Should capnography be used as a guide for choosing a ventilation strategy in circulatory shock caused by severe hypothermia? Observational case-series study.

Background: Severe accidental hypothermia can cause circulatory disturbances ranging from cardiac arrhythmias through circulatory shock to cardiac arrest. Severity of shock, pulmonary hypoperfusion and ventilation-perfusion mismatch are reflected by a discrepancy between measurements of CO ₂ levels in end-tidal air (EtCO ₂ ) and partial CO ₂ pressure in arterial blood (PaCO ₂ ). This disparity can pose a problem in the choice of an optimal ventilation strategy for accidental hypothermia victims, particularly in the prehospital period. We hypothesized that in severely hypothermic patients capnometry should not be used as a reliable guide to choose optimal ventilatory parameters.
Methods: We undertook a pilot, observational case-series study, in which we included all consecutive patients admitted to the Severe Hypothermia Treatment Centre in Cracow, Poland for VA-ECMO in stage III hypothermia and with signs of circulatory shock. We performed serial measurements of arterial blood gases and EtCO ₂ , core temperature, and calculated a PaCO ₂ /EtCO ₂ quotient.
Results: The study population consisted of 13 consecutive patients (ten males, three females, median 60 years old). The core temperature measured in esophagus was 20.7-29.0 °C, median 25.7 °C. In extreme cases we have observed a Pa-EtCO ₂ gradient of 35-36 mmHg. Median PaCO ₂ /EtCO ₂ quotient was 2.15.
Discussion and Conclusion: Severe hypothermia seems to present an example of extremely large Pa-EtCO ₂ gradient. EtCO ₂ monitoring does not seem to be a reliable guide to ventilation parameters in severe hypothermia.