What is type 2 respiratory failure?

Type 2 Respiratory Failure

Type 2 respiratory failure is defined by a PaO₂ <8 kPa (60 mmHg) AND a PaCO₂ >6 kPa (45 mmHg), representing failure of ventilatory pump function that leads to inadequate elimination of carbon dioxide. 1

Definition and Key Characteristics

• Type 2 respiratory failure is characterized by hypoxemia (PaO₂ <8 kPa or 60 mmHg) combined with hypercapnia (PaCO₂ >6 kPa or 45 mmHg) 1, 2
• It differs from Type 1 respiratory failure, which features hypoxemia with normal or low carbon dioxide levels 2
• The primary pathophysiological mechanism is alveolar hypoventilation, leading to carbon dioxide retention 1
• This condition represents a failure of the ventilatory pump function, resulting in inadequate elimination of CO₂ produced by metabolism 1

Common Causes

• Chronic Obstructive Pulmonary Disease (COPD) exacerbations are a leading cause 2, 3
• Neuromuscular disorders affecting respiratory muscles 2
• Chest wall deformities such as scoliosis and thoracoplasty 4, 2
• Drug overdoses affecting respiratory drive 5
• Central nervous system events impairing respiratory control 5
• Obesity hypoventilation syndrome 2

Pathophysiological Mechanisms

• Alveolar hypoventilation is the primary mechanism, where minute ventilation is insufficient relative to CO₂ production 1, 6
• Increased airway resistance, end-expiratory lung volume, and intrinsic PEEP (PEEPi) contribute significantly during acute respiratory failure 4
• Inspiratory muscle dysfunction plays a role in chronic hypercapnia 4
• Increased mechanical workload leads to greater energy consumption by inspiratory muscles 4
• V/Q (ventilation-perfusion) abnormalities worsen during acute exacerbations 4

Clinical Manifestations

• Symptoms are often non-specific, requiring a high index of suspicion 6
• Clinical presentation may include:
  • Altered mental status ranging from confusion to somnolence 5
  • Headache and peripheral vasodilation due to hypercapnia 5
  • Tachypnea and use of accessory respiratory muscles 2
  • Asterixis (flapping tremor) in severe cases 5
• Arterial blood gas analysis is essential for diagnosis, showing pH <7.35 with elevated PaCO₂ in acute cases 7

Management Principles

• Target oxygen saturation of 88-92% for patients at risk of hypercapnic respiratory failure 1, 2
• Caution with high-flow oxygen as it may worsen hypercapnia in certain patients 1
• Non-invasive ventilation (NIV) should be considered when pH <7.35 and PaCO₂ >6 kPa 1, 4
• NIV is particularly indicated in:
  • COPD with respiratory acidosis (pH 7.25-7.35) 4
  • Hypercapnic respiratory failure from chest wall deformity or neuromuscular disease 4
  • Weaning from tracheal intubation 4
• Invasive ventilation should be considered when pH <7.25 with persistent hypercapnia despite optimal therapy 1
• Respiratory stimulants like doxapram may be useful in selected cases 8

Monitoring and Prognostic Factors

• Regular arterial blood gas analysis is crucial for monitoring treatment response 2
• Arterial hydrogen ion concentration [H+] is an important prognostic factor for survival 8
• Patients with [H+] ≥55 nmol/l (pH ≤7.26) have higher mortality rates 8
• Additional poor prognostic indicators include advanced age, hypotension, and elevated urea 8
• Continuous pulse oximetry and use of early warning scores are recommended 2

Cautions and Contraindications

• NIV is not indicated in patients with:
  • Impaired consciousness 4
  • Severe hypoxemia 4
  • Copious respiratory secretions 4
• High-flow nasal therapy (HFNT) currently lacks sufficient evidence to recommend as initial management for acute Type 2 respiratory failure 3