“The most beautiful thing we can experience is the mysterious, it is the source of all true art and science. He to whom this emotion is a stranger, who can no longer pause to wonder and stand rapt in awe, is as good as dead: his eyes are closed.” –Albert Einstein.
I’m not sure the above quote has much direct relevance to today’s blog, but it came to mind after reading “we still have more to learn” in a recent editorial. The editorial elaborated on another study showing that hypotonic fluids increase the risk of hyponatremia (J Pediatr 2014; 165: 163-9, editorial 14-15). The editorial cautions that “intravenous fluid therapy is a prescription much like antibiotics or chemotherapy. What we prescribe for intravenous fluids must fit the patient’s history and condition.”
The article was a systemic review of published studies. Though 1634 citations were screened, only 10 studies (n=893) were included as independent randomized controlled trials. Hypotonic fluids were defined as tonicity <250 mmol/L; isotonic fluids were defined as normal saline (0.9%), Ringer lactate, Hartmann solution, and any other fluid with tonicity approaching that of normal serum. The key findings:
- Hypotonic fluids increase the relative risk (RR) of hyponatremia (Na <135) with RR of 2.37
- Moderate hyponatremia (Na <130) risk was increased further with RR of 6.1.
- Sub-group analysis of half-normal saline showed relative risk for hyponatremia was 2.42.
The editorialists comment that much has changed in the 55+ years since Holliday and Segar’s publication in 1957 describing maintenance fluid requirements. These changes include sicker patients who are at increased risk for non-osmotic ADH release. Thus, even patients receiving isotonic fluids are at some risk for hyponatremia. However, the key point is that maintenance fluids are not appropriate for replacement of losses and in the perioperative setting.
Bottomline: Think twice before using a hypotonic fluid especially on admission or after surgery. While there is no perfect intravenous fluid for all patients at all times, in many patients, isotonic fluids will be more favorable by reducing the risk of hyponatremia.
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