High-dose ketamine hydrochloride maintains somatosensory and magnetic motor evoked potentials in primates

Monitoring the descending neural motor volleys (MEPs), in comparison to muscle action potentials, allows sensitive motor assessment under anesthesia irrespective of the use of muscular blockade and status of skeletal musculature. Ketamine hydrochloride (KH) had preserved muscle MEPs on a pre-established primate model. The present work examines the effect of incremental hypnotic KH dosages thoracic neural on somatosensory (SEP) and MEPs recorded epidurally in response to transcranial magnetic stimulation (TMS). Through a small thoracic T11-T12 laminotomy, an insulated double bipolar electrode was inserted epidurally and cephalad in seven cynomolgus monkeys. Thoracic spinal TMS-MEPs, and SEPs, were tested against graded increase of KH doses (0.01, 0.018, 0.032, 0.056, 0.1, and 0.18 mg kg(-1) min(-1) i. v. infusion). The direct (D-) and indirect (I-) epidural MEP peaks were well-defined under sole KH infusion. The waveforms were consistent at various dosages. At the highest cumulative dose (0. 18 mg kg(-1) min(-1) total 6.5 mg kg(-1) over 150 min), I-5 was host and I-3 and I-4 latencies were delayed. The scalp and spinal SEP showed no significant change. Recording of both neural D- and I- MEPs and SEPs is feasible under high sole i.v. KH. It is the first agent to maintain up to four later I-1 peaks. The reproducibility of both modalities is unquestionable under KH-based deep anesthesia. This reflects the maintenance of state of neural excitability under KH.