Cerebral function analysis during deep hypothermia and total circulatory arrest in infant lambs.

Deep hypothermia with total circulatory arrest is an important technique in the surgical treatment of complex congenital heart defects. However, the clinical use of this technique has been accompanied by occasional postoperative neurological abnormalities. Twenty new born lambs (four groups of five) were subjected to deep hypothermia (15 degrees C) and circulatory arrest for 30 min, 45 min, 60 min and 90 min respectively. Their brain electrical response was monitored by means of the Cerebral Function Analysing Monitor (CFAM), which produces a detailed analysis of the electroencephalogram amplitude and analyses the frequency of the waveforms into standard, beta, alpha, theta, and delta bands. After induction of circulatory arrest both the voltage and frequency recordings became isoelectric within 30-180 seconds and remained flat for the duration of the arrest. During the rewarming phase of the latency of time to initial appearance of electrical activity and continuous CFAM recording showed a good correlation with the duration of arrest and also a significant increase (p less than or equal to 0.001) when the circulatory arrest was maintained beyond 45 min. These findings suggest an increasing risk of neurologic damage when the arrest period is longer than 45 min.