PULMONARY CLEARANCE OF ANAESTHETIC AGENTS A Theoretical Study BY

The pulmonary clearance of anaesthetic agents (Q) represents a useful index of their elimination from the lungs. Its value depends on pulmonary blood flow (<J), alveolar ventilation (VA), and anaesthetic blood solubility (X) according to equation: Cl = (VAQ)/(VA + XQ). When the alveolar ventilation and pulmonary blood flow are constant the pulmonary clearance of the anaesthetic depends on its blood solubility. In this case the lower the blood solubility is, the higher the value of pulmonary clearance becomes. For each anaesthetic agent a change in alveolar ventilation or in pulmonary blood flow will produce a change in pulmonary clearance which in its turn depends on anaesthetic blood solubility. When X = (VA/Q) 2 a change in alveolar ventilation or in pulmonary blood flow will affect the pulmonary clearance to the same extent. When the anaesthetic blood solubility value is higher than (VA/Q)a, its pulmonary clearance is predominantly affected by alveolar ventilation, and when anaesthetic blood solubility is lower than (VA/Q) 3 its pulmonary clearance is predominantly dependent on pulmonary blood flow. Changes in pulmonary clearance produced by changes in alveolar ventilation (9C1/3VA) are larger with halothane, nitrous oxide and cyclopropane than with agents of greate