What should be increased on a BiPAP (Bilevel Positive Airway Pressure) machine in a patient with CO2 narcosis?

BiPAP Management in CO2 Narcosis

In CO2 narcosis, increase the IPAP (inspiratory positive airway pressure) on BiPAP to augment ventilation and reduce PaCO2, while maintaining adequate EPAP to prevent upper airway collapse. 1

Primary Adjustment: Increase IPAP (Pressure Support)

The key to reversing hypercapnia with BiPAP is increasing the pressure support (PS = IPAP - EPAP), which directly augments tidal volume and minute ventilation 2:

• Start with IPAP 15 cmH2O and EPAP 4-5 cmH2O, then rapidly escalate IPAP to 20-30 cmH2O within 10-30 minutes based on patient size and severity of acidosis 1
• Target tidal volume of approximately 10 mL/kg ideal body weight when increasing IPAP 2
• Higher IPAP (up to 30 cmH2O) may be required for larger patients or more severe acidosis 1
• Increase IPAP in 2 cmH2O increments until symptoms improve and CO2 normalizes 2

Monitoring Response to IPAP Increases

Assess effectiveness within 2-4 hours of BiPAP initiation 1:

• Monitor arterial blood gas pH and PaCO2 - BiPAP should improve pH and reduce PaCO2 within this timeframe 1
• Track respiratory rate (should decrease), SpO2, and mental status 1
• Use transcutaneous or end-tidal PCO2 monitoring if available to guide adjustments 2
• Monitor tidal volume and respiratory rate from the BiPAP device display 2

EPAP Considerations

While IPAP is the primary adjustment, EPAP serves important functions 2:

• Maintain EPAP at 4-8 cmH2O to prevent upper airway collapse 1
• EPAP helps maintain upper airway patency but does not directly improve ventilation 2
• The pressure support (IPAP minus EPAP) is what augments ventilation and reduces CO2 2

Critical Pitfalls to Avoid

Never administer supplemental oxygen alone without ventilatory support in CO2 narcosis - this removes the hypoxic drive to breathe and worsens hypercapnia 3:

• Oxygen should only be added after optimizing BiPAP pressure support 2
• BiPAP is the primary measure to reverse hypoventilation and decrease PaCO2 3
• Constantly monitor CO2 levels when administering any oxygen 3

Watch for CO2 rebreathing with certain BiPAP circuits - standard exhalation devices can cause exhaled gas to flow back into ventilator tubing, increasing dead space and blunting PaCO2 reduction 4. Use non-rebreather valves or plateau exhalation devices to eliminate this problem 4.

Failure Criteria Requiring Intubation

If pH remains <7.15 or continues deteriorating despite optimized BiPAP settings (IPAP 20-30 cmH2O), this indicates BiPAP failure and necessitates immediate intubation 1. Other absolute indications for intubation include imminent respiratory arrest, severe respiratory distress unresponsive to initial BiPAP, or depressed consciousness 1.

Mode Selection

Use spontaneous-timed (ST) mode with a backup rate rather than spontaneous mode alone 2:

• Set backup rate at 13-20 breaths per minute to ensure adequate ventilation if patient effort decreases 2
• This prevents apnea and maintains minute ventilation even if respiratory drive is suppressed 2