Plasma Levels of Thiopental Necessary for Anesthesia

This study determined the plasma levels of thiopental necessary for anesthesia in human patients. In Group I, corneal reflex (CR) and trapezius muscle response (TMR) showed highly significant correlations (P For CR loss, thiopental requirements were 39.4 ± 2.5 μg/ml (mean ± SE) for total plasma thiopental and 5.9 ± 0.4 μg/ml for free plasma thiopental. For TMR loss, thiopental requirements were 42.4 ± 2.8 μg/ml for total plasma thiopental and 6.3 ± 0.6 μg/ml for free plasma thiopental. Nitrous oxide, 67 per cent, decreased these requirements 67–71 per cent. Age, sex, and weight of the patient and serum albumin level had little effect on thiopental requirements. Mean percentage of free thiopental was 14.4 ± 0.3 per cent of total. It is concluded that: 1) losses of corneal reflex, trapezius muscle response, and response to surgical stimulation all define essentially the same depth of thiopental anesthesia; 2) total plasma thiopental levels of 39–42 μg/ml and free plasma thiopental levels of 5.9–6.3 μg/ml produce surgical anesthesia in human subjects.