Patho-pharm Exam 2 PDF - Water & Sodium Balance

I. Water and Sodium Balance A. Overview: Involves the composition and movement of body fluids Body solutions are composed of solvents (water) & solutes (electrolytes) Function interdependently B. Functions of body fluids...

I. Water and Sodium Balance A. Overview: Involves the composition and movement of body fluids Body solutions are composed of solvents (water) & solutes (electrolytes) Function interdependently B. Functions of body fluids Serves as a lubricant and as a solvent for chemical reactions called metabolism. It transports oxygen, nutrients, chemical messengers, and waste products to their destinations. Plays an important role in the regulation of body temperature. C. Body Fluid Variations Sex: Total percent of body water in men is around 60%, and women 50% Fat content: Contains little water, women have greater % of body fat than men Age: The elderly have more fat and less water, newborns have less fat and more water. 2 F&E  D. Gains and Losses of Total Body Water Regulated by intake and output Fluid gains: liquids (1400), foods (700), oxidative metabolism (300). Total equals approximately 2400 ml/day. Fluid Losses: urine (1 -2 L/QD), feces (100-200 ml/QD), lungs & skin (500- 1000 ml/QD). Total equals approximately 2400 ml/day. E. Body Fluid Compartments Intracellular (ICF): All fluid within cell = 2/3 of TBW Extracellular (ECF): Fluid outside of cell = 1/3 of TBW Intravascular: blood plasma Interstitial: space between cells and outside blood vessels Other: Lymph, synovial, intestinal, cerebrospinal, sweat, urine, pleural, peritoneal cavity, pericardial Note: Babies, ECF > ICF = high risk for fluid volume deficit, water bottle 3 F&E  F. Classifications of Body Fluids Interchangable terms: concentration, osmolality, tonicity Serum osmolality equals the number of osmoles per 1 L of solution (N=275-295). Sodium determines serum osmolality and it can be estimated by doubling the serum sodium level (N=135-145). Isotonic—serum osmolality Hypotonic—serum osmolality Hypertonic—serum osmolality G. Overview of fluid and Electrolyte Movement Osmosis: Water moves through a semipermeable membrane from an area of lower particle concentration to an area of higher particle concentration until concentrations are equalized on both sides of the membrane. Diffusion: Particles move from an area of higher particle concentration to an area of lower particle concentration, and may or may not be able to pass through semi-permeable membrane. Active Transport: requires energy in the form of ATP 4 F&E H. Capillary fluid Movement Hydrostatic Pressure: Pushing force of a fluid generated by the heart’s pumping action Oncotic/Colloid Osmotic Pressure or COP: The pulling force exerted by colloids (proteins) in a solution Starling’s Law of the Capillaries Filtration: fluid movement into or out of the capillaries At the arterial end of the capillary, hydrostatic pressure pushes water out of the capillary into the tissue, carrying nutrients with it. At the venous end of the capillary, oncotic pressure pulls water back into the capillary, carrying wastes with it. 5 F&E I. Chemical Regulation of Water Balance 1. Thirst occurs with a 2% water loss or increased osmolality Physiology: Osmoreceptors (hypothalamus) are activated by a dry mouth, hyperosmolality, or plasma volume depletion. The person experiences thirst. Plasma volume is restored and dilutes ECF osmolality after drinking water. Disorders affecting thirst mechanism: coma, inability to swallow, stroke 2. Antidiurectic Hormone (ADH) ADH is stimulated when there is a water deficit, an increase in plasma osmolarity, or a decrease in plasma volume (BP drops) Physiology: Osmoreceptors stimulate the release of ADH from the Pituitary Gland. ADH increases the permeability of water in the distal tubules and the collecting duct, decreasing urine output (increasing concentration), water is reabsorbed into blood plasma. The increase in circulating blood plasma causes the blood pressure to increase. 6 F&E  Disorders Affecting ADH: Syndrome of Inappropriate Antidiuretic Hormone (SIADH): excessive ADH secretion = excessive water retention Diabetes Insipidus (DI): decreased ADH secretion = excessive water excretion J. Chemical Regulation of Sodium Balance 1. Aldosterone is the primary regulator of sodium Aldosterone is stimulated when there is a decrease in Na levels or an elevation in K levels through the Renin Angiotension Aldosterone System (RAA) Note: water follows Na, Na and K have inverse relationships Physiology: Na levels are regulated at the renal tubule by the macula densa. When Na levels decrease, renin is released from the renal tubule. Renin enters the bloodstream, binds with angiotension (plasma protein) and is converted to angiotension I. Angiotension I is rapidly converted to Angiotension II by the angiotensin- converting enzyme in the small blood vessels of the lungs. 7 F&E  Angiotension II is a potent vasoconstrictor. The constricted vessels in the renal tubules decrease glomerular filtration slowing blood flow through the kidney so less sodium is filtered. The constricted blood vessels increase blood pressure. Angiotension II also stimulates the adrenal cortex to secrete aldosterone. Aldosterone increases the reabsorption of Na and excretion of K in the urine. Increased Na retention increases plasma osmotic pressure causing hypothalamus to secrete ADH, which increases water reabsorption 2. Atrial Natriuretic Peptide Hormone (ANP) ANP is activated with prolonged aldosterone elevation, chronic retention of fluid or excessive secretion (adrenal tumor) 8 F&E  Physiology: Atrial muscle stretching inhibits the secretion of ADH, renin, and aldosterone in the kidney tubules, which decreases Na reabsorption in tubules. Na and water is excreted, decreasing blood volume and BP II. Body Fluid Imbalances A. ECF Imbalances 1. Isotonic Volume Deficit (Dehydration) Equal Na and water loss, normal serum osmolality Primarily an ECF loss, ICF is not disturbed Causes: Hemorrhage, decreased intake, vomiting, diarrhea, gastric suctioning, fever, environmental heat, excessive sweating, large burns, diuretics, third-space fluid shifts Symptoms: Increased thirst, urine concentrated with high specific gravity, dry skin with tenting, dry tongue, decreased tearing, tachycardia, weak, thready pulse, tachypnea, sunken eyeballs, flat neck veins, increased body temperature, acute weight loss Treatment: 9 F&E  Monitor VS, Isotonic IV fluids (NS or RL), monitor intake and output, daily weights, monitor labs Labs: Serum Osm _______ BUN _____ Sodium _______ Cr _____ Chloride ________ H/H _____ Potassium _______ Urine output ______ Sp Gr ______ 2. Isotonic Volume Excess (Overhydration) Equal gain of Na and water, normal serum osmolality Causes: Renal failure, CHF, excessive IV fluids and water Symptoms: Acute weight gain (excess of 5% body weight), dependent and generalized edema, hypertension, full bounding pulse, JVD, pulmonary edema (SOB or dyspnea, crackles, cough) Treatment: Monitor VS, Na and water restriction, monitor intake and output, daily weights, monitor labs, diuretics 10 F&E  Labs: Serum Osm _______ BUN _____ Sodium _______ Cr _____ Chloride ________ H/H _____ Potassium _______ Urine output ______ Sp Gr ______ B. ICF Imbalances 1. Hypertonic Fluid Volume Deficit (Cellular Dehydration) Excess Na in proportion to water, High serum osmolality Treatment consists of decreasing Na and replacing water with hypotonic IV fluids Labs: Serum Osm _______ BUN _____ Sodium _______ Cr _____ 11 F&E  Chloride ________ H/H _____ Potassium _______ Urine output ______ Sp Gr ______ 2. Hypotonic Fluid Volume Excess (Cellular Overhydration) Low Na in proportion to water, Low serum osmolality Treatment consists of increasing Na and decreasing water with hypertonic IV fluids Labs: Serum Osm _______ BUN _____ Sodium _______ Cr _____ Chloride ________ H/H _____ Potassium _______ Urine output ______ Sp Gr ______ C. Edema Classifications: 1. Localized: Sprain or organ system (brain, lungs, heart, peritoneal cavity) 2. Generalized: More uniform distribution in interstitial spaces 3. Dependent: Gravity dependent areas (legs, sacral area) 4. Third Space Shifting: excess fluid trapped in interstitial spaces, causing extreme changes in capillary permeability. Cells may become dehydrated 12 F&E  Causes of third space shifting: Increased hydrostatic pressure, decreased blood osmotic pressure, increased capillary membrane permeability, lymphatic obstruction Symptoms: acute weight gain, edema in dependent areas Treatment: Goal is to mobilize fluid to intravascular compartment to increase glomerular filtration. Restrict Na and fluid intake, diuretic therapy, adequate dietary intake (protein), support hose IV. IV Fluid Administration Isotonic/Crystalloids: Hypotonic: Hypertonic: Colloids: Albumin, Blood products Side effects: watch for edema, altered coagulation (bleeding) Increase COP and move fluid from interstitial compartment to vascular compartment V. Electrolytes Unit of measure = mEq/L A. Sodium (135-145 mEq/L) Major cation in ECF Regulation: Direct—Aldosterone, Indirect—ADH, ANP 13 F&E