Can excessive use of normal saline (NS) in a patient with acute kidney injury (AKI) and hyperchloremia lead to hyperchloremic acidosis?

Can Excessive Normal Saline in AKI Lead to Hyperchloremic Acidosis?

Yes, excessive normal saline administration in patients with acute kidney injury absolutely causes hyperchloremic acidosis, and a chloride level of 110 mEq/L represents significant hyperchloremia that warrants immediate switching to balanced crystalloid solutions. 1

Mechanism and Evidence

Normal saline (0.9% NaCl) contains a supraphysiologic chloride concentration of 153 mEq/L, which is substantially higher than physiological levels. 2, 3 When administered in large volumes, particularly to patients with impaired renal chloride excretion due to AKI, this leads to:

• Hyperchloremic metabolic acidosis through dilution of bicarbonate and direct chloride accumulation 1
• Renal vasoconstriction that worsens kidney perfusion 1, 4
• Increased risk of progressive AKI and need for renal replacement therapy 1

Clinical Significance in Your Patient

A chloride level of 110 mEq/L is elevated (normal: 98-106 mEq/L) and indicates ongoing hyperchloremia. 1 In the context of AKI, this represents:

• Active saline-induced metabolic derangement that will worsen with continued normal saline 1, 2
• Increased 30-day mortality risk - hyperchloremia in ~20% of surgical patients was associated with increased mortality in a propensity-matched study of 22,851 patients 1
• Higher risk of major adverse kidney events (MAKE) - the SMART trial of 15,802 critically ill patients demonstrated 15.4% vs 14.3% MAKE rates with saline vs balanced crystalloids 1

Immediate Management Algorithm

Step 1: Stop Normal Saline Immediately

• Discontinue all 0.9% saline infusions 2, 3
• If any saline must be used, limit to maximum 1-1.5 L total 2, 5

Step 2: Switch to Balanced Crystalloids

• Primary choice: Lactated Ringer's (LR) - contains physiologic chloride (109 mEq/L) and lactate that metabolizes to bicarbonate to correct acidosis 2, 5
• Alternative: Plasma-Lyte - similar benefits with acetate/gluconate buffers 2, 3
• These solutions reduce major adverse kidney events compared to saline 1

Step 3: Monitor Acid-Base Status

• Check arterial or venous blood gas to assess degree of metabolic acidosis 2
• Calculate base excess and strong ion difference (SID = Na - Cl; normal >31 mEq/L) 6
• Critical threshold: BE-Cl < -7 mEq/L (or SID <31 mEq/L) independently predicts AKI with odds ratio 2.8 6

Step 4: Track Renal Function

• Monitor serum creatinine, urine output, and electrolytes every 4-6 hours 2, 5
• Assess for progression of AKI using RIFLE or KDIGO criteria 6

Important Caveats and Contraindications

When to avoid Lactated Ringer's:

• Traumatic brain injury - use normal saline instead to avoid hypotonic fluid shifts into damaged cerebral tissue 2, 5
• Severe lactic acidosis or liver failure - consider bicarbonate-buffered solutions instead, as lactate metabolism may be impaired 2, 5
• Severe hyperkalemia - though LR contains only 4-5 mEq/L potassium, which is rarely contraindicated unless K+ >6.5 mEq/L 2

Dose-Response Relationship: The evidence strongly suggests that adverse outcomes from normal saline are volume-dependent. 1 Two recent large RCTs (19,136 patients) showed no difference between saline and balanced solutions, but patients received only small amounts of study fluid, highlighting that large volumes are particularly harmful. 1

Supporting Evidence Strength

The recommendation to use balanced crystalloids over normal saline in AKI is supported by:

• High-quality RCTs: SMART trial (15,802 patients) and SALT trial (974 patients) both demonstrated reduced MAKE with balanced crystalloids 1
• Multiple international guidelines: British Journal of Anaesthesia 2024, World Journal of Emergency Surgery 2023, and KDIGO 2014 all recommend balanced crystalloids over saline 1
• Mechanistic studies: Both animal models and human volunteer studies confirm saline causes renal vasoconstriction and decreased GFR 4, 7

Common Pitfall to Avoid

Do not continue normal saline "because the patient is already hyperchloremic." This represents ongoing harm. The hyperchloremia will not resolve without stopping the source and switching to balanced solutions that allow renal chloride excretion (if kidney function permits) or dilution of serum chloride. 2, 8 Studies in patients with pre-existing CKD and prerenal AKI show that while both fluids improve kidney function similarly, Lactated Ringer's provides superior acid-base balance correction. 8