Guide — IV Therapy
IV Therapy Fundamentals for Nurses
Intravenous therapy is one of the most commonly performed nursing interventions in acute care. Understanding fluid classification, osmolarity effects, and clinical indication is essential for safe administration and accurate patient monitoring.
11 min read · IV Therapy
Educational use only. IV therapy decisions require prescriber orders and clinical assessment. Fluid selection and rates must be individualized based on patient condition, lab values, and clinical indication. This material supports nursing education and exam review. It is not medical advice and is not a substitute for clinical judgment, institutional policy, or medical direction. Always follow facility protocols and current provider orders.
Purpose and Indications
IV therapy delivers fluids, electrolytes, medications, blood products, and nutrition directly into the vascular system. The IV route provides rapid systemic distribution and is the most reliable route for patients who cannot tolerate oral intake or require precise delivery.
| Indication | Clinical Example |
|---|---|
| Volume replacement | Hemorrhagic shock, dehydration, burns, large fluid losses from vomiting or diarrhea |
| Fluid maintenance | NPO status, reduced oral intake, post-operative patients |
| Electrolyte correction | Hypokalemia, hyponatremia, hypocalcemia, hypomagnesemia |
| Medication delivery | Antibiotics, vasopressors, chemotherapy, analgesics |
| Blood and blood products | Packed red blood cells, FFP, platelets, albumin |
| Nutrition (TPN/TNA) | Prolonged NPO, GI malabsorption, critical illness |
Fluid Compartments
Total body water (TBW) accounts for approximately 60% of body weight in adult males and 50% in adult females. Understanding fluid distribution helps predict how IV solutions will behave after administration.
Intracellular (ICF)
~40% TBW
Inside cells — primary electrolytes: K⁺, Mg²⁺, phosphate
Interstitial
~15% TBW
Between cells and vasculature — site of edema formation
Intravascular (plasma)
~5% TBW
Inside blood vessels — direct access via IV therapy
The extracellular fluid (ECF) = interstitial + intravascular. IV fluids initially enter the intravascular space and distribute based on their osmolarity and oncotic properties.
Fluid Classification by Osmolarity
Normal serum osmolarity is approximately 275–295 mOsm/L. IV fluids are classified relative to this range. Osmolarity determines the direction of water movement across cell membranes via osmosis.
Isotonic Fluids (approximately 270–310 mOsm/L)
Same osmolarity as blood — no net movement of water across cell membranes. Expands intravascular volume without causing cellular swelling or shrinkage.
Examples
Use: Volume replacement, maintenance, blood transfusion diluent, pre/post-surgery hydration. NS is the most common IV fluid in acute care.
Hypotonic Fluids (<270 mOsm/L)
Lower osmolarity than blood — water moves from vascular space INTO cells (osmosis). Rehydrates cells and reduces serum osmolarity.
Examples
Use: Cellular dehydration, diabetic ketoacidosis (after osmolarity corrected), hypernatremia. Caution: Can cause cerebral edema if given too rapidly; avoid in head injury or hyponatremia.
Hypertonic Fluids (>310 mOsm/L)
Higher osmolarity than blood — water moves from cells INTO vascular space. Expands vascular volume by drawing fluid from interstitial and intracellular spaces.
Examples
Use: Severe hyponatremia (symptomatic), cerebral edema (controlled), TPN. Caution: Requires central line for 3% NaCl and above; risk of pulmonary edema and osmotic demyelination syndrome if corrected too rapidly.
Maintenance vs Replacement Fluids
| Type | Goal | Common Fluids | Clinical Context |
|---|---|---|---|
| Maintenance | Replace daily insensible losses — maintain normal fluid balance | D5½NS + 20 mEq KCl, 0.9% NS | NPO patients, post-operative patients without active deficits |
| Replacement | Correct an existing fluid deficit or ongoing abnormal losses | LR, NS (bolus), electrolyte solutions | Dehydration, hemorrhage, vomiting/diarrhea, GI losses, burns |
| Resuscitation | Rapidly restore intravascular volume and perfusion | NS 1L bolus, LR, blood products, albumin | Shock, sepsis, hemorrhage, trauma |
Nursing Monitoring Responsibilities
IV Site Assessment
- Assess IV site every 1–4 hours (more frequently for high-risk infusions)
- Inspect for infiltration (swelling, pallor, coolness), extravasation (burning, blistering), or phlebitis (redness, warmth, induration along vein tract)
- Verify catheter securement and dressing integrity at each assessment
- Change peripheral IV sites per facility policy (typically every 72–96 hours)
Fluid Balance Monitoring
- Accurate intake and output (I&O) documentation — include all IV fluids
- Daily weights (same time, same scale, same clothing) — most accurate I&O indicator
- Assess for fluid overload: crackles, peripheral edema, elevated BP, JVD, dyspnea
- Assess for dehydration: poor skin turgor, dry mucous membranes, decreased UOP, tachycardia, hypotension
Laboratory Monitoring
- Serum electrolytes (Na⁺, K⁺, Cl⁻, HCO₃⁻) — before and during IV electrolyte therapy
- BUN and creatinine — renal function affects fluid handling
- Serum osmolarity — especially with hypertonic or hypotonic fluids
- Glucose — dextrose-containing solutions and diabetic patients
Infusion Verification
- Verify infusion rate against order — at each shift and after any pump adjustment
- Verify correct fluid and additives — right solution, right concentration, right rate
- Check infusion pump programming (smart pump drug library entries)
- Confirm tubing and filter integrity — replace per facility policy
Documentation
Accurate IV therapy documentation is a legal and safety requirement. Required elements include:
- IV site insertion: date, time, catheter gauge, insertion site location, number of attempts, dressing type, patient education provided
- Fluid administration: solution name and concentration, rate (mL/hour), additives, infusion start and end times
- Site assessment findings: appearance of site, patient-reported comfort, interventions taken
- IV site change: reason for removal, appearance at removal, new site location
- Complications: infiltration, phlebitis, extravasation — extent, interventions, provider notification, patient response
- I&O: all IV fluid volumes included as intake; urine output documented every 4–8 hours or per order
NCLEX Pearls
- ✦Isotonic fluids (NS, LR) stay in the vascular space and are used for volume replacement — they do not significantly change cell size.
- ✦Hypotonic fluids (0.45% NS) cause water to move INTO cells — risk of cellular swelling and cerebral edema.
- ✦Hypertonic fluids (3% NaCl) draw water OUT of cells — use for symptomatic hyponatremia; can cause osmotic demyelination if corrected too quickly.
- ✦D5W is isotonic in the bag but becomes hypotonic after glucose is metabolized — do NOT use for volume resuscitation.
- ✦Lactated Ringer's is contraindicated with blood transfusions — calcium in LR causes clotting in blood products.
- ✦Daily weight is the most accurate single measure of fluid balance — 1 kg = approximately 1 L of fluid.
- ✦Peripheral IV sites should be changed every 72–96 hours — or sooner if signs of complication develop.
Related Resources
Standards & sources
Fact-checked Jun 21, 2026This page is written to align with Infusion Nurses Society (INS) Standards of Practice · CDC (CLABSI prevention) · Institute for Safe Medication Practices (ISMP). It is an educational summary, not a citation of any single document — always verify specific doses, values, and protocols against current guidelines and your facility policy. How we source content →