Comparison of the incidences of hyponatremia in adult postoperative critically ill patients receiving intravenous maintenance fluids with 140 mmol/L or 35 mmol/L of sodium: retrospective before/after observational study.

PURPOSE

The purpose of this study was to compare the incidences of hyponatremia in adult postoperative critically ill patients receiving isotonic and hypotonic maintenance fluids.

METHODS

In this single-center retrospective before/after observational study, we included patients who had undergone an elective operation for esophageal cancer or for head and neck cancer and who received postoperative intensive care for >48 h from August 2014 to July 2016. In those patients, sodium-poor solution (35 mmol/L of sodium; Na) had been administered as maintenance fluid until July 2015. From August 2015, the protocol for postoperative maintenance fluid was revised to the use of isotonic fluid (140 mmol/L of sodium; Na). The primary outcome was the incidence of hyponatremia (<135 mmol/L) until the morning of postoperative day (POD) 2.

RESULTS

We included 179 patients (Na: 87 patients, Na: 92 patients) in the current study. The mean volume of fluid received from ICU admission to POD 2 was not significantly different between the two groups (3291 vs 3337 mL, p = 0.84). The incidence of postoperative hyponatremia was 16.3% (15/92) in the Na cohort, which was significantly lower than that of 52.9% (46/87) in the Na group (odds ratio = 0.17, 95% confidence interval 0.09-0.35, p < 0.001]. The incidences of hypernatremia, defined as serum sodium concentration >145 mmol/L, were not significantly different between the two groups.

CONCLUSION

In this study, the use of intravenous maintenance fluid with 35 mmol/L of sodium was significantly associated with an increased risk of hyponatremia compared to that with 140 mmol/L of sodium in adult postoperative critically ill patients.