Changes in oxygenation variables during progressive hypothermia in anesthetized patients

Area of Science:

• Anesthesiology and Critical Care Medicine
• Cardiovascular Physiology
• Metabolic Physiology

Background:

• Deliberate hypothermia is increasingly utilized in neurosurgery to mitigate neurological damage.
• Understanding the physiological impact of hypothermia on systemic oxygenation is crucial for patient management.

Purpose of the Study:

• To investigate the effects of progressive body core temperature reduction on whole-body oxygenation variables during intracranial surgery.
• To compare oxygenation parameters between patients undergoing hypothermia and a normothermic control group.

Main Methods:

• 13 patients undergoing elective intracranial surgery were cooled to 32.0°C (Hypothermic Group).
• A control group (n=6) maintained a core temperature of 35.5°C.
• Cardiac index (CI), whole-body oxygen delivery (DO2), oxygen consumption (VO2), carbon dioxide production (VCO2), and energy expenditure (EE) were measured using thermodilution and indirect calorimetry.

Main Results:

• In the Hypothermic Group, VO2, VCO2, EE, P50, and oxygen extraction ratio (O2ER) significantly decreased (p < 0.05) as temperature dropped from 35.5°C to 32.0°C.
• These variables remained unchanged in the Control Group.
• At 32.0°C, VO2, VCO2, EE, P50, and O2ER were significantly lower in the Hypothermic Group compared to the Control Group.
• DO2 remained stable in both groups throughout the study.

Conclusions:

• Progressive hypothermia in anesthetized patients undergoing intracranial surgery effectively reduces metabolic rate (VO2, VCO2, EE).
• Hypothermia does not alter overall oxygen delivery (DO2).
• The observed decrease in O2ER is potentially linked to a leftward shift in the oxyhemoglobin dissociation curve, indicated by a reduced P50.