1. Fluids And Electrolytes

Fluid Compartments

Body fluids are distributed across different compartments:

Intracellular fluid (ICF): Fluid inside cells, making up about 2/3 of total body water.

Extracellular fluid (ECF): Fluid outside cells, further divided into:
- Vascular space (within blood vessels).
- Connective tissue & bones.
- Transcellular fluid (specialized fluids like cerebrospinal fluid (CSF) and intraocular fluid in the eyes) (Perry et al., 2022).

Third spacing: Fluid trapped in areas where it is not available for normal use, such as:
- Pleural space (pleural effusion).
- Pericardium (pericardial effusion).
- Peritoneum (ascites) (Smeltzer et al., 2021).

Body Fluid Transport Mechanisms

Fluids move within the body through various mechanisms:

Diffusion: Movement of solutes from higher to lower concentration.
Hydrostatic pressure: The force exerted by a fluid against a wall (e.g., blood pressure).
Filtration: Movement of water and solutes due to pressure differences.
Osmotic pressure: The ability of a solution to draw water from a lower concentration to a higher concentration. Osmotic pressure prevents the solvent from passing into a solution through osmosis (Hinkle & Cheever, 2022).

Hormonal Regulation:

Hormones are secreted directly into the bloodstream and travel to their target organs. The release of hormones is often regulated by negative feedback mechanisms. For example, when blood glucose levels rise, the pancreas releases insulin to lower glucose levels. Once glucose levels return to normal, insulin secretion decreases.

Albumin & Osmotic Pressure

Albumin plays a critical role in maintaining oncotic pressure (the form of osmotic pressure exerted by proteins in blood plasma).

Normal albumin levels: 3.5-5.0 g/dL.
Low albumin (< 3.5 g/dL) can result in edema, as there is insufficient oncotic pressure to retain fluid in the vascular compartment (Potter & Perry, 2021).

Hypoalbuminemia & Proteinuria

Conditions leading to low albumin levels include:

Protein loss through urine (Proteinuria):

1. Nephrotic syndrome
2. Glomerulonephritis
3. Renal failure
4. Preeclampsia

Reduced protein intake:

Malnutrition
Anorexia
Alcohol abuse

Decreased protein synthesis:

Liver failure (Smeltzer et al., 2021).

Clinical Scenario (QUIZ):

A malnourished patient with renal failure and proteinuria has an albumin level below 3.5 g/dL, leading to reduced oncotic pressure, fluid retention, and edema. Treatment involves managing fluid intake and addressing the underlying cause.

Fluid Balance in 24 Hours

Fluid Intake:

Ingested water → 1200-1500 mL
Food → 800-1100 mL
Metabolic oxidation → 300 mL
Total daily intake → 2300-2900 mL

Fluid Output:

Urine → 1500 mL/day
Insensible losses:
- Skin → 600-800 mL
- Lungs → 400-600 mL
- Gastrointestinal tract → 100 mL
Total daily output → 2600-3000 mL (Hinkle & Cheever, 2022).

Homeostasis and Fluid Regulation

Homeostasis maintains fluid and electrolyte balance through several mechanisms:

Kidneys: Regulate urine output (~1500 mL/day or 30-50 mL/hour).
- Oliguria: < 400 mL/day.
- Anuria: < 100 mL/day.
Adrenal glands: Release aldosterone, which promotes:
- Sodium (Na⁺) and water retention.
- Potassium (K⁺) excretion.
Posterior pituitary: Releases Antidiuretic Hormone (ADH, Vasopressin) to regulate water retention (Perry et al., 2022).

Key Assessment: Daily Weights

Daily weight monitoring is the most accurate indicator of fluid balance.
Rapid weight gain may indicate fluid retention:
- 0.5-1 lb (0.2-0.5 kg) increase in 24 hours → Report to MD.
- 1 lb weight gain = ~500 mL fluid retention.
- 0.5 lb (0.2 kg) weight gain = ~250 mL fluid retention (Potter & Perry, 2021).

References

Hinkle, J. L., & Cheever, K. H. (2022). Brunner & Suddarth’s textbook of medical-surgical nursing (15th ed.). Wolters Kluwer.
Perry, A. G., Potter, P. A., & Ostendorf, W. R. (2022). Clinical nursing skills & techniques (10th ed.). Elsevier.
Potter, P. A., & Perry, A. G. (2021). Fundamentals of nursing (10th ed.). Elsevier.
Smeltzer, S. C., Bare, B. G., Hinkle, J. L., & Cheever, K. H. (2021). Brunner & Suddarth’s textbook of medical-surgical nursing (14th ed.). Wolters Kluwer.