Fluid and Electrolyte Balance 2020 copy PDF

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FLUID AND ELECTROLYTE BALANCE The human body is made up of 50 – 60% water (this is greater in infants and children and decreases with age). Body fluids are located either: x Intracellular (40% of body weight) x Extracellular (20% of body weight) Fluid balance is a constantly shifting process influenced by many factors.

Fluid and Electrolyte Transport Passive transport systems: Active Transport System: x Diffusion – random movement of particles in all directions through a solution x Filtration – transfer of water and solutes across membranes x Osmosis – movement of water across a membrane from a less concentrated solution to a more concentrated solution

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Pumping – the mechanism by which solutes can be moved against a concentration gradient. Dependent on the presence of ATP.

Fluid Types: ¾ Isotonic Solution –No fluid shift, solutions are equally concentrated. Normal saline solution (0.9% NaCl), lactated ringers, dextrose 5% in water (D5W), 5% albumin, Hetastarch ¾ Hypotonic Solution – Lower solute concentration. Fluid shifts from hypotonic solution into the more concentrated solution to create a balance (cells swell). Half-normal saline solution (0.45% NaCl), 0.33% sodium chloride, dextrose 2.5% in water ¾ Hypertonic Solution – Higher solute concentration. Fluid is drawn into the hypertonic solution to create a balance (cells shrink). 5% dextrose in normal saline (D5/0.9% NaCl), Dextrose 5% in halfnormal saline (D5.45NS), dextrose 5% in lactated ringer’s, 3% sodium chloride, 25% albumin, 7.5% sodium chloride Hydrostatic Pressure and Colloid Osmotic Pressure: Tissue fluids and plasma in the capillaries have hydrostatic and colloid pressure. Hydrostatic pressure forces fluid and solutes through the capillary walls. When the hydrostatic pressure inside the capillary is greater than the pressure in the surrounding interstitial space, fluids and solutes inside the capillary are forced out into the interstitial space. This also happens in reverse. Intake + Output = Fluid Balance Sensible losses: ~~Starling’s Law~~ Insensible losses: Fluid flows ONLY when there is a difference in pressure x Urination x Evaporation from Extracellular and Intracellular fluid shifts occur related to x Defecation skin changes in pressure within the compartments. x Wound drainage x Respiration loss from lungs

How the Body Regulates Fluid Volume: Kidneys –  Capillary pressure forces fluid through the walls and into the tubule  H2O or electrolytes are then either retained or excreted  Urine becomes more dilute or more concentrated based on the needs of the body Antidiuretic hormone (ADH) –  Produced by the hypothalamus  Stored in the pituitary gland  Restores blood volume by increasing or decreasing excretion of water  Increased osmolality or decreased blood volume stimulates the release of ADH  The kidneys reabsorb water  May be released by stress, pain, surgery and some meds. Renin-angiotensin-aldosterone system –  Renin is secreted in kidneys (amount of renin produced depends on blood flow and amount of Na in the blood)  Produces angiotensin II (vasoconstrictor)  Angiotensin causes peripheral vasoconstriction  Angiotensin II stimulates the production of aldosterone Aldosterone –  Secreted by the adrenal gland response to angiotensin II  The adrenal gland may be also stimulated by the amount of Na and K+ in the blood  Causes the kidneys to retain Na and H2O  Leads to increases in fluid volume and Na levels  Decreases the reabsorption of K+  Maintains B/P and fluid balance Baroreceptor Reflex –  Respond to a fall in arterial blood pressure  Located in atrial walls, vena cava, aortic arch and carotid sinus  Constricts afferent arterioles of the kidney resulting in retention of fluid.

Fluid Imbalances Dehydration – loss of body fluids = increased concentration of solutes in the blood and a rise of serum Na+ levels. Fluid shifts out of the cells into the blood to restore balance and cells shrink from fluid loss and can no longer function properly. Hypovolemia – Isotonic fluid loss from the extracellular space. Caused by excessive fluid loss (hemorrhage), decreased fluid intake, third space fluid shifting. Hypervolemia – Excess fluid in the extracellular compartment as a result of fluid or sodium retention, excessive intake, or renal failure. Occurs when compensatory mechanisms fail to restore fluid balance – leads to heart failure and pulmonary edema. Water intoxication – Hypotonic extracellular fluid shifts into cells to attempt to restore balance. Cells swell. Caused by SIADH, rapid infusion of hypotonic solution, excessive tap water NG irrigation or enemas, or psychogenic polydipsia. Diagnostic Tests for Fluid and Electrolyte Imbalances Urine – Urine pH specific gravity Urine osmolarity Urine creatinine clearance Urine sodium Urine potassium

Blood – Serum hematocrit – 40-54%/men 38-47% for women Serum creatinine – 0.6 – 1.5 mg/dl BUN – 8-20 mg/dl Serum osmolality Assessment for Serum albumin – 3.5-5.5 g/dl Serum electrolytes Fluid/Electrolyte

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potential factors which place the patient at risk Vital signs I/O Body Weight Skin Mucous Membranes Vascular system...