difference among groups was demonstrable (P = 0.892). Four patients reported having no recollection of drain removal; three had Entonox.
The VAS pain scores were analyzed separately according to drain size. The difference between baseline and drain-removal VAS pain scores in all the patients from whom a 19F drain was removed, irrespective of the analgesia used, was –5.5 mm (SD, 21.3 mm), compared with 10.1 mm (SD, 35.4 mm) for the 28F drains (P = 0.0164; Student’s t-test).
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Discussion
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This study was designed to determine whether there was a difference in the effectiveness of the three methods of analgesia currently used in our institution. In the context of pain scores comparable with other studies (6), the results demonstrated that IV morphine or infiltration with subcutaneous bupivacaine was significantly more effective than inhaled Entonox in reducing pain scores associated with chest drain removal.
Several difficulties were anticipated in demonstrating such a difference. First, there is the problem of measuring pain. Although originally developed for use in measuring chronic pain (10,11), the VAS is a well described tool for acute pain assessment. Variability in VAS scores is a well recognized phenomenon (12), and the relationship between changes in pain severity and changes in pain scores is not always consistent (13,14). Second, we considered it unethical not to allow our patients to receive the analgesia necessary to ensure comfort during their stay in the ICU, and, not surprisingly, the median VAS at baseline was 19.5 mm. The conventionally accepted VAS score that corresponds to adequate analgesia is <30 mm. It has been recorded that the pain associated with removal of each drain is dissimilar (6); we therefore recorded the worst pain the patient recalled immediately after the procedure.
The pain as recorded on the VAS on removal of the drains was less than the baseline pain score in both the morphine and bupivacaine groups. In the Entonox group, there was an increase in VAS pain score on drain removal compared with baseline. Our pain scores in the morphine and bupivacaine groups were much lower than those reported by Carson et al. (2). In the morphine group, this probably relates to a larger dose of morphine and a longer time allowed for it to achieve its peak therapeutic effect. We also used a larger dose of local anesthetic. Although Entonox appears to be the least effective of the analgesic regimens in terms of pain score reduction, it appears to produce amnesia, which contributes to the low VRS 24 hours after drain removal.
This study has several limitations. Patients with increased PaCO2 (>6.5 kPa) were excluded. This possibly excluded patients who might have experienced an adverse effect from additional morphine for drain removal. Because it was our intention to start from a baseline of patient comfort, this required examining the efficacy of the three techniques against a background of opiate. This preexisting opiate load will have masked some of the difference in efficacy among the three study maneuvers. During the study, smaller 19F flexible fluted silicone drains were introduced in addition to the 28F rigid plastic tubes. However, although representing a different level of stimulus, they were evenly distributed among the groups. Therefore, although the study was not designed specifically to evaluate the difference between these two drain sizes, we took the opportunity retrospectively to compare the pain scores. Our study confirms an earlier finding (15) that pain scores are lower on removal of the smaller drains.
Our study did not detect a difference among groups in sedation scores, oxygenation, or time to discharge from the ICU. There was an increase in the PaCO2 in the morphine group compared with the others after drain removal, but it did not reach statistical or clinical significance. All three analgesic regimens were accompanied by hemodynamic stability during drain removal. In particular, there was no difference in heart rate, systolic blood pressure, or diastolic blood pressure within or among groups.
We conclude that both bupivacaine and morphine provide effective analgesia for drain removal after cardiac surgery. Entonox was a less effective analgesic. Bupivacaine, morphine, and Entonox all provide hemodynamic stability for mediastinal chest drain removal and are similar in their effects on sedation, oxygenation, PaCO2, and time to discharge from the ICU after cardiac surgery. The additional equipment required, together with its reduced capacity to provide analgesia, makes Entonox an unfavorable choice for drain removal in the postsurgical cardiac patient.
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Appendix 1
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Appendix 2
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Appendix 3
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Subcutaneous bupivacaine was injected according to the following protocol. An imaginary rectangular line 1 cm lateral to the lateral border of the drain-insertion sites and running 1.5 cm superiorly and inferiorly was infiltrated with 10 mL of the local anesthetic. A circular area with a 1-cm radius was infiltrated around each drain with the remaining 10 mL.
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References
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Accepted for publication July 12, 2004.
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Abstract
Introduction
