MAST and adrenergic-resistant anaphylaxis.
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This study was designed to determine the effect of military antishock trousers (MAST) use on the presenting emergency center trauma score (TS) in an urban prehospital setting. Sixty-eight patients were assigned randomly to study and control groups in a prospective investigation of the use of MAST on injured patients with hypotension. Thirty-two control patients, whose mean initial systolic BP was 59 +/- 32 mm Hg, and 36 MAST-treated patients, whose mean initial BP was 55 +/- 31 mm Hg, were found to be well matched for age; sex; type and location of injuries; initial field TS; response, field management, and transport times; and the total amount of intravenous crystalloid infused. Our results demonstrated no significant difference between the control and MAST-treated groups in the presenting emergency department TS (9.8 +/- 6.6 vs 10.6 +/- 5.9). These data conflict with the widely accepted belief that MAST will always enhance conventional support for improving the prehospital condition of injured patients with significant hypotension.
To determine if clinically accessible hemodynamic and blood gas measurements are of value in predicting outcome of countershock after prolonged ventricular fibrillation (VF) and artificial cardiopulmonary support, 14 dogs were studied during 30 minutes of VF using two randomly assigned closed-chest techniques. Seven dogs underwent conventional CPR; the other seven were supported with a pneumatic thoracic vest and abdominal binder, which were inflated synchronously with the airway. Ascending aortic (Ao), right atrial (RA), and instantaneous coronary perfusion pressures (Ao - RA) were measured at five-minute intervals. Ao and RA blood samples were analyzed at 10, 20, 25 and 30 minutes for PO2, PCO2, and pH. After 25 minutes, 1 mg epinephrine was given intravenously, and five minutes later defibrillation was attempted. If unsuccessful, repeated countershocks, conventional pharmacologic therapy, and artificial support were continued. If a perfusing spontaneous cardiac rhythm did not result within an additional 30 minutes, the experiment was terminated. Six animals developed a perfusing cardiac rhythm after one or more countershocks (Group 1); eight failed to develop a perfusing rhythm after repeated countershocks and an additional 30 minutes of resuscitative effort (Group 2). Five Group 1 dogs received vest/binder artificial support. When measured values were averaged over the study period, Group 1 was found to have a significantly greater Ao end-diastolic pressure (AoEDP) and peak diastolic coronary perfusion pressure (CPP) when compared to Group 2 (23 +/- 6 vs 14 +/- 8 mm Hg, P less than .05; and 22 +/- 6 vs 5 +/- 10 mm Hg, P less than .01, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)
Our study examined the efficacy of four treatment modalities in controlling hemorrhage and achieving hemodynamic stabilization in hemorrhagic shock: intravenous fluid replacement (IV); military antishock trousers used concomitantly with fluids (MAST); balloon occlusion at the level of the diaphragm with concomitant fluid replacement (balloon); and a combination of MAST inflation, balloon occlusion, and fluid resuscitation (MAST and balloon). Twenty-eight mongrel dogs were anesthetized, and the spleen was exposed and completely crushed. The abdomen was closed, and treatment was initiated and continued for four hours or until the dog died. For all conditions the hematocrit dropped during the course of the experiment; balloon occlusion was effective at slowing this drop (P less than .0001), but MAST had no statistically significant effect. Animals with balloons bled more slowly into the abdominal cavity than did animals in the other two groups (P less than .0001). MAST also were effective at slowing the bleeding (P less than .05). Of the balloon and the MAST and balloon dogs, all except one survived the entire four hours; this difference between balloon and nonballoon dogs is significant (P = .002). MAST did not have a statistically significant effect on survival. Perfusion pressure (PP) declined during the course of the experiment, and the balloon was effective at slowing this decline (P less than .0001); none of the other comparisons was statistically significant.
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Ten healthy male volunteers were studied to compare the effects of simultaneous versus sequential inflation of antishock trousers (AST) and simultaneous inflation pressures of 20, 40, and 100 mm Hg on blood volume displacement centrally. Radioisotope scans were used to determine the change in blood volume distribution with various inflation methods and inflation pressures of the AST. Our data suggest that the minimum inflation pressure that displaces blood centrally is 40 mm Hg, and that higher inflation pressures displace a greater percentage of the total blood volume to the central circulation than do lower pressures. The difference is small, however, and probably has no clinical effect. No difference was suggested between simultaneous and sequential inflation.
A comparison of several maneuvers that are believed to increase vagal tone was made by measuring the carotid sinus with an ultrasound device. For 20 healthy volunteers the mean carotid sinus diameter was 5.7 mm supine, 6.1 mm in the Trendelenberg position, 6.5 mm after supine medical antishock trousers (MAST) inflation, 7.0 mm after MAST inflation in the Trendelenberg position, and 7.3 mm during a headstand. Each mean value was significantly different (P less than .01) from each of the others. These results have important implications for the treatment of dysrhythmias such as paroxysmal supraventricular tachycardia.
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A 33-year-old man with a history of progressive weight loss, weakness, and darkened skin color collapsed in cardiorespiratory arrest. His down time, with CPR, was more than 60 minutes, with 20 minutes of documented asystole. He was resuscitated, with global neurological deficits that eventually cleared following aggressive rehabilitation therapy. The diagnosis of Addison's disease was suggested by clinical hyperpigmentation and a roentgenographic narrowed cardiac silhouette. Cardiac arrest is an unusual complication of adrenal insufficiency.
Cardiac output, pulse rate, blood pressure, and distal abdominal aortic blood flow were measured in ten healthy volunteers during sequential inflation of medical antishock trousers. Full inflation of all three compartments decreased distal aortic blood flow by three quarters (P less than .001) and increased blood pressure by 10% (P less than .001), but had no effect on cardiac output or pulse rate. Inflation to lower pressures was markedly less effective.
Irreversible hypotension with subsequent cardiovascular collapse has been reported as a catastrophic complication of inappropriate pneumatic antishock garment (PASG) deflation. This study was undertaken to analyze the cardiodynamic response by which PASG deflation produces hypotension. Five normovolemic patients undergoing cardiac catheterization for atypical chest pain syndrome volunteered for this study. Serial measurements of right atrial, right ventricular, pulmonary artery, left ventricular, and aortic pressures were obtained with subjects supine at the following times: prior to inflation of the PASG; during PASG inflation at 100 mm Hg; and during rapid PASG deflation. Pulmonary and aortic flow velocities were recorded in two patients. The application of external pressure with PASG produced a significant increase in left and right heart pressures (P less than .05). Sudden PASG deflation produced significant transient hypotensive changes (P less than .01). When PASG deflation hemodynamics were compared to preinflation data, mean arterial pressure decreased 14 mm Hg (P less than .01); mean pulmonary pressure decreased 6 mm Hg (P less than .01); and mean right atrial and left ventricular end-diastolic pressures decreased 4 and 6 mm Hg, respectively (P less than .01). An analysis of right and left heart hemodynamic data suggests that the early hypotensive response associated with PASG deflation is consistent with a reduction in left ventricular afterload followed by a decrease in preload.
In an attempt to maximize the hemodynamic effects of antishock trousers, a pair of such trousers was modified to a five-bladder trouser (one abdominal, two thigh, and two calf bladders) and inflated using three different inflation sequences. These three sequences were simultaneous inflation of all five bladders; concurrent inflation of the calf and thigh bladders and then inflation of the abdominal bladder (standard inflation); and sequential inflation of the calf, thigh, and abdominal bladders. Simultaneous inflation resulted in the greatest increase in blood pressure and the smallest increase in end-diastolic volume, stroke volume, and cardiac output. The standard inflation sequence resulted in slightly higher increases in end-diastolic volume, stroke volume, and cardiac output than the sequential inflation sequence, and a significantly larger increase in cardiac output than the simultaneous inflation sequence. Our study indicates that of the three sequences used, the standard inflation sequence produces the greatest blood return to the heart.
As a result of experimental data and favorable clinical impressions, the pneumatic antishock garment (PASG) has gained widespread acceptance as a reasonable standard of care in emergency medical services (EMS) systems. It is currently legislated as required equipment for medical rescue vehicles in two-thirds of the United States. But despite a decade of widespread use, prospective, randomized, controlled trials that demonstrate the efficacy of the PASG have not been published. Furthermore, certain complications have been reported and concerns have been raised about the use of the PASG under certain circumstances, such as penetrating thoracic injury. In the fall of 1983, the City of Houston EMS system embarked on a long-term prospective evaluation of PASG use in hypotensive victims of injury in the urban prehospital setting. All victims of injury whose systolic blood pressure was 90 mm Hg or less when they initially presented to paramedics in the field were entered into the study. All patients received the identical treatment protocol, with the sole exception of PASG application and inflation to full pressure prior to intravenous catheterization on an alternate day basis. Prospectively collected demographic data have demonstrated that the two resulting groups of PASG and no-PASG patients are well matched in terms of age, sex, injury type, anatomic location of the injury, initial field trauma score, injury severity score and probabilities of survival, as well as the amounts of IV fluids infused in the prehospital setting and the response, scene, and transport times.(ABSTRACT TRUNCATED AT 250 WORDS)
A study was performed to determine the percentage of fluid that enters the central circulation following infusion in a peripheral vein beneath an inflated pneumatic antishock garment (PASG) during hemorrhagic shock in a canine model. Seven mongrel dogs were bled acutely to a systolic blood pressure of 50 to 60 mm Hg. The PASG then was inflated. One to two microcuries of Technetium-99-labeled macroaggregated albumin was infused into a peripheral vein in the hind leg, followed by a 10-mL/kg fluid bolus. The albumin particles that reached the central circulation were trapped in the pulmonary capillary bed. Following infusion, a full body scan was performed. The percentage of injected fluid entering the central circulation was calculated by comparing the total body counts to counts localized to the thorax. Average mean arterial pressure was 111 mm Hg prior to bleeding, 47 mm Hg prior to shock trouser inflation, and 66 mm Hg after inflation. The percentage of injected Technetium-99-labeled albumin that reached the central circulation ranged from 80.5% to 99.6%, with a mean of 91.3%. We conclude that a significant percentage of IV fluids infused beneath inflated PASG will reach the central circulation.
Experimental data have suggested that pneumatic external counterpressure improves outcome in intra-abdominal hemorrhage by either a tamponade effect and/or elevation in central systemic blood pressure. As a result, the empiric use of the pneumatic antishock garment (PASG) has become a standard of care, even to the point where the device has been legislated as required equipment on emergency medical rescue vehicles. However, the effect of the PASG on intra-abdominal hemorrhage has not been evaluated in randomized clinical trials. The purpose of this study was to evaluate the effect of the PASG on the survival of hypotensive patients with penetrating abdominal injuries. During a 2 1/2-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 delivered by the same municipal emergency medical services system, and all patients subsequently were transported to the same regional trauma facility. The patients were randomized into control and pneumatic external counterpressure groups by an alternate-day assignment of PASG use. The resulting study populations (control, n = 104; PASG, n = 97) 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 PASG treatment groups (81 of 104 vs 67 of 97). From these data we conclude that, contrary to previous claims, the PASG provides no significant advantage in improving survival in the urban prehospital management of penetrating abdominal injuries.
A 48-year-old man with Wolff-Parkinson-White syndrome presented with paroxysmal supraventricular tachycardia. Prior episodes had required inpatient drug therapy or cardioversion. Attempts at conversion to normal sinus rhythm with vagal maneuvers were unsuccessful. Inflation of military antishock trousers resulted in rapid termination of the arrhythmia and avoidance of hospitalization.
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