Minimum alveolar concentration of isoflurane for tracheal extubation in deeply anesthetized children

The end-tidal anesthetic gas concentration required to prevent the anesthetized patient from coughing or moving during or immediately after tracheal extubation is not known.

We studied 19 nonpremedicated children between 4 and 9 yr of age (5.5 +/- 1.8, mean +/- standard deviation), ASA physical status 1 or 2, undergoing muscle surgery for correction of strabismus. General anesthesia was induced by a mask using halothane, nitrous oxide, and oxygen, and the trachea was intubated. Anesthesia was maintained with either isoflurane, nitrous oxide, and oxygen (12 patients), or isoflurane, air, and oxygen (7 patients). However, nitrous oxide was discontinued before the end of surgery. At the end of surgery, a predetermined end-tidal isoflurane concentration was achieved, a steady state maintained for at least 10 min, and the trachea was extubated. In patients who coughed or bucked on the endotracheal tube during suctioning of the stomach or pharynx, or who moved or coughed within 1 min of tracheal extubation, or who developed breath-holding or laryngospasm after tracheal extubation, extubation was considered as unsatisfactory. Results were plotted as satisfactory or unsatisfactory extubation versus end-tidal isoflurane concentration. End-tidal concentration of isoflurane at which tracheal extubation was accomplished in 50% of patients satisfactorily was estimated by probit analysis.

The minimum alveolar concentration of isoflurane at which 50% of patients had satisfactory tracheal extubation was found to be 1.27% (standard error +/- 0.04%).

In 50% of anesthetized children age 4-9 yr tracheal extubation may be accomplished without coughing or moving at 1.27% end-tidal isoflurane concentration.