Ventilatory and arterial blood gas patterns in coma

Breathing pattern	Metabolic pattern	pH, PaCO₂, HCO₃	Specific conditions
Hyperventilation	Metabolic acidosis	pH <7.3, PaCO₂ <30 mmHg, HCO₃ <17 mmol/L	Uremia, diabetic ketoacidosis, lactic acidosis, salicylates, methanol, ethylene glycol.
Hyperventilation	Respiratory alkalosis	pH >7.45, PaCO₂ <30 mmHg, HCO₃ >17 mmol/L	Hepatic failure, acute sepsis, acute salicylate intoxication, cardiopulmonary states with hypoxemia, psychogenic causes.
Hypoventilation	Respiratory acidosis	pH <7.35 (if acute), PaCO₂ >90 mmHg, HCO₃ >17 mmol/L	Respiratory failure from central (eg, brain or spinal cord) or peripheral nervous system disease, chest conditions or deformities. Coma only with severe hypercarbia.
Hypoventilation	Metabolic alkalosis	pH >7.45, PaCO₂ >45 mmHg, HCO₃ >30 mmol/L	Vomiting, alkali ingestion. Usually no impairment of consciousness; if so, suspect psychogenic unresponsiveness or additional cause.

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