Acute hypercapnic respiratory failure
Acute hypercapnic (type II, ventilatory) respiratory failure is alveolar hypoventilation with arterial PCO2 above 45 mm Hg and acidemia, from pump failure or dead-space ventilation. Confirm with an arterial blood gas in every suspected patient, then treat the precipitant while titrating noninvasive or invasive ventilation to reverse the acidosis.
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What this article covers
- Overview
Ventilatory (type II) failure from inadequate alveolar ventilation: occurs when ventilation cannot clear metabolically produced CO2, so arterial PCO2 rises; distinct from acute hypoxemic respiratory…
- Epidemiology
COPD exacerbation is the leading precipitant in the hospital and ICU, driving the decision for noninvasive ventilation.
- Risk factors
Advanced COPD, especially with a prior hypercapnic exacerbation or pulmonary hypertension.
- Pathophysiology
Decreased respiratory drive: central causes (stroke, encephalitis, meningitis, hypothermia, hypothyroidism, anesthesia, central apnea) or sedating drugs blunt the respiratory center's response to rising CO2.
- Clinical features
Somnolence and altered mental status from CO2 narcosis, sometimes with myoclonic jerks, are the hallmark but nonspecific presenting features.
- Differential diagnosis
Acute hypoxemic (type I) respiratory failure: hypoxemia from shunt, often refractory to oxygen alone, without significant hypercapnia until late, unlike the dead-space/pump-failure physiology here.
- Diagnosis
Confirm with an arterial blood gas: acute hypercapnia is PaCO2 above 45 mm Hg with pH below 7.35 and near-normal bicarbonate (22-26 mEq/L); chronic hypercapnia shares the PaCO2 threshold but has pH…
- Management
First, assess airway protection, mental status, and hemodynamic stability.
- Complications
Respiratory arrest from progressive CO2 narcosis, particularly if oxygen is given without addressing the underlying hypoventilation in a neuromuscular or opioid-related cause.
- Prognosis
Early, well-timed NPPV for COPD exacerbation with hypercapnic acidosis reduces intubation, hospital stay, and mortality; delayed intubation after a failed trial raises mortality risk, making the 2-hour reassessment the key decision point.
- Prevention
Target SpO2 88% to 92% with supplemental oxygen in COPD or other chronic hypercapnic disease to avoid oxygen-driven worsening of hypercapnia.
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