TIBIAL PRESSURE ALGESIMETRY: The Significance of Changes in Pain Threshold with reference to the Assessment of Analgesia

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Abstract
A controlled investigation of tibial pressure algesimetry was undertaken in 100 patients to determine the significance of changes in pain threshold with reference to their use as a method of measuring analgesia. Pethidine 1.6 mg/kg was used as a standard analgesic and atropine 0.009 mg/kg aaed as a control. Individual results were very variable, but provided enough subjects were investigated, the analgesic action of pethidine could be demonstrated. The relationship between analgesic potency, the change in pain threshold and the number of cases required to demonstrate a change of statistical significance is discussed. Pethidine 1.6 mg/kg with atropine 0.009 mg/kg produced a mean rise in pain threshold of 16.2 per cent in 50 subjects. Atropine alone produced a rise of 1.1 per cent in 50 subjects. The difference in pain threshold raising effects between the two groups was significant (P=0.0014). A minimum of two groups of about 20 cases is likely to be required before a rise in pain threshold due to pethidine 1.6 mg/kg can be demonstrated to a statistically significant degree in a hospital patient population.