Measurement of AutoPEEP and total PEEP

AutoPEEP may also be referred to as air-trapping, breath stacking, dynamic hyperinflation, inadvertent PEEP, or occult PEEP.

AutoPEEP is a common phenomenon in mechanically ventilated patients with long expiratory time constants (RCexp), for example patients with chronic obstructive pulmonary disease or acute severe asthma.

IMPORTANT: The resulting AutoPEEP cannot be seen on the airway pressure curve shown on the ventilator’s screen during normal breath delivery.

(Figure 1 below: Source Garcia Vicente et al. (García Vicente E, Sandoval Almengor JC, Díaz Caballero LA, Salgado Campo JC. Ventilación mecánica invasiva en EPOC y asma [Invasive mechanical ventilation in COPD and asthma]. Med Intensiva. 2011;35(5):288-298. doi:10.1016/j.medin.2010.11.0042​))

AutoPEEP predisposes the patient to increased work of breathing, barotrauma, hemodynamic instability and difficulty in triggering the ventilator. Failure to recognize the hemodynamic consequences of AutoPEEP may lead to inappropriate fluid restriction or unnecessary vasopressor therapy. AutoPEEP can potentially interfere with weaning from mechanical ventilation.

Caregivers should monitor whether AutoPEEP is occurring during ventilation, and set their ventilation control parameters accordingly to avoid the negative consequences of AutoPEEP.

All Hamilton Medical Ventilators have the unique capability of showing AutoPEEP as a monitoring parameter on a breath-by-breath basis. It is calculated using the LSF method applied to the entire breath (Iotti GA, Braschi A, Brunner JX, et al. Respiratory mechanics by least squares fitting in mechanically ventilated patients: applications during paralysis and during pressure support ventilation. Intensive Care Med. 1995;21(5):406-413. doi:10.1007/BF017074093​). However in special circumstances for example when severe dynamic hyperinflation is present, the AutoPEEP calculated by LSF can underestimate the actual AutoPEEP. In these cases it can be obtained by performing an expiratory hold maneuver.

Measuring the total PEEP with an expiratory hold maneuver (see Figure 2 below):

Ensure the Paw waveform is displayed.

1. Open the Hold window.
2. Wait until the Paw waveform plot restarts from the left side.
3. Wait for the next inspiration.
4. Then select Exp hold. Wait for 3 to 5 seconds, then select Exp hold or press the P&T knob again to deactivate the hold maneuver and close the window.
5. After the maneuver, the Hold window closes, and the freeze function is activated automatically.
6. Measure the total PEEP by examining points after flow reached zero on the pressure curve with the cursor.
7. Calculate AutoPEEP by subtracting extrinsic PEEP from the total PEEP.

If AutoPEEP is present unintentionally, caregivers should consider adapting the control parameters to avoid air-trapping by increasing the exhalation time. Use of large-diameter endotracheal tubes, bronchodilators, short inspiratory times, long expiratory times, lower respiratory rates and the use of sedatives can be necessary to avoid the dynamic hyperinflation caused by air-trapping.

All Hamilton Medical ventilators feature the intelligent ventilation mode Adaptive Support Ventilation (ASV®). ASV automatically employs lung-protective strategies to minimize complications from AutoPEEP.

Relevant devices: HAMILTON-G5/S1 (sw v2.8x and later); HAMILTON-C3 (sw v2.0.x and later), HAMILTON-C6 (sw v1.1.x and later)

See full citation for (Iotti, G., & Braschi, A. (1999). Measurements of respiratory mechanics during mechanical ventilation. Rhäzüns, Switzerland: Hamilton Medical Scientific Library.1​) below.