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The curious case of the MAST trousers


Paul E. Pepe MD discussing the Medical Anti-Shock Trousers, once thought to save lives

Paul E. Pepe came to the our department today to discuss his long history of clinical research in emergency medicine, pre-hospital medicine, and critical care. Dr. Pepe was one of the authors of the influential 1994 Bickell paper in the New England Journal. That paper, which was published when I just started medical school showed that giving intravenous fluids to patients with penetrating injuries caused more deaths. I remember the debate about this study in the years after it was published. Even though it showed convincingly that pumping these trauma victims full of saline made them die more often, most MDs and medics had a different take away. They thought the paper supported the “scoop and run” idea, e.g. fast transport with little on-scene time, instead of “stay and play”, performing interventions in the field. And so, by and large, we continued to give IV fluids to trauma victims.

Since then, evidence has reinforced Pepe’s message, and fluids have been shown to be harmful not only in penetrating trauma, but also in blunt trauma, acute surgical emergencies involving bleeding, and possibly some medical causes of bleeding, like gastrointestinal bleeding.

Gradually, the idea that IV fluids, particularly crystalloids, are harmful in uncontrolled bleeding has gathered evidence and our practice has slowly changed. We worry now that IV fluid dilutes clotting factors, and can dislodge soft clots, and disrupt the glycocalyx – the protein sugar coating inside blood vessels that has various important functions. The dilution of clotting factors is a dominant theme, at least in my department, and so the focus has changed from IV crystalloid in patients with bleeding to blood products, such as fresh frozen plasma. At least we can all agree that IV crystalloid is bad for patients with bleeding – a message that Dr. Pepe reinforced during his talk today.

But I promised we’d discuss trousers here. I remember seeing MAST trousers when I started training (MAST stands for Medical Military Anti-shock Trousers, which makes the term a bit redundant, like when my mom says I work in the ER room). MAST were like an enormous blood pressure cuff that covered the entire lower body. However, by the time I was in residency, MAST were on the way out, have failed to live up to their promising name. In fact, MAST had been shown to have a measurable clinical effect – they raised blood pressure. They accomplished this by moving the blood volume in the lower extremities into the central body. This was how they were supposed to prevent bleeding to death and to save lives of trauma victims. Bickell and Pepe showed in the 1980s that MAST were ineffective at saving lives in hypotensive patients with penetrating abdominal injuries. So even when they made hypotensive patients less hypotensive, MAST did not have the desired effect on mortality. As Dr. Pepe discussed, trauma surgeons at his hospital were convinced that MAST were “the instrument of the devil” because they were anecdotally associated with bad outcomes. Pepe and his colleagues showed that despite increasing blood pressures, they were useless in saving lives.

There are a couple of important lessons here, actually three. First, it can take a long time for disproven therapies to be ushered out to the dustheap of failed interventions. I saw MAST being used in the 1990s. Second, when doing studies, choosing the right outcome variable is key. Blood pressure might be thought as a surrogate endpoint for improvement in these bleeding patients. In fact, raising the blood pressure, either with fluids, or with MAST, does no good, and can harm bleeding patients. The primary end-point should be mortality, since that is what patients and their families care about, not a meaningless increase in blood pressure. Finally, the failure of MAST puts the lie to the idea that low blood pressure itself is harmful in hemorrhagic shock. Fixing blood pressure, whether by fluids, or MAST, or with pressors, does not help the patient.

This brings me to the idea that low blood pressure itself might be helpful in bleeding states. I contend that there is no evidence that normalizing blood pressures helps patients in this context. Pepe today said that the benefit of giving fluid – he recommends giving whole blood – is to prevent patients with long transport times from dying before getting to the operating room. I agree that blood transfusion is useful in that setting, but that requires careful patient selection. The bigger picture is that most patients are not going to die in transport and we may be doing them a disservice by increasing blood pressure by any means.

The curious case of the MAST trousers, once thought to be an essential tool for paramedics and in the military, and now nearly forgotten, reminds us that we can misunderstand the physiology of trauma and critical illness. Normalizing blood pressure can do more harm than good.

Postscript: read Levi 2005: Vasovagal fainting as an evolutionary remnant of the fight against hemorrhage. Full text here

Pepe Lecture

Listening to Dr. Pepe describe EMS whole blood transfusion in the field

Categories: Uncategorized

Joe Alcock

Emergency Physician, Educator, Researcher, interested in the microbiome, evolution, and medicine

1 reply

  1. Interesting article. Imho, a few misconceptions.. first, it was first called military, not medical as some civilians call mast. It was my understanding and training mast was developed in viet nam and the premise was not to elevate bp, but to prevent the pressure from going too low. Mast also was an air splint substitute and quasi tourniquet for the lower part of the body. We had more problems with untrained er personnel (drs included) who would walk into the room and promptly cut them off the patient (1500$ at the time) causing the patient to crash.
    What you describe in your article came after i left the field.
    Considering the methods you describe is the cause of the problems. I saw a program recently were a variation of mast is being used to treat patients with edema problems caused by unrelated issues including heart failure.

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