title: Prevalence, Timing, Causes, and Outcomes of Hyponatremia in Hospitalized Orthopaedic Surgery Patients.
abstract: BACKGROUND
  Hyponatremia is common among orthopaedic patients and is associated with adverse clinical outcomes. We examined the prevalence, timing, causes, and outcomes of hyponatremia in adult hospitalized orthopaedic surgery patients.
  
  
  METHODS
  We evaluated the medical records of 1067 consecutive orthopaedic surgery patients admitted to a tertiary academic institution. The medical records were reviewed to investigate hyponatremia (serum sodium <135 mEq/L) that (1) had been present on hospital admission or (2) had developed postoperatively. The primary outcomes were the prevalence and timing of, and risk factors for, presentation with or development of hyponatremia. Secondary outcomes were hospital length of stay, total hospital cost, and discharge disposition. Multivariable logistic regression models were used to assess the variables associated with hyponatremia and the effects of hyponatremia on clinical outcomes.
  
  
  RESULTS
  Of the 1067 patients, seventy-one (7%) had preoperative hyponatremia and 319 (30%) developed hyponatremia postoperatively. Of the latter, 298 (93%) developed hyponatremia within forty-eight hours postoperatively. Compared with patients with normonatremia, those who presented with hyponatremia, on the average, were older (67.2 versus 60.5 years, p < 0.001), had longer hospital stays (4.6 versus 3.3 days, p < 0.001), incurred higher hospital costs ($19,200 versus $17,000, p = 0.006), and were more likely to be discharged to an extended-care facility (odds ratio [OR] = 2.87, p < 0.001). Developing hyponatremia postoperatively resulted, on average, in a longer hospital stay (3.7 versus 3.3 days, p = 0.002) and greater hospital cost ($18,800 versus $17,000, p < 0.001). Age (OR = 1.13 per decade, p = 0.012), spine surgery (OR = 2.76 versus knee, p < 0.001), hip surgery (OR = 1.76 versus knee, p < 0.001), and the amount of lactated Ringer solution used (OR = 1.16, p = 0.002) increased the risk of developing hyponatremia.
  
  
  CONCLUSIONS
  Hyponatremia in orthopaedic patients is associated with longer, costlier hospitalizations. The factors that significantly increased the risk of developing postoperative hyponatremia were an older age, spine fusion, hip arthroplasty, and the amount of lactated Ringer solution used.
authors.affiliation: Departments of Internal Medicine (E.H.), Orthopedics and Rehabilitation (C.D.), and Anesthesiology (B.M.), Milton S. Hershey Medical Center, Pennsylvania State University College of Medicine, 500 University Drive, MC H034, Hershey, PA 17033. E-mail address for E. Hennrikus: ehennrikus@hmc.psu.edu.
authors.forename: Eileen
authors.initials: E
authors.lastname: Hennrikus
authors.affiliation: Department of Internal Medicine, University of British Columbia, 2775 Laurel Street, 10th Floor, Vancouver, BC V5Z 1M9, Canada.
authors.forename: George
authors.initials: G
authors.lastname: Ou
authors.affiliation: Senior Medical Officer, Special Boat Team 22, Stennis Space Center, MS 39520.
authors.forename: Bradley
authors.initials: B
authors.lastname: Kinney
authors.affiliation: Department of Public Health Sciences, Penn State Hershey College of Medicine, 90 Hope Drive, Hershey, PA 17033.
authors.forename: Erik
authors.initials: E
authors.lastname: Lehman
authors.affiliation: Department of Orthopedics, University of Rochester, 601 Elmwood Avenue, Box 665, Rochester, NY 14642.
authors.forename: Robert
authors.initials: R
authors.lastname: Grunfeld
authors.affiliation: Rocky Vista University College of Osteopathic Medicine, 8401 South Chambers Road, Parker, CO 80134.
authors.forename: Jane
authors.initials: J
authors.lastname: Wieler
authors.affiliation: Cardiovascular Division Internal Medicine, University of Miami Miller School of Medicine, 1600 NW 10th Avenue, Miami, FL 33136.
authors.forename: Abdulla
authors.initials: A
authors.lastname: Damluji
authors.affiliation: Departments of Internal Medicine (E.H.), Orthopedics and Rehabilitation (C.D.), and Anesthesiology (B.M.), Milton S. Hershey Medical Center, Pennsylvania State University College of Medicine, 500 University Drive, MC H034, Hershey, PA 17033. E-mail address for E. Hennrikus: ehennrikus@hmc.psu.edu.
authors.forename: Charles
authors.initials: C
authors.lastname: Davis
authors.affiliation: Departments of Internal Medicine (E.H.), Orthopedics and Rehabilitation (C.D.), and Anesthesiology (B.M.), Milton S. Hershey Medical Center, Pennsylvania State University College of Medicine, 500 University Drive, MC H034, Hershey, PA 17033. E-mail address for E. Hennrikus: ehennrikus@hmc.psu.edu.
authors.forename: Berend
authors.initials: B
authors.lastname: Mets
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D017721:Hospital Costs / Q000706:statistics & numerical data; D006760:Hospitalization / Q000191:economics / Q000706:statistics & numerical data; D006801:Humans; D007010:Hyponatremia / Q000191:economics / Q000453:epidemiology / Q000209:etiology / Q000628:therapy; D007902:Length of Stay / Q000191:economics / Q000706:statistics & numerical data; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D019637:Orthopedic Procedures / Q000191:economics; D017063:Outcome Assessment, Health Care; D010414:Pennsylvania; D011183:Postoperative Complications / Q000191:economics / Q000453:epidemiology / Q000209:etiology / Q000628:therapy; D057234:Preoperative Period; D015995:Prevalence; D012189:Retrospective Studies; D012307:Risk Factors