Fluid and electrolyte balance

Question 1

what are the major fluid compartments of the body

Answer 1

plasma, interstitial fluid, intracellular

Question 2

what is the normal volume of plasma

Answer 2

3L

Question 3

what is the normal volume of interstitial fluid

Answer 3

11L

Question 4

what is the normal volume in intracellular fluid

Answer 4

28L

Question 5

what is the intracellular concentration of potassium

Answer 5

150 mM

Question 6

what is the normal plasma conc of potassium

Answer 6

4.5 mM

Question 7

what is the normal plasma conc of Na

Answer 7

130 mM

Question 8

what are the major gains of water to the body

Answer 8

food and water, and food oxidation

Question 9

what are the major losses of water from the body

Answer 9

urine, faeces, sweat, insensible loss

Question 10

what is insensible water loss

Answer 10

transepidermal diffusion
evaporation from the respiratory tract

these losses are solute free and can’t be controlled or prevented
causes heat loss

Question 11

what sensors monitor body fluid

Answer 11

hypothalamic osmoreceptors
low pressure baroreceptors in the right atria
high pressure sensors in the carotid sinus

Question 12

what ion is the key driver of total plasma volume

Answer 12

sodium

if sodium drops then the volume will fall (due to osmolality being tightly controlled)

Question 13

how can sodium be controlled

Answer 13

kidneys/ urine output

controlled indirectly via volume sensors

Question 14

how is the amount of sodium reabsorbed changed

Answer 14

rate of flow, aldosterone, ANP

change in GFR

Question 15

if blood osmolality changes how does the volume change

Answer 15

increases

also increase in ADH

Question 16

what happens when there is an increase in volume

Answer 16

detected by baroreceptors
decrease in renin and aldosterone
increase in ANP
decrease sodium and water retention

Question 17

how is potassium lost from the body

Answer 17

mostly urine (little is lost in sweat and faeces unlike with sodium)

so controlled by the kidney

Question 18

describe the control of potassium in the kidneys

Answer 18

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

Question 19

what is the effect of aldosterone on the DCT

Answer 19

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

Question 20

what is Conn’s syndrome

Answer 20

hyperaldosteronism leading to hypertension from increased fluid volume and hypokalaemia

Question 21

what is 5% dextrose solution

Answer 21

an IV fluid
effectively just adding water as the glucose is metabolised

distributes into all body compartments

Question 22

what is isotonic saline

Answer 22

0.9% NaCl

Question 23

what is plasmalyte

Answer 23

an IV fluid which closely mimics normal plasma, so does not enter cells

Question 24

what are the features of 4.5% albumin (colloid)

Answer 24

supplied in 0.9% NaCl
tends to stay in plasma
blood product

Question 25

what is hydrolysed gelatin (colloid)

Answer 25

supplied in 0.9% NaCl stays in plasma protein is metabolised over time

Question 26

what questions should you ask before prescribing fluid

Answer 26

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

Question 27

what are the features of DKA

Answer 27

``` dehydration tachycardia hypotension reduced consciousness Kussmaul's respiration acetone on breath abdominal pain vomiting ```

Question 28

what causes dehydration in DKA

Answer 28

hyperglycaemia vomiting kaussmaul resp reduced intake due to reduced consciousness

Question 29

what fluid would you give an adult with DKA

Answer 29

1L 0.9% saline over one hour

Question 30

what IV insulin would you give someone with DKA

Answer 30

infusion of 6 units in one hour

Question 31

why is potassium important in DKA

Answer 31

there may be raised or possibly lowered potassium insulin pushes potassium into cells and so must be monitored

Question 32

how should you treat someone with DKA and very low potassium

Answer 32

hold insulin until potassium has normalised

Question 33

how should you treat someone with DKA and normal potassium

Answer 33

give 20-30 mmol/L/hour of potassium if potassium is raised it should still be checked every 2 hours

Question 34

what ion channel is important for maintaining the concentrations in the intracellular fluid

Answer 34

Na- K atp-ase