Background: The purpose of this study was to simulate first aid by mechanical use of a limb tourniquet on a thigh with and without bone to better understand best caregiving practices.
Methods: Two investigators studied simulated first aid on a new pool "noodle," a plastic cylinder with a central air tunnel into which we inserted a wood dowel to simulate bone. Data were gathered by group (study and control, n = 12 each). The control group comprised data collected from simulated tourniquet use on the model with bone present. The study group comprised data from simulated tourniquet use on the model without bone.
Results: Comparing compression with and without bone, the mean volumes of compressed soft tissues alone were 303mL and 306mL, respectively. When bone was present, the volume of soft tissues was squeezed more, yielding a smaller size by 3mL (1%). The bone had a volume of 41mL and pressed statically outward with an equal force oppositely directed to the inward compression of the overlying soft tissues. With bone removed and compression applied, the mean residual void was 16mL, because 25mL (i.e., 41mL minus 16mL) of soft tissues had collapsed inward. The volume of the limb under the tourniquet with and without bone was 344mL and 322mL, respectively. The collapse volume, 25mL, was 3mL more than the difference of the mean volume of the limb under the tourniquet. More limb squeeze (22mL) looked like better compression, but it was actually worse-an illusion created by collapse of the hidden void.
Conclusion: In simulated first aid, mechanical modeling demonstrated how tourniquet compression applied to a limb squeezed the soft tissues better when underlying bone was present. Bone loss altered the compression profile and may complicate control of bleeding in care. This knowledge, its depiction, and its demonstration may inform first-aid instructors.