For a tracheostomized patient on CPAP mode, what are the appropriate PEEP, pressure support (PASB), and FiO2 settings to maintain adequate oxygenation?

CPAP Mode Ventilator Settings for Tracheostomized Patients

For a tracheostomized patient on CPAP mode, initiate with PEEP 5-10 cm H₂O, pressure support (PASB) 0 cm H₂O (since true CPAP provides no inspiratory support), and FiO₂ titrated to maintain SpO₂ 92-96%. 1

Understanding CPAP Mode Mechanics

• CPAP maintains constant positive airway pressure throughout the respiratory cycle without providing inspiratory pressure support 2
• In true CPAP mode, there is no pressure support (PASB = 0), as the patient breathes spontaneously against a continuous positive pressure 2
• If your ventilator allows "pressure support" adjustment in CPAP mode, this actually converts it to a bilevel mode (similar to BiPAP), not pure CPAP 2

Initial PEEP Settings

Start with PEEP 10 cm H₂O for most patients requiring respiratory support:

• Multiple guidelines recommend initiating CPAP at 10 cm H₂O for patients with acute respiratory compromise 1
• For post-thoracotomy or cardiac surgery patients, PEEP 9-10 cm H₂O consistently improves oxygenation and maintains positive tracheal pressure throughout the respiratory cycle 3
• Lower PEEP (5 cm H₂O) may allow negative inspiratory pressure swings in 50% of patients, risking alveolar derecruitment 3

Adjust PEEP based on clinical response:

• Increase PEEP to 12-15 cm H₂O if oxygenation remains inadequate despite FiO₂ 0.6 1
• Maximum PEEP up to 15-20 cm H₂O may be required for severe hypoxemia, though monitor closely for hemodynamic compromise 1
• In COPD patients with dynamic hyperinflation, PEEP 5 cm H₂O reduces inspiratory work by counterbalancing intrinsic PEEP 4

FiO₂ Titration Strategy

Target SpO₂ 92-96% in most patients:

• Maintain SpO₂ above 90% but no higher than 96% to avoid hyperoxia-related complications 1
• For patients with chronic CO₂ retention or COPD, target SpO₂ 88-92% 5
• Start with FiO₂ 0.6 and titrate downward as tolerated once PEEP is optimized 1

Avoid excessive FiO₂:

• FiO₂ >0.6 should prompt PEEP escalation rather than further oxygen increases 1
• High FiO₂ (>0.8) increases atelectasis formation and should be avoided 1
• Never use hyperoxia (SpO₂ >96%) as it increases mortality without benefit 1, 5

Pressure Support Considerations

In true CPAP mode, pressure support = 0 cm H₂O:

• CPAP provides only continuous positive pressure without inspiratory assistance 2
• If the patient requires inspiratory support, switch to pressure support ventilation (PSV) or BiPAP mode rather than remaining in CPAP 5, 6
• Pressure support of 5-7 cm H₂O above PEEP may be added if transitioning from CPAP to PSV for patients with increased work of breathing 4

Monitoring and Adjustment Algorithm

Within the first 1-2 hours:

• Assess respiratory rate (should decrease to <25 breaths/min), work of breathing (reduced accessory muscle use), and SpO₂ stability 5, 6
• If SpO₂ remains <90% despite PEEP 10 cm H₂O and FiO₂ 0.6, increase PEEP by 2 cm H₂O increments to maximum 15 cm H₂O 1
• If respiratory rate remains >25-30 breaths/min or work of breathing is excessive, the patient likely needs inspiratory pressure support (transition to PSV/BiPAP) 6

Obtain arterial blood gas if:

• SpO₂ targets cannot be achieved with PEEP ≤15 cm H₂O and FiO₂ ≤0.6 1
• Patient develops signs of CO₂ retention (somnolence, confusion, hemodynamic instability) 5
• Clinical deterioration occurs despite optimized settings 1

Common Pitfalls to Avoid

• Do not use ZEEP (zero PEEP) in tracheostomized patients on CPAP—this causes rapid alveolar derecruitment and worsens oxygenation 1, 2
• Do not increase FiO₂ beyond 0.6 without first optimizing PEEP—this exposes patients to oxygen toxicity without addressing the underlying recruitment problem 1
• Do not continue CPAP if the patient has high work of breathing or tachypnea >30 breaths/min—these patients need inspiratory pressure support, not just PEEP 6
• Do not apply PEEP >15 cm H₂O without hemodynamic monitoring—excessive PEEP decreases cardiac output and may worsen tissue oxygen delivery despite improved PaO₂ 2

Failure Criteria Requiring Mode Change

Transition to full ventilatory support (pressure control or volume control) if:

• SpO₂ <90% persists despite PEEP 15 cm H₂O and FiO₂ 1.0 for >2 hours 1, 6
• Respiratory rate remains >30 breaths/min or patient develops paradoxical breathing 6
• Hemodynamic instability develops (hypotension, tachycardia unresponsive to fluids) 1
• Mental status deteriorates or patient becomes unable to protect airway 1