PATHOPHYSIOLOGY MODULE 09: FLUID AND ELECTROLYTE BALANCE 100% CORRECT ANSWERS STUDY GUIDE.

PATHOPHYSIOLOGY MODULE 09: FLUID AND ELECTROLYTE BALANCE 100% CORRECT ANSWERS STUDY GUIDE. NURSING 2PF3 MODULE 9: FLUID AND ELECTROLYTE BALANCE Learning Outcomes Upon conclusion of this unit the student will: 1. Describe the mechanisms of fluid balance and imbalance at the capillary level. 2. Discuss Na+ and H2O balance and imbalances in terms of the physiologic mechanisms, possible causes, manifestations, and possible diagnostic measures and treatment. 3. Describe disorders of K+ balance. 4. Briefly discuss disorders of calcium, phosphate and magnesium balance. Some Key Terms:  Osmotic pressure: the pressure which needs to be applied to prevent the inward flow of water across a semipermeable membrane  Oncotic pressure or colloid osmotic pressure: is a form of osmotic pressure exerted by proteins in a blood vessel’s plasma that usually tends to pull water into the circulatory system. It is the opposing force of hydrostatic pressure  Osmolarity: the osmolar concentration in 1L of solution (mOsm/L). Usually used when referring to fluids outside of the body  Osmolality: the osmolar concentration in 1kg of water (mOsm/kg of H2O). Usually used when describing fluid inside the body. Because 1 L of water weighs 1 kg, the terms osmolarity and osmolaity are often used interchangeably Fluid Balance at the Capillary Level  Fluid Balance:  Fluid balance is determined by the push and pull of fluids across the semi-permeable capillary membrane. It is important to remember that the normal movement of fluid depends on the integrity of the capillary membrane  Fluid balance at the level of the capillary relies on a balance between opposing forces: - Pushing force of hydrostatic pressure - Pulling force of oncotic pressure  Hydrostatic pressure: “Push” - Hydrostatic pressure is the pushing force exerted by a fluid. - Inside the capillaries, the hydrostatic pressure is the same as the capillary filtration pressure, bt30Htthtildd10lOMoARcPSD| NURSING 2PF3 Module 9: Fluid and Electrolyte Balance  Colloid osmotic pressure: “Pull” - The colloid osmotic pressure is the pulling force created by the presence of evenly dispersed particles, such as the plasma proteins, that cannot pass through the pores of the capillary membrane - The capillary colloid osmotic pressure is normally about 28 mm Hg throughout the length of the capillary bed. In contrast, the interstitial colloid osmotic pressure represents a pulling pressure exerted by the small amounts of plasma proteins that leak through the pores of the capillary wall into the interstitial space. This pressure is only 8 mm Hg. - At the venous end of the capillary, much of the fluid has moved into the interstitial space leaving the solutes behind—this creates higher capillary osmotic pressure which effectively pulls fluid from the interstitial space back into the vessel - Some particles like glucose and electrolytes move from the vessel into the interstitial space and create interstitial colloidal osmotic pressure, pulling a small amount of fluid into the interstitial space  Capillary fluid balance: - The lymphatic system represents an accessory system by which fluid can be returned to the circulatory system. - Normally, the forces moving fluid out of the capillary into the interstitium are greater than those returning fluid to the capillary. Any excess fluids and osmotically active plasma proteins that may have leaked into the interstitum are picked up by vessels of the lymphatic system and returned to the circulation. - Without the function of the lymphatic system, excessive amounts of fluid would accumulate in the interstitial space.  Fluid Imbalance:  Increased capillary hydrostatic pressure: - If hydrostatic pressure continues to be high at the venous end of the capillary, net fluid movement will be out of the capillary - Can be caused by: Increasedfluidpressure(egHypertension)lOMoARcPSD| NURSING 2PF3 Module 9: Fluid and Electrolyte Balance - Because albumin is the most prevalent colloid (or solid) in the plasma, any clinical situation that results in decreased serum albumin can result in a decrease of capillary oncotic pressure. Common medical diagnoses associated with low serum albumin include burns, liver disease, malnutrition, and excess wound drainage  Increased interstitial colloid osmotic pressure: - When solutes or particles escape from the vessel into the interstitial fluid, they will take fluid with them and hold that fluid in the interstitial space. Thus the net fluid movement will be out of the capillary and into the interstitial space - The capillary membrane should allow only some solutes to escape. Capillary permeability increases in response to the chemical mediators of the inflammatory process = ”leaky capillaries”  Increased tissue hydrostatic pressure: - Can occur due to obstruction of the lymphatics, causing an obstruction of lymph flow and inability to remove excess fluid (i.e. lymphedema) - Normally, osmotically active plasma proteins and other large particles that cannot be reabsorbed through the pores in the capillary membrane rely on the lymphatic system for movement back into the circulatory system. This increases tissue hydrostatic pressure. - Additionally, there is increased interstitial colloid osmotic pressure and increased tissue oncotic pressure which continues to pull fluid from the vessel - Lymphatic obstruction can occur due to liver disease or because of physical obstruction from surgery Edema & Third-Spacing  Edema  What is edema? Edema represents an increase/accumulation of fluid in the interstitial space. This fluid is not readily available for exchange with the rest of extracellular fluid so is called nonfunctional fluid and represents a loss of intravascular fluid volume.  Causes of edema: 1. Increased capillary hydrostatic pressure causes fluid to move into the tissue 2. A decrease in plasma proteins results in a decrease in capillary oncotic pressure (the lack of pull factors means that fluid remains in the interstitial space instead of moving back to the vessel) 3. Leaky capillaries or increased capillary permeability results in the loss of intravascular proteins and other solids to the interstitial space (this movement is accompanied by fluid and the solutes keep the fluid in the interstitial space) 4. Lymphatic obstruction results in decreased absorption of interstitial fluid)  Third-Spacing:  What is third spacing? Third-spacing refers to transcellular fluid accumulation, a small subdivision of the extracellular fluid compartment, which includes various body spaces (e.g. joint spaces, pericardial and pleural cavities, the peritoneum and ocular fluid)  Causes of third-spacing: -NormallyfluidmovesinandoutoftranscellularspacesusingthesamemechanismsthathavelOMoARcPSD| NURSING 2PF3 Module 9: Fluid and Electrolyte Balance  Manifestations of Edema: The signs, symptoms and effects of edema are determined by its location  Brain: - In the brain, edema is most frequently associated with infections or trauma, both of which initiate an inflammatory response - Because the skull is an enclosed space with little room for excess fluid, cerebral edema is lifethreatening - Signs of increased intracranial pressure include headache, altered level of consciousness, or coma, abnormal pupil size or reflexive response, changes in patterns of respiration, and changes in muscle tone, and abnormal posturae.  Airway: - Swelling of the airway constitutes an acute, life-threatening condition that is frequently due to an inflammatory response to allergens or to microorganisms - Airway swelling may result in difficulty swallowing, anxiety, stridor, and possible airway obstruction and asphyxia  Lungs: - When fluid is forced out of the capillaries at the level of the lungs and accumulates around the alveoli, the result is a decrease in gas exchange and a decrease in the ability of the lungs to inflate - Manifestations will vary depending on the cause and location of the fluid shift but will certainly include dyspnea - Patients may also have anxiety or restlessness, diminished breath sounds and/or crackles on auscultation  Abdomen: - The term for fluid that collects in the peritoneal cavity is ascites. This is an example of thirdspacing - Perhaps this accumulation is due to increased intravascular hydrostatic pressure that results when the portal vein is affected by liver cirrhosis or perhaps it results from a significant inflammatory response to something like an abdominal tumor or pancreatitis - You might see an increase in abdominal girth and a protruding embolitis - Your client might complain of abdominal discomfort and if the accumulation of fluid is considerable, of shortness of breath when the expansion of the diaphragm is impeded by fluid  Intestine: - Clients may also experience a third space loss of fluid inside the lumen and wall of the intestine if the intestine is obstructed  Peripheral Edema: - Often due to obstruction of venous blood flow which increases capillary hydrostatic pressure, or to obstruction of lymphatic drainage. - Peripheral edema can occur (predominantly in the lower extremities in ambulatory patients). In bedridden patients, this edema can occur in the sacral area. In both cases this is referred to as dependent edema - Edema that is related to salt retention (discussed in a few minutes) is usually pitting edema lOMoARcPSD| NURSING 2PF3 Module 9: Fluid and Electrolyte Balance control the cause (e.g. Increased capillary hydrostatic pressure due to malnutrition=low album levels—solve by having patient consume diet rich in protein) 2. Control the underlying mechanism: - It is possible that the mechanism responsible for edema is a lack of albumin intravascularly, but the reason for this problem is that a massive inflammatory response has caused increased capillary permeability, therefore protein is leaking from the vessels. Treatment of this problem would be more complex and perhaps require transfusions of albumin or other colloid solutions to increase the capillary oncotic pressure - Unless problem of increased permeability is resolved, albumin will continue to move to the interstitial space and will take fluid with it = increased edema - Problem will be further complicated by the bodies fluid conserving mechanisms (kidneys will conserve water and sodium effectively increasing in capillary hydrostatic pressure = increased edema) 3. Treat Symptoms: Diuretic therapy is commonly used where there is increased extracellular fluid volume (e.g. in clients with hypertension) 4. Supportive Measures: Often the treatment of edema includes implementation of supportive measures - E.g.: Pregnant woman with swelling of ankles due to increased hydrostatic pressure may be taught to keep legs elevated whenever possible and to avoid standing for prolonged periods of time - E.g: Clients with peripheral edema due to heart disease may be advised to wear supportive stockings to increase interstitial fluid pressure thereby providing some resistance to the movement of fluid from the capillary to the interstitial space Maintaining Sodium and Water Balance  Maintaining vascular volume:  The movement of body fluids between intracellular and extracellular fluid compartments depends on extracellular fluid levels of water and sodium.  The major regulatory of sodium and water valance is the amount of circulating blood volume. Our bodies continuously strive to maintain adequate vascular volume to effectively perfuse tissues – supplying them with nutrients and removing wastes.  Fluid Balance Receptors:  There are two types of receptors (or sensors) that pick up messages in the body about the adequacy of our circulating fluid volume 1. Osmoreceptors: located in the hypothalamus; keep track of the osmolality (concentration) of the blood. Reminder: Sodium is the predominantly osmotically active particle in the blood 2. Baroreceptors: located in the blood vessel walls and in the kidneys; measure the stretch in the vessel walls that is produced by blood volume and blood pressure ThereareseveralmechanismsoffluidbalancethatthebodyusesinresponsetomessagesfromthelOMoARcPSD| NURSING 2PF3 Module 9: Fluid and Electrolyte Balance  Maintaining Sodium and Water Balance:  Thirst: - Normally we drink without being reminded by the thirst mechanism. However, sometimes our bodies experience unanticipated decreases of blood volume or increases in osmolality that alert the body to take corrective action (e.g. if you eat a lot of salty food, your thirst mechanism will prompt you to drink more) - Thirst develops with even a small change in fluid volume or osmolality. Thirst is a primary regulator of water intake  Anti-diuretic hormone (ADH) (vasopressin): - ADH is made in the hypothalamus, and stored in the posterior pituitary - When hypothalamus senses low blood volume or increased osmolality, it sends signals to the posterior pituitary to release ADH - ADH acts on the kidneys tubule to retain water and therefore increases blood volume and reduces serum osmolality - Once the problem has been corrected (ie. shift in blood volume or osmolality), the hypothalamus gets the message and stops the cycle through a negative feedback loop  Sympathetic Nervous System: - Responds to changes in arterial blood pressure and blood volume in several ways - Lowers glomerular filtrate rate GFR o By regulating the constriction or relaxation of efferent or afferent arterioles in the kidney, the amount of glomerular filtrate can be controlled o If SNS is stimulated, the afferent arterioles will constrict, limiting the amount of blood flow to the kidney and lowering glomerular filtration pressure - Stimulates tubular reabsorption of sodium - Stimulates renin release  R-A-A-S (Renin Angiotensin Aldosterone System): - If the circulating blood volume drops, there is less blood flow to the glomerulus so less renal perfusion pressure. The juxtaglomerular cells in the kidney sense the reduced stretch of the afferent arteriole because of the reduced blood flow -ThiscausesanincreaseinthereleaseofreninwhichactsasanenzymetoconvertlOMoARcPSD| NURSING 2PF3 Module 9: Fluid and Electrolyte Balance potassium is lost. When sodium is reabsorbed, it brings water with it, resulting in an increase in circulating blood volume  Natriuretic Peptides: - Atrial naturietic peptide (ANP) and basic natriuretic peptide (BNP) provide a counterbalance to the activity of baroreceptors, ADH and RAAS - In response to an increase in blood volume/pressure, these cells cause the kidney to increase sodium and water excretion by suppressing renin levels, decreasing aldosterone release, and causing vasodilation Risk for Fluid Imbalances  Infants:  Infants have a higher percentage of body water than adults and more than half their total body water is in the extracellular compartment.  Infants ingest and excrete a relatively higher amount of water daily than adults. In fact, an infant may exhange up to half his daily extracellular fluid, meaning that they have a smaller reserve of body fluids than adults. The daily fluid exhange is greater in infants because of their high metabolic rate.  Another reason why infants are at risk for fluid imbalanes is because their immature kidneys to are unable to concentrate urine efficiently.  Finally, infants also lose a relatively greater fluid loss from their skin than adults because of their proportionally greater body surface area.  Both infants and young children have immature homeostatic regulating mechanisms so don’t respond as efficiently as adults to small changes in fluid imbalances.  Elderly:  Aging kidneys experience a decrease in glomeruli and a decrease in the GFR (glomermular filtration rate). There is also a decrease in ability to concentrate urine.  They are slower to respond to sodium and water imbalances, including having a decreased response to ADH and a decrease in secretion of aldosterone.  The elderly have a reduction in total body water.  Research has shown that thirst sensation decreases with age—fluid intake, therefore, is not necessarily regulated by thirst but can instead, be associated with food intake. If an elderly person is eating poorly it is likely that he or she is also drinking poorly.  Obese:  Obsese individuals are at risk because their percentage of total body water is much less than that of a lean person. This means that they have less body water to lose. lOMoARcPSD| NURSING 2PF3 Module 9: Fluid and Electrolyte Balance Assessing Fluid Balance  Accurate, ongoing assessment is also vital in detecting fluid or electrolyte imbalances early  Understanding the reasons behind the signs and symptoms helps nurses to know what changes are relevant and what interventions might be appropriate  Clinical manifestations of fluid imbalance include: 1. Thirst, mucous membranes, turgor, tearing: may indicate fluid imbalance - The subjective symptom of thirst may be an indicator of fluid and electrolyte imbalance. - Dry mouth could be due to fluid volume deficit, or could simply be the result of mouth breathing o Trick to determine the difference: look in areas where cheeks and gums meet. In mouth breathing, these areas will remain moist, while in fluid volume deficit they will be dry - Skin turgor: the elasticity of the skin that allows it to return to normal position after it has been pinched might be a helpful assessment. In individuals with fluid volume deficit, the skin flattens more slowly after a pinch has been released o When checking turgor, remember the test measures not just interstitial fluid volume but also skin elasticity. Older clients or those with recent weight loss might show signs of decreased skin elasticity; obese infants might maintain skin turgor even when in fluid volume deficit o Because skin turgor varies with age, nutritional status, race, and complexion, it might not be the best indicator of fluid imbalance - In infants, tearing is considered a reliable indicator of fluid volume with decreased tearing in patients with volume deficit .