Postoperative sodium concentrations after cardiac surgery using histidine- tryptophan-ketoglutarate cardioplegia and cardiopulmonary bypass – a retrospective study

Introduction: Histidine-tryptophan-ketoglutarate (HTK) cardioplegia is used to induce cardiac arrest during cardiopulmonary bypass (CPB) in cardiac surgery. HTK cardioplegia is hyponatremic (15 mmol/L) and slightly hyperosmolar (310 mOsm/kg) and can induce hyponatremia when it enters systemic circulation. The purpose of this study is to investigate the effect of HTK cardioplegia, cannulation strategy and intraoperative correction of sodium levels on postoperative sodium concentration. Secondly, the effect of the sodium concentrations on postoperative agitation is evaluated. Methods: Patients who underwent cardiac surgery using CPB and HTK cardioplegia were included in this retrospective study. Sodium concentrations of arterial blood gases (ABG) and laboratory blood samples were analyzed at multiple points in time. It was recorded if the perfusionist corrected intraoperative hyponatremia with hypertonic saline or sodium bicarbonate 8.4%. Characteristics of the patients, intraoperative data and the patient’s Richmond Agitation-Sedation Scale (RASS) score were collected. Results: The median sodium concentration on ABG [IQR] decreased from 139 mmol/L [138-140] to 125.5 mmol/L [122-130] (p < 0.001) after the administration of HTK cardioplegia. The median sodium concentration after the administration of HTK cardioplegia was significantly lower in the group with single cannulation than with double cannulation (123 mmol/L [121-125] vs. 130 mmol/L [128-133]; p<0.001). The median sodium concentration increased to 134 mmol/L [133-136] (p=0.007) at T6. There was no significant difference in postoperative sodium concentration between patients who received correction intraoperatively and those who did not, or between patients who had agitation and those who had not. Conclusions: The administration of HTK cardioplegia induced acute hyponatremia during cardiac surgery mainly in patients with single venous cannulation. Postoperatively, a normalization of sodium concentrations can be observed. No difference in postoperative sodium concentration was observed with or without intraoperative correction of sodium. Intraoperative correction of hyponatremia shows no benefit or harm on postoperative sodium concentrations. Hyponatremia could be avoided or at least diminished by using double venous cannulation.