Work of Breathing into Snow in the Presence versus Absence of an Artificial Air Pocket Affects Hypoxia and Hypercapnia of a Victim Covered with Avalanche Snow: A Randomized Double Blind Crossover Study

Abstract

Presence of an air pocket and its size play an important role in survival of victims buried in the avalanche snow. Even small air pockets facilitate breathing. We hypothesize that the size of the air pocket significantly affects the airflow resistance and work of breathing. The aims of the study are (1) to investigate the effect of the presence of an air pocket on gas exchange and work of breathing in subjects breathing into the simulated avalanche snow and (2) to test whether it is possible to breathe with no air pocket. The prospective interventional double-blinded study involved 12 male volunteers, from which 10 completed the whole protocol. Each volunteer underwent two phases of the experiment in a random order: phase “AP”—breathing into the snow with a one-liter air pocket, and phase “NP”—breathing into the snow with no air pocket. Physiological parameters, fractions of oxygen and carbon dioxide in the airways and work of breathing expressed as pressure-time product were recorded continuously. The main finding of the study is that it is possible to breath in the avalanche snow even with no air pocket (0 L volume), but breathing under this condition is associated with significantly increased work of breathing. The significant differences were initially observed for end-tidal values of the respiratory gases (EtO2 and EtCO2) and peripheral oxygen saturation (SpO2) between AP and NP phases, whereas significant differences in inspiratory fractions occurred much later (for FIO2) or never (for FICO2). The limiting factor in no air pocket conditions is excessive increase in work of breathing that induces increase in metabolism accompanied by higher oxygen consumption and carbon dioxide production. The presence of even a small air pocket reduces significantly the work of breathing.

PDEModelica and Breathing in an Avalanche

“…The exact identification of the values is a subject of additional research. However, the resulting trends are consistent with expectation and plausibility personally confirmed by the authors of (Roubík et al, 2015) . The CO 2 concentration in the cavity rises with each expiration (Figure 2) and is rising towards an equilibrium.…”

“…Due to small pressure differences, the gas is modeled as incompressible. The only significant pressure difference could occur at the boundary between the cavity and the snow, but Roubík et al (Roubík et al, 2015) did experience only small pressure differences.…”

“…Roubík et al carried out an experiment (Roubík et al, 2015) where the volunteers were breathing through a tube whose end opened into a cavity in snow of various volumes. They proved that the size of the cavity has a significant impact on the concentration of O 2 and CO 2 in the inspired and expired air.…”

Materials Suitable to Simulate Snow During Breathing Experiments for Avalanche Survival Research

“…During the experiment, a two-liter air pocket was present between volunteer and the tested materials. The presence of air pocket or its size were selected as a typical configuration of already published experimental studies [8,9,15].…”

“…Safety of the volunteers during the experiment was assured by advanced monitoring and continuous evaluation of their physiological parameters. Furthermore, a clinician with a specialty in anesthesia and emergency medicine continuously assessed the state of the volunteer [15] and could terminate the experiment at any time. The breathing experiment would be terminated due to one or more of the following reasons [15]: request of the volunteer; decision made by the anesthesiologist or the investigator testing the consciousness of the volunteer; end-tidal partial pressure of carbon dioxide (PaCO2) in the expired gas higher than or equal to 60 mm Hg [16]; presence of nitrous oxide in the breathing gas at any measurable concentration; or breathing in the material over 30 min.…”