Fluids and electrolytes Flashcards
Define:
- Osmolality
- Osmolarity
- Tonicity
- Osmosis
OsmolaLity = osmoles per kg of solvent (usually water)
OsmolaRity = osmoles per litre of solution
Tonicity = a solution’s solute concentration relative to that of another solution on the opposite side of a cell membrane. So if a solution is hypertonic, hypotonic or isotonic
Osmosis = movement of fluid from an area of low solute concentration (lots of water) to high solute concentration (less water)
Where is most sodium found, extracellularly or intracellularly?
What about:
- potassium
- calcium
- chloride
Most Na is extra-cellular
Most K is intracellular
Ca - extracellular
Cl - extracellular
What fluids do we have?
What’s in them
Normal saline:
- usually 0.9%
- 9g NaCl per 1L of water
Dextrose
- usually 5%
- glucose and water
Hartmann’s
- Na, K, Cl, Ca, lactate
Which fluids are used in resuscitation? Which ones aren’t?
0.9% saline: isotonic
Hartmann’s: isotonic and most physiological
NOT dextrose, because it is essentially water once the glucose has been used up. This leaves water, which is hypotonic (low solute conc) fluid will move from vessels to cells by osmosis. Cells could burst
Colloids not used
Define:
- sensible
- insensible
- 3rd space losses
Sensible: fluid loss you can measure (blood, urine)
Insensible: fluid loss you can’t measure (exhalation, sweat)
3rd space: loss of fluid from functional compartments to non-functional compartments (ascites)
What are the cons of each type of fluid?
NaCl:
- can cause hypernatraemia if too much given too quickly
- using NaCl only as a maintenance fluid causes Na load on kidneys leading to kidney toxicity
- can cause hyperchloraemic acidosis
Hartmann’s:
- not for maintenance use, b/c too much Na and not enough K
- can’t add K or Mg
Dextrose:
- Bad for resuscitation, as essentially water when glucose used up by cells. Water is hypotonic so most of it goes into cells rather than vasculature
- too much too fast can cause hyponatraemia
Describe how you carry out fluid resuscitation.
NaCl or Hartmann’s
500ml
Over less than 15 mins
Can keep giving 500ml until you’ve given a total of 2000 ml. If no improvement still, call anaesthetists.
Which type of shock would you NOT give fluid bolus in?
Cardiogenic shock
If there’s heart failure, the excess fluid will just cause oedema
In children how would you decide how much maintenance fluid to give?
Maintenance:
4ml/kg for first 10kg
2ml/kg for next 10kg
1ml/kg for any kg after that
Correct loss:
deficit = weight x % deficit x 10
Add both together
How much fluid would you give as a fluid bolus in children?
20ml/kg of 0.9% saline
Except in DKA, neonates and trauma patients where you give 10ml/kg
In adults how do you give maintenance fluid?
Adults need 25-30ml/kg/day of water
What ways can you assess fluid status?
Cutaneous circulation Capillary refill time (should be less than 2 secs) Pulse rate 60-100 BP around 120/80 Mucous membranes Urine output
What’s normal urine output?
What about for a 70kg man per day?
0.5ml/kg/hr is the minimum
70kg man: 0.5 x 70 x 24 = 840ml minimum
Clinical features of hypervolaemia?
Cough +/- white frothy sputum
SOB, pulmonary oedema
Fluid in serosal cavities: pleural, peritoneal
Peripheral oedema
Bilateral basal crepitations
Raised JVP
S3/S4 heart sounds
Tachycardia
Management of fluid overload?
Stop IV fluids
Sublingual nitrate: reduces preload
IV nitrate: reduces pre and afterload
Diuretics: IV furosemide
Oxygen
CPAP
What’s the difference between ‘group and save’ and ‘cross match’?
G+S: the analysis of the sample to determine ABO group
Cross match: the lab providing red cell products for the patient
What would happen to the cells if you were to give an isotonic fluid?
What about hypotonic?
What about hypertonic?
Isotonic: won’t result in any significant fluid shifts
Hypotonic: fluid will go by osmosis from the vasculature (low solute conc due to the hypotonic fluid given) to the cells (high solute conc). Fills the cells with fluid so they could burst
Hypertonic: fluid will move by osmosis from the cells (low solute) into the vasculature (high solute)
What ECG changes would you see in hyperkalaemia?
Tall tented T waves
Flattening or absence of P waves
Wide QRS
What ECG changes would you see in hypokalaemia?
Flattened / inverted T waves
U waves (come after T waves)
Depressed ST segment
Prolonged QT
How does spironolactone work?
Aldosterone antagonist
Blocks Na+/K+ pump
- This pump normally pumps Na+ from urine to blood
- Spiro prevents this
- So Na+ is not pumped to blood and is excreted in urine
- Water follows Na+ so there is excretion of water too
Blocks Na+/K+ ATPase pump
- This pump normally pumps K+ from blood to urine
- Spiro prevents this
- So K+ is not pumped into urine, so is retained in blood
It also reduces cardiac fibrosis and LV remodelling And inflammation (in atherosclerosis)
What must you make patients aware of when taking spironolactone?
Don’t have a high K diet, since spiro is already making patient retain more K than usual.. don’t want hyperkalaemia
Don’t take NSAIDs
Don’t take ACEi, ARBs
Clinical features of hypovolaemia?
Absent JVP
Decreased skin turgor
Dry mucous membranes
Low BP
Oliguria/anuria
Orthostatic hypotension
Peripherally shut down
Prolonged CRT
Shock: hypotensive + tachycardia
How many litres of fluid is in an average 70kg man?
What compartments is the fluid split into?
Where is most of the fluid?
42 litres
Intracellular
Extracellular:
- intravascular
- interstitial
Most of it is intracellular
Describe Na and K concentrations in each compartment?
Intracellular:
- K high
- Na low
Extracellular (both)
- K low
- Na high
When isotonic fluids go in where do they go?
Mostly stay in extracellular compartment (mainly interstitial)
What is a hypertonic fluid?
Example?
When hypertonic fluids go in what do they do?
Have a higher solute concentration
So they increase plasma tonicity and therefore draw fluid out of cells into bloodstream
Mannitol, hypertonic saline
What is a hypotonic fluid? What do they do?
Have a lower solute concentration
They lower serum osmolality
Rarely used
Why is dextrose not used in fluid resuscitation?
Because only 80ml of 100ml goes into vasculature. The rest goes into cells
