MAST Suit Research Articles

Prevention of Vascular Air Embolism

incidence in the control group. 4 We found that this method could be reliable and effective to prevent clinically significant VAE without deleterious side effects. Since that time, we have routinely used this method of prevention in 30‐40 procedures performed in sitting children each year. In our experience, MAST suit inflation and PEEP induce a reliable and sustained increase in right atrial pressure, sufficient to increase jugular bulb venous pressure above atmospheric level in children, and to prevent clinically significant VAE. We do agree with Minski et al. that PEEP alone cannot be recommended as a routine prevention method, because hemodynamic disturbances related to its use balance negatively its potentially beneficial effect on intrathoracic and right atrial pressures, especially in seated anesthetized patients. Preventive low levels of PEEP are so only used to amplify the increase in right atrial pressure, and to restore adequate ventilation in lower lung compartments that could be compressed with MAST suit inflation. Considering the potential hazards of this method, with “venous” pressure inflation, namely 40 mmHg in the abdominal compartment and 30 mmHg in the lower limbs compartment, we never observed the described potential risks of hypoperfusion to intraabdominal organs, and compartment syndromes. In our experience, urine output, which could be very sensitive to hypoperfusion of the kidneys during abdominal compression, never decrease under 1 ml · kg 1 ·h 1 . Moreover, we demonstrated that plasma creatine phosphate kinase level, which could reliably reflect muscular hypoperfusion and ischemia during MAST inflation, was not significantly increased in children with prolonged MAST inflation. When comparing the incidence of VAE occurrence during procedures performed in the prone or sitting position with PEEP and MAST suit inflation in children, we did notfind a significant difference, with only one episode of VAE related to a major surgical vascular effraction during dural closure occurring in a sitting patient. 5 This could be an additional argument to maintain the use of the sitting position in selected patients, provided that detection and prevention of VAE could be as efficiently secured in both situations. We therefore recommend consideration of the use of a MAST suit and moderate PEEP levels in children when surgical conditions require positioning of the patient in the sitting position.

A review of emergency equipment carried and procedures performed by UK front line paramedics

Objectives: To assess which items of resuscitation equipment are carried on United Kingdom (UK) front line ambulances and what procedures paramedics are able to perform. To compare these findings with those of a previous survey in 1997. Method: Postal survey to the chief executives of all the UK ambulance services and direct comparison with the data from 1997. Results: Nasopharyngeal airway usage (NPA) has increased (21–55%) and the laryngeal mask airway (LMA) (from 10 to 26%). No services employ the Combitube. 94% of services use a Hudson type trauma mask (increase of 17%). One service no longer allows its paramedics to deliver 12–15 l of oxygen. 68% of trust paramedics can perform needle thoracocentesis (increase of 35%). No paramedics perform chest drain insertion. All services have 14G intravenous cannulae available and 45% carry the intraosseous needle (increase of 30%). No services employ the MAST suit. There is an increase by 29% in the use of crystalloids and a decrease in the use of colloids of 22%. 23% of fluid resuscitation protocols are based upon the principles of hypotensive resuscitation. Spinal boards and extrication devices are used by 97% of services. The use of inflatable splints has decreased (38–23%). There has been a minor increase in the use of traction splints to 74% of services. The use of Entonox is universal. Nalbuphine (Nubain) is the most widely used opiod. The use of morphine/diamorphine has doubled to 10% with a further 26% to introduce their use. 29% of services have equipped some vehicles with automatic external defibrillators. Conclusions: The equipment available to UK paramedics and procedures that they may perform continues to expand. There are still variations in the basic management of airway, breathing and circulation care and only some services are keeping up to date with current medical thinking, for example the increasing use of crystalloids and hypotensive resuscitation. It remains to be seen whether the widespread use of Nalbuphine as a first line analgesic may decrease as the use of natural strong opiates becomes more widespread.

Sudden deterioration in an elderly trauma patient

Dr. Ron Walls: Today’s case is that of a 75-yr-old woman who presented to the emergency department (ED) by helicopter after a rollover motor vehicle crash. She was an unrestrained front seat passenger and was ejected, landing approximately 20 feet from the vehicle. Upon arrival at the scene, the patient was found awake and alert, following commands. It was unclear whether the patient had suffered loss of consciousness. The initial vital signs in the field were: blood pressure (BP) 90 by palpation, pulse 110 beats/min, and respirations 20 breaths/min. The patient’s neck was immobilized in a cervical collar and a peripheral intravenous (IV) line was inserted. As she was being loaded onto the helicopter, her level of responsiveness deteriorated, and her systolic BP decreased to 80 mmHg. She was intubated by using rapid sequence intubation with lidocaine, fentanyl, and succinylcholine. A second intravenous line was placed, and she was transported to our hospital. Her husband, the unrestrained driver, had remained in the car and was taken to a local hospital with minor injuries. Are there any questions about prehospital management? Dr. Adler: There does not appear to be evidence that a MAST suit controls hemorrhage, but it may stabilize an unstable pelvic fracture by limiting soft tissue and vascular damage and by reducing the degree of hemorrhage.

Mast 96

The Military Anti-Shock Trouser, or MAST suit, is a controversial device that has been used to support blood pressure in hypotensive trauma patients. Most studies on humans have shown that the device has limited clinical utility. In this study, a telephone survey of all 50 State Emergency Medical Services was conducted to determine the nature and extent of MAST suit usage in the United States. The trend in MAST suit usage in San Diego County over the last 7 years was also analyzed. Thirty (60%) states still require MAST suits to be carried on ambulances. In San Diego County, MAST suit inflations for adult, hypotensive (systolic blood pressure <90 mmHg,) blunt trauma patients has declined from 37% in 1987, to 2% in 1993. Despite a lack of data supporting efficacy in areas of severe hypotensive shock, blunt trauma, long transport times, and pelvic fractures, states continue to expend resources on the MAST suit. It is for this reason that we believe that the clinical use of the MAST suit should be based upon medical control philosophy rather than legislation.

Prevention of venous air embolism in paediatric neurosurgical procedures performed in the sitting position by combined use of MAST suit and PEEP

We studied 60 children undergoing neurosurgical procedures in the sitting position. Routine monitoring included ECG, pulse oximetry, invasive arterial pressure, in particular mean arterial pressure (MAP), and right atrial pressure (RAP). Children were allocated to two groups. In group B lower body positive pressure and positive end-expiratory pressure (PEEP) were used for preventing venous air embolism (VAE). In this group, antishock trousers (MAST suit) were adjusted in supine children. After induction of anaesthesia, different positions were studied: supine and sitting before MAST suit inflation, sitting with MAST suit inflated up to a pressure of 40 mmHg in the lower compartments and 30 mmHg in the abdominal compartment, and finally a combination of lower body positive pressure and PEEP of 8-10 cm H2O. In group A no MAST suit or PEEP was used. Continuous monitoring of end-tidal carbon dioxide pressure throughout (PE'CO2) was used to detect VAE. In order to evaluate the transmission of pressures from the right atrium to the veins at the base of the skull, jugular bulb venous pressure (JBVP) was measured in 20 patients by retrograde catheterization. The incidence of VAE was compared in the two groups. On placing children into the sitting position, a significant decrease in RAP and JBVP was noted without significant changes in MAP in the two groups. Inflation of the MAST suit induced a dramatic increase in RAP and JBVP, reinforced by addition of PEEP. There was a strong positive relationship between RAP and JBVP. There were no deleterious side effects or differences between the two groups in peroperative blood product requirements or surgical general conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

The season of goodwill

I feel that the survival of this patient was due to a number of factors: 1. 1. The scoop and run policy was the most appropriate in this case. 2. 2. The cooperation between the ambulance crews and the hospital staff allowed the patient to receive prompt efficient care. The paramedics were able to supplement the trauma team using their skills when appropriate. 3. 3. The journey time to hospital was short. 4. 4. The MAST suit and the Cardiopump were an excellent combination which provided both the instant infusion associated with the suit and the improved cardiac output of the Cardiopump.

Thoracocardiography: Part 2: Noninvasive Measurement of Changes in Stroke Volume; Comparisons to Impedance Cardiograph

The thoracocardiograph (TCG) displays cardiac oscillations transmitted to the external surface of the thorax through inductive plethysmographic transducers placed transversely around the thorax near or about the xiphoid process. Such signals, with the appearance of ventricular volume curves, were used to compute changes of stroke volume (SV) and cardiac output (CO) in normal subjects. Their values were compared with changes of SV and CO measured with the impedance cardiograph (IC). Increases of SV and CO were produced with subcutaneous terbutaline and there was excellent agreement between TCG and IC values, best from TCG transducers placed at the xiphoid process and 3 cm caudal to it, although TCG locations 6 cm caudad and 3 cm cephalad to the xiphoid were also satisfactory. Since the site 3 cm caudad to the xiphoid process is known to anatomically transect solely a segment of the left ventricle, it was designated the TCG-Reference location. Both TCG and IC derived SV were not altered during postural shifts about a horizontal axis. Neither TCG nor IC showed the expected large decreases of SV from supine posture to head-up tilt. With baseline TCG and IC measurements in 60 degrees head-up tilt. MAST suit application increased CO measured with TCG but not with IC. Neither TCG nor IC revealed alteration of CO with nasal CPAP up to 10 cm H2O despite a rise in functional residual capacity (FRC) level of 870 ml. This investigation indicates that TCG has promise as a near continuous, noninvasive monitor of SV and CO in normal subjects if postural axis is fixed and does not require highly trained personnel or labor-intensiveness for its operation.

Use of the MAST suit in the postoperative care of patients after the Fontan procedure

Use of the MAST suit in the postoperative care of patients after the Fontan procedure

Interventions in the therapy of electromechanical dissociation

Electromechanical dissociation (EMD) is a major arrest rhythm for which there is often inadequate treatment. The purpose of this study was to evaluate the different pharmacological and non-pharmacological interventions considered in the treatment of EMD. During the 6-year period, January 1st, 1980 to December 31st, 1985, 503 evaluable adult patients presented in a non-traumatic, non-poisoning cardiopulmonary arrest with the initial rhythm of EMD. One hundred nineteen patients obtained a pulse during resuscitation efforts following drug administration. The average time to obtaining pulses after the last drug administration was 1.97 +/- 2.21 min. The following drugs were last administered prior to transient pulses: bicarbonate, 31/119 (26%); epinephrine, 26/119 (22%); atropine, 26/119 (22%); dopamine, 13/119 (11%); calcium, 11/119 (9%); isoproterenol, 7/119 (6%); other drugs, 5/119 (4%). Ninety-five percent of the successful resuscitations received eight or less drug interventions and all saves received three or less drug interventions. Two hundred twenty-four patients (44.5%) had 288 non-pharmacological interventions. Twenty-three patients developed a pulse after intervention in the following distribution: MAST suit (N = 9), pericardiocentesis (N = 6), fluid challenge (N = 5), needle thoracostomy (N = 1), and intervention combinations (N = 2). The time interval between intervention and the onset of pulse was as follows: MAST suit, 4 +/- 2.8 min; pericardiocentesis, 3.7 +/- 3.6 min; fluid challenge, 4.8 +/- 4.1 min; needle thoracostomy, 6 min. The overall save rate for intervention patients was 0.9% whereas for those not having intervention it was 7.2% (P less than or equal to 0.0003).(ABSTRACT TRUNCATED AT 250 WORDS)

MAST Suits-Reply

In Reply.— We acknowledge the studies of Harman et al and Kron et al 1,2 indicating that elevation of intra-abdominal pressure impairs renal function. Inflation of the abdominal portion of the MAST suit is likely to increase intra-abdominal pressure, but this does not necessarily create the same situation as that experienced by the patients of Kron et al, 2 in whom increased intra-abdominal pressure resulted from postoperative complications, such as bleeding. Animal studies of renal compromise from MAST inflation have yielded variable results. Several human studies have suggested that any renal compromise is not clinically significant. Begin et al 3 reported no cases of renal failure in 47 patients with MAST use. Wayne and MacDonald 4 found a renal failure rate in hypotensive patients treated with MAST of 1%, a rate comparable with that of other studies where MAST was not employed. Despite the infrequency of renal failure with MAST

MAST Suit Update

In recent years, the use of the MAST suit has become commonplace. While no controlled human studies have shown the device's efficacy, extensive clinical experience suggests that it is practical and useful in combating shock, stabilizing fractures, and promoting hemostasis. Studies indicate that the antishock trousers elevate blood pressure primarily by increasing peripheral vascular resistance. Proper application and removal of the device are crucial. A number of potential complications exist, but are infrequent and rarely should preclude MAST suit use. Further studies are necessary to prove the efficacy of the device and clearly define its role in patient management.

Bee-sting anaphylaxis: The use of medical antishock trousers

There is a large population of unprotected individuals who are susceptible to Hymenoptera-induced anaphylaxis. Medical antishock trousers (the MAST suit) can play an important role in field treatment of anaphylactic shock. Upon application, both blood pressure and cerebral perfusion are preserved despite clinically profound vasodilation. The MAST suit mechanically increases peripheral resistance, analogous to the vasoconstrictive effects of adrenaline. In the two cases presented, the MAST suit reversed significant hypotension caused by Hymenoptera envenomation. Both patients recovered fully. Based on the suit's effectiveness in bee-sting anaphylaxis, it would seem that extended indications exist for using the MAST suit in other forms of low-resistance shock.

Alterations in mast suit pressure with changes in ambient temperature

A study was undertaken to test the hypothesis that change in ambient air temperature has an effect on MAST suit pressure according to the ideal gas law. Two different MAST suits were tested on Resusci-Annie dummies. The MAST suits were applied in a cold room at 4.4°C and warmed to 44°C. Positive linear correlations were found in nine trials, but the two suits differed in their rate of increase in pressure. Three trials using humans were conducted showing increased pressure with temperature but at a lesser rate than with dummies. A correlation of 0.5 to 1.0 mm Hg increase in MAST suit pressure for each 1.0°C increase in ambient temperature was found. Implications are discussed for the use of the MAST suit in environmental conditions where the temperature changes.

ICP changes following application of the MAST suit.

The MAST suit is used primarily in the field to raise arterial pressure in patients with hemorrhagic shock. By 'squeezing' blood back to the heart and compressing arteries, the suit acts to transfuse the patient as well as to compress bleeding sites. Because of the sudden increase in venous return with abdominal compression, its use has been questioned after closed head injury, cardiac tamponade, and/or tension pneumothorax. A study was devised to evaluate the MAST suit in dogs following hemorrhage and hemorrhage with the creation of a tension pneumothorax, cardiac tamponade, and mass intracranial lesion. Pulmonary artery, central venous, systemic arterial, and intracranial pressures were monitored in control dogs before and after hemorrhage and application of the MAST suit. Following hemorrhage, the inflated MAST suit raised systolic arterial pressure as well as central venous, pulmonary artery, and intracranial pressures. The rise in intracranial pressure mirrored the rise in venous pressure and never reached potentially harmful levels in the hemorrhaged animals and animals with a mass intracranial lesion. In the animals with cardiac tamponade and tension pneumothorax, inflation of the abdominal portion of the MAST suit produced a marked rise in central venous and intracranial pressures. This was altered by either relieving the lesion or reducing the pressure of the abdominal portion of the MAST suit.

External counterpressure and the MAST suit: Current and future roles

External counterpressure devices, such as the MAST suit, may be lifesaving not only in acute hypovolemia secondary to abdominal, pelvic and lower extremity trauma, but in a number of other shock states as well. Expanded use of the MAST suit may well include not only supra-diaphragmatic injuries, but diverrse entities such as pericardial tamponade, tension pneumothorax, and leaking aortic aneurysm, and as an adjunct to cardiopulmonary resuscitation. The limited adverse effects of the MAST suit, in conjunction with its rapidly favorable and rapidly reversible hemodynamic effect, make it an important tool not only in prehospital care and in the emergency department, but in a wide variety of hospital circumstances. For this reason emergency physicians must not only be aware of uses of the MAST suit themselves, but should be prepared to disseminate this information to the general medical community.

Traumatic injuries of the abdominal aorta

Despite immediate operation, patients with abdominal aortic injuries and profound hypovolemic shock do not respond to the usual methods of resuscitation and die soon after celiotomy, prior to control and repair of the aortic injury. The rate of aortic hemorrhage exceeds the ability to restore blood volume. Shock becomes “irreversible.” In such patients tamponade of the aortic injury may be effected by the use of an external counterpressure device such as a G-suit or MAST suit. These devices, used in conjunction with transthoracic aortic occlusion, may raise blood pressure sufficiently to perfuse the critical coronary and cerebral circulation, allowing time to correct acidosis and locate, control, and repair the aortic injury. Early aggressive therapy should result in increased survival.