Why the medical standard for saline is based on a century-old scientific error
In short: For nearly 150 years, doctors have used normal saline as a go-to medical fluid. Yet, the 0.9% concentration we call normal is not actually equivalent to human blood. This common medical staple, born from a cholera pandemic, is now being challenged by more precise alternatives in critical care.
The medical use of saline traces back to the 1831 Indian Blue cholera pandemic. William Brooke O'Shaughnessy, an Edinburgh Medical School graduate, proposed injecting cholera patients with oxygenated salts to combat severe dehydration. His method was soon adopted by physician Thomas Latta. While early solutions varied wildly in composition, the specific 0.9% concentration—now known as normal saline—gained its name from flawed 1882–83 research by Dutch physiologist Hartog Jacob Hamburger. His in vitro studies incorrectly identified 0.9% as the salt concentration of human blood, when the actual figure is closer to 0.6%.
Despite this mismatch, normal saline became a ubiquitous tool for rehydration, wound cleaning, and even breast augmentation. It is a crystalloid medication that provides 154 mEq/L of sodium and chloride. However, its physiological inaccuracy has consequences. Rapid infusion of large volumes can cause metabolic acidosis, a complication that has led modern clinicians to favor alternatives like Ringer's lactate solution. A 2018 randomized, controlled trial of 15,000 intensive care patients demonstrated that lactated Ringer's reduced the combined risk of mortality, persistent kidney issues, or the need for dialysis from 15% to 14% compared to normal saline.
Modern medicine now employs a spectrum of saline concentrations for specific needs. Hypertonic solutions, such as 3% or 7% NaCl, are used in critical care to manage intracranial pressure or hydrate thick mucus in cystic fibrosis patients. Conversely, lower concentrations are often paired with dextrose to maintain safe osmolality. As medical technology advances, the field is moving toward precision resuscitation. For instance, the PRECISE trial, deployed in June 2024 across six Emory Healthcare hospitals, uses machine learning to identify sepsis patients who might benefit from specific fluid types, signaling a shift away from the one-size-fits-all approach of traditional saline therapy.
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Sources
- Summary by Intellect · source: Saline (medicine)
- Also: Development to implementation to evaluation: step-by-step approach to embedding a clinical trial of a machine learning algorithm in the electronic health record.
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