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Acute Medicine > Fluids and electrolytes > Flashcards

Fluids and electrolytes Flashcards

1
Q

Define:

  • Osmolality
  • Osmolarity
  • Tonicity
  • Osmosis
A

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)

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2
Q

Where is most sodium found, extracellularly or intracellularly?

What about:

  • potassium
  • calcium
  • chloride
A

Most Na is extra-cellular

Most K is intracellular

Ca - extracellular
Cl - extracellular

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3
Q

What fluids do we have?

What’s in them

A

Normal saline:

  • usually 0.9%
  • 9g NaCl per 1L of water

Dextrose

  • usually 5%
  • glucose and water

Hartmann’s
- Na, K, Cl, Ca, lactate

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4
Q

Which fluids are used in resuscitation? Which ones aren’t?

A

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

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5
Q

Define:

  • sensible
  • insensible
  • 3rd space losses
A

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)

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6
Q

What are the cons of each type of fluid?

A

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
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7
Q

Describe how you carry out fluid resuscitation.

A

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.

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8
Q

Which type of shock would you NOT give fluid bolus in?

A

Cardiogenic shock

If there’s heart failure, the excess fluid will just cause oedema

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9
Q

In children how would you decide how much maintenance fluid to give?

A

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

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10
Q

How much fluid would you give as a fluid bolus in children?

A

20ml/kg of 0.9% saline

Except in DKA, neonates and trauma patients where you give 10ml/kg

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11
Q

In adults how do you give maintenance fluid?

A

Adults need 25-30ml/kg/day of water

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12
Q

What ways can you assess fluid status?

A 
Cutaneous circulation
Capillary refill time (should be less than 2 secs)
Pulse rate 60-100
BP around 120/80
Mucous membranes
Urine output
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13
Q

What’s normal urine output?

What about for a 70kg man per day?

A

0.5ml/kg/hr is the minimum

70kg man: 0.5 x 70 x 24 = 840ml minimum

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14
Q

Clinical features of hypervolaemia?

A

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

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15
Q

Management of fluid overload?

A

Stop IV fluids

Sublingual nitrate: reduces preload

IV nitrate: reduces pre and afterload

Diuretics: IV furosemide

Oxygen

CPAP

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16
Q

What’s the difference between ‘group and save’ and ‘cross match’?

A

G+S: the analysis of the sample to determine ABO group

Cross match: the lab providing red cell products for the patient

17
Q

What would happen to the cells if you were to give an isotonic fluid?

What about hypotonic?

What about hypertonic?

A

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)

18
Q

What ECG changes would you see in hyperkalaemia?

A

Tall tented T waves
Flattening or absence of P waves
Wide QRS

19
Q

What ECG changes would you see in hypokalaemia?

A

Flattened / inverted T waves
U waves (come after T waves)
Depressed ST segment
Prolonged QT

20
Q

How does spironolactone work?

A

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)
21
Q

What must you make patients aware of when taking spironolactone?

A

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

22
Q

Clinical features of hypovolaemia?

A

Absent JVP

Decreased skin turgor

Dry mucous membranes

Low BP

Oliguria/anuria

Orthostatic hypotension

Peripherally shut down

Prolonged CRT

Shock: hypotensive + tachycardia

23
Q

How many litres of fluid is in an average 70kg man?

What compartments is the fluid split into?

Where is most of the fluid?

A

42 litres

Intracellular

Extracellular:

  • intravascular
  • interstitial

Most of it is intracellular

24
Q

Describe Na and K concentrations in each compartment?

A

Intracellular:

  • K high
  • Na low

Extracellular (both)

  • K low
  • Na high
25
Q

When isotonic fluids go in where do they go?

A

Mostly stay in extracellular compartment (mainly interstitial)

26
Q

What is a hypertonic fluid?
Example?

When hypertonic fluids go in what do they do?

A

Have a higher solute concentration

So they increase plasma tonicity and therefore draw fluid out of cells into bloodstream

Mannitol, hypertonic saline

27
Q

What is a hypotonic fluid? What do they do?

A

Have a lower solute concentration

They lower serum osmolality

Rarely used

28
Q

Why is dextrose not used in fluid resuscitation?

A

Because only 80ml of 100ml goes into vasculature. The rest goes into cells

Acute Medicine (15 decks)

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