What are the guidelines for selecting intravenous fluids (type, volume, and rate) based on a patient's volume status, electrolyte and acid‑base balance, organ dysfunction, and clinical goal?

Guidelines for Selecting Intravenous Fluids

Primary Recommendation: Use Balanced Isotonic Crystalloids First-Line

For the vast majority of hospitalized patients requiring intravenous fluid therapy—whether for resuscitation, maintenance, or replacement—balanced isotonic crystalloids (Ringer's Lactate or Plasmalyte) should be the default choice. 1, 2 This recommendation is based on consistent evidence showing reduced mortality and fewer major adverse kidney events compared to 0.9% saline, particularly in critically ill patients. 2

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Fluid Selection Algorithm by Clinical Scenario

Sepsis and Septic Shock

• Administer balanced crystalloids as first-line therapy with an initial bolus of 30 mL/kg for adults. 2 Some patients will require several liters during the first 24-48 hours. 2
• Target endpoints: mean arterial pressure ≥65 mmHg, urine output ≥0.5 mL/kg/h, improved mental status and peripheral perfusion. 2
• Evidence: The SMART trial demonstrated that balanced crystalloids reduced major renal events (death, renal replacement therapy, or persistent doubling of creatinine) with an OR of 0.80 (95% CI 0.67-0.94) and trended toward lower 30-day mortality (OR 0.80,95% CI 0.67-0.97) in sepsis patients. 1
• Avoid 0.9% saline due to increased risk of hyperchloremic metabolic acidosis and renal vasoconstriction. 2

Hemorrhagic Shock and Trauma

• Use balanced crystalloids (Ringer's Lactate or Plasmalyte) as the initial resuscitation fluid, especially when large volumes (5-10 L in first 24 hours) are anticipated. 2
• Rationale: Balanced solutions mitigate the additive metabolic acidosis from both hemorrhagic shock and saline-induced hyperchloremia. 2
• Avoid synthetic colloids (hydroxyethyl starch, gelatins) due to increased acute renal failure risk (RR 1.34,95% CI 1.0-1.8) without mortality benefit. 2

Perioperative Fluid Management

• Administer balanced isotonic crystalloids at 1-2 mL/kg/h intraoperatively and aim for a mildly positive cumulative fluid balance of +1-2 L by end of surgery. 2
• Do not use 0.45% saline for routine adult perioperative maintenance or resuscitation. 2
• The potassium content of Ringer's Lactate (≈4 mmol/L) is safe unless specific contraindications exist (rhabdomyolysis, severe hyperkalemia >6.5 mmol/L). 2

Volume Depletion in Geriatric Patients

Assessment:

• After excessive blood loss: Check for postural pulse change ≥30 beats/min from lying to standing, or severe postural dizziness preventing standing (97% sensitive, 98% specific for blood loss ≥630 mL). 1
• After vomiting/diarrhea: Presence of ≥4 of these 7 signs indicates moderate-to-severe volume depletion: confusion, non-fluent speech, extremity weakness, dry mucous membranes, dry tongue, furrowed tongue, sunken eyes. 1

Treatment:

• Administer isotonic fluids via oral, nasogastric, subcutaneous, or intravenous routes. 1
• For severe dehydration (serum osmolality >300 mOsm/kg or calculated osmolarity >295 mmol/L) in patients unable to drink, consider intravenous fluids. 1

Pediatric Maintenance Fluid Therapy

• Use isotonic balanced solutions providing glucose to restrict IV maintenance fluid volumes in most hospitalized children. 1
• Initial bolus for sepsis: 20 mL/kg, with some requiring up to 110 mL/kg during early resuscitation. 2
• Monitor plasma electrolytes, serum glucose, and fluid balance regularly. 1

Burn Resuscitation

• Adults: Modified Parkland formula of 2-4 mL/kg/%TBSA of balanced crystalloid over first 24 hours (half in first 8 hours, remainder over next 16 hours), targeting urine output 0.5-1 mL/kg/h. 2
• Children: Calculate daily basal requirement using Holliday-Segar 4-2-1 rule, then add modified Parkland formula (3-4 mL/kg/%TBSA) for total fluid intake of approximately 6 mL/kg/%TBSA over first 48 hours. 2

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Specific Fluid Types and Their Indications

When to Use Hypertonic Saline (3% or 7.5%)

• Symptomatic hyponatremia and hyponatremic encephalopathy. 3
• Increased intracranial pressure in traumatic brain injury with focal neurological signs. 3
• Administration: Can be given via peripheral IV at maximum rate of 50 mL/hour with close monitoring. 3
• Do NOT use for volume resuscitation in hemorrhagic shock (meta-analyses of 2,932 patients showed no mortality benefit). 3

When to Consider Albumin

• No routine recommendation for albumin as first-line therapy in sepsis or septic shock, as it does not reduce mortality or renal replacement therapy requirement compared to crystalloids. 1
• Potential secondary benefits: Lower cardiovascular SOFA scores, shorter vasopressor duration, and reduced fluid volumes compared to crystalloids in some studies (ALBIOS, SAFE). 1
• The 2021 Surviving Sepsis Campaign suggested albumin addition to crystalloids in patients requiring large volumes, but current evidence is insufficient for a firm recommendation. 1
• Cost consideration: Albumin is substantially more expensive without proven mortality benefit. 2

Fluids to Avoid

• Hydroxyethyl starch: Increased risk of acute kidney injury, coagulation disturbances, and bleeding without mortality benefit. 2
• Gelatins: No superiority over crystalloids, with potential for anaphylactic reactions. 1
• 0.45% saline in adults: Not endorsed for routine perioperative maintenance or resuscitation due to hyponatremia risk. 2

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Volume and Rate Considerations

Resuscitation Phase

• Administer fluids rapidly when patient is hypovolemic and needs immediate resuscitation. 1
• Stop or interrupt fluid resuscitation when:
  • No improvement in tissue perfusion with volume loading 2
  • Pulmonary crepitations develop (indicating overload or cardiac dysfunction) 2

Maintenance Phase

• Assess fluid and electrolyte needs: Meet orally or enterally when possible; use IV fluids only if oral/enteral route not feasible. 1
• Monitor hourly: Urine output, mean arterial pressure, heart rate, mental status, and peripheral perfusion. 2
• Use advanced monitoring (echocardiography, cardiac output monitoring) when available to guide therapy. 2

Special Populations

• Heart failure: Use balanced crystalloids with careful volume monitoring and point-of-care ultrasonography to assess cardiac function, IVC preload, and dynamic stroke volume changes. 2
• Cirrhotic patients with sepsis-induced hypotension: Albumin showed higher rates of shock reversal and 1-week survival compared to normal saline. 2

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Monitoring Requirements

Electrolyte Monitoring

• Routinely monitor serum electrolytes (particularly sodium and chloride) in all patients receiving crystalloid fluids to detect therapy-related disturbances. 2
• Check plasma osmolality in geriatric patients with suspected dehydration (>300 mOsm/kg indicates severe dehydration). 1

Acid-Base Balance

• Large volumes of 0.9% saline cause hyperchloremic metabolic acidosis due to supraphysiologic chloride concentration (154 mmol/L), leading to renal vasoconstriction and acute kidney injury. 2
• Balanced crystalloids maintain better acid-base balance and should be used when large volumes are required. 1, 2

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Critical Pitfalls to Avoid

• Do not use large volumes of 0.9% saline (>5 L in 24 hours) due to association with increased mortality and major adverse kidney events. 2
• Do not assume potassium addition makes 0.9% saline safer for large volume use. 2
• Do not use synthetic colloids based on outdated protocols; they increase renal failure risk without benefit. 2
• Do not reduce sodium provision for hypertensive patients; they require isotonic fluid resuscitation comparable to normotensive patients. 2
• Do not use hypotonic balanced solutions in traumatic brain injury to prevent cerebral edema. 2