Fluid and Electroltyes

This lecture introduces fluid and electrolyte balance as essential for homeostasis and overall health. It outlines the nursing role in identifying and responding to imbalances and the learning objectives, which include understanding fluid and electrolyte functions and the impact of imbalances.

Body fluid is categorized into intracellular fluid (2/3 of total) and extracellular fluid (intravascular, interstitial, and trans-cellular fluid). Osmosis is explained as the movement of water across a semi-permeable membrane to equalize solute concentration. Key 'power particles' that control fluid balance are salt, sugar, and protein.

Hydrostatic pressure, exerted by fluid within blood vessels, is influenced by heart contractility and blood volume, acting as a 'pushing force.' Osmotic pressure, determined by serum proteins (especially albumin), acts as a 'pulling force,' drawing water into capillaries. Colloid oncotic pressure specifically refers to albumin's osmotic pressure. The balance between these pressures determines fluid movement in and out of capillaries, ensuring tissue hydration and circulation. Colloids are described as volume expanders (e.g., blood products, albumin).

Fluid can be drawn into the vascular space by increased plasma osmotic pressure (e.g., compression stockings, IV albumin). Conversely, fluid can move from the intravascular space into interstitial areas, leading to volume deficit (e.g., ascites). When fluid moves from cells to the vascular space, it can cause cellular dehydration (e.g., hypernatremia, where water follows high sodium).

Healthy individuals gain fluids through eating and drinking, maintaining equal intake and output. Clinical intake includes IV fluids, TPN, and tube feedings. Fluid loss occurs through kidneys (normal urine output ~1 mL/kg/hr, minimum 0.5 mL/kg/hr), skin (sweating, evaporation, burns), lungs (300 mL/day from breathing, increasing with respiratory rate/coughing), and GI tract (100-200 mL/day in fecal matter, increasing with diarrhea, fistulas, vomiting, drains, ostomies, and blood loss).

The kidneys filter blood, reabsorb water, regulate electrolytes, excrete waste, and regulate acid-base balance. The heart and blood vessels pump blood and regulate blood pressure, which is tied to blood volume. Baroreceptors in the heart and arteries sense blood volume changes, signaling the heart to adjust. Osmoreceptors in the hypothalamus detect solute concentration, triggering ADH release to conserve water and inducing thirst. The pituitary gland stores and releases ADH. Adrenal glands produce aldosterone to increase sodium and water reabsorption. Parathyroid glands control calcium and phosphate. Natriuretic peptides reduce fluid volume by promoting sodium and urine excretion, counterbalancing aldosterone.

The RAAS system is activated by hypotension. Renin converts angiotensinogen to Angiotensin I, which is then converted to Angiotensin II by ACE. Angiotensin II signals thirst, releases aldosterone (increasing sodium and water reabsorption), and signals the pituitary to release ADH (causing vasoconstriction and increased renal tubule permeability for fluid absorption), all to increase blood pressure.

Key lab values include CBC (hemoglobin, hematocrit to assess hydration and blood loss), BMP/CMP (BUN, creatinine for kidney function; serum osmolality for solute concentration and hydration, BNP for heart stress/fluid overload), and urinalysis (urine specific gravity for concentration, urine osmolality, urine sodium).

Hypovolemia involves loss of both water and electrolytes, distinct from dehydration (loss of water only). Causes include abnormal fluid loss (vomiting, diarrhea, sweating, GI suctioning, bleeding) and decreased intake. Third-space shifts (burns, ascites) also cause hypovolemia. Clinical manifestations include circulatory problems (low blood pressure, increased heart rate). Immediate intervention is crucial.

Management starts with oral fluids if possible. Otherwise, IV fluids are administered: isotonic (0.9% NaCl, Lactated Ringer's) to increase blood volume without fluid shifts, often for rescue (e.g., severe hypotension); hypotonic (0.45% NaCl) to deliver free water to cells (dehydration, gastric fluid loss), caution for cellular swelling; hypertonic (Dextrose 5% Normal Saline) for hyponatremia/hypoglycemia, caution for fluid overload. Colloids (albumin, blood products) also restore blood volume. Nursing management includes physical assessment, strict intake/output monitoring, daily weights, vital sign monitoring, encouraging oral intake, and advocating for IV fluids or tube feeding.

Hypervolemia is an expansion of extracellular fluid due to abnormal retention of water and sodium. Causes include heart failure, kidney injury, liver cirrhosis, excessive salt intake, and over-hydration with sodium products. Early indicators involve respiratory (shortness of breath, crackles, cough, increased respiratory rate) and circulatory issues (increased blood pressure, bounding pulses, JVD, peripheral edema, ascites). Prompt recognition and intervention are vital.

Medical management includes diuretics or dialysis. Dietary restrictions may involve fluid restrictions and low-sodium diets. Nursing management parallels hypovolemia: physical assessment, hourly or q8hr intake/output, daily weights, vital sign monitoring, and monitoring response to medications (especially diuretics) and promoting rest.

Elderly patients are at high risk for fluid imbalances due to decreased physiological functions (cardiac, renal, respiratory), reduced body water, muscle mass, and increased fat stores. Their ability to conserve water and sense thirst diminishes, increasing dehydration risk and potential for delirium with fluid volume deficit.

Electrolytes are active chemicals with positive (cations: sodium, potassium, calcium, magnesium, hydrogen) or negative (anions: chloride, bicarbonate, phosphate, sulfate, protein ions) electrical charges. Sodium is a key cation in extracellular fluid; its concentration affects overall ECF concentration, and water follows its movement. Potassium is a major ion predominantly found in intracellular fluid; small changes in ECF potassium can cause cardiac disturbances, with high levels (hyperkalemia) being dangerous.

A reference guide for normal electrolyte ranges is provided, emphasizing the importance of memorizing these values for nursing practice. The course will focus on sodium, potassium, magnesium, and calcium, building upon previous knowledge of electrolyte imbalance manifestations.