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Fluid & Electrolyte Basics

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1 Fluid & Electrolyte Basics
Disclaimer - Pocket Prof Apps has used reasonable efforts to ensure that the information provided is both accurate and current. However, your education is ultimately your responsibility, and Pocket Prof Apps makes no guarantee to the accuracy or applicability of any information provided, and assumes no liability for your reliance on any information we provide. Further, the information provided in resources published by Pocket Prof Apps represents the understanding and opinions of the presenters and authors, and may or may not be consistent with the opinions or preferences of your own professors. We therefore recommend that you use information provided by Pocket Prof Apps to supplement your other education resources, and not replace your own study, group discussions, and class lectures. This is a review of the basics of Fluid & Electrolytes. Another video will be available for Fluid & Electrolyte Disorders. Please note our standard disclaimer in the small print to the left. It basically states that we do everything we can to provide accurate, up-to-date information. However, this video is not designed to replace your professor’s information, but instead to supplement. ©2013 by Pocket Prof Apps

2 Homeostasis Body fluids are in constant motion transporting nutrients, electrolytes, and oxygen to cells while carrying away waste products Many disease and treatments affect this balance Homeostasis really means “constant stability” – “Human body works best when some conditions are kept within a narrow range of normal” – Iggy book; esp temp, electrolytes, pH, blood volume; our body has mechanisms in place to control homeostasis (ie. sweating and vessel dilation when we are in hot temps) In terms of fluid volume/composition, homeostasis is very important for the body – amount of water or electrolytes can affect the functioning of all cells, tissues, and organs Body fluids are in constant motion transporting nutrients, electrolytes, and oxygen to cells while carrying away waste products Imbalances can be caused by illness, altered fluid intake, prolonged vomiting or diarrhea (ie. metastatic breast cancer causes hypercalcemia, chemo is given which causes nausea/vomiting which causes decreased sodium so IV fluids are given but they cause fluid overload) Goal is for intake and output to be equal (taking into account losses through skin, resp, GI, and renal systems)

3 Water More important to life than any other nutrient
Carries nutrients and waste products Participates in metabolic reactions, food digestion Solvent for minerals, vitamins, glucose Lubricant and cushion for the joints, eyes, spinal cord Aids in regulation of body temp Maintains blood volume 60% of an adult’s body weight (more in a child, less in the elderly) Found in foods (but not in alcohol) Daily need is about 2000 mL 1 liter of water weighs 1 kg Water is the primary fluid in the body and is more impt to life than any other nutrient, we can survive only a few days without water because most physiologic processes occur only in a watery environment, water delivers electrolytes & nutrients and carries away wastes, it’s a solvent, a lubricant, & a cushion for our joints and eyes, it helps us regulate body temp and certainly helps us to maintain blood volume Water balance is affected by age, gender, muscle mass (has more water), fat cells (have no water); 60% of an adult’s body weight is water, more in a child and less in the elderly – Why is this important? These populations are at higher risk of F&E imbalances (elderly have less total body water, obese have less total body water than a lean person of the same weight, women have less total body water than men) Daily need is mL (remember needs are increased with conditions like fever, increased metabolism, etc.), found in foods too (not alcohol  - acts as a diuretic so it dehydrates you) 1 Liter of water weights 1 kg – Why is this important? Sudden change in weight is a good indicator of fluid volume

4 Fluid Intake and Loss Intake sources Liquids (1500 mL/day)
Solid foods (800 mL/day) Metabolism (300 mL/day) Fluid loss routes Kidney ( mL/day) Skin ( mL/day) Lungs (400 mL/day) GI tract ( mL/day) Drainage from fistulas/drains, GI suction, salivation Intake Output Measurable Oral fluid, tube feedings Urine Parenteral fluid Emesis Enemas Feces Retained irrigation fluid Drainage from body cavities Not Measurable Solid foods Sweating Metabolism Vaporization through lungs Intake is regulated through the thirst drive (triggered by a rising blood osmolarity or a decreasing blood volume) (thirst doesn’t work for everyone – ie. pt in a coma), we also get fluids from metabolic processes - intake comes as 60% fluid, 30% food, 10% metabolic water Output – kidney loss is closely regulated and adjustable; What is the minimum amt of urine per day to get rid of waste? mL; kidneys concentrate or dilute the urine as needed – 60% urine, 28% insensible (lungs, skin), 8% sweat, 4% feces Insensible water loss is important b/c it can be significant (ie. trauma, burns, extreme stress, fever); tachypnea; mechanical ventilation; ulcerative colitis Think about intake and output and what is (should be) measurable and what isn’t – gives you a new perspective

5 Electrolytes Chemicals dissolved in the body fluid, distribution affects fluid balance Regulated by intake, output, acid-base balance, hormones, and cell integrity Sodium Major extracellular electrolyte Controls and regulate water balance Potassium Major intracellular electrolyte Helps maintain intracellular water balance Transmit nerve impulses to muscles and contract skeletal and smooth muscles Electrolytes are chemicals dissolved in body fluids and their distribution affects fluid balance, they are commonly measured in mEq and include salts, acids, bases, and some proteins – have more osmotic power (non-electrolytes do not have an electrical charge and don’t dissociate in water and include glucose, lipids, creatinine, and urea) Normal range of electrolytes is very narrow, even small changes can cause major problems; we get most of our electrolytes from food and the kidneys control most excretion or reabsorption Sodium Major extracellular electrolyte Controls and regulate water balance Potassium Major intracellular electrolyte Helps maintain intracellular water balance Transmit nerve impulses to muscles and contract skeletal and smooth muscles

6 F&E Labs Sodium (Na) Determines whether water is retained, excreted, or moved Imbalances cause neuro problems Potassium (K) Increased with poor kidney function Decreased with excessive urination, diarrhea, vomiting Imbalances cause cardiac problems Chloride (Cl) Works with sodium to maintain osmotic pressure Decreased with excessive vomiting or diarrhea Are blood draws from the ECF or the ICF? ECF Serum electrolytes – substances (acids, bases, salts) that circulate in the blood and control things such as muscle contraction, cardiac function; BMP measures 4 common electrolytes and 2 indicators of kidney function – Na, K, Cl, HCO3, BUN, creatinine Chloride – exchanges with HCO3, hangs out with Na in the ECF, when there is acidosis it can’t be reabsorbed (increases), buffers acid-base imbalances

7 F&E Labs Calcium (Ca) Transmission of nerve impulses, heart and muscle contractions, blood clotting, formation of teeth and bone Requires Vit D for absorption Phosphate (PO4) Balance is intertwined with calcium Other tests BUN 6-20 Creatinine Hematocrit 42-52% (males), 37-47% (females) Total protein, albumin A change in phosphate levels will cause an equal and opposite change in calcium levels and vice versa BMP includes glucose, Ca, electrolytes (Na, K, CO2, CL), BUN, creatinine (kidney function) CMP – all of the above plus albumin, total protein, liver enzymes (ALP, ALT, AST, bilirubin)

8 FYI – Hematocrit normal is 3 times the hemoglobin (10-14 is normal)
Lab Normals – Magic 4 Electrolyte Range Magic 4 Potassium 3.5 – 5.5 4 Chloride 98 – 106 104 Sodium 140 pH 7.35 – 7.45 7.4 pCO2 35 – 45 40 HCO3 22 – 26 24 FYI – Hematocrit normal is 3 times the hemoglobin (10-14 is normal) This is just a quick way to try to keep some of these normal ranges straight in your head – don’t memorize ranges (memorize the middle number)

9 Osmolarity and Osmolality
Indicates the water balance of the body Serum osmo is mOsm/kg High is water deficit (concentrated) Low is water excess (dilute) Urine osmo is mOsm/kg (avg mOsm/kg) Together are used to determine what is causing a sodium imbalance The terms are often used interchangeably, osmolarity is particles/L and osmolality is particles/kg and is really just a slightly different calculation, you will hear both terms and most labs are reported as osmolality; more importantly pay attention to serum versus urine Measures the concentration of dissolved particles, mostly determined by sodium, glucose, and BUN - osmo is a solute(Na, K, glucose, urea, etc.) to water ratio Urine osmo tells us the concentrating ability of the kidneys and if there is a problem with ADH, it is a more accurate calculation of urine concentration than specific gravity Urine high – concentrated - too little water (dehydration) or high levels of salt or sugar or damage to the kidneys (high levels of urine) or DI Urine low – dilute - too much water (overhydration) or low level of salt or SIADH Comparing serum osmo with urine osmo helps determine how well the kidneys are working to remove water and electrolytes from the blood and determines what is really causing a sodium imbalance (fluids or kidneys) – normal ratio is 1:3 – urine to serum, can also use urine and serum osmo to help determine what is causing a water/sodium imbalance; as one rises or lowers, the other should too So, let’s look at a little more patho to further understand osmo

10 Distribution of body fluids & Electrolytes
Intracellular (2/3) – K+, PO4- Extracellular (1/3) – Na+, Cl- Interstitial (lymph) and transcellular (cerebrospinal, pleural, peritoneal, synovial fluids) Intravascular (blood plasma) Water is divided into two spaces – ICF (fluid inside the cells) and ECF (fluid outside of the cells) Cells must maintain a balance of 2/3 body fluids inside the cell (intracellular) and 1/3 body fluid outside the cell, if too much water enters then the cell can rupture, if too much water leaves then the cell dehydrates and collapses; movement of major minerals controls the movement of water (if a negative ion moves in then a positive ion has to move out); as electrolytes move, so does water ECF if where we do our blood draw and get our lab values – this includes the interstitial, transcellular, and intravascular fluids; Interstitial fluids is the fluid between cells (sometimes called the “third space”) – blood, lymph, bone, connective tissue, and transcellular fluids (transcellular is an area enclosed by a membrane (ie. CSF, pleural, peritoneal, joint space), intravascular fluids is the blood plasma within the blood vessels Osmolality of all body fluids are supposed to be equal so changes in solute concentrations are quickly followed by osmotic changes (usu. in the ECF), also a change in electrolytes will cause acid-base problems If ECF is hypertonic, water moves from ICF to ECF If ECF is hypotonic, water moves from ECF to ICF (into the cells)

11 Regulation of Fluid & Electrolyte Movement
Filtration Diffusion Active Transport Osmosis Fluids and electrolytes constantly shift from compartment to compartment to facilitate body processes such as tissue oxygenation, acid-base balance, and urine formation. Because cell membranes separating the body fluid compartments are selectively permeable, water can pass through them easily. However, most ions and molecules pass through them more slowly. Fluids and solutes move across these membranes by four processes: osmosis, diffusion, filtration, and active transport. Filtration – differences in water volume, ie. hydrostatic pressure; usu. happens at the tissue capillary level from capillaries to interstitial fluid, ie. edema; “water-pushing” (hydrostatic) pressure moves fluids thru the membranes (cell & vessel walls) Diffusion – Like melting a lump of sugar into a cup of water, impt in transport of gases; sometimes requires the assistance of a transport system (facilitated diffusion – ie. insulin and glucose); similar to filtration but more about movement of particles than movement of fluid (also includes gas transport & electrolytes) Osmosis – movement of water (only) between two compartments separated by a semipermeable membrane, we use this when we talk about hypertonic/isotonic/hypotonic fluids, causes cells to shrink or swell; thirst is an example, sweating causes the cells to shrink and makes us thirsty Active transport – molecules have to move against the concentration gradient requiring active energy and a transport system (pump), sodium-potassium pump requiring ATP which move 2 substances at the same time in opposite directions against concentration gradients, requires, used to control cell volume and intracellular concentration

12 Regulation of Water Balance
(JG cells) Kidneys Sense low Na, low volume Release renin Converts angiotensinogen to angiotensin I which converts to angiotensin II Stimulates release of aldosterone (RAAS) (adrenal cortex) Senses low serum osmo or low Na Releases aldosterone Reabsorbs Na into the blood, increases K excretion in the urine Increases serum osmo Hypothalamus Senses high serum osmo or high Na Stimulates thirst Triggers release of ADH (vasopressin) from posterior pituitary Retains water in the blood Concentrates urine Mildly constricts blood vessels Decreases serum osmo Heart Senses high volume through stretch receptors in the right atrium Secretes ANP, BNP Inhibits ADH Stops the RAAS Increases Na excretion through the urine Dilates blood vessels Fluids maintain blood volume which maintains blood pressure Kidneys are the major regulatory organ of fluid balance, hypothalmus stimulates thirst, endocrine system also helps control F&E balance with the pituitary releasing ADH and the adrenal cortex releasing aldosterone, even the heart gets involved by releasing natriuretic peptides Kidneys releases renin when the juxtaglomerular cells sense low sodium or low blood volume, this begins the RAAS (renin-angiotension-aldosterone system Kidneys also have the adrenal cortex which senses low serum osmo or low sodium and releases aldosterone which causes the body to retain sodium in the blood and excrete potassium in the urine; because sodium causes osmotic (water-pulling) pressure water will try to follow sodium; all of this ultimately increases serum osmo (aldosterone protects Na balance by preventing Na loss – since water follows Na it also helps with water balance) Hypothalamus senses high serum osmo or high Na and stimulates thirst (which doesn’t help if someone is in a coma) and the release of ADH (vasopressin – secreted by the pituitary), ADH works opposite of aldosterone causing the body to retain water and concentrate the urine which decreases serum osmo, it also mildly constricts blood vessels raising the BP (ADH is an example of negative feedback – as water level decreases, ADH increases) Baroreceptors in the right atrium of the heart sense high volume and secretes natriuretic peptides (secreted by the atria and ventricles of the heart - ANP (atria) or BNP (brain – from the ventricles of the heart); this stops the RAAS and causes the kidney to stop reabsorbing sodium and increase glomerular filtration which causes increased urine output (with a high sodium in the urine) decreasing blood volume and blood osmolarity, it also dilates the blood vessels

13 Fluid Spacing First spacing Second spacing Third spacing Normal Edema
Ascites Burn edema When capillary or interstitial pressures change, fluid can shift from one compartment to another (albumin causes return of fluid to the vascular compartment from the tissue spaces – decreased protein levels cause 3rd spacing) Fluid shifts if capillary or interstitial pressures are altered (ie. Edema, dehydration) First spacing – normal distribution of fluid in ICF and ECF Second spacing – abnormal accumulation of interstitial fluid (ie. Edema) Third spacing – fluid accumulation in part of body where it is not easily exchanged with ECF (trapped – ie. Ascites, sequestration with peritonitis, edema with burns) fluid is trapped and unavailable for use Plasma to interstitial fluid movement (edema) is caused by: increased venous hydrostatic pressure so nothing can get into the capillary (ie. Fluid overload, heart failure, liver failure, varicose veins, restrictive clothing, tourniquets) Decreased plasma oncotic pressure so fluid can’t be drawn back into the capillary (ie. Low protein, renal problems, malnutrition) Increased interstitial oncotic pressure so capillary walls are damaged and proteins accumulate (ie. Trauma, burns, inflammation) Interstitial fluid to plasma movement is caused by: -Administration of colloids, dextran, mannitol, hypertonic solutions -Increased tissue hydrostatic pressure (ie. SCDs, TED hose)

14 IV Fluids Isotonic Hypertonic Hypotonic Plasma Expanders NS D5W LR
D51/2NS D10W Hypotonic 1/2NS Plasma Expanders Isotonic – crystalloids; equal to body fluid, keeps fluid in the intravascular volume without causing a fluid shift from one compartment to the other; usually used for replacement or maintenance fluids (D5W if given rapidly will become hypotonic b/c dextrose is rapidly metabolized into water and carbon dioxide) Hypertonic – thicker than body fluid, shifts fluid into the blood plasma by moving fluid from tissue cells; causes cells to shrink; usually used for replacing electrolytes, hyponatremia (watch for wet breath sounds, sodium levels) Hypotonic – thinner than body fluid, shifts fluid from intravascular to the tissue cells; usually used for hydrating cells (enlarging them) but can deplete the circulatory system Plasma Expanders - Albumin exerts colloid osmotic or oncotic pressure, which tends to keep fluid in the intravascular compartment by pulling water from the interstitial space back into the capillaries Colloids – volume expanders, dextran solutions, amino acids, hetastarch, plasmanate Dextran is not a substitute for whole blood because it doesn’t have any products that can carry oxygen Hetastarch is isotonic and can decrease platelet and hematocrit counts and is contraindicated in bleeding disorders, CHF, renal dysfunction Plasmanate can be used instead of plasma or albumin to replace body protein Blood and blood products – whole blood, packed RBCs, plasma, albumin Lipids – fat emulsion solutions, indicated when IV therapy lasts longer than 5 days

15 Gerontologic considerations
Percent of body weight of water is decreased Structural changes in the kidney and decreased renal blood flow Decreased GFR Decreased creatinine clearance Loss of ability to concentrate urine and thus conserve water Decrease in renin and aldosterone Increase in ADH and ANP Loss of subcutaneous tissue Decrease in thirst mechanism Musculoskeletal changes Mental status changes Incontinence % of body weight of water is down to 45-50% (less than normal adult) b/c of decreased muscle mass, puts them at greater risk for dehydration Kidney changes - Decrease in renin/aldosterone means the body can’t retain sodium or excrete potassium, Increased ADH means more water is reabsorbed, Increased ANP means more sodium and water are excreted which lowers blood volume and blood pressure Loss of subcu tissue means increased loss of moisture through the skin and skin turgor assessment is inaccurate (instead use Is/Os and daily wts) Musculoskeletal changes may mean an inability to hold a glass Mental status changes may mean confusion or disorientation Incontinence may cause older adults to intentionally decrease their fluid intake

16 Assessment Considerations
History – nutrition, I/Os, insensible losses, use of diuretics/laxatives, weight changes, kidney or endocrine disorders, LOC, mental status, depression, eating disorders, alcohol intake Physical – hydration status, skin turgor, mucous membranes, I/Os Dx tests – electrolyte levels, BUN, glucose, creatinine, pH, bicarb, osmolality, Hgb, Hct, urine dipstick, urine pH, urine specific gravity Remember that skin turgor is done on the sternum, forehead, or back of hand, not good assessment for elderly

17 Watch for more videos coming soon.
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19 Image Attribution Slide 1 – Flickr by Randy Le'Moine Photography, no attribution required Slide 2 – Flickr by TipsTimes, By Anna Frodesiak (Own work) [Public domain or CC0], via Wikimedia Commons Slide 3 – no attribution required Slide 10 - Slide 13 – By James Heilman, MD (Own work) [CC-BY-SA-3.0 ( or GFDL (], via Wikimedia Commons Slide Slide 15 - "Photo by Chalmers Butterfield"." [CC-BY-2.5 (, GFDL ( or CC-BY-SA-3.0 (], from Wikimedia Commons

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