Military Anti-Shock Trousers

Military Anti-Shock Trousers are medical devices used to treat severe blood loss.

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Usually called "MAST", and sometimes "Pneumatic Anti-Shock Garments" or "PASG", they were invented by the U.S. military during the Vietnam war. MAST look like a pair of pants. 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.

MAST are typically carried and used by Emergency medical technicians and paramedics, although 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.

References

• Davis JW, McKone TK, Cram AE. "Hemodynamic effects of military anti-shock trousers (MAST) in experimental cardiac tamponade." Annals of Emergency Medicine. 1981 Apr;10(4):185-6. [1]

• IVPreHospital.com. FYI: Pneumatic Anti-Shock Garments (PASG) [2]

• Mattox, Kenneth L, MD. "Permissive Hypotension." January 2003. [3]

• Traverso LW, Lee WP, DeGuzman LR, Bellamy RF. "Military antishock trousers prolong survival after otherwise fatal hemorrhage in pigs." Journal of Trauma. 1985 Nov;25(11):1054-8. [4]