IV Fluids: Study Notes

1. Types of IV Fluids

A. Crystalloids – Water with small solutes (e.g., Na⁺, Cl⁻, Dextrose). Most common.
B. Colloids – Contain large molecules (e.g., albumin) that expand plasma volume.

2. Crystalloids: Classified by Tonicity

Tonicity = effective osmolarity vs plasma; determines water movement.

A. Hypotonic Fluids
Examples: 0.45% NaCl (Half-Normal Saline), D5W
Effect: Water moves into cells → ↑ Intracellular Fluid (ICF)
Indications: Hypernatremia, maintenance fluids
Risks: Hyponatremia, cerebral edema, hemolysis; do not bolus

B. Isotonic Fluids
Examples: 0.9% NaCl, Lactated Ringer’s (LR)
Effect: Stays in extracellular space → ↑ Extracellular Fluid (ECF), vascular expansion
Indications: Hypovolemia, fluid resuscitation, maintenance
Risks: Hypervolemia; NS → hyperchloremic metabolic acidosis, hyperkalemia; LR → avoid in liver failure, incompatible with blood transfusions

C. Hypertonic Fluids
Examples: 3% NaCl
Effect: Pulls water out of cells → ↑ ECF, shrinks cells
Indications: Severe hyponatremia (<120 mEq/L), cerebral edema
Risks: Osmotic demyelination if corrected too fast, hypernatremia, acidosis, hyperkalemia

3. Colloids

Examples: Albumin 5% or 25%
Effect: ↑ Oncotic pressure → draws fluid from interstitial space into vascular space
Indications: Hypovolemic shock, decompensated cirrhosis, large-volume paracentesis
Risks: Expensive, hypervolemia, allergic reactions, no significant benefit over crystalloids for general resuscitation

4. Vascular Access

1. Peripheral IV: First-line for most patients

2. Intraosseous (IO): Emergency access if IV fails

3. Central Line: For vasopressors, hypertonic solutions, CVP monitoring, difficult access

5. Clinical Approach to Fluid Administration

Step 1: Assess Volume Status
Hypervolemia: JVD, crackles, edema → avoid fluids
Hypovolemia: Dry mucosa, poor turgor, flat veins, oliguria, hypotension

Step 2: Determine Hemodynamic Stability
Hypotensive: Give 500–1000 mL isotonic bolus over 15–30 min (smaller if CHF)
Normotensive but hypovolemic: Fluid challenge 250–500 mL or passive leg raise; continue only if SV ↑ >12%

Step 3: Maintenance Fluids
Use if ongoing losses or NPO
Choose fluid:

• Normal sodium → LR or NS

• Hypernatremia → Hypotonic

• Hypovolemic hyponatremia → Isotonic
  Rate Calculation: Adults → Weight(kg) + 40 mL/hr; Pediatrics → Holiday-Segar (4-2-1 rule)

6. Summary Table: Crystalloid Fluids

Fluid Type	Examples	Tonicity	Primary Effect	Indications	Key Risks
Hypotonic	0.45% NaCl, D5W	Low	↑ ICF	Hypernatremia, Maintenance	Hyponatremia, Cerebral Edema, Hemolysis (if rapid)
Isotonic	0.9% NaCl, LR	Equal	↑ ECF, vascular expansion	Hypovolemia, Fluid Resuscitation, Maintenance	Hypervolemia, NS: acidosis/hyperkalemia; LR: avoid in liver failure
Hypertonic	3% NaCl	High	↓ ICF, ↑ ECF	Severe hyponatremia, Cerebral Edema	Osmotic demyelination, Hypernatremia, Acidosis, Hyperkalemia