Differentials
Hyperventilation secondary to metabolic acidosis
SIGNS / SYMPTOMS
Diabetic ketoacidosis and acidosis from other causes (e.g., aspirin toxicity) have laboured (Kussmaul) breathing.
INVESTIGATIONS
Arterial blood gas analysis shows metabolic acidosis (low pH, low bicarbonate) and hyperventilation (decreased PaCO₂). Pulse oximetry shows normal oxygen saturation.
Hyperventilation secondary to anxiety
SIGNS / SYMPTOMS
Acute panic attack and other forms of anxiety often present with marked respiratory distress characterised by "air hunger" or a feeling of dyspnoea.
INVESTIGATIONS
Arterial blood gas analysis shows respiratory alkalosis with an elevated pH and decreased PaCO₂. Pulse oximetry shows normal oxygen saturation.
Sleep apnoea
SIGNS / SYMPTOMS
Marked sleep apnoea may present with hypoventilation and prolonged apnoeic spells while sleeping.
INVESTIGATIONS
During apnoeic spells, arterial blood gas analysis may show decreased PaO₂ and elevated PaCO₂ and pulse oximetry shows hypoxia. When awake and stimulated by daily routines, arterial blood gases are often normal. Sleep apnoea is diagnosed by a formal sleep study.
Obesity
SIGNS / SYMPTOMS
Marked obesity may present with hypoventilation and prolonged apnoeic spells while sleeping.
INVESTIGATIONS
During apnoeic spells, arterial blood gas analysis may show decreased PaO₂ and elevated PaCO₂ and pulse oximetry shows hypoxia. When awake and stimulated by daily routines, arterial blood gases are often normal.
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