PCO2 and hypothermia

Q: 42 years old homeless gentleman is admitted to the ICU after a snowstorm in Illinois with hypothermia of 33°C. Patient is intubated. Central arterial lines are placed. Arterial Blood Gas (ABG) was sent. The actual PaCO2 of the patient should be considered _____________ than the value reported by blood gas machine? (select one)

A) higher

B) lower

Answer: B

In hypothermia, patient's actual PaCO2 should be considered lower than the value reported by blood gas machine. When a patient's core temperature is 33°C, the patient's actual PaCO2 may be 6-7 mmHg lower than the value reported by blood gas machine. It is recommended that slightly higher PaCO2 values be targeted in hypothermic patients. Unintended hyperventilation may cause cerebral vasoconstriction.

Although the quest to find a proper formula to determine actual PH depending on degree of hypothermia has been ongoing for six decades, no exact formula can be trusted with full confidence.

#ventilators

#acid-base

#hypothermia

References:

1. Sitzwohl C, Kettner SC, Reinprecht A, et al. The arterial to end-tidal carbon dioxide gradient increases with uncorrected but not with temperature-corrected PaCO2 determination during mild to moderate hypothermia. Anesth Analg 1998; 86:1131.

2. AUSTIN WH, LACOMBE EH, RAND PW. PH-TEMPERATURE CONVERSION FACTORS AND PCO2 FACTORS FOR HYPOTHERMIA. J Appl Physiol. 1964 Sep;19:893-6. doi: 10.1152/jappl.1964.19.5.893. PMID: 14207740.

3. Kofstad J. Blood gases and hypothermia: some theoretical and practical considerations. Scand J Clin Lab Invest Suppl. 1996;224:21-6. doi: 10.3109/00365519609088622. PMID: 8865418.

4. Chaney B, Emmady PD. Blood Gas Temperature Correction. [Updated 2023 May 8]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK557769/