What is the recommended type and volume of maintenance fluid for patients in the Intensive Care Unit (ICU)?

Maintenance Fluid Management in the ICU

Use balanced isotonic crystalloid solutions (Ringer's Lactate or Plasmalyte) as the default maintenance fluid in ICU patients, with careful attention to avoiding fluid overload through daily reassessment and restrictive volume strategies. 1

Fluid Type Selection

Primary Recommendation: Balanced Crystalloids

• Balanced crystalloid solutions should be the first-line choice for maintenance fluid therapy in critically ill adults, as they reduce major adverse kidney events and mortality while maintaining better acid-base balance compared to 0.9% saline 1, 2.
• The SMART trial (15,802 ICU patients) demonstrated that balanced crystalloids resulted in lower rates of the composite outcome of death, new renal replacement therapy, or persistent renal dysfunction (14.3% vs 15.4%, OR 0.91, p=0.04) 2.
• Balanced solutions have electrolyte compositions closer to plasma (chloride: 98-108 mmol/L) versus normal saline (154 mmol/L), reducing the risk of hyperchloremic metabolic acidosis 3, 1.

Important Exception: Traumatic Brain Injury

• In patients with acute brain injury or traumatic brain injury, use isotonic crystalloids such as 0.9% NaCl, Plasmalyte, or Isofundine, but avoid Ringer's Lactate due to its relative hypotonicity and associated increased mortality in this population 1, 4.
• A subgroup analysis showed higher mortality with balanced crystalloids in TBI patients (RR 1.25,95% CI 1.02-1.54) 4.

Avoid Colloids

• Crystalloid solutions should be strongly preferred over colloids for maintenance therapy 3.
• Hydroxyethyl starch is associated with renal failure, coagulopathy, and increased transfusion requirements 3.
• Albumin provides no mortality benefit and is significantly more expensive, with no role in routine maintenance fluid therapy 3.

Volume Management Strategy

Restrictive Approach

• Adopt a restrictive fluid strategy to prevent fluid overload, as both inadequate and excessive IV fluid administration lead to poor outcomes including prolonged mechanical ventilation, increased infection risk, and organ dysfunction 3, 1.
• Avoid cumulative positive fluid balance, which is associated with prolonged mechanical ventilation and increased length of stay 3.

Specific Volume Recommendations

• In patients at risk of increased ADH secretion (common in critical illness), restrict maintenance fluid to 65-80% of calculated requirements (e.g., Holliday-Segar formula in pediatrics) 3.
• In patients with heart failure, renal failure, or hepatic failure, restrict maintenance fluid to 50-60% of calculated requirements to avoid edematous states 3.
• Account for ALL fluid sources when calculating daily totals: IV fluids, blood products, IV medications (infusions and boluses), arterial/venous line flushes, and enteral intake 3.

Initial Resuscitation vs Maintenance

• For sepsis-induced hypoperfusion requiring resuscitation, administer at least 30 mL/kg of balanced crystalloid within the first 3 hours, targeting MAP ≥65 mmHg 1.
• After initial resuscitation, transition to restrictive maintenance strategy with careful monitoring 3.

Fluid Composition Details

Electrolytes and Additives

• Add appropriate potassium to maintenance fluids based on clinical status and regular monitoring to avoid hypokalemia 3.
• Include glucose in maintenance fluids (2.5-5% dextrose) with blood glucose monitoring at least daily to prevent hypoglycemia while avoiding hyperglycemia 3.
• There is insufficient evidence to recommend routine supplementation of magnesium, calcium, phosphate, vitamins, or trace elements in the absence of documented deficiency 3.
• In patients with severe liver dysfunction, avoid lactate-buffered solutions to prevent lactic acidosis 3.

Monitoring and Reassessment Algorithm

Daily Assessment Requirements

• Reassess fluid balance and clinical status at least daily while patients receive IV maintenance fluids 3.
• Monitor electrolytes regularly, especially sodium levels, to detect and prevent dysnatremias 3.
• Use dynamic variables (pulse pressure variation, stroke volume variation) rather than static variables (CVP) to predict fluid responsiveness 1.
• Normalize lactate levels when elevated and reassess frequently using heart rate, blood pressure, oxygen saturation, respiratory rate, temperature, and urine output 1.

Clinical Response Targets

• Target mean arterial pressure ≥65 mmHg in patients requiring vasopressors 1.
• Monitor for signs of adequate tissue perfusion: capillary refill, skin temperature, mottling, pulse quality, blood pressure, and mental status 3.
• Discontinue or reduce maintenance fluids when clinical improvement plateaus or signs of fluid overload develop 3.

Common Pitfalls to Avoid

• Do not use 0.9% saline for large-volume maintenance therapy due to risk of hyperchloremic metabolic acidosis, which impairs renal function 3, 1, 5.
• Do not use hypotonic solutions in critically ill patients due to risk of hyponatremia 3.
• Do not continue liberal fluid administration without daily reassessment, as "fluid creep" leads to cumulative positive balance and worse outcomes 3.
• Do not rely on CVP or pulmonary artery occlusion pressure for fluid management decisions, as these static measures do not predict fluid responsiveness 1.
• Do not use synthetic colloids (hydroxyethyl starch, gelatin) due to increased risk of renal dysfunction and coagulopathy 3, 6.

Transition to Enteral Route

• Consider transitioning to oral or enteral route for maintenance fluids when hemodynamically stable and tolerated, as this reduces length of stay 3.