• P Gauneau, P Alfonsi, P Duvaldestin, F Guirimand, and M Chauvin.
• Département d'Anesthésie-Réanimation, Hôpital Ambroise-Paré, Boulogne-sur-Seine.
• Ann Fr Anesth Reanim. 1989 Jan 1;8(5):493-6.

AbstractHalothane was administered to 10 ASA or 11 patients undergoing elective peripheral surgery. The vaporizer was included in the delivery gas line of the semiclosed system. Löwe's square root of time model of uptake was used to calculate the required doses of halothane. In order to reach an alveolar concentration corresponding to 1.3 MAC, 0.5 vol % of halothane (1.3 MAC) combined with 60 vol % of nitrous oxide (0.6 MAC) were administered at a fresh of 20 ml.kg-1. The ventilation controlled in order to maintain end-tidal CO2 partial pressure at a 5 vol %. Inspiratory halothane concentration was measured during the inspiratory plateau. The alveolar fraction was defined as being the mean end expiratory concentration. The latter was well above the theoretical values during the first 9 min of anaesthesia (0.85% at the 4 th min). This concentration then decreased progressively, becoming less than the expected value after 15 min (0.4% at the 30 th min). Löwe's model would therefore seem to lead to a gross overestimation of the amount of anaesthetic vapour to be delivered to a patient at the beginning of anaesthesia, and an underestimation thereafter.

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