Objective: To investigate the effects of asynchronous independent lung ventilation and synchronous independent lung ventilation with different levels of positive end-expiratory pressure (PEEP) and tidal volumes on hemodynamics and gas exchange in dogs with a hydrochloric acid induced acute lung injury.
Methods: Twelve dogs with hydrochloric acid induced acute lung injury (left lung) were ventilated with volume controlled ventilation (VCV). The animals were randomly divided by random digit table into 2 groups. The first group (group NS, n = 6) received asynchronous independent lung ventilation with the left lung PEEP 10 cm H2O (1 cm H2O = 0.098 kPa), VT 3.5 ml/kg and the right lung PEEP 0 cm H2O, VT 5 ml/kg. The second group (group S, n = 6) received synchronous independent lung ventilation with the parameters as same as group NS. HR, mABP, mPAP, PAWP, CO and blood gas levels were measured during ventilation with different levels of PEEP (15, 20, 25 cm H2O) and VT (5, 7.5, 10 ml/kg) for 30 min.
Results: (1) After 30 min ventilation, no significant differences for hemodynamics and gas exchange were found between group NS and group S when Left lung PEEP was 15 or 20 cm H2O and VT was 5 or 7.5 ml/kg. (2) After 30 min ventilation, HR, mABP, CO, PaO2/FiO2, SvO2 in group NS [(98 ± 8) beats/min, (84 ± 6) mm Hg (1 mm Hg = 0.133 kPa), (1.10 ± 0.13) L/min, (199 ± 14) mm Hg and (55 ± 6)%, respectively] were significantly lower than those in group S [(124 ± 9) beats/min, (103 ± 7) mm Hg, (1.52 ± 0.28) L/min, (221 ± 15) mm Hg and (62 ± 4)%, respectively] when PEEP was 25 cm H2O (all P < 0.01). (3) After 30 min ventilation, HR, mABP, CO, PaO2/FiO2, SvO2 in group NS [(92 ± 6) beats/min, (83 ± 9) mm Hg, (1.23 ± 0.08) L/min, (196 ± 8) mm Hg and (57 ± 2)%, respectively] were significantly lower than those in group S [(122 ± 10) beats/min, (104 ± 4) mm Hg, (1.56 ± 0.12) L/min, (216 ± 14) mm Hg and (63 ± 4)%, respectively] when VT was 10 ml/kg (all P < 0.01).
Conclusions: In this animal model, the hemodynamics kept stable when the difference between the left lung PEEP and the right lung PEEP was less than 20 cm H2O. Synchronous independent lung ventilation caused less hemodynamic compromise when higher PEEP (> 25 cm H2O) was used because of the marked asymmetry in the mechanics of the 2 lungs.