Postoperative hyperchloremia is associated with worse outcome than normal plasma chloride

Most of us use lactated Ringer’s solution for fluid therapy intraoperatively, though in some institutions the preferred solution is normal saline.  Normal saline’s chloride concentration is 154 mEq/l, substantially higher than typical serum chloride concentration (100-100 mEq/l).  Given saline’s higher chloride concentration, do patients who receive that solution get hyperchloremic acidosis?  If they do, what are the implications?

In their study “Hyperchloremia After Noncardiac Surgery Is Independently Associated with Increased Morbidity and Mortality: A Propensity-Matched Cohort Study,” Dr. Stuart A. McCluskey, Department of Anesthesia and Pain Management, Toronto General Hospital, University Health Network, Toronto, Ontario, Canada, and colleagues compared outcomes in patients who were hyperchloremic with outcomes in patients with normal serum chloride after inpatient, noncardiac, nontransplant surgery. This was a retrospective study using propensity-matched and logistic multivariable analysis.

The authors first compared almost 5,000 hyperchloremic patients to almost 18,000 patients whose chloride level was normal after surgery.  Hyperchloremic patients were older (63 years vs. 60 years), more likely female, underwent longer procedures (219 min vs. 159 min), had more comorbidities, received more blood products, had a higher 30-day mortality rate (3.4% vs. 1.3%), stayed in the hospital longer, and were more likely to have postoperative pulmonary edema, pulmonary embolism, myocardial ischemia, myocardial infarction, atrial fibrillation and cardiovascular events.

They matched over 4,000 patients who were postoperatively hyperchloremic to a similar number of patients who were not based on gender, emergent surgery, last preoperative hemoglobin, main procedure service, procedure time, and minimum hemoglobin on postoperative day 1.  Patients who were hyperchloremic had a higher 30-day mortality rate (3% vs. 2%), stayed in the hospital longer (7 days vs. 6 days), and were more likely to have postoperative renal dysfunction (defined as > 25% reduction in creatinine clearance).  Similar findings were seen for patients undergoing non-oncologic surgery, oncologic surgery, high-risk, low- or moderate-risk surgery.

The authors then performed a logistic regression analysis to determine which factors would predict 30-day mortality. Postoperative hyperchloremia was the sole predictor.

This was a retrospective analysis and the authors did not determine why patients became hyperchloremic.  More specifically, they did not compare patients who received lactated Ringer’s solution to those who received normal saline.  Certainly the use of normal saline is associated with hyperchloremia, however.

As noted in the accompanying editorial titled “Should “Normal” Saline Be Our Usual Choice in Normal Surgical Patients?” by Drs. John F. Butterworth IV (Department of Anesthesiology, Virginia Commonwealth University School of Medicine, Richmond, VA) and Monty G. Mythen  (Centre for Anaesthesia, University College London, London, United Kingdom) “(1) hyperchloremia is more common with 0.9% saline than with balanced crystalloid solutions; (2) hyperchloremia is associated with worse outcomes; (3) there are better alternatives to 0.9% saline in most clinical situations (excluding hypochloremic metabolic alkalosis); and (4) until an adequately powered randomized clinical trial proves us wrong, 0.9% saline will not be our crystalloid of choice for intravascular volume resuscitation in surgical patients.”