Abstract:

To compare the differences of effects between   four kinds methods  on setting t
he optimal positive end expiratory pressure （PEEP）in animal models  with acute respiratory distress syndrome(ARDS),and to clarify the  feasibility of these methods to  confirm the optimal PEPP and to provide basis for ARDS treatment in clinic.
Methods The ARDS pig models were induced by intravenously infusing oleic acid(n=7).The optimal PEEP  level was determined by four kinds of  methods after lun
g recruitment:such as optimal PaO2 + PaCO2 method,optimal oxygenation method,optimal static compliance（Cst） method,and optimal dynamic compliance (Cdyn) method. Intrapulmonary shunt fraction（Qs/Qt）,plateau airway pressure (Pplat),Cst,dynamic compliance(Cdyn),oxygen index（OI）,central venous pressure（CVP）,cardiac output(CO), global end-diastolic volume(GEDV), intra-thoracic blood volume(ITBV),extravascular lung water（EVLW） of ARDS pigs were recorded before infusing oleic acid，after s
tabilization of ARDS model and at optimal  PEEP level. Results The optimal PEEP
（cmH2O） eleterminated by  optimal PaO2 + PaCO2  method(13.14±1.35),optimal oxygenation method( 13.43±1.51),optimal Cst method( 14.43±4.12 )and  optimal cdyn method(14.14±2.91) had no significant differences (P>0.05).The values of OI,Cst,Cdyn and arterial oxygen saturation(SaO2) in ARDS model were  significantly lower than those at the baseline level (P<0.05).Compared with ARDS model，the values of OI,Cst,Cdyn and SaO2 were significantly improved after using optimal  PEEP(P<0.05).The value of Qs/Qt was increased in   ARDS model compared with the baseline level(P<0.05);and the value of
SaO2 was decreased(P<0.05).The values of Qs/Qt and SaO2 were   decreased to the baseline level after using optimal PEEP.The values of CO,GEDV,and ITBV showed no significant differences(P>0.05) between the baseline level，ARDS model and optimal PEEP level；the value of EVLW in ARDS m
odel was significantly higher than that at the baseline level (P<0.05)，but the optimal PEEP did not change EVLW. Conclusion The four kinds of methods can  identify the optimal PEEP.The optimal PEEP can improve lung compliance and oxygenation，and decrease the intrapulmonary shunt，but has no effect on heart function.

Key words: acute respiratory distress syndrome, positive end expiratory pressure, static compliance, dynamic compliance