Effects of two stepwise lung recruitment strategies on respiratory function and haemodynamics in anaesthetised pigs

BACKGROUND Lung recruitment manoeuvres and positive end-expiratory pressure (PEEP) can improve lung function during general anaesthesia. Different recruitment manoeuvre strategies have been described in large international trials: in the protective ventilation using high vs. low PEEP (PROVHILO) strategy, tidal volume ( V T ) was increased during volume-controlled ventilation; in the individualised peri-operative open-lung approach vs. standard protective ventilation in abdominal surgery (iPROVE) strategy, PEEP was increased during pressure-controlled ventilation. OBJECTIVES To compare the effects of the PROVHILO strategy and the iPROVE strategy on respiratory and haemodynamic variables. DESIGN Randomised crossover study. SETTING University hospital research facility. ANIMALS A total of 20 juvenile anaesthetised pigs. INTERVENTIONS Animals were assigned randomly to one of two sequences: PROVHILO strategy followed by iPROVE strategy or vice-versa ( n = 10/sequence). In the PROVHILO strategy, V T was increased stepwise by 4 ml kg −1 at a fixed PEEP of 12 cmH 2 O until a plateau pressure of 30 to 35 cmH 2 O was reached. In the iPROVE strategy, at fixed driving pressure of 20 cmH 2 O, PEEP was increased up to 20 cmH 2 O followed by PEEP titration according to the lowest elastance of the respiratory system (E RS ). MAIN OUTCOME MEASURES We assessed regional transpulmonary pressure (P trans ), respiratory system mechanics, gas exchange and haemodynamics, as well as the centre of ventilation (CoV) by electrical impedance tomography. RESULTS During recruitment manoeuvres with the PROVHILO strategy compared with the iPROV strategy, dorsal P trans was lower at end-inspiration (16.3 ± 2.7 vs. 18.6 ± 3.1 cmH 2 O, P = 0.001) and end-expiration (4.8 ± 2.6 vs. 8.8 ± 3.4 cmH 2 O, P < 0.001), and mean arterial pressure (MAP) was higher (77 ± 11 vs. 60 ± 14 mmHg, P < 0.001). At 1 and 15 min after recruitment manoeuvres, E RS was higher in the PROVHILO strategy than the iPROVE strategy (24.6 ± 3.9 vs. 21.5 ± 3.4 and 26.7 ± 4.3 vs. 24.0 ± 3.8 cmH 2 O l −1 ; P < 0.001, respectively). At 1 min, P aO 2 was lower in PROVHILO compared with iPROVE strategy (57.1 ± 6.1 vs. 59.3 ± 5.1 kPa, P = 0.013), but at 15 min, values did not differ. CoV did not differ between strategies. CONCLUSION In anaesthetised pigs, the iPROVE strategy compared with the PROVHILO strategy increased dorsal P trans at the cost of lower MAP during recruitment manoeuvres, and decreased E RS thereafter, without consistent improvement of oxygenation or shift of the CoV. TRIAL REGISTRATION This study was registered and approved by the Landesdirektion Dresden, Germany (DD24–5131/338/28).