Electrolytes and Fluid Balance PDF

Electrolytes Active Transport:  They are classified as either anions or cations based on  A mechanism that requires energy to move ions across the type of charge they carry. cellular membranes. i. Cations...

Electrolytes Active Transport:  They are classified as either anions or cations based on  A mechanism that requires energy to move ions across the type of charge they carry. cellular membranes. i. Cations Diffusion/Passive Transport: - Electrolytes with a positive charge that move toward  The passive movement of ions (no energy consumed) the cathode. across a membrane. ii. Anions  Depends on both the size and charge of the ion being - Electrolytes with a negative charge that move transported. toward the anode.  Depends on the nature of the membrane through which it Functions: is passing.  Volume and osmotic regulation  May be altered by physiologic and hormonal processes. *ions involved: Sodium, Chloride, Potassium  Myocardial rhythm and contractility *Distribution of water in the various body fluid *ions involved: Potassium, Magnesium, Calcium compartments is controlled by maintaining the concentration of electrolytes and proteins in the individual compartments.  Regulation of adenosine triphosphatase ion pumps *ions involved: Magnesium Osmolality:  Acid–base balance  A physical property of a solution that is based on the *ions involved: Bicarbonate, Chloride, Potassium concentration of solutes (expressed as millimoles) per  Blood Coagulation kilogram of solvent (w/w). *ions involved: Calcium, Magnesium  Thirst and Arginine Vasopressin Hormone (AVP)  Neuromuscular Excitability - Secretion are stimulated by the hypothalamus in *ions involved: Calcium, Potassium, Magnesium response to an increased osmolality of blood.  Production and use of ATP from glucose *eg. Magnesium, Phosphate  Water =  Osmolality  Concentration of particles Water  Water =  Osmolality  Average water content of the human body varies from 40% to 75% of total body weight *Triggers antidiuretic hormone* *Note: values declining with age and especially with Regulation of Blood Volume: obesity.  Adequate blood volume is essential to maintain blood  Women have lower average water content than do men. pressure and ensure good perfusion to all tissues and *Note: result of a higher fat content. organs.  Universal Solvent  Renin–angiotensin–aldosterone hormone system Functions: - Responds primarily to a decreased blood volume.  Transports nutrients to cells Other Factors Affecting Blood Volume:  Determines cell volume by its transport into and out of 1. Atrial Natriuretic Peptide (ANP) cells *Note: Released from the myocardial atria in response to  Removal of waste products by way of urine volume expansion, promotes Na+ excretion in the kidney.  Acts as the body's coolant by way of sweating 2. Volume receptors independent of osmolality Location: stimulate the release of AVP  Located in both intracellular and extracellular *Note: conserves water by renal reabsorption compartments 3. Glomerular filtration rate (GFR)  Intracellular fluid (ICF) *Note: - The fluid inside the cells and accounts for about two- - Increases with volume expansion thirds of total body water. - Decreases with volume depletion  Extracellular fluid (ECF) 4. All other things equal - It accounts for the other one-third of total body *Note: increased plasma Na+ will increase urinary Na+ water. Supplemental notes: - Salt: the main determinant of ECF  Urine osmolality values may vary widely depending on  Sub divided into two: water intake and the circumstances of collection. 1. Intravascular ECF (plasma  Generally decreased in diabetes insipidus and polydipsia 2. Interstitial cell fluid (excessive H2O intake). *surrounds the cells in the tissue  Increased in the syndrome of inappropriate antidiuretic  Normal plasma is about 93% water, with the remaining hormone (SIADH) secretion and hypovolemia. volume occupied by lipids and proteins.  Determination of Osmolality Specimen: such as ethanol, methanol, ethylene glycol,  Can be measured using SERUM or URINE isopropanol, lactate, or β-hydroxybutyrate.  Major electrolyte concentrations, mainly Sodium,  Two formulas are presented, each having theoretic Chloride, and Bicarbonate. advantages and disadvantages. *Note: provide the largest contribution to the osmolality value of serum. Discussion:  Samples must be free of particulate matter to obtain accurate results.  Turbid serum and urine samples should be centrifuged before analysis to remove any extraneous particles. Reference Range:  If reusable sample cups are used, they should be Reference Ranges for Osmolality thoroughly cleaned, disinfected, and dried between each Serum 275-295 mOsm/kg use to prevent contamination.  Osmolal Gap Urine (24-h) 300-900 mOsm/kg  The difference between the measured osmolality and Urine/Serum Ratio 1.03-3.0 the calculated osmolality. Random Urine 50-1200 mOsm/kg  It indirectly indicates the presence of osmotically active substances other than Na+, urea, or glucose, Osmolal Gap 5-10 mOsm/kg Electrolytes: SODIUM Introduction Causes of Hyponatremia  Sodium is the most abundant cation in the ECF, 1. Depletional- Caused representing 90% of all extracellular cations. by an absolute losses of  It largely determines the osmolality of the plasma. the total body sodium CAUSES  Also known as “Natrium” a. RENAL LOSSES Diuretics  It is the major contributor of osmolality Primary and Secondary  It is the principle osmotic particle outside the cell Hypoaldosteronism Addison’s Disease Regulation  Three processes are of primary importance: b. NONRENAL LOSSES Gastrointestinal 1. The intake of water in response to thirst Diarrhea - Stimulated or suppressed by plasma osmolality. Vomiting Skin 2. The excretion of water Burns, Trauma, Excessive Sweat - Largely affected by AVP release in response to a. Renal Losses changes in either blood volume or osmolality.  There is a diminished tubular reabsorption and renal - Decrease water intake results to increase plasma osmolality. tubular acidosis - AVP minimizes renal water loss *The tubular transport are also impaired 3. The blood volume status 2. Dilutional - Affects Na+ excretion through aldosterone, Hyponatremia- loss due angiotensin II, and ANP. to an increase in water CONDITIONS *Note: The kidneys have the ability to conserve or excrete large volume amounts of Na+, depending on the Na+ content of the ECF and the a. SIADH blood volume. (Syndrome of Inappropriate Anti-diuretic Hormone) Clinical Applications secretion b. General edema Congestive Heart Failure Hyponatremia Cirrhosis  Hyponatremia is one of the most common electrolyte Nephrotic Syndrome disorders and can be assessed either by the cause of the c. Hyperglycemia decrease or with the osmolality level.  SIADH causes an increase in water retention  Hyponatremia is defined as a serum/plasma level less because of increased AVP (ADH) production. than 135 mmol/L, and levels below 130 mmol/L are  Cirrhosis & Nephrotic Syndrome: decrease in clinically significant. plasma proteins results in decrease colloidal osmotic pressure.  3. Artifactual Causes of Hypernatremia Aka Hyperlipidemia 1. Excess Water Loss PSEUDOHYPONATREMIA, Gastrointestinal Losses Vomiting Caused by analytical errors Diarrhea Hyperproteinemia In vitro hemolysis Excessive Sweating Fever Excercise Symptoms of Hyponatremia  Between 125 and 130 mmol/L: 2. Sodium Gain - Primarily gastrointestinal (GI) Diabetes Insipidus Hypothalamic  Below 125 mmol/L Nephrogenic - Severe neuropsychiatric symptoms  Related to the absolute or relative absence of ADH - Nausea and vomiting, muscular weakness,  The collecting ducts cannot adequately do you absorb water headache, lethargy, and ataxia. and large quantity of water are excreted per day. - More severe symptoms also include seizures, coma,  Because of The water loss the plasma osmolality increases and respiratory depression which stimulates the thirst center  Below 120 mmol/L for 48 hours or less 3. Decreased Water Intake (Acute hyponatremia) Infants, older people, mentally challenged people - considered a medical emergency Occurs in people with adipsia (Impaired thirst sensation) Hypernatremia Symptoms of Hypernatremia  Results from excess loss of water relative to Na+ loss,  Symptoms most commonly involve the CNS as a result of decreased water intake, or increased Na+ intake or the hyperosmolar state. retention.  These symptoms include:  Occurs when the plasma sodium concentration is >145  Altered mental status, lethargy, irritability mmol/L restlessness, seizures, muscle twitching,  Can occur from water loss or from sodium gain hyperreflexes  Fever, nausea or vomiting, difficult respiration, *Note: Hypernatremia is less commonly seen in hospitalized and increased thirst patients than is hyponatremia Determination of sodium Specimen  Spectrophotometry (AAS)  Serum  Ion-Selective Electrode (ISEs)  Plasma  ISEs are the most routinely used method in clinical laboratories.  Urine  Sweat is also suitable for analysis Ion-Selective Electrode  Using Plasma: lithium heparin, ammonium heparin, and  It uses a semipermeable membrane to develop a lithium oxalate are suitable anticoagulants. potential produced by having different ion concentrations  Whole blood samples may be used with some analyzers. on either side of the membrane.  Urine Na+ analyses: specimen of choice is a 24-hour  There are two types of ISE measurement, based on collection sample preparation: direct and indirect. *Note: Hemolysis does not cause a significant change in serum  Direct Method or plasma values as a result of decreased levels of intracellular - Provides an undiluted sample to interact with Na+. the ISE membrane.  Indirect Method Methods - A diluted sample is used for measurement.  Chemical Methods  There is no significant difference in results, except when  Outdated because of large sample volume samples are hyperlipidemic or hyperproteinemic. requirements and lack of precision.  In these cases, direct ISE is more accurate.  Flame Emission Spectrophotometry  Atomic Absorption CLINICAL CHEMISTRY 2 LECTURE/TRINIDAD/LCB URINE FORMATION - Introduction As the blood comes through there is a high pressure in The components of a Urine Filtrate: WATER the glomerulus, called the hydrostatic pressure. Electrolytes Hydrostatic Pressure: pushes blood out of the capillaries to the tissues of the body Glucose Once they are at the kidney, capillary bed pushes Amino Acids greater at around 50 mmHg. *Urea *Creatinine Proteins and Cells do not go to the glomerulus. WHY? *Urea and Creatinine is considered as Waste Products *Because they are too big to go through the filtration membrane. Example: RBC, WBC, and Platelets Glomerulus Capsule: also known as The filtration membrane is negatively charge, same as capsule with proteins. Thus, they repel each other. Every time your heart contracts it pushes about 70 mL Proximal convoluted tubule of Blood from one ventricle, it does that about 72 times/ minute, 4-5 L of blood/minute. Loop of Henle: Only a fraction of that goes through the kidney The nephron loop Made up of thin descending Loop of Henle and thick The 20% only goes to the kidney. ascending Loop of Henle Only almost 1 L of blood; and only the plasma gets filtered 60% of that 1 L is plasma = 600mL Distal convoluted tubule The 20% of the 600 mL only gets filtered = 120 mL/minute Produces 120 mL of filtrate per minute in both of the kidneys. Collecting Duct/Tubule The kidneys produces 172,800 mL of filtrate/day or 173 L of Representation of a nephron filtrate/day Glomerular Filtration Only 1% of the 175L gets excreted= 1.73 L/day Blood comes in to the afferent arteriole. Tubular Reabsorption Blood goes to the glomerulus. Everything that is filtered (99% filtration) goes back to Blood passes through the glomerulus and moves to the the blood. Efferent arteriole. The Proximal Convoluted Tubule reabsorbs about The continuous part of the efferent arteriole is called the 65% filtrate. Peritubular capillaries. The Loop of Henle reabsorbs 15% of filtrate. The Peritubular Capillaries have the Nephron, because The Distal Convoluted Tubule reabsorbs 15% of what gets filtered in the nephron doesn’t necessarily filtrate. stay in the nephron. The Collecting Duct reabsorbs 4% of filtrate. 99% of the filtrate actually goes back to the blood URINE FORMATION= Glomerular Filtration - Tubular Reabsorption through these Peritubular Capillaries. CLINICAL CHEMISTRY 2 LECTURE/TRINIDAD/LCB Tubular Secretion The nephron can also receive substances from the blood This is called Secretion Process Excretion No information added Supplemental Reading? Summary 1. Glomerular Filtration 2. Tubular Reabsorption 3. Tubular Secretion 4. Excretion Supplemental Reading 1. Glomerular Filtration (Tuft, Capillary Bed) The glomerulus is the first part of the nephron and functions to filter incoming blood. The volume of blood filtered per minute is the glomerular filtration rate (GFR), and its de- termination is essential in evaluating renal function. 2. Tubular Reabsorption When the substances move from the tubular lumen to the peritubular capillary plasma, the process is called tubular reabsorption. With the exception of water and chloride ions, the process is active; that is, the tubular epithelial cells use energy to bind and transport the sub- stances across the plasma membrane to the blood. 3. Tubular Secretion The tubular secretion describes the movement of substances from peritubular capillary plasma to the tubular lumen. The tubular secretion also describes when tubule cells secrete products of their own cellular metabolism into the filtrate in the tubular lumen. Transport across the membrane of the cell is again either active or passive. CLINICAL CHEMISTRY 2 LECTURE/TRINIDAD/LCB CHLORIDE (Cl-) Introduction Electrical Neutrality: Major extracellular anion. 1. Na+ is reabsorbed along with Cl - in the proximal It is the only anion to serve as an enzyme activator. tubules. It is the chief counter ion of Sodium in the extracellular In effect, Cl- acts as the rate-limiting component fluid. 2. Electroneutrality is also maintained by Cl - through the Concentration: chloride shift. 103 mmol/L with median plasma and interstitial fluid Carbon Dioxide within the tissue diffuses out into both concentrations. the plasma and the red cell. HCO3- diffuses out into the plasma and Cl- diffuses into 154 mmol/L inorganic anion concentration. the red cell to maintain the electric balance of the cell. Erythrocytes (RBC): 45 to 54 mmol/L Other Tissue Cells: only -1 mmol/L Absorption Chloride ions in food are almost completely absorbed Functions from the intestinal tract. 1. Maintenance of water distribution Glomeruli 2. Osmotic Pressure - They are filtered and passively absorbed with Na+. 3. Anion-Cation Balance in the ECF Loop of Henle (thick ascending limb) 4. Maintains electrical neutrality - Cl- is actively reabsorbed by the chloride pump - Promotes passive reabsorption of Na+. CLINICAL APPLICATIONS Hypochloremia Decreased plasma concentration of Cl-. Occurs with excessive loss of Cl - from prolonged vomiting, diabetic ketoacidosis, aldosterone deficiency, or salt losing renal diseases such as pyelonephritis. Encountered in high serum HCO3- concentration. Compensated respiratory acidosis or metabolic alkalosis. Hyperchloremia Increased plasma concentration of Cl -. Occur when there is an excess loss of HCO3- as a result of GI losses, RTA, or metabolic acidosis. DETERMINATION OF CHLORIDE Specimen A method using coulometric generation of silver Serum or Plasma may be used ions (Ag+), which combine with Cl- to quantitate Lithium Heparin: the anticoagulant of choice the Cl- concentration. Whole blood samples: Consult the instrument’s operation manual for acceptability. Urine Analysis: 24-hour collection is the specimen of choice. WHY? Because of the large diurnal variation. When all Cl- in a patient is bound to Ag+, excess NOTE: or free Ag+ is used to indicate the endpoint. Hemolysis does not cause a significant change in As Ag+ accumulates, the coulometric generator serum or plasma values. and timer are turned off. With marked hemolysis, levels may be decreased as a 3. Mercurimetric Titration (Schales and Schales Method) result of a dilutional effect. Indicator: diphenylcarbazone Methods End product: HgCl2 1. Ion-Selective Electrode 4. Whitehorn Titration Method Most commonly used. Done using spectrophotometric reading ISE measurement, an ion-exchange membrane is Reagent: diphenylcarbazone used to selectively bind Cl- ions. End Product: reddish complex 2. Amperometric-coulometric Titration Reference Range  MAGNESIUM (Mg2+) Introduction Magnesium is the fourth most abundant cation in the body and second most abundant intracellular ion. The average human body (70 kg) contains 1 mole (24g) of Mg2+. 53% of Mg2+ in the body is found in Bone 46% in muscle and other organs and Soft Tissue less than 1% is present in Serum and Red Blood Cells It is an essential cofactor of more than 300 enzymes. Of the Mg2+ present in serum: 1/3 is bound to a protein. (Albumin) Remaining 2/3 - 61% exists in the free or ionized state *Similar to Ca2+, it is the free ion that is physiologically active in the body. - 5% is complexed with other ions * PO4- and citrate Regulation Absorption of Mg2+ Rich sources of Mg2+: The renal threshold for Mg2+ is approximately 0.60– Raw nuts 0.85 mmol/L. Dry cereal Factors Affecting Mg2+ levels in the Blood “Hard” Drinking Water Parathyroid hormone (PTH) Vegetables Increases the renal reabsorption of Mg2+ and Meats enhances the absorption of Mg2+ in the intestine. Fish Aldosterone and Thyroxine Fruit Increases the renal excretion of Mg2+ Absorption and Overall Regulation The small intestine may absorb 20%–65% of the Supplemental Notes: dietary Mg2+. Of the non-protein-bound Mg2+ that gets filtered by The overall regulation of body Mg2+ is controlled the glomerulus largely by the kidney. 25%–30% is reabsorbed by the proximal Loop of Henle: major renal regulatory site convoluted tubule (PCT) 50%–60% of filtered Mg2+ is reabsorbed in the Unlike Na, in which 60%–75% is absorbed in the ascending limb. PCT. Normally, only about 6% of filtered Mg+ is excreted in the urine per day.  CLINICAL APPLICATIONS Hypomagnesemia Hypomagnesemia is most frequently observed in hospitalized individuals in intensive care units or those receiving diuretic therapy or digitalis therapy (Cardiac Heart Failure, Atrial Fibrillation). These patients most likely have an overall tissue depletion of Mg2! as a result of severe illness or loss, which leads to low serum levels. Hypomagnesemia is rare in non-hospitalized individuals. Hypermagnesemia The most common is renal failure (GFR,