Effects of two stepwise lung recruitment strategies on respiratory function and haemodynamics in anaesthetised pigs: A randomised crossover study.

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 (VT) 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, VT was increased stepwise by 4 ml kg-1 at a fixed PEEP of 12 cmH2O until a plateau pressure of 30 to 35 cmH2O was reached. In the iPROVE strategy, at fixed driving pressure of 20 cmH2O, PEEP was increased up to 20 cmH2O followed by PEEP titration according to the lowest elastance of the respiratory system (ERS). MAIN OUTCOME MEASURES: We assessed regional transpulmonary pressure (Ptrans), 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 Ptrans was lower at end-inspiration (16.3 ±â€Š2.7 vs. 18.6 ±â€Š3.1 cmH2O, P = 0.001) and end-expiration (4.8 ±â€Š2.6 vs. 8.8 ±â€Š3.4 cmH2O, P  < 0.001), and mean arterial pressure (MAP) was higher (77 ±â€Š11 vs. 60 ±â€Š14 mmHg, P < 0.001). At 1 and 15 min after recruitment manoeuvres, ERS was higher in the PROVHILO strategy than the iPROVE strategy (24.6 ±â€Š3.9 vs. 21.5 ±â€Š3.4 and 26.7 ±â€Š4.3 vs. 24.0 ±â€Š3.8 cmH2O l-1; P  < 0.001, respectively). At 1 min, PaO2 was lower in PROVHILO compared with iPROVE strategy (57.1 ±â€Š6.1 vs. 59.3 ±â€Š5.1 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 Ptrans at the cost of lower MAP during recruitment manoeuvres, and decreased ERS 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).

Effects of Positive End-Expiratory Pressure and Spontaneous Breathing Activity on Regional Lung Inflammation in Experimental Acute Respiratory Distress Syndrome.

OBJECTIVES: To determine the impact of positive end-expiratory pressure during mechanical ventilation with and without spontaneous breathing activity on regional lung inflammation in experimental nonsevere acute respiratory distress syndrome. DESIGN: Laboratory investigation. SETTING: University hospital research facility. SUBJECTS: Twenty-four pigs (28.1-58.2 kg). INTERVENTIONS: In anesthetized animals, intrapleural pressure sensors were placed thoracoscopically in ventral, dorsal, and caudal regions of the left hemithorax. Lung injury was induced with saline lung lavage followed by injurious ventilation in supine position. During airway pressure release ventilation with low tidal volumes, positive end-expiratory pressure was set 4 cm H2O above the level to reach a positive transpulmonary pressure in caudal regions at end-expiration (best-positive end-expiratory pressure). Animals were randomly assigned to one of four groups (n = 6/group; 12 hr): 1) no spontaneous breathing activity and positive end-expiratory pressure = best-positive end-expiratory pressure - 4 cm H2O, 2) no spontaneous breathing activity and positive end-expiratory pressure = best-positive end-expiratory pressure + 4 cm H2O, 3) spontaneous breathing activity and positive end-expiratory pressure = best-positive end-expiratory pressure + 4 cm H2O, 4) spontaneous breathing activity and positive end-expiratory pressure = best-positive end-expiratory pressure - 4 cm H2O. MEASUREMENTS AND MAIN RESULTS: Global lung inflammation assessed by specific [F]fluorodeoxyglucose uptake rate (median [25-75% percentiles], min) was decreased with higher compared with lower positive end-expiratory pressure both without spontaneous breathing activity (0.029 [0.027-0.030] vs 0.044 [0.041-0.065]; p = 0.004) and with spontaneous breathing activity (0.032 [0.028-0.043] vs 0.057 [0.042-0.075]; p = 0.016). Spontaneous breathing activity did not increase global lung inflammation. Lung inflammation in dorsal regions correlated with transpulmonary driving pressure from spontaneous breathing at lower (r = 0.850; p = 0.032) but not higher positive end-expiratory pressure (r = 0.018; p = 0.972). Higher positive end-expiratory pressure resulted in a more homogeneous distribution of aeration and regional transpulmonary pressures at end-expiration along the ventral-dorsal gradient, as well as a shift of the perfusion center toward dependent zones in the presence of spontaneous breathing activity. CONCLUSIONS: In experimental mild-to-moderate acute respiratory distress syndrome, positive end-expiratory pressure levels that stabilize dependent lung regions reduce global lung inflammation during mechanical ventilation, independent from spontaneous breathing activity.

Ultra-low-dose sequential computed tomography for quantitative lung aeration assessment-a translational study.

BACKGROUND: Quantitative lung computed tomography (CT) provides fundamental information about lung aeration in critically ill patients. We tested a scanning protocol combining reduced number of CT slices and tube current, comparing quantitative analysis and radiation exposure to conventional CT. METHODS: In pigs, CT scans were performed during breath hold in a model of lung injury with three different protocols: standard spiral with 180 mAs tube current-time product (Spiral180), sequential with 20-mm distance between slices and either 180 mAs (Sequential180) or 50 mAs (Sequential50). Spiral scans of critically ill patients were collected retrospectively, and subsets of equally spaced slices were extracted. The agreement between CT protocols was assessed with Bland-Altman analysis. RESULTS: In 12 pigs, there was good concordance between the sequential protocols and the spiral scan (all biases ≤1.9%, agreements ≤±6.5%). In Spiral180, Sequential180 and Sequential50, estimated dose exposure was 2.3 (2.1-2.8), 0.21 (0.19-0.26), and 0.09 (0.07-0.10) mSv, respectively (p < 0.001 compared to Spiral180); number of acquired slices was 244 (227-252), 12 (11-13) and 12 (11-13); acquisition time was 7 (6-7), 23 (21-25) and 24 (22-26) s. In 32 critically ill patients, quantitative analysis extrapolated from 1-mm slices interleaved by 20 mm had a good concordance with the analysis performed on the entire spiral scan (all biases <1%, agreements ≤2.2%). CONCLUSIONS: In animal CT data, combining sequential scan and low tube current did not affect significantly the quantitative analysis, with a radiation exposure reduction of 97%, reaching a dose comparable to chest X-ray, but with longer acquisition time. In human CT data, lung aeration analysis could be extrapolated from a subset of thin equally spaced slices.