The Rise and Fall of MAST/PASG

The device that everyone knew worked

There's a particular danger in a treatment that obviously does something. MAST did something: you inflated the trousers, the blood pressure went up, and everyone in the back of the truck felt better. The number on the cuff was reassuring. It took twenty years and a couple of hard trials to prove that the reassuring number was, in a lot of patients, a lie that killed them.

Where the trousers came from

The Medical (or Military) Anti-Shock Trousers, also called the Pneumatic Anti-Shock Garment (PASG), descend from the aviator's G-suit. Cutler and Daggett published the trauma application, "Application of the 'G-suit' to the control of hemorrhage in massive trauma," in *Annals of Surgery* in 1971. The premise was intuitive: inflate bladders around the legs, abdomen, and pelvis, raise central blood pressure, and tamponade bleeding below the diaphragm. It saw use in the Vietnam era and arrived in civilian EMS with strong field-anecdote credentials.

The institutional stamp came fast. In 1977, the American College of Surgeons Committee on Trauma listed MAST as essential equipment for ambulances. Through the late 1970s and into the 1980s, MAST was the standard of care for the hypotensive trauma patient. It was on the rig because the spec said so, and you applied it because the protocol said so.

When the evidence arrived

The trouble is that raising blood pressure isn't the same as helping the patient. If a vessel in the chest is torn, driving the pressure up can blow off a forming clot and increase bleeding, while the inflated abdomen splints the diaphragm and makes breathing worse.

Two studies broke the device's back. In 1989, Mattox and colleagues published a prospective randomized trial of 911 hypotensive trauma patients in the *Journal of Trauma*. Overall mortality was 31% with MAST versus 25% without (p = 0.05), and the harm was worst in patients with thoracic and cardiac injuries. The Houston Fire Department, where MAST had been mandatory, stopped carrying it. Then in 1994, Bickell and colleagues published in the *New England Journal of Medicine* a trial of 598 patients with penetrating torso injuries, showing that delaying fluid resuscitation until surgical control improved survival (70% vs. 62%). That study didn't test MAST directly, but it demolished the underlying belief: that propping up the pressure before you've stopped the bleeding is good for the patient. It helped launch permissive hypotension, the approach I work under now.

The cautionary tale, not the trousers

The trousers themselves are a footnote. What I keep is the pattern, because it repeats. A treatment with an obvious, visible effect, raising a blood pressure, becomes doctrine before anyone runs the trial. The effect we can see crowds out the outcome we actually care about, survival, and questioning it looks like negligence. Then the data shows up fifteen years late and tells us we were harming people the whole time.

That's why the modern push toward hemorrhage control looks the way it does. The thinking that replaced MAST runs straight through whole blood in rural systems, prehospital TXA, and freeze-dried plasma: treat the actual problem, the lost blood and the failure to clot, instead of chasing a reassuring number on the monitor. The lesson MAST teaches isn't "the trousers were dumb." It's that EMS has to hold its standards of care loosely enough to put them down when the evidence turns, even when they feel right in your hands.

Sources

• PubMed — Mattox et al., Prospective MAST Study in 911 Patients, J Trauma 1989
• New England Journal of Medicine — Bickell et al., Immediate versus Delayed Fluid Resuscitation (1994)
• LITFL — Military Anti-Shock Trousers (MAST)
• NCBI StatPearls — MAST Pants
• PMC — Military anti-shock garment: Historical relic or device with unrealized potential?