S52 The effect of age on arterial oxygen content in patients with pulmonary arteriovenous malformations (PAVMs)

Introduction and objectives It is recognised that age-associated changes in the chest wall and lung parenchyma lead to decreased efficiency of ventilation and gas exchange, resulting in reduced arterial partial pressure of oxygen (PaO 2 ) and haemoglobin saturation (SaO 2 ). The total oxygen content of arterial blood (CaO 2 ) depends upon SaO 2 , as well as haemoglobin concentration. Our goal was to examine serial changes in arterial oxygen content with age in a cohort with hypoxaemia due to pulmonary arteriovenous malformations (PAVMs). Methods Retrospective longitudinal follow-up data was collected for 100 consecutive PAVM patients presenting to a tertiary care institutional clinic between 1984 and 2001, and reviewed until 2015. Subjects provided up to 30 (median 9) separate annual datasets. SaO 2 was measured by pulse oximetry in the supine and erect postures, and the mean SaO 2 was calculated after 7, 8, 9 and 10 min standing. Haematological and biochemical blood indices evaluated haemoglobin, haematinics, and iron indices. CaO 2 in mls of oxygen per dL (ml/dL) of blood was calculated using the equation: [SaO 2 (%) x haemoglobin (g/dL) X 1.34]/100. Data were analysed using STATA IC v13.1. Results Age and PAVM-treatment associated changes in SaO 2 were mostly accompanied by opposing changes in haemoglobin levels that maintained the CaO 2 . Two major patterns were observed. The first was the expected increase in haemoglobin with lower SaO 2 , due to secondary erthyrocytosis and polycythaemia. The second, less well recognised, was an increase in SaO 2 when haemoglobin fell, most commonly when subjects developed iron deficiency and anaemia. Nevertheless, excluding participants with iron deficiency, CaO 2 decreased with age (Figure 1, r 2 = -0.0654; p Conclusions The body maintains arterial oxygen content within a normal range using well-known erythropoeitic mechanisms in response to hypoxaemia. Despite this feedback mechanism, in patients with pulmonary arteriovenous malformations, overall arterial oxygen content still decreases with age.