Paradoxical responses to positive end-expiratory pressure in patients with airway obstruction during controlled ventilation

Crit Care Med. 2005 Jul;33(7):1519-28. doi: 10.1097/01.ccm.0000168044.98844.30.


Objective: To reevaluate the clinical impact of external positive end-expiratory pressure (external-PEEP) application in patients with severe airway obstruction during controlled mechanical ventilation. The controversial occurrence of a paradoxic lung deflation promoted by PEEP was scrutinized.

Design: External-PEEP was applied stepwise (2 cm H(2)O, 5-min steps) from zero-PEEP to 150% of intrinsic-PEEP in patients already submitted to ventilatory settings minimizing overinflation. Two commonly used frequencies during permissive hypercapnia (6 and 9/min), combined with two different tidal volumes (VT: 6 and 9 mL/kg), were tested.

Setting: A hospital intensive care unit.

Patients: Eight patients were enrolled after confirmation of an obstructive lung disease (inspiratory resistance, >20 cm H(2)O/L per sec) and the presence of intrinsic-PEEP (> or =5 cm H(2)O) despite the use of very low minute ventilation.

Interventions: All patients were continuously monitored for intra-arterial blood gas values, cardiac output, lung mechanics, and lung volume with plethysmography.

Measurements and main results: Three different responses to external-PEEP were observed, which were independent of ventilatory settings. In the biphasic response, isovolume-expiratory flows and lung volumes remained constant during progressive PEEP steps until a threshold, beyond which overinflation ensued. In the classic overinflation response, any increment of external-PEEP caused a decrease in isovolume-expiratory flows, with evident overinflation. In the paradoxic response, a drop in functional residual capacity during external-PEEP application (when compared to zero-external-PEEP) was commonly accompanied by decreased plateau pressures and total-PEEP, with increased isovolume-expiratory flows. The paradoxic response was observed in five of the eight patients (three with asthma and two with chronic obstructive pulmonary disease) during at least one ventilator pattern.

Conclusions: External-PEEP application may relieve overinflation in selected patients with airway obstruction during controlled mechanical ventilation. No a priori information about disease, mechanics, or ventilatory settings was predictive of the response. An empirical PEEP trial investigating plateau pressure response in these patients appears to be a reasonable strategy with minimal side effects.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Airway Obstruction / complications*
  • Airway Obstruction / physiopathology
  • Airway Obstruction / therapy*
  • Asthma / complications
  • Asthma / physiopathology
  • Asthma / therapy
  • Female
  • Hemodynamics
  • Humans
  • Lung Volume Measurements
  • Male
  • Middle Aged
  • Monitoring, Physiologic
  • Positive-Pressure Respiration / adverse effects*
  • Pulmonary Disease, Chronic Obstructive / complications
  • Pulmonary Disease, Chronic Obstructive / physiopathology
  • Pulmonary Disease, Chronic Obstructive / therapy
  • Ventilators, Mechanical