Artificial Air Pocket Research Articles

Comparative Effectiveness of an Artificial Air Pocket Device to Delay Asphyxiation in Supine Individuals Critically Buried in Avalanche Debris

Approximately 70% of individuals critically buried in avalanche debris die within 35 minutes as a result of asphyxial cardiac arrest. An artificial air-pocket device (AAPD) that separates inhaled air from exhaled air may delay the onset of severe hypoxemia and eventual asphyxia during snow burial. To investigate the efficacy of a new AAPD during snow burial in a supine position. This comparative effectiveness trial was performed in winter 2016 with data analysis in November 2016 and November 2022. Each trial used a simulated critical avalanche burial scenario, in which a trough was dug in a snow pile and an additional air pocket of 0.5 L volume was punched into the lateral wall for each control trial. All participants were buried in a supine position. Trials could be voluntarily terminated at any time, with a maximum length of 60 minutes; trials were automatically terminated if the participant's peripheral oxygen saturation (Spo2) dropped to less than 84%. Each participant conducted 2 trials, one in which they breathed into the AAPD (intervention trial) and the other in which they breathed into the prepared air pocket (control trial). Measurements included Spo2, cerebral oxygenation, ventilatory parameters, respiratory gas concentrations, and visual-analogue scales. Kaplan-Meier survival curves and rank test for matched survival data were used to analyze the total burial time in each trial. A total of 13 volunteers (9 men; mean [SD] age, 33 [8] years) were exposed to the intervention and control trials. Intervention trials were terminated less often (2 of 13 trials) as a result of hypoxemia than control trials (11 of 12 trials). Similarly, survival curves showed a longer duration of burial in the intervention compared with the control trials for the time to reach an Spo2 less than 84% (rank test for matched survival data: P = .003). The intervention trials, compared with the control trials, also had slower rates of decrease in fraction of inspired oxygen (mean [SD] rate, -0.8 [0.4] %/min vs -2.2 [1.2] %/min) and of increase in fraction of inspired carbon dioxide (mean [SD] rate, 0.5 [0.3] %/min vs 1.4 [0.6] %/min) and expired ventilation per minute (mean [SD] rate, 0.5 [1.0] L/min2 vs 3.9 [2.6] L/min2). This comparative effectiveness trial found that the new AAPD was associated with delaying the development of hypoxemia and hypercapnia in supine participants in a critical burial scenario. Use of the AAPD may allow a longer burial time before asphyxial cardiac arrest, which might allow longer times for successful rescue by companions or by prehospital emergency medical services.

Hypoxia and hypercapnia effects on cerebral oxygen saturation in avalanche burial: A pilot human experimental study

BackgroundA sufficient supply of oxygen is crucial to avoid hypoxic cardiac arrest and brain damage within 30 min in completely-buried avalanche victims. Snow density influences levels of hypoxia and hypercapnia. The goal of this study was to investigate the effects of hypoxia and hypercapnia on cerebral oxygenation (ScO2) in humans breathing into an artificial air pocket. MethodsEach subject breathed into a closed system (air-tight face mask – plastic tube – snow air-pocket of 4 L) up to 30 min. Each subject performed three tests in different snow densities. ScO2 was measured by a near-infrared spectroscopy (NIRS) device. Measurements included peripheral oxygen saturation (SpO2), end-tidal carbon dioxide (ETCO2), air pocket gases and blood gases. Snow density was assessed via standard methods and micro-computed tomography. Based on predetermined criteria, tests were classified based on whether they were terminated before 30 min and the reason for termination. The categories were: completed tests (30 min), tests terminated before 30 min when SpO2 dropped to ≤75% and tests that were terminated before 30 min by requests of the subjects. General linear models were used to compare termination groups for changes in ScO2, ETCO2, SpO2 and air pocket gases, and a multivariate analysis was used to detect factor independent effects on ScO2. ResultsScO2 was decreased in the group in which the tests were terminated for SpO2 ≤ 75% caused by a decrease in oxygen supply in high snow densities. In the completed tests, an increase in ScO2 occurred despite decreased oxygen supply and decreased carbon dioxide removal. ConclusionsOur data show that ScO2 determined by NIRS was not always impaired in humans breathing into an artificial air pocket despite decreased oxygen supply and decreased carbon dioxide removal. This may indicate that in medium to low snow densities brain oxygenation can be sufficient, which may reflect the initial stage of the triple H (hypothermia, hypoxia, and hypercapnia) syndrome. In high snow densities, ScO2 showed a significant decrease caused by a critical decrease in oxygen supply. This could lead to a higher risk of hypoxic cardiac arrest and brain damage.

Effects of snow properties on humans breathing into an artificial air pocket \u2013 an experimental field study

Breathing under snow, e.g. while buried by a snow avalanche, is possible in the presence of an air pocket, but limited in time as hypoxia and hypercapnia rapidly develop. Snow properties influence levels of hypoxia and hypercapnia, but their effects on ventilation and oxygenation in humans are not fully elucidated yet. We report that in healthy subjects breathing into snow with an artificial air pocket, snow density had a direct influence on ventilation, oxygenation and exhaled CO2. We found that a rapid decline in O2 and increase in CO2 were mainly associated with higher snow densities and led to premature interruption due to critical hypoxia (SpO2 ≤ 75%). However, subjects in the low snow density group demonstrated a higher frequency of test interruptions than expected, due to clinical symptoms related to a rapid CO2 accumulation in the air pocket. Snow properties determine the oxygen support by diffusion from the surrounding snow and the clearance of CO2 by diffusion and absorption. Thus, snow properties are co-responsible for survival during avalanche burial.

The Influence of Snow Density on O2 and CO2 Levels in Subjects Breathing into an Artificial Airpocket

The Influence of Snow Density on O2 and CO2 Levels in Subjects Breathing into an Artificial Airpocket

Comparison of Dose Distributions With TG-43 and Collapsed Cone Convolution Algorithms Applied to Accelerated Partial Breast Irradiation Patient Plans

Tocompare the treatment plans for accelerated partial breast irradiation calculated by the new commercially available collapsed cone convolution (CCC) and current standard TG-43-based algorithms for 50 patients treated at our institution with either a Strut-Adjusted Volume Implant (SAVI) or Contura device. We recalculated target coverage, volume of highly dosed normal tissue, and dose to organs at risk (ribs, skin, and lung) with each algorithm. For 1 case an artificial air pocket was added to simulate 10% nonconformance. We performed a Wilcoxon signed rank test to determine the median differences in the clinical indices V90, V95, V100, V150, V200, and highest-dosed 0.1cm(3) and 1.0cm(3) of rib, skin, and lung between the two algorithms. The CCC algorithm calculated lower values on average for all dose-volume histogram parameters. Across the entire patient cohort, the median difference in the clinical indices calculated by the 2 algorithms was <10% for dose to organs at risk, <5% for target volume coverage (V90, V95, and V100), and <4cm(3) for dose to normal breast tissue (V150 and V200). No discernable difference was seen in the nonconformance case. We found that on average over our patient population CCC calculated (<10%) lower doses than TG-43. These results should inform clinicians as they prepare for the transition to heterogeneous dose calculation algorithms and determine whether clinical tolerance limits warrant modification.

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.

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.

Advanced Avalanche Safety Equipment of Backcountry Users: Current Trends and Perceptions

Backcountry travelers should carry a standard set of safety gear (transceiver, shovel, and probe) to improve rescue chances and reduce mortality risk. Many backcountry enthusiasts are using other advanced equipment such as an artificial air pocket (eg, the AvaLung) or an avalanche air bag. Our goal was to determine the numbers of backcountry users carrying advanced equipment and their perceptions of mortality and morbidity benefit while carrying this gear. A convenience sample of backcountry skiers, snowboarders, snowshoers, and snowmobilers was surveyed between February and April 2014. Participants of this study were backcountry mountain users recruited at trailheads in the Wasatch and Teton mountain ranges of Utah and Wyoming, respectively. Questions included prior avalanche education, equipment carried, and perceived safety benefit derived from advanced equipment. In all, 193 surveys were collected. Skiers and snowboarders were likely to have taken an avalanche safety course, whereas snowshoers and snowmobilers were less likely to have taken a course. Most backcountry users (149, 77.2%), predominantly skiers and snowboarders, carried standard safety equipment. The AvaLung was carried more often (47 users) than an avalanche air bag (10 users). The avalanche air bag had a more favorable perceived safety benefit. A majority of participants reported cost as the barrier to obtaining advanced equipment. Standard avalanche safety practices, including taking an avalanche safety course and carrying standard equipment, remain the most common safety practices among backcountry users in the Wasatch and Tetons. Snowshoers remain an ideal target for outreach to increase avalanche awareness and safety.

Hypoxia and hypercapnia during respiration into an artificial air pocket in snow: implications for avalanche survival

Snow avalanche case reports have documented the survival of skiers apparently without permanent hypoxic sequelae, after prolonged complete burial despite there being only a small air pocket on extrication. We investigated the underlying pathophysiological changes in a prospective, randomised 2×2 crossover study in 12 volunteers (28 tests) breathing into an artificial air pocket (1- or 2-l volume) in snow. Peripheral SpO 2, ETCO 2, arterialised capillary blood variables, air pocket O 2 and CO 2, snow density, and snow conditions at the inner surface of the air pocket were determined. SpO 2 decreased from a median of 99% (93–100%) to 88% (71–94%; P<0.001) within 4 min of breathing into the air pocket; the reduction was greater at 1 l, than 2 l, volume air pocket ( P=0.013, intention to treat P=0.003) and correlated to snow density ( r=0.50, P=0.021, partial correlation coefficient). ETCO 2 rose simultaneously from median 5.07 kPa (3.47–6.93 kPa) to 6.8 kPa (5.87–8.27 kPa; P<0.001), with consequent respiratory acidosis. Despite premature interruption due to hypoxia (SpO 2≤75%) in 17 of 28 tests (61%), a respiratory steady state prevailed in five tests until protocol completion (30 min). We conclude that the degree of hypoxia following avalanche burial is dependent on air pocket volume, snow density and unknown individual personal characteristics, yet long-term survival is possible with only a small air pocket. Hence, the definition of an air pocket, “any space surrounding mouth and nose with the proviso of free air passages” is validated as the main criterion for triage and management of avalanche victims. Our experimental model will facilitate evaluating the interrelation between volume and inner surface area of an air pocket for survival of avalanche victims, whilst the present findings have laid the basis for future investigation of possible interactions between hypoxia, hypercapnia, and hypothermia (triple H syndrome) in snow burial.

Technological Advances in Avalanche Survival

Over the last decade, a proliferation of interest has emerged in the area of avalanche survival, yielding both an improved understanding of the pathophysiology of death after avalanche burial and technological advances in the development of survival equipment. The dismal survival statistics born out of the modern era of winter recreation unmistakably reveal that elapsed time and depth of burial are the most critical variables of survival and the focus of newer survival devices on the market. Although blunt trauma may kill up to one third of avalanche victims, early asphyxiation is the predominant mechanism of death, and hypothermia is rare. A survival plateau or delay in asphyxiation may be seen in those buried in respiratory communication with an air pocket until a critical accumulation of CO2 or an ice lens develops. The newest survival devices available for adjunctive protection, along with a transceiver and shovel, are the artificial air pocket device (AvaLung), the avalanche air bag system (ABS), and the Avalanche Ball. The artificial air pocket prolongs adequate respiration during snow burial and may improve survival by delaying asphyxiation. The ABS, which forces the wearer to the surface of the avalanche debris by inverse segregation to help prevent burial, has been in use in Europe for the last 10 years with an impressive track record. Finally, the Avalanche Ball is a visual locator device in the form of a spring-loaded ball attached to a tether, which is released from a fanny pack by a rip cord. Despite the excitement surrounding these novel technologies, avalanche avoidance through knowledge and conservative judgment will always be the mainstay of avalanche survival, never to be replaced by any device.

Respiration during snow burial using an artificial air pocket.

Asphyxia is the most common cause of death after avalanche burial. A device that allows a person to breathe air contained in snow by diverting expired carbon dioxide (CO2) away from a 500-cm3 artificial inspiratory air pocket may improve chances of survival in avalanche burial. To determine the duration of adequate oxygenation and ventilation during burial in dense snow while breathing with vs without the artificial air pocket device. Field study of physiologic respiratory measures during snow burial with and without the device from December 1998 to March 1999. Study burials were terminated at the subject's request, when oxygen saturation as measured by pulse oximetry (SpO2) dropped to less than 84%, or after 60 minutes elapsed. Mountainous outdoor site at 2385 m elevation, with an average barometric pressure of 573 mm Hg. Six male and 2 female volunteers (mean age, 34.6 years; range, 28-39 years). Burial time, SpO2, partial pressure of end-tidal CO2 (ETCO2), partial pressure of inspiratory CO2 (PICO2), respiratory rate, and heart rate at baseline (in open atmosphere) and during snow burial while breathing with the device and without the device but with a 500-cm3 air pocket in the snow. Mean burial time was 58 minutes (range, 45-60 minutes) with the device and 10 minutes (range, 5-14 minutes) without it (P=.001). A mean baseline SpO2 of 96% (range, 90%-99%) decreased to 90% (range, 77%-96%) in those buried with the device (P=.01) and to 84% (range, 79%-92%) in the control burials (P=.02). Only 1 subject buried with the device, but 6 control subjects buried without the device, decreased SpO2 to less than 88% (P=.005). A mean baseline ETCO2 of 32 mm Hg (range, 27-38 mm Hg) increased to 45 mm Hg (range, 32-53 mm Hg) in the burials with the device (P=.02) and to 54 mm Hg (range, 44-63 mm Hg) in the control burials (P=.02). A mean baseline PICO2 of 2 mm Hg (range, 0-3 mm Hg) increased to 32 mm Hg (range, 20-44 mm Hg) in the burials with the device (P=.01) and to 44 mm Hg (range, 37-50 mm Hg) in the control burials (P=.02). Respiratory and heart rates did not change in burials with the device but significantly increased in control burials. In our study, although hypercapnia developed, breathing with the device during snow burial considerably extended duration of adequate oxygenation compared with breathing with an air pocket in the snow. Further study will be needed to determine whether the device improves survival during avalanche burial.