The Effect of High Dose Sodium Thiopental on Brain Stem Auditory and Median Nerve Somatosensory Evoked Responses in Humans

Open Access
Publisher Website
Google Scholar
Abstract
Median nerve somatosensory evoked potientials (MnSSEPs), brain stem auditory evolked responses (BAERs) and the cortical EEG were recorded in 6 patients during a 62-min infusion of sodium thiopental (STP) at a rate of 1.25 mg .cntdot. kg-1 .cntdot. min-1 (total dose, 77.5 mg/kg). The EEG became isoelectric after 22 .+-. 8 (SD) min of STP infusion. Dose-related changes in the latencies and amplitudes of various evoked response wave forms were observed. In no instance was any component of either the MnSSEP or the BAER rendered unobtainable by STP adminstration. For the MnSSEP, progressive increases in the central conduction time (5.33 .+-. 0.41 ms preinduction vs. 7.46 .+-. 1.2 ms at t [time] = 60 min) and in the latency of the cortical primary specific complex were observed simultaneously with significant reductions in the amplitude of the latter (2.10 .+-. 0.85 .mu.V preinduction vs. 0.85 .+-. 0.55 .mu.V at t = 60 min). Changes in the latency and amplitude of the response recorded over the upper cervical spine (C2) were not statistically significant in this small population. For the BAER, progressive and significant increases in the latencies of Waves I, III, V (e.g., Wave V latency: 6.16 .+-. 0.24 vs 6.87 .+-. 0.31 ms) and in the I-III, III-V and the I-V interwave latencies were observed. The amplitudes of the BAER components were not significantly altered. The administration of a dose of STP in excess of twice that required to produce EEG isoelectricity can be compatible with effective monitoring of MnSSEPs and BAERs. STP produces dose-related changes in both evoked response wave forms, which must be considered in the interpretation of responses elicited during STP anesthesia.