Fluids

Question 1

given a patients weight how do you calculate the intravascular, intracellular and extravascular fluid volumes

Answer 1

TBW = 0.6 * body weight
e.g. 70kg man has 42 litres of water

ECF = 1/3 of total fluid (14L)
ICF = 2/3 total fluid ((28L)

interstitial fluid = 3/4 of ECF
plasma = 1/4 fluid
transcellular fluid = roughly 500ml

Question 2

how does total body water content change with weight and age

Answer 2

neonates = 80% water
children = 70%
women and obese men = 50%

Question 3

what are sensible fluid losses

Answer 3

urinary losses

Question 4

what are insensible fluid losses

Answer 4

sweat, lung, faeces

Question 5

what is the minimum urine output for physiologically normal kidneys

Answer 5

0.5ml/kg/hour

Question 6

what are acceptable maintenance fluid regimes

Answer 6

‘one salty 2 sweet’ - 1x 1L normal saline + 20mmolKCL over 8 hours, 2x1L 5% dextrose + 20mmol KCL over 8 hours for 24 hour cover

NICE: 30mmol/kg/day (adults)

Paeds regime also can be applied - 100ml/kg/day for first 10kg, 50 for next 10 and 25 for each subsequent

Question 7

what is the minimum requirement of glucose per day

Answer 7

40mmol

Question 8

what is the minimum requirement of postassium per day

Answer 8

1mmol/kg/day

Question 9

what is the minimum requirement of sodium per day

Answer 9

2mmol/kg/day

Question 10

what is the general rule for fluid losses in a patient with pyrexia

Answer 10

10% more fluid requiredq

Question 11

what does the RAAS do

Answer 11

efferent renal artery constriction, peripheral vasoconstriction, sympathetic activation, release of aldosterone leading to distal Na absorption

also leads to increased cardiac muscle stretch leading to pump failure over time

Question 12

what are the signs of dehydration

Answer 12

mild: headache, lack of energy, tiredness
moderate: dry mouth, increased alertness, sunken eyes, muscle cramps
severe: confusion, disorientation, tachycardia, tachypnoea, low bp

Question 13

what metabolic derrangement occurs with excessive vomiting

Answer 13

hypochloremic, hypokalaemic metabolic alkalosis

Question 14

how do you treat excessive vomiting causing metabolic derrangement

Answer 14

saline IV + 20mmol potassium with review

Question 15

what metabolic derragements occur in a high volume output pancreatic/ileal/jejunal/bile fistula

Answer 15

metabolic acidosis due to low bicarbonate levels

high potassium even if total potassium is depleted

Question 16

what metabolic derrangements are caused by diarrhoea

Answer 16

hyperchloraemic metabolic alkalosis + hypokalaemia if profuse

Question 17

whats the treatment for diarrhoea + metabolic derrangement

Answer 17

oral rehydration therapy

IV fluids if necessary

Question 18

how should you give fluids with cerebral oedema

Answer 18

2/3 maintenance of an isotonic solution (saline fine)

Question 19

what metabolic derrangement is seen on acute tubular necrosis

Answer 19

hyperkalaemia, hypermagnesia, hyperphosphataemia, hyponatraemia, hypocalcaemia

metabolic acidosis

Question 20

what are some essential bloods if you suspect dehydration

Answer 20

FBC, U+E, lactate and glucose

Question 21

what metabolic derrangement might be extected in a patient with cardiac failure

Answer 21

Patients are at risk of dilutional hyponatraemia in severe CCF due to dietary sodium restriction and the inability to excrete water (RAAS over activation).

Hypokalaemia can result from prolonged
administration of diuretics, or hyperkalaemia can occur in severe heart failure leading to reductions in GFR, particularly if they are on potassium sparing diuretics/ ACEls.