Influence of the end inspiratory pause on respiratory mechanics and tidal gas distribution of surgical patients ventilated under a tailored open lung approach strategy: A randomised, crossover trial

Abstract

Background: The effect of modifying the end inspiratory pause (EIP) on respiratory mechanics and gas distribution of surgical patients ventilated with an open lung approach (OLA) has not been addressed before.

Methods: Prospective, randomised, crossover study carried out in a tertiary hospital. Subjects were assigned to receive an initial EIP of 10% or 30% of the total inspiratory time. We compared standard ventilation [time 0: tidal volume (V_T) 7 mL × kg^-1, respiratory rate (RR) 13, inspiratory:expiratory (I:E) rate 1:2, positive end-expiratory pressure (PEEP) 5 cm H₂O and EIP 10% and 30% for groups 1 and 2, respectively) with tailored OLA (similar parameters except for a tailored PEEP after a stepwise recruitment manoeuvre), followed by a crossover assignment sequence between groups (times 2-4).

Results: We included 32 adult subjects undergoing major surgery. Tailored OLA strategy was associated with a significant increase in PEEP, plateau pressure (P_plat), PaO₂, and compliance of the respiratory system (C_RS) with a significant decrease in driving pressure (P_driv) and PaCO₂, and a more homogeneous gas distribution in both groups. A significantly lower PEEP (p < 0.001), P_driv (5 [5-6] versus 6.5 [6-8] cmH₂O; p < 0.001) and mean airway pressure (P_mean; p < 0.001) together with a higher C_RS (77 [67-87] versus 58 [52-70] ml*cmH₂O^-1; p < 0.001) were observed when an EIP of 30% was applied as compared to an EIP of 10%.

Conclusion: The use of a tailored OLA strategy combined with a longer EIP is associated with a higher C_RS, and a lower P_driv, P_mean and PEEP. Additional studies are necessary to assess if the improved ventilatory conditions observed with a longer EIP are associated with better patients' outcomes. Trial registration at clinicaltrials.gov with identifier: NCT03568786.

Keywords: Driving pressure; Electric impedance; End-inspiratory pause; Lung compliance; Positive end expiratory pressure; Pulmonary gas exchange.