Evolution of somatosensory evoked potentials after cardiac arrest induced hypoxic-ischemic injury

Aim: We tested the hypothesis that early recovery of cortical SEP would be associated with milder hypoxic-ischemic injury and better outcome after resuscitation from CA. Methods: Sixteen adult male Wistar rats were subjected to asphyxial cardiac arrest. Half underwent 7. min of asphyxia (Group CA7) and half underwent 9. min (Group CA9). Continuous SEPs from median nerve stimulation were recorded from these rats for 4. h immediately following CA, and at 24, 48, and 72. h. Clinical recovery was evaluated using the Neurologic Deficit Scale. Results: All rats in group CA7 survived to 72. h, while only 50% of rats in group CA9 survived to that time. Mean NDS values in the CA7 group at 24, 48, and 72. h after CA were significantly higher than those of CA9. The N10 (first negative potential at 10. ms) amplitude was significantly lower within 1. h after CA in rats that suffered longer CA durations. SEPs were also analyzed by separating the rats into good (NDS ≥ 50) vs. bad (NDS <50) outcomes at 72. h, again showing significant difference in N10 and peak-to-peak amplitudes between the two groups. In addition, a smaller N7 potential was consistently observed to recover earlier in all rats. Conclusions: The diminished recovery of N10 is associated with longer CA times in rats. Higher N10 and peak-to-peak amplitudes during early recovery are associated with better neurologic outcomes. N7, which may represent thalamic activity, recovers much earlier than cortical responses (N10), suggesting failure of thalamocortical conduction during early recovery.