AUTONOMIC CONTROL OF HEART-RATE AFTER BRAIN INJURY IN CHILDREN

Objectives: To study sequential changes in heart rate, respiratory rat e, blood pressure, heart rate power spectra, and plasma catecholamine concentrations in patients with acute brain injury and correlate these variables with the severity of neurologic dysfunction and patient out come. Design: Prospective, clinical study. Setting: Pediatric intensiv e care unit. Patients: Thirty-seven pediatric patients with acute brai n injury caused by trauma, anoxia/ischemia, hemorrhage, or infection, Interventions: None. Measurements and Main Results: We found significa nt associations between low-frequency (0.01 to 0.15 Hz) heart rate pow er and severity of neurologic dysfunction (as assessed by the admissio n Glasgow Coma Scale) (p < .001) and patient outcome (as assessed by t he Glasgow Outcome Scale) (p = .05). The admission (p = .05) and maxim um (p < .001) values for low-frequency heart rate power and the minimu m value for high-frequency (0.15 to 0.50 Hz) heart rate power obtained during hospitalization (p = .001) predicted an increased likelihood o f survival. Ten brain dead patients had significantly decreased low fr equency heart rate power (p = .008) and plasma norepinephrine (p = .01 5), epinephrine (p = .03), and dopamine (p = .04) concentrations when compared with six non-brain dead patients with a Glasgow Coma Scale sc ore of 3. Conclusions: Our results imply that autonomic nervous system control of heart rate is disrupted in proportion to the degree of neu rologic insult in children after acute brain injury. Thus, heart rate power spectral analysis and plasma catecholamine concentrations may pr ove to be useful adjuncts in determining severity of neurologic injury and prognosis for recovery in children suffering from brain injury. I n addition, these techniques may aid in the determination of brain dea th.