Hemodynamic and oxygen transport patterns after head trauma and brain death: implications for management of the organ donor.

OBJECTIVES: The aims of the present study were to describe the temporal hemodynamic and oxygen transport patterns of patients with head injuries as well as the patterns of those who became brain dead to better understand the role of underlying central regulatory hemodynamic mechanisms and ultimately to improve rates of organ donation. METHODS: We studied 388 consecutive noninvasively monitored patients with severe head trauma; 79 of these became brain dead. Monitoring was started shortly after admission to the emergency department and was designed to describe the sequence of cardiac, pulmonary, and tissue perfusion functions by cardiac index (CI), mean arterial pressure, heart rate, arterial saturation by pulse oximetry (Sapo2), and transcutaneous oxygen and carbon dioxide (Ptco2/Fio2 and Ptcco2) patterns. The latter were used as markers of tissue perfusion or oxygenation. RESULTS: Patients with head injuries who subsequently became brain dead initially had low CI with poor tissue perfusion beginning shortly after emergency department admission. This was followed by a prolonged period characterized by high CI (4.43 +/- 1.3 L x min(-1) x m2) and enhanced tissue oxygenation (Ptco2/Fio2 238 +/- 186). In the late or end stage of brain death, hemodynamic deterioration and collapse led rapidly to arrest. In attempts to maintain hemodynamic stability for organ donation, the effects of various therapies on the hemodynamic patterns were preliminarily described. CONCLUSIONS: The hyperdynamic state with exaggerated peripheral tissue perfusion or oxygenation in brain-dead patients associated with loss of central vasoconstrictive mechanisms of the stress response resulted in unopposed peripheral metabolic vasodilatation producing high CI and tissue perfusion.

Effects of age and obesity on hemodynamics, tissue oxygenation, and outcome after trauma.

OBJECTIVE: The aims of this study are (1) to describe the early time course of hemodynamic and tissue perfusion/oxygenation patterns in the elderly and in obese patients who survive and those who die after trauma; and (2) to evaluate postinjury hemodynamic patterns for use as guides for resuscitation and subsequent treatment. METHODS: We noninvasively monitored 625 trauma patients upon arrival in the emergency department to assess the temporal hemodynamic patterns associated with age and obesity. Cardiac index (CI), mean arterial pressure, and heart rate were monitored to assess cardiac function, pulse oximetry (Sapo2) to reflect changes in pulmonary function and transcutaneous oxygen (PtcO2), carbon dioxide (PtcCO2), and oxygen delivery (DO2) to reflect tissue perfusion. We evaluated these hemodynamic data after they were stratified by the patient age and body mass index. RESULTS: When all trauma patients were considered together, the predominant findings were high CI, transient hypotension, tachycardia, normal pulmonary function, and reduced tissue oxygenation. The elderly and, to a lesser extent the obese, had lower flow and tissue perfusion. The survivors had higher CI and better tissue oxygenation than did the nonsurvivors of each category. CONCLUSIONS: Elderly and obese nonsurvivors of severe injury had low CI with reduced tissue oxygenation associated with organ failures and death. The study suggests that survivors' CIs and tissue oxygenation may be used as markers of circulatory deterioration and shock as well as resuscitation.

Hemodynamic patterns preceding circulatory deterioration and death after trauma.

OBJECTIVE: To describe the sequence of hemodynamic changes associated with sudden circulatory deterioration compared with those of terminal patients to identify the earliest signs warning of shock and death. METHODS: This is a prospective observational study of 89 patients with thermodilution cardiac index and continuous noninvasive hemodynamic monitoring who had episodes of circulatory deterioration. These data were compared with the data of a second group of 24 patients in their terminal stage just before death. RESULTS: The earliest indications of impending collapse were decreased cardiac index, and tissue perfusion reflected by decreased transcutaneous O2 tension (PtcO2). This was followed by reduced blood pressure, tachycardia, reduced arterial hemoglobin saturation, and increased transcutaneous CO2 tension (PtcCO2). This pattern of changes was more pronounced in the nonsurvivors and was seen in exaggerated form in terminal patients. CONCLUSION: Sequential hemodynamic patterns revealed reduced blood flow and poor tissue perfusion as the earliest warning signs in both circulatory deterioration and death. These were followed by reduced mean arterial pressure, tachycardia, and low values of pulse oximetry. Adequate blood flow and even distribution of flow are needed for tissue perfusion.

A mathematical program to predict survival and to support initial therapeutic decisions for trauma patients with long-bone and pelvic fractures.

AIM: To test a mathematical program to monitor early haemodynamic patterns of patients with fractures, predict survival and support initial therapeutic decisions. METHODS: A mathematical search and display program based on non-invasive haemodynamic monitoring was used to study 430 consecutively monitored patients with fractures during the first 48 h after admission to the emergency department of an inner city public hospital. We studied four types of fractures: simple extremity fractures, long-bone fractures, pelvic fractures and fractures incidental to severe trauma. The program continuously displayed haemodynamic patterns and predicted survival probability (SP), which was evaluated by the actual outcome at hospital discharge. The program also assessed the effectiveness of therapies according to haemodynamic responses. RESULTS: The cardiac index, heart rate, mean arterial pressure, arterial saturation and transcutaneous oxygen tensions at the initial resuscitation were significantly higher in survivors than in non-survivors. After the first 48 h, the haemodynamic patterns were more influenced by fever, sepsis, complications and organ failures. The calculated survival probability averaged 81%+/-18% in the first 48 h for survivors and 72%+/-20% for non-survivors. CONCLUSION: Early continuous non-invasive haemodynamic monitoring using the proposed information system is helpful in predicting outcome and guiding therapy for patients with fractures.

Hemodynamic patterns of blunt and penetrating injuries.

BACKGROUND: The aims of this prospective observational study were to describe early hemodynamic patterns of blunt and penetrating truncal injury and to evaluate outcomes prediction using noninvasive hemodynamic monitoring with a mathematical model tested against actual in-hospital outcomes. The hypothesis was that traumatic shock is a circulatory disorder that can be monitored by noninvasive hemodynamic parameters that reflect cardiac, pulmonary, and tissue perfusion functions. STUDY DESIGN: The cardiac index (CI), heart rate (HR), mean arterial pressure (MAP), pulse oximetry (SapO(2)), transcutaneous oxygen tension indexed to FiO(2) (PtcO(2)/FiO(2)), and carbon dioxide (PtcCO(2)) tensions were monitored beginning shortly after emergency department admission in 657 emergency patients with severe blunt and penetrating chest, abdominal, and extremity trauma. Of these, 113 patients had associated head injury, and these patients also were analyzed separately. A search and display mathematical model, with a decision support program, was based on continuous online, real-time, noninvasive hemodynamic monitoring. RESULTS: There were similar patterns in the blunt and penetrating injuries; the cardiac index, mean arterial pressure, pulse oximetry, transcutaneous oxygen tension indexed to FiO(2), and survival probability values of the survivors were significantly higher (p < 0.01) than the corresponding values of those who died, although heart rate and carbon dioxide tension were higher in the nonsurvivors during the first 24 hours after their emergency department admission. These patterns occurred more rapidly in patients with penetrating injuries. After initial resuscitation in the emergency department, results were correlated with actual outcomes at hospital discharge and found to be 88% correct. CONCLUSIONS: Early noninvasive hemodynamic monitoring with a computerized information system provided a feasible pattern recognition program for outcomes prediction and therapeutic decision support.

Noninvasive hemodynamic monitoring for combat casualties.

The aims of this study were to develop and to test a noninvasive hemodynamic monitoring system that could be applied to combat casualties to supplement conventional vital signs, to use an advanced information system to predict outcomes, and to evaluate the relative effectiveness of various therapies with instant feedback information during acute emergency conditions. In a university-run inner city public hospital, we evaluated 1,000 consecutively monitored trauma patients in the initial resuscitation period, beginning shortly after admission to the emergency department. In addition to conventional vital signs, we used noninvasive monitoring devices (cardiac index by bioimpedance with blood pressure and heart rate to measure cardiac function, arterial hemoglobin oxygen saturation by pulse oximetry to reflect changes in pulmonary function, and tissue oxygenation by transcutaneous oxygen tension indexed to fractional inspired oxygen concentration and carbon dioxide tension to evaluate tissue perfusion). The cardiac index, mean arterial pressure, pulse oximetry (arterial hemoglobin oxygen saturation), and transcutaneous oxygen tension/fractional inspired oxygen concentration were significantly higher in survivors, whereas the heart rate and carbon dioxide tension were higher in nonsurvivors. The calculated survival probability was a useful outcome predictor that also served as a measure of severity of illness. The rate of misclassification of survival probability was 13.5% in the series as a whole but only 6% for patients without severe head injuries and brain death. Application of noninvasive hemodynamic monitoring to acute emergency trauma patients in the emergency department is feasible, safe, and inexpensive and provides accurate hemodynamic patterns in continuous, on-line, real-time, graphical displays of the status of cardiac, pulmonary, and tissue perfusion functions. Combined with an information system, this approach provided an early outcome predictor and evaluated, with an objective individualized method, the relative efficacy of alternative therapies for specific patients.

Evaluation of invasive and noninvasive hemodynamic monitoring in trauma patients.

OBJECTIVES: The aim of this study was to compare a recently developed and improved noninvasive hemodynamic monitoring system with the conventional invasive monitoring by pulmonary artery catheterization (PAC) in acute emergency trauma patients. METHODS: In a large, university-run, inner city public hospital, we monitored 993 trauma patients noninvasively; 262 of these were simultaneously monitored with both noninvasive hemodynamic and invasive PAC monitoring. The noninvasive monitoring was begun shortly after admission to the emergency department and the invasive PAC monitoring was started in the operating room, or as soon as the patient arrived in the intensive care unit. Noninvasive monitoring included cardiac index (CI) by the IQ or Physio Flow bioimpedance device, together with mean arterial blood pressure, heart rate, pulse oximetry (SapO2), transcutaneous oxygen (PtcO2), and carbon dioxide (PtcCO2) tensions. We compared CI by simultaneous measurements with both invasive and noninvasive methods 907 times in 262 patients. RESULTS: The CI by thermodilution (CItd) correlated well with simultaneous measurements with the bioimpedance (CIbi), r2 = 0.915, r2 = 0.84, p < 0.001. The bias and precision of simultaneous measurements was -0.070 +/- 0.47 L/min/m2; agreement was considered satisfactory. In the initial resuscitation period of both monitoring systems, the CI, mean arterial blood pressure, SapO2, and tissue perfusion (reflected by invasive DO2 and VO2, and by noninvasive PtcO2/FiO2 ratio) were higher in survivors than in nonsurvivors, whereas heart rate values were higher in the nonsurvivors. We concluded that noninvasive hemodynamic monitoring provided a feasible, safe, inexpensive, accurate, continuous, on-line real-time graphic displays that are equivalent to the essential features of invasive pulmonary artery catheter monitoring.

Outcome prediction by a mathematical model based on noninvasive hemodynamic monitoring.

BACKGROUND: The aims are to apply a mathematical search and display model based on noninvasive hemodynamic monitoring, to predict outcome early in a consecutively monitored series of 661 severely injured patients. METHODS: A prospective observational study by a previously designed protocol in a Level I trauma service in a university-run inner city public hospital was conducted. The survival probabilities were calculated at the initial resuscitation on admission and at subsequent intervals during their hospitalization beginning shortly after admission to the emergency department. Cardiac function was evaluated by cardiac output (CI), heart rate (HR), and mean arterial blood pressure (MAP), pulmonary function by pulse oximetry (SapO2), and tissue perfusion function by transcutaneous oxygen indexed to FiO2, (PtcO2/FiO2), and carbon dioxide (PtcCO2) tension. RESULTS: The survival probability (SP) averaged 89 +/- 0.4% for survivors and 75.7 +/- 1.6% (p < 0.001) for nonsurvivors in the first 24-hour period of resuscitation. The CI, MAP, SapO2, PtcO2, and PtcO2/FiO2 were significantly higher in survivors than in nonsurvivors in initial resuscitation, whereas HR and PtcCO2 were higher in nonsurvivors. CONCLUSIONS: During the initial resuscitation period, misclassifications were 102 of 661 or 15%. The SP provided early objective criteria to evaluate hospital outcome and to track changes throughout the hospital course based on a large database of patients with similar clinical-hemodynamic states.

Stochastic model for outcome prediction in acute illness.

The aims were to apply a stochastic model to predict outcome early in acute emergencies and to evaluate the effectiveness of various therapies in a consecutively monitored series of severely injured patients with noninvasive hemodynamic monitoring. The survival probabilities were calculated beginning shortly after admission to the emergency department (ED) and at subsequent intervals during their hospitalization. Cardiac function was evaluated by cardiac output (CI), heart rate (HR), and mean arterial blood pressure (MAP), pulmonary function by pulse oximetry (SapO(2)), and tissue perfusion function by transcutaneous oxygen indexed to FiO(2),(PtcO(2)/FiO(2)), and carbon dioxide (PtcCO(2)) tension. The survival probability (SP) of survivors averaged 81.5+/-1.1% (SEM) and for nonsurvivors 57.7+/-2.3% (p<0.001) in the first 24-hour period of resuscitation and subsequent management. The CI, SapO(2),PtcO(2)/FiO(2) and MAP were significantly higher in survivors than in nonsurvivors during the initial resuscitation, while HR and PtcCO(2) tensions were higher in the nonsurvivors. Predictions made during the initial resuscitation period in the first 24-hours after admission were compared with the actual outcome at hospital discharge, which were usually several weeks later; misclassifications were 9.6% (16/167). The therapeutic decision support system objectively evaluated the responses of alternative therapies based on responses of patients with similar clinical-hemodynamic states.

Survival, hemodynamics, and tissue oxygenation after head trauma.

BACKGROUND: The aims of this study were to describe the early time course of hemodynamic and tissue perfusion and oxygenation patterns in survivors and nonsurvivors after head injury; to suggest physiologic mechanisms responsible for the observed patterns; and to evaluate postinjury parameters that might be useful for treatment. The hypothesis was that reduced hemodynamics and tissue oxygenation and reduced arterial oxygen saturation affect outcomes. STUDY DESIGN: Sixty patients with head trauma were noninvasively monitored on arrival in the emergency department to assess the temporal hemodynamic patterns associated with head injury; patients who were brain dead were excluded because they have very different hemodynamic patterns. Cardiac index, mean arterial pressure, and heart rate were monitored to assess cardiac function, pulse oximetry to reflect changes in pulmonary function, and transcutaneous oxygen and carbon dioxide to reflect tissue perfusion function. Patients were stratified by inhospital survival outcomes, the Glasgow Coma Scale, and the presence or absence of associated somatic injuries. RESULTS: When all head injured patients were considered together, the predominant findings were high cardiac index, hypertension, mild tachycardia, normal pulmonary function, and reduced tissue oxygenation. The subset of survivors and those with high Glasgow Coma Scale had greater than normal cardiac index responses (4.02 +/- 0.01 (SEM) L/min/m2, p < 0.01 versus normal) and better tissue oxygenation (217 +/- 2 mmHg PtcO2/FiO2) than nonsurvivors (70 +/- 3 mmHg, p < 0.01) and those with low Glasgow Coma Scale (160 +/- 2, p < 0.05). Patterns of patients with associated somatic injuries were similar to those with isolated head injury. CONCLUSIONS: The study suggested that survivors' cardiac index, tissue oxygenation, and arterial oxygen saturation may be considered as markers of resuscitation. Nonsurvivors of head injury had normal blood flow with reduced tissue oxygenation that might have contributed to unfavorable outcomes.

Continuous noninvasive monitoring of cardiac performance and tissue perfusion in pediatric trauma patients.

PURPOSE: The aim of this study was to assess the accuracy of a continuous survival probability prediction using noninvasive measures of cardiac performance and tissue perfusion in severely injured pediatric patients. METHODS: Review of all patients entered into a prospective noninvasive monitoring protocol. Cardiac index (CI) was measured using a thoracic bioimpedance device and tissue perfusion was assessed by transcutaneous carbon dioxide (Ptcco(2)) tension and oxygen tension indexed to the fraction of inspired oxygen (Ptco(2)/Fio(2)). Survival probability (SP) was continuously calculated using a stochastic analysis program. RESULTS: There were 45 patients with a total of 953 data sets. The mean age was 11 years (range, 1-16 years) with a mean Injury Severity Score of 24 (+/-16). There was no difference between survivors (n = 32) and nonsurvivors (n = 13) at study entry for heart rate, blood pressure, CI, or pulse oximetry (all P > .05). However, survivors demonstrated higher Ptcco(2) (45 vs 35), higher Ptco(2)/Fio(2) (236 vs 156), and higher predicted SP (89% vs 62%) compared with nonsurvivors at study entry and throughout the monitoring period (all P < .01). For the entire data set, the strongest independent predictors of survival were Ptco(2)/Fio(2) and SP. The area under the receiver operating characteristic curve for mortality prediction was 0.83 for SP and 0.71 for Ptco(2)/Fio(2), compared with 0.6 for heart rate, 0.51 for blood pressure, and 0.53 for CI. Similar hemodynamic patterns were observed for all injury patterns with the exception of those with severe brain injury. CONCLUSIONS: Thoracic bioimpedance and transcutaneous monitoring give critical real-time hemodynamic and tissue perfusion data that can provide early identification of pathologic flow patterns and accurately predict survival.

A stochastic control program to predict outcome and to support therapeutic decisions: a preliminary report.

BACKGROUND AND OBJECTIVES: Early noninvasive hemodynamic monitoring with an outcome predictor and a therapeutic decision support system may be useful to identify and correct hemodynamic deficiencies in emergency patients. The first aim was to apply a stochastic (probability) search and display model to predict outcome as early as possible. The second aim was to explore the usefulness of a therapeutic decision support system to evaluate the relative effectiveness of various therapies. METHODS: A stochastic control and display program based on noninvasive hemodynamic monitoring was applied in 100 consecutive critically ill patients admitted to the emergency department of an inner city public hospital. The program continuously displayed the noninvasive hemodynamic data and the patient's predicted survival probability (SP) that was based on the patient's diagnosis, covariates, and hemodynamic data. The accuracy of the SP at the initial resuscitation on admission to the emergency department (ED) was evaluated by the actual outcome at hospital discharge. The therapeutic decision support program evaluated the relative effectiveness of various therapies on based on their hemodynamic and SP responses and outcome of patients with similar clinical-hemodynamic states. RESULTS: The cardiac index, mean arterial pressure, arterial saturation, transcutaneous oxygen and carbon dioxide tensions were appreciably higher in survivors than in nonsurvivors in the initial resuscitation. Heart rate was higher in the nonsurvivors. The calculated Survival Probability (SP) of survivors averaged 81 +/- 1.4% in the first 24-hour observation period. It was 58 +/- 2.2% for nonsurvivors during this period. Misclassifications were 10/100 or 10%.

Outcome prediction in chest injury by a mathematical search and display program.

OBJECTIVE: This study applies a stochastic or probability search and display model to prospectively predict outcome and to evaluate therapeutic effects in a consecutively monitored series of 396 patients with severe thoracic and thoracoabdominal injuries. STUDY DESIGN: Prospective observational study of outcome prediction using noninvasive hemodynamic monitoring by previously designed protocols and tested against actual outcome at hospital discharge in a level 1 trauma service of a university-run, inner-city public hospital. METHODS: Cardiac index (CI), heart rate (HR), mean arterial pressure (MAP), arterial oxygen saturation measured by pulse oximetry (Sp(O2)), transcutaneous oxygen tension (PtC(O2)), and transcutaneous carbon dioxide tension (Ptc(CO2)) were monitored beginning shortly after admission to the emergency department. The stochastic search and display model with a decision support program based on noninvasive hemodynamic monitoring was applied to 396 severely ill patients with major thoracic and thoracoabdominal trauma. The survival probability (SP) was calculated during initial resuscitation continuously until patients were stabilized, and compared with the actual outcome when the patient was discharged from the hospital usually a week or more later. RESULTS: The CI, Sp(O2), Ptc(O2), and MAP were appreciably higher in survivors than in nonsurvivors. HR and Ptc(CO2) were higher in the nonsurvivors. The calculated SP in the first 24-h observation period of survivors of chest wounds averaged 83 +/- 18% (+/- SD) and 62 +/- 19% for nonsurvivors. Misclassifications were 9.6%. The relative effects of alternative therapies were evaluated before and after therapy, using hemodynamic monitoring and SP as criteria. CONCLUSIONS: Noninvasive hemodynamic monitoring with an information system provided a feasible approach to early outcome predictions and therapeutic decision support.

Mathematical program for outcome prediction and therapeutic support for trauma beginning within 1 hr of admission: a preliminary report.

OBJECTIVES: The aims were a) to noninvasively monitor acute emergency trauma patients beginning within 1 hr after admission to the emergency department; b) to prospectively predict outcome; and c) to evaluate the relative effectiveness of various modes of therapy. DESIGN: Prospective outcome prediction study using a mathematical search and display model based on noninvasive hemodynamic monitoring. SETTING: A level I trauma service in a large university-run inner-city public hospital. PATIENTS: We studied 185 consecutively noninvasively monitored emergency patients. INTERVENTIONS: We noninvasively monitored cardiac index, mean arterial blood pressure, heart rate, pulse oximetry, and transcutaneous oxygen and carbon dioxide tensions beginning within 1-hr after emergency admission. MEASUREMENTS AND MAIN RESULTS: The cardiac index, pulse oximetry, transcutaneous oxygen tension, transcutaneous carbon dioxide tension, and mean arterial blood pressure were higher in survivors than in nonsurvivors in the initial resuscitation period and at the hemodynamic nadir. Heart rate and transcutaneous carbon dioxide tension were higher in the nonsurvivors. The calculated survival probability in the first hour observation period of survivors averaged 85 +/- 14% vs. 69 +/- 16% for nonsurvivors (p = .0001). Misclassifications of the series as a whole were 11.3%; after excluding brain death from severe head injury, there were 6.4% misclassifications. A decision support system evaluated the effects of various therapies based on responses of patients with similar clinical-hemodynamic states. CONCLUSION: Noninvasive hemodynamic monitoring and an information system provided a feasible approach to predict outcome early and to evaluate prospectively the efficacy of various therapies.

The effect of obesity on bioimpedance cardiac index.

BACKGROUND: Cardiac performance may be assessed noninvasively at the patient's bedside by using thoracic bioimpedance. However, it is unclear if this technique can be used reliably in critically injured obese patients because of increased body habitus and chest wall mass. METHODS: A prospectively maintained database was used to identify all trauma patients admitted to the intensive care unit who underwent simultaneous measurement of cardiac performance by using both thoracic bioimpedance and thermodilution. Patients were divided into 2 groups based on their body mass index (BMI). Patients with a BMI less than 30 kg/m(2) were classified as nonobese, and patients with a BMI of 30 kg/m(2) or greater were categorized as obese. RESULTS: There were 285 patients who underwent 1,138 simultaneous measurements of cardiac index by using both bioimpedance and thermodilution. There were 211 nonobese patients (BMI = 25 +/- 3 kg/m(2)) and 74 obese patients (BMI = 34 +/- 4 kg/m(2)). Bioimpedance correlated well with thermodilution for the entire population (r = .84, P < .0001), and was reliable equally in obese (r = .85, P < .0001) and nonobese (r = .82, P < .0001) patients. There actually was less test bias in the obese group (-.06 +/- .69) than in the nonobese group (-.16 +/- .75, P = .04). CONCLUSIONS: Thoracic bioimpedance technology may be used reliably as a noninvasive alternative to pulmonary artery catheterization for assessment of cardiac performance in critically injured obese patients.

Is noninvasive hemodynamic monitoring appropriate for the elderly critically injured patient?

BACKGROUND: Noninvasive hemodynamic monitoring in critically ill patients using bioimpedance technology has been shown to be a reliable alternative to invasive thermodilution techniques. However, there have been some concerns that the bioimpedance method may be unreliable in elderly patients with an atherosclerotic and rigid thoracic aorta. The purpose of the present study was to evaluate the effect of age on the reliability of noninvasive bioimpedance technology in measuring cardiac index. METHODS: This is a retrospective analysis of prospectively collected data in critically injured patients admitted to the surgical intensive care unit. All patients had simultaneous measurement using thermodilution cardiac index (TDCI) and bioimpedance cardiac index (BICI). The population was divided into three age groups (<55 years, 55-70 years, and >70 years). The correlation between TDCI and BICI was calculated for each age group. RESULTS: There were 1,138 simultaneous measurements of TDCI and BICI in 285 patients. The BICI correlated well with TDCI in all three age groups (r = 0.82 for group <55 years, r = 0.87 for group 55-70 years, and r = 0.80 for group >70 years). CONCLUSION: Noninvasive cardiac index monitoring in elderly patients is reliable and correlates well with standard thermodilution techniques.

Autonomic activity in trauma patients based on variability of heart rate and respiratory rate.

OBJECTIVE: To evaluate the effects of sympathetic and parasympathetic nervous system activity on the heart rate and other hemodynamic variables in acute emergency patients with mild to moderately severe trauma. DESIGN: Clinical study. SETTING: Level 1 university-run trauma service. PATIENTS: Fourteen trauma patients studied immediately after admission to the emergency department. INTERVENTIONS: We measured heart rate and respiratory rate variability by spectral analysis in the early period of mildly to moderately injured patients and compared the patterns of the low- (Lfa) and high-frequency (Hfa) areas of variability. MEASUREMENTS AND MAIN RESULTS: The Lfa is the area under the spectral analysis curve within the frequency range of 0.04-0.10 Hz. This area reflects primarily the tone of the sympathetic nervous system as mediated by the cardiac nerve. The respiratory area or Hfa is a 0.12 Hz-wide frequency range centered around the fundamental respiratory frequency defined by the peak mode of the respiratory power spectrum. It is indicative of vagal outflow reflecting parasympathetic nervous system activity. The Lfa/Hfa, or "L/R ratio," reflects the balance between the sympathetic and parasympathetic nervous systems. The hemodynamic effects of bursts of autonomic activity in response to injury were explored by heart rate and respiratory rate variability measured with non-invasive hemodynamic monitoring consisting of bioimpedance cardiac output, heart rate, and mean arterial pressure to measure cardiac function and transcutaneous oxygen (PtcO2) to reflect tissue perfusion. During sudden surges of autonomic activity, we described increased heart rate variability reflecting increased Lfa and to a lesser degree to Hfa. Slightly later there was increased heart rate, mean arterial pressure, and cardiac index but decreased tissue perfusion indicated by the decreased PtcO2/FIO2 ratio. CONCLUSIONS: Surges in autonomic activity in the period immediately after emergency department admission of trauma patients were associated with pronounced increases in cardiac index, mean arterial pressure, and heart rate and reduced tissue oxygenation.