A Randomized Controlled Trial on Local Anesthetics in the Wound: What do the Numbers Mean?

Abstract

When analyzing the efficacy of a postoperative analgesic technique, it is important to remember that acute pain is influenced by many subjective variables. First, the patient’s cultural and psychosocial background will affect pain perception. Second, relief at having completed the surgical “ordeal” as well as euphoria following surgical delivery may decrease the centrality of pain in the immediate postoperative period. Finally, anxiety, depression, or learning that a specific postoperative pain regime does not provide pain relief or intrinsically induces pain may affect patient perception of postoperative pain. This, in our opinion, is the message of Dr. Rowlingson’s editorial. It should be remembered that prestudy power analysis is a limited tool because it is based on results of a similar (but by definition different) study. Furthermore, post hoc power analysis is used to define the likelihood of a type I or type II statistical error. Because the entire battery of tests used in our study (visual analog scale scores at rest, on coughing, and after leg raise, “rescue” opioid administration, patient satisfaction) showed no difference between the groups, there is no clinically significant reason to suspect the occurrence of a statistical error. This study was associated with an 80% power to detect a 11.3 mg/6h (α = 0.05, two-tailed) and a 14.5 mg/6h (α = 0.01, two-tailed) difference in “rescue” morphine administration. Because this difference was over a 6-h period, our instillation system did not significantly improve patient care. Furthermore, we do not believe that a smaller difference in “rescue” morphine administration is required to persuade the Health Care Provider that this specific postoperative analgesic technique does not work. Brian Fredman, MB BCh Edna Zohar, MD Robert Jedeikin, MBChB, FFA(S.A.)