Chapter 230: Pneumatic Antishock Garment (MAST Trousers)

INTRODUCTION

The pneumatic antishock garment (PASG) is a device aimed at treating hypovolemic shock in the prehospital setting. Its primary purpose has been in the transport of patients with hemorrhagic shock due to trauma. It has been used in cases of nontraumatic hemorrhage (i.e., ruptured ectopic pregnancy and ruptured aortic aneurysm). The PASG is more commonly known as the Military Antishock Trouser, Medical Antishock Trouser, or MAST (Figure 230-1). The PASG was first invented during the Vietnam War.^1,2 An earlier version called the “G-suit” dates to 1903 and served mainly to prevent postural hypotension and venous pooling in pilots.³

The evidence supporting PASG use is mixed. Initial reports described successes in increasing systemic blood pressure and controlling intra-abdominal hemorrhage in trauma patients with hypovolemic shock.^4,5 A large retrospective analysis of 1120 PASG-applied patients in 1983 revealed a 24-hour survival rate of 73%.⁶ Approximately 84% of survivors had an increase in systolic blood pressure, a decrease in heart rate, or evidence of enhanced tissue perfusion. Prospective studies have concluded that PASG provides no advantage to survival.^7,8 A Cochrane review concluded that there is no evidence to suggest that PASG reduces mortality or hospitalization.⁹ The Advanced Trauma Life Support (ATLS) course has previously supported its use “to control bleeding from pelvis or lower extremity fractures” but states that its use “should not interfere with rapid reestablishment of intravascular volume by intravenous fluid infusion.” It also cautions against prolonged application leading to compartment syndrome.¹⁰ PASG is not part of the current ATLS protocol.¹¹

Another garment called the Non-Pneumatic Antishock Garment (NASG) has been recommended by the World Health Organization (Figure 230-2). It acts as a temporizing measure for postpartum obstetrical hemorrhage in poorly resourced areas of the world.¹²

ANATOMY AND PATHOPHYSIOLOGY

The antishock garment works by several proposed mechanisms. The garment provides circumferential pressure on the abdomen and lower extremities. It can enhance venous return from the lower extremities and acts as an autotransfusion. The antishock garment produces a small autotransfusion effect. It can increase the total peripheral vascular resistance (PVR). The increased PVR provides the most blood pressure elevation. Its actions on the lower extremity vasculature lead to increased preload, afterload, stroke volume, and cardiac output.^13,14 The antishock garment shunts the blood to the brain, heart, and vital organs. One study proposes that the antishock garment’s ...