Transtracheal electrical stimulation of the spinal cord for intraoperativemonitoring of the motor pathway

Because of the suppressant effects of anesthetic drugs and muscle relaxants on motor responses elicited by either magnetic or electrical transcranial stimulation, intraoperative monitoring of the motor system, and especially monitoring of lower limb function, presents many difficulties. The upper part of the spinal cord was stimulated in 14 anesthetized and rel axed dogs with a cathode attached to the intratracheal tube and an anode fi xed above the upper cervical spinous processes. Action potentials evoked by single and serial stimuli were recorded from the exposed right femoral ner ve and quadriceps muscle Averaging was necessary for serial stimulations. Reproducible early and late responses to both single and serial stimulation s were recorded during regular anesthesia. The origin of the different resp onses is discussed. Transtracheal stimulation of the spinal cord is easy to perform and the res ponses recorded from the peripheral nerve or limb muscle are well reproduci ble in regular anesthesia. The method seems to be appropriate for intraoper ative monitoring of the thoracolumbar spine.