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Blood gases,

Blood gases are commonly measured, and with a logical, systematic approach they may be easily interpreted. Blood gases provide information about: ventilation oxygenation and alveolar-arterial O2 gradient acid-base status Note that to convert from kiloPascals to millimetres of mercury, multiply by 7.5. The normal range for PaO2 is 11.3-13.3 kPa (82,5 to 97mmHg). A partial pressure less than 8 kPa (60mmHg) defines respiratory failure. Arterial hypoxaemia is commonly due to pulmonary disease: poor gas transfer: type I respiratory failure PaCO2 is typically low hypoventilation: type II respiratory failure PaCO2 is typically raised Arterial hypoxaemia may occur when the lungs are normal: low inspired partial pressure of oxygen e.g. altitude ventilation-perfusion mismatch right to left shunts: congenital heart disease arteriovenous malformation of the pulmonary vessels Measurement of the alveolar-arterial (A-a) gradient is useful in hypoxic patients and may help to distinguis