Military Anti-shock Trousers

Military anti-shock trousers are medical devices used to treat severe blood loss. They are also indicated for the stabilization of unstable pelvic fractures in the field prior to transport.

Usually called "MAST", and sometimes "pneumatic anti-shock garments" (PASG), they were invented by Lt. Col. Burton Kaplan during the Vietnam War. MAST look like a pair of trousers. They are opened and placed around the legs and pelvis of the patient. Each leg and the pelvic section may then be inflated, applying pressure to the lower half of the body. The trousers can be used with sager traction splints and dressings already in place.

MAST are typically carried and used by emergency medical technicians and paramedics, although they are sometimes carried by fire department first responder trucks, and, in some states, first responders can apply and inflate them under direct medical control.

The exact way in which MAST help is uncertain. The most common theory is that the pressure decreases blood flow to the legs (thus increasing availability of blood to the rest of the body) and actually squeezes blood out of the lower body. It may be that increased perfusion to the brain and other organs also have indirect benefits.

There is some controversy over use of MAST (see IVPreHospital.com and Mattox 2003). One question is whether the increased peripheral vascular resistance may reduce cardiac output or rupture existing clots. Due to these questions and several human studies that have shown no advantage to patients with a high degree of blood loss above the pelvis, MAST trousers are being used much less often now than they were the 1980s and early '90s. Another reason they have fallen into disuse is the tendency for emergency room nurses and physicians to cut the inflated trousers off, which causes a catastrophic drop in blood pressure, as well as equipment destruction and an increased strain on budgets.

I. G. Roberts et alii sought to quantify the effect on mortality and morbidity of the use of MAST in patients following trauma, and published the data in the Cochrane Database of Systematic Reviews article "Medical anti-shock trousers (pneumatic anti-shock garments) for circulatory support in patients with trauma". Trials were identified by searches of the Cochrane Injuries Group's specialised register (April 2007), the Cochrane Central Register of Controlled Trials (issue 1, 2007), MEDLINE (April 2007), EMBASE (April 2007), ISI Web of Science (April 2007), National Research Register (issue 1, 2007) and PubMed (April 2006). In addition they checked the reference lists of relevant trials and reviews and contacted researchers in the field for unpublished data and ongoing trials. The relative risk of death with MAST was 1.13 (95% CI 0.97 to 1.32). Duration of hospitalisation and of intensive care unit stay was longer in the MAST treated group. The weighted mean difference in the length of intensive care unit stay was 1.7 days (95% CI 0.33 to 2.98). The authors concluded that there is no evidence to suggest that MAST/PASG application reduces mortality, length of hospitalisation or length of ICU stay in trauma patients and it is possible that it may increase these. These data do not support the continued use of MAST/PASG in the situation described. However, it should be recognised that, due to the poor quality of the trials, conclusions should be drawn with caution.