Intrathecal morphine for coronary artery bypass graft surgery revisited

Abstract

We read with great interest Chaney et al's1Chaney MA Nikolov MP Blakeman BP Bakhos M Intrathecal morphine for coronary artery bypass graft procedure and early extubation revisited.J Cardiothorac Vasc Anesth. 1999; 13: 574-578Abstract Full Text PDF PubMed Scopus (48) Google Scholar study regarding intrathecal morphine in coronary artery bypass graft (CABG) surgery patients and early extubation. Dr. Chaney and colleagues are to be congratulated for completing this rigorous, placebo-controlled, double-blind study. It is possible, however, that the study design, although accomplishing methodologic goals, biases the clinical results. In the current study, as in Chaney's previous study,2Chaney MA Furry PA Fluder EM Slogoff S Intrathecal morphine for coronary artery bypass grafting and early extubation.Anesth Analg. 1997; 84: 241-248PubMed Google Scholar the use of intrathecal narcotics is an adjunct to the primary, balanced anesthetic technique. It is not surprising that his use of intrathecal morphine was no different from placebo because it simply supplements what is an adequate anesthetic for fast-track cardiac surgery. Similarly, the use of intrathecal morphine in this situation could be expected to increase sedation and prolong time to extubation in certain patients. Fentanyl, 10 μg/kg, and midazolam, 0.2 mg/kg, are quite sufficient, when combined with volatile anesthetics and vasoactive agents, to provide perioperative analgesia and sedation in patients undergoing cardiopulmonary bypass (CPB). In private practice, many clinicians use significantly smaller doses of opioids and benzodiazepines to achieve rapid extubation (J Turner: personal communication). Intraoperative analgesia is further accomplished by use of volatile agents, whereas patient-controlled analgesia with morphine adequately addresses postoperative pain management needs. It has been our clinical impression that patients undergoing CPB have smaller postoperative analgesia requirements than patients undergoing non-CPB sternotomy. Although this situation has not been investigated, we speculate that cerebral edema and inflammation associated with even routine, uneventful bypass3Taylor KM Central nervous system effects of cardiopulmonary bypass.Ann Thorac Surg. 1998; 66: S20-S24Abstract Full Text Full Text PDF PubMed Scopus (95) Google Scholar may alter the sensorium sufficiently to account for this decrease. An ongoing study at this institution seems to indicate that intrathecal morphine at a dose of 5 μg/kg is adequate for postoperative pain control. No intravenous opioid or benzodiazepine is used in the preoperative and intraoperative periods. The intrathecal mor-phine is the sole fixed analgesic, rather than a supplement. Intraoperative amnesia and analgesia are accomplished with volatile anesthetics, whereas stress and hemodynamics are managed by other vasoactive agents, such as β-blockers and vasodilators. Aprotinin is also used liberally in high doses for its anti-inflammatory effects. Use of bispectral index monitoring throughout the intraoperative period facilitates this technique further by guiding clinicians in the use of volatile agents for hypnosis. Of the 10 patients we have studied so far, all have been easily extubated within the first hour of surgery, several immediately in the operating room during dressing application. So far, we have not experienced complications, such as reintubation or hypoxia and hypercarbia, and the patients have experienced a significantly shorter intensive care unit stay. We hope to submit our data for peer review in the near future. In conclusion, we believe that narcotics and benzodiazepines used in the perioperative period significantly affect the clinical short-term outcome after the use of intrathecal morphine for CABG surgery. It is possible that severely limiting or elim-inating parenteral use of these agents may allow clinicians to realize the combined benefits of early extubation and satisfac-tory pain control offered by intrathecal morphine. An additional variable to consider is decreased requirement for pain medica-tion after CPB, which may be accomplished by smaller doses of intrathecal morphine than those used by Chaney. Although our data have yet to undergo peer review, other studies have also shown the effectiveness of intrathecal morphine at significantly smaller doses.4Taylor A Healy M McCarroll M Moriarty DC Intrathecal morphine: One year's experience in cardiac surgical patients.J Cardiothorac Vasc Anesth. 1996; 10: 225-228Abstract Full Text PDF PubMed Scopus (30) Google Scholar, 5Swenson JD Hullander RM Wingler K Leivers D Early extubation after cardiac surgery using combined intrathecal sufentanil and morphine.J Cardiothorac Vasc Anesth. 1994; 8: 509-514Abstract Full Text PDF PubMed Scopus (44) Google Scholar, 6Tobias JD Deshpande JK Wetzel RC et al.Postoperative analgesia: Use of intrathecal morphine in children.Clin Pediatr. 1990; 29: 44-48Crossref PubMed Scopus (36) Google Scholar