Use of Lactated Ringer’s solution does not eliminate the risk of strong ion difference-related metabolic acidosis following on-pump cardiac surgery

There is a growing interest in the effects of plasma sodium levels on postoperative outcomes. A trend of using balanced crystalloid solutions is based on the extensive data on chloride and the strong ion difference-related acidosis. However, effects of sodium are often overlooked in this context. The aim of the study was to establish the effects of the routine use of Lactated Ringer’s Solution (RL) on postoperative changes in sodium concentrations and whether these changes result in metabolic acidosis. We performed database analysis of 358 consecutive elective on-pump cardiac surgery cases in a tertiary referral university hospital. Approval from the institutional ethics committee was obtained for this study. Intraoperative fluid balance was 2726±1073 ml and the total volume of intravenous infusions in the first 24 hours was 5865 (±1073) ml, 95% of which was RL; 58% of the patients had metabolic acidosis with a base excess below (–)2 mmol L–1 on arrival at the intensive care unit. There was a significant correlation between a strong ion difference and base excess (p less than 0.01). A significant improvement in metabolic acidosis was noted within the first 24 hours, from a base excess of (–)2.49±2.8 to 0.32±2.6 mmol L–1 (p less than 0.001). All of the improvement in the base excess is explained by a change in the strong ion difference from the mean value of 31±4.3 to 34.2±3.6 mmol L–1 (p less than 0.001). Changes in the strong ion difference were primarily driven by changes in the serum sodium concentration, which were three-fold higher compared to those of chloride [–2.36 (±2.6) mmol L–1 (p less than 0.001) and 0.84 (±3.2) mmol L–1, respectively (p = 0.01)]. In conclusion, our data confirm that there is a direct correlation between a strong ion difference and base excess following on-pump cardiac surgery. The use of RL prevented significant hyperchloraemia, but did not eliminate the risk of strong ion difference-related metabolic acidosis. The change in the strong ion difference was primarily linked to perioperative changes in the serum sodium concentration.