Ventilator Settings in Type-2 Respiratory Failure
Initial Mode Selection
For type-2 respiratory failure (hypercapnic respiratory failure), start with Assist-Control Volume Ventilation (ACVC) mode as the default initial setting, as it guarantees consistent alveolar ventilation and provides complete ventilatory support with a backup rate that prevents apneas. 1, 2
Why ACVC Over PSV Initially
- ACVC ensures a set number of mandatory breaths per minute while allowing patient-triggered breaths, all delivering the same preset tidal volume—critical when respiratory drive is impaired in type-2 failure 1, 2
- PSV is not recommended as the initial mode in acute type-2 respiratory failure because it lacks a backup rate and depends entirely on patient effort, which may be inadequate in hypercapnic patients 2
- ACVC compensates for air leaks and ensures consistent tidal volume delivery despite changes in compliance or resistance, which is essential during the unstable acute phase 1, 3
ACVC Mode: Initial Settings
Tidal Volume
- Set tidal volume at 6 mL/kg predicted body weight (PBW), NOT actual body weight 1, 2
- Calculate PBW: Men = 50 + 2.3 × (height in inches - 60); Women = 45.5 + 2.3 × (height in inches - 60) 1, 2
- Never exceed 8-10 mL/kg PBW, as higher volumes increase mortality risk 1
- In type-2 respiratory failure with obstructive disease (COPD, asthma), accept permissive hypercapnia rather than increasing tidal volume above these limits 1
Respiratory Rate
- Set respiratory rate at 10-15 breaths/min for patients with obstructive airway disease to allow adequate expiratory time and prevent air trapping 1
- Do not attempt to normalize PaCO₂ rapidly—higher target PaCO₂ levels are acceptable based on pre-morbid bicarbonate levels 1
Inspiratory-to-Expiratory (I:E) Ratio
- Set I:E ratio to 1:2 or 1:3 in obstructive disease to prolong expiratory time and limit dynamic hyperinflation 1
- A lower %IPAP time is desirable in patients with obstructive airway disease to allow sufficient expiratory time as expiratory airflow is reduced 4
PEEP
- Start with PEEP of 3-5 cmH₂O as a physiologic baseline 1
- Avoid setting PEEP levels that exceed intrinsic PEEP (iPEEP) in obstructive disease, as this may worsen hyperinflation 1
- In COPD patients, PEEP can offset intrinsic PEEP and reduce ventilatory work, but must be carefully titrated 4
Plateau Pressure
- Maintain plateau pressure (Pplat) ≤30 cmH₂O to prevent alveolar overdistension and ventilator-induced lung injury 1, 2
- Monitor plateau pressure by performing an inspiratory hold maneuver (0.5-1 second pause at end-inspiration) 1
FiO₂
- Adjust FiO₂ to maintain SpO₂ 88-94% in most patients with type-2 respiratory failure 1
- In asthma specifically, target SpO₂ >96% 1
PSV Mode: When and How to Use
Indications for PSV
- PSV should be reserved for weaning phases or prolonged ventilation in stable patients, not as the initial mode in acute type-2 respiratory failure 2
- PSV is preferred during assisted or spontaneous breathing phases when patient comfort and synchrony are priorities, after the acute phase has stabilized 3
- PSV offers superior respiratory comfort because it does not limit inspiratory flow, allowing the ventilator to match variable patient demand 3
Initial PSV Settings
Pressure Support Level
- Set initial pressure support at 18-27 cmH₂O to achieve a tidal volume of 6-8 mL/kg and make the breathing pattern regular 5, 6
- The pressure support level should be titrated to reduce patient work of breathing to 0.3-0.6 J/L (normal physiologic range for partial respiratory muscle unloading) 5
- For total respiratory muscle unloading, increase PSV to approximately 31 cmH₂O (range varies by patient) until patient work decreases to 0 J/L 5
EPAP (Expiratory Positive Airway Pressure)
- Set EPAP at 3-5 cmH₂O to vent exhaled gas through the exhaust port and offset intrinsic PEEP 4
- EPAP serves to recruit underventilated lung and has beneficial effects on triggering 4
Backup Rate
- When using PSV in type-2 respiratory failure, always add a backup rate to prevent apneas if respiratory drive fails 4
- Set backup rate at 6-8 breaths per minute as a safety net 4
Inspiratory Time
- At a respiratory rate of 15 breaths per minute, set inspiratory time to 1.2-1.6 seconds (corresponding to 30-40% IPAP time) 4
- A lower %IPAP time is desirable in obstructive airway disease to allow sufficient expiratory time 4
Critical Monitoring Parameters
- Continuously monitor delivered tidal volume, plateau pressure, and auto-PEEP throughout mechanical ventilation 1
- Perform regular inspiratory hold maneuvers to measure plateau pressure, especially after any ventilator adjustments 1
- Monitor for patient-ventilator asynchrony, which is more common with PSV than ACVC 7
- In PSV, ensure EPAP levels (3-5 cmH₂O) are adequate to eliminate rebreathing, especially when respiratory frequency increases 4
Common Pitfalls to Avoid
- Never use actual body weight for tidal volume calculations—always use predicted body weight 1, 2
- Do not hyperventilate patients in an attempt to rapidly normalize PaCO₂—this causes cerebral vasoconstriction, hemodynamic instability, and increased mortality 2
- Do not start with PSV alone in acute type-2 respiratory failure without a backup rate, as inadequate respiratory drive will lead to hypoventilation 2
- In PSV, ensure the exhalation port is functioning properly—occlusion can cause rebreathing and worsening hypercapnia 4
- Avoid high tidal volumes (>8-10 mL/kg PBW) even if the patient appears to tolerate them, as this increases mortality 1
Transition Strategy
- Begin with ACVC in the acute phase of type-2 respiratory failure to ensure adequate ventilation and CO₂ clearance 1, 2
- Transition to PSV when the patient is stable, sedation is weaned, and spontaneous breathing efforts are consistent 3
- During the transition, monitor work of breathing and ensure the patient is not over-assisted (which can delay weaning) or under-assisted (which increases respiratory distress) 5, 7
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