Heart rate variability and its association with mortality in prehospital trauma patients.

BACKGROUND Accurate prehospital triage of trauma patients is difficult, especially in mass casualty situations. Accordingly, the U.S. Military has initiated a program directed toward improving noninvasive prehospital triage algorithms based on available physiologic data. The purpose of this study was to assess heart rate variability and its association with mortality in prehospital trauma patients. METHODS Trauma patients without significant head injury requiring helicopter transport were identified from a retrospective research database. An equal number, unmatched sample of patients who lived were compared with those who died (n = 15 per group). All patients were transported to a single Level I urban trauma center. The primary independent variable was mortality. Patients with Abbreviated Injury Scale head scores >2 were excluded from the analysis, so that the effects seen were based on hemorrhagic shock. Age, sex, Glasgow Coma Scale score (GCS), blood pressure, pulse pressure, pulse, intubation rate, SpO2, mechanism of injury, transport time, and time of death after admission were recorded. R-waves from the first available 120 seconds of usable data were detected from normal electrocardiograms and heart rate variability was assessed. RESULTS Patients who died demonstrated a lower GCS (7.9 +/- 1.4 versus 14.4 +/- 0.2; p = 0.0001) and higher intubation rate (53% of patients who died versus 0% patients who lived). Pulse rate, arterial pressure, and SpO2 were not distinguishable statistically between groups (p = 0.08), but pulse pressure was lower in patients who died (39 +/- 3 versus 50 +/- 2 mm Hg; p = 0.01). Compared with patients who lived, those who died had lower normalized low-frequency (LF) power (42 +/- 6 versus 62 +/- 4 LFnu; p = 0.009), higher high-frequency (HF) power (42 +/- 3 versus 32 +/- 3 HFnu; p = 0.04) and higher HF-to-LF ratio (144 +/- 30 versus 62 +/- 11nu; p = 0.01). With absolute HF/LF adjusted for GCS, the intergroup variance accounted for by HF/LF was reduced to 6% (p = 0.16). CONCLUSIONS Analysis of heart rate variability provides insight into adequacy of autonomic compensation to severe trauma. In our cohort of trauma patients, low pulse pressures coupled with relatively higher parasympathetic than sympathetic modulation characterized and separated patients who died versus patients who survived traumatic injuries when standard physiologic measurements are not different. These data do not suggest advantages of heart rate variability analysis over GCS scores, but suggest future possibilities for remote noninvasive triage of casualties when GCS scores are unattainable.

[1]  H. Barcroft,et al.  POSTHÆMORRHAGIC FAINTING: STUDY BY CARDIAC OUTPUT AND FOREARM FLOW , 1944 .

[2]  William H Cooke,et al.  Human cerebrovascular and autonomic rhythms during vestibular activation. , 2004, American journal of physiology. Regulatory, integrative and comparative physiology.

[3]  D. Hoyt,et al.  Analysis of heart-rate variability: a noninvasive predictor of death and poor outcome in patients with severe head injury. , 1997, The Journal of trauma.

[4]  B. Wallin,et al.  Sympathetic outflow to muscles during vasovagal syncope. , 1982, Journal of the autonomic nervous system.

[5]  W. Cooke,et al.  Power spectral analysis imperfectly informs changes in sympathetic traffic during acute simulated microgravity. , 2000, Aviation, space, and environmental medicine.

[6]  Victor A. Convertino,et al.  Association between vasovagal hypotension and low sympathetic neural activity during presyncope , 2002, Clinical Autonomic Research.

[7]  Kathy L Ryan,et al.  Lower body negative pressure as a model to study progression to acute hemorrhagic shock in humans. , 2004, Journal of applied physiology.

[8]  D. Ferguson,et al.  Profound sympathoinhibition complicating hypovolemia in humans. , 1989, Annals of internal medicine.

[9]  J Ludbrook,et al.  Hemodynamic and neurohumoral responses to acute hypovolemia in conscious mammals. , 1991, The American journal of physiology.

[10]  John B Holcomb,et al.  Scientific priorities and strategic planning for resuscitation research and life saving therapy following traumatic injury: report of the PULSE Trauma Work Group. , 2002, Academic emergency medicine : official journal of the Society for Academic Emergency Medicine.

[11]  J. Taylor,et al.  Controlled breathing protocols probe human autonomic cardiovascular rhythms. , 1998, American journal of physiology. Heart and circulatory physiology.

[12]  W. Cooke,et al.  Dynamic cerebral autoregulation is preserved during acute head-down tilt. , 2003, Journal of applied physiology.

[13]  W. Shoemaker,et al.  Current controversies in shock and resuscitation. , 2001, The Surgical clinics of North America.

[14]  M. Malik,et al.  Sympathovagal balance: a critical appraisal. , 1998, Circulation.

[15]  Alberto Malliani,et al.  The Pattern of Sympathovagal Balance Explored in the Frequency Domain. , 1999, News in physiological sciences : an international journal of physiology produced jointly by the International Union of Physiological Sciences and the American Physiological Society.

[16]  R. Cohen,et al.  Power spectrum analysis of heart rate fluctuation: a quantitative probe of beat-to-beat cardiovascular control. , 1981, Science.

[17]  D. Hoyt,et al.  Spectral analysis of heart rate variability in the ICU: a measure of autonomic function. , 1996, The Journal of surgical research.

[18]  D. Laude,et al.  Stroke volume monitored by modeling flow from finger arterial pressure waves mirrors blood volume withdrawn by phlebotomy , 2004, Clinical Autonomic Research.

[19]  U. Rosenschein,et al.  Analysis of coronary ultrasound thrombolysis endpoints in acute myocardial infarction (ACUTE trial). Results of the feasibility phase. , 1997, Circulation.

[20]  A. Malliani,et al.  Heart rate variability. Standards of measurement, physiological interpretation, and clinical use , 1996 .

[21]  A. Porta,et al.  Relationship between spectral components of cardiovascular variabilities and direct measures of muscle sympathetic nerve activity in humans. , 1997, Circulation.

[22]  D L Eckberg,et al.  Human responses to upright tilt: a window on central autonomic integration , 1999, The Journal of physiology.

[23]  B. Sayers,et al.  Analysis of heart rate variability. , 1973, Ergonomics.

[24]  G. Breithardt,et al.  Heart rate variability: standards of measurement, physiological interpretation and clinical use. Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology. , 1996 .

[25]  R. Bellamy.  The causes of death in conventional land warfare: implications for combat casualty care research. , 1984, Military medicine.

[26]  Bernard Swynghedauw,et al.  Brain death assessment using instant spectral analysis of heart rate variability , 2002, Critical care medicine.

[27]  Victor A Convertino,et al.  Heart rate variability and spontaneous baroreflex sequences: implications for autonomic monitoring during hemorrhage. , 2005, The Journal of trauma.