Background: Scenarios with increased intracranial pressure or haemodynamic instability often require mechanical ventilation applying the lowest possible pressures. The benefits of flow-controlled ventilation (FCV) on respiratory mechanics and gas exchange have been demonstrated previously, however, the effects of a possible setting with negative end-expiratory pressure has yet to be explored. We aimed at comparing gas exchange and haemodynamic parameters applying FCV with negative and positive end-expiratory pressures (EEP).

Methods: Nine pigs were anaesthetized and assigned in a random order to FCV with increasing positive EEPs (3, 6, 9 cmH₂O) and decreasing negative EEPs (-3, -6, -9 cmH₂O). Airway pressures (Paw), arterial partial pressures of oxygen and carbon dioxide along with hemodynamic parameters were assessed following 20 min ventilation at each EEP step (EEP 3-6-9).

Results: Applying negative EEPs during FCV resulted in significantly lower Paw than with positive EEPs (9.2±1.5 vs. 14.5±1.6 and cmH₂O at EEP 3; 8.7±1.6 vs 17.2±2.0 cmH₂O at EEP 6; 7.5±1.4 vs. 20.0±2.5 cmH₂O at EEP 9; p<0.05 for all). No differences in gas exchange were evidenced between the application of positive and negative EEPs. At EEP 6 and 9, increased mean arterial pressure and cardiac output was observed with negative EEP compared to positive EEP (p<0.05 respectively).

Conclusions: FCV applied with negative EEP improved haemodynamics and required lower Paw to maintain equal gas exchange as provided with positive EEP. Therefore, FCV with negative EEP may be a promising alternative in patients with increased intracranial pressure or haemodynamic instability.