Pulmonary arterio‐venous fistula

Abstract

Anaesthetists are familiar with the Riley concept' of lung function which imagines that functioning alveoli all have the same ratio of ventilation to perfusion, and that a proportion of the blood flowing through the lungs takes no part in gas exchange whatever. During the breathing of 100% oxygen this blood shunting is attributed to anatomical pathways and perfusion of non-ventilated alveoli, while during air breathing, alveolar abnormalities of the ratio of ventilation to perfusion, in addition to shunting, constitute the venous admixture occurring through the lungs. The size of the shunt or venous admixture as a percentage of the total flow can be calculated by using the Shunt Equation.In an awake, normal man, at rest, that proportion of the cardiac output which in the Riley idiom takes no part in gas exchange amounts to a mean of 6.4Z3 when breathing air, while in the anaesthetised subject this venous admixture increases to 9-21 %." When ventilation is controlled, when the patient's position is altered and when disturbances of the chest mechanics by thoracotomy take place, further changes in the size of the lung shunt occur. The presence of pulmonary arteriovenous fistulae inevitably gives rise to an additional proportion of the cardiac output which does not take part in gas exchange, and the opportunity has been taken, when a patient suffering from such a condition presented for thoracotomy, to study the changes in venous admixture at various stages during the procedure.Preoperative data A male patient, aged 27 years, and weighing 62 kg, presented in hospital after repeated haemoptyses. He was known to have pulmonary arterio-venous fistulae and at the age of 16 had undergone a left upper lobe resection for this disease. He had also suffered from nose bleeds in the past but gave no history suggesting the presence of fistulae elsewhere or the occurrence of paradoxical emboli passing through the lungs. There was no family history of a similar condition.On physical examination the patient was seen to have marked central cyanosis and clubbing of fingers and toes. There were no thrills or murmurs over the chest, no other abnormalities, and particularly no evidence of generalised telangiectasia of the mucous membranes.Investigations showed : haemoglobin 20.3 g/dl and PCV 54.4%; the platelet count was 247 x lo9/] and coagulation studies were normal. Pulmonary function studies showed a FVC 4.75 litre, FEV, 4.1 litre and PEFR of 585 I/min and the ECG was normal. Right heart catheterisation and pulmonary angiography revealed the presence of multiple pulmonary arterio-venous fistulae, most numerous in the right lung and especially in the right middle lobe, while the SurgeryA right thoracotomy was undertaken to ligate some of the most accessible fistulae near the surface of the right lung in the expectation that the shunt would be reduced and the hazard of bleeding diminished.Two large fistulae, one in the middle lobe and one in the posterior segment of the upper lobe were dissected out along with the related vessels an...