Fever increases heart rate and respiratory rate; a prospective observational study of acutely admitted medical patients

Background: The relationship between increase in body temperature, heart rate, and respiratory rate has only been studied in young, healthy subjects. Aim: To show the changes in heart and respiratory rate associated with fever in acutely admitted medical patients. Design: A prospective observational cohort study Methods: Vital parameters from 4,493 patients were retrospectively extracted. Linear and multiple variable regression analysis was used to calculate the change in heart and temperature rate for every degree rise in temperature (i.e. ΔHR/°C and ΔRR/°C) in the entire study group and in those with low (<36.1°C), normal (36.1-38°C) and high (>38°C) body temperatures. Results: The ΔHR/°C and ΔRR/°C was 7.2±0.4 beats per minute (bpm) and 1.4 ±0.1 (1.2 to 1.62) breaths per minute (bpm). Adjusting for age, oxygen saturation and mean blood pressure, the results were 6.4±0.4 (5.7 to 7.1) bpm and 1.2±0.1 (1.0 to 1.4) bpm. In low, normal and high body temperature the ΔHR/°C were 2.7±1.9, 6.9±1.9 and 7.4±0.9 bpm, respectively; for ΔRR/°C the values were -0.5±0.5, 1.5±0.5 and 2.3±0.3 bpm, respectively. Conclusions: We only found a modest association between fever and changes in heart rate and respiratory rate.