ABSTRACT
Objective To investigate the changes in intrapulmonary shunting during controlled hypotension induced by sodium nitroprusside(SNP)in patients undergoing naso-endoscopic operation.Methods Forty ASAⅠorⅡpatients of both sexes(23 male,17 female)aged 16-50 yrs weighing 50-75 kg undergoing naso-endoscopic operation under general anesthesia with muscle relaxation and mechanical ventilation were studied.Radial artery was cannulated for direct BP monitoring and blood sampling.Right internal jugular vein was cannulated and the catheter was advanced into right ventricle.Blood sample taken from right ventricle was used as mixed venous blood instead of blood from pulmonary artery.ECG,MAP,HR and P_(ET) CO_2 were continuously monitored during operation Cardiac output was monitored with noninvasive cardiac function monitor(NC-COM.)based on impedance principle.SNP infusion was started at the beginning of operation at 1-3?g?kg~(-1)?min~(-1) and was then adjusted.MAP was reduced by 30%-40% and maintained at this level until the end of operation.Blood samples were taken from artery and right ventricle simultaneously before SNP infusion(T_1,baseline)at 30 and 60 min of hypotension(T_2,T_3)and at 20 min after BP returned to the baseline level(T_4)for blood gas analysis.Qs/Qt was calculated.Results Qs/Qt was significantly increased during controlled hypotension at T_2 and T_3 as compared to the baseline value(P＜0.01)and returned to the baseline level at T_4.HR was increased and cardiac output and stroke volume was significantly reduced during hypotension as compared to the baseline value.Conclusion The intrapulmonary shunting is increased and the hemodynamics is depressed during SNP-induced controlled hypotension and they return rapidly to baseline level after SNP is discontinued.No hypoxemia develops during SNP- induced hypotension.