PHYSIOLOGICAL CHANGES ASSOCIATED WITH UNILATERAL PULMONARY VENTILATION DURING OPERATIONS ON THE LUNG

Abstract

To FACILITATE the work of the thoracic surgeon it has become accepted procedure in certain circumstances to collapse the diseased lung being operated upon. To accomplish this, the technique most frequently used by the anaesthetist in this country calls for the insertion of a double lumen bronchial tube. This makes it possible to isolate the intact dependent lung from the diseased upper one and thus to prevent contamination of the sound lung. On the other hand, collapse of the uppermost lung causes serious functional respiratory modifications which call for special compensatory measures to avoid hypoxaemia. The purpose of this report is to stress again that optimum maintenance of oxygenation is crucial to the prevention of sustained cellular hypoxia and to show how this may be achieved. METHODS Eighteen patients were studied during routine operations on the lung carried out in the full lateral position. Pertinent clinical information on the patients included in this series is listed in Table I. Premedication consisted of meperidine, 50 to 75 mg and atropine sulfate 0.4 mg administered intramuscularly one hour before the operation. After induction with thiopentone 4 to 6 mg/kg body weight, succinylcholine 2 mg/kg of body weight was given intravenously and the larynx was sprayed with 4 per cent lidocaine. After passage of the bronchial tube its position was checked by auscultation before and after posturing of the patient in the lateral position. Anaesthesia was maintained with halothane 0.5 to 1.5 per cent vapourized in 95.5 to 98.5 per cent oxygen. Nitrous oxide may be added later, depending upon Pao= levels. Muscular relaxation was maintained by intermittent doses of D-tuboeurarine. The lungs were ventilated with a volume-preset Engstrom ventilator at a frequency of 16 cycles per minutes. A tidal volume of 19. ml/kg body weight was used. Following induction, the radial artery was cannulated percutaneously with a 90-gauge teflon catheter. Evaluation of pertinent parameters was done on two occasions during the operation. The first assessment was carried out after the patient had been postured in the lateral position and the pleural cavity had been opened for more than ten minutes with both lungs ventilated and perfused. At this time three samples were collected for analysis. A sample of venous blood from the pulmonary artery was taken directly by the surgeon, one of arterial blood was drawn from the previously cannulated radial artery and a sample of mixed expired