Giacomo Strapazzon with study participant in Braies (Bz)
© Eurac Research | Annelie Bortolotti
In a pioneering volunteer trial, Eurac Research scientists were able to measure the level of cerebral oxygenation in a simulated avalanche burial situation using near-infrared spectroscopy (NIRS). Their aim was to determine parameters for the possible prolongation of victim survival without incurring the effects of neurological damage due to three H syndrome (from hypoxia, hypercapnia and hypothermia). The results were recently published in the prestigious journal Resuscitation.
When rescuers extract a living avalanche victim from the snow, their greatest fear is of the neurological damage that the prolonged lack of oxygen may have caused. However, the cold actually helps. If the heart can continue to beat under the snow, the body temperature will gradually drop and protect the brain cells from permanent damage ̶ despite a gradual decrease in blood oxygen levels and an increase in carbon dioxide in the blood due to a lack of adequate air exchange. These adverse effects are known amongst medical circles and rescue personnel as three H syndrome (hypoxia, hypercapnia and hypothermia), what is not known however, is why the syndrome only occurs in certain cases? Could its occurrence be influenced by the level of oxygenation in the brain? And what role does the characteristics of the avalanche’s snow play in these cases?
The answers to these questions could help to improve the treatment of avalanche patients once they have emerged however, attaining them is not straightforward. Although three H syndrome is a condition observable in humans it’s highly difficult to simulate. Eurac Research mountain emergency medicine experts attempted a simulation in Braies, Val Pusteria, Bolzano.
The test took place inside a cavity created within an artificial avalanche whereby 12 volunteers were instructed to breathe for 30 minutes via a space which had been cleared in front of their mouths. The simulated burial was interrupted at the request of the volunteers either when they experienced breathlessness and an excessive sensation of discomfort, or when the researchers detected an excessive decrease in blood oxygen levels. During the tests, the researchers monitored the volunteers' cerebral oxygenation using NIRS (near-infrared spectroscopy), a non-invasive diagnostic method that uses sensors to measure the oxygenation of specific tissues in real time.
By using NIRS in this study, we have confirmed both the importance of adequate cerebral oxygenation for survival without consequences, as well as the characteristics of the snow in an avalanche burial.Giacomo Strapazzon
Volunteers who were able to complete the test had increased brain saturation and in a real-world situation, would have been the ones likely to have developed three H syndrome: their bodies cooled down but the snow still provided sufficient oxygen and carbon dioxide removal. In contrast, the subjects who could not complete the test showed declining brain saturation, possibly due to there not being enough oxygen in the snow or adequate carbon dioxide removal putting the subjects at risk of developing a dangerous condition which, if prolonged, would result in brain damage (as well as cardiovascular damage owing to a disruption of the protective cooling process and even cardiac arrest). The experiment not only demonstrated, for the first time, the link between oxygenation of the human brain, air in the snow and the onset of three H syndrome but also how, up to a certain threshold, reduced availability of oxygen does not always lead to a reduction in oxygen in the brain. The brain has self-regulating and compensating mechanisms which, under certain conditions and periods of time, guarantee an adequate supply of oxygen.
"By using NIRS in this study, we have confirmed both the importance of adequate cerebral oxygenation for survival without consequences, as well as the characteristics of the snow in an avalanche burial. With low and medium density snow, the chances of the victim avoiding a state of asphyxiation are greater," explains Giacomo Strapazzon, lead author of the article and deputy director of the Eurac Research Institute of Mountain Emergency Medicine. "As is often the case with basic research, the results obtained are not reflected in today’s clinical practice. If we continue in this direction, we could evaluate how NIRS might improve the pre-hospitalisation triage and treatment of avalanche victims to understand whether, at the time of extraction, patients are already suffering brain damage," Strapazzon concludes.
See the full article on Resuscitation (open access) Hypoxia and hypercapnia effects on cerebral oxygen saturation in avalanche burial: A pilot human experimental study
Additional Eurac Research Institute of Emergency Medicine publications from the Bozen-Bolzano Institutional Archive BIA (Bozen-Bolzano Institutional Archive).
In focus: Braies snow density study
In addition to measuring brain saturation with NIRS, the main objective of the study conducted in Braies in 2014, was to demonstrate the existence of a relationship between the characteristics of snow and the possibility of breathing under an avalanche via a cavity in front of the victim’s mouth. To achieve this, scientists from Eurac Research, the University of Innsbruck and the Institute for Snow and Avalanche Research (SLF) in Davos monitored the vital parameters of 12 volunteers breathing via cavities within artificial avalanches characterised by snow of different consistencies. The trial was simulated in January when the snow tends to be light and dry and then in February and March when the snow becomes heavier and wetter. Analyses of the parameters showed that in the presence of less dense and drier snow, the volunteers had sufficient levels of blood oxygenation and were able to breathe adequately for the entire thirty minutes. Dense, wet snow, on the other hand, has similar effects to that of a plastic bag: it restricts gas exchange between the cavity and the surrounding snow and quickly inhibits the ability to breathe. Almost all the tests conducted with this type of snow were aborted due to the rapid development of oxygen deficiency in the volunteers' blood. The standalone study originally published in 2017 by Scientific Reports - Nature’s online journal presented the methods by which snow provides oxygen and, in some cases, is also able to absorb the carbon dioxide emitted by the victim, thereby delaying asphyxiation.