What are the indications for mechanical ventilation (MV)?

Indications for Mechanical Ventilation

Mechanical ventilation should be initiated when there is respiratory failure with acidosis (pH < 7.35), hypercapnia (PaCO2 > 6-8 kPa or 45-60 mmHg), and respiratory rate > 24 breaths/min despite optimal medical therapy and oxygen administration. 1

Primary Indications for Mechanical Ventilation

Respiratory Failure

• Refractory hypoxemia: PaO2 < 60 mmHg despite high-flow oxygen therapy 1
• Respiratory acidosis: pH < 7.35 with hypercapnia (PaCO2 > 45-60 mmHg) 1
• Increased work of breathing: Respiratory rate > 35 breaths/min 1
• Decreased vital capacity: < 15 ml/kg 1

Airway Protection

• Inability to protect the airway (impaired consciousness, excessive secretions) 1
• Respiratory arrest 1

Specific Clinical Scenarios

• Severe ARDS: PaO2/FiO2 ratio ≤ 100 mmHg 2
• COPD exacerbation with:
  • Severe acidosis (pH < 7.25) and hypercapnia (PaCO2 > 60 mmHg) 1
  • Failed non-invasive ventilation (NIV) 1

Choice of Ventilation Mode

Non-invasive Positive Pressure Ventilation (NIPPV)

NIPPV should be considered as first-line ventilatory support for COPD exacerbations with respiratory failure, with success rates of 80-85% 1.

Contraindications for NIPPV include:

• Respiratory arrest
• Cardiovascular instability (hypotension, arrhythmias, myocardial infarction)
• Impaired mental status or inability to cooperate
• Copious/viscous secretions with high aspiration risk
• Recent facial or gastro-esophageal surgery
• Craniofacial trauma or fixed nasopharyngeal abnormality
• Burns
• Extreme obesity 1

Invasive Mechanical Ventilation

Indications for intubation and invasive ventilation:

1. NIPPV failure:
   • Worsening of ABGs and/or pH in 1-2 hours
   • Lack of improvement in ABGs and/or pH after 4 hours 1
2. Severe respiratory failure:
   • Severe acidosis (pH < 7.25)
   • Severe hypercapnia (PaCO2 > 60 mmHg)
   • Life-threatening hypoxemia (PaO2/FiO2 < 200 mmHg)
   • Tachypnea > 35 breaths/min 1

Ventilation Strategies

Initial Settings

• Mode: Volume-cycled ventilation using assist-control mode is appropriate initially 1
• Tidal volume: 4-8 ml/kg predicted body weight 2
• PEEP: Titrate based on severity of respiratory failure:
  • Mild hypoxemia: 5-8 cmH2O
  • Moderate: 8-12 cmH2O
  • Severe: 12-15+ cmH2O 2
• Plateau pressure: Maintain ≤ 30 cmH2O 2
• Driving pressure: Target < 15 cmH2O 2
• Oxygenation target: Arterial oxygen saturation ~90% (PaO2 ~60 mmHg) 1

Advanced Strategies for Refractory Cases

• Prone positioning: Strongly recommended for severe ARDS (PaO2/FiO2 ≤ 100 mmHg) 2
• Neuromuscular blockade: Consider for severe ARDS or ventilator dyssynchrony 2
• ECMO: Consider for selected patients with severe refractory ARDS 2, 3

Common Pitfalls and Caveats

1. Delayed intubation: Waiting too long to initiate mechanical ventilation can worsen outcomes. Early recognition of respiratory failure is critical.

2. Overreliance on NIPPV: While NIPPV is effective in many cases, recognizing NIPPV failure promptly is essential to prevent delayed intubation and worse outcomes 1.

3. Ventilator-induced lung injury: Avoid excessive tidal volumes and plateau pressures to prevent further lung injury 2, 4.

4. Fluid management: Judicious fluid management is important in patients with respiratory failure to prevent worsening pulmonary edema 1.

5. Patient-ventilator dyssynchrony: Monitor for and address dyssynchrony, which can increase work of breathing and worsen outcomes 5.

6. Inadequate sedation: Appropriate sedation is necessary to prevent patient-ventilator dyssynchrony and self-inflicted lung injury 4.

By following these guidelines for initiating mechanical ventilation and optimizing ventilator settings, clinicians can support patients through respiratory failure while minimizing complications and improving outcomes.