Early electrophysiologic markers predict functional outcome associated with temperature manipulation after cardiac arrest in rats

OBJECTIVE:: Therapeutic hypothermia after cardiac arrest improves survival and functional outcomes, whereas hyperthermia is harmful. The optimal method of tracking the effect of temperature on neurologic recovery after cardiac arrest has not been elucidated. We studied the recovery of cortical electrical function by quantitative electroencephalography after 7-min asphyxial cardiac arrest, using information quantity (IQ). DESIGN:: Laboratory investigation. SETTING:: University medical school and animal research facility. SUBJECTS:: A total of 28 male Wistar rats. INTERVENTIONS:: Using an asphyxial cardiac arrest rodent model, we tracked quantitative electroencephalography of 6-hr immediate postresuscitation hypothermia (at 33°C), normothermia (37°C), or hyperthermia (39°C) (n = 8 per group). Neurologic recovery was evaluated using the Neurologic Deficit Score. Four rats were included as a sham control group. MEASUREMENTS AND MAIN RESULTS:: Greater recovery of IQ was found in rats treated with hypothermia (IQ = 0.74), compared with normothermia (IQ = 0.60) and hyperthermia (IQ = 0.56) (p < .001). Analysis at different intervals demonstrated a significant separation of IQ scores among the temperature groups within the first 2 hrs postresuscitation (p < .01). IQ values of >0.523 at 60 mins postresuscitation predicted good neurologic outcome (72-hr Neurologic Deficit Score of ≥60), with a specificity of 100% and sensitivity of 81.8%. IQ was also significantly lower in rats that died prematurely compared with survivors (p < .001). IQ values correlated strongly with 72-hr Neurologic Deficit Score as early as 30 mins post-cardiac arrest (Pearson's correlation 0.735, p < .01) and maintained a significant association throughout the 72-hr experiment. No IQ difference was noted in sham rats with temperature manipulation. CONCLUSIONS:: The enhanced recovery provided by hypothermia and the detrimental effect by hyperthermia were robustly detected by early quantitative electroencephalographic markers. IQ values during the first 2 hrs after cardiac arrest accurately predicted neurologic outcome at 72 hrs.