Ventilator airway pressure “rabbit-ear” pattern
The “rabbit-ear” appearance on the airway pressure waveform signifies patient–ventilator dyssynchrony in which inspiratory efforts occur during a phase when the ventilator does not deliver an effective breath, often because inspiratory triggering must overcome intrinsic (auto) PEEP. [1][2]
Mechanistic significance
Intrinsic (auto) PEEP results from incomplete lung emptying, which leaves trapped air at end-expiration and creates a baseline positive pressure that must be overcome before effective triggering and lung inflation occur. [2]
When triggering is insufficiently sensitive or expiratory time is too short, inspiratory efforts can fail to trigger a ventilator breath immediately, or can trigger with a delay, producing an abnormal pattern on the pressure waveform. [1]
Clinical implications
Auto-PEEP and related breath stacking increase the work of breathing and can worsen hemodynamics through increased intrathoracic pressure. [2]
Auto-PEEP is commonly associated with obstructive lung physiology, high respiratory rate, and expiratory flow limitation that shorten expiratory time. [2]
Supporting waveform-based clinical clues
Auto-PEEP is suggested by failure of the monitored signal to return to baseline before the next breath. [2]
Auto-PEEP is also suggested by elevated plateau pressure measurements and by signs of active expiratory effort. [2]
Bedside actions indicated by this pattern
Respiratory rate should be reduced to lengthen expiratory time and reduce inspiratory-to-expiratory ratio-driven air trapping. [2]
Inspiratory flow should be increased to support delivery during inspiration and indirectly allow more time for exhalation. [2]
Tidal volume should be reduced to decrease the time required for complete exhalation and to reduce air trapping. [2]
Bronchospasm and mucus plugging should be treated to reduce dynamic airflow obstruction that promotes intrinsic PEEP. [2]
Common pitfalls to avoid
Overly aggressive ventilator settings that increase air trapping can perpetuate a cycle of escalating auto-PEEP with increased work of breathing and ventilatory demand. [2]
Escalation of applied extrinsic PEEP should be approached cautiously in dynamic hyperinflation states because extrinsic PEEP may initially add to auto-PEEP and worsen intrathoracic pressure if not titrated appropriately. [2]
Differential considerations
Airway pressure waveform abnormalities can also reflect ventilator–circuit issues or inspiratory effort patterns that alter how airway pressure behaves relative to passive mechanics, requiring assessment beyond pattern recognition alone. [1]
Ineffective triggering from an inadequate trigger threshold can produce ventilator nonresponse to inspiratory efforts, which can appear as an abnormal pressure pattern depending on the ventilator’s display and mode. [1]
Targets for ventilator adjustment when intrinsic PEEP is suspected
Inspiratory-to-expiratory ratio should be adjusted toward an expiratory time longer than inspiration, with a stated target range for ratio of 1:3 to 1:5 in the presence of auto-PEEP physiology. [2]
Extrinsic PEEP should remain below 75% to 85% of the measured auto-PEEP during cautious titration using small increments and static pressure assessment. [2]