[Effect of lung stress index upon titration of positive end-expiratory pressure at post-recruitment in patients with acute respiratory distress syndrome].
OBJECTIVE
To investigate the relationship of stress index and positive end-expiratory pressure (PEEP) in patients with acute respiratory distress syndrome (ARDS) and to determine the relationship of stress index, lung recruitment, oxygenation and respiration mechanics.


METHODS
Fourteen ARDS patients were enrolled. During volume control ventilation with constant inspiratory flow, the pressure-time (P-t) curve was fitted to a power equation: P = a x time(b) + c, where coefficient b (stress index) describes the shape of curve: b = 1, straight curve; b < 1, progressive increase in slope; and b > 1, progressive decrease in slope. Positive end-expiratory pressure (PEEP) was set to obtain b value between 0.9 and 1.1 after application of a recruiting maneuver (RM). PEEP was changed to obtain 0.6 < b < 0.8 and 1.1 < b < 1.3. The sequence of experimental conditions was random. Recruited volume (RV) was measured by static pressure-volume curve method. Hemodynamics, pulmonary mechanics and gas exchange were observed simultaneously.


RESULTS
PEEP at b < 1, b = 1 and b > 1 were (8.3 +/- 1.5) cm H2O, (15.0 +/- 1.9) cm H2O and (18.4 +/- 1.9) cm H2O respectively with a significant difference (P < 0.001). At b = 1 and b > 1, the partial arterial oxygen tension (PaO2/FiO2) [(350 +/- 113) mm Hg, (338 +/- 124 mm Hg)] were higher than that [165 +/- 60) mm Hg] of pre-RM (P < 0.05). the plateau pressure (Pplat) at b = 1 [(29 +/- 4) cm H2O] and b > 1 [(33 +/- 7) cm H2O] post-RM were significantly higher than that at b < 1 [(22 +/- 4) cm H2O] (P < 0.05); the Pplat at b > 1 was higher than that [(25 +/- 16) cm H2O] pre-RM (P < 0.05). Compared with the static pulmonary compliance (Cst) at b = 1 [(39 +/- 11) ml/cm H2O], Cst at b > 1 [(26 +/- 7) ml/cm H2O] decreased significantly (P < 0.05). The RV at b = 1 and b > 1 [(402 +/- 204) ml, (588 +/- 269) ml] were significantly higher than that at pre-RM and b < 1 [(136 +/- 111) ml, (175 +/- 122) ml] (P < 0.05). At pre-RM, b < 1, b = 1 and b > 1, HR, mean arterial pressure (MAP) and lactate showed no significant difference (P > 0.05).


CONCLUSIONS
Stress index at post-RM can be an excellent method of PEEP titration for ARDS patients.
Huang
Ying-Zi
YZ
Department of Critical Care Medicine, Nanjing Zhongda Hospital, School of Clinical Medicine, Southeast University, Nanjing 210009, China.
Yang
Yi
Y
Liu
Song-Qiao
SQ
Yang
Cong-Shan
CS
Qiu
Hai-Bo
HB
D000293:Adolescent; D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D008168:Lung / Q000503:physiopathology*; D008170:Lung Compliance; D008297:Male; D008875:Middle Aged; D011175:Positive-Pressure Respiration; D012128:Respiratory Distress Syndrome / Q000503:physiopathology* / Q000628:therapy*; D055815:Young Adult