Retrospective study of temperature rhythms of intensive care patients.

The hourly rectal temperature record of 15 patients who spent greater than or equal to 8 days in the ICU were analyzed for circadian rhythmicity. Using cosinor analysis, a statistically significant rhythm in a period of 24 h was present on 80% of the patient days studied. The position of the acrophase, or peak, of the rhythm varied markedly both between patients and within patients, with changes of several hours from day to day. There was a tendency for the amplitude of the rhythm to be greater when the patients were unconscious than when they were conscious and in those patients who died compared with those who survived.