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MD2 Cardio > Fluid Assessment and Balance > Flashcards

Fluid Assessment and Balance Flashcards

1
Q

What % of body weight is total body water (TBW)? On average how many litres is this?

A

60%, ~42L

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2
Q

What % of TBW is ECF?

A

1/3

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3
Q

What % of TBW is ICF?

A

2/3

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4
Q

How does ECF vary?

A

With osmolar (sodium and chloride) content, which is subject to intake less than excretion or vice versa

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5
Q

What is the impact of sodium intake and the menstrual cycle on ECV?

A

On average ECV ~14L, +/- 1L due to impact of sodium and menstrual cycle

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6
Q

When does ICV vary?

A

Fairly constant

Can vary with water intake and plasma sodium concentration

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7
Q

How can ECV be assessed?

A

History
Abnormal intake or excretion
Examination of CVS (tissue turgor, mucous membranes, BP, JVP, oedema)
Urine concentration/sodium content

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8
Q

What is NOT a good guide to ECV?

A

Plasma sodium concentration

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9
Q

How can ICV be assessed?

A

History
Physical examination (limited value)
Plasma sodium or osmolality (parallels IC osmolality)

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10
Q

What is NOT a good guide to ICV?

A

Physical examination is of limited value

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11
Q

Which fluid compartment does the administration of saline affect?

A

Sodium remains in ECV and water follows osmols

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12
Q

List 5 causes of hypovolaemia

A

Diarrhoea and vomiting
Disease: CV, DM, renal, intracranial, intrathoracic
Denial of oral intake: peri-operative, coma
anti-Diuretic hormone (ADH): osmotically inappropriate secretion (ectopic production, altered control - baroreceptors, intracranial, intrathoracic, CVD)
Drugs: Diuretics, anti-Diabetics, anti-Depressants/anti-psychotics

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13
Q

Give 3 examples of anti-depressants which may cause hypovolaemia

A

Lithium
Carbamazepine
SSRIs

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14
Q

Describe the ECV and ICV in terms of their composites

A

ECV: sodium, chloride (an environment supporting IC osmolality, cell membrane transport and delivery of nutrients and removal of waste - i.e. the circulation)
ICV: potassium, organic anions (an environment supporting IC function and cell membrane transport)

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15
Q

TBW 42L + 3L 150mmol/L saline = 45L

How is this distributed into the ECV and ICV? What signs may be seen?

A

Water follows osmols, sodium remains in ECV, so 3L is added to ECV resulting in oedema, possible raised JVP, pulmonary oedema if existing CVD disease
Plasma sodium and osmolality unchanged
ICV unchanged

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16
Q

TBW 42L + 3L water = 45L

How is this distributed in the ECV and ICV?

A

No osmolar capture of water
ECV gains 1/3 (1L): changes are hard to detect, there may be mild oedema, plasma sodium and osmolality decrease by ~7%
ICV gains 2/3 (2L): Sx and signs unlikely, assessed by plasma sodium or osmolality (if renal perfusion and ADH control normal, rapid excretion of excess water follows)

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17
Q

TBW 42L - 3L fluid loss of sodium rich fluid (diarrhoea) = 39L
What are the effects on ECV and ICV? What signs may be seen?

A

ECV loses 3L: low BP, tachycardia, low JVP, axillary dryness, peripheral vasoconstriction, low urine sodium but concentrated urine
NB Plasma sodium normal
ICV unchanged

18
Q

“Dehydration”
TBW 42L - 3L from failure to drink (unconscious) and obligatory loss = 39L
What are the effects on ECV and ICV? What signs may be seen?

A

ECV loses 1/3 (1L): hard to detect O/E unless CVD, plasma sodium/osmolality increased by ~7%
ICV loses 2/3 (2L): dry tongue, axilla, low tissue turgor in young patients, plasma sodium/osmolality increased by 7%, concentrated urine

19
Q

21 year old female with 6/7 N+V, diarrhoea
Has noticed marked weight loss of 3kg and is drinking but not eating
O/E: cold fingers and feet (hypoperfused and vasoconstricted), HR 100, BP 120/80 lying and 100/60 standing (postural drop)
Plasma Na+ 138 mmol/L, creatinine 80 umol/L (both normal)
ICV, ECV, body sodium?

A

ICV normal
ECV low
Body sodium low

20
Q

64 year old female presents with 3/12 productive cough with haemoptysis and recent confusion
O/E: BP 160/90 lying and standing, HR 76, RR 20, JVP not raised, signs of consolidation in apex of R lung
Plasma Na+ 120 mmol/L (low), creatinine 70 umol/L (normal)
ICV, ECV, body sodium?

A

SiADH! Keeping on water
ICV high
ECV high
Body sodium normal

21
Q

77 year old man found by relatives comatose after 3/7 of no contact with him
O/E: evidence of hemiplegia (new), BP 100/70, HR 90, dry mucosa, cold periphery
Plasma Na+ 157 mmol/L (high), urine sodium 10 mmol/L (low)
ICV, ECV, body sodium?

A

Increased ADH secretion
ICV low
ECV low
Body sodium normal

22
Q

67 year old man, with long-standing IHD, presents SOB with obvious pulmonary oedema and with massive peripheral oedema; he has gained 15kg weight since last reviewed
O/E: BP 100/60, HR 120, JVP 15cm
Plasma Na+ 120mmol/L (low), creatinine 180 umol/L (high)
ICV, ECV, body sodium?

A

ICV high
ECV high
Total body sodium normal/high

23
Q

36 year old female presents with an exacerbation of UC, manifest by excessive diarrhoea; she feels cold and complains dizziness when she stands up, and is also thirsty and has been drinking a lot
O/E: BP 90/60, HR 120, JVP not visible
Plasma Na+ 120mmol/L (low), urine Na+ 3 mmol/L (low), plasma creatinine 110 umol/L (high)
ICV, ECV, body sodium?

A

ICV low?? (losing Na+)
ECV low
Total body sodium low

24
Q

62 year old woman presents with a few days regurgitation of food/vomiting on a background of difficulty in swallowing solids since a gastric stapling operation 15 years ago
She is on lithium for bipolar disorder and reports a weight loss of 7kg
O/E: looks unwell, BP 100/60, HR 120, JVP not visible, cold periphery, dry tongue
Plasma Na+ 165 mmol/L (high), osmolality 330 (high), creatinine 272 umol/L (high), urine Na+ 12 mmol/L (low), chloride 8 mmol/L (very low)
ICV, ECV, body sodium?

A

Lithium causing diabetes insipidus (losing water)
ICV low
ECV low
Body sodium normal

25
Q

60 year old female piano teacher presents with 4/7 Hx severe watery diarrhoea, and is now thirsty and also gets dizzy when standing up
O/E: looks unwell, BP 90/60 (lying) and 70/40 (standing), HR 100 and JVP is not visible lying down
Plasma Na+ 155 mmol/L (high), creatinine 80 umol/L (normal)
Fluid and electrolyte status is most likely represented by:
a) increased total body Na+
b) decreased ECV
c) normal total body Na+
d) increased IC water content
e) normal osmolality

A

b)

26
Q

You are on a camping trip in the Western Desert, when your 26 year old friend starts vomiting blood and continues to do so, while you drive to the nearest cattle station
On arrival your friend looks pale and has a weak, rapid pulse
While they call the air ambulance, you find they have an IV giving set and 2 sorts of IV fluid
You decide to give him some IV fluid. Which of the following would you choose:
a) 5% dextrose
b) 150 mmolar NaCl

A

b)

27
Q

You are on a camping trip in the Western Desert, when your 26 year old friend starts vomiting blood and continues to do so, while you drive to the nearest cattle station
On arrival your friend looks pale and has a weak, rapid pulse
While they call the air ambulance, you find they have an IV giving set and 2 sorts of IV fluid
How much fluid would you give him, while waiting for the air ambulance (ETA 2/24):
a) 1L over 2hrs, reassessing every 15 mins
b) 2L over 2hrs, reassessing every 30 mins
c) 1L as rapidly as possible, then reassess

A

c)
Pros: rapid resuscitation and prevention of cardiac arrest
Cons: can precipitate HF if pre-existing CVD or cause APO

28
Q

List 3 causes of high plasma osmolality/sodium

A

Water intake insufficient due to:

1) Obligatory water loss (urine, sweat)
2) Access to water
3) Increased loss (diabetes insipidus, nephrogenic diabetes insipidus, osmotic diuresis)

29
Q

List 4 causes of low plasma osmolality/sodium

A

Water intake > ability to excrete (normal 20 L/day) reduced with:

1) Increased ADH (siADH, baroreceptor stimulation, lack of glucocorticoids)
2) Decreased distal tubule flow (decreased renal perfusion)
3) Other tubular factors limiting free water excretion
4) Drugs (e.g. diuretics, carbamazepine, antidepressants esp SSRIs), with variable contributions from above factors

30
Q

Why do changes in ECV usually occur without a change in plasma sodium concentration?

A

Because osmotic control frequently overrides volume control

31
Q

Do changes in ECV and blood always correlate?

A

Yes, unless there is hypoalbuminaemia or leaky capillaries

32
Q

What % of total body K+ does plasma K+ represent?

A

2%

33
Q

76 year old previously healthy woman presents for a check up and found to have HTN on repeated measurement (BP 170/100); she has been commenced on irbesartan
BP now 155/90 but testing reveals:
Plasma Na+ 138 mmol/L, K+ mmol/L (high), creatinine 150 umol/L (high)
BSL, bicarb, other electrolytes normal
ICV, ECV, Na+, K+?

A 
ARB results in decreased eGFR, results in increased K+
ICV normal
ECV normal
Na+ normal/low
K+ high
34
Q

76 year old previously healthy woman presents for a check up and found to have HTN on repeated measurement (BP 170/100); she has been commenced on irbesartan
BP now 155/90 but testing reveals:
Plasma Na+ 138 mmol/L, K+ mmol/L (high), creatinine 150 umol/L (high)
HCT (Avopro) was added and BP now 125/70, but complains of bouts of dizziness on standing up
Now plasma creatinine 160 umol/L (high), K+ 5.3 mmol/L (normal) and Na+ 125 mmol/L (low)
ICV, ECV, Na+, K+?

A

ICV high?
ECV normal? low?
Na+ low
K+ normal

Would get rid of the thiazide and never prescribe again (has failed these)

35
Q

What are the complications of high ECV and low ECV?

A

High ECV: pulmonary oedema, mortality

Low ECV: poor perfusion (brain, kidney, etc)

36
Q

What are the complications of high vs low osmolality?

A

High: improvable mental function
Low: improvable mental function, decreased falls (achieve plasma Na+ >135)

37
Q

Complications of high or low K+

A

Cardiac arrhythmia

Muscle weakness

38
Q

Principles of osmolality and plasma Na+/K+

A

Plasma Na+ does not tell you body sodium content, Hx and CV examination do (and ECV)
Intracellular osmols are relatively constant and there are no osmolar gradients, so plasma osmolality (or sodium concentration) reflects ICV (inversely)
An abnormal plasma K+ can reflect a shift or abnormal content

39
Q

23 year old insulin-dependent diabetic develops severe glandular fever, with fever, anorexia and a sore throat; presents feeling awful
O/E: looks unwell, BP 110/60, HR 110, RR 24
Ix: BSL 20, pH 7.25, pCO2 24, plasma K+ 6.5 mmol/L, Na+ 140 mmol/L, HCO3- 10
ICV, ECV, Na+, K+?

A

ICV normal
ECV low
Na+ normal
K+ low (due to N+V, diarrhoea seen in ketoacidosis; in Mx, insulin drives K+ into cells, fluids drives ketones into cells, UO increases and more K+ is lost)

40
Q

What does an abnormal plasma K+ reflect?

A

Shift between intra- and extra-cellular space or deficiency or excess
If there is no evidence of shift, plasma K+ reflects total body K+

41
Q

Give 4 examples of agents which shifts K+ into cells

A 
Insulin
B agonists
Aldosterone
Alkalosis
NB Their absence or opposites shift K+ out of cells
42
Q

What K+ level is of concern in a stable patient?

A

Less than 3.0

>6.0

MD2 Cardio (11 decks)

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