EFFECT OF LIDOCAINE ON SOMATOSENSORY EVOKED-RESPONSE AND CEREBRAL BLOOD-FLOW AFTER CANINE CEREBRAL AIR-EMBOLISM

Background and Purpose: Victims of air embolism often recover rapidly on hyperbaric treatment then deteriorate again, even if hyperbaric treatment is continued. In previous animal experiments, lidocaine has been shown to improve recovery of somatosensory evoked response amplitude after air embolism. However, animals in these experiments rarely deteriorated. We have shown that the induction of air embolism and transient hypertension in canines produces deterioration despite hyperbaric treatment, and we decided to test the effect of lidocaine on somatosensory evoked potential recovery and cerebral blood flow in this model. Methods: Dogs were treated with repeated doses of lidocaine or equivalent volumes of saline during hyperbaric therapy after internal carotid air embolism and transient hypertension. The investigators were unaware of treatment group assignment during the experiments. The amplitude of the median nerve somatosensory evoked potential and cerebral blood flow measured with carbon-14-labeled iodoantipyrine autoradiography were used to assess effect of therapy. Results: Lidocaine-treated dogs recovered 60+/-10% (mean+/-95% confidence limits) of the baseline somatosensory evoked potential amplitude 220 minutes after air embolism; saline-treated dogs recovered 32+/-10% (a significant difference at p<0.01). Lidocaine-treated dogs also had higher cerebral blood How values than saline-treated dogs 220 minutes after air embolism. Conclusions: Lidocaine ameliorated the delayed deterioration of evoked potential associated with air embolism and hypertension in this canine model. The improved cerebral blood flow may be a mechanism of action of lidocaine or an associated effect of improved neuronal survival.