[Relationship of stress index with lung recruitment and gas exchange in dogs with acute respiratory distress syndrome].
OBJECTIVE
To determine the relationship of stress index with lung recruitment and gas exchange in dogs with acute respiratory distress syndrome (ARDS).


METHODS
The ARDS model was induced by infusion of oleic acid intravenously in anesthetized dogs. During volume control ventilation with constant inspiratory flow, the pressure-time (P-t) curve was fitted to a power equation: P = a.time(b)+c, where coefficient b (stress index) describes the shape of the curve: b = 1, straight curve; b < 1, progressive increase in slope; and b > 1, progressive decrease in slope. Tidal volume (V(T)) was 6 ml/kg, and positive end-expiratory pressure (PEEP) was set to obtain a b value between 0.9 and 1.1 before (b = 1) and after (b = 1 after recruiting maneuver) application of a recruiting maneuver (RM). PEEP was changed to obtain 0.6 < b < 0.8 and 1.1 < b < 1.3. Experimental condition sequence was random. Recruited volume (RV) was measured by static pressure-volume curve method. Hemodynamics, pulmonary mechanics and gas exchange were observed at the same time.


RESULTS
At b = 1 without RM, the PEEP was (5.0 +/- 3.0) cm H2O, the RV was (27 +/- 15) ml, and the RV increased to (166 +/- 84) ml significantly at b = 1 after RM [PEEP (10.8 +/- 2.3) cm H2O (1 cm H2O = 0.098 kPa), q = 3.18, P < 0.01]. At 1.1 < b < 1.3 after RM, the PEEP was (16.8 +/- 1.1) cm H2O and the RV was (262 +/- 57) ml, which was higher than that at b = 1 after RM (q = 2.54, P = 0.023). At 0.6 < b < 0.8 after RM, the PEEP was (5.6 +/- 2.2) cm H2O and the RV was lower than that at b = 1 after RM (q = 2.85, P = 0.013). The partial pressure of oxygen in arterial blood (PaO2) in b = 1, 0.6 < b < 0.8 and 1.1 < b < 1.3 after RM were (319 +/- 49) mm Hg (1 mm Hg = 0.133 kPa), (246 +/- 57) mm Hg and (314 +/- 27) mm Hg respectively, which was higher than the PaO2 at b = 1 without RM [(153 +/- 64) mm Hg, all q = 2.81, all P < 0.05]. The PaO2 at 0.6 < b < 0.8 was lower than that at b = 1 after RM (q = 2.81, P = 0.005), while there was no significant difference between the PaO2 at 1.1 < b < 1.3 and that at b = 1 after RM. The peak airway pressure and plateau pressure at 1.1 < b < 1.3 were higher than those at b = 1 after RM (q = 6.02, 5.72, all P < 0.05).


CONCLUSIONS
In the b = 1 after RM, there were better PaO2 and lower airway pressure, suggesting that b = 1 after RM may be a good indicator for PEEP titration.
Qiu
Hai-bo
HB
Department of Critical Care Medicine, Zhong-da Hospital and School of Clinical Medicine, Southeast University, Nanjing 210009, China.
Chen
Yong-ming
YM
Yang
Yi
Y
Shen
Ju-fang
JF
Li
Jia-qiong
JQ
Wu
Bin
B
Li
Na
N
D000818:Animals; D004195:Disease Models, Animal; D004285:Dogs; D005260:Female; D008168:Lung / Q000378:metabolism* / Q000503:physiopathology*; D008297:Male; D010100:Oxygen / Q000378:metabolism; D011175:Positive-Pressure Respiration; D011661:Pulmonary Stretch Receptors / Q000378:metabolism* / Q000503:physiopathology*; D012123:Pulmonary Ventilation; D012128:Respiratory Distress Syndrome / Q000378:metabolism* / Q000503:physiopathology*
D010100:Oxygen