ANAESTHETICS AND THE “MOLECULAR LUNG”

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Abstract
In six unpremedicated adult female patients during anaesthesia with the anaesthetic agent enflurane (Ethrane), measurements of cardiac output and pulmonary venous admixture were obtained at three levels of arterial carbon dioxide tension (means 18.2, 39.9, and 57.6 mm Hg respectively) during constant volume mechanical ventilation. Cardiac output was well maintained (means 4.70, 5.03, and 7.94 l./min during hypo-carbia, eucarbia, and hypercarbia respectively). The response to carbon dioxide resembled that seen in awake man; suggesting that, in contrast to halothane anaesthesia, myocardial contractility and autonomic reactivity were essentially normal. Pulmonary venous admixture remained constant (means 8.5,8.5, and 8.6 per cent during hypocarbia, eucarbia, and hypercarbia respectively). Changes in the alveolar-arterial oxygen tension difference (mean A-a Po2 diff.: hypocarbia 90; eucarbia 82; and hypercarbia 61 mm Hg) were attributable to increased mixed venous oxygen tension as a result of changes in cardiac output while the oxygen consumption remained constant.

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