Hypo- and hypernatraemia in surgical patients: is there room for improvement?

BACKGROUND: Up to 30% of surgical inpatients develop complications related to fluid and electrolyte therapy. We sought to study the occurrence of hypo- and hypernatraemia in these patients to inform current standards of care.

METHODS: This prospective audit took place over 80 days in a university hospital. Patients with a serum sodium concentration less than 130 or greater than 150 mmol/l were included. Daily intakes of Na(+), K(+) and Cl(-), and fluid balance were recorded before and after development of dysnatraemia. Fluid balance charts were assessed, as was the presence of documented patient weights. Patients were followed up until one of these milestones was reached: normonatraemia, death, or hospital discharge.

RESULTS: During the study period 55 (4%) of the 1,383 surgical admissions met the inclusion criteria. Fifteen patients had hypernatraemia, 13 (87%) of whom were identified on ICU/HDU. In the days preceding the hypernatraemia, patients received (in mmol/day) a median (IQR) of 157 (76-344) Na(+), 38 (6-65) K(+), 157 (72-310) Cl(-), and 1.96 (1.13-2.96) L water. In the days preceding the hyponatraemia, patients received 50 (0-189) Na(+), 0 (0-10) K(+), 56 (0-188) Cl(-), and 1.45 (0-2.60) L water. Before the dysnatraemias only 28% of fluid balance charts were completed accurately. During the audit 42% of patients were not weighed. Dysnatraemic patients had a higher hospital mortality rate than those who did not develop dysnatraemia (12.7 vs. 2.3%, P < 0.001).

CONCLUSIONS: Four percent of surgical inpatients developed dysnatraemias, which were associated with increased mortality. Fluid balance documentation was suboptimal and daily weights were not measured routinely, even in patients with severe electrolyte derangements.