Intravenous saline, a mainstay of hydration therapy since 1831, may produce more kidney complications and result in lower survival than lactated Ringer’s solution or Plasma-Lyte A, according to two large studies from Vanderbilt University Medical Center in Nashville, Tennessee.

“The absolute difference in survival and kidney failure does not look like much on the surface. But this becomes a big deal on a population level,” coauthor Dr. Wesley Self told Reuters Health in a telephone interview.

One study looked at critically-ill adults. The other looked at non-critically ill patients. Both yielded the same conclusion.

The studies were published online February 27 in The New England Journal of Medicine to coincide with a presentation at the Society of Critical Care Medicine’s annual congress in San Antonio, Texas

Dr. Self’s team estimated that switching from saline to balanced crystalloids (lactated Ringer’s solution or Plasma-Lyte A) would lead to at least 100,000 fewer deaths or cases of kidney damage each year in the U.S. alone.

But in a journal editorial, Dr. John Myburgh of the George Institute for Global Health in Sydney, Australia, said the results, while informative, “do not provide unequivocal clinical direction.”

He noted that both tests were open-label and done at one U.S. medical center – Vanderbilt.

“At Vanderbilt, we have changed practice,” said Dr. Self, an associate professor of emergency medicine. “Nationally, I would hope hospitals and doctors would review the data and come to their own conclusion. I think a lot of doctors will change practice.”

He said the costs of saline and lactated Ringer’s are similar.

In the SMART study of 15,802 critically-ill patients, rates of major kidney events (a composite outcome that included death from any cause) were 14.3% with balanced crystalloids versus 15.4% with saline (P=0.04).

In-hospital mortality at 30 days, one element of the primary outcome, was 10.3% in the balanced fluids group and 11.1% with saline (P=0.06).

In the companion study of 13,347 non-critically ill patients, known as SALT-ED, rates of major kidney events at 30 days were 4.7% with balanced crystalloids and 5.6% with saline (P=0.01).

The type of IV fluid did not affect the number of days in the hospital among non-critically ill patients. In addition, the in-hospital death rates were similar between the two groups: 1.4% with balanced crystalloids and 1.6% with saline (P=0.36).

Dr. Self said that while lactated Ringer’s is a standardized solution, there are various other balanced solutions, and they differ in cost. “Whether one is better than the other, that research will have to be done in the future.”