What maintenance IV fluid is recommended for a patient with Acute Kidney Injury (AKI) and metabolic acidosis after receiving a normal saline (NS) bolus?

Maintenance IV Fluid After Normal Saline Bolus in AKI with Metabolic Acidosis

Switch to a balanced crystalloid solution (lactated Ringer's or Plasmalyte) for maintenance IV fluids at approximately 75-100 mL/hour (1-1.5 mL/kg/hour), as these solutions prevent worsening of the hyperchloremic metabolic acidosis caused by normal saline while maintaining adequate renal perfusion. 1, 2

Why Balanced Crystalloids Are Superior

The concern with continuing normal saline is well-established: normal saline contains 153 mEq/L of chloride and induces hyperchloremic metabolic acidosis, renal vasoconstriction, and worsens kidney injury when given in large volumes. 3 This is particularly problematic in your patient who already has metabolic acidosis and AKI.

Balanced crystalloid solutions (lactated Ringer's or Plasmalyte) are strongly preferred over 0.9% saline because they reduce the risk of hyperchloremic acidosis and associated kidney injury. 1, 4 Recent evidence demonstrates:

• Balanced crystalloids are associated with faster resolution of metabolic acidosis compared to normal saline 5, 6
• Plasmalyte contains acetate and gluconate (not lactate) as buffers, making it appropriate even in patients with lactic acidosis 2
• The British Journal of Anaesthesia specifically recommends buffered crystalloid solutions like Plasmalyte at 75-100 mL/hour in patients with lactic acidosis and AKI 2

Specific Fluid Selection Algorithm

First choice: Plasmalyte or lactated Ringer's 1, 2, 4

• These provide balanced electrolytes without excessive chloride
• They contain buffers (acetate/gluconate or lactate) that help correct acidosis

Important caveat: Check potassium level first 1, 2

• If hyperkalemia is present, avoid potassium-containing solutions (lactated Ringer's contains 4 mEq/L potassium)
• In this case, use Plasmalyte or continue normal saline cautiously until potassium normalizes

Target Maintenance Rate

Administer 75-100 mL/hour (approximately 1-1.5 mL/kg/hour) of balanced crystalloid 1, 2, 4

• This rate maintains adequate renal perfusion without causing fluid overload
• Adjust based on hemodynamic parameters and urine output

Critical Monitoring Parameters

Reassess fluid status every 6-12 hours and monitor: 1, 4

• Urine output (target >0.5 mL/kg/hour) 1, 4
• Signs of fluid overload (pulmonary edema, peripheral edema, elevated JVP) 1
• Hemodynamic stability (blood pressure, cardiac output) 1
• Electrolytes (particularly potassium and chloride) 1, 2

What NOT to Do

Do not continue normal saline for maintenance - this will worsen the hyperchloremic metabolic acidosis and potentially worsen AKI 3, 1, 4

Do not use colloids (albumin or hydroxyethyl starch) - these increase mortality, AKI progression, and bleeding risk 3, 1

Do not use diuretics to treat the AKI itself - diuretics should only be used if volume overload develops (Level 1B evidence) 3, 1, 4

When to Restrict Fluids

Stop or significantly reduce maintenance fluids if: 1, 4

• Signs of fluid overload develop (pulmonary edema, significant peripheral edema)
• Hemodynamic stability is achieved and patient is euvolemic
• Urine output remains adequate without additional fluid support

Fluid accumulation is associated with significantly higher mortality in AKI patients, making conservative fluid management essential once hemodynamic stability is achieved. 1

Special Consideration for Severe Acidosis

If the patient has severe lactic acidosis requiring renal replacement therapy, KDIGO specifically recommends bicarbonate-buffered dialysate over lactate-buffered solutions. 2 However, for IV maintenance fluids, balanced crystalloids remain the appropriate choice.