DETERMINANTS OF THIOPENTAL INDUCTION DOSE REQUIREMENTS

Dose requirements for thiopental anesthetic induction have significant age- and gender-related variability. We studied the association of th e patient characteristics age, gender, weight, lean body mass, and car diac output with thiopental requirements. Doses of thiopental, infused at 150 mg/min, required to reach both a clinical end-point and an ele ctroencephalographic (EEG) end-point were determined in 30 males and 3 0 females, aged 18-83 yr. Univariate least squares linear regression a nalysis revealed outliers in the relationships of age, weight, lean bo dy mass, and cardiac output to thiopental dose at clinical and EEG end points. Differential weighting of data points minimized the effect of outliers in the construction of a robust multiple linear regression mo del of the relationship between several selected independent variables and the dependent variables thiopental dose at clinical and EEG endpo ints. The multiple linear regression model for thiopental dose at the clinical end-point selecting the regressor variables age, weight, and gender (R2 = 0.76) was similar to that for age, lean body mass, and ge nder (R2 = 0.75). Thiopental dose at the EEG end-point was better desc ribed by models selecting the variables age, weight, and cardiac outpu t (R2 = 0.88) or age, lean body mass, and cardiac output (R2 = 0.87). Although cardiac output varied with age, age always remained a selecte d variable. Because weight and lean body mass differed with gender, th eir selection as variables in the model eliminated gender as a selecte d variable or minimized its importance.