Peter A Maningas

Epidemiology of trauma: Military experience

Battle injuries sustained in conventional warfare are more likely to be lethal than are injuries sustained by civilians. Depending on the tactical situation, mortality may range from 20% to more than 80% of all casualties. The American experience indicates that about 90% of the total mortality occurs on the battlefield. Such casualties, those classified as killed in action, die before reaching medical care. More than 90% of all battle injuries (morbidity) are caused by penetrating missiles. Exsanguination from wounds of the heart/great vessels and penetrating/perforating wounds of the skull cause the majority of battlefield deaths. The frequency distribution of injury severity appears to be bimodal. A large peak occurs at low injury severity and indicates a population of casualties with relatively benign soft tissue wounds. A smaller peak at high injury severity represents those killed in action.

Small-volume infusion of 7.5% NaCl in 6% dextran 70® for the treatment of severe hemorrhagic shock in swine

In the initial treatment of the hypovolemic trauma patient, commonly used crystalloids have little clinical benefit in the small volumes generally infused during transport. We evaluated the efficacy of a small-volume infusion of 7.5% NaCl in 6% Dextran 70 as a treatment modality for an otherwise lethal hemorrhage in swine. Sixty chronically instrumented swine were randomized into one of four treatment groups: 0.9% NaCl (NS, n = 15), 7.5% NaCl (HS, n = 15), 6% Dextran 70 (DEX, n = 16), and 7.5% NaCl in 6% Dextran 70 (HSD, n = 14). Each animal was bled 46 mL/kg in 15 minutes. Five minutes after the completion of hemorrhage, the animals were infused with their respective treatment in a volume (11.5 mL/kg) equal to 25% of the shed blood. Of those animals receiving HSD, 100% survived until euthanized at 96 hours. In comparison, animals infused with NS, HS, and DEX had 96-hour survival values of 13%, 53%, and 69%, respectively. The survival rate of the HSD group was significantly better than that of the NS group (P less than .001) and the HS group (P less than .01). The infusion of HSD increased mean arterial pressure, PCO2, and plasma bicarbonate to a significantly greater extent than NS alone (P less than .05). These results demonstrate that a small-volume infusion of the hypertonic sodium chloride/dextran solution is superior to equal volumes of a standard crystalloid in resuscitating animals from hemorrhagic shock.

Current shock models and clinical correlations

No useful purpose is served by developing therapeutic interventions that are applicable only in nonexistent patient populations. The history of laboratory hemorrhagic shock research may be a case in point because although many interventions have been proposed on the basis of animal experimentation, few if any have found a place in the treatment of human beings. For a laboratory shock model to have clinical relevance, it must replicate important aspects of shock as seen in human beings during or following massive blood loss. The difficulty in developing an animal model that incorporates these human aspects--hypothermia, hypoxia, hypotension, acidosis, coagulopathy, etc--must not be underestimated. Four methodological factors to consider are animal species, anesthesia, tissue trauma, and nociceptive effects. The development of an animal shock model will require several compromises and the results, whether dealing with mechanisms or therapeutic outcomes, must be considered suspect until confirmatory data are obtained from human studies.

Hypertonic sodium chloride solutions for the prehospital management of traumatic hemorrhagic shock: A possible improvement in the standard of care?

Acute hemorrhage is a major cause of death in both civilian and military trauma. The suboptimal effect of the volume of standard crystalloids that can be infused during transport has resulted in a need for a more efficacious fluid for the prehospital management of both civilian and military trauma. Markedly hypertonic sodium chloride solutions have been shown to improve transiently the hemodynamic consequences of shock in animal models. The use of small volumes of 7.5% NaCl in 6% dextran 70 has resulted in a solution superior to equal volumes of standard crystalloids in the ability to resuscitate animals from hemorrhagic shock. The hypertonic sodium chloride/dextran solution has the potential advantages of improving survival, producing a beneficial hemodynamic effect with smaller fluid volumes, reducing total fluid requirements during resuscitation, and being stored easily. This solution may prove valuable in the early resuscitation of the hypovolemic trauma patient and merits further clinical trials.

Regional blood flow during hypothermic arrest

Little is known about the efficacy of CPR in the setting of hypothermia-induced cardiac arrest. We measured organ blood flow produced by conventional closed-chest CPR in eight swine following normothermic KCl-induced cardiac arrest and in seven swine surface-cooled until cardiac arrest occurred. Radiomicrospheres were injected in the unanesthetized basal state, after five minutes of CPR, and after 20 minutes of CPR. After five minutes of CPR, the cardiac output and cerebral and myocardial blood flows (mean +/- SD) of hypothermic animals were 15.3 +/- 7.5 mL/min/kg, 0.16 +/- 0.11 mL/min/g, and 0.20 +/- 0.15 mL/min/g, respectively. Mean percentage flows were 7%, 15%, and 8%, respectively, of those measured in the unanesthetized prearrest state, and 50%, 55%, and 31%, respectively, of the flow produced during CPR in normothermic animals. Blood flow during hypothermic CPR did not change significantly over time; however, during normothermic CPR, cardiac output and cerebral and myocardial flows decreased so that at 20 minutes there were no significant differences from those values measured in hypothermic animals. The reduction in organ flow produced by external chest compression in hypothermic animals may be a result of the changes in the viscoelastic properties of the thorax that occur during profound hypothermia.

Guidelines for the prehospital use of thrombolytic agents

Recognizing that prehospital thrombolytic therapy may provide benefit to certain subsets of patients, the routine prehospital use of thrombolytic agents should be discouraged pending further scientific delineation and documentation of those subgroups. ACEP encourages further investigation to document feasibility, efficacy, cost-effectiveness, and safety of use of these agents in this environment. Detailed education is needed in such areas as contraindications and the mechanics of drug administration. Online medical direction is paramount to the successful use of these agents in the prehospital setting.

Lack of efficacy of naloxone in a fixed-volume hemorrhage model

Animal studies using a reservoir model of hemorrhagic shock have shown the narcotic antagonist naloxone to be of value in reversing the hemodynamic effects of severe hemorrhage. We conducted a study to evaluate the ability of naloxone to limit the deleterious effects of a fixed-volume hemorrhage. Fifteen mongrel dogs were bled 50% of their estimated blood volumes during one hour. This was followed by a one-hour stabilization period; reinfusion during a 30-minute period; and finally, an additional one-hour monitoring period. Eight dogs received 2 mg/kg IV naloxone 30 minutes prior to hemorrhage and 2 mg/kg/hr for the duration of the study. Seven control dogs received an equivalent volume of saline without naloxone. Pulmonary capillary wedge pressure, central venous pressure, cardiac output, heart rate, blood pressure, arterial and mixed venous blood gases, and serum lactate were measured at 19 intervals throughout the study period. Mean arterial pressure, cardiac index, and systemic vascular resistance were calculated for each sampling period. With the exception of serum lactates, which were higher in the naloxone group, there were no significant differences between the groups in the mean values calculated for each sampling interval (P less than .05, two-tailed independent t test). Furthermore, the changes in hemodynamic parameters observed during the hemorrhage, stabilization, reinfusion, and monitoring periods were not significantly different. We conclude that in this fixed-volume hemorrhage model, naloxone does not prevent or reverse hemodynamic deterioration.

Transcutaneous oxygen tension measurements during graded hemorrhage and reinfusion

Measurement of transcutaneous oxygen tension (PtCO2) has been suggested as a useful monitoring tool in the hypovolemic patient. Our study was undertaken to evaluate changes in PtCO2 that occur during graded hemorrhage and reinfusion, and to compare PtCO2 values to standard cardiorespiratory and biochemical parameters during hypovolemia. Seven mongrel dogs were bled 50% of their estimated blood volume (44 mL/kg) over one hour. This was followed by a one-hour monitoring period, a 30-minute reinfusion period, and an additional one-hour monitoring period. Pulmonary capillary wedge pressure (PCWP), central venous pressure (CVP), cardiac output (CO), mean arterial pressure (MAP), mixed venous oxygen tension (MvO2), arterial blood gases, and PtCO2 were measured serially throughout the study period. Cardiac index (CI), peripheral vascular resistance (PVR), O2 consumption, delivery, and percentage of extraction were calculated for each sampling period. A statistically significant fall in CI, MvO2 and PCWP occurred following the first 10% of blood loss; PtCO2 and MAP fell significantly after 20% hemorrhage; CVP fell after 30% hemorrhage. PtCO2 rose significantly after the first 10% of reinfusion, and it continued to rise during the entire reinfusion period, as did MvO2, CO, MAP, CVP, and PCWP. In contrast to the other measured variables, the elevations in PtCO2, and MvO2 were more pronounced early in the reinfusion period. During postreinfusion monitoring, PtCO2, MvO2, CO, and PCWP fell significantly despite maintenance of prehemorrhage MAP and CVP. Overall PtCO2 correlated well with MvO2 and the O2 extraction ratio, and to a lesser extent with CI, MAP, and O2 delivery.(ABSTRACT TRUNCATED AT 250 WORDS)