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Saline Soliloquy: Shaking Up Our Thoughts on Perioperative Hyponatremia: Commentary on an article by E. Hennrikus, MD, et al.: "Prevalence, Timing, Causes, and Outcomes of Hyponatremia in Hospitalized Orthopaedic Surgery Patients".

A salient analysis of this report byHennrikus et al. will help us to better care for our sickest postoperative patients. The authors make a compelling case for attention to and treatment of hyponatremia that occasionally presents preoperatively but more commonly develops postoperatively, particularly in older patients who have undergone spine surgery or hip arthroplasty. Prior publications have stated that mild cases of hyponatremia (serum sodium [Na] level of 130 to 134 mEq/L) are generally asymptomatic. However, Hennrikus et al. cite recent research studies inwhichmild hyponatremiawas considered to be a contributing cause of common postoperative problems such as nausea, vomiting, short-termmemory loss, lethargy, loss of appetite, confusion, and headache. Often, the patients in the series reported by Hennrikus et al., who were treated in 2010, did not develop hyponatremia until forty-eight hours postoperatively, a finding that speaks against rapid discharges, especially of older patients, following major reconstructive or complicated surgery. This finding is of particular interest because of current trends toward shorter average hospital stays afforded by improved pain management and early mobilization. The authors’ large retrospective series has important limitations. First, 18% of the patients were excluded because of a lack of documentation of preoperative and postoperative electrolyte levels. Assuming that these were healthier patients, the true overall incidence of patients presenting with or developing hyponatremia is likely lower than reported. Second, as was previously reported by Mc Causland et al., the association of postoperative hyponatremia in adult orthopaedic surgery patients with hospital length of stay, hospital cost, and discharge disposition is clear. However, this association may not be causative; it may be simply due to hyponatremia being more likely in older patients who have undergone long orthopaedic surgery. Third, the authors did not delineate the range or severity of the hyponatremia in their patients, reporting only that the Na level fell below 135 mEq/L. Rudge and Kim reported on cohorts of patients with moderately (<135 mEq/L) and, less often, severely (<130 mEq/L) low Na levels. The algorithm in Figure 2 of the paper by Hennrikus et al. is particularly useful. It draws a distinction between (1) hyponatremia due to excessive infusion of low-Na-content fluid and/or excessive free water (the more common scenario) and (2) hyponatremic patients with concentrated urine and edema who might, in my opinion, be best treated in consultation with a hospitalist. Surgeons reviewing preoperative and postoperative electrolyte imbalances, who heretofore may have focused primarily on ruling out hypokalemia, will now be more attentive to recognizing, avoiding, and treating hyponatremia. John R. Tongue, MD* Oregon Health Sciences University, Portland, Oregon