Abstracts of Posters Presented at the International Anesthesia Research Society; 72nd Clinical and Scientific Congress; Orlando, FL; March 7-11, 1998: Ambulatory Anesthesia
Introduction: Lumbar disc surgery is increasingly being performed on an outpatient basis, and poorly controlled post-operative pain is a reason for unplanned hospital admission. Various modalities to decrease post-operative narcotic requirements have been described, including epidural steroids,  epidural morphine  and oral non-steroidal agents .
Purpose: This randomized double-blind study compared the effect of preoperative pain and narcotic use, as well as intra-operative administration of intravenous ketorolac, intra-muscular injection of bupivacaine, or placebo on post-operative morphine (MSO (4)) requirements as measured by patient controlled analgesia in the first 24 hours after surgery.
Materials and Methods: After IRB approval and informed consent, 30 patients (ASA I-II) undergoing inpatient single-level lumbar microdiscectomy with a standardized general anesthetic were randomly assigned to receive either ketorolac (30 mg intravenously), bupivacaine 0.25% (15 cc injected into the paraspinous muscles via the surgical wound), or saline placebo, immediately prior to wound closure. Post-operatively all patients received demand-only intravenous MSO4 patient controlled analgesia (PCA), with a demand dose of 1.0 mg as frequently as every 6 minutes. MSO4 demand (mg requested) and usage (mg delivered) were compared between the three groups at 30 min, 1, 4, 8, 16, 20 and 24 hours post-operatively by one way ANOVA. Pre-operative narcotic use was noted. Pre- and post-operative pain was assessed using the scale standard for PCA in this institution (0 - 5 scale with 0 = no pain and 5 = most severe pain), and pre-operative pain was correlated to post-operative MSO4 use and demand by simple regression and Pearson correlation. Significance was assumed at P < 0.05.
Results: There were no group differences in age, sex, weight, disc level, pre-operative pain, nor were there differences postoperatively in time to voiding, ambulation or incidence of nausea and vomiting. With the greater access to post-operative narcotic provided by PCA, the total dose of MSO4 demanded in 24 hours in all groups (placebo=22.8 +/- 20.3 mg, bupivacaine=28.3 +/- 27.7 mg, and ketorolac=20.1 +/- 15.5 mg) was greater in this study than previously reported (12 +/- 1.9 mg); however, there was no relationship between group assignment and either post-operative use of or demand for MSO4 via PCA although sample size is small. There was, however, a significant correlation between pre-operative pain and post-operative narcotic demand (r=0.46, P < 0.01) and usage (r=0.37, P < 0.05). There was no correlation between pre-operative narcotic use and either pre-operative pain scores or post-operative MSO4 use or demand.
Conclusions: No difference in post-operative narcotic requirement was seen in patients undergoing single level lumbar microdiscectomy receiving either intravenous ketorolac or intramuscular bupivacaine as compared to placebo; however, a much larger study would be necessary to demonstrate a difference. Post-operative narcotic requirements are increased, however, in those patients who are in severe pain pre-operatively, regardless of pre-operative narcotic use. This suggests that those patients in severe pain pre-operatively are less likely to be successful outpatient surgical candidates.
The authors would like to thank Abbott, Inc. for the loan of two PCA pumps used in this study.
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