Download 2015 NURS1004 Week 7 Lecture Fluids in Health care: Tonicity and

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).