Dispelling the Myths about Lactated Ringer’s
and (Ab)Normal Saline in Critical Patients
BY BLAKE BRIGGS, MD
We give IV crystalloids nearly every shift, and we debate them nearly as often. Some discussion has focused on Plasma-Lyte, but it is not readily available in most EDs, so we generally focus on lactated Ringer’s (LR) and normal saline (NS). We owe our patients the best care, so it’s time to finally put to rest the many false claims and myths that swirl around this debate. (EMCrit.org. Feb. 27, 2018; https://bit.ly/3pHqM1J.)
With a pH of 5.5, NS is an acidic fluid. (Int J Med Sci. 2013;10:747; https://bit.ly/3gdA3eI.) It has a 40 percent higher concentration of chloride compared with plasma, and does not reflect the myriad components of human plasma. Many of us were trained to use NS, so sadly it has stuck around. It’s a status quo practice decision we continue to make simply because no one thinks to change it. ED stockrooms and resuscitation bays are full of NS bags.
Large saline volumes can be harmful to patients because NS causes a nonanion gap, hyperchloremic metabolic acidosis. This likely doesn’t matter for the hungover teenager or the patient with a stomach bug who is being sent home after one IV liter, but what about our critically ill patients? Many of them are acidotic to begin with (e.g., diabetic ketoacidosis, septic shock), so it seems counterintuitive and downright negligent to give them NS and worsen their acidosis. Multiple animal models found that acidosis from NS caused earlier death, worsening kidney function, oliguria, and reduced muscle tissue oxygen levels. (Anesthesiology. 2016;125:744; Chest. 2004;125:243.) LR, meanwhile, is more alkaline, containing 28 mEq/L of bicarbonate. (StatPearls. January 2021; PMID: 29763209.)
Animal studies may not be enough to change practice, so thankfully the SMART-ED trial provides more definitive evidence. A total of 15,802 critically ill patients in the ED were assigned a default fluid upon their arrival (NS or balanced crystalloid), and this was continued in the ICU. The median amount of fluid administered was one liter. Those who received NS were found to have a higher rate of death (26.3% v. 31.2%, CI 0.59-0.93) and kidney injury (35.4% v. 40.1%, CI 0.63-0.97). (Trials. 2017;18:178; https://bit.ly/3zkn3LS.)
A sister study performed at the same institution (SALT-ED) found that admitted patients who received a median of one liter of NS had a higher risk of renal failure within 30 days (n=13,347; 5.6% v. 4.7%, CI 0.70-0.95). (N Engl J Med. 2018;378:819; https://bit.ly/3veSSCs.) Even more damning, those who already had kidney injury at the time of admission were more susceptible to further renal damage from NS (37.6% v. 28%, p<0.001).
Perhaps one of the most pervasive myths about LR is hyperkalemia, which is interesting because no literature supports the claim that LR infusions significantly raise serum potassium levels. In fact, in a patient who is hyperkalemic to begin with, LR, which has a lower potassium concentration than the patient’s potassium concentration, will pull the patient’s potassium level toward 4 mEq/L, decreasing it. (Surg Clin North Am. 2012;92:189; EMCrit.org. Sept. 29,2014; https://bit.ly/3cxWGrY.)
Ironically, NS is the dangerous one in hyperkalemia. Because it is acidic, NS causes potassium to shift into the blood in exchange for H+ ions. Unfortunately, there are no direct ED studies on this subject, but four randomized controlled trials, each performed during kidney transplant surgery, directly compared LR with NS. (Anesth Analg. 2005;100:1518; Ren Fail. 2008;30:535; https://bit.ly/3xe6eAj; Saudi J Kidney Dis Transpl. 2012;23:135; https://bit.ly/3vdaxKY; Br J Anaesth. 2017;119:606; https://bit.ly/3cxfE28.) One study demonstrated that 19 percent of the patients receiving NS developed hyperkalemia compared with none in the LR group, and patients in the NS group also had higher rates of metabolic acidosis. (Surg Clin North Am. 2012;92:189.) All four studies showed no evidence that LR causes hyperkalemia.
Another myth is that LR routinely increases serum lactate levels. LR contains sodium lactate, not lactic acid, and it has been shown to increase lactate levels, but not significantly, in healthy volunteers, even with large 30 mL/kg boluses. (J Emerg Med. 2018;55:313.) LR in comparison with NS also does not cause significant lactate elevation. Mild to moderate hepatic injury should not be an absolute contraindication to LR. It is likely that the harm from a large-volume crystalloid infusion is more dangerous in severe cirrhosis or those with acute liver failure rather than theoretical lactate elevation. At our shop, LR is only about 25 cents more than NS. Most institutions report similar prices, so cost should not factor into choosing between LR and NS.
LR should be the go-to crystalloid in most medically ill patients, especially those who require large IV crystalloid resuscitation (e.g., diabetic ketoacidosis, sepsis, rhabdomyolysis). Does it matter if we give one liter of NS to a non-sick patient who is likely being discharged? Unlikely, but why create confusion over who gets LR or NS? Let’s make it easier on our physician colleagues, nurses, pharmacists, and other health care team members to start IV crystalloids. If you want your shop to stock the most readily available go-to fluid in the ED, a balanced crystalloid like LR should be exclusively used. Providing the most up-to-date care that reduces the chance of harm for our patients starts with changing how we give IV crystalloids.
Dr. Briggs is an assistant professor of emergency medicine at the University of South Alabama in Mobile. He is the founder, podcast co-host, and editor-in-chief of EM Board Bombs (https://www.emboardbombs.com), a multiplatform educational tool designed to provide board prep and focus on what you need to know for the practice of emergency medicine. Follow him on Twitter @blakebriggsmd.