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Body Temperature and Heart Rate – Are They Related?

March 10, 2021

Written by Aaron Lacy 

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There is a linear increase of heart rate associated with elevated temperatures in critically ill patients. For each 1°C increase in body temperature, there was an associated heart rate increase by 9.46 beats/minute in females and 7.24 beats/minute in males.

Why does this matter?
It has long been thought that fever causes tachycardia, but to what extent? In the critically ill patient, there are many potential causes of tachycardia, and knowing to what degree tachycardia can be attributed to temperature alone would be useful in evaluating ill patients.

Is it just the fever making them tachycardic?
This was a retrospective review of prospectively collected data in 9,046 patients admitted to an ICU in Denmark over a 13-year period who had simultaneous recorded pairings of both heart rate and temperature (n = 472,941). Invasive temperature monitoring was used in 98% of the included patients. In temperatures ranging from 32°C to 42°C, there was a 7.24 (+/- 0.29) beats/min/1°C and 9.46 (+/- 0.44) beats/min/1°C increase in heart rate for men and women, respectively (p = 0.014).

Multiple linear regression modeling showed there was no significant relationship with age (p = 0.16), hemoglobin (p = 0.67), magnesium (p = 0.93), base excess (p = 0.54), norepinephrine (p = 0.29), dobutamine (p = 0.96), or dopamine (p = 0.35). There was an association with the SOFA score, with each 1-point increase in overall SOFA score associated with 0.68 beats/min increase in heart rate (p < 0.0001). These findings mirror a similar study done in United States emergency departments.

When an ill patient presents with elevated heart rate, consider doing a correction for temperature to help better assess the current level of resuscitation and illness in your patient. To make it easier to remember, it’s women ~10 per °C; men ~7 per °C.

The Relationship Between Heart Rate and Body Temperature in Critically Ill Patients. Crit Care Med. 2021 Jan 20. doi: 10.1097/CCM.0000000000004807. Online ahead of print.

What are your thoughts?