[Comparative study of recruitment maneuver guided by pressure-volume curve on respiratory physiology and lung morphology between acute respiratory distress syndrome of pulmonary and extrapulmonary origin in canine models].

OBJECTIVE: To determine effects of recruitment maneuver (RM) guided by pressure-volume (P-V) curve on respiratory physiology and lung morphology in canine models of acute respiratory distress syndrome of pulmonary or extrapulmonary origin (ARDSp and ARDSexp).

METHODS: Twenty-four healthy dogs were randomly divided into two groups with 12 dogs each: ARDSexp and ARDSp. Each dog in ARDSexp group was injected with oleic acid 0.1 ml/kg through femoral vein, and each dog in ARDSp group received hydrochloric acid 2 ml/kg via trachea. Subsequently, dogs with both models were randomly subdivided into lung protective ventilation strategy (LPVS) group and LPVS+RM group, respectively. Dogs in LPVS group were given LPVS only without RM. RM guided by P-V curve was performed in LPVS+RM group followed by LPVS and pressure controlled ventilation (PCV) mode was selected. Phigh was set at upper inflection point (UIP) of the P-V curve, positive end-expiratory pressure (PEEP) was set at lower inflection point (LIP)+2 cm H(2)O (1 cm H(2)O=0.098 kPa), and the duration of RM was 60 seconds. The duration of mechanical ventilation (MV) in both subgroups was 4 hours. The oxygenation index (PaO(2)/FiO(2)), relative lung mechanical indexes were measured in two ARDS models before establishment of ARDS model, and before and after RM. The UIP and LIP were calculated with P-V curve. The percentage of different volume in ventilation of lung accounting for total lung volume was compared by CT scan.

RESULTS: The PaO(2)/FiO(2), UIP and LIP did not showed significant differences among all groups before ARDS and before RM. PaO(2)/FiO(2) and respiratory system compliance (Crs) were significantly elevated in LPVS+RM group of both models 4 hours after RM compared with corresponding LPVS group [PaO(2)/FiO(2) (mm Hg, 1 mm Hg=0.133 kPa) of ARDSexp model: 263.9±69.2 vs. 182.8±42.8, Crs (ml/cm H(2)O) of ARDSexp model: 11.3±4.2 vs. 9.7±3.7; PaO(2)/FiO(2) (mm Hg) of ARDSp model: 193.4±33.5 vs. 176.4±40.2, Crs (ml/cm H(2)O) of ARDSp model: 10.1±3.9 vs. 9.0±3.9, P<0.05 or P<0.01], and the airway pressure was significantly declined compared with corresponding LPVS group [peak inspiratory pressure (PIP), cm H(2)O ] of ARDSexp model: 24.1±7.4 vs. 30.2±8.5, plateau pressure (Pplat, cm H(2)O) of ARDSexp model: 19.1±7.3 vs. 25.6±7.7; PIP (cm H(2)O) of ARDSp model: 26.6±8.4 vs. 29.6±10.3, Pplat (cm H(2)O) of ARDSp model: 21.9±7.3 vs. 25.1±8.4, P<0.05 or P<0.01]. Moreover, PaO(2)/FiO(2), Crs, PIP and Pplat were improved better in ARDSexp model than ARDSp model (P<0.05 orP<0.01). Compared with LPVS maneuver, RM plus LPVS maneuver could significantly decrease the proportion of closure and hypoventilation region, and increase the proportion of normal ventilation region in both models [closure region of ARDSexp model: (9.9±3.1)% vs. (16.3±5.2)%, hypoventilation region of ARDSexp model: (10.2±4.2)% vs. (23.4±6.7)%, normal ventilation region of ARDSexp model: (76.2±12.3)% vs. (57.5±10.1)%; closure region of ARDSp model: (14.3±4.8)% vs. (18.2±5.1)%, hypoventilation region of ARDSp model: (17.4±6.3)% vs. (24.1±5.9)%, normal ventilation region of ARDSp model: (63.2±10.7)% vs. (54.6±11.3)%, P<0.05 or P<0.01]. All of the ventilation regions were better improved with ARDSexp model than ARDSp model (all P<0.05).

CONCLUSION: RM guided by P-V curve could help obtain better oxygenation, improve pulmonary compliance and lung ventilation in ARDSexp and ARDSp, and better treatment effects are seen in ARDSexp dogs than ARDSp dogs.