What are the indications of respiratory failure?

Indications of Respiratory Failure

Respiratory failure is indicated by arterial blood gas abnormalities showing PaO₂ <60 mmHg or SaO₂ <88% for hypoxemic failure, and PaCO₂ ≥45 mmHg with pH <7.35 for hypercapnic failure, often accompanied by clinical signs of respiratory distress including tachypnea >35 breaths/min, altered mental status, and use of accessory muscles. 1

Types of Respiratory Failure and Their Indications

Hypoxemic Respiratory Failure (Type I)

• PaO₂ <60 mmHg or SaO₂ <88% while breathing room air 1
• Clinical manifestations:
  • Dyspnea at rest that interferes with conversation
  • Use of accessory respiratory muscles
  • Tachypnea (respiratory rate >24 breaths/min)
  • Tachycardia
  • Cyanosis
  • Altered mental status
  • Pulse oximetry showing desaturation despite supplemental oxygen

Hypercapnic Respiratory Failure (Type II)

• PaCO₂ ≥45 mmHg with pH <7.35 1, 2
• Clinical manifestations:
  • Decreased level of consciousness/confusion
  • Headache (especially morning headaches suggesting nocturnal hypoventilation)
  • Asterixis (flapping tremor)
  • Warm, flushed skin
  • Bounding pulse
  • Respiratory rate >35 breaths/min or paradoxically slow breathing 3
  • Vital capacity below 15 ml/kg 3

Disease-Specific Indications of Respiratory Failure

COPD Exacerbation

• Severe acidosis (pH <7.25) and hypercapnia (PaCO₂ >8 kPa or 60 mmHg) 3
• Respiratory rate >24 breaths/min despite optimal medical therapy 3
• Worsening of ABGs and/or pH in 1-2 hours despite non-invasive ventilation 3
• Tachypnea >35 breaths/min 3

Asthma Exacerbation

• Signs of impending respiratory failure include: 3
  • Inability to speak
  • Altered mental status
  • Intercostal retraction
  • Worsening fatigue
  • PaCO₂ of 42 mm Hg or greater (particularly concerning as asthma typically presents with hypocapnia)
  • PEF <25% of predicted or personal best
  • Minimal or no relief from frequent inhaled SABA
  • Drowsiness (predictor of impending respiratory failure)

Acute Respiratory Distress Syndrome (ARDS)

• PaO₂/FiO₂ ratio categorization: 4
  • Mild: 201-300 mmHg
  • Moderate: 101-200 mmHg
  • Severe: ≤100 mmHg
• Refractory hypoxemia despite high FiO₂
• Increased work of breathing
• Decreased lung compliance

Indications for Mechanical Ventilation

Non-invasive Positive Pressure Ventilation (NIPPV)

• Indications in COPD: 3

  • Respiratory acidosis (pH <7.35, PaCO₂ >6-8 kPa or 45-60 mmHg)
  • Respiratory rate >24 breaths/min
  • Moderate to severe dyspnea with use of accessory muscles

• Contraindications to NIPPV: 3

  • Respiratory arrest
  • Cardiovascular instability
  • Impaired mental status/inability to cooperate
  • Copious respiratory secretions
  • Recent facial or upper airway surgery
  • Vomiting or bowel obstruction

Invasive Mechanical Ventilation

• Absolute indications: 3
  • Respiratory arrest
  • Failure of NIPPV (worsening ABGs after 1-2 hours, lack of improvement after 4 hours)
  • Severe acidosis (pH <7.25) with hypercapnia (PaCO₂ >60 mmHg)
  • Life-threatening hypoxemia (PaO₂/FiO₂ <200 mmHg)
  • Tachypnea >35 breaths/min
  • Inability to protect airway
  • Altered mental status/coma
  • Cardiovascular instability

Monitoring for Respiratory Failure

• Clinical evaluation: 3

  • Chest wall movement
  • Coordination of respiratory effort
  • Accessory muscle recruitment
  • Heart and respiratory rates
  • Mental state

• Laboratory assessment: 3

  • Arterial blood gas analysis (pH, PaCO₂, PaO₂)
  • Continuous pulse oximetry (SpO₂)
  • FEV₁ or PEF measurements (when possible)
  • Consider transcutaneous CO₂ monitoring where available

Pitfalls to Avoid

• Delaying intubation once it is deemed necessary in severe asthma 3
• Overlooking hypercapnia in patients with normal lung function tests, especially those with neuromuscular disorders 5
• Failing to recognize that respiratory failure can progress rapidly in asthma exacerbations 3
• Underestimating the severity of respiratory failure when relying solely on oxygen saturation without arterial blood gases 3
• Overlooking sleep-related breathing disorders as contributors to respiratory failure 5

Remember that respiratory failure is a medical emergency requiring prompt recognition and intervention to prevent further deterioration and potential death. The decision to initiate mechanical ventilation should be based on both clinical assessment and objective measurements of gas exchange.