[Clinical research of using optimal compliance to determine positive end-expiratory pressure]

To observe the availability and security of optimal compliance strategy to titrate the optimal positive end-expiratory pressure (PEEP), compared with quasi-static pressure-volume curve (P-V curve) traced by low-flow method.

Fourteen patients received mechanical ventilation with acute respiratory distress syndrome (ARDS) admitted in intensive care unit (ICU) of Tianjin Third Central Hospital from November 2009 to December 2010 were divided into two groups(n = 7). The quasi-static P-V curve method and the optimal compliance titration were used to set the optimal PEEP respectively, repeated 3 times in a row. The optimal PEEP and the consistency of repeated experiments were compared between groups. The hemodynamic parameters, oxygenation index (OI), lung compliance (C), cytokines and pulmonary surfactant-associated protein D (SP-D) concentration in plasma before and 2, 4, and 6 hours after the experiment were observed in each group.

(1) There were no significant differences in gender, age and severity of disease between two groups. (2)The optimal PEEP [cm H(2)O, 1 cm H(2)O=0.098 kPa] had no significant difference between quasi-static P-V curve method group and the optimal compliance titration group (11.53 ± 2.07 vs. 10.57 ± 0.87, P>0.05). The consistency of repeated experiments in quasi-static P-V curve method group was poor, the slope of the quasi-static P-V curve in repeated experiments showed downward tendency. The optimal PEEP was increasing in each measure. There was significant difference between the first and the third time (10.00 ± 1.58 vs. 12.80 ± 1.92, P < 0.05). And the optimal compliance titration method had good reproducibility as the optimal PEEP without significant difference in each measure. (3) After the quasi-static P-V curve traced, the heart rate (HR, bpm), temperature (centigrade), interleukin-6 (IL-6, ng/L), tumor necrosis factor-α (TNF-α, ng/L), SP-D (μg/L) showed a gradually increasing tendency, the mean artery pressure (MAP, mm Hg, 1 mm Hg = 0.133 kPa), continuous cardiac index [CCI, L×min(-1)×m(-2)], OI (mm Hg), and C [ml/cm H(2)O] showed a gradually decreased tendency, all of these parameters reached the peak or trough at 6 hours after the experiment, and there was significance compared with those before experiment (HR: 117.34 ± 8.53 vs. 93.71 ± 5.38, temperature: 38.05 ± 0.73 vs. 36.99 ± 1.02, IL-6: 144.84 ± 23.89 vs. 94.73 ± 5.91, TNF-α: 151.46 ± 46.00 vs. 89.86 ± 13.13, SP-D: 33.65 ± 8.66 vs. 16.63 ± 5.61, MAP: 85.47 ± 9.24 vs. 102.43 ± 8.38, CCI: 3.00 ± 0.48 vs. 3.81 ± 0.81, OI: 62.00 ± 21.45 vs. 103.40 ± 37.27, C: 32.10 ± 2.92 vs. 49.57 ± 7.18, all P < 0.05). The results suggested that the drawing of quasi-static P-V curve would aggravate the lung injury. And in optimal compliance titration method group, there were no significant differences in HR, MAP, temperature, CCI, OI, C, cytokines and SP-D before and after titration.

Optimal compliance titration method has good reproducibility, safety and usability.