Continuous ketamine infusion for one- lung anaesthesia

Abstract

The mechanism which normally affects distribution of blood flow through unventilated areas of the lung is hypoxic pulmonary vasoconstriction; this acts to divert the blood to well ventilated alveoli, resulting in a better ratio of ventilation to perfusion.Several reports have focused attention on the reduction or abolition of this reflex in the unventilated lung by most of the volatile anaesthetic agents used in clinical practice. This response was not abolished by the intravenous anaesthetic agents.One hundred and ten patients undergoing elective pulmonary resection were studied to evaluate the effect of a continuous infusion of ketamine during one-lung anaesthesia, by observing the changes in Pao~aS a reflection of shunt. Ketamine was chosen as the intravenous agent for its positive inotropic and chronotropic action. Additionally, by providing both analgesia and hypnosis, we were able to admininster inspired oxygen concentrations of 50-100 per cent without concern that the patient might have recall for events during operatior,We have demonstrated that in all cases a Pao2 in excess of 9.31 kPa (70 ton-) was achieved with ketamine and Flo~ 1.0 as well as an increase in shunt fraction from 25.9 per cent (Ftoz0.5) to 36.0 per cent (Flo~ 1.0).We feel that ketamine provides a satisfactory alternative to the volatile agents for one-lung anaesthesia in patients where relative hypoxaemia might be unacceptable during operation.ONE LONe VENTILATION with a high inspired oxygen fraction, a volatile anaesthetic agent and a muscle relaxant is commonly used for endobronchial anaesthesia, despite the fact that this technique has been associated with significant arterial hypoxaemia (Pao2 less than 9.33 kPa (70 torr)) in 15-25 per cent of cases. '-3 This figure agrees with our own review of 100 cases of pulmonary resection for carcinoma anaesthetized with halothane and Flo2 1.0 during one-lung anaesthesia, where the Pao2 was less than 9.33 kPa (70 torr) in 20 per cent. The main factors contributing to this arterial hypoxaemia are: (1) Excessive pulmonary shunting in the unventilated, non-dependent lung. 4-6 (2) The development of atelectatic areas in the ventilated dependent lung, secondary to a reduction in functional residual capacity and increase in airway closure, leading to a relative mismatching of ventilation and blood flow with an increase in venous admixture. 6-8 (3) A reduction in cardiac output due to anaesthetic agents, 9-It mechanical ventilation, 6,~:'~3 and manipulations during operation.The major cause of hypoxaemia during onelung anaesthesia is persistence of blood flow through the unventilated lung. Hypoxic pulmoAvron I. Weinreich, M.D., Associate Clinical Professor;

Predicting arterial oxygenation during one-lung anaesthesia

“…Previously, it was thought that this was not possible. 7 There is no consensus on the intraoperative PaO 2 value that defines hypoxaemia. Various authors have implied that the minimal acceptable level is between 50-80 mmHg during OLA.…”