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

Abstract

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 (V T : 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 (≥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 MainResults-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 zeroexternal-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.* See also p. 1652.The authors have no financial interest to disclose. -12). Besides the associated hemodynamic impairment, patients with obstructive pulmonary disease frequently experience dyssynchrony during assisted ventilation and difficulty triggering mechanical breaths (2)(3)(4)6,9,10,13,14). This difficulty is caused by the large difference between alveolar and upstream pressures at end-expiration (intrinsic positive end-expiratory pressure, or intrinsic-PEEP), imposing an increased load on inspiratory muscles. NIH Public AccessUnder such conditions, external-PEEP application minimizes pressure differences across obstructed airways, reducing the effort to trigger the ventilator (2-4,9,10). ...

Anesthesia for patients with severe chronic obstructive pulmonary disease

“…If external PEEP is less than or equal to PEEP i then there should be no significant increase in alveolar pressure, and alveolar emptying should improve due to decreased dynamic airway compression [30]. This is supported by a study [31] demonstrating that the addition of PEEP to some (i.e. five of eight patients studied), but not all, patients with COPD or asthma exacerbation may actually reduce end-inspiratory plateau pressure, thus indicating less air trapping.…”

Effect of Albuterol on Expiratory Resistance in Mechanically Ventilated Patients

“…Nonetheless, it has not been clearly determined in which patients applied PEEP improves lung emptying, or the optimum PEEP for each patient. 14 …”

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“…33 Hyperinsufflation increases the positive intrathoracic pressure, accentuating the decrease in venous return and preloading of both ventricles, and increasing the pulmonary vascular resistances and thus right ventricle post-loading. Hypotension is the most common effect of diminished preload, and is accentuated by hypovolemia.…”