Plain NSS is Identical to 0.9% Normal Saline and 0.9% NaCl
Plain Normal Saline Solution (NSS), 0.9% normal saline, and 0.9% NaCl are all the same solution—they are simply different names for the identical fluid containing 154 mEq/L each of sodium and chloride. 1, 2
Terminology Clarification
The following terms are interchangeable and refer to the exact same crystalloid solution:
- Plain NSS (Normal Saline Solution)
- 0.9% normal saline
- 0.9% NaCl
- 0.9% sodium chloride
- Normal saline (NS)
All contain 154 mEq/L (or 154 mmol/L) of both sodium and chloride, making them isotonic but not physiologic. 1, 2
Important Clinical Context: The "Normal" Misnomer
Despite being called "normal" saline, this solution is actually not physiologically normal—it contains supraphysiologic concentrations of chloride (154 mEq/L) compared to human plasma (approximately 98-106 mEq/L). 3, 4 The term "normal" has no convincing scientific or historical basis and appears to be based on historical fallacy and misconception. 2
Clinical Implications of Using 0.9% Saline
When administering large volumes of any form of NSS/0.9% saline/0.9% NaCl, be aware of these risks:
Metabolic Complications
- Hyperchloremic metabolic acidosis develops with administration of large volumes, as the supraphysiologic chloride load causes dilution of bicarbonate and direct chloride accumulation. 5, 3
- Hyperchloremia (chloride >110 mEq/L) is associated with increased 30-day mortality in surgical patients. 5, 6
Renal Complications
- Renal vasoconstriction and increased risk of acute kidney injury occur with large-volume administration. 5, 3
- The SMART trial (15,802 critically ill patients) demonstrated higher rates of major adverse kidney events (MAKE) with 0.9% saline compared to balanced crystalloids. 5, 3
Current Guideline Recommendations
Buffered crystalloid solutions (such as Lactated Ringer's or Plasma-Lyte) are strongly recommended over 0.9% saline/NSS for most clinical scenarios, particularly when large volumes are anticipated. 5 This recommendation is based on high-quality evidence showing:
- Lower mortality rates with balanced crystalloids in sepsis-induced hypotension (adjusted HR 0.71,95% CI 0.51-0.99). 7
- Reduced major adverse kidney events compared to normal saline. 5, 3
- Prevention of hyperchloremic acidosis. 5, 4
When 0.9% Saline May Still Be Appropriate
- Traumatic brain injury (TBI): Current data support use of 0.9% saline over hypotonic balanced solutions to prevent cerebral edema, though whether this benefit is due to salt load or tonicity remains unclear. 5, 6
- Limited volumes: If 0.9% saline must be used, restrict to maximum 1-1.5 L to minimize hyperchloremic effects. 3, 6