Fluid and Electrolyte Imbalances LEARNING OUTCOMES: Upon conclusion of this unit the student will: Describe the mechanisms of fluid balance and imbalance at the capillary level. Discuss Na+and H2O balance and imbalances in terms of the physiologic mechanisms,possible causes,manifestations, and possible diagnostic measures and treatment. Describe disorders of K+ balance. Briefly discuss disorders of calcium, phosphate and magnesium balance. KEY TERMS/CONCEPTS: ACEacidosisADHascites baroreceptorsBUNcapillary permeability colloid osmotic pressure ECGedemaextracellular fluidGFRhematocrithydrostatic pressurehyper-/hypo-calcemiahyper-/hypo-kalemia hypo/hyper-natremiainterstitial fluidintracranial pressureisotonic imbalancesjuxtaglomerular cellslymphedemanatriuretic peptidesosmolarity/osmolalityosmoreceptorspitting edemaRAA-systemserum albuminsympathetic NSthird spacing REQUIRED READINGS: Porth pathophysiology: -Chapter 30, Structure and Function of the Kidney, pp. 710-729. -Chapter 31, Disorders of Fluid and Electrolyte Balance, pp. 730-764 Tutorial Take Home Points •Isotonic Gains/Losses •Disproportionate Gains/Losses –Hyper/Hypo-natremia –Hyper/Hypo-kalemia •Special populations (infants, elderly, obese) •Best to treat the cause of fluid imbalance rather than symptoms alone (when possible) •When correcting electrolyte imbalances do so slowly… –Always monitor patient reaction to interventions (TANNER)
Third-spacing is characterized by:Which of the following is the primary solute found in ECF?Which of the following would be the most reliable indicator of an isotonic fluid volume deficit in an elderly patient?Which of the following would be of the highest priorityWhat fluid imbalance is Baby Blue most likely suffering from?assessing fluid balance in an infant?interventions appropriate to treat Baby Chapter 31 What can cause increased capillary hydrostatic pressure? List the four mechanisms that can lead to fluid imbalance at the capillary level Why might increased hydrostatic pressure be a bad thing For mechanisms of the edema List the Electrolytes Body fluids are distributed between the INTRACELLULAR (ICF) and the EXTRACELLULAR FLUID (ECF) compartments ICF consists of fluid contained within all of the billions of cells in the body. It is the larger of the two compartments (2/3 of the bodys fluid) ICF has a high concentrations of POTASSIUM, CALCIUM, PHOSPHOROUS, and MAGNESIUM. ECF consists of all the fluids outside the cells, including those in the INTERSTITIAL or TISSUE SPACES & BLOOD VESSELS ECF - including blood plasma and interstitial fluids contains large amounts of SODIUM and CHLORIDES, moderate amounts of BICARBONATE, but only small amounts of POTASSIUM, MAGNESIUM, CALCIUM and PHOSPHOROUS It is the ECF levels of electrolytes in the blood or blood plasma that re measured clinically (homeostasis of the ECF). Electrolytes are substances that dissociate in solution to form charged particles, or ions such as sodium and chloride, potassium. Nonelectolytes are particles that do not dissociate into ions such as glucose and urea. The amount of electrolytes and solutes in body fluids is expressed as a concentration or amount of solution in given volume of fluid, such as millimoles per liter (Canadian) Capillary-interstitial fluid exchange – four forces control the movement of water between the capillary and interstitial space 1. The capillary filtration pressure (capillary hydrostatic pressure), which pushes water out of the capillary into the interstitial spaces; 2. The capillary colloidal osmotic pressure, which pulls water back into the capillary; 3. The interstial hydrostatic pressure which oposes the movement of water out of the capillary into the interstitial spaces. Capillary colloidal osmotic pressure – is the osmotic pressure generated by the plasma proteins that are too large to pass through the pores of the capillary wall. The term “colloidal osmotic pressure” differentiates this type of osmotic pressure from the osmotic pressure that develops at the cell membrane from the presence of electrolytes and nonelectrolytes. Because PLASMA PROTEINS do not normally penetrate the capillary pores and b/c their concentration is greater in the plasma than in the interstitial Fluids, is Capillary Colloidal Osmotic pressure that pulls fluids back into the capillary. Lymphatic system – represents an accessory route whereby fluid from the interstitial spaces can return to the circulation. More important the lymphatic system provides a means for removing plasma proteins and osmotically active particulate matter from the tissue spaces, neither of which can be reabsorbed into the capillaries. Causes of Edema Increased capillary pressure (increased capillary filtration pressure aka increased hydrostatic pressure) As the capillary filtration pressure rises, the movement of vascular fluid into the interstitial spaces increases. Decreased colloidal osmotic pressure Plasma proteins exert the osmotic force need t pull fluid back into the capillary from the tissue spaces. PP constitutes a mixture of proteins, including ALBUMIN, globulins, and fibrinogen. Edema due to decreased capillary colloidal osmotic pressure usually is the result of inadequate production of abnormal loss of plasma proteins, mainly albumin. Plasma proteins are synthesized in the liver. In persons with sever liver failure, the impairs synthesis of albumin results in a decrease in colloidal osmotic pressure. In starvation and malnutrition, edema develops because there is a lack of amino acids for plasma protein synthesis. Most common site of plasma protein loss is the kidney (large amounts of albumin filtered out of the blood and lost in urine). Large amounts of plasma protein are also lost when large areas of skin are injured or destroyed. Edema is common problem during the early stages of a burn, resulting from capillary injury and loss of plasma proteins. Increased capillary permeability When capillary pores become enlarged or the integrity of the capillary wall is damaged, capillary permeability is increased. Plasma proteins and other osmotically active particles leak into the interstitial spaces, increasing the tissue colloidal osmotic pressure and thereby contributing to the accumulation of interstitial fluid. Obstruction of lymphatic flow (Lymphedema) Osmotically active plasma proteins and other particles that can’t be reabsorbed through the pores in the capillary; membrane rely on the lymphatic system for movement back into the circulatory system. Malignant involvement of lymph structures and removal of lymph nodes at the time of cancer surgery are common causes of lymphedema, as is infection and trauma involving the lymphatic channels and lymph nodes. p. 735 gives examples of what can cause each of these issues. Third-Spacing Accumulation – the loss into or trapping of ECF in the transcellular space. The serous cavities are part of the transcellular compartment located in strategic body areas where there is movement of body structures, the pericardial sac, the peritoneal cavity, and the pleural cavity. The serous cavities are closely linked with lymphatic drainage systems. The milking action of the moving structures sucha s the lungs, continually forces fluid and plasma proteins back intot he circulation, keeping these caities empty. Any obstruction to lymph flow causes fluid accumulation I the serous cavities. The prefix HYDRO may be used to indicate the presence of excessive fluid, as in hydrothorax, which means excessive fluid in the pleural cavity. The accumulation nof fluid in the peritoneal cavity is called ASCITES. The transudation of fluid into the seous cavities is also referred to as Effusion. Effusion can contain blood, plasma proteins, inflammatory cells (i.e. pus), and ECF.