呼气相压力-容积曲线在急性呼吸窘迫综合征犬肺开放策略中的应用价值

Applicability of deflation limbs of pressure volume curves in the open lung approach in dogs with acute respiratory distress syndrome

目的研究急性呼吸窘迫综合征(ARDS)犬呼气相压力-容积(P-V)曲线的特点及其在实施肺开放策略中的应用价值。方法采用大注射器法绘制ARDS犬呼气相和吸气相P-V曲线,根据曲线转折点选择不同水平的呼气末正压(PEEP),分析动脉血气、肺呼吸力学和血流动力学变化规律。结果①ARDS犬P-V曲线吸气相有两个转折点:低位拐点(LIP)及高位拐点(UIP),压力分别为(8.77±0.88)cm H2O和(13.75±0.66)cm H2O;呼气相曲线仅一个拐点(PPMC,d),压力为(10.67±0.83)cm H2O。②当PEEP从0逐渐增加到PPMC,d+2 cm H2O时,PaO2逐渐升高,静动脉分流/总血流量比值.Qs/.Qt逐渐降低;气道平台压、峰压、平均气道压逐渐升高;心排出量(CO)逐渐下降,肺循环阻力(PVR)、体循环阻力(SVR)逐渐升高。与PLIP比较,PEEP在PPMC,d及PPMC,d+2 cm H2O时PaO2显著升高[(366.67±33.00)cm H2O和(431.30±19.23)cm H2O比(309.40±30.71)cm H2O,P<0.05],Q.s/.Qt显著降低[14.38±1.48)%和(12.14±0.94)%比(17.35±1.29)%,P<0.05]。PPMC,d和PPMC,d+2 cm H2O时PaO2和.Qs/.Qt水平均与健康犬的PaO2[(446.78±49.80)cm H2O]和.Qs/.Qt[(12.25±1.08)%]水平接近,其中.Qs/.Qt变化与健康犬比较差异无统计学意义,但对循环的抑制作用却明显增强。结论对病变早期的犬ARDS采用“肺开放策略”是可行的,适当水平的通气压力可使损伤肺组织基本开放,PEEP可选择在PPMC,d或稍高于PPMC,d的水平。

Objective To study the characteristics of the deflation limbs of pressure volume （P-V） curves in dogs with acute respiratory distress syndrome （ARDS） during mechanical ventilation, and to explore its applicability in the open lung strategy. Methods The super-syringe technique was used to obtain the deflation and inflation limb curves, and to ascertain the inflection points of the curves. The effects of PEEP at different levels on hemodynamics, gas exchange and lung mechanics were observed. Results There were two inflectionpoints on the inflation limbs of P-V curves in ARDS dogs, ie. the pressure of low inflection points （LIP） and upper inflection points （UIP） were （8.77 ± 0.88）cmH2O and （13.75± 0.66）cmH2O, respectively. The deflation limbs of pressure-volume curves had only one inflection point （PPMC.d） with a pressure of （10.67 ± 0.83） cmH2O.When PEEP increased from 0 to PPMC,d ＋ 2cmH2O, partial pressure of arterial oxygen （PaO2）, plateau pressure, peak pressure, mean airway pressure, PVR, and SVR were increased gradually while the ratio of shunted blood to total perfusion （Qs/Qt）, and cardiac output （CO） were decreased gradually.There was a significant increase of PaO2 at the PPMC.a[ （366.67 ± 33.00） cmH2O] and PPMC, d ＋ 2cmH2O [（431.30 ± 19.23） cmH2O ] compared with that at the PLIP [ （309.40 ± 30.71 ） cmH2O] （ both P 〈 0.05）. Qs/Qt was decreased significantly at the PPMC,d[（14.38 ± 1.48）%] and PPMC,d ＋ 2cmH2O [（12.14 ± 0.94）%] compared to PuP [ （ 17.35 ± 1.29） % ] （both P 〈 0.05）. Both PaO2 and QaO2 at the PPMC,d and PPMC,d ＋ 2cmH2O were similar to normal dogs＇ PaO2[ （446.78 ± 49.80）cmH2O] arid [（ 12.25 ± 1.08）%], and Qs/Qt had no significantly statistical difference with the normal dogs. While circulative resistance was increased significantly as the result of PEEP increased to PPMC,d ＋ 2cmH2O. Conclusions Open lung strategy is beneficial in early ARDS and proper airway pressure may open the injured hmg mostly. It is recommend that PEEP be set at the level of PPMC,d or slightly above the PPMC,d.