The Relationship Between Heart Rate and Body Temperature in Critically Ill Patients

Abstract

Objective: The presence of tachycardia in critically ill patients is frequently used as an indication of severity of illness and to guide treatment decisions but can be influenced by body temperature, thus confounding its interpretation. There are few data available on the relationship between body temperature and heart rate in critically ill patients.

Design: Retrospective analysis of prospectively collected data.

Setting: Mixed medical-surgical university hospital ICU.

Patients: All patients admitted to the ICU between November 2006 and August 2019.

Measurements and main results: Body temperature was recorded in the electronic medical records at least hourly, from invasive measurements (esophageal probe, indwelling urinary catheter, pulse contour cardiac output monitoring system, or pulmonary artery catheter) or manual tympanic recordings. Heart rate was monitored continuously and hourly values were recorded in the electronic medical record. Change in heart rate with change in body temperature was assessed by extracting pairs of simultaneous body temperature and corresponding heart rate measurements from the electronic medical record: 472,941 simultaneous pairs were obtained from the 9,046 patients admitted during the study period. Each 1°C increase in body temperature between 32.0°C and 42.0°C was associated with an 8.35 beats/min increase in heart rate. Crude linear regression showed an r2 of 0.855 between body temperature and heart rate. Heart rate increased more in females than in males (9.46 vs 7.24 beats/min for each 1°C, p < 0.0001); this relationship was not affected by age or adrenergic drugs. The increase in heart rate was related to the severity of organ dysfunction.

Conclusions: Increase in body temperature is associated with a linear increase in heart rate of 9.46 beats/min/°C in female and 7.24 beats/min/°C in male patients. These observations will help to correctly interpret heart rate values at different body temperatures and enable more accurate evaluation of other factors associated with tachycardia.