[Effect of unilateral lung recruitment maneuver on hemodynamics and dead space ratio in pigs with unilateral acute respiratory distress syndrome].

OBJECTIVE

To compare unilateral lung and traditional lung recruitment maneuver (RM) in animals with unilateral acute respiratory distress syndrome (ARDS) by implementing independent lung ventilation, and to explore the rational mechanical ventilation strategy for unilateral lung lesions.

METHODS

Healthy hybrid pigs were used as experimental animals, and they were divided into two groups according to random number table method (sealed concealed envelope). There were 20 pigs in each group. According to different methods of lung RM, the conventional mechanical ventilation (i.e. implementing ventilation for both lung by using a ventilator) was performed as control group; the individual lung ventilation (that was, implementing ventilation for both lung individually by using two ventilators) as independent lung ventilation group. The model of left lung ARDS was reproduced, and the respective RM was implemented according to respective method of the two groups. The differences in hemodynamic parameters and dead space ratio (VD/VT) between two groups under the RM pressure of 20, 40, 60 cmH₂O (1 cmH₂O=0.098 kPa) were observed.

RESULTS

(1) Hemodynamics parameters changes: with the increase in RM pressure, the heart rate (HR) in control group showed a tendency of gradual increase, and the level at 60 cmH₂O was significantly higher than that at 20 cmH₂O (192.65 ± 22.99 bpm vs. 178.20 ± 18.25 bpm, P<0.05). Mean arterial pressure (MAP) showed a tendency of gradual decrease, and that at 60 cmH₂O was lower significantly than that at 20 cmH₂O and 40 cmH₂O (78.55±25.77 mmHg (1 mmHg=0.133 kPa) vs. 112.40 ± 10.84 mmHg, 106.15 ± 13.54 mmHg, both P<0.01). Cardiac output (CO) gradually lowered, and the differences at 20, 40, 60 cmH₂O were logistically significant (11.14 ± 2.65 L/min, 9.56 ± 2.17 L/min, 6.01 ± 1.39 L/min, P<0.05 or P<0.01). With an increase in RM pressure, the difference in HR, MAP, CO in independent lung ventilation group were not significant, and the HR at 60 cmH₂O was significantly lower than that of the control group (178.20 ± 18.26 bpm vs. 192.65 ± 22.99 bpm, P<0.05), and MAP and CO were significantly higher than those of the control group (MAP: 110.80 ± 11.60 mmHg vs. 78.55 ± 25.77 mmHg, CO: 9.68 ± 2.08 L/min vs. 6.01 ± 1.39 L/min, both P<0.01). (2) VD/VT changes: with an increase in RM pressure, the oxygenation index (PaO₂/FiO₂) in control group showed a tendency of gradual decrease, and the level at 60 cmH₂O was significantly lower than that at 20 cmH₂O and 40 cmH₂O (126.40 ± 37.55 mmHg vs. 187.40 ± 21.66 mmHg, 175.20 ± 23.00 mmHg, both P<0.01). On the right side, VD/VT showed a tendency of gradual increase, and there was statistical significance in paired comparison among 20, 40, 60 cmH₂O (0.52 ± 0.12, 0.60 ± 0.15, 0.72 ± 0.12, P<0.05 or P<0.01). There was no obvious change on the left side. Along with the increase in RM pressure, the PaO₂/FiO₂ of independent lung ventilation group showed a tendency of gradual increase, and that at 40 cmH₂O and 60 cmH₂O were significantly higher than that at 20 cmH₂O (244.45 ± 53.93 mmHg, 270.05 ± 53.42 mmHg vs. 205.65 ± 31.33 mmHg, P<0.05 and P<0.01), and the level at 20, 40, 60 cmH₂O was higher than that of the control group (205.65±31.33 vs. 187.40 ± 21.66, P<0.05; 244.45 ± 53.93 vs. 175.20 ± 23.00, P<0.01; 270.05 ± 53.42 vs. 126.40 ± 37.55, P<0.01). There were no changes in VD/VT on both sides, and VD/VT on the right side was significantly lower than that of the control group when the inflation pressure was 20, 40, 60 cmH₂O (0.38 ± 0.14 vs. 0.52 ± 0.12, 0.43 ± 0.11 vs. 0.60 ± 0.15, 0.50 ± 0.13 vs. 0.72 ± 0.12, all P<0.01).

CONCLUSIONS

For severe ARDS caused by single lung injury, implementation of independent lung RM on the basis of independent lung mechanical ventilation for individual lung was significantly superior to the traditional lung RM for the improvement of hemodynamic parameters and VD/VT.