Individualized flow-controlled ventilation compared to best clinical practice pressure-controlled ventilation: a prospective randomized porcine study

Abstract

Background: Flow-controlled ventilation is a novel ventilation method which allows to individualize ventilation according to dynamic lung mechanic limits based on direct tracheal pressure measurement at a stable constant gas flow during inspiration and expiration. The aim of this porcine study was to compare individualized flow-controlled ventilation (FCV) and current guideline-conform pressure-controlled ventilation (PCV) in long-term ventilation.

Methods: Anesthetized pigs were ventilated with either FCV or PCV over a period of 10 h with a fixed FiO₂ of 0.3. FCV settings were individualized by compliance-guided positive end-expiratory pressure (PEEP) and peak pressure (P_peak) titration. Flow was adjusted to maintain normocapnia and the inspiration to expiration ratio (I:E ratio) was set at 1:1. PCV was performed with a PEEP of 5 cm H₂O and P_peak was set to achieve a tidal volume (V_T) of 7 ml/kg. The respiratory rate was adjusted to maintain normocapnia and the I:E ratio was set at 1:1.5. Repeated measurements during observation period were assessed by linear mixed-effects model.

Results: In FCV (n = 6), respiratory minute volume was significantly reduced (6.0 vs 12.7, MD - 6.8 (- 8.2 to - 5.4) l/min; p < 0.001) as compared to PCV (n = 6). Oxygenation was improved in the FCV group (paO₂ 119.8 vs 96.6, MD 23.2 (9.0 to 37.5) Torr; 15.97 vs 12.87, MD 3.10 (1.19 to 5.00) kPa; p = 0.010) and CO₂ removal was more efficient (paCO₂ 40.1 vs 44.9, MD - 4.7 (- 7.4 to - 2.0) Torr; 5.35 vs 5.98, MD - 0.63 (- 0.99 to - 0.27) kPa; p = 0.006). P_peak and driving pressure were comparable in both groups, whereas PEEP was significantly lower in FCV (p = 0.002). Computed tomography revealed a significant reduction in non-aerated lung tissue in individualized FCV (p = 0.026) and no significant difference in overdistended lung tissue, although a significantly higher V_T was applied (8.2 vs 7.6, MD 0.7 (0.2 to 1.2) ml/kg; p = 0.025).

Conclusion: Our long-term ventilation study demonstrates the applicability of a compliance-guided individualization of FCV settings, which resulted in significantly improved gas exchange and lung tissue aeration without signs of overinflation as compared to best clinical practice PCV.

Keywords: Pulmonary atelectasis; Respiration, artificial; Respiratory mechanics; Stress mechanical; Tomography, X-ray computed; Ventilator-induced lung injury.

Fig. 1

The pressure-volume loop (PV loop) obtained from intratracheal pressure measurement in a pilot animal. In the left graph, ventilation was performed without positive end-expiratory pressure (PEEP) and a peak pressure (P_peak) of 25 cm H₂O, showing a sigmoid shape of the PV loop. After compliance-guided pressure adjustment PEEP was set to 4 cm H₂O and P_peak to 18 cm H₂O, resulting in an almost linear relation between pressure and volume (right graph)

Fig. 2

Course of parameters over 10-h ventilation with FCV or PCV. a Respiratory minute volume (MV). b Arterial partial pressure of carbon dioxide. c Arterial partial pressure of oxygen at a fixed 0.3 fraction of inspired oxygen

Fig. 3

The Hounsfield unit (HU) distribution after 10 h of ventilation. Defining lung tissue aeration as non-aerated (HU 100 to − 100), poorly aerated (HU − 101 to − 500), normal aerated (HU − 501 to − 900), and overdistended (HU − 901 to − 1000) revealed no increase in overdistended, but a significant decrease in non-aerated lung tissue (p = 0.026)