What are the differences between types of intravenous (IV) fluids for fluid resuscitation?

Differences Between IV Fluids for Resuscitation

Balanced crystalloids (Plasma-Lyte, Isofundine) should be your first-line choice for fluid resuscitation in most critically ill patients, as they reduce mortality and adverse renal events compared to normal saline, while synthetic colloids (hydroxyethyl starch, gelatins) should be avoided due to increased mortality and renal failure risk. 1, 2

Crystalloid Solutions: The Primary Choice

Isotonic Crystalloids (280-310 mOsm/L)

Balanced crystalloids are superior to normal saline for most resuscitation scenarios:

• Plasma-Lyte contains sodium 140 mmol/L, potassium 5 mmol/L, chloride 98 mmol/L, acetate 27 mmol/L, with osmolarity 295 mOsm/L 1
• Isofundine contains sodium 145 mmol/L, potassium 4 mmol/L, chloride 127 mmol/L, calcium 2.5 mmol/L, acetate 27 mmol/L, gluconate 23 mmol/L, malate 5 mmol/L, with osmolarity 309 mOsm/L 1
• 0.9% Normal Saline contains sodium 154 mmol/L, chloride 154 mmol/L, with osmolarity 308 mOsm/L 1

The electrolyte composition of balanced crystalloids more closely resembles plasma, reducing the risk of hyperchloremic metabolic acidosis that occurs with large volumes of normal saline 2, 3. In septic shock patients, balanced crystalloids are associated with lower in-hospital mortality (17.7% vs 20.2% with saline alone) 4.

Hypotonic Crystalloids (< 280 mOsm/L)

Ringer's Lactate is hypotonic with osmolarity 277 mOsm/L, containing sodium 130 mmol/L, potassium 4 mmol/L, chloride 108 mmol/L, calcium 0.9 mmol/L, and lactate 27.6 mmol/L 1. This solution must be avoided in traumatic brain injury patients due to increased mortality risk (HR 1.78, p=0.035) from cerebral edema 1, 2.

Special Population Considerations

Traumatic Brain Injury Patients

Use isotonic 0.9% normal saline exclusively in patients with acute brain injury:

• Hypotonic solutions worsen cerebral edema and increase mortality 1, 2
• Isotonic solutions (280-310 mOsm/L) are recommended to reduce mortality and improve neurological prognosis 2
• Balanced crystalloids show no superiority over normal saline in this population, with only reduced hyperchloremia as a benefit 1

Sepsis and Septic Shock

Balanced crystalloids are first-line therapy:

• Hydroxyethyl starch is contraindicated—it increases mortality and renal replacement therapy requirements 1
• Gelatins should not be used due to increased renal failure risk 1
• The European Medicines Agency banned HES for sepsis resuscitation in 2013 1
• When colloids are added to crystalloids, hospital length of stay and costs increase without survival benefit 4

ESRD and Perioperative Patients

Balanced crystalloids like Plasma-Lyte are preferred over normal saline:

• Normal saline causes hyperchloremic metabolic acidosis, renal vasoconstriction, and decreased kidney perfusion 5
• The potassium content (4-5 mmol/L) in balanced solutions does not cause clinically significant hyperkalemia even in at-risk patients 1, 5
• Target mildly positive fluid balance (+1-2 L) by end of surgery 5

Pediatric Populations

Use 20 mL/kg boluses with reassessment:

• Initial bolus of 20 mL/kg for children with severe sepsis, severe malaria, or dengue shock syndrome 1
• Avoid routine bolus fluids in children with "severe febrile illness" who are not in shock 1
• Frequent reassessment is critical to detect deterioration early 1

Colloid Solutions: Limited Role

Synthetic Colloids (Avoid)

Hydroxyethyl starch and gelatins should not be used:

• HES increases mortality and acute renal failure in sepsis (demonstrated in VISEP, 6S, CHEST trials) 1
• Gelatins show no mortality benefit and increase renal failure risk 1
• Both impair hemostasis and coagulation 2, 6

Albumin (Selective Use Only)

Albumin has limited indications and lacks general clinical benefit:

• May be considered in severe hypoalbuminemia with fluid overload 7
• Useful in cardiopulmonary bypass priming (target hematocrit 20%, albumin 2.5 g/100 mL) 7
• Not justified for chronic nephrosis, cirrhosis, or protein-losing enteropathies 7
• Remains intravascular only when capillary integrity is intact 8

Critical Pitfalls to Avoid

High-volume normal saline administration causes:

• Hyperchloremic metabolic acidosis 2, 3
• Renal vasoconstriction and decreased perfusion 5, 3
• Hypernatremia and hypokalemia 8

Using hypotonic solutions in brain injury dramatically increases mortality through cerebral edema 1, 2.

Synthetic colloid use in sepsis violates regulatory warnings and increases death rates 1, 6.

Practical Algorithm

1. Start with balanced crystalloids (Plasma-Lyte, Isofundine) for most resuscitation scenarios 1, 2
2. Exception: Use normal saline for traumatic brain injury patients 1, 2
3. Avoid all synthetic colloids (HES, gelatins) in sepsis and critical illness 1
4. Reserve albumin for specific indications like severe hypoalbuminemia with volume overload or cardiopulmonary bypass 7
5. Never use hypotonic solutions in patients with or at risk for cerebral edema 1, 2