What are the initial Non-Invasive Ventilation (NIV) settings for a patient requiring NIV, specifically the inspiratory positive airway pressure (IPAP) and expiratory positive airway pressure (EPAP) levels?

Initial NIV Settings

Start with IPAP 10-15 cmH₂O and EPAP 4-8 cmH₂O in bi-level pressure support mode for patients requiring non-invasive ventilation. 1

Pre-Initiation Steps

• Obtain arterial blood gases before starting NIV to confirm respiratory acidosis (pH <7.35) and guide therapy, as NIV is specifically indicated when acidosis persists despite maximal medical treatment. 1
• Provide controlled oxygen using a 24% Venturi mask at 2-3 L/min, nasal cannula at 1-2 L/min, or 28% Venturi mask at 4 L/min before ABG results are available. 1

Initial Pressure Settings

• Set IPAP at 10-15 cmH₂O initially, then titrate upward based on patient response. 1 For chronic NIV in severe COPD, inspiratory pressures must reach 20-25 cmH₂O to meaningfully increase tidal volume and reduce work of breathing, but start lower in the acute setting. 2
• Set EPAP at 4-8 cmH₂O, which offsets intrinsic PEEP in COPD patients and improves breath triggering. 1, 3 The EPAP also serves to vent exhaled gas through the exhaust port and recruit underventilated lung. 3
• Maintain a pressure difference (IPAP minus EPAP) of at least 5 cmH₂O to provide adequate ventilatory support. 1

The physiologic rationale for EPAP is critical: in COPD patients with dynamic hyperinflation, intrinsic PEEP can reach 10-15 cmH₂O, creating a threshold load that must be overcome before inspiratory flow begins. 4 EPAP levels of 3-5 cmH₂O offset this recoil pressure, though higher levels are rarely tolerated despite the theoretical benefit. 4

Mode and Backup Rate

• Use Spontaneous/Timed (S/T) mode with a backup rate of 10-14 breaths/min, set equal to or slightly less than the patient's spontaneous sleeping respiratory rate. 1 This ensures mandatory breaths if the patient has frequent central apneas or inappropriately low respiratory rate. 1
• Bi-level pressure support ventilators are preferred as they are simpler to use, cheaper, more flexible, and have been validated in the majority of randomized controlled trials. 1, 4

Timing and Oxygenation Parameters

• Set inspiratory time to achieve an I:E ratio of approximately 1:2 (30% IPAP time) to allow adequate expiratory time and prevent air trapping. 1
• Target SpO₂ 88-92% to avoid worsening hypercapnia from excessive oxygen. 1 Use pulse oximetry to guide oxygen titration rather than oxygen analyzers in the circuit, which are unreliable. 1

Interface Selection

• Use a full-face mask initially in the acute setting, then transition to a nasal mask after 24 hours as the patient improves. 1 Approximately 20-30% of patients with acute respiratory failure cannot be managed by NIV, often due to poor mask fit causing patient-ventilator asynchrony. 3

Monitoring and Reassessment

• Recheck ABGs after 30-60 minutes of NIV or immediately if clinical deterioration occurs. 1
• Expect rapid improvement in dyspnea, respiratory rate, and work of breathing within the first hour. 3 Most trials showing positive response note early improvement in PaO₂, pH, and PaCO₂ at 1 hour and certainly at 4-6 hours. 3
• If pH and PaCO₂ normalize, continue NIV with target SpO₂ 88-92%. 1

Critical Pitfalls to Avoid

• Avoid high-flow oxygen as it increases the risk of worsening respiratory acidosis and hypercapnia in COPD patients. 1 Maintain strict SpO₂ target of 88-92%. 1
• Watch for rebreathing, especially in tachypneic patients: EPAP levels of 3-5 cmH₂O do not completely eliminate rebreathing during bi-level pressure support when respiratory frequency increases. 3, 4 This can paradoxically worsen hypercapnia in anxious patients who fail to improve. 4
• Ensure the exhaust port is patent: occlusion by sputum can exacerbate hypercapnia through rebreathing. 3
• Ensure I:E ratio of 1:2 or greater to prevent dynamic hyperinflation and auto-PEEP. 1
• If asynchrony cannot be resolved by adjusting trigger sensitivity, switch to timed or assist-control mode to provide mandatory breaths. 1, 4

Criteria for Treatment Failure

• Consider intubation if: worsening ABGs and/or pH within 1-2 hours, lack of improvement after 4 hours of NIV, severe acidosis, life-threatening hypoxemia, or altered mental status. 1
• Lack of progress toward correction of pH, PaO₂, and PaCO₂ by 4-6 hours has been associated with failure of NIV. 3

Equipment Considerations

• Humidification is not normally necessary during acute NIV, as heated humidifiers or heat-moisture exchangers can impair trigger function. 1, 3
• The ventilator must be capable of supporting inspiratory flows of at least 60 l/min, as distressed COPD patients may have peak inspiratory flow rates exceeding this threshold. 3