Paramedics in the 1970s and
1980s often used Medical Anti-Shock Trousers (MAST), also called the
Pneumatic Anti-Shock Garment (PASG), for all forms of trauma. It was
the standard of care. On many occasions, I came to believe that I had
seen patients pulled from the jaws of death after MAST application. In
EMS circles, we told stories about doctors or nurses removing or
cutting off MAST in the emergency department, only to have the patient
become immediately hypotensive and die. EMS people were not the only
true believers in MAST. They were often a common component of trauma
resuscitation rooms and operating rooms. Invariably, we would have to
retrieve the MAST from the OR, as they remained on the patient until
the surgical lesion was repaired. We knew the MAST worked. We had seen
it work. But, did the MAST really work?
The concept of the MAST was first
described in 1903 by famed surgeon George W. Crile as a "pneumatic
rubber suit" to decrease postural hypotension in neurosurgical patients.1,2
During World War II, Crile's suit was used to prevent blackout in
pilots who were subjected to high G forces while flying combat
aircraft. The National Aeronautics and Space Administration (NASA)
claimed responsibility for developing the medical anti-shock trousers
at their Ames Research Center in the 1960s.3 MAST were introduced into medical practice during the war in Vietnam and called "Military Anti-Shock Trousers."4
The value of MAST in the military setting was documented when soldiers
with massive trauma, previously considered fatal, were able to survive
a 45-minute helicopter ride to a definitive care hospital.5 MAST were introduced into civilian EMS in the 1970s.6
It was postulated that the MAST
reversed hypotension by three different mechanisms: 1) Increasing
peripheral vascular resistance; 2) tamponading of intra-abdominal
bleeding; and 3) autotransfusion of blood from the lower extremities
and abdomen to the head and upper trunk.
Most authorities supported the
theory that MAST provided a significant autotransfusion. McSwain
estimated the amount of blood autotransfused to be 750–1,000 mL.7
In another paper, McSwain estimated that approximately 20% of a
patient's blood volume was autotransfused into the heart, brain and
lungs following application of MAST.8 Dillman also estimated
the amount of blood autotransfused to be approximately 20% of the total
blood volume (approximately 1,200 mL in an 85-kg man).9
Based upon these reports, the EMS textbooks of the era picked up the
information on MAST, and it was incorporated into day-to-day EMS
teaching. The first paramedic textbook stated: "The pressure applied to
the legs squeezes at least 2 units of blood out of these extremities,
where it is less critically needed, and into the systemic circulation.
The net effect is as if the patient were given a 2-unit transfusion of
blood; in a sense, then, it is an AUTOTRANSFUSION, since the patient is
transfusing himself with blood from his extremities. (Remember, though,
that the converse is also true. When the MAST is deflated, blood
returns to the legs, and it is as if the patient suddenly lost 2 units
of blood. Thus, the MAST is never deflated until adequate volume
replacement has been achieved.)"10 The first edition of
Basic Trauma Life Support stated the following: "No one has proven how
MAS trousers work, but the most likely mechanism is an increase in
peripheral vascular resistance by way of circumferential compression.
The important thing is that they do work to improve blood pressure and
cerebral circulation in the hemorrhagic or spinal shock victim."11
Likewise, the first edition of Pre-Hospital Trauma Life Support stated,
"If the patient is hypotensive or there is suspicion of bleeding within
the abdomen, the pneumatic anti-shock garment (PASG) should then be
placed on the patient and inflated until an adequate blood pressure is
obtained. The early use of the PASG will assist in reducing rapid
Applying the Scientific Method
Later, researchers applied the
scientific method to study the effects and effectiveness of the MAST
and found that the actual benefits were far less than originally
thought. Researchers at Valley Medical Center in Fresno, CA, evaluated
the effects of the MAST on healthy volunteers. After removing one liter
of blood from the volunteers, the MAST were applied. The amount of
blood auto-transfused from the lower extremities and abdomen to the
head and upper trunk was measured using sequential radioisotope scans.
They found that application of the MAST resulted in an auto-transfusion
of less than 5% of the patient's total blood volume. This was
approximately 300 mL in an 85 kg man.13
This amount was much less than initial estimates that ranged from
750–1,200 mL. A similar study measured the amount of blood
auto-transfused following MAST application to dogs who were suffering
hemorrhagic shock following phlebotomy. Again, the amount of blood
auto-transfused was approximately 5% of the total blood volume.14
Based on these studies, statements about the auto-transfusion
capabilities of the MAST were dropped. Instead, teaching was changed
and stated only that MAST increased peripheral vascular resistance.
Researchers then began to look at
patient outcomes following application of the MAST. The initial study
that questioned the benefit of the MAST was conducted in Houston, TX,
in 1989 using the Houston Fire Department EMS system. During a 2½-year
period, 201 consecutive patients presenting with penetrating anterior
abdominal injuries and an initial prehospital systolic blood pressure
of 90 mm Hg or less were entered into the study. All prehospital care
was provided by the Houston Fire Department and all patients were
delivered to the same regional trauma facility (Ben Taub Hospital). The
patients were randomized into control and MAST groups by an
alternate-day assignment of MAST use. The resulting study groups were
found to be well matched for survival probability indices, prehospital
response and transport times, and the volume of IV fluids received. The
results demonstrated no significant difference in the survival rates of
the control and MAST treatment groups. Based on these data, researchers
concluded that, contrary to previous claims, the MAST provides no
significant advantage in improving survival in urban prehospital
management of penetrating abdominal injuries.15
Another prospective, randomized
study investigated 291 traumatic shock patients greater than 15 years
of age with blunt or penetrating trauma and a systolic blood pressure
of 90 mm Hg or less with clinical signs of hypotension. The patients
were randomly assigned to a MAST or non-MAST group. The researchers
found that there were no significant differences in hospital stay or
mortality between MAST and non-MAST patients. Similarly, in the subset
of patients with blunt trauma, MAST were not found to be beneficial.16
In a prestigious Cochrane Review, researchers performed a meta-analysis
of the two studies described above and found that the duration of
Intensive Care Unit (ICU) stay was 1.7 days longer in the MAST-treated
group. They concluded that there was no evidence to suggest that
MAST/PASG reduce mortality, length of hospitalization or length of ICU
stay in trauma patients. In fact, they found, MAST may actually
increase these. They concluded that the data do not support the
continued use of MAST/PASG in trauma patients.17
Based on available data, in 1997
the National Association of EMS Physicians issued a position paper on
use of MAST/PASG in modern EMS.18
The association concluded that MAST are definitely beneficial in
ruptured abdominal aortic aneurysm and possibly beneficial in
hypotension due to pelvic fracture, anaphylactic shock refractory to
standard therapy, otherwise uncontrollable lower extremity hemorrhage
and severe traumatic hypotension (palpable pulse, no blood pressure).19
Even considering these possibilities, any benefit from application of
the MAST may be accomplished through rapid transport to a trauma
center. Many EMS services have kept MAST for use in possible pelvic and
lower extremity fractures. Patients with femur fractures are best
treated with traction splints, while patients with pelvic fractures can
be treated with a long backboard or similar device. Furthermore, the
MAST are expensive (approximately $500 per pair) and take up valuable
storage space on the ambulance. MAST are a relic of our past and belong
in EMS museums, not on modern ambulances or rescue vehicles.
1. Crile GW. Blood Pressure in Surgery: An Experimental and Clinical Research. Philadelphia, PA: JB Lippincott Company, 1903.
2. Crile GW. The Cartwright Prize Essay for 1903. Philadelphia, PA: JB Lippincott Company, 1903.
3. National Aeronautics and Space Administration. 1996 Space Technology Hall of Fame. Innovation 4(2), 1996.
4. Schwab CW, Gore D. MAST: medical antishock trousers. Surgery Annual 15:41–59, 1983.
5. Cutlet BS, Daggett WM. Application of the "G-Suit" to the control of
hemorrhage in massive trauma. Ann Surg 173:511–514, 1972.
6. Kaplan BC, Civetti JM, Nagel EL, et al. The military anti-shock
trouser in civilian prehospital care. J Trauma 13(10):843–848, 1973.
7. McSwain NE. Pneumatic trousers in the management of shock. J Trauma 17(9):719–724, 1977.
8. McSwain NE. MAST pneumatic trousers: A mechanical device to support
blood pressure. Medical Instrumentation 11(6):334–336, Nov–Dec 1977.
9. Dillman PA. The biophysical response to shock trousers. J Emerg Nurs 3(6):21–25, 1977.
10. Caroline NL. Emergency Care in the Streets. Boston, MA: Little, Brown and Company, 1979, p. 86.
11. Campbell JE. Basic Trauma Life Support: Advanced Prehospital Care. Bowie, MD: Brady Communications Company, 1985, p. 54.
12. Butman AE, Paturas JL, McSwain NE, Dineen JP. Pre-Hospital Trauma Life Support. Akron, OH: Emergency Training, 1986, p. 98.
13. Bivins HG, Knopp R, Tiernan C, et al. Blood volume displacement
with inflation of antishock trousers. Ann Emerg Med 11(8):409–412, 1982.
14. Lee HR, Blank WF, Massion WH, et al. Venous return in hemorrhagic
shock after application of military anti-shock trousers. Am J Emerg Med
15. Bickell WH, Pepe PE, Bailey ML, et al. Randomized trial of
pneumatic antishock garments in the prehospital management of
penetrating abdominal injuries. Ann Emerg Med 16(6):653–658, 1987.
16. Chang FC, Harrison PB, Beech RR, Helmar SD. PASG: Does it help in
the management of traumatic shock? J Trauma 39(3):453–456, 1995.
17. Dickinson K, Roberts I. Medical anti-shock trousers (pneumatic
anti-shock garments) for circulatory support in patients with trauma.
Cochrane Review, The Cochrane Library, 2002, p. 4.
18. O'Connor RE, Domeier R. Use of the Pneumatic AntiShock Garment
(PASG): NAEMSP Position Paper Prehosp Emerg Care 1(1):32–35, 1997.
19. Chapleau W. PASG: Bad wrap or bad rap? Emerg Med Serv 31(1):75–76, 2002.
Bryan Bledsoe, DO, FACEP, EMT-P, is an emergency physician,
author and former paramedic whose writings include: Paramedic Care:
Principles and Practice and Paramedic Emergency Care.