Effect Of Controlled Hypotension Using Nitroglycerin Or Nitroprusside Sodium On Bleeding Of Muscle In Dogs

Objective: Controlled hypotension can decrease blood loss, thereby improving operating conditions, and decreasing the need for blood transfusions. We found, however, it did not reduce blood loss significantly sometimes. In this randomized prospective study, we examined the effect of nitroglycerin(NTG) and nitroprusside sodium(SNP) at decreasing blood loss during controlled hypotension.Methods: Ten healthy adult mongrel dogs, weighing 11~16kg, were anesthetized with inhalation of isoflurane and oxygen combined with infusion of fentanyl and atracurium. The animals was mechanically ventilated, and the ventilation pattern was adjusted to maintain the pressure of end tidal carbon dioxide(PETCO2) in the range of 30~35mmHg. Inspired oxygen fraction and PETCO2 were measured continuously. Freed the left carotid artery and internal jugular vein, carotid artery for the invasive blood pressure(BP) monitoring and a Swan-Ganz thermodilution catheter inserted into the pulmonary artery via the internal jugular vein for monitoring CO by the thermodilution and CVP. The animals were randomly divided into group NTG(5) and group SNP(5). When anesthesia levelled off and stabilized for twenty minutes, recorded hemodynamic variables SBP, DBP, MAP, CVP, HR, CO as the former base values(average of 3 times) before controlled hypotension, and measured the amount of bleeding before controlled hypotension (cutting the muscle of one back upper limb of the animals between the vertex of femur and the middle of knee joint to measure the amount of bleeding). According to the grouping used NTG and SNPrespectively to make BP decline to the range of 45~50mmHg. When reached the goal of hypotension and stabilized for twenty minutes, recorded these hemodynamic variables again as antihypertensive values(average of 3 times), and cut the muscle of the other back upper limb for measuring the amount of bleeding after controlled hypotension.Results: Compared statistical analysis shows that there weren't significant differences for HR and CVP between before and after controlled hypotension in both two groups. SBP, DBP, MAP all decreased significantly after controlled hypotension in both two groups(P<0.05, P<0.01, or P<0.001 ). CO reduced significantly after controlled hypotension in group NTG(P<0.05), there wasn't significant differences for CO between before and after controlled hypotension in group SNP. The amount of bleeding after hypotension significantly reduced after controlled hypotension in both two group(P<0.01), compares between groups shows that the difference of the amounts of bleeding between before and after controlled hypotension in group SNP was much more than group NTG(P<0.01).Conclusion: NTG and SNP can both significantly reduce SBP, DBP, MAP and the amount of bleeding of muscle of the dogs during controlled hypotension, but the effect of reducing bleeding amount of SNP during controlled hypotension is significantly stronger than NTG maybe because of its stronger effect of reducing DBP.