Clonidine administration during intraoperative monitoring for pediatric scoliosis surgery: Effects on central and peripheral motor responses

To study the effect of clonidine administrated as a co-analgesic during scoliosis surgery, on the neuromonitoring of spinal motor pathways. Using standardized intraoperative monitoring, we compared the time course of peripherally and transcranially electrically evoked motor potentials (TcEMEPs) before and after injection of a single bolus of clonidine in children under total intravenous anesthesia (TIVA). MEP data were obtained from 9 patients and somatosensory evoked potentials (SSEPs) were obtained from 2 patients. The potential effect of clonidine on mean blood pressure (BP) was controlled. TcEMEPs from upper and lower limbs rapidly showed significant drops in amplitude after the injection of clonidine. Amplitudes reached minimal values within five minutes and remained very weak for at least 10–20minutes during which monitoring of the central motor pathways was severely compromised. SSEPs were not altered during maximal amplitude depression of the TcEMEPS. This is the first report showing that clonidine severely interferes with neuromonitoring of the spinal cord motor pathways. The results are discussed in light of the literature describing the effects of dexmedetomidine, another α-2 adrenergic agonist. The experimental and literature data point to central mechanisms taking place at both the spinal and cerebral levels. Therefore, clonidine as well as other α-2 adrenergic agonists should be used with extreme caution in patients for whom neuromonitoring of the motor pathways is required during surgery.