Fluid and Electrolytes Lecture Notes PDF

Fluid and electrolytes DR SOPHIE CHEN Acknowledgement: A/PROF KELLY LAMBERT (prepared slides) Lecture Objectives  Describe the mechanisms that cause edema  Describe causes & effects of dehydration  Define causes & effects of isotonic, hypotonic, and hypertonic water and solute altera...

Fluid and electrolytes DR SOPHIE CHEN Acknowledgement: A/PROF KELLY LAMBERT (prepared slides) Lecture Objectives  Describe the mechanisms that cause edema  Describe causes & effects of dehydration  Define causes & effects of isotonic, hypotonic, and hypertonic water and solute alterations.  Identify the major causes & consequences of abnormal levels of Na, K, Ca, P, Mg.  Define the terms associated with alterations in these electrolytes If you want to pass  Read the textbook chapters  Try alternative sources eg podcasts, youtube , google images  Using the think about questions, try the teachback method  Read the readings !  Important assumed knowledge Understanding of fluid balance & imbalance especially the terms:  Intracellular fluid (ICF) & Extracellular fluid (ECF)  Interstitial fluid (fluid b/w cells & out of blood vessels)  Intravascular fluid (blood plasma) Lecture objectives Fluid excess Electrolyte Oedema Imbalances in Na, K, Mg, Ca Fluid deficit Case studies Dehydration What is normal ? Normal fluid distribution CSF < 1% Normal fluid balance  All fluid movement in the body is governed by osmosis and tonicity  Osmosis = movement of H20 across a semi permeable membrane  Osmotic pressure =pressure needed to oppose (i.e. stop) the movement of water across the membrane Normal fluid balance  Tonicity = solute concentration of 2 solutions separated by a semipermeable membrane  Tonicity determines the movement of water and cell size across the cell membrane. Normal fluid balance  Particles that are ‘osmotically’ active:  Na+, Cl-, HCO3- (90-95% of osmotic pressure (op))  Glucose, Blood Urea ( OP OP > HP Push>pull Pull>push Movement Movement of of fluid out fluid into the of capillary capillary Arterial end Venous end  What is oedema / edema ?  Abnormal accumulation of fluid in interstitial space  Can be local or generalised  Eg sprained ankle / bee sting vs legs / arms ie a more uniform distribution What is oedema / edema ? Localised oedema Generalised oedema ie uniform distribution of fluid in interstitial space What causes oedema ?  ↓ colloids = ↓ osmotic pressure  Eg loss of plasma proteins eg proteinuria in kidney disease  Eg decreased production eg CLD, malnutrition Osmotic pressure is reduced (ie the magnet drawing water into the blood vessels is reduced)…➔promotes movement of fluid out of capillaries into areas of higher osmotic pressure…➔reduces the return of fluid into the capillaries…➔ resulting in oedema  Albumin maintains plasma osmotic pressure between the blood vessel & interstitial fluid Albumin Blood vessel cells Tissues  Albumin Blood vessel cells Tissue oedema Why does it occur ?   capillary pressure Eg increased blood volume APO, CHF   capillary permeability Eg burn, allergy, injury  Obstructed lymph flow  Eg. Removal glands in cancer, tight clothing, pregnancy  WHY ? Gravity alters the blood flow…pressure in veins & thus return of fluid to capillaries Question ?  Why do wounds heal more slowly in people with oedema ?  A: Oedema compresses arteries in the area = reduced blood flow & capillary exchange and supply of nutrients for cell energy, function and reproduction  Blood vessel Fluid in interstitial space causes oedema  Case study: Nephrotic syndrome (NB: Aldosterone stimulates Na retention, low blood volume stimulates ADH to retain water)  example  Child has generalised oedema with a puffy face, distended abdomen and oedematous legs.  He has gained weight but is not eating much  Pathology tests show high levels of protein in the urine, which has a high specific gravity.  Blood levels of Na are low  Blood vessel Fluid in interstitial space causes oedema  Questions: teachback 1. Explain how the hypoalbuminemia is causing generalised oedema. 2. Explain why the boy is retaining sodium and water. 3. Explain why skin breakdown is common in patients with prolonged oedema. Answers 1. Hypoalbuminemia – lower osmotic pressure promoting a shift of fluid from capillaries into the interstitial fluid 2. Albumin loss – decreased blood volume – increased secretion of renin & aldosterone as well as ADH = Na+ & water retention 3. Prolonged oedema interferes with arterial circulation & capillary exchange reducing mitosis in the skin & predisposing to skin breakdown Lecture objectives Fluid excess Electrolyte Oedema Imbalances Na, K, Mg, Ca Fluid deficit Case studies Dehydration Normal fluid balance  8-10L ECF excreted into GI tract…  Most reabsorbed in the ileum & proximal colon. 150-200ml = lost in faeces.  Vomiting & diarrhea alter reabsorprtion rates & /or increase secretion of fluid into GI tract How does dehydration occur ? 1. Inadequate intake 2. Excess losses 3. Or both Causes of dehydration Vomiting & diarrhea insufficient H20 intake eg elderly / comatose person drainage of any portion of digestive system excessive sweating diabetic ketoacidosis Fluid deficit - dehydration Eg. vomiting - water is lost from the digestive system…  water moves vascular compartment → digestive tract  If deficit continues - water will shift from cells Types of diarrhoea  Osmotic – too much water drawn into bowel eg lactose intolerance. Retain solutes eg Na and lose water  Secretory –when Cl- is lost, Na & water will follow eg cholera. Losses are isotonic but massive  Inflammatory – damage and destruction to epithelium eg Campylobacter. Inefficient absorption of water and loss of protein and electrolytes  Hypermobility eg due to medication What is lost in diarrhoea ?  Fluid  Na  Bicarbonate  K  Protein (if inflammatory) Fluid deficit - dehydration General guide: 80kg person Mild fluid loss  2% of body weight ie 1.6kg Moderate loss  5% of body weight ie 4kg Severe dehydration  8% of body weight ie 6.4kg At risk of dehydration  Infants & elderly are particularly vulnerable  Why ? Altered body water proportion; reduced thirst sensation; reduced ability to conserve fluid quickly Infants & dehydration  Infants /kids have a higher TBW & higher metabolic rates & higher insensible fluid losses & higher turnover of fluids and solute.  Combined with kidneys that are slower and more limited in ability to compensate for fluid loss means that… Infants & dehydration  Infants /kids require proportionally greater volumes of water than adults to maintain their fluid equilibrium and are more susceptible to volume depletion. Types of dehydration Isotonic  loss of water & Inadequate intake dehydration electrolytes or XS loss (hypovolemia) Hypotonic loss of more electrolytes Electrolyte wasting dehydration than water disorders Hypertonic loss of more water than Diuretic therapy dehydration electrolytes Fluid deficit - dehydration  eg. Isotonic dehydration eg sweating=loss of H2O & NaCl  Losing electrolytes affects water balance due to osmotic pressure changes between compartments  To restore balance = electrolytes & water must be replaced not just one component – choice of IV fluid crucial  Fluid replacement ? Where do sports type drinks fit ?  Electrolytes replace lost Na, restoring better balance in the body.  H20 alone would dilute electrolytes in ECF, decreasing OP and lead to further fluid shifts in the body.  Glucose = nutrient for cells with higher metabolic rate, thus reducing the risk of acidosis. Fluid deficit - dehydration Effects of dehydration:  Dry mucous membranes in mouth  Decreased skin turgor or elasticity  Blood pressure is reduced, pulse is weak  Fatigue  Change in blood parameters eg electrolytes  Increased hematocrit (ratio RBC: blood volume) Fluid deficit - dehydration Compensation:  thirst mechanism  concentration of urine (specific gravity increases) example  3/12 baby with severe watery diarrhoea + fever for 24 hours.  She is apathetic and responds weakly to stimulation. Could she be dehydrated ? Why ? Why not ? example  The condition has been diagnosed as viral gastroenteritis  Losses of fluid as diarrhoea and sweating place her at high risk of dehydration Questions case 2 1. List the type of electrolyte & fluid losses resulting from diarrhoea & fever. 2. List other signs or data that would provide helpful information to determine if she is dehydrated. 3. Explain why infants become dehydrated very quickly. Answers case 2 1. D: water, Na+, K+, HCO3, glucose & other nutrients F: water, NaCl (sweat), CO2 (increased respirations) 2. Appearance of oral mucosa & skin (dehydration), change in body weight, urine output, pulse, BP, respirations, serum electrolytes, arterial blood gases, hematocrit. 3. Decreased ability of kidneys to compensate for losses; increased metabolism and demand for water, electrolytes & glucose; greater loss of water through increased body surface area. Severe Dehydration example  30 year old female collapses and is diagnosed with severe dehydration  She has sweated profusely and nausea caused her to vomit her gatorade and water Severe Dehydration  What is the outcome of her excessive sweating ? Severe Dehydration  What is the outcome of her excessive sweating  A: lost more water than electrolytes Severe Dehydration  Where has the water moved from and into ?  Severe Dehydration  Where has the water moved from and into ?  A: ICF to ECF, ie intracellular dehydration  Severe Dehydration  What are the clinical manifestations of severe dehydration ?  What are the signs and symptoms?  Severe Dehydration What are the clinical manifestations of severe dehydration ? A:Dry mucous membranes, decreased tissue turgor, decreased urine output, decreased vascular volume What are the signs and symptoms?  Severe Dehydration  What are the clinical manifestations of severe dehydration ?  A:Dry mucous membranes, decreased tissue turgor, decreased urine output, decreased vascular volume  What are the signs and symptoms?  A:Agitation, confusion, headache, decreased reflexes, coma Lecture objectives Fluid excess Electrolyte Oedema Imbalances Na, K, Mg, Ca Fluid deficit Case studies Dehydration