Acute effects of 40% oxygen supplementation in adults with cyanotic congenital heart disease.

T his study examined the acute effects of 40% oxygen supplementation in adults with cyanotic congenital heart disease (CCHD). These young patients have significant morbidity and premature mortality, relating in part to their cyanotic state. We have shown that systemic arterial oxygen saturation (SAOS) increases significantly when these patients are administered 40% oxygen, irrespective of their underlying congenital cardiovascular diagnosis or the presence of pulmonary hypertension. Forty per cent oxygen supplementation increased SAOS above 85% in the majority of patients, with none having an SAOS less than 80%. This improvement in saturation may be clinically important because significant erythrocytosis is unusual if SAOS is greater than 85% and it is this physiological adaptation which is responsible for many of the symptoms experienced by these patients. About 10% of adults with congenital heart disease are cyanosed and although their functional capacity is good up to the third decade, it declines along with quality of life thereafter when complications and symptoms related to the cyanotic state become more frequent. Cyanosis occurs when hypoxaemia stimulates erythropoiesis causing erythrocytosis. This re-establishes tissue oxygen delivery at the expense of an elevated haematocrit and leads to symptoms including, headaches, impaired mentation, lassitude, and myalgia, all of which have an impact on quality of life and physical ability. In addition to these hyperviscosity symptoms, there is a direct relation between SAOS and exercise capacity in these patients and a low SAOS is a recognised risk factor for death. The fundamental physiological fault in CCHD is the diversion of systemic venous blood into the systemic arterial circulation, therefore SAOS is determined by the amount of pulmonary blood flow and the degree of right to left shunting. It is generally believed that pulmonary vascular reactivity in adults with CCHD is negligible and therefore the use of pulmonary vasodilators, such as supplemental oxygen to increase oxygen saturation, is not advocated. In the absence of evidence to support oxygen therapy it is felt the risk of mucosal dehydration and epistaxis outweighs any benefits. Patients who use home oxygen (25–40%) however, do report an improvement in symptoms. We therefore examined the acute effects of 40% oxygen supplementation on SAOS in 29 adults with CCHD.