I bring you a weekly bite-sized chunk of the science behind helicopter human factors and CRM in practice, simplifying the complex and distilling a helicopter related study into a summary of less than 500 words.
TITLE:
Respiratory function in hoist rescue: comparing slings, stretcher, and rescue basket.
WHAT?
Study comparing the respiratory effects of four commonly used helicopter hoist-rescue devices: a single rescue sling, double sling, stretcher and rescue basket. The aim was to see what effect that both chest compression and casualty position during hoisting could have on breathing and other physiological measures, particularly in already compromised casualties.
WHERE?
The study was conducted at the CareFlight base in New South Wales, Australia, using its winch training simulator.
WHEN?
Published in Aviation, Space, and Environmental Medicine in 2011.
WHY?
Hoist devices are normally chosen on the basis of circumstances and limitations at the point of extraction including factors such as safety, water/mountain rescue, speed, and casualty condition, but the device chosen itself may adversely affect casualty physiology. Previous research has demonstrated respiratory restriction during sling and stretcher rescue, including a near-fatal incident involving a severely asthmatic casualty in a single sling. The authors therefore wanted to determine whether a semi-recumbent rescue basket could provide a physiologically safer alternative.
HOW?
27 healthy adults completed a randomized crossover trial, experiencing all four devices while suspended approximately 20 cm above the ground. Researchers measured lung function using spirometry, together with oxygen saturation, heart rate and respiratory rate, and compared these with normal measurements when seated.
FINDINGS:
The single sling was found to produce by far the greatest respiratory impairment. Lung function was measured through:
FEV₁ : Forced Expiratory Volume in one second is the volume of air a person can forcibly blow out during the first second after taking a full breath and reflects how effectively air can be expelled from the lungs. It fell by 17% when suspended in a sling.
FVC : Forced Vital Capacity is the total volume of air a person can forcibly exhale after taking the deepest possible breath. This fell by 19.8% and inspiratory capacity by 28.3%.
Heart and respiratory rates increased and oxygen saturation fell by an average of 3%.
The double sling produced smaller reductions, while the stretcher caused modest reductions in expiratory measures. The rescue basket produced no significant deterioration in any measured outcome.
SO WHAT?
The study demonstrates that the rescue device can itself become a physiological stressor. A single sling compresses the chest while leaving the casualty vertically suspended. This has also been associated with orthostatic problems in previous research. A double sling is more benign because it supports the legs, while the semi-recumbent basket avoids both chest suspension and fully supine positioning.
The implications may be greatest for casualties with reduced physiological strength through trauma, immersion, hypothermia, exhaustion, asthma or cardiac disease. It is likely that effects demonstrated in healthy volunteers could become clinically important in real rescue patients.
This supports treating casualty physiology as part of hoist equipment selection, rather than assuming the quickest or most effective attachment method is physiologically neutral. The authors recommend caution with single slings, regard double slings as a more benign alternative, and suggest wider consideration of rescue baskets where operationally practical.
REFERENCE:
Murphy, D., Garner, A., & Bishop, R. (2011). Respiratory function in hoist rescue: Comparing slings, stretcher, and rescue basket. Aviation, Space, and Environmental Medicine, 82(2), 123–127. https://doi.org/10.3357/ASEM.2591.2011
