Expiratory Flow Limitation During Mechanical Ventilation

Abstract

Expiratory flow limitation (EFL) is present when the flow cannot rise despite an increase in the expiratory driving pressure. The mechanisms of EFL are debated but are believed to be related to the collapsibility of small airways. In patients who are mechanically ventilated, EFL can exist during tidal ventilation, representing an extreme situation in which lung volume cannot decrease, regardless of the expiratory driving forces. It is a key factor for the generation of auto- or intrinsic positive end-expiratory pressure (PEEP) and requires specific management such as positioning and adjustment of external PEEP. EFL can be responsible for causing dyspnea and patient-ventilator dyssynchrony, and it is influenced by the fluid status of the patient. EFL frequently affects patients with COPD, obesity, and heart failure, as well as patients with ARDS, especially at low PEEP. EFL is, however, most often unrecognized in the clinical setting despite being associated with complications of mechanical ventilation and poor outcomes such as postoperative pulmonary complications, extubation failure, and possibly airway injury in ARDS. Therefore, prompt recognition might help the management of patients being mechanically ventilated who have EFL and could potentially influence outcome. EFL can be suspected by using different means, and this review summarizes the methods to specifically detect EFL during mechanical ventilation.

Airway Closure during Surgical Pneumoperitoneum in Obese Patients

“…This is consistent with the hypothesized cause for airway collapse in spontaneously breathing patients with active expiration, highlighting the close relationship between this condition and the wider concept of expiratory flow limitation. 3,28 Importantly, in our patients with airway closure, the increase in the expiratory driving pressure (i.e., plateau pressure minus set PEEP) produced by pneumoperitoneum did not result in reduction in end-expiratory lung volume, which is itself a diagnostic criterion for certifying limited expiratory flow. 3 Other authors reported respiratory mechanics compatible with airway closure during laparoscopic surgery in obese patients, showing that neither the "critical pressure" (i.e., the airway opening pressure) nor end-expiratory esophageal pressure was modified by surgical pneumoperitoneum and suggesting that this procedure could not act as a compression force for lungs and airways at end expiration.…”

“…3,28 Importantly, in our patients with airway closure, the increase in the expiratory driving pressure (i.e., plateau pressure minus set PEEP) produced by pneumoperitoneum did not result in reduction in end-expiratory lung volume, which is itself a diagnostic criterion for certifying limited expiratory flow. 3 Other authors reported respiratory mechanics compatible with airway closure during laparoscopic surgery in obese patients, showing that neither the "critical pressure" (i.e., the airway opening pressure) nor end-expiratory esophageal pressure was modified by surgical pneumoperitoneum and suggesting that this procedure could not act as a compression force for lungs and airways at end expiration. 6,7 Differently, our findings indicate that pneumoperitoneum increases esophageal pressure and airway opening pressure: in previous case series, 6,7 patients were studied in the supine or reverse Trendelenburg position, while our study shows pneumoperitoneum effects in head-down position.…”

Airway Clearance Techniques for Mechanically Ventilated Patients: Insights for Optimization

“…12 However, patients with unstable airways or reduced lung volumes may be susceptible to expiratory flow limitation during compressive or forced expiratory maneuvers, which is believed to be related to the collapsibility of airways. 28,29 If the airways collapse, the downstream flow drops to zero and secretion removal is interrupted. 12,28 In mechanically ventilated patients, expiratory flow limitation is frequently observed in individuals with COPD, obesity, and cardiac failure, and this limitation is influenced by fluid status, the patient's position, bronchoconstriction, and ventilatory conditions.…”

Biomedical engineer’s guide to the clinical aspects of intensive care mechanical ventilation

“…Moreover, improved modelling, for example adding EIT signals, may improve alignment between the ventilator and the patient by modelling patient efforts. Expiratory flow limitation (EFL) is believed to occur when smaller airways constrict during expiration, isolating areas of residual high pressure and thus limiting gas exchange [ 209 ]. Appropriate MV settings, especially PEEP, for patients with EFL can be very different than typical care; improved modelling could aid detection and PEEP titration to deliver appropriate patient-specific care [ 209 ].…”

“…Expiratory flow limitation (EFL) is believed to occur when smaller airways constrict during expiration, isolating areas of residual high pressure and thus limiting gas exchange [ 209 ]. Appropriate MV settings, especially PEEP, for patients with EFL can be very different than typical care; improved modelling could aid detection and PEEP titration to deliver appropriate patient-specific care [ 209 ]. MV intended to be protective can negatively affect hemodynamics in ARDS patients [ 1 ].…”