AVA-CO2-R: Impact of CO2 Absorption on Gas Exchange and Ventilation Patterns While Breathing Into a Snow Air Pocket - An Experimental Study

Introduction

Background and aims

Asphyxia is by far the most common cause of death after critical avalanche burial. The presence of an air pocket increases the survival chances , but expired air rich in carbon dioxide (CO2) progressively displaces oxygen (O2) in the air pocket, a phenomenon known as displacement asphyxia. In addition, an increase in the inspired concentration of CO2 (FiCO2) reduces the alveolar partial pressure of O2 (PAO2), as explained by the alveolar gas equation. Underlining this, a recent experimental porcine study showed that an increased FiCO2 is the leading cause of the decrease in PaO2. By removing CO2 in an experimental avalanche burial, normoxia persisted even after 90 minutes of burial, while, in the absence of CO2 removal, hypoxemia and hypercapnia occurred after only 10 minutes. Additionally, hypercapnia increases pulmonary vascular resistance, reduces cardiac output and can lead to life-threatening hemodynamic instability. Hypercapnia can speed up the cooling rate, and the combination of hypothermia with hypoxia and hypercapnia may result in a worse neurological outcome in completely buried avalanche patients compared to patients suffering solely hypothermic cardiac arrest.

Taken together, these findings suggest that removing CO2 from the air-pocket could prevent, or at least delay, the hypercapnic condition with its deleterious consequences and consequently increase the survival after complete avalanche burial.

The main aim of the study is to investigate the effectiveness of soda lime in removing CO2 while breathing into a snow air pocket, and to assess its impact on gas exchange, ventilation patterns, and hemodynamics.