Intraoperative Heart Failure

In the operating room, to differentiate left heart failure from right heart failure, one may be able to get some idea simply by looking at the heart. If the right ventricle appears to be sluggish and the left ventricle is contracting normally, the answer may be clearly visible and vice versa. Hemodynamic parameters can also give us some idea whether there is right heart failure versus left heart failure. If there are high pulmonary artery pressures and high CVP, (i.e. elevated right heart pressures), and despite this the left ventricular wedge pressure is low and cardiac output is poor, then right ventricular failure is presumed to have occurred. Conversely, if an elevated wedge pressure exists but the cardiac index is low then one can presume left heart failure. This will help determine whether an RVAD, LVAD or both are necessary for weaning from cardiopulmonary bypass. If the surgeon is unable to re-animate the heart after cardiopulmonary bypass, the problem may be either distention of the heart, electrolyte or blood gas problems, or the problem may be automaticity or conduction problems which can be solved by pacing. If the patient is severely hyperkalemic and has related myocardial dysfunction and the standard methods of lowering the potassium are ineffective, (i.e. glucose, insulin, Kayexelate, bicarbonate, calcium and Lasix), then hemodialysis is necessary. If the patient has cardiac asystole refractory to pacing, but if inspection of the heart reveals good color without massive edema or hemorrhage, the prognosis is good and one may be able to convert into ventricular fibrillation using calcium or epinephrine. If there is terminal asystole, such as a heart severely damaged by anoxia, poor myocardial protection, etc., this is ominous and is best managed by a period of cardiopulmonary bypass to let the heart rest. A case of sustained ventricular contraction, i.e. stone heart (synonymous with a calcium paradox) can sometimes be treated with Inderal or reperfusion with cardioplegia. The cause is often the absence of calcium within the cardioplegia solution and then reinfusing the heart with calcium containing blood. A small amount of calcium must always be used in the cardioplegia solutions to prevent this phenomenon from occurring. For ventricular fibrillation refractory to shocking, it must be confirmed that electrolytes and blood gases have normalized and that anti-arrhythmics have been given. If the patient is still refractory, one should cross-

clamp the aorta again and give 500 cc of cardioplegia at body temperature, then release the cross-clamp and pace the heart. If the heart continues to degenerate to ventricular fibrillation despite a brief period of normal contraction, one may try to pace the heart during a normal period to prevent fibrillation.

Areas of subendocardial ischemia are better treated by nitroglycerin than Nipride. Nitroglycerin increases the endocardial to epicardial blood flow ratio. It is a less powerful arterial dilator than Nipride and so maintains myocardial perfusion pressure. Nipride increases the epicardial to endocardial flow ratio. It is a powerful arterial dilator and the resulting steal syndrome would flow away from fixed obstructions. The catecholamine levels fall to normal within 20 minutes of cardiopulmonary bypass and by 4-8 hours postoperatively the sympathetic tone decreases and the extremities begin to vasodilate accounting in part for the myocardial dysfunctions seen 4-8 hours postoperatively.

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