Feb. 27, 2018 -- Saline solution has been a staple of modern medicine for over 150 years -- doctors go through enough at U.S. hospitals to fill an Olympic-sized swimming pool every 5 days.
Surprisingly, though, it hasn’t been well-studied in clinical trials; and many doctors have questioned whether giving people so much salt is really the safest option. Each bag of saline contains the same amount of sodium as 20 snack-sized bags of potato chips.
Doctors use IV saline to replenish lost fluids, flush wounds, deliver medications, and sustain patients through surgery, dialysis, and chemotherapy. Saline IVs have even found a place outside the hospital, as a trendy hangover remedy.
“It has high levels of sodium and chloride, levels that are higher than the blood. We thought that those high levels of sodium and chloride might actually cause some problems for patients when you give it to them,” said Wesley Self, MD, an associate professor of medicine at Vanderbilt University School of Medicine in Nashville.
Self was part of a team of doctors who recently put saline to the test in two new studies presented at the Society of Critical Care Medicine’s annual conference and published in The New England Journal of Medicine.
A Different Solution?
While saline is still the dominant fluid -- given to about 80% of hospitalized patients -- it’s not the only one. Other mixtures, known as balanced fluids, have been developed as doctors try to more closely match the chemistry and electrolyte balance of healthy blood.
For more than a year, the emergency room and intensive care units at Vanderbilt rotated the IV fluid used to hydrate patients. On even-numbered months, they used saline, and on odd-numbered months, doctors could choose between either lactated Ringer's or Plasma-Lyte-A. Both Ringer's and Plasma-Lyte have less sodium than saline, along with other electrolytes. Most of the patients on balanced fluids in the study got lactated Ringer's.
Not all patients were included. Doctors chose not to test the balanced fluids for patients with brain injuries because, in theory, differences in their chemistry might have increased swelling --something that’s critical to control.
Doctors followed patients enrolled in the study for 30 days to see how they fared.
The differences were small but statistically significant, which means the outcomes probably weren’t just due to chance.
The choice of fluid seemed to be most important for the sickest patients.
Patients admitted to the ICU who got the balanced fluids were slightly less likely to die, need dialysis, or have injury to their kidneys, compared with patients who got saline.
Out of 7,942 patients who got balanced fluids, 1,139 had one of those complications, compared with 1,211 of the 7,860 patients who got saline -- an absolute difference of just 1.1%
For patients who weren’t critically ill, the choice of IV hydration also seemed to cut their chances of kidney problems, though the difference between groups was smaller, less than 1%.
On an individual level, that may not sound like much, Self says, but “when you think about the millions and millions of people who get this treatment, it becomes very important.”
The study authors estimate that at least 100,000 hospitalized patients a year could avoid death or kidney damage if doctors used balanced fluids instead of saline.
The results were convincing enough that Vanderbilt has switched its go-to IV solution to balanced fluids instead of saline.
The studies have changed other doctors’ minds, too.
June Ree, MD, is the associate chairwoman of the emergency department at Lenox Hill Hospital in New York City.
Ree, who wasn’t involved in the study, said she was glad to see it, especially since her hospital and others have recently struggled with a shortage of saline because of the lingering effects of Hurricane Maria on Puerto Rico.
“I’ve always relied on normal saline, because that’s what I’m used to,” she says.
“After reading this study, I think I would be more open to giving lactated Ringer's to more of my patients, especially those with kidney disease,” she adds.
The study had important limits. It wasn’t blinded, meaning doctors and nurses knew what solutions their patients were getting, something that might have swayed the results, since it could have allowed a doctor’s personal feelings about which solution might be best for patients to creep in.
It was limited to a single hospital, something else that could have introduced bias.
And the studies didn’t break out the type of serious problems that happened, which could range from death to kidney problems.
Still, experts said even with these flaws, the study was an important real-world test, one that should start to make hospitals think about what they’re putting in a patient’s IV.
“Many clinicians will look at these two trials and will conclude, on the basis of what we now know, that balanced fluids are better for patients,” said Paul Young, MD, who is medical director of the Wakefield Hospital ICU in Wellington, New Zealand.
“This will be a massive change for the U.S.A., where saline has been the dominant intravenous fluid,” says Young, who was not involved in the current study.
Whether that may impact the cost charged to patients remains to be seen. Currently, at Vanderbilt, Self says the cost of a bag of saline and lactated Ringers is the same. A bag of normal saline can range between $300 and $500 dollars.
For those who remain unconvinced, Young says there are two more large studies coming -- one from Brazil and one from Australia -- that may help better settle the question.