Fluids & Electrolytes
Fluid and electrolyte balance links many NCLEX topics: heart failure, kidney disease, burns, GI losses and IV therapy. Questions usually give you a client situation and ask you to spot the imbalance, pick the right fluid, or choose the safest nursing action. This topic organizes the essentials so you can reason through any scenario.
Key facts
- Signs of fluid volume deficit: tachycardia, low blood pressure, dry mucous membranes, concentrated urine.
- Signs of fluid volume excess: edema, crackles, bounding pulse, weight gain, jugular venous distention.
- Daily weights are the most accurate bedside measure of fluid change. About 1 kg equals roughly 1 L of fluid.
- Isotonic fluids (0.9% saline, lactated Ringer's) expand intravascular volume.
- Hypotonic fluids (0.45% saline) move water into cells. Use caution with clients at risk of increased intracranial pressure.
- IV potassium is always diluted and infused with a pump. It is never given by IV push.
Fluid volume deficit and excess
Fluid volume deficit comes from losses such as vomiting, diarrhea, bleeding, burns or poor intake. The body compensates with a faster heart rate and less urine. Older adults and infants lose fluid reserves quickly, so the NCLEX often uses them to test early recognition. Priority actions include monitoring vital signs and intake and output, giving prescribed fluids, and preventing falls from orthostatic hypotension.
Fluid volume excess is common in heart failure, kidney failure and overly fast IV infusions. Crackles in the lungs and shortness of breath mean fluid is affecting gas exchange, which moves this ahead of peripheral edema on your priority list. Typical actions are raising the head of the bed, slowing or stopping the infusion, giving prescribed diuretics and restricting sodium and fluid.
Choosing IV fluids
Match the fluid to the goal. Isotonic solutions stay mostly in the bloodstream and are used for volume replacement. Hypotonic solutions move water into cells and treat cellular dehydration, but they can worsen cerebral edema. Hypertonic solutions pull fluid out of cells and are given only with close monitoring in specific situations.
Expect NCLEX questions to test safety around infusions: checking the site for infiltration, recognizing circulatory overload, and knowing that potassium needs dilution and a pump. When in doubt, choose the answer that protects the heart, lungs and brain.
- Isotonic: 0.9% NaCl, lactated Ringer's
- Hypotonic: 0.45% NaCl
- Hypertonic: 3% NaCl (specialized use only)
Sodium and potassium
Hyponatremia may result from excess water, SIADH or diuretics, and shows up as confusion and a risk of seizures. Hypernatremia often reflects water loss and causes thirst, restlessness and neurologic changes. Correction should be gradual.
Potassium is closely tied to heart rhythm. Loop and thiazide diuretics can lower it. Kidney failure and potassium-sparing diuretics can raise it. Make sure urine output is adequate before giving potassium replacement.
Calcium and magnesium
Low calcium makes nerves irritable: numbness and tingling, muscle cramps, positive Chvostek and Trousseau signs, and a risk of laryngospasm and seizures. It can follow a thyroidectomy or parathyroid surgery, so the NCLEX links those procedures to calcium monitoring.
Magnesium moves in the same direction as calcium in many cases. Clients receiving IV magnesium, for example in pre-eclampsia, need monitoring of respirations, deep tendon reflexes and urine output. Loss of reflexes or slowed breathing suggests toxicity.
Practice: 3 original questions
1. A client with heart failure receiving IV fluids develops crackles and shortness of breath. What should the nurse do first?
Answer and rationale
Correct: B. These are signs of fluid volume excess affecting breathing. Slowing the infusion and positioning the client upright are the immediate priorities, followed by notifying the provider.
2. After a thyroidectomy, a client reports tingling around the mouth. Which lab result should the nurse check?
Answer and rationale
Correct: C. Tingling around the mouth suggests hypocalcemia, which can follow accidental injury to the parathyroid glands during a thyroidectomy.
3. Which IV fluid should the nurse question for a client with a head injury?
Answer and rationale
Correct: C. Hypotonic 0.45% saline moves water into cells and can worsen cerebral edema in a client with a head injury.
Related Nurseclex guides
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