Tourniquet and Episiotomy Pain as Test Models For Aspirin-Like Analgesics

¹ Division of Clinical Pharmacology, Departments of Medicine and Pharmacology and Therapeutics, University of Cincinnati College of Medicine, Cincinnati, Ohio 45219.

Experience with experimental pain techniques in man has been diverse; tourniquet pain is reported both as sensitive and insensitive to aspirin analgesia. In earlier unpublished studies using this pain model in normal subjects we also found conflicting results. In the present placebo-controlled double-blind trials the sensitivity of the tourniquet pain model to aspirin analgesia was evaluated first in 20 healthy nonpuerperal female volunteers. Then, to determine whether a correlation exists between tourniquet and natural pain relief, 26 healthy consenting postpartum ward patients acted as subjects for an evaluation of episiotomy pain as a test model and also for a reevaluation of the tourniquet pain model. It was postulated that under these circumstances tourniquet pain would respond to aspirin in those patients in whom aspirin had relieved episiotomy pain.

The sensitivity of the tourniquet model to aspirin analgesia in normal nonpuerperal women was validated by the finding that aspirin 1.2 Gm delayed significantly the appearance of threshold pain compared with placebo (P<.05). In addition, in postpartum patients episiotomy pain was found to be significantly relieved by aspirin 1.2 Gm (P<.05). However, in the same group of patients tourniquet pain (threshold and suprathreshold) was not demonstrably affected by aspirin on the second postpartum day nor 8-12 months later. No suggestion of aspirin analgesia against tourniquet pain was present even in those patients with greatest relief of natural pain by aspirin. Uncontrolled nondrug variables may have accounted for these conflicting results. This and our previous experience has led us to conclude that tourniquet pain is an unreliable method for evaluating aspirin-like analgesics. The special significance of the present study is that tourniquet pain was an unsatisfactory test model for evaluating aspirin analgesia in the same subjects in whom this standard analgesic had relieved natural pain.

Note:

The authors gratefully acknowledge the cooperation and assistance of the faculty, house staff, and nursing personnel of the Department of Obstetrics and Gynecology, Cincinnati General Hospital, University of Cincinnati College of Medicine, and the assistance of Miss Patricia Gilmore, L.P.N., research nurse.

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