What is IV crystalloid?

What is IV Crystalloid?

IV crystalloids are aqueous solutions containing water and small molecules (electrolytes, glucose, or buffers) that can freely cross semipermeable membranes, used for intravascular volume expansion, with approximately 25% remaining in the intravascular space and 75% distributing to the interstitial compartment. 1

Composition and Types

Crystalloid solutions are categorized into two main groups based on their electrolyte composition:

Unbalanced Crystalloids

• Normal saline (0.9% NaCl): Contains 154 mEq/L of both sodium and chloride, with supraphysiologic chloride content 1
• Other saline concentrations: Available as 0.45% (hypotonic), 3% and 20% (hypertonic) 2
• Dextrose 5%: Provides free water once glucose is metabolized 2

Balanced Crystalloids

• Ringer's Lactate: Contains physiologic electrolyte concentrations with lactate as a buffer 3
• Plasma-Lyte R: Contains sodium 140 mEq/L, potassium 5 mEq/L, chloride 98 mEq/L, magnesium 3 mEq/L, and acetate buffer 27 mEq/L, with osmolarity of 294 mOsm/L 4
• These solutions more closely approximate plasma electrolyte composition 5

Pharmacokinetics and Distribution

Only 25% of infused crystalloid remains in the intravascular compartment after one hour, with the remaining 75% distributing to the interstitial space. 1, 6 This is fundamentally different from colloids, which retain nearly their entire volume intravascularly when capillary integrity is intact 6.

The volume expansion ratio of crystalloids compared to colloids is approximately 1:1.5, meaning crystalloids require 2-4 times the volume to achieve equivalent intravascular expansion 5, 6.

Clinical Advantages

Crystalloids offer several practical benefits:

• Lower cost compared to colloid solutions 1, 2
• Lower risk of allergic reactions 2
• Greater availability in most clinical settings 1
• Preferred safety profile in critically ill patients, particularly regarding renal function and mortality 5

Complications of Crystalloid Administration

Normal Saline-Specific Issues

Large volume administration of 0.9% saline causes:

• Hyperchloremic metabolic acidosis due to supraphysiologic chloride content 7, 1, 8
• Renal vasoconstriction leading to decreased glomerular filtration 7, 3
• Acute kidney injury at higher rates than balanced solutions 8
• Hypernatremia and hypokalemia 1

General Crystalloid Complications

• Hypervolemia when excessive volumes are administered 1
• Pulmonary edema risk, particularly in elderly patients or those with cardiac dysfunction 6
• Dilutional effects on plasma proteins and coagulation factors with massive resuscitation 6

Current Guideline Recommendations

The European Society of Anaesthesiology (2024) recommends balanced crystalloids over 0.9% saline for perioperative fluid management with high-quality evidence. 7

For patients with sepsis or septic shock, balanced crystalloids are probably recommended over 0.9% saline as first-line therapy to reduce mortality and renal adverse events. 7

In haemorrhagic shock, balanced crystalloids are probably recommended rather than 0.9% NaCl as first-line fluid therapy to reduce mortality and adverse renal events (GRADE 2+). 5

Contraindications to Specific Crystalloids

Lactated Ringer's Should Be Avoided In:

• Severe metabolic alkalosis (lactate is metabolized to bicarbonate) 3
• Lactic acidosis with decreased lactate clearance (impaired hepatic metabolism) 3
• Severe hyperkalemia (contains 4 mEq/L potassium) 3
• Traumatic brain injury or risk of increased intracranial pressure (slightly hypotonic) 3

Balanced Solutions Considerations

The potassium content (5 mEq/L in Plasma-Lyte R) should not be considered a contraindication even in mild-to-moderate hyperkalemia or renal dysfunction, as randomized studies showed comparable plasma potassium concentrations between balanced fluids and normal saline 4. Physiologically, it is impossible to create potassium excess using fluid with potassium concentration equal to or lower than the patient's plasma concentration 4.

Crystalloids vs Colloids

Crystalloid solutions should be preferred over colloid solutions (hydroxyethyl starches, gelatins) in patients with haemorrhagic shock to reduce mortality and renal replacement therapy requirement (GRADE 2-). 5

Despite colloids having superior volume expansion capacity, this advantage does not translate to improved mortality or reduced postoperative complications 5. Hydroxyethyl starch is associated with increased renal failure, haemostasis disorders, and higher transfusion requirements 5. The European Medicines Agency recommended in 2013 that HES no longer be used for volume resuscitation, particularly in sepsis 7.

Human albumin shows no benefit in haemorrhagic shock and is significantly more expensive than crystalloids 5.