Maintenance Fluid in Critical Care (Adult ICU)
In modern critical care, maintenance fluid is prescribed far less frequently than in the past because:
- Early enteral nutrition provides water.
- Many IV medications already deliver substantial fluid.
- Excess maintenance fluid contributes significantly to fluid overload, prolonged ventilation, AKI, and mortality.
Definition
Maintenance fluid replaces
- Insensible water loss
- Urinary electrolyte losses
- Normal stool losses
It does NOT replace
- Blood loss
- Vomiting
- Diarrhea
- NG suction
- Third-space losses
- Burns
- Sepsis-induced capillary leak
Those require replacement or resuscitation fluids, not maintenance fluids.
Traditional Maintenance Fluid
Historically
D5 + 0.45% NaCl + 20 mmol KCl/L
or
D5W with potassium
These regimens are now used less commonly in ICU because hypotonic fluids increase the risk of hyponatremia, especially in patients with elevated ADH.
Maintenance fluid is now highly individualized
Instead of one “fluid of choice,” clinicians ask:
- Does the patient actually need IV maintenance?
- How much water do they already receive?
- Do they need sodium?
- Do they need glucose?
- Do they need potassium?
IFA(International Fluid Academy) does not recommend a single “maintenance fluid of choice.”Maintenance fluids should be prescribed like any other drug—only when indicated, at the correct dose, for the shortest necessary duration.
Components of Daily Maintenance Requirement
- Water: 25/kg/day or 1ml/kg/hour
- Sodium: ~1 mmol/kg/day
- Potassium: ~1 mmol/kg/day
- Chloride: ~1 mmol/kg/day
- Glucose: 50–100 g/day or 1-1.5g/kg/day to limit starvation ketosis(It is not intended to meet caloric needs.)
Reduce volumes to 20–25 mL/kg/day (or less) in older adults, renal impairment, or cardiac failure.
Potassium Supplementation
Add potassium only if
- Adequate urine output
- No hyperkalemia
- No severe AKI
- No ESRD/anuria
Typical addition 20–40 mmol/L
Maximum concentration depends route (peripheral vs central).
Patients Who Should NOT Receive Routine Potassium
- Hyperkalemia
- AKI
- CKD stage 5
- Dialysis
- Anuria
- Tumor lysis syndrome
- Adrenal insufficiency until corrected
Rate of Maintenance Fluid
- Typical 50–100 mL/hr
- Individualize based on—Weight,Age,Renal function,Cardiac function,Hidden fluid intake
Example-70 kg adult(25 mL/kg/day) ≈1750 mL/day ≈73 mL/hr
Choice of Maintenance Fluid
Balanced Crystalloids (Preferred)
Examples
- Lactated Ringer’s
- Plasma-Lyte
Advantages
- Lower chloride load
- Less hyperchloremic metabolic acidosis
- Potential reduction in major adverse kidney events (shown in large pragmatic ICU and ED trials).
|
Organization / Guideline |
Recommendation on Maintenance Fluid |
|
ISCCM Textbook of Critical Care |
Recommends ½ DNSas routine maintenance in stable fasting adults |
|
NICE CG174 (UK) |
Calculate daily water, Na, K, Cl, glucose requirements individually,No single fluid; commonly D5 + 0.18–0.45% saline + KCl |
|
Surviving Sepsis Campaign (2021) |
No recommendation for routine maintenance fluid |
|
ESICM (European Society of Intensive Care Medicine) |
Maintenance fluids should be individualized,Generally balanced crystalloids if isotonic maintenance is required; supplement free water/glucose separately if needed |
|
SCCM (Society of Critical Care Medicine) |
No specific maintenance fluid recommended |
|
International Fluid Academy (IFA) |
No universal maintenance fluid |
|
ADQI (Acute Disease Quality Initiative) |
Individualized fluid prescription |
|
ESPEN (Clinical Nutrition) |
Maintenance fluids should account for water delivered via EN/PN |
|
AAGBI/CPOC (Perioperative UK) |
Use balanced maintenance and avoid excess sodium/chloride |
Conditions Where Normal Saline Is Preferred
- Vomiting
- Hypochloremic metabolic alkalosis
- TBI
- Cerebral edema
- Symptomatic hyponatremia (hypertonic saline when indicated)
- Severe hyperkalemia (common practice)
- Blood transfusion(avoid calcium containing fluids) (traditional practice)
Patients Requiring Less Maintenance Fluid
- Heart failure
- Pulmonary edema
- ARDS
- AKI
- CKD
- Elderly
- Liver cirrhosis
- Nephrotic syndrome Often require 15–20 mL/kg/day or less, with frequent reassessment.
Sources of Daily Water Loss
|
Route |
Daily Loss |
|
Urine |
1000–1500 mL |
|
Skin |
300–500 mL |
|
Lungs |
300–400 mL |
|
Stool |
100–200 mL |
Total ≈2–2.5 L/day
Insensible Water Loss
- Occurs from Skin,Respiratory tract
- Contains Almost no electrolytes
- Normally ≈10–15 mL/kg/day or ≈700–1000 mL/day
Increased by
- Fever Increase ≈10–12% per °C above 37°C
- Hyperventilation
- Burns
- Open abdomen
- Large wounds
- Phototherapy
- ECMO
Decreased by
- Mechanical ventilation with humidification
- Hypothermia
- Sedation
- Neuromuscular blockade
When Maintenance Fluid Is Needed
- Nil per oral (NPO)
- No enteral feeding
- No significant ongoing losses
- Hemodynamically stable
- No dehydration
- No shock
Examples
- Acute stroke awaiting swallow evaluation
- Postoperative patient
- Sedated ventilated patient without enteral access
- Short bowel obstruction awaiting surgery
When Maintenance Fluid Is NOT Needed
- Ongoing resuscitation
- Fluid overloaded
- Anuric dialysis patient
Hidden Fluid Sources (“Fluid Creep”)
Many ICU patients receive significant fluid unintentionally from medications and nutrition. Before prescribing maintenance fluid, calculate these sources.
|
Source |
Typical Volume/day |
|
IV antibiotics |
500–1500 mL |
|
Vasopressors |
100–500 mL |
|
Sedation infusions |
200–800 mL |
|
Nutrition |
1000–2000 mL |
|
Flushes |
200–500 mL |
|
Drug diluents |
Variable |
Fluid creep can exceed 2–3 L/day, making additional maintenance fluid unnecessary.
Monitoring
Daily assessment should include
Clinical
- Body weight (best marker of cumulative fluid balance)
- Blood pressure
- Heart rate
- Capillary refill
- Peripheral edema
- JVP
- Lung auscultation
- Urine output
- Fluid balance chart
- POCUS (IVC, lung ultrasound, VExUS when appropriate)
Signs of Excess Maintenance Fluid
- Weight gain
- Peripheral edema
- Pulmonary edema
- Raised JVP
- Increasing oxygen requirement
- Pleural effusion
- Ascites
- Positive cumulative fluid balance
- Hyperchloremic acidosis (with saline)
- Hyponatremia (with hypotonic fluids)
Signs of Inadequate Maintenance
- Thirst (if awake)
- Hypernatremia
- Rising urea
- Low urine output (after excluding hypovolemia and AKI)
- Weight loss
- High urine osmolality
Practical ICU Approach
- Does the patient need resuscitation, replacement, or maintenance?
- Account for fluid creep (medications, nutrition, flushes).
- Use enteral water whenever possible.
- Prescribe 25–30 mL/kg/day (or less in fluid-sensitive patients).
- Add potassium only if appropriate.
- Monitor daily weight, cumulative fluid balance, electrolytes, renal function, and bedside ultrasound.
- Stop maintenance fluids as soon as oral or enteral intake becomes adequate.
Landmark Trials on Choice of Crystalloid (Normal Saline vs Balanced Salt Solutions)
|
Trial |
Primary Outcome |
Main Result |
|
SPLIT |
AKI |
No difference |
|
SMART |
MAKE30(Modest reduction in major adverse kidney events) |
Balanced crystalloids reduced MAKE30 (14.3% vs 15.4%) |
|
SALT-ED |
Hospital-free days |
No difference in primary outcome; lower MAKE30 with balanced crystalloids |
|
BaSICS |
90-day mortality |
No significant difference |
|
PLUS |
90-day mortality |
No significant difference in mortality or AKI |
Key References
- NICE Clinical Guideline CG174: Intravenous Fluid Therapy in Adults in Hospital.
- Surviving Sepsis Campaign (2021): International Guidelines for Management of Sepsis and Septic Shock.
- Malbrain MLNG, et al. Principles of fluid management and stewardship in critically ill patients (ROSE concept).Ann Intensive Care.
- Semler MW, Self WH, et al. SMART Trial. Balanced crystalloids versus saline in critically ill adults. NEJM 2018.
- Self WH, et al. SALT-ED Trial. Balanced crystalloids versus saline in noncritically ill adults. NEJM 2018.