fluid balance and electrolytes Flashcards
what percentage of the body weight of an adult is made up of water?
50-70%
what are the major fluid compartments of the body, and what percentage of fluid do they contain?
intracellular fluid (ICF) - two thirds
extracellular fluid (ECF) - one third
how is the ECF further compartmentalised?
what percentage of the ECF does each comprise?
interstitial fluid - 80% of ESF intravascular fluid (plasma)- 20% of ESF
what is the ICF mostly comprised of?
cytoplasm water electrolytes (mostly K+ and Mg+) proteins waste products
what is interstitial fluid mostly comprised of?
water electrolytes (mostly Na+, Cl- and HCO3-) amino acids hormones neurotransmitters lymph waste products
what is interstitial fluid?
fluid which bathes or surrounds the cells
what is intravascular fluid mostly comprised of?
water electrolytes/ions proteins whole blood (Plasma, RBCs, WBCs) glucose clotting factors hormones CO2/O2
normal serum levels for sodium?
135-145 mEq/L
normal serum levels for potassium?
3.5-5 mEq/L
normal serum levels for magnesium?
1.5-2 mEq/L
normal serum levels for chloride?
98-110 mEq/L
normal serum levels for bicarbonate?
22-28 mEq/L
normal serum levels for calcium?
2-2.5 mmol/L
what is hydrostatic pressure?
the pressure exerted by fluids, such as blood and tissue fluid, against the walls of the capillaries/blood vessels
what is oncotic pressure?
the pressure exerted by proteins (mostly albumin) to pull fluid back into the vessels
what is the source of hydrostatic pressure?
the pumping action of the heart
what is another name for osmotic pressure?
colloid osmotic pressure
what else apart from hydrostatic pressure and oncotic pressure will affect fluid movement between compartments?
osmotic gradient
what provides an osmotic gradient, which drives the shift of water between compartments?
solutes – electrolytes (charged particles) and other molecules (proteins, glucose, lipids)
why does the osmotic gradient affect fluid movement between compartments?
water is the only substance which can easily cross the blood vessel endothelial wall (semi-permeable membrane) so osmosis will shift fluids acording to solute concentration
what is osmolarity?
what is it measured in?
the measure of solute concentration within a solution
mOsm/L
what does increased serum osmolarity mean?
an increase in concentrations in solutes in the blood - this means the patient is dehydrated and may need fluid replacement
what is tonicity?
the relative concentration of solutes in two fluids, aka the ability of an extracellular solution to make water move into or out of a cell by osmosis
what is an isotonic solution?
ICF and ECF have same number of ions - no net movement into or out of cells (normal saline 0.9%NaCl)
what is a hypertonic solution?
more ions in the ECF - water is drawn out of cells, cells lyse (10% dextrose)
what is a hypotonic solution?
ECF has fewer ions, so water is drawn into cells and they swell and burst (0.25% NaCl)
when might you use a hypertonic solution?
in the case of cerebral oedema, it can reduce swelling in the brain by drawing water out of brain cells (you might use mannitol)
what is osmolarity in the body fluid compartments?
osmolarity in the body fluid compartments is 300 mOsm/L
examples of an isotonic solution?
0.9% sodium chloride
Hartmann’s
5% dextrose in water
what are hypotonic solutions used for in IVT?
in the management of hyperosmolar diabetes and metabolic alkalosis
example of a hypotonic solution?
- 45% sodium chloride (or .33% or .2%)
2. 5% dextrose in water
examples of a hypertonic solution?
10% dextrose in water
20% dextrose in water
50% dextrose in water (mannitol)
when are hypertonic solutions used in IVT?
usually only when glucose needs to be replaced, rather than to influence fluid volume
but can be used to promote diuresis, or to manage cerebral oedema
what is the difference between pitting oedema and non-pitting oedema?
in pitting oedema, lymphatic system is overwhelmed and can’t drain fluid adequately
in non-pitting, lymphatic system is blocked and cannot drain fluid at all
OR the oedema is not due to fluid only, but rather tissue deposits. Pressing on this “oedema” will not disperse this tissue elsewhere → “non-pitting”
underlyling causes of non-pitting oedema?
lymphoedema (lymphatic drainage blocked)
Grave’s disease (underlying tissue deposits)
common causes of pitting oedema?
diseases that cause fluid and sodium retention
protein deficiency
venous congestion
increased capillary permeability
clinical manifestations of pulmonary oedema?
dyspnoea, chest pain
cyanosis, hypoxaemia
frothy, pink cough
restlessness and anxiety
common causes of hypernatraemia?
dehydration
hormonal imbalances of ADH and aldosterone
clinical manifestations of hypernatraemia?
thirst nausea weakness muscle twitch seizures confusion coma
electrolytes: role of sodium?
nerve transmission
muscle contraction
maintains normal concentration of ECF
regulates BP and BV
common causes of hyponatraemia?
excess water accumulation in the body → dilutes Na+
loss of Na+ due to vomiting, diarrhoea, sweating, diuretics, excessive urine output
clinical manifestations of hyponatraemia?
N+V
headache, confusion, lethargy
irritability, muscle weakness, cramps
seizures and coma
electrolytes: role of potassium?
nerve transmission, muscle contraction, normal heart rhythms, concentration of ICF
common causes of hyperkalaemia
increased dietary intake of potassium
common causes of hypokalaemia?
starvation leading to reduced intake
vomiting/diarhoea
redistribution of K+ in insulin-dependant diabetic patients
clinical manifestations of hypokalaemia?
arrhythmias
cramps, muscle weakness
clinical manifestations of hyperkalaemia?
arrhythmias, cardiac arrest, death
confusion, numbness
electrolytes: role of calcium?
nerve transmission muscle contraction strong bones and teeth blood clotting enzyme reactions
electrolytes: role of magnesium?
enzyme reactions; cardiac and respiratory function
electrolytes: role of chloride?
acid/base balance, nerve transmission
how much plasma volume does a textbook male have?
3 litres
what is an appropriate level of fluid for most patients to meet fluid maintenance requirements?
about 30ml/kg/day (1 - 1.5 ml per kg per hour)
what is ascites?
fluid collecting in the abdomen
main ions inside cells?
potassium, magnesium, proteins
main ions outside cells?
sodium, chloride, bicarbonate
how is the water/sodium regulated in the body?
not enough water in blood - ADH, aldosterone cause water to be reabsorbed in kidneys, BP increases
too much water - ADH and aldosterone inhibited, urine becomes more dilute
two signs of hypercalcemia?
trousseau’s sign, chvostek’s sign
is 5% dextrose hypotonic or isotonic?
isotonic in the bag, hypotonic in the body (so it’s a good fluid for dehydration. also used for hypoglycaemia/ insulin shock)
another name for Hartmann’s solution?
CSL (compound sodium lactate)
Ringer’s lactate solution
sodium lactate solution
