Could heart rate variability predict outcome in patients with severe head injury? A pilot study

Despite major improvements in the resuscitation of patients with head injur y, the outcome of patients with head trauma often remains poor and difficul t to establish. Heart rate variability (HRV) analysis is a noninvasive tool used to measure autonomic nervous system (ANS) activity. The aim of this p rospective study was to investigate whether HRV analysis might be a useful adjunct for predicting outcome in patients with severe head injury. Twenty patients with severe head trauma (Glasgow Coma Scale [GCS] less than or equ al to 8) underwent 24-hour electrocardiogram recording 1 day after trauma a nd again 48 hours after withdrawal of sedative drugs. Heart rate variabilit y was assessed, in both time domain and spectral domain. The authors initia lly compared ton Day 1) HRV in patients who processed to brain death to HRV in survivors; then during the awakening period compared HRV in surviving p atients with good recovery (GCS greater than or equal to 10) to HRV in pati ents characterized by a worsened neurologic state (GCS < 10). Statistical a nalysis used the Kruskal-Wallis test, P < .05. To assess whether HRV could predict evolution to brain death, receiver operating characteristic (ROC) c urves were generated the day after trauma for Total Power, natural logarith m of high-frequency component of spectral analysis (LnHF), natural logarith m of low-frequency component of spectral analysis (LnLF), and root mean squ are for successive interval differences (rMSSD). Seven patients died betwee n Day 1 and Day 5 after trauma, Six of those had progressed to brain death. In these six patients, at Day 1, Global HRV and parasympathetic tone were significantly higher. Referring to the area under the rMSSD ROC curve, HRV might provide useful information in predicting early evolution of patients with severe head trauma. During the awakening period, global HRV and the pa rasympathetic tone were significantly lower in the worsened neurologic stat e group. In conclusion, HRV could be helpful as a predictor of imminent bra in death and a useful adjunct for predicting the outcome of patients with s evere head injury.