MISC - Fluid assessment

Question 1

What (5) factors does fluid balance involve?

Answer 1

• Diarrhoea & vomiting
• CVs, DM, renal, intracranial & intrathoracic
• Poor oral intake
• ADH
• Drugs: diuretics, antidiabetic & antidepressive, antipsychotic drugs (e.g. lithium, Carbamezapine, SSRI’s and more)

Question 2

Describe the total body water

• % of body weight
• volume in a 70kg male

Answer 2

60% of body weight

42L in a 70kg male

Question 3

What does water follow?

If saline is given, what (ICF or ECF) is changed?

Answer 3

• osmosis with no osmolar gradients b/w ICF & ECF

- osmols and sodium remains in ECV -> if saline is given, ECF increases but ICF is unchanged

Question 4

Describe extracellular volume

• % of total body water. Its volume
• (2) ions
• how is it assessed
• its (2) components
• how is it adjusted

Answer 4

(1/3) 14L

· SODIUM, CHLORIDE
· An environment supporting intracellular osmolality, cell membrane transport and delivery of nutrients and removal of waste (circulation)

· Assessed by history, abnormal intake or excretion, oedema, examination of the cardiovascular system and urine concentration/ sodium content. NB: Plasma sodium concentration is a poor guide to content, cardiac failure impacts on assessment.

2 components:
· interstitial (3L) and intravascular (11L). examine oedema, CVS, urine concentration and sodium content.

· Adjust by modifying sodium and water intake/concentration

· Changes in ECF volume (IV + interstitial) and blood volume (IV) correlate unless there is hypoalbuminemia or leaky capillaries (infections etc)!!

Question 5

How is ECV changed?

Answer 5

With sodium.

LOW SODIUM CONTENT, LOW ECV; HIGH SODIUM CONTENT, HIGH ECV AND VICE VERSA

Question 6

Describe intracellular volume

• % of total body water. Volume
• components
• 2 main types of ions
• how is it assessed
• how is it adjusted

Answer 6

(2/3) 28L

· POTASSIUM, ORGANIC ANIONS
· An environment supporting intracellular function and cell membrane transport

Osmolar, (potassium + organic anions) content, is held fairly constant. But ICV does vary when water intake, less than excretion or vice versa, leading to changes in ICV and ECV osmolality (AND PLASMA SODIUM CONCENTRATION).

· Assessed by history, physical examination (limited value) and plasma sodium or OSMOLALITY, which parallel intracellular osmolality.

Adjust by modifying water intake

Question 7

How much water do we need a day

Answer 7

20-30mL/kg/day

Question 8

How much Na+ do we need per day?

Answer 8

1mM /kg/day

Question 9

Describe (3) Types of fluids

• Crystalloids
• Colloids
• Dextrose

Answer 9

1. Crystalloids: (small molecular weight) e.g. Saline
   · Used to replace ECF (they’re isotonic) and does not change ICF
   · Only 1/3 or 1/4 remains intravascularly - hence if blood is lost, 3-4x volume needs to be administered
   · Lactate gets metabolised into bicarbonate in the liver
2. Colloids (large molecular weight).
   · Used to replace IVS (intravascular space)
   · Important in capillary fluid dynamics as they exert an osmotic force across the wall of capillaries.
   · Blood
   · Plasma/albumin proteins (major component)
   · Synthetics (rarely used)
3. 5% dextrose: Used to replace TBW. 3/42 stays in IV space (70mL) - not suitable for pt who have bled or post-op