Reverse Triggering during Venovenous Extracorporeal Membrane Oxygenation: Magnitude of the Reverse Triggering Effort Mediated by Inspiratory Pressure

An 18-year-old woman was intubated for severe vaping-associated lung injury resulting in an extreme obstructive pulmonary disease with the shedding of bronchial epithelial tissue. She was on pressurecontrolled ventilation (4 mL/kg IBW, respiratory rate 10/min) and veno-venous extracorporeal membrane oxygenation (VV-ECMO; settings: blood flow 3.7 L/min, sweep gas flow (SGF) 4.5 L/min, FiO2 100%) because of severe hypercapnia and barotrauma pneumomediastinum) to provide lung rest for the epithelial tissue to regenerate. On day 5 of VV-ECMO and with high-dose sedation with propofol, midazolam, sufentanyl and ketamine (Richmond Agitation and Sedation Scale score -5) and
low-dose neuromuscular blockade, she demonstrated reverse triggering (RT)[1,2](Fig.1). Esophageal pressure (Pes) monitoring was used aiming to achieve lung- and diaphragm-protective targets[3] for effort and transpulmonary driving pressures (PL) by modifying ventilator pressure (Ppeak), SGF or set
respiratory rate. With sedation and other settings kept constant, increasing Ppeak reduced the magnitude of RT efforts; however, the resultant dynamic PL
increased (Fig.1). Adjusting SGF (4.5–6 –8 L/min) did not alter the magnitude or rate of RT efforts (∆Pes remained constant at 13.7±1.0 cmH2O for all
conditions). Changing the set rate (applied range 6–18/min) changed the RT pattern in a nonpredictable manner. Phase-locking was constant across RT breaths during all conditions. Increasing PEEP as potential modifiable factor of effort[4] was not studied to limit the risks of hyperinflation in this patient.
RT is complex and a multitude of factors can mediate respiratory entrainment[1]. Our unique observation during VV-ECMO suggests that the magnitude of RT efforts was mediated by lung/chest wall receptors upon passive insufflation (Hering-Breuer reflex), and not by CO2 (no influence of
different SGFs). It also highlights the importance of quantifying effort during RT. Because of the high lung stress during RT, rocuronium was increased to resume fully-controlled ventilation.