Etomidate Augmentation of Scalp Recorded Somatosensory Waves: Time Course, Reproducibility, and Dose Effect

Abstract

Bolus etomidate (ETOM) transiently increases the amplitude of scalp recorded somatosensory evoked potentials (SSEP). The reproducibility of this augmentation and its dose-response relationship are unknown. In unpremedicated patients, we studied the effect on the SSEP of repetitive administration of single doses of ETOM (0.1 mg/kg, iv bolus) in six patients and increasing doses of ETOM in six additional patients. Anesthesia was induced with fentanyl (15–20 tg/kg, iv) plus thiopental (1–2 mg/kg, iv) and maintained with 0.4%–0.8% isoflurane in oxygen, and the surgical incision was infiltrated with bupivacaine (0.5% without epinephrine). ETOM administration was delayed for 30 min following anesthesia induction. In group 1, 0.1 mg/kg ETOM was administered iv as a bolus three times at 30 min intervals. In group 2, 0.05, 0.1, or 0.2 mg/kg was administered at 30-min intervals in random order in each patient. SSEP were measured immediately before and once each minute for 5 min after ETOM administration following nondominant median nerve stimulation. In group 3 (n = 5) the time of wave augmentation was determined using continuous SSEP stimulation following 0.2 mg/kg ETOM.

In group 1, administration of 0.1 mg/kg ETOM (three trials) increased the latency of N20 and P23 by 1.0–1.4 ms and 1.3–2.6 ms, respectively (P < 0.05). P15N20 amplitude was increased by about 50% (P < 0.05). and N20P23 amplitude increased to 174% of control (P < 0.05). The amplitude increase was similar during the three ETOM administrations for both P15N20 and N20P23. Latency remained elevated by about 1.5 ms and amplitude remained elevated (P15N20 = 138%; N20P23 = 150%) 5 min following injection. Mean arterial blood pressure (MABP) was unchanged by 0.1 mg/kg etomidate. In group 2, 0.05 mg/kg ETOM altered neither amplitude nor latency. However, 0.1 mg/kg and 0.2 mg/kg increased N20P23 amplitude to 161 ± 33 and 230 ± 10% of control (P < 0.05), respectively. N20 and P23 latency were increased by ETOM 0.1 mg/kg by about 1.0 ms, while 0.2 mg/kg increased N20 latency by 1.0 ms and P23 latency by 1.5 ms. In group 3, the time for SSEP augmentation to reach 50% of maximum was about 2 min. Bolus administration of ETOM (0.1 mg/kg) reproducibly increased SSEP amplitude, and a larger dose (0.2 mg/kg) further increased amplitude augmentation. Thus, intermittent injection of ETOM can be used to augment small SSEP waves with reproducible increases in wave amplitude.