ABG measurement: Temp effect

Basic, Basic Sciences

The electrodes in a blood gas analyzer are maintained at 37°C. Therefore, all ABG measurements are made at 37°C regardless of the patient’s body temperature. However, the solubility of a gas (CO2, O2) in liquid (blood) is inversely proportional to the temperature of the liquid. Therefore, when the patient’s body temperature is below 37°C the reported PaO2 and PaCO2 will be lower than the actual values in the patient (temperature decreases --> solubility increases --> partial pressure decreases), and the opposite is true when the patient’s body temperature is above 37°C. Likewise, pH is also temperature-dependent and decreases with increasing temperature. Normal values adjusted for temperature are shown in the table below.

Alternatively, corrected values can be estimated according to the following relationships:

Physiologic PO2 (mmHg) = Measured PO2 - 5 * [37°C - Body Temperature (°C)]

Physiologic PCO2 (mmHg) = Measured PCO2 - 2 * [37°C - Body Temperature (°C)]

Physiologic pH = Measured pH + 0.015 * [37°C - Body Temperature (°C)]

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Christopher Spencer, MD