Hypokalemia. Physiological abnormalities during cardiopulmonary bypass

Sellke F, Feng J. Potassium and Cardiac Surgery

Potassium homeostasis affects cardiac rhythm and contractility, along with vascular reactivity and vascular smooth muscle proliferation. This chapter will focus on potassium dynamics during and after cardiac surgery involving cardioplegic arrest and cardiopulmonary bypass (CPB). Hyperkalemic, hypothermic solutions are frequently used to induce cardioplegic arrest and protect the heart during cardiac surgery involving CPB. Common consequences of hyperkalemic cardioplegic arrest and reperfusion include microvascular dysfunction involving several organ systems and myocardial dysfunction. Immediately after CPB, blood potassium levels often drop precipitously due to a variety of factors, including CPB -induced electrolyte depletion and frequent, long-term administration of insulin during and after surgery. Meanwhile, some patients with pre-existing kidney dysfunction may experience postoperative hyperkalemia following cardioplegia. Any degree of postoperative hyper/hypokalemia significantly elevates the risk of cardiac arrythmias and subsequent myocardial failure. Therefore, proper management of blood potassium levels during and after cardioplegia/CPB is crucial for optimizing patient outcomes following cardiac surgery.

Potassium concentrations and ventricular ectopy: a prospective, observational study in post-cardiac surgery patients

OBJECTIVE

To determine whether a correlation exists between concentrations of intracellular and extracellular potassium and to determine the frequency of ventricular ectopy in patients after cardiac operations.

DESIGN

Prospective, observational clinical evaluation.

SETTING

Surgical-respiratory intensive care unit of a university-affiliated tertiary care center.

PATIENTS

Continuous 24-hr electrocardiographic monitoring was performed, and serum (extracellular) and erythrocyte (intracellular) potassium concentrations ([K+]e and [K+]i) were determined, before cardiopulmonary bypass, immediately postoperatively, and at 2, 4, 12, and 20 hrs after elective coronary bypass grafting in 31 patients.

INTERVENTIONS

None. Potassium replacement was left to the discretion of the attending physicians.

MEASUREMENTS AND MAIN RESULTS

Although the mean [K+]e varied significantly during the postoperative 24-hr period (p<.0001), the [K+]i did not (p = .953). No significant correlations were found between premature ventricular beats and [K+]i, [K+]e, or [K+]i/[K+]e (all p>.05). However, among the few patients who had one or more episodes of ventricular tachycardia (VT) within 30 mins of a study K+ sample, the mean [K+]e was significantly lower during the episode(s) of VT compared with the mean [K+]e in the absence of VT (p<.01).

CONCLUSIONS

Although it is clear that over the clinically acceptable range of [K+]e and [K+]i concentrations seen in this population, there is no correlation between potassium concentrations and the occurrence of premature ventricular beats, the infrequent association of more serious ventricular ectopy, VT, with lower [K+]e concentrations supports the practice of using serum potassium to guide potassium replacement in patients after cardiac operations.

Systemic effects of multidose hypothermic potassium cardioplegia

The purpose of this study was to investigate the changes in serum and urine potassium before, during, and after the administration of potassium cardioplegia using a solution containing 28 mEq/L of potassium chloride in 20 consecutive patients with acquired heart disease. The data obtained suggest that the concentration of potassium administered does not result in inordinately elevated serum potassium levels (peak, 4.6 +/- 0.18 mEq/L at 2 hours of multidose hypothermic potassium cardioplegia) during or after infusion. Additionally, the urinary excretion of potassium increased during infusion and eventually exceeded the amount of potassium infused. While hypothermic potassium cardioplegia appears to be a safe and efficient method of myocardial protection, continued surveillance of postoperative potassium levels remains necessary to detect obligatory urinary potassium excretion following cardiopulmonary bypass and operation.

Dynamics of serum potassium change during acute respiratory alkalosis

In summary, one should be aware that hyperventilation and hypokalaemia occur frequently in the operating room under ordinary clinical conditions. An awareness of the rapidity with which these changes occur, and their extent as well as their potential hazards, should cause consideration of more aggressive attempts to maintain normocarbia and to use supplemental potassium during anaesthesia, particularly in patients with cardiac disease.