Multimodel quantitative analysis of somatosensory evoked potentials after cardiac arrest with graded hypothermia.

Cardiac arrest (CA) is one of the most prominent causes of morbidity and mortality in adults. Therapeutic hypothermia (TH) is a recommended treatment to improve survival and functional outcome following CA, however, it is unclear what degree of TH is most beneficial. It has been suggested that TH of 33°C provides no survival or outcome benefits over TH of 36°C. Additionally, there is a lack of verified objective quantitative prognostic tools for comatose CA patients under TH. In this study, we calculated three quantitative markers of somatosensory evoked potentials (SSEP) to examine their potential to track recovery in the early period following CA under graded TH. A total of 16 rats were randomly divided among 4 temperature groups (n=4/group): normothermia (N0, 36.5-37.5°C), hypothermia 1 (H1, 30-32°C), hypothermia 2 (H2, 32-34°C) and hypothermia 3 (H3, 34-36°C). All rats underwent a 15min baseline SSEP recording followed by 9min asphyxial-CA, resulting in severe cerebral injury, and immediate temperature management following resuscitation for 6 hours. SSEP recordings were maintained in 15 min intervals from 30min-4hrs after resuscitation. The N10 amplitude, N10 latency and quantitative SSEP phase space area (qSSEP-PSA) were calculated for the early recovery period and normalized to their respective baselines. Functional recovery was determined by the neurological deficit scale (NDS). N10 amplitude was significantly larger in H1, H2 and H3 compared to N0. N10 latency was significantly longer in H1 than all temperature groups and all hypothermia groups had significantly longer latencies than N0. qSSEP-PSA had significantly better recovery in H1 and H2 than N0. Animals with good outcome (72hr NDS>50) had better recovery of all markers. N10 amplitude was significantly correlated with N10 latency and qSSEP-PSA. The results importantly demonstrate that quantified SSEPs have the potential to objectively track recovery following CA with graded TH.