How do you calculate auto peep (intrinsic positive end-expiratory pressure) using an inspiratory hold maneuver in a mechanically ventilated patient?

Calculating Auto-PEEP Using Inspiratory Hold Maneuver

You cannot calculate auto-PEEP using an inspiratory hold maneuver—you must use an end-expiratory occlusion (expiratory hold) maneuver instead. 1

Correct Method: End-Expiratory Occlusion Technique

The gold standard for measuring static auto-PEEP (intrinsic PEEP) requires occluding the expiratory port, not performing an inspiratory hold 1.

Step-by-Step Procedure

Manual Technique:

• Occlude the expiratory port at the ventilator during the last 0.5 seconds of expiration 1
• Ensure the patient is passive (sedated/paralyzed) to avoid artifacts from active expiratory muscle contraction 1
• Read the plateau pressure that develops on the airway pressure display—this represents the auto-PEEP value 1

Automated Technique (Preferred):

• Use ventilators equipped with an end-expiratory occlusion hold button (e.g., Siemens Servo 900C/300, Puritan-Bennett 7200 series, Dräger EVITA) 1, 2
• Press the expiratory hold button at end-expiration 1
• The ventilator automatically performs rapid occlusion and displays the auto-PEEP measurement 1, 2
• This method avoids gas compression artifacts in ventilator tubing 1

Critical Technical Considerations

Timing Requirements:

• The occlusion must occur exactly at end-expiration, approximately 3 seconds into the expiratory phase 1
• Small variations in timing (near end-expiration) do not substantially affect measurements because expelled volume per unit time is minimal due to extreme airway compression 1

Patient State Requirements:

• The patient must be completely passive during measurement 1
• Active expiratory muscle contraction will falsely elevate the measured pressure 1
• Active inspiratory efforts will confound the measurement 1

Why Inspiratory Hold is Wrong

An inspiratory hold (plateau pressure maneuver) measures plateau pressure during inspiration to assess respiratory system compliance and driving pressure—it does not measure auto-PEEP 1. The expiratory pause maneuver has been studied for measuring inspiratory muscle pressure during assisted ventilation, but this is a different application 3.

Alternative Method for Spontaneously Breathing Patients

When patients have active respiratory efforts and cannot be made passive, auto-PEEP measurement becomes complex and requires 1:

• Esophageal balloon catheter insertion to measure pleural pressure changes 1
• Measure the decrease in pleural pressure from end-expiration to the onset of inspiratory flow—this represents dynamic auto-PEEP (PEEPi,dyn) 1
• Correct for expiratory muscle activity by subtracting the corresponding change in gastric pressure (requires gastric balloon) 1
• Note that dynamic auto-PEEP measured this way is significantly less than static auto-PEEP 1

Important caveat: Even with corrections, the measured value may not truly quantify dynamic hyperinflation due to unpredictable interactions between diaphragmatic contraction increasing gastric pressure and simultaneous expiratory muscle relaxation decreasing it 1.

Clinical Context and Expected Values

High-Risk Populations:

• Severe COPD exacerbations: auto-PEEP can reach 10-15 cm H₂O 4
• Acute severe asthma: similarly elevated values 1, 4
• Any patient receiving high minute ventilation with insufficient expiratory time 4

Why Measurement Matters:

• Auto-PEEP creates an inspiratory threshold load that patients must fully overcome before triggering the ventilator 1, 4
• This significantly increases work of breathing and can cause ineffective triggering efforts 1, 4
• Applying external PEEP at 50-85% of measured auto-PEEP can reduce this threshold load and improve patient-ventilator synchrony 4, 5
• Never set external PEEP higher than measured auto-PEEP, as this worsens hyperinflation and causes hemodynamic compromise 4, 5