3.2 Fluids & Electrolytes
Key Takeaways
- Daily weight is the single most reliable indicator of fluid status: 1 kg of weight change equals approximately 1 liter of fluid gain or loss
- Hypokalemia flattens T waves and produces U waves; hyperkalemia produces peaked T waves and a widened QRS — and low potassium dramatically increases digoxin toxicity risk
- Chvostek and Trousseau signs point to hypocalcemia; the antidote for life-threatening hypermagnesemia is IV calcium gluconate
- Never infuse IV potassium faster than 10 mEq/hr peripherally (20 mEq/hr via central line with cardiac monitoring), and never give it IV push
- For any transfusion reaction, the first action is to STOP the transfusion and keep the vein open with normal saline, then notify the provider and blood bank
Last updated: August 2026
Fluid Volume Deficit vs. Fluid Volume Excess
Fluid Volume Deficit (FVD)
Fluid volume deficit is loss of water and electrolytes from the extracellular space. Causes: vomiting, diarrhea, nasogastric suction, diuretics, hemorrhage, burns, diabetic ketoacidosis, poor intake.
- Assessment: thirst, dry mucous membranes, poor skin turgor (unreliable in older adults — check the sternum or forehead), tachycardia, weak thready pulse, orthostatic hypotension (a drop of more than 20 mm Hg systolic on standing), flat neck veins, decreased urine output with high specific gravity (>1.030), elevated BUN out of proportion to creatinine, elevated hematocrit (hemoconcentration), acute weight loss.
- Management: isotonic fluid replacement (0.9% sodium chloride or lactated Ringer's) for extracellular losses; treat the underlying cause (antiemetics, antidiarrheals); strict intake and output; daily weight; fall precautions for orthostatic dizziness.
Fluid Volume Excess (FVE)
Fluid volume excess is fluid retention in the extracellular space. Causes: heart failure, renal failure, cirrhosis, excessive IV fluid administration, corticosteroids, syndrome of inappropriate antidiuretic hormone (SIADH).
- Assessment: weight gain (the earliest and most sensitive sign — 1 kg ≈ 1 L), peripheral edema, jugular vein distention, crackles on auscultation, dyspnea, bounding pulse, hypertension, S3 heart sound, ascites, dilute urine with low specific gravity, decreased hematocrit (hemodilution).
- Management: sodium and fluid restriction, diuretics (furosemide), semi-Fowler position for dyspnea, daily weight, meticulous skin care over edematous tissue, and monitoring potassium during diuresis.
Exam pearl: both conditions share tachycardia and confusion as late signs. The differentiators are neck veins (flat vs. distended), lung sounds (clear vs. crackles), pulse quality (thready vs. bounding), and blood pressure (low/orthostatic vs. elevated).
Electrolyte Imbalances: Causes, Signs, ECG Changes, Treatment
| Electrolyte (normal) | Imbalance | Common Causes | Key Signs | ECG Changes | Treatment |
|---|---|---|---|---|---|
| Sodium 135-145 mEq/L | Hyponatremia <135 | SIADH, diuretics, excess hypotonic fluid | Confusion, lethargy, seizures, nausea; severe <120 risks cerebral edema | None specific | Fluid restriction; 3% hypertonic saline slowly for severe symptomatic cases (correct no faster than ~8-10 mEq/L/24 hr to avoid osmotic demyelination) |
| Hypernatremia >145 | Dehydration, diabetes insipidus, osmotic diuresis | Thirst, irritability, seizures, coma | None specific | Hypotonic fluids (0.45% NaCl or D5W); treat DI with desmopressin; correct gradually | |
| Potassium 3.5-5.0 mEq/L | Hypokalemia <3.5 | Loop/thiazide diuretics, vomiting, NG suction, insulin | Muscle weakness, leg cramps, ileus, shallow respirations; potentiates digoxin toxicity | Flattened T waves, ST depression, prominent U waves | Oral KCl preferred; IV KCl max 10 mEq/hr peripheral, never IV push |
| Hyperkalemia >5.0 | Renal failure, ACE inhibitors/ARBs, spironolactone, acidosis, tissue injury | Muscle weakness, paresthesias, dysrhythmias | Peaked T waves, widened QRS, sine wave pre-arrest | IV calcium gluconate first, insulin + dextrose, sodium polystyrene sulfonate, dialysis | |
| Calcium 8.5-10.5 mg/dL | Hypocalcemia <8.5 | Hypoparathyroidism (post-thyroidectomy), vitamin D deficiency, pancreatitis, chronic kidney disease | Positive Chvostek (facial twitch) and Trousseau (carpopedal spasm), paresthesias, tetany, laryngospasm | Prolonged QT interval | IV calcium gluconate for symptomatic; keep tracheostomy tray at bedside after thyroidectomy |
| Hypercalcemia >10.5 | Malignancy, hyperparathyroidism, prolonged immobility | Lethargy, confusion, constipation, polyuria, kidney stones | Shortened QT interval | Aggressive normal saline hydration, then loop diuretic; calcitonin, bisphosphonates | |
| Magnesium 1.3-2.1 mEq/L | Hypomagnesemia <1.3 | Chronic alcohol use disorder, diuretics, diarrhea, poor nutrition | Hyperactive reflexes, tremors, seizures; refractory hypokalemia and hypocalcemia | Prolonged QT, torsades de pointes | IV magnesium sulfate; monitor deep tendon reflexes and respiratory rate |
| Hypermagnesemia >2.1 | Renal failure, excess magnesium-containing antacids/laxatives, over-replacement | Diminished deep tendon reflexes, hypotension, bradycardia, respiratory depression | Prolonged PR/QRS, heart block | Stop magnesium sources; IV calcium gluconate is the antidote; dialysis if severe | |
| Phosphate 3.0-4.5 mg/dL | Hypophosphatemia <3.0 | Refeeding syndrome, alcohol withdrawal, diabetic ketoacidosis treatment | Muscle weakness, rhabdomyolysis, respiratory failure | None specific | Oral or IV phosphate replacement; feed malnourished patients slowly |
| Hyperphosphatemia >4.5 | Renal failure, excess intake, hypoparathyroidism | Usually from reciprocal hypocalcemia: tetany, calcifications | From low calcium: prolonged QT | Phosphate binders (sevelamer, calcium acetate) with meals; dialysis |
High-yield pairings the exam loves: hypokalemia + digoxin = toxicity; hypomagnesemia makes hypokalemia impossible to correct until the magnesium is replaced; hyperphosphatemia drags calcium down (they have an inverse relationship); refeeding a starved patient causes phosphate, potassium, and magnesium to crash.
IV Fluid Types
- Isotonic (0.9% sodium chloride, lactated Ringer's): stays in the extracellular space. Use for fluid volume deficit, hemorrhage, shock, and blood transfusions (only 0.9% NaCl is compatible with blood). Caution in heart failure and renal failure — these fluids can cause overload. Lactated Ringer's contains potassium, so use cautiously in renal failure and hyperkalemia; avoid large volumes in liver disease (lactate metabolism) and increased intracranial pressure.
- Hypotonic (0.45% sodium chloride, 0.33% NaCl): shifts fluid into cells. Use for cellular dehydration, hypernatremia, and diabetic ketoacidosis after initial resuscitation. Danger: cerebral edema and increased intracranial pressure — monitor neurological status; avoid in patients with head injury or stroke.
- Hypertonic (3% NaCl, 5% NaCl, D5 0.9% NaCl, D5LR): pulls fluid from cells into the vasculature. Use for severe symptomatic hyponatremia and to reduce cerebral edema. Requires close monitoring, usually in the ICU with central access and frequent sodium checks, because rapid shifts cause demyelination and fluid overload.
Blood Product Administration
Product Types
- Packed red blood cells (PRBCs): restore oxygen-carrying capacity in anemia and hemorrhage. One unit typically raises hemoglobin by about 1 g/dL.
- Platelets: for thrombocytopenia or platelet dysfunction; infuse rapidly (short shelf life), often through a smaller filter per policy.
- Fresh frozen plasma (FFP): replaces clotting factors — warfarin reversal with bleeding, liver disease, disseminated intravascular coagulation.
- Cryoprecipitate: fibrinogen and factor VIII/von Willebrand factor replacement.
- Albumin: volume expander for hypoproteinemia, burns, ascites — carries no clotting factors and is not a blood typing concern.
Safety Steps
- Informed consent signed before transfusion (verify the provider obtained it; the nurse confirms understanding and teaches signs of reaction).
- Two-clinician verification at the bedside: patient name and ID number against the wristband, blood type and Rh, unit number, expiration date, and crossmatch compatibility.
- Baseline vital signs before starting; use only 0.9% normal saline as the companion fluid; dedicate the line to blood (no medications).
- Stay with the patient for the first 15 minutes — most severe reactions occur early. Infuse slowly at first; complete each unit within 4 hours.
Transfusion Reactions and Immediate Response
| Reaction | Cause | Signs | Response |
|---|---|---|---|
| Acute hemolytic | ABO incompatibility | Fever, chills, flank/back pain, hypotension, red-brown urine, anxiety | STOP immediately; keep vein open with NS using new tubing; notify provider and blood bank; send bag and tubing to lab; draw samples; monitor for shock and renal failure |
| Febrile non-hemolytic | Antibodies to donor WBCs | Fever, chills without hemolysis | Stop; notify; antipyretics; may restart per policy after hemolysis excluded |
| Allergic | Reaction to donor plasma proteins | Urticaria, itching, flushing | Stop; antihistamines (diphenhydramine); may resume mild reactions per policy; anaphylaxis requires epinephrine |
| Transfusion-related acute lung injury (TRALI) | Donor antibodies attacking recipient lungs | Acute respiratory distress within 6 hours | Stop; oxygen, respiratory support; report to blood bank |
| Transfusion-associated circulatory overload (TACO) | Volume infused too fast for a compromised heart | Dyspnea, crackles, JVD, hypertension | Stop or slow; upright position; diuretics; prevent by infusing slowly in heart failure patients |
The universal first action for any suspected reaction: stop the transfusion and keep the line patent with normal saline. Everything else — notification, specimens, medications — comes after the patient is no longer receiving the offending unit.
Test Your Knowledge
Fifteen minutes after a unit of packed red blood cells is started, a patient develops fever, chills, and low back pain, and the blood pressure falls from 128/74 to 92/50 mm Hg. What is the nurse's first action?
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D
Test Your Knowledge
A patient receiving furosemide and digoxin reports nausea and blurred yellow-tinged vision. The potassium is 3.0 mEq/L and the digoxin level is 2.6 ng/mL. Which finding best explains this clinical picture?
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B
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D
Test Your Knowledge
A patient with heart failure receiving a unit of packed red blood cells becomes acutely dyspneic with crackles, jugular vein distention, and a blood pressure of 168/96 mm Hg. Which intervention should the nurse anticipate after stopping the transfusion?
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B
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D