Fluid and electrolyte balance Flashcards
what are the major fluid compartments of the body
plasma, interstitial fluid, intracellular
what is the normal volume of plasma
3L
what is the normal volume of interstitial fluid
11L
what is the normal volume in intracellular fluid
28L
what is the intracellular concentration of potassium
150 mM
what is the normal plasma conc of potassium
4.5 mM
what is the normal plasma conc of Na
130 mM
what are the major gains of water to the body
food and water, and food oxidation
what are the major losses of water from the body
urine, faeces, sweat, insensible loss
what is insensible water loss
transepidermal diffusion
evaporation from the respiratory tract
these losses are solute free and can’t be controlled or prevented
causes heat loss
what sensors monitor body fluid
hypothalamic osmoreceptors
low pressure baroreceptors in the right atria
high pressure sensors in the carotid sinus
what ion is the key driver of total plasma volume
sodium
if sodium drops then the volume will fall (due to osmolality being tightly controlled)
how can sodium be controlled
kidneys/ urine output
controlled indirectly via volume sensors
how is the amount of sodium reabsorbed changed
rate of flow, aldosterone, ANP
change in GFR
if blood osmolality changes how does the volume change
increases
also increase in ADH
what happens when there is an increase in volume
detected by baroreceptors
decrease in renin and aldosterone
increase in ANP
decrease sodium and water retention
how is potassium lost from the body
mostly urine (little is lost in sweat and faeces unlike with sodium)
so controlled by the kidney
describe the control of potassium in the kidneys
potassium is freely filtered
reabsorbed again in the PCT
controlled secretion at the DCT
secretion is linked to Na reabsorption
intracellular potassium acts as a reservoir in order to regulate change
what is the effect of aldosterone on the DCT
increases activity of the basolateral sodium pump
increases the number of sodium pumps
increases the number of sodium and potassium channels in the apical membrane
this causes increases reabsorption of sodium and increased secretion of potassium
what is Conn’s syndrome
hyperaldosteronism leading to hypertension from increased fluid volume and hypokalaemia
what is 5% dextrose solution
an IV fluid
effectively just adding water as the glucose is metabolised
distributes into all body compartments
what is isotonic saline
0.9% NaCl
what is plasmalyte
an IV fluid which closely mimics normal plasma, so does not enter cells
what are the features of 4.5% albumin (colloid)
supplied in 0.9% NaCl
tends to stay in plasma
blood product
what is hydrolysed gelatin (colloid)
supplied in 0.9% NaCl
stays in plasma
protein is metabolised over time
what questions should you ask before prescribing fluid
what volume is my patient starting from
does my patient need IV fluid
Am I prescribing maintenance fluid, replacement fluid or resuscitation fluid
what volume and what type of fluid
what are the features of DKA
dehydration tachycardia hypotension reduced consciousness Kussmaul's respiration acetone on breath abdominal pain vomiting
what causes dehydration in DKA
hyperglycaemia
vomiting
kaussmaul resp
reduced intake due to reduced consciousness
what fluid would you give an adult with DKA
1L 0.9% saline over one hour
what IV insulin would you give someone with DKA
infusion of 6 units in one hour
why is potassium important in DKA
there may be raised or possibly lowered potassium
insulin pushes potassium into cells and so must be monitored
how should you treat someone with DKA and very low potassium
hold insulin until potassium has normalised
how should you treat someone with DKA and normal potassium
give 20-30 mmol/L/hour of potassium
if potassium is raised it should still be checked every 2 hours
what ion channel is important for maintaining the concentrations in the intracellular fluid
Na- K atp-ase
