| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
From Departments of Anaesthesiology and Cardiovascular Surgery, Cukurova University, School of Medicine, Adana, Turkey.
Address correspondence to: Dr. Tayfun Guler, Cukurova University, School of Medicine, Department of Anaesthesiology, 01330, Balcali, Adana, Turkey. Phone: + 90 532 357 22 24; Fax: + 90 322 338 67 42; E-mail: tayguler{at}cu.edu.tr
 |
Abstract |
|---|
 TOP Abstract IntroductionMethodsResultsDiscussionReferences |
|---|
Methods: With Faculty Ethics approval, 60 consenting adults undergoing elective coronary artery surgery were randomly assigned to receive either morphine PCA alone (group PCA-A, n = 30) or morphine PCA plus a background infusion (group PCA-B, n = 30) for 24 hr postoperatively. Pain scores with verbal rating scale (VRS; from 0 to 10) at rest, sedation scores, morphine consumption and delivery/demand ratios were assessed at zero, one, two, four, six, 12 and 24 hr after surgery. Hemodynamic variables and arterial blood gases were also recorded in the same periods.
Results: Sedation scores in the two groups were similar. At all study periods after the first postoperative hour, VRS remained below 5 in both groups. Pain scores were significantly lower in the background infusion group, which also had greater cumulative morphine consumption (61.7 ± 10.9 mg vs 38.5 ± 16.2 mg). There were no episodes of hypoxemia or hypertension.
Conclusion: Morphine PCA effectively controlled postoperative pain after cardiac surgery. The addition of a background infusion of morphine enhanced analgesia and increased morphine consumption.
|
Introduction |
|---|
|
TOPAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
This prospective, randomized clinical study was designed to test the hypothesis that adding a standardized background morphine infusion to morphine PCA would improve postoperative analgesia without increasing morphine consumption or side effects, in patients extubated in the operating room after coronary artery surgery.
|
Methods |
|---|
|
TOPAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
Patients received their usual cardiac medication preoperatively. All were instructed preoperatively on the use of the PCA device, with instruction booklets and bedside discussions. They were also instructed on the use of the verbal rating scale (VRS) for the measurement of postoperative pain.6
Anesthetic protocol
Patients were premedicated with im morphine sulphate, 0.1 mg•kg–1, 30 min before surgery. Anesthesia was induced with iv propofol 0.5 mg•kg–1 and remifentanil 0.5 µg•kg–1 in all patients. Neuromuscular relaxation was induced by vecuronium 0.1 mg•kg–1, and maintained by a bolus administration of 0.03 mg•kg–1 at 30 min intervals. After intubation, anesthesia was maintained with propofol (0.5–2.0 mg•kg–1•hr–1) and remifentanil (5–20 µg•kg–1•hr–1). Ventilation with an oxygen/nitrous oxide mixture was controlled, at a tidal volume of 10 mL•kg–1 and a respiratory rate of 10 breaths•min–1, to produce an end-tidal carbon dioxide partial pressure of about 40 mmHg.
Surgical protocol
Surgery was performed in a standard fashion through a median sternotomy with saphenous veins and internal thoracic arteries harvested as conduits. A standard crystalloid prime was used in the cardiopulmonary bypass (CPB) circuit. Myocardial protection was achieved with intermittent, antegrade, warm blood cardioplegia. Non-pulsatile CPB flow was maintained between 1.5 and 2 L•min–1•m–1 using a membrane oxygenator. Patients were not actively cooled, but their core temperature was allowed to drift to 32 to 34°C. Active rewarming to 37°C was completed before aortic cross-clamp removal.
Extubation protocol
Fifteen minutes before the end of surgery, muscle relaxation was reversed with iv neostigmine, 0.05 mg•kg–1 and atropine sulphate, 0.01 mg•kg–1. All patients were extubated in the operating room when awake, and were cooperative and normoventilating when transferred to the cardiovascular care unit. Postoperatively, forced air warming was used to maintain body temperature between 36.5° and 37.5°C.
Postoperative analgesia
Postoperative analgesia was started just before sternal closure with a standardized loading dose of morphine sulphate, 0.15 mg•kg–1 via a PCA device (Abbott Acute Pain Manager-APM, Pain Manager Provider, North Chicago, IL, USA). After extubation, patients were randomly allocated into either the PCA alone group (PCA-A, n = 30) or PCA plus continuous background infusion group (PCA-B, n = 30; random number table generated by a computer program). Each code was indicated on a data form sealed in an envelope and opened by the anesthesiologist.
After arrival at the cardiovascular care unit, both groups were allowed to use supplemental bolus PCA doses, 0.015 mg•kg–1, with a lockout time of 15 min. In addition, Group PCA-B received a standardized background infusion, 0.03 mg•kg–1•hr–1. PCA was discontinued after 24 hr. Patients complaining of pain despite PCA therapy also received supplemental morphine doses of 0.01 mg•kg–1. The study started at time 0, immediately after extubation. Scores for pain, sedation and hemodynamic variables SBP, diastolic blood pressures, heart rate and peripheral oxygen saturation (SpO2) were recorded at zero, one, two, four, six, 12 and 24 hr postoperatively. Morphine consumption was assessed at the same intervals. Supplementary morphine and any side effects (such as nausea, vomiting, cough suppression, constipation, urinary retention and pruritus) associated with the procedure were also recorded.
Pain was assessed by a VRS from 0 to 10 (0 = no pain, 10 = the worst pain imaginable) and sedation on a six-point scale described by Ramsay et al. (1 = anxious and agitated or restless or both; 2 = cooperative, oriented, tranquil; 3 = responds to commands only; 4= brisk response to a light glabellar tap or loud auditory stimulus; 5 = sluggish response to a light glabellar tap or loud auditory stimulus; 6 = no response to light glabellar tap or loud auditory stimulus).14
Statistical analysis
The primary endpoint was defined as a reduction in VRS scores throughout the procedures, a 30% reduction being regarded as clinically significant. The sample size was determined by power analysis; with a power of 0.8 and significance level of 0.05, 22 subjects per study group were required. Statistical analyses were performed using the statistical package SPSS v 10.0 (SPSS Inc., Chicago, IL, USA). Normality was checked for each continuous variable. For between-group comparisons the Student’s t test was used for normally distributed variables, and the Mann-Whitney U test for non-normally distributed data. Time dependent data within groups were analyzed by repeated measure analyses. Friedman’s and Wilcoxon’s rank sum tests were used to evaluate the differences compared to baseline. The incidence of complications between the groups was analyzed by the Chi-square test. Data were reported as mean (95% confidence interval) or median (min-max) and P value < 0.05 was accepted as statistically significant.
|
Results |
|---|
|
TOPAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
). There were no differences between groups in sex, age, height and weight. There were no significant differences in SpO2 values between groups, and no great variations or differences in hemodynamic data, values remaining within the normal range throughout the study period.
|
); (P < 0.05).
|
). In spite of this, there were no significant differences in mean sedation scores between groups at any study period, including before the PCA was started (Table II). Sedation was only affected by time; it decreased significantly with time in both groups (P < 0.05).
Three patients in group PCA-A complained of pain and were given a single iv dose of morphine (0.01 mg•kg–1). Five (two in PCA-A, and three in PCA-B) experienced nausea and received a single 4 mg iv dose of ondansetron. There were no significant differences between groups in the incidence of postoperative nausea. Other side effects were mostly minor (Table III).
|
|
Discussion |
|---|
|
TOPAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
After coronary artery bypass surgery, PCA gives better pain control than traditional nurse-controlled analgesia according to Pettersson et al.9 and Boldt et al.,10 although this was not confirmed by Tsang et al.11 Another recent study showed no improvement in pain control or neurohumoral response in patients extubated in the operating room after CABG surgery.15 Background opiate infusions increase morphine consumption and sedation, and thus can increase the incidence of respiratory depression.4,5 However they may be beneficial in cardiac surgery patients who have greater opioid requirements (caused by pain from the sternotomy) and who must in any case be closely monitored.
Our study confirmed the beneficial effect of a background infusion; although the cumulative dose of morphine was increased, VRS scores were reduced. Pain relief was acceptable in both groups after the first postoperative hour, a similar number of patients in each group requiring supplemental bolus morphine. Tsang et al.11 reported a lower VAS score (< 3) during the first postoperative hour after cardiac surgery with PCA morphine. An initial loading dose of morphine was followed by 1 or 2 mg every 15 min until VAS < 3 was achieved. Thereafter patients used a standardized 1 mg demand bolus with a lockout time of ten minutes. The continuous infusion rate was also set at 1 mg per hour during the first 24 hr.
Tsang et al., after sufentanil anesthesia, used much smaller loading doses of PCA morphine (average 2.4 ± 5.1 mg) than us, and yet achieved a VAS < 3, a much better result than ours during the first postoperative hour. The lack of residual effect of propofol-remifentanil anesthesia may explain this difference.11 Our loading doses of morphine were 11.6 ± 1.7 mg in group PCA-A and 10.6 ± 2.2 mg in group PCA-B, yet VRS scores exceeded 5 during the first postoperative hour in both groups. Dal et al.15 also used smaller loading and bolus doses of morphine than ours. Their PCA included a 3-mg loading dose of morphine, and a 1-mg bolus dose with a 15-min lockout period. Thus our loading doses of morphine were greater, VRS scores at the first hour were similar, but were lower thereafter in both groups in our study.
Adding a background infusion to a morphine PCA may increase cumulative morphine consumption without improving pain relief,3,4,16,17 but in our study, VRS scores decreased after the first hour. Two recent studies reported cumulative morphine consumption as 29 mg and 35.99 mg for 24 hr in cardiac surgery patients.18,19 Dal et al. reported a mean cumulative morphine consumption for PCA plus infusion of 32.8 mg, and 18.5 mg without infusion, for the first 24 hr.15 We too found a greater cumulative morphine consumption and lower VRS scores with the background infusion, but similar sedation scores in the two groups.
Respiratory depression, the most important side effect of morphine PCA, may be more common (1.1 to 3.9% incidence) when a background infusion is added.20,21 Morphine 20 µg•kg–1•hr–1 significantly increases the incidence of respiratory depression, sedation, nausea and vomiting.17 However, a background infusion of morphine 0.5 mg•hr–1 produced no significant respiratory depression in patients extubated after cardiac surgery.15 We used 30 µg•kg–1•hr–1, and observed no respiratory depression or hypoxemia. Our two groups suffered similar incidences of nausea; other side effects (cough suppression, urinary retention, and constipation) were mostly minor.
Finally, effective pain relief requires flexible dosage, the ability to deliver the dose to the patient truly "on demand," and regular monitoring of the adequacy of analgesia and of any drug-related side effects. PCA with a background infusion can be used effectively and safely in cardiac surgery patients who, in any case, require close observation. However, in this patient population, PCA instructions may need to be repeated during the early postoperative period because of incomplete recovery of higher cognitive function and disorientation in the ICU environment.
We conclude that, in patients extubated in the operating room after coronary artery bypass surgery, the addition of a background morphine infusion to morphine PCA increases morphine consumption and improves pain relief, without increasing side effects.
|
Acknowledgments |
|---|
|
Footnotes |
|---|
|
References |
|---|
|
TOPAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
2 Gust R, Pecher S, Gust A, Hoffmann V, Bohrer H, Martin E. Effect of patient-controlled analgesia on pulmonary complications after coronary artery bypass grafting. Crit Care Med 1999; 27: 2218–23.[Medline]
3 O’Connor CJ. Pain relief and pulmonary morbidity after cardiac surgery. Crit Care Med 1999; 27: 2314–6.[Medline]
4 Checketts MR, Gilhooly CJ, Kenny GN. Patient-maintained analgesia with target-controlled alfentanil infusion after cardiac surgery: a comparison with morphine PCA. Br J Anaesth 1998; 80: 748–51.
5 Macintyre PE. Safety and efficacy of patient-controlled analgesia. Br J Anaesth 2001; 87: 36–46.
6 Walder B, Schafer M, Henzi I, Tramer MR. Efficacy and safety of patient-controlled opioid analgesia for acute postoperative pain. A quantitative systematic review. Acta Anaesthesiol Scand 2001; 45: 795–804.[Medline]
7 Lam KK, Chan MT, Chen PP, Kee WD. Structured preoperative patient education for patient-controlled analgesia. J Clin Anesth 2001; 13: 465–9.[Medline]
8 Myles PS, Buckland MR, Cannon GB, et al. Comparison of patient-controlled analgesia and nurse-controlled infusion analgesia after cardiac surgery. Anaesth Intensive Care 1994; 22: 672–8.[Medline]
9 Pettersson PH, Lindskog EA, Öwall A. Patient-controlled versus nurse-controlled pain treatment after coronary artery bypass surgery. Acta Anaesthesiol Scand 2000; 44: 43–7.[Medline]
10 Boldt J, Thaler E, Lehmann A, Papsdorf M, Isgro F. Pain management in cardiac surgery patients: comparison between standard therapy and patient-controlled analgesia regimen. J Cardiothorac Vasc Anesth 1998; 12: 654–8.[Medline]
11 Tsang J, Brush B. Patient-controlled analgesia in postoperative cardiac surgery. Anaesth Intensive Care 1999; 27: 464–70.[Medline]
12 Rapanos T, Murphy P, Szalai JP, Burlacoff L, Lam-McCulloch J, Kay J. Rectal indomethacin reduces postoperative pain and morphine use after cardiac surgery. Can J Anesth 1999; 46: 725–30.
13 Searle NR, Roy M, Bergeron G, et al. Hydromorphone patient-controlled analgesia (PCA) after coronary artery bypass surgery. Can J Anaesth 1994; 41: 198–205.
14 Ramsay MA, Savege TM, Simpson BR, Goodwin R. Controlled sedation with alphaxolone-alphadolone. Br J Med 1974; 2: 656–9.
15 Dal D, Kanbak M, Caglar M, Aypar U. A background infusion of morphine does not enhance postoperative analgesia after cardiac surgery. Can J Anesth 2003; 50: 476–9.
16 Dawson PJ, Libreri FC, Jones DJ, Libreri G, Bjorkstein AR, Royse CF. The efficacy of adding a continuous intravenous morphine infusion to patient-controlled analgesia (PCA) in abdominal surgery. Anaesth Intensive Care 1995; 23: 453–8.[Medline]
17 Doyle E, Harper I, Morton NS. Patient-controlled analgesia with low dose background infusions after lower abdominal surgery in children. Br J Anaesth 1993; 71: 818–22.
18 Munro AJ, Long GT, Sleigh JW. Nurse-administered subcutaneous morphine is a satisfactory alternative to intravenous patient-controlled analgesia morphine after cardiac surgery. Anesth Analg 1998; 87: 11–5.
19 Zimmermann AR, Kibblewhite D, Sleigh J. Comparison of morphine/droperidol and tramadol/droperidol mixture for patient controlled analgesia (PCA) after cardiac surgery: a prospective, randomised, double-blind study. Acute Pain 2002; 4: 65–9.
20 Schug SA, Torrie JJ. Safety assessment of postoperative pain management by an acute pain service. Pain 1993; 55: 387–91.[Medline]
21 Smythe MA, Zak MB, O’Donnell MP, Schad RF, Dmuchowski CF. Patient-controlled analgesia versus patient-controlled analgesia plus continuous infusion after hip replacement surgery. Ann Pharmacother 1996; 30: 224–7.[Abstract]
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
