How is Expiratory Positive Airway Pressure (EPAP) calculated?

Calculation of Expiratory Positive Airway Pressure (EPAP)

EPAP is typically set at 4-5 cm H₂O as a starting point for most adult patients and then titrated based on the presence of obstructive respiratory events, with adjustments made in increments of at least 1 cm H₂O at intervals no shorter than 5 minutes. 1

Basic EPAP Calculation Principles

Starting Values

• Adults (≥12 years): Start with EPAP of 4 cm H₂O 1, 2
• Children (<12 years): Start with EPAP of 4 cm H₂O 1, 2
• Maximum recommended EPAP:
  • Adults: 20 cm H₂O 1
  • Children: 15 cm H₂O 1

Titration Process

EPAP should be increased by at least 1 cm H₂O (and not more than 2.5 cm H₂O) with intervals no shorter than 5 minutes when the following events are observed 1:

• Obstructive apneas:

  • Adults: ≥2 obstructive apneas
  • Children: ≥1 obstructive apnea

• Hypopneas:

  • Adults: ≥3 hypopneas
  • Children: ≥1 hypopnea

• Respiratory effort-related arousals (RERAs):

  • Adults: ≥5 RERAs
  • Children: ≥3 RERAs

• Snoring:

  • Adults: ≥3 minutes of loud or unambiguous snoring
  • Children: ≥1 minute of loud or unambiguous snoring

EPAP in Bi-level Positive Airway Pressure (BPAP)

When using BPAP, the calculation of EPAP follows these guidelines:

1. Starting EPAP: 4 cm H₂O 1
2. Starting IPAP: 8 cm H₂O 1
3. Minimum IPAP-EPAP differential: 4 cm H₂O 1
4. Maximum IPAP-EPAP differential: 10 cm H₂O 1

EPAP should be increased along with IPAP for obstructive apneas, while only IPAP needs to be increased for hypopneas, RERAs, and snoring 1.

Clinical Considerations for EPAP Adjustment

Intrinsic PEEP (PEEPi) Compensation

In patients with airflow limitation (e.g., COPD), EPAP helps counterbalance intrinsic PEEP, which can:

• Reduce work of breathing
• Improve ventilator triggering
• Decrease patient effort 1

However, EPAP levels >5 cm H₂O are rarely tolerated in patients with severe COPD despite PEEPi potentially reaching 10-15 cm H₂O 1.

Exploration Phase

After elimination of respiratory events, an additional "exploration" of up to 5 cm H₂O above the pressure that controls respiratory events may be performed to:

• Reduce residual high airway resistance
• Normalize inspiratory flow limitation curves
• Potentially improve sleep quality 1, 2

Patient Comfort Considerations

If a patient awakens complaining of high pressure:

1. Restart at a lower pressure that the patient reports as comfortable enough to allow return to sleep
2. Resume titration from this lower pressure 1, 2

Pitfalls and Caveats

1. Excessive EPAP: Setting EPAP too high may:

   • Increase work of breathing 3
   • Reduce exercise tolerance in COPD patients 3
   • Cause patient discomfort and reduce adherence 1

2. Insufficient EPAP: Setting EPAP too low may:

   • Fail to counterbalance PEEPi in patients with obstructive lung disease 1
   • Result in persistent upper airway obstruction 1
   • Lead to ineffective ventilator triggering 1

3. Measurement challenges: In actively breathing patients, accurate measurement of required EPAP may need specialized equipment:

   • Esophageal balloon to estimate pleural pressure changes 1
   • End-expiratory airway occlusion technique 1

4. Mask interface considerations: EPAP requirements may differ based on the interface used:

   • Oronasal masks typically require higher pressures than nasal masks 4

Alternative Approaches to EPAP Determination

While manual titration is the gold standard, predictive equations have been developed to estimate initial EPAP settings. These typically incorporate:

• Body mass index (BMI)
• Apnea-hypopnea index (AHI)
• Neck circumference
• Lowest oxygen saturation 5, 4, 6

However, these equations explain only about 26% of the variance in optimal pressure levels and should be used only as starting points for subsequent titration 5.