Metabolic Manipulation and Therapeutic Hypothermia

Area of Science:

• Physiology
• Thermoregulation
• Metabolic Rate

Background:

• Hypothermia induces physiological changes, including reduced metabolic rate and oxygen consumption (VO2).
• Limited human data exist on the precise relationship between core temperature reduction and VO2 changes.

Purpose of the Study:

• To quantify the reduction in resting VO2 as core body temperature is decreased in lightly sedated healthy individuals.
• To establish the relationship between core temperature and metabolic rate in a controlled human model.

Main Methods:

• Participants were cooled using intravenous cold saline and surface cooling pads.
• Shivering was suppressed using dexmedetomidine.
• Resting VO2 was measured via indirect calorimetry at core temperatures of 37°C, 36°C, 35°C, 34°C, and 33°C.

Main Results:

• Resting VO2 declined with decreasing core temperature, showing a median reduction of 20.8% from 37°C to 33°C in the absence of shivering.
• The most significant average decrease in VO2 per degree Celsius was 13.7%, occurring between 37°C and 36°C.
• Shivering onset halted further temperature decrease and led to an increase in VO2.

Conclusions:

• In lightly sedated humans, metabolic rate decreases by approximately 5.2% for every 1°C drop in core temperature from 37°C to 33°C.
• The substantial metabolic rate decrease between 37°C and 36°C suggests potential subclinical shivering or other homeostatic responses at these temperatures.