Introduction
Medical anti-shock trousers (MAST), military anti-shock trousers, or pneumatic anti-shock garments (PASG) are medical devices made of synthetic inflatable air bladders applied to a patient’s abdomen, pelvis, and lower extremities.[1] These devices include 1 abdominal compartment and 2 leg compartments, which attach to a pump or inflation unit with valves to control the pressure within each air bladder. The underlying physiologic concept of these devices is simple: apply pressure to the lower extremities to auto-transfuse or shift the patient’s blood volume from the abdomen, pelvis, and lower extremities to the upper body and central circulation. It was also thought these devices increased overall peripheral vascular resistance, halted intraabdominal and lower extremity bleeding, and splinted lower extremity fractures.
Medical anti-shock trousers were first described in 1903 by surgeon G.W. Crile as he tried to augment blood pressure with a "pneumatic rubber suit" during neurosurgical procedures. Decades later, the term military anti-shock trouser was coined during the Vietnam War, when medics applied the device in the field before airlifting soldiers out of a combat zone to a hospital for definitive care.[2][3] Upon the conclusion of the Vietnam War in 1975, military surgeons and combat medics returned to the United States. They advocated for using these devices in pre-hospital and critical care settings. In 1977, the Committee on Trauma for the American College of Surgeons listed MAST as an essential device in all ambulances. Throughout the United States in the late 1970s and 1980s, MAST devices were the standard of care for hypotensive trauma patients, as evidenced by the American College of Surgeons’ Advanced Trauma Life Support guidelines.[4][5] These devices were utilized heavily through the 1980s, and as late as 1996, 30 states required MAST devices on all ambulances.[6] These devices were applied in various settings, including aviation, combat, pre-hospital, and critical care settings.
Despite a period of widespread use, MAST devices have been the subject of much debate and research and are currently rarely used. Initial studies in the 1970s suggested that as much as 20% of a patient's total blood volume was auto-transfused to the upper body by application of the MAST device.[7][8] However, further studies performed in the 1980s refuted these early findings, suggesting that only 5% or less of a patient’s overall blood volume was auto-transfused by these devices in both human and dog models.[9][10] During this period, some studies showed harmful complications of device use, which included compartment syndrome and lower extremity ischemia, amongst others.[11] In 1989, the Houston Fire Department partnered with Ben Taub Hospital to investigate the use of MAST devices in the prehospital environment. This study, which enrolled 201 patients randomized either to MAST application or standard care, did not demonstrate an improvement in mortality rates in penetrating abdominal trauma.[12] Further studies corroborated these findings and could not show a significant difference in the length of hospitalization or intensive care unit stay.[13] Amidst this controversy, the National Association of Emergency Medical Services Physicians published a 1997 position paper citing support for MAST in certain cases, including ruptured abdominal aortic aneurysm, pelvic fracture with subsequent hypotension, and severe traumatic hypotension.[14] Of these recommendations, the only high-level evidence, considered Class I, existed for a ruptured abdominal aortic aneurysm.[15] In 2002, a Cochran review demonstrated an increase in intensive care unit length of stay by 1.7 days. It concluded there was no evidence to suggest a reduction in mortality from using MAST.[5] Given these findings, many hospital systems and EMS agencies gradually abandoned using these devices. An article published in the United Kingdom in 1995 suggested that only 1 out of every 5 UK hospitals and 1 out of every 12 UK EMS systems continued to use these devices.[16]
Anatomy and Physiology
The MAST device is applied approximately 1 inch inferior to the costal margin and covers the abdomen, pelvis, and lower extremities.
Indications
Currently, there are no widely accepted indications for using these devices. Specifically, the American College of Surgeons’ Advanced Trauma Life Support and American College of Emergency Physicians’ guidelines do not recommend using them.
Traditional Indications
- Hypotension associated with suspected pelvic or femur fractures
- Ruptured abdominal aortic aneurysm
- Stabilization of pelvic and femur fractures
Contraindications
Contraindications include:
- Congestive heart failure (CHF)
- Myocardial infarction
- Stroke
- Pregnancy
- Thoracic hemorrhage
- Diaphragmatic injury
- Head injuries
- Abdominal injury with evisceration
- Uncontrolled bleeding above the level of the garment
- Impaled object to the abdomen or lower extremity
Equipment
A list of equipment includes:
- Medical anti-shock trousers
- Pump or inflation device
- Sphygmomanometer
- Stethoscope
Personnel
Only medical professionals who have received appropriate training should deploy the MAST device. These professionals include physicians, nurses, and emergency medical personnel. Only 1 trained person is required to apply the MAST device.
Preparation
Place the MAST device on a stretcher or long backboard before transferring the patient. Transfer the patient to the stretcher or backboard and perform a physical examination to identify contraindications for MAST application or injuries the device covers once inflated. Apply and inflate the MAST device if no contraindications exist.
Technique or Treatment
Steps to treat MAST pants include:
- Evaluate the need for MAST by assessing injuries and obtaining vital signs.
- Unfold MAST and lay it flat on a backboard or stretcher before moving the patient.
- Perform a secondary survey to identify injuries that the device covers, dressing wounds as necessary. Remove all clothing and foreign objects as the device presses them into the patient’s skin.
- While maintaining spine immobility, place the patient on the MAST device so that the top of the garment is approximately 1 inch inferior to the costal margin.
- Secure and fasten the leg sections. Ensure all creases are removed.
- Secure and fasten the abdominal section (unless contraindicated). Ensure all creases are removed and that the garment has not changed position relative to the patient’s chest wall.
- Attach the pump and check all valves for closure.
- Inflate leg compartments.
- Re-assess the patient and obtain repeat vital signs.
- If the patient’s systolic blood pressure is between 100 to 110 mm Hg, ensure valves are closed and continue to monitor the patient’s blood pressure. Do not attempt to increase the systolic blood pressure beyond 110 mm Hg.
- If the patient’s systolic blood pressure is not 100 to 110 mm Hg, inflate the abdominal compartment (unless contraindicated).
- Continue monitoring the patient's systolic blood pressure, adding air to the device as needed to maintain a systolic blood pressure between 100 to 110 mm Hg.
- Remove MAST only when the patient has been adequately resuscitated and under the direction of a physician in a controlled setting.
Complications
The complications that can manifest with MAST pants are as follows:
- Lower extremity ischemia
- Compartment syndrome
- Respiratory failure
- Increased intracranial pressure
- Acute kidney injury
- Metabolic acidosis
Clinical Significance
MAST devices are still discussed in protocols and textbooks for several EMS agencies in the United States. However, most hospital systems and EMS agencies have abandoned the use of these devices due to the paucity of supporting evidence and the relatively high cost compared to other treatment modalities. There are no widely accepted indications for MAST use, and doing so falls outside the standard of medical care in most developed nations. As of the writing of this topic, there is insufficient evidence to support the continued use of these devices.
Enhancing Healthcare Team Outcomes
An evidence-based team approach involving clinicians in MAST use is recommended. Resuscitation of critically ill patients is a topic of constant scrutiny and frequent disagreement among leaders in the field, and many studies have been published on this topic each year. The MAST device is an example of 1 of the many practices that were once the standard of care but expired as medical knowledge advanced. It is the responsibility of medical professionals to advance the knowledge and tools available to provide the best medical care. As medical knowledge and technology advance, so should the standard of care medical professionals provide their patients.