What are the recommended ventilator settings for a patient with hypercapnic respiratory failure, possibly due to Chronic Obstructive Pulmonary Disease (COPD), Amyotrophic Lateral Sclerosis (ALS), or Obesity Hypoventilation Syndrome, with or without a history of obstructive sleep apnea?

Ventilator Settings for Hypercapnic Respiratory Failure

For patients with hypercapnic respiratory failure, initiate non-invasive ventilation (NIV) using bi-level pressure support with IPAP 10-15 cmH₂O, EPAP 4-8 cmH₂O, backup rate 10-14 breaths/min, and target oxygen saturation of 88-92%. 1

Initial Assessment and Indications for NIV

Start NIV when PaCO₂ ≥6.5 kPa (49 mmHg) persists after one hour of optimal medical therapy, accompanied by pH <7.35 and respiratory rate >23 breaths/min. 2

• Obtain arterial blood gases before initiating ventilation to guide therapy 1
• For PaCO₂ between 6.0-6.5 kPa (45-49 mmHg), continue optimal medical care with close monitoring rather than automatically initiating NIV 2
• Approximately 20% of acute COPD exacerbations will normalize pH with medical therapy alone when oxygen saturation is targeted to 88-92% 2

NIV Settings for COPD and General Hypercapnic Failure

Pressure Settings

• Begin with IPAP of 10-15 cmH₂O 1
• Set EPAP at 4-8 cmH₂O 1
• Maintain pressure difference between IPAP and EPAP of at least 5 cmH₂O 1
• Use bi-level pressure support as the most effective mode of NIV 1

Timing and Rate Settings

• Set backup respiratory rate equal to or slightly less than patient's spontaneous sleeping respiratory rate, with minimum of 10-14 breaths/min 1
• Set inspiratory time to achieve I:E ratio of approximately 1:2 (30% IPAP time) to allow adequate time for exhalation and prevent air trapping 1
• Consider using Spontaneous/Timed mode with backup rate if patient has frequent central apneas or inappropriately low respiratory rate 1

Oxygenation

• Target oxygen saturation of 88-92% to avoid worsening hypercapnia 1
• Prior to ABG availability, use 24% Venturi mask at 2-3 L/min, nasal cannulae at 1-2 L/min, or 28% Venturi mask at 4 L/min 1
• Titrate FiO₂ to maintain SpO₂ between 88-92% 1

Special Considerations for Obesity Hypoventilation Syndrome

Obese patients with severe acute hypercapnic respiratory failure require higher EPAP settings (10-15 cmH₂O range) to recruit collapsed lung units and overcome upper airway obstruction. 3

• Use pressure-controlled mechanical ventilation initially 3
• IPAP >30 cmH₂O may be required due to high impedance to inflation 3
• Prolong inspiratory time with I:E ratio of 1:1 to increase delivered tidal volume 3
• If resulting tidal volume is still inadequate, consider volume-controlled ventilation or volume-assured mode 3
• Forced diuresis is often indicated as fluid retention commonly contributes to ventilatory failure and may exceed 20 L 3
• Place in HDU/ICU for NIV given greater risk of failure and difficult intubation 3

Monitoring and Reassessment Protocol

Recheck arterial blood gases after 30-60 minutes of NIV or if clinical deterioration occurs. 1

• Reassess ABGs at 1-2 hours after initiating NIV to evaluate response to treatment 1, 2
• If pH and PCO₂ normalize, continue with target oxygen saturation of 88-92% 1
• Consider intubation if worsening of ABGs and/or pH in 1-2 hours or lack of improvement after 4-6 hours of NIV 1, 4

Location of Care Based on Severity

• Patients with pH >7.25 can receive NIV on a respiratory ward with appropriate monitoring 1
• Patients with pH <7.25 require HDU or ICU setting where immediate intubation is available 1, 2
• Patients with pH <7.30 should receive NIV in HDU/ICU settings 2

Invasive Mechanical Ventilation Settings (When NIV Fails)

Intubate when NIV fails, evidenced by worsening ABGs and/or pH in 1-2 hours, lack of improvement after 4-6 hours, severe acidosis, life-threatening hypoxemia, or inability to protect airway. 1, 4

Initial Ventilator Settings

• Use assist-control mode initially to ensure adequate ventilation 1
• Set tidal volume at 6 ml/kg predicted body weight (may increase to 8 ml/kg if not tolerated) 1
• Target plateau pressure less than 30 cmH₂O to prevent barotrauma 1
• Set PEEP between 4-8 cmH₂O to offset intrinsic PEEP and improve triggering 1
• Set initial respiratory rate between 10-14 breaths/min 1
• Allow adequate expiratory time with I:E ratio of approximately 1:2 or 1:3 to prevent air trapping and dynamic hyperinflation 1
• Consider permissive hypercapnia if hemodynamically stable 1

Long-Term NIV Considerations for Chronic Stable Hypercapnia

For chronic stable hypercapnic COPD (PaCO₂ >45 mmHg, not during exacerbation), use nocturnal NIV in addition to usual care. 3

• Screen for obstructive sleep apnea before initiating long-term NIV 3
• Do not initiate long-term NIV during an admission for acute-on-chronic hypercapnic respiratory failure; reassess for NIV at 2-4 weeks after resolution 3
• Target normalization of PaCO₂ in patients with hypercapnic COPD on long-term NIV using high-intensity NIV settings 3
• Do not use in-laboratory polysomnogram to titrate NIV in patients with chronic stable hypercapnic COPD who are initiating NIV 3

Critical Pitfalls to Avoid

• Excessive oxygen therapy leading to worsening hypercapnia - maintain target saturation of 88-92% 1
• Inadequate expiratory time causing dynamic hyperinflation and auto-PEEP - ensure appropriate I:E ratio of 1:2 or longer 1
• Excessive tidal volumes increasing risk of ventilator-induced lung injury - use low tidal volumes of 6 ml/kg 1
• Delayed escalation to invasive ventilation when NIV is failing - monitor closely and intubate if worsening after 1-2 hours 1, 2
• Attempting NIV in patients with altered mental status, copious secretions, or inability to protect airway 1
• Failure to recheck ABGs at 1-2 hours to assess response 1
• Underestimating fluid overload in obesity hypoventilation syndrome - consider forced diuresis 3

Alternative Modes for NIV Failure

If patients show insufficient PaCO₂ reduction with fixed-level pressure support NIV, consider switching to average volume-assured pressure support (AVAPS) mode. 5

• AVAPS mode creates significantly better PaCO₂ change rate than fixed PS-NIV in patients not responding to initial therapy 5
• Higher Charlson Comorbidity Index and higher PaCO₂ upon admission predict AVAPS mode requirement 5
• Most patients (92.8%) reaching clinical stability with AVAPS-NIV can return to fixed-level PS-NIV and maintain acceptable PaCO₂ levels 5