Mean skin temperature during anaesthesia: an assessment of formulae in the supine surgical patient.

The mean skin temperature was calculated from measurements made in 22 patients under general anaesthesia. The results from 11 different formulae were compared with a system involving 15 temperature sites on the skin, each given a weighting factor in proportion to the fraction of total surface area which it represented. If accuracy is required, the mean skin temperature should be measured in surgical patients using a formula which involves at least 10 skin sites. Incorrect estimation of stored body heat results from an erroneous value for the mean skin temperature, and this occurred more frequently when the number of skin sites was reduced.