ABSTRACT
Objective To investigate the effect of dexamethasone on the pulmonary gas exchange in patients undergoing cardiac valve replacement under cardiopulmonary bypass(CPB).Methods Forty ASAⅡorⅢpatients aged 29-47 yrs weighing 50-69 kg undergoing cardiac valve replacement under CPB were randomly divided into 2 groups(n=20 each):dexamethasone group received dexamethasone 0.5 mg?kg~(-1) after induction of anesthesia and control group received normal saline(NS).Blood samples were taken before operation(T_0) immediately before CPB(T_1)and immediately after discontinuation of CPB(T_2)for determination of plasma total and active matrix metallo-proteinase-9(MMP-9)concentration(by enzyme-linked immuno-absorbent and fluorometric enzyme-linked immuno-absorbent assay respectively)and MMP-9 gene expression(RT-PCR).Blood samples were taken from radial artery at T_1 and T_2 for blood gas analysis.A-aDO_2 was calculated.Results MMP-9 gene expression and plasma total and active MMP-9 concentrations were significantly increased at T_2 as compared with those at T_0 in both groups and were significantly lower in dexamethasone group than in control group(P＜0.05 or 0.01).The A-aDO_2 at T_2 was significantly smaller in dexamethasone group than in control group.Conclusion Dexamethasone can inhibit the increase in gene expression,protein synthesis and activation of MMP-9 and decrease in gas exchange across alveolar-capillary membrane caused by CPB and protect the lungs during open heart surgery performed under CPB.