Fluid Homeostasis

Question 1

What is the body composition of water?

Answer 1

Total water: 60% of 70kg = 42L

2/3 intracellular = 28L
1/3 extracellular = 14L
􀀐 Plasma = 3L (21% of ECF)
􀀐 Interstitial = 10L
􀀐 Transcellular = 1L

Question 2

What is osmotic pressure?

Answer 2

Pressure which needs to be applied to prevent the inflow
of water across a semipermeable membrane.
􀁸 i.e. the ability of a solute to attract water.

Question 3

What is oncotic pressure?

Answer 3

form of osmotic pressure exerted by

proteins.

Question 4

What is hydrostatic pressure?

Answer 4

􀁸 Pressure exerted by a fluid at equilibrium due to the force
of gravity.

Question 5

How is distribution within the extra cellular fluid determined?

Answer 5

Distribution w/i the ECF is determined by Starling’s
forces.

􀂃 Capillary and interstitial oncotic pressure.
􀂃 Capillary and interstitial hydrostatic pressure.
􀂃 Filtration coefficient (capillary permeability)

Question 6

What can cause third space losses (surgical)?

Answer 6

decrease in ECF

􀁸 Bowel obstruction 􀄺 􀄻 fluid reabsorption 􀄺 3rd space
loss
􀁸 Sudden diuresis on day 2-3 post op = recovery of ileus
􀁸 Peritonitis 􀄺 ascites 􀄺 3rd space loss

Question 7

What are the indications for enteral nutrition?

Answer 7

􀁸 Catabolic: sepsis, burns, major surgery
􀁸 Coma/ITU
􀁸 Malnutrition
􀁸 Dysphagia: stricture, stroke

Question 8

What are the complications of enteral?

Answer 8

NGT
􀂃 Nasal trauma
􀂃 Malposition or tube blockage

Feeding
􀂃 Feed intolerance leading to  diarrhoea
􀂃 Electrolyte imbalance
􀂃 Aspiration
􀂃 Refeeding syndrome

Question 9

What are the indications for parenteral nutrition?

Answer 9

􀁸 Prolonged obstruction or ileus (>7d)
􀁸 High output fistula
􀁸 Short bowel syndrome
􀁸 Severe Crohn’s
􀁸 Severe malnutrition
􀁸 Severe pancreatitis
􀁸 Unable to swallow: e.g. oesophageal Ca

Question 10

How is parenteral nutrition monitored?

Answer 10

Standard
􀂃 Wt., fluid balance and urine glucose daily
􀂃 Zn, Mg weekly

Initially
􀂃 Blood glucose, FBC, U+E + PO4 3x /wk
􀂃 LFTs 3x /wk

Once stable
􀂃 Blood glucose, FBC, U+E + PO4 daily
􀂃 LFTs weekly

Question 11

What are the complications of parenteral nutrition?

Answer 11

Line-related

􀂃 Pneumothorax / haemothorax
􀂃 Cardiac arrhythmia
􀂃 Line sepsis
􀂃 Central venous thrombosis 􀄺 PE or SVCO

Feed-related

􀂃 Villous atrophy of GIT
􀂃 Electrolyte disturbances
 Refeeding syndrome
 Hypercapnoea from excessive CO2
production
􀂃 Hyperglycaemia and reactive hypoglycaemia
􀂃 Line sepsis: 􀄹 risk c¯ TPN
􀂃 Vitamin and mineral deficiencies

Question 12

What is refeeding syndrome?

Answer 12

Life-threatening metabolic complication of refeeding via

any route after a prolonged period of starvation.

Question 13

What is the pathophysiology of refeeding syndrome?

Answer 13

􀁸 decreased carbs causes catabolic state with decreased insulin, fat and protein
catabolism and depletion of intracellular PO4

􀁸 Refeeding causes increased insulin in response to carbs and increased
cellular PO4 uptake.

􀁸 leading to hypophosphataemia:
􀂃 Rhabdomyolysis
􀂃 Respiratory insufficiency
􀂃 Arrhythmias
􀂃 Shock
􀂃 Seizures

Question 14

What patients are at risk of refeeding syndome?

Answer 14

􀁸 Malignancy
􀁸 Anorexia nervosa
􀁸 Alcoholism
􀁸 GI surgery
􀁸 Starvation