What are the advantages and disadvantages of using half normal saline (0.45% sodium chloride solution) versus normal saline (0.9% sodium chloride solution) in patients with varying degrees of dehydration, shock, and underlying medical conditions, such as impaired renal function, heart failure, and liver disease?

Advantages and Disadvantages of Half Normal Saline vs Normal Saline

Direct Answer

Use normal saline (0.9% NaCl) or balanced crystalloids (Ringer's lactate, Plasmalyte) for resuscitation and initial fluid therapy in critically ill patients, avoiding half normal saline (0.45% NaCl) in these settings. Half normal saline has limited clinical utility and is primarily reserved for specific maintenance fluid scenarios in stable pediatric patients, while normal saline and balanced crystalloids are the evidence-based choices for volume expansion and resuscitation. 1, 2

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When to Use Normal Saline (0.9% NaCl)

Advantages of Normal Saline

• Effective for volume expansion and resuscitation in hypovolemic shock, trauma, and critical illness 1, 3
• Appropriate for specific clinical scenarios including head injury, alkalosis, or hyponatremia 3
• Standard of care for diabetic ketoacidosis (DKA) with initial fluid therapy at 10-20 mL/kg/h in adults 1
• Prevents cerebral edema risk in pediatric DKA when used at controlled rates (10-20 mL/kg/h initially, not exceeding 50 mL/kg over first 4 hours) 1

Disadvantages of Normal Saline

• Causes hyperchloremic metabolic acidosis when administered in large volumes, particularly problematic in patients with renal impairment 4, 5, 6
• Associated with renal vasoconstriction and acute kidney injury compared to balanced crystalloids 2, 4
• Higher incidence of major adverse kidney events versus balanced solutions 4, 5
• Should be limited to 1-1.5 L maximum in patients with mild renal impairment to minimize adverse effects 4

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When to Use Balanced Crystalloids Instead

Superior Alternative to Normal Saline

Balanced crystalloids (Ringer's lactate, Plasmalyte) are strongly recommended over 0.9% saline in most critically ill patients, particularly those with sepsis, AKI, or renal impairment. 1, 2, 4

• Reduces mortality and major renal events in sepsis patients with odds ratio 0.80 (95% CI 0.67-0.94) for major renal events 1
• Prevents hyperchloremic acidosis that worsens kidney injury 2, 4
• Faster DKA resolution compared to normal saline (13 vs 17 hours, p=0.02) 6
• Preferred in kidney transplant recipients due to reduced risk of delayed graft function 4

Specific Balanced Crystalloid Recommendations

• Use Plasmalyte at 75-100 mL/h (1-1.5 mL/kg/h) in patients with lactic acidosis and AKI 2
• Plasmalyte contains acetate and gluconate (not lactate), making it appropriate for lactic acidosis 2
• Target urinary flow rates >150 mL/h for 6 hours post-procedure in contrast-induced AKI prevention with isotonic fluids at approximately 1.5 mL/kg/h 1

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Half Normal Saline (0.45% NaCl): Limited Role

When Half Normal Saline May Be Considered

• Maintenance fluid in stable pediatric patients under 5 years in general wards (not for resuscitation) 7
• Transition maintenance therapy after initial resuscitation in specific pediatric scenarios 1

Critical Disadvantages and Contraindications

• Never use for initial resuscitation or volume expansion in any patient population 1
• Increases risk of hyponatremia compared to isotonic solutions, though one pediatric study showed non-significant difference (14.3% vs 6%, RR 2.6, p=0.07) 7
• Explicitly not recommended for patients at increased risk of contrast-induced AKI 1
• Inferior to normal saline in historical comparisons for reducing renal tubular toxicity 1

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Clinical Algorithm for Fluid Selection

Step 1: Identify Clinical Scenario

Resuscitation/Volume Expansion Needed (shock, severe dehydration, DKA, sepsis):

• First choice: Balanced crystalloids (Ringer's lactate, Plasmalyte) 1, 2, 6
• Alternative: Normal saline if balanced crystalloids unavailable 1, 3
• Never use half normal saline 1

Maintenance Fluids in Stable Patients:

• Adults: Isotonic crystalloids preferred 2, 4
• Pediatrics (stable, general ward): Either isotonic or half normal saline acceptable 7
• Post-resuscitation pediatric DKA: 5% dextrose in 0.25 normal saline with 20 mEq/L KCl 8

Step 2: Assess for Contraindications to Normal Saline

Use balanced crystalloids instead of normal saline if:

• Sepsis or septic shock present 1
• Acute kidney injury or renal impairment (eGFR <60) 2, 4
• Kidney transplant recipient 4
• Large volume resuscitation anticipated (>1-1.5 L) 4
• Lactic acidosis present 2

Normal saline may be preferred if:

• Head injury with concern for cerebral edema 3
• Pre-existing alkalosis 3
• Severe hyponatremia 3

Step 3: Monitor for Complications

With normal saline, monitor for:

• Serum chloride elevation and hyperchloremic acidosis 4, 5
• Worsening renal function (creatinine, urine output) 2, 4
• Acid-base status (pH, bicarbonate) 5

With half normal saline (if used), monitor for:

• Hyponatremia development (check sodium at 12 and 24 hours) 7
• Neurological symptoms of hyponatremia 7

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Common Pitfalls to Avoid

• Do not use half normal saline for resuscitation in any clinical scenario—this is associated with worse outcomes compared to isotonic solutions 1
• Do not continue normal saline beyond 1-1.5 L in patients with renal impairment without switching to balanced crystalloids 4
• Do not use oral fluids alone in patients at increased risk of contrast-induced AKI—intravenous isotonic crystalloids are required 1
• Do not force diuresis with loop or osmotic diuretics to prevent contrast-induced AKI—this does not reduce risk 1
• Do not use starch-containing colloids in patients at risk for or with established AKI—they are associated with harm 2