Marichal A, Hess W, Scheiber G
Institut für Anästhesiologie, Universitätsklinikum, GHS Essen.
Anaesthesist. 1992 Dec;41(12):752-9.
Hypertension is a common phenomenon in patients undergoing aortocoronary bypass grafting. This hypertension increases myocardial oxygen consumption and can be prevented by application of vasodilators. A possible cause is activation of the renin angiotensin system. Magnesium is a potent vasodilator and has a beneficial effect after myocardial ischaemia. The study was performed to analyse the influence of magnesium infusion on the haemodynamic status and plasma renin activity in patients undergoing aortocoronary bypass grafting. METHODS. Eighteen patients (NYHA classification II-III) undergoing bypass surgery were divided into two groups, a magnesium and a control group. The magnesium group (n = 9) received 0.8 mEq/kg per h magnesium aspartate as an infusion for 15 min while still awake. After induction of anaesthesia, the magnesium infusion was reduced to 0.2 mEq/kg per h and stopped after aortic cannulation was completed. Plasma magnesium levels and concentrations within erythrocytes were measured. Anaesthesia was induced by flunitrazepam (0.01 mg/kg), fentanyl (0.005 mg/kg) and pancuronium (0.1 mg/kg). After intubation, patients were normoventilated with N2O/O2 = 1:1 and isoflurane (0.5-1.0 vol%). Additional doses of fentanyl (0.0025 mg/kg) were injected before the incision and before sternotomy. Mean arterial pressure, heart rate, cardiac index, total peripheral resistance, pulmonary vascular resistance, mean pulmonary arterial pressure, pulmonary capillary wedge pressure, left ventricular stroke work index, right ventricular stroke work index, intrapulmonary shunt and plasma renin activity were evaluated at five predefined points: (1) prior to magnesium infusion; (2) after magnesium infusion; (3) 10 min following induction of anaesthesia under steady-state conditions; (4) after sternotomy; (5) after aortic cannulation. RESULTS. Concerning the haemodynamic parameters (MAP, RAP, PAP, PCWP) no significant difference between the two groups could be demonstrated. In the control group peripheral resistance (TPR) was higher following sternotomy and aortic cannulation than in the magnesium group. Magnesium prevented decrease of the cardiac index (CI) under steady-state conditions, during sternotomy and following aortic cannulation. Left and right ventricular stroke work indexes (LVSWI and RVSWI) were higher in the magnesium group. Plasma renin levels were not significantly different between the two groups. CONCLUSION. Patients undergoing cardiac surgery benefit from magnesium administration in the pre-bypass phase. Due to its vasodilating effect, magnesium lowers the output impedance of the left ventricle and improves cardiac pumping function. It opposes detrimental cardiovascular responses to sternotomy and following aortic cannulation. Also of importance is the advantageous effect of magnesium on cardiac arrest elicited by cardioplegia and for reactivation of the ischaemic myocardium.
高血压是接受主动脉冠状动脉搭桥术患者中的常见现象。这种高血压会增加心肌耗氧量，可通过应用血管扩张剂来预防。一个可能的原因是肾素 - 血管紧张素系统的激活。镁是一种有效的血管扩张剂，对心肌缺血后有有益作用。本研究旨在分析在接受主动脉冠状动脉搭桥术的患者中输注镁对血流动力学状态和血浆肾素活性的影响。方法。18例（纽约心脏协会心功能分级II - III级）接受搭桥手术的患者被分为两组，镁组和对照组。镁组（n = 9）在患者清醒时以每小时0.8 mEq/kg的速度输注门冬氨酸镁15分钟。麻醉诱导后，镁输注速度降至每小时0.2 mEq/kg，并在完成主动脉插管后停止。测量血浆镁水平和红细胞内浓度。通过氟硝西泮（0.01 mg/kg）、芬太尼（0.005 mg/kg）和潘库溴铵（0.1 mg/kg）诱导麻醉。插管后，患者以N2O/O2 = 1:1和异氟烷（0.5 - 1.0 vol%）进行正常通气。在切口前和胸骨切开术前注射额外剂量的芬太尼（0.0025 mg/kg）。在五个预定时间点评估平均动脉压、心率、心脏指数、总外周阻力、肺血管阻力、平均肺动脉压、肺毛细血管楔压、左心室每搏功指数、右心室每搏功指数、肺内分流和血浆肾素活性：（1）镁输注前；（2）镁输注后；（3）麻醉诱导后10分钟稳态条件下；（4）胸骨切开术后；（5）主动脉插管后。结果。关于血流动力学参数（平均动脉压、右房压、肺动脉压、肺毛细血管楔压），两组之间未显示出显著差异。在对照组中，胸骨切开术和主动脉插管后外周阻力（总外周阻力）高于镁组。镁可防止在稳态条件下、胸骨切开术期间和主动脉插管后心脏指数（CI）的下降。镁组的左、右心室每搏功指数（左心室每搏功指数和右心室每搏功指数）更高。两组之间血浆肾素水平无显著差异。结论。接受心脏手术的患者在旁路手术前阶段从镁给药中获益。由于其血管扩张作用，镁降低了左心室的输出阻抗并改善了心脏泵血功能。它对抗胸骨切开术和主动脉插管后的有害心血管反应。镁对心脏停搏液引起的心脏停搏以及对缺血心肌的再激活的有利作用也很重要。
