The theoretical basis for using apnoeic oxygenation via the non-ventilated lung during one-lung ventilation to delay the onset of arterial hypoxaemia.

At the time one-lung ventilation is initiated, nitrogen from the atmosphere may enter the non-ventilated lung via a double-lumen tube connector that has been left open to air, even momentarily. Ongoing oxygen uptake from the non-ventilated lung raises the partial pressure of nitrogen. This should lead to activation of hypoxic pulmonary vasoconstriction and a reduction in intra-pulmonary shunting. However, in spite of this, some patients still become hypoxaemic. In such cases, it may be advantageous to have excluded nitrogen from the non-ventilated lung by connecting it to an oxygen source at ambient pressure. Ongoing apnoeic oxygenation, while the airways are patent, and as the lung collapses, should delay the onset of arterial desaturation. In this paper we review the theoretical basis for apnoeic oxygenation during one-lung ventilation, and in particular on oxygen uptake by the non-ventilated lung prior to and during its subsequent collapse.