The Patient with Heart Failure

Fluid management of heart failure is directed to optimize cardiac preload, avoid overadministration of sodium, diminish edema, and correct common electrolyte abnormalities. Maintaining ideal cardiac preload during rapid fluid shifts that occur perioperatively is facilitated with direct or indirect measures of preload and cardiac contractile function. Measures of preload include CVP, thermodilution cardiac output, end-diastolic volume, echocardiography, PAOP, and left atrial pressure. Measures of cardiac contractile function include stroke volume, ejection fraction, and stroke work. Patients with a history of cardiac failure scheduled for major or prolonged surgery should have monitoring instituted preoperatively and an intravascular fluid challenge (i.e., 500 to 1000 mL/70 kg of crystalloid) performed to identify the optimal preload level. Tissue edema is avoided by frequent monitoring of preload and arterial blood pressure coupled with support of contractility and control of vascular resistance. These patients have impaired ability to excrete fluids during the fluid mobilization, which occurs postoperatively. Because the ECF volume is usually already expanded in these patients, the initial rates of fluid infusion intraoperatively should be at the lower ranges of estimates. Similarly, maintenance of intravascular volume without expansion of the interstitial space favors the use of colloid during the immediate perioperative period. Postoperatively, hemodynamic monitoring is continued until fluid mobilization is complete. The goal postoperatively is to give as little crystalloid as required to maintain adequate overall cardiovascular performance. Perioperative patients commonly receive more than 200 mEq of sodium per day, including maintenance fluids, saline used to measure cardiac output, sodium from antibiotics administration, and sodium infused with vasoactive medications and inotropic agents. Fluid should be maintained at a low maintenance level, and flush fluids and sodium dosage should be measured. As soon as urine output begins to increase or filling pressures or diastolic volume begins to rise, maintenance fluids should be stopped completely. If preload becomes excessive, diuretics should be administered.

Patients with heart failure have primary electrolyte problems because of compensatory physiologic mechanisms activated by the impaired cardiac performance. These are then complicated by therapy with diuretics, digitalis, vasodilators, and ACE inhibitors. Hyponatremia is common because of excess activation of the vasopressin system despite sodium retention. Treatment is directed at excreting the excess water load with diuretics, which should increase free water excretion more than sodium excretion. Sodium administration is not indicated unless volume depletion is documented. Aldosterone activation and diuretics lead to loss of potassium and magnesium. These ions are crucial for maintaining the stability of cardiac electrophysiology, as well as the effectiveness of digitalis and catecholamine. Ionized calcium is crucial for cardiac contractility, and hypocalcemia is extremely common during the perioperative period. Ionized calcium must be measured and corrected routinely. Severe hypophosphatemia often coexists with abnormalities of calcium, potassium, and magnesium and leads to depressed contractility.