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2015 NURS1004 Week 7 Lecture Fluids in Health care: Tonicity and IV solutions 1. Readings : Martini et al. 10th ed. (2015) p. 5367, 1042-1055. Or Martini 9th ed p 27-40, 9981011 Or International ed. p 51-64, 1096-1109 Moles & osmoles Moles per litre refers to the number of particles per litre of solution. (1 mol/L = 6.023×1023 particles per litre) Chemical Bonds Form molecules and/or compounds Molecules Two or more atoms joined by strong bonds Compounds Two or more atoms OF DIFFERENT ELEMENTS joined by strong or weak bonds Compounds are all molecules, but not all molecules are compounds H2 = molecule only H2O = molecule and compound Ionic Bonds One atom—the electron donor—loses one or more electrons and becomes a cation, with a positive charge (+ve) Another atom—the electron acceptor—gains those same electrons and becomes an anion, with a negative charge (-ve) Attraction between the opposite charges then draws the two ions together Covalent Bonds Involve the sharing of pairs of electrons between atoms One electron is donated by each atom to make the pair of electrons Sharing one pair of electrons is a single covalent bond Sharing two pairs of electrons is a double covalent bond Sharing three pairs of electrons is a triple covalent bond One type of compound (those made of nonmetal atoms) are “covalent molecular” and that the other type of compound (those made of metal atoms and non-metal atoms) are “ionic non-molecular”. When glucose dissolves in water, it separates into molecules of C6H12O6 (ie groups of 24 bonded atoms). Thus when 180 g of glucose (1mole) dissolves in a litre of water it produces 1mole of separate particles (called molecules). When sodium chloride dissolves in water, it separates into individual Na+ ions and Cl- ions which are not attached to each other. Thus when 58.5 g of the compound Na+Cl- (1 mole) dissolves in a litre of water it produces 1 mole of Na+ ions and an additional mole of Cl- - a total of 2 moles (!) of dissolved separate particles (called ions). The effects of osmosis depend only on the number of solute particles per litre of solution NOT on the chemical identity of the particles (or their size). Since 1 mole of solid ionic compound can become 2 moles of particles (ions) when dissolved, we introduce the concept of the “osmole” (= the amount of substance which must be dissolved in order to produce 6.02 × 1023 dissolved particles). For most covalent-molecular substance (eg glucose) No. of osmoles = No. of moles 1 mole of glucose = 1 osmole of glucose But for ionic substances (eg Na+Cl-) No. of osmoles = No. of moles X No. of ions in the formula. 1 mole of Na+Cl- = 2 osmoles of ions Lecture Part II 2-Properties of Water Water accounts for up to 50% female & 60% male of your total body weight •A solution is a uniform mixture of two or more substances It consists of a solvent, or medium, in which atoms, ions, or molecules of another substance, called a solute, are individually dispersed Properties of Water Solubility the ability to dissolve a solute in a solvent to make a solution. Reactivity, most body chemistry occurs in water. High Heat Capacity & has ability to absorb and retain heat. Lubrication to moisten and reduce friction The Properties of Aqueous Solutions Ions and polar compounds undergo ionization, or dissociation in water Polar water molecules form hydration spheres around ions and small polar molecules to keep them in solution Electrolytes and body fluids Electrolytes are inorganic ions that conduct electricity in solution. Electrolyte imbalance seriously disturbs vital body functions Hydrophilic and hydrophobic compounds Hydrophilic hydro- = water, philos = loving •Interacts with water - Includes ions and polar molecules Hydrophobic phobos = fear •Does NOT interact with water- Includes nonpolar molecules, fats, and oils Colloids and Suspensions • Colloid - A solution of very large organic molecules eg. blood plasma • Suspension - A solution in which particles settle (sediment) eg. whole blood ( with Plasma removed) 3. Intravenous therapy This involves the direct addition of a solution to the circulation usually through a peripheral vein but sometimes via the vena cava. The main purposes are: water replacement electrolyte replacement provision of nutrients drug administration Tonicity is a critical property of I.V. fluids. 4. Tonicity Isotonic solution: a solution with osmolarity within the range of blood osmolarity (280 – 300 mosmol/l). When added to blood an isotonic solution causes no net movement of water into or out of cells. Examples: 5% glucose; 0.9% sodium chloride; 0.3% Na+Cl-)+ 3.3% glucose is used in paediatrics. (9.5% sucrose is isotonic). If isotonic saline is added to ECF (blood) the osmolarity of blood does not change, no osmosis results, but blood volume increases. If isotonic glucose is administered, the glucose is rapidly absorbed by cells (metabolised) leaving water to be distributed to all compartments (so the body is rehydrated and blood osmolarity decreases somewhat). If the water is not required by the body, and the kidneys are working properly, it is excreted in urine. Hypotonic solution: a solution with an effective concentration less than that of blood. Causes net movement of water into cells. Hypertonic solution: a solution with an effective concentration greater than that of blood. Causes movement of water out of cells. eg 20% mannitol (“osmitrol”) eg 0.45% Saline with 5% Glucose with K+Cl20mmol/L (for mildly unwell children) 3. Water in the body Water as % of body mass Adult males 60-65 Adult females 50-55 Infants 80 Adults > 65years 40-50 Roles for water: 1. temperature control (perspiration). 2. transport of nutrients & wastes (blood, interstitial fluid, urine, lymph, CSF). 3. hydrolysis of food components in the gut during digestion, eg: C12H22O11 + H2O C6H12O6 + C66H12O6 sucrose glucose fructose 4. maintain blood volume (& so BP) Water intakes: Food consumed provides ~ 48% of our water Liquids drunk provide ~ 40% Produced by metabolism ~ 12% (catabolism of glucose, fatty acids & building proteins from amino acids) Water losses: 43% in urine, 7% in faeces, 33% evaporated from skin 17% evaporated from lungs 5. Fluid “Compartments” of the Body Comparison of ICF & ECF composition from bone; causing kidneys to reabsorb Ca; (& PO4 elimination); increasing Ca absorption from gut. The concentrations of solutes in the fluid within cells (ICF) is very different to the fluid that is outside cells (ECF) Compartments % of body water Vascular 7 % Interstitial 18 % ECF Connective tissue fluid 10 % Intra-cellular fluid (ICF) 63 Trans-cellular 2% Vascular compartment = within blood vessels. Sometimes blood is used synonymously with ECF (because interstitial fluid is “the same” as blood but without blood cells or the plasma proteins – albumin, globulin, fibrinogen) 6. Fluid and electrolyte balance This is the maintenance of the concentrations of all the components of the body’s fluid compartments within their normal ranges. Balance is achieved substantially by regulating urine production in the nephron of the kidney due to: • filtration of blood (in the glomerulus) • active transport of ions • osmosis of water • passive diffusion of ions (Processes occur in the tubule). The kidney has a remarkable capacity to recover water and many solutes from the filtrate. 7. Electrolyte balance Electrolytes are ionic substances (Na+, K+, Ca2+, Mg2+, Cl-, HCO3-) or substances which form ions when they dissolve. Electrolyte balance depends on the ability of the kidneys to recover ions from urine and on hormonal influences. The most important hormone (for electrolyte balance) is aldosterone. Aldosterone stimulates the kidneys to reabsorb Na+ ions from filtrate (and in exchange, excrete K+ions). Parathyroid hormone (PTH) increases Ca++ blood concentration by: stimulating release 8. Water balance Daily Water Intake Daily Water Output Drink 1600ml Kidneys 1500ml Food 700ml Skin 500ml Metab. 200ml Lungs 300ml G.I.T. 200ml Total 2500ml 2500ml Note that the (immeasurable) water intake as food & metabolism is approx = (immeasurable) output via skin, lungs & gut ! Nurses record in a “fluid balance chart” the daily inputs (inc IV fluid) & outputs (inc vomit & wound drainage) Minimum (non-pathological) daily urine output for adults is about 500ml. In healthy person water balance is maintained by: • thirst sensation which causes a person to drink and increase water intake, • anti-diuretic hormone (ADH) which stimulates the kidneys to recover more water from urine thereby reducing water loss. 9. Fluid and Electrolyte Imbalance Dehydration occurs when water losses exceed water intake the changes observed are: increases in serum sodium concentration, osmolarity and an increase in haematocrit. Dehydration is corrected by increased oral intake of hypotonic solutions (ie drink water) or I.V. administration of 5% glucose. Persons vulnerable to dehydration are infants, obese people and elderly people. 10. Sodium imbalance Hyponatremia = serum conc. < 134mmol/l Caused by: 1. excess of water intake over output with the result that sodium in serum is diluted. This may be seen in a condition called syndrome of inappropriate antidiuretic hormone (SIADH) 2. loss of sodium as occurs in burns, diarrhoea, vomiting, diuretic drug administration, 3. shift of water from the cells as occurs in uncontrolled diabetes 4. drinking much too much water 5. alcoholism (beer drinking) Correcting Hyponatremia Restriction of water intake for dilutional hyponatremia Increased sodium intake when sodium loss has occurred. Reduction of blood glucose levels in cases of uncontrolled diabetes. Hypernatremia = Serum conc. > 145mmol/l Caused by: excessive loss of water in most cases. The extracellular fluid is usually hypertonic. Occasionally caused by sudden large gain of sodium as in I.V. administration. Corrected by intake of fluids free of sodium. 11. Potassium Imbalance Potassium is a very important electrolyte because its concentration affects heart action. Hypokalemia = Serum conc. < 3.5mmol/l Caused by: • diuretics • fluid loss from the G.I. tract (vomiting, • diarrhoea) • congestive heart failure Corrected by: Increased intake of potassium or, in severe cases, I.V. administration (this must be done with great care). Hyperkalemia = Serum conc. > 5mmol/l Caused by: • Addison’s disease (reduced aldosterone) • tumor lysis syndrome • myocardial infarction Corrected by: • decreased intake of potassium • increased fluid intake • administration of bicarbonate • ion-exchange resin • dialysis Early detection of potassium imbalances can be done by inspection of the ECG (hypo: depressed ST hyper: widened QRS segment, spiked T wave).