Overview
This lecture covers fluid balance in the body, including solution osmolarity, how to calculate intake and output (I&O), and recognizing/treating fluid volume deficit and excess—essential knowledge for nursing fundamentals.
Solution Osmolarity
- Hypertonic solutions have higher osmolarity than body fluids, causing water to leave cells and cells to shrivel.
- Isotonic solutions have equal osmolarity to body fluids, causing no net movement of water in or out of cells (e.g., normal saline, lactated Ringer’s).
- Hypotonic solutions have lower osmolarity than body fluids, causing water to enter cells and cells to swell or burst.
- Examples of hypertonic fluids: D10W, 3% saline, 5% saline.
- Examples of hypotonic fluids: 0.45% (half-normal) saline, 0.225% (quarter-normal) saline.
Calculating Intake and Output (I&O)
- Intake includes all fluids entering the body: oral fluids, IV fluids, flushes, liquid meds, gastric lavage, and bladder irrigation.
- Output includes all measurable fluids leaving the body: urine, emesis (vomit), blood, wound or chest tube drainage.
- Sensible losses (measurable): urine, blood; insensible losses (not measurable): sweat, respiration.
- I&Os are recorded in milliliters (mL); 1 fluid ounce equals 30 mL.
- Record ice chips at half their original volume; 100 mL of ice chips counts as 50 mL intake.
Fluid Volume Deficit
- Signs include hypotension (low blood pressure), tachycardia (fast heart rate), weak/thready pulse.
- Lab findings: increased hematocrit, blood osmolality, BUN, urine-specific gravity, and urine osmolality.
- Treat with isotonic IV fluids; report urine output <30 mL/hr to provider.
Fluid Volume Excess
- Signs include weight gain, edema, tachycardia, hypertension (high BP), dyspnea, crackles in lungs, jugular vein distension, and bounding pulses.
- Lab findings: decreased hematocrit, hemoglobin, serum osmolality, urine-specific gravity.
- Treat with diuretics or procedures to remove fluid (e.g., paracentesis).
- Report weight gain of 1–2 lbs in 24 hours or 3 lbs in a week to the provider.
Key Terms & Definitions
- Osmolarity — concentration of solutes per liter of solution.
- Isotonic — same osmolarity as body fluid; no fluid shift.
- Hypertonic — higher osmolarity than body fluid; draws water out of cells.
- Hypotonic — lower osmolarity than body fluid; pushes water into cells.
- Sensible loss — fluid loss that can be measured (urine, blood).
- Insensible loss — fluid loss that cannot be measured (sweat, breathing).
Action Items / Next Steps
- Memorize signs, symptoms, and lab changes for fluid volume deficit and excess.
- Practice calculating intake/output in milliliters and converting fluid ounces.
- Know the examples of hypertonic, isotonic, and hypotonic solutions.
- Review next content: electrolytes and electrolyte imbalances.