#### Learning points You have been called to see a 69 year old man on a surgical ward because he has become drowsy and short of breath. He had a large bowel resection the previous day, has a background of type 2 diabetes, and is a current smoker. On examination his arterial blood pressure is 104/65 mm Hg, his heart rate 132 beats/min and irregular, and his respiratory rate 22 breaths/min; his oxygen saturations with pulse oximetry are 94% on supplemental oxygen via a 40% Venturi-type mask. He is slightly confused and is complaining of abdominal pain despite using patient controlled analgesia with morphine. His chest is clear on auscultation. You take a blood specimen for analysis of arterial blood gases for rapid biochemical evaluation to guide diagnosis and initial management. Table 1⇓ shows the results. It is important to adopt a systematic approach to interpreting results of arterial blood gases, as outlined in table 2⇓, preceded by a brief history and focused clinical examination. View this table: Table 1 Report of arterial blood gases for the hypothetical patient described View this table: Table 2 Guide to systematic approach to analysis of a report of arterial blood gases ### Step 1: Assess oxygenation Arterial oxygen tension (PaO2) is the partial pressure of oxygen in arterial blood. The main determinants of PaO2 are the inspired …