Background: Sudden cardiac death remains to be the most devastating outcome for patients who undergo cardiac surgery. Surgical stress in combination with postoperative pain are key factors of such tragedy. Preemptive analgesia (PA) is supposed to provide optimal postoperative pain management, and epidural morphine infusion to provide effective pain relief and stress reduction after cardiac surgery. Heart rate (HR) variability seems to correlate to the survival of acute myocardial infarction (AMI) patients. This study was conducted to evaluate the benefits of PA for coronary artery bypass grafting (CABG) patients in the sense of improvement in postoperative respiratory and cardiovascular functions, and its correlation to HR and HR variability.
Methods: A total of 40 patients who underwent CABG from June 1995 to December 1995 were randomly selected and divided into two groups (Group A and Group B). Group A (n = 20) was treated with conventional postoperative analgesia of intravenous (i.v.) meperidine HCl (Demerol). Group B (n = 20) was treated with PA using epidural infusion of local anesthetics plus ketamine and morphine during surgery and then using intermittent epidural morphine infusion for postoperative pain control when necessary, and Demerol was given intravenously as in group A. Postoperative pain intensity was measured by a modified visual analogue pain scale from 0 to 10 (0 = no pain, 10 = severe pain). Perioperative HR and HR variability data based on 24-hour electrocardiograph (ECG) Holter monitoring along with data on respiratory and cardiovascular functions were gathered, analyzed, and compared between Group A and Group B.
Results: Effective analgesia (mean pain score of 0-2) was achieved in 50% of Group A patients and 75% of Group B patients. Group B with the reduced dosage of demerol also had the benefits of smaller degree of respiratory insufficiency, earlier extubation, and less incidence of re-intubation as compared with Group A. For HR comparison between Group A and Group B, statistically significant differences (p < 0.05) were observed in 3 out of the 16 postoperative time segments. For HR variability comparison between Group A and Group B, statistically significant difference (p < 0.05) was observed in one of the time segments while another segment showed marginal significance (p = 0.061). Group B patients also maintained better overall respiratory and cardiovascular functions.
Conclusions: PA method through the use of epidural anesthesia along with morphine infusion provided better postoperative pain relief and more stable respiratory and cardiovascular functions in our patients with cardiac surgery. Although the differences in HR and HR variability between the control and the PA groups were not statistically significant throughout the period studied, the potential benefits of better understanding the relationship between postoperative pain control and HR variability justify further studies to be conducted.