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Biomedical subjects

N Sheffer

Publications and source records attributed to N Sheffer.

5 recordsLinked to original sources
PubMed1999

Computer simulation of hypothermia during "damage control" laparotomy.

"Damage control" is a surgical strategy for the staged repair of severe trauma that aims to avoid an irreversible physiologic insult marked by a self-propagating combination of hypothermia, coagulopathy, and acidosis. The point beyond which the physiologic insult becomes irreversible, however, remains ill-defined. The aim of this study was to address this problem by means of a dynamic computer model of heat loss during laparotomy for exsanguinating hemorrhage. A single compartment model was developed using a graphic modeling tool and was implemented to calculate the time interval from the beginning of laparotomy to a core temperature of 32 degrees C, which is a marker of irreversible physiologic derangement in injured patients. A series of simulation runs showed that the exposed peritoneum is the dominant factor contributing to heat loss; the bleeding rate has a less marked effect. Elevation of the ambient temperature and rapid abdominal closure are effective interventions available to the surgeon to modify the heat loss curve. This study shows that during a "damage control" laparotomy for exanguinating hemorrhage the window of opportunity for salvage before the onset of an irreversible physiologic insult is no longer than 60 to 90 minutes.

Computer Simulation↗
PubMed1997

Myocardial O2 balance during fluid resuscitation in uncontrolled hemorrhage: computer model.

OBJECTIVE: To study myocardial oxygen balance during fluid resuscitation for uncontrolled hemorrhage. DESIGN: A computer simulation. MATERIALS AND METHODS: A mathematical model of the cardio-vascular system was used to simulate uncontrolled hemorrhage with and without fluid replacement. The parameters of initial bleeding rates, fluid replacement, and time intervals were selected to approximate typical values encountered in an urban emergency medical services system. The model was used to calculate myocardial oxygen supply and demand, and the time from injury to myocardial oxygen deficit was calculated for each fluid regimen. MAIN RESULTS: The model predicts an exponential decline in bleeding rate when no fluids are administered. Optimal fluid infusion rate was predicted as a function of initial bleeding rate. The time to a negative myocardial oxygen balance was shorter when a fluid bolus (100 mL/min or more) was given compared with no fluid administration. CONCLUSIONS: For uncontrolled hemorrhage at initial bleeding rates of 100 mL/min or more, the time interval from injury to cardiac oxygen deficit is inversely related to the infusion rate. A detailed study of the myocardial oxygen balance provides a pathophysiologic rationale for fluid restriction in the initial management of uncontrolled hemorrhage.

Computer Simulation↗
PubMed1993

A computer model for analysis of fluid resuscitation.

Injuries involving massive blood loss, such as burns, combat wounds, and injuries resulting from car accidents, require fluid resuscitation. The risk involved in fluid therapy is overloading of the circulation, resulting in pulmonary edema which can lead to death. The risk of pulmonary edema may be eliminated by proper determination of maximal infusion volume and rate. Reabsorption of fluid from the extravascular compartment and infusion of fluid following blood loss results in reduction of the hematocrit. This is accompanied by an increase in the heart's preload and afterload. Coronary driving pressure and flow increase due to increased volume. However, because of the reduced hematocrit this increase in coronary flow may not be sufficient to compensate the myocardium, in terms of oxygen supply, for the increase in oxygen consumption. A model of the cardiovascular system, including an extravascular compartment, was designed to analyze the effects of fluid infusion on hemodynamic variables, cardiac oxygen balance, and the redistribution of fluid between intravascular and extravascular compartments. The results indicate that edema is not the only possible adverse effect of overloading the cardiovascular system with fluid. The simulation demonstrated that in certain cases the heart's oxygen balance can become negative. Limiting the rate of infusion can reduce this risk.

Animals↗