Effect Of Nicardipine On Systematic And Gastrointestinal Perfusion And Oxygenation During Cardiopulmonary Bypass In Cardiac Operation

Complications such as coma, delirium, gastrointestinal hemorrhage and renal failure after cardiopulmonary bypass (CPB) affect rehabilitation and postoperative quality of life seriously. Many factors contribute to it comprehensively. Tissue perfusion inadequacy and oxygen metabolism disturbance are the most important reasons. During cardiopulmonary bypass, how to monitor the tissue perfusion and prevent hypoperfusion has become a hotspot recently. When the microenvironment of the body changes, circulation blood flow redistributes away from visceral regions to vital organs to guarantee the perfusion of myocardium, brain and kidney as a regulatory mechanism. So gastrointestinal tract is called as"sentinel organ"of predicting systemic hypoxia-ischemia. Many research reported that gastrointestinal tonometry could assess the perfusion and oxygenation of visceral organs reliably and sensitively. In our study, air-tonometry was adopted to monitor gastrointestinal mucosa perfusion continuously during cardiopulmonary bypass. As one of the dihydropyridine calcium antagonists, Nicardipine not only has the effect of expansion of arterioles and coronary artery to decrease peripheral vascular resistance but also prevents ischemia of myocardium, brain and kidney. This study was carried out to investigate the effect of CPB on hemodynamics, systematic and gastrointestinal perfusion. At the same time we observed whether nicardipine has the function of improving gastrointestinal perfusion and oxygenation during cardiopulmonary bypass, and provide a new method for reducing patients, postoperative complications and improving prognosis.Objective: This study was carried out to investigate the effect of cardiopulmonary bypass on hemodynamics, systematic and gastrointestinal perfusion by using gastric tonometry. And with the use of nicardipine during CPB, we can also observe whether nicardipine has the function of improving gastrointestinal perfusion and oxygenation. We also discuss its mechanisms.Methods: Twenty-six adult patients scheduled for cardiac valve replacement were divided randomly into two groups: conventional anesthetic group (group C) and nicardipine group (group N) with 13 patients each. After the completion of induction of anesthesia, all patients were inserted the Tonometry Catheters nasogastrically and its position confirmed by auscultation over the epigastrium. Gastric intramucosal partial pressure of carbon dioxide (PgCO₂) is measured by infrared spectroscopy every 10 minutes internals using the Tonocap. A Swan-Ganz catheter was inserted into the pulmonary artery via the right internal jugular vein to perform cardiac output by the thermodilution. The patients were mechanically ventilated after tracheal intubation and PET CO₂ was maintained at 35-45mmHg. Conventional methods of anesthesia and cardiopulmonary bypass were adopted, in group C such as nitroglycerin was given instead of nicardipine if the arterial blood pressure need to lower; while in group N nicardipine was titrated at the rate of 0.5μg/kg/min to maintain mean arterial blood pressure not below 70mmHg before or after CPB and not below 50mmHg during CPB. General indicators and hemodynamic parameters were monitored continuously. Pulmonary arteriole blood were extracted from Swan-Ganz catheter to measure mixed venous oxygen saturation (SvO₂) and arterial blood from radial artery to determine blood-gas analysis at the following time points: before CPB (T1), 30min after beginning of CPB (T2), 20min after weaning from CPB (T3) and the end of operation (T4). The delivery of oxygen (DO₂), consumption of oxygen (VO₂) and oxygen extraction ratio (ERO₂) were calculated. SvO₂, DO₂, VO₂ and ERO₂ were to reflect systematic oxygenation. At the above each time point PgCO₂ was recorded by Tonocap, gastric luminal PCO₂-arterial PCO₂ (Pg-aCO₂) and gastric intramucosal pH (pHi) were calculated to evaluate gastrointestinal perfusion and oxygenation. Results: In both two groups significant increase in cardiac index(CI) at T3,T4 compared with T1(P<0.01) and CI in group N was notably increased compared with group C after weaning from CPB(P<0.01); At T2,T3 systemic vascular resistance index (SVRI) in group C was obviously decreased with T1(P<0.01), while SVRI in group N was decreased at T2,T3,T4 with T1(P<0.01). At T4 SVRI was significantly decreased in group N compared with group C (P<0.01). In both two groups increase in SvO₂ at T2 compared with T1(P<0.01), at T3,T4 SvO₂ in group C gradually descent but that in group N hasn't so change. In both two groups decrease in DO₂,VO₂and ERO₂ at T2 compared with T1(P<0.05). DO₂ of T3,T4 in group N was significantly higher than that in group C(P<0.01) while VO₂ in two groups was increased at T3 compared with T1(P<0.05) and at T4 remained unchanged. And ERO₂ in group C was higher than that in group N after completion of CPB(P<0.05). In group C significant increase in PgCO₂ and decrease in pHi at T3,T4 compared with T1 and contrary result was seen at T2 compared with T1(P<0.01). In group N only pHi decreased at T4 compared with T1(P<0.01). The tendency of Pg-aCO₂ was the same as PgCO₂. At T3,T4 pHi in group C was below of 7.35, but group N was properly opposite.Conclusions: There were gastric mucosal hypoperfusion and disorder of oxygenation during hypothermic CPB, as shown by reduced pHi and increased PgCO₂. Nicardipine can maintain systematic and gastrointestinal tissue perfusion and oxygenation. Nicardipine has the effect of gastrointestinal protection. Gastrointestinal air-tonometry is a sensitive and noninvasive method that monitors gastrointestinal tissue perfusion continuously. Tonometry should be applied extensively in clinical anesthesia performance.