C5.8 Arterial blood gas measurement

Arterial blood gas analysis should be considered in all patients with severe disease, those being considered for domiciliary oxygen therapy (eg, whose FEV₁ is <40% predicted or <1 L, whose oxygen saturation as measured by pulse oximetry [SpO₂] is <92%), those with pulmonary hypertension, and those with breathlessness out of propor­tion to their clinical status). Respiratory failure is defined as a PaO₂ <60mmHg (8kPa) or PaCO₂ >50mmHg (6.7kPa). The latter is termed ‘ventilatory failure’ and is accompanied by either compensated (chronic) or uncompensated (acute) acidosis. Acute respiratory acidosis indicates a need for assisted ventilation.