What are the BiPAP (Bilevel Positive Airway Pressure) settings to control respiratory rate in respiratory alkalosis?

BiPAP Settings for Controlling Respiratory Rate in Respiratory Alkalosis

For respiratory alkalosis, BiPAP settings should include an IPAP of 8-12 cmH2O, EPAP of 3-5 cmH2O, and a backup rate set 2-4 breaths below the patient's spontaneous respiratory rate to help normalize ventilation and reduce respiratory alkalosis.

Understanding Respiratory Alkalosis and BiPAP Therapy

Respiratory alkalosis is characterized by primary hypocapnia (PaCO2 <35 mmHg) with subsequent alkalization of body fluids 1. It typically results from hyperventilation, which can be caused by various conditions including anxiety, pain, hypoxemia, or central nervous system disorders.

BiPAP therapy can help manage respiratory alkalosis by:

• Controlling excessive respiratory rate
• Normalizing tidal volumes
• Reducing work of breathing
• Improving ventilation-perfusion matching

Initial BiPAP Settings for Respiratory Alkalosis

1. IPAP (Inspiratory Positive Airway Pressure):

   • Start at 8-12 cmH2O 2
   • Adjust based on patient comfort and response

2. EPAP (Expiratory Positive Airway Pressure):

   • Start at 3-5 cmH2O 2
   • Lower EPAP helps reduce resistance to exhalation

3. Backup Rate Setting:

   • Set 2-4 breaths below the patient's spontaneous respiratory rate 2, 3
   • This is critical for respiratory alkalosis as it helps prevent excessive ventilation
   • Example: If patient's spontaneous rate is 24, set backup rate to 20-22

4. Mode Selection:

   • Use Spontaneous-Timed (ST) mode rather than Spontaneous mode 3
   • ST mode ensures a minimum respiratory rate while allowing spontaneous breathing

Titration Protocol

1. Initial Assessment:

   • Measure baseline arterial blood gases (ABGs)
   • Document respiratory rate, SpO2, and work of breathing

2. Progressive Adjustments:

   • After starting with initial settings, monitor for 30-60 minutes
   • Obtain repeat ABGs to assess PaCO2 and pH
   • If respiratory alkalosis persists (pH >7.45, PaCO2 <35 mmHg):
     • Decrease IPAP by 1-2 cmH2O (to reduce tidal volume)
     • Consider further reducing backup rate by 1-2 breaths/min
   • If patient develops respiratory acidosis (overcorrection):
     • Increase IPAP by 1-2 cmH2O
     • Consider increasing backup rate

3. Inspiratory Time Adjustment:

   • Set inspiratory time (IPAP time) to 30-40% of the respiratory cycle 3
   • For respiratory alkalosis, aim for shorter inspiratory times (closer to 30%)
   • This allows more time for exhalation and helps prevent air trapping

Monitoring and Adjustments

1. Continuous Monitoring:

   • Respiratory rate and pattern
   • Oxygen saturation (target 88-92%) 2
   • Patient comfort and synchrony with the device

2. Serial Blood Gas Measurements:

   • Obtain ABGs within 1-2 hours of initiation 2
   • Target pH 7.35-7.45 and PaCO2 35-45 mmHg
   • Repeat ABGs after significant setting changes

3. Potential Complications to Monitor:

   • CO2 rebreathing (can worsen respiratory alkalosis) 4
   • Patient-ventilator asynchrony
   • Mask leaks (can affect delivered pressures)

Special Considerations

1. Exhalation Devices:

   • Use appropriate exhalation devices to prevent CO2 rebreathing 4
   • CO2 rebreathing can counteract efforts to correct respiratory alkalosis

2. Contraindications:

   • BiPAP should be avoided in hemodynamically unstable patients 2
   • Not recommended for patients with severely depressed mental status or copious secretions

3. Caution in Low PCO2 Patients:

   • Studies have shown that low PCO2 may be predictive of BiPAP failure in some conditions 3
   • Close monitoring is essential in these patients

Practical Algorithm for BiPAP Adjustment in Respiratory Alkalosis

1. Start with IPAP 8-10 cmH2O, EPAP 3-5 cmH2O
2. Set backup rate 2-4 breaths below spontaneous rate
3. Use ST mode with inspiratory time 30-35% of respiratory cycle
4. After 30-60 minutes, check ABGs:
   • If pH >7.45 and PaCO2 <35: Decrease IPAP by 1-2 cmH2O and/or reduce backup rate
   • If pH 7.35-7.45 and PaCO2 35-45: Maintain current settings
   • If pH <7.35: Increase IPAP by 1-2 cmH2O
5. Repeat ABGs after 1-2 hours and adjust as needed

By following this approach, BiPAP can effectively help normalize ventilation in patients with respiratory alkalosis while providing respiratory support.