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

A controlled investigation of tibial pressure algesimetry wasundertaken in 100 patients to determine the significance ofchanges in pain threshold with reference to their use as a methodof measuring analgesia. Pethidine 1.6 mg/kg was used as a standardanalgesic and atropine 0.009 mg/kg aaed as a control. Individualresults were very variable, but provided enough subjects wereinvestigated, the analgesic action of pethidine could be demonstrated.The relationship between analgesic potency, the change in painthreshold and the number of cases required to demonstrate achange of statistical significance is discussed. Pethidine 1.6mg/kg with atropine 0.009 mg/kg produced a mean rise in painthreshold of 16.2 per cent in 50 subjects. Atropine alone produceda rise of 1.1 per cent in 50 subjects. The difference in painthreshold raising effects between the two groups was significant(P=0.0014). A minimum of two groups of about 20 cases is likelyto be required before a rise in pain threshold due to pethidine1.6 mg/kg can be demonstrated to a statistically significantdegree in a hospital patient population.