Noninvasive monitoring of the autonomic nervous system and hemodynamics of patients with blunt and penetrating trauma.

Background: To describe early effects of sympathetic (SNS) and parasympathetic nervous system (PSNS) activities measured by heart rate (HR) and respiratory rate variabilities simultaneously with noninvasive hemodynamic patterns in patients with blunt and penetrating trauma.

Methods: Descriptive study of 168 monitored trauma patients in a level I university-run trauma service. We studied HR and respiratory rate variability by spectral analysis as a measure of autonomic nervous system (ANS) activity in severe blunt and penetrating injuries beginning shortly after their admission to the emergency department. The low frequency area is the area under the HR spectral analysis curve within the frequency range of 0.04 Hz to 0.10 Hz. This area primarily reflects the tone of the SNS as mediated by the vagus nerve. The respiratory frequency area, sometimes referred to as the high frequency area, is a 0.12 Hz-wide frequency range centered around the fundamental respiratory frequency defined by the peak mode of the respiratory activity power spectrum. It is indicative of vagal outflow reflecting PSNS activity. The low frequency area/respiratory frequency area, or L/R ratio, reflects the balance of the SNS and the PSNS. ANS was studied simultaneously with noninvasive hemodynamic patterns after blunt and penetrating thoracic or abdominal injury beginning shortly after admission. We measured cardiac index by bioimpedance, HR, and mean arterial pressure (MAP) to evaluate cardiac function, pulse oximetry (SapO2) to reflect changes in respiratory function, and transcutaneous oxygen indexed to fractional inspired oxygen (PtcO2/FIO2) to reflect tissue perfusion.

Results: ANS activity markedly increased especially in the nonsurvivors at 12 hours to 24 hours after admission. Compared with survivors, the nonsurvivors had lower MAP, CI, and PtcO2/FIO2 values associated with increased ANS activity.

Conclusions: In the nonsurvivors, low flow, low MAP, and reduced tissue perfusion were associated with pronounced increases in PSNS and lesser increases in SNS activity. In the survivors, higher CI, MAP, and PtcO2/FIO2 values were associated with lesser increases in both PSNS and SNS activities.