Two directions, one assessment set
Fluid imbalance goes in only two directions, and each produces a consistent cluster. In deficit, the vascular space is under-filled: heart rate rises to compensate, blood pressure falls especially on standing, mucous membranes dry, skin turgor becomes poor, urine concentrates and output falls below thirty millilitres per hour, and weight drops.
In excess, the vascular space is overfull and fluid moves into the interstitium and the lungs: crackles appear, respirations increase, neck veins distend, peripheral oedema develops, the pulse becomes bounding, blood pressure rises and weight climbs. Older adults and clients with heart or kidney failure are the populations at greatest risk.
Weight is the arbiter. It is more sensitive than intake and output records, which are frequently incomplete, and more objective than skin turgor, which is unreliable in older adults. One kilogram of weight change approximates one litre of fluid. If a question offers weight as an assessment option alongside softer measures, weight is usually the better answer.
- •Deficit: tachycardia, orthostatic hypotension, dry membranes, concentrated urine
- •Excess: crackles, oedema, JVD, bounding pulse, weight gain
- •1 kg weight change ≈ 1 litre of fluid
- •Urine output below 30 mL/hr is reportable in an adult
Choosing and monitoring IV solutions
Tonicity determines where the water goes. Isotonic solutions have roughly the same osmolality as plasma, so they remain in the vascular compartment and expand circulating volume; they are the go-to for hypovolaemia, haemorrhage and shock. Lactated Ringer's is generally avoided in liver failure, and normal saline in large volumes can produce a hyperchloraemic acidosis.
Hypotonic solutions are more dilute than plasma, so water shifts out of the vessels and into cells. They are used for cellular dehydration and hypernatraemia, but they carry the risk of cerebral oedema and are contraindicated in clients with raised intracranial pressure or extensive burns.
Hypertonic solutions are more concentrated than plasma, so they pull water out of cells and into the vascular space. They are used carefully in severe hyponatraemia and cerebral oedema, require close monitoring for fluid overload, and are typically given slowly and often via a central line depending on concentration.
| Tonicity | Examples | Fluid movement | Typical use and caution |
|---|---|---|---|
| Isotonic | 0.9% NaCl, lactated Ringer's, D5W in the bag | Stays in the vascular space | Hypovolaemia and shock; caution in heart failure |
| Hypotonic | 0.45% NaCl, 0.33% NaCl | Into the cells | Cellular dehydration; avoid in raised ICP and burns |
| Hypertonic | 3% NaCl, D10W, D5 in 0.9% NaCl | Out of the cells | Severe hyponatraemia, cerebral oedema; watch for overload |
IV complications and immediate actions
Infiltration occurs when fluid leaks into surrounding tissue: the site becomes cool, pale, swollen and the infusion slows. Stop the infusion, remove the catheter, elevate the limb and apply the appropriate compress. Extravasation is the same event with a vesicant drug and is more serious, requiring the infusion to be stopped while leaving the catheter in place initially so residual drug can be aspirated per protocol.
Phlebitis presents as a warm, red, tender, sometimes cord-like vein. Discontinue the infusion, apply a warm compress and restart in a different site. Infection at the site adds purulent drainage and possibly systemic signs and requires provider notification and culture.
Two emergencies deserve memorising. Circulatory overload presents with dyspnoea, crackles, hypertension and a bounding pulse; slow the infusion to a keep-open rate, sit the client upright, apply oxygen and notify the provider. Air embolism presents with sudden dyspnoea, chest pain, hypotension and anxiety; clamp the line, place the client on the left side in Trendelenburg to trap air in the right atrium, administer oxygen and call for help immediately.
- •Infiltration: cool, pale, swollen — stop, remove, elevate
- •Phlebitis: warm, red, tender cord — stop, warm compress, restart elsewhere
- •Overload: slow to keep-open, sit upright, oxygen, notify
- •Air embolism: clamp, left side Trendelenburg, oxygen, emergency response
Tying fluids to electrolytes and renal content
Fluid balance never appears alone. It travels with electrolytes, renal function and cardiac output, and the strongest candidates study the cluster together. A client on furosemide for heart failure is simultaneously a fluid question, a potassium question and a cardiac question, and the exam will happily test all three in one item.
Practise by predicting. When you read a stem describing a treatment, predict the fluid consequence and the electrolyte consequence before looking at the options. Prediction before reading options is the habit that most improves accuracy across this content area.
Then work through adult health and fundamentals sets with full rationales so you meet these scenarios in the form the exam uses, including four-client prioritisation items where a fluid-overloaded client with crackles must be compared against other clients.