Fluid Balance Flashcards

1
Q

What is the approximate percentage and volume of water in a 70kg male?`

A

~60% (female: ~55%)

= ~42l

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2
Q

What percentage of total body water is intracellular? What are the approximate concentrations of the different ions in the intracellular compartment?

A

2/3 (70kg male: ~28l)

[Na+] = 12mmol/l
[K+] = 150mmol/l
[Cl-] = 4mmol/l
[HCO3-] = 12mmol/l
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3
Q

What percentage of total body water is extracellular?

A

1/3 (70kg male: ~14l)

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4
Q

What percentage of extracellular fluid is interstitial? What are the approximate concentrations of the different ions in the interstitial compartment?

A

4/5 (70kg male: ~14l)

[Na+] = 144mmol/l 
[K+] = 4mmol/l 
[Cl-] = 114mmol/l
[HCO3-] = 30mmol/l
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5
Q

What percentage of extracellular fluid is intravascularl? What are the approximate concentrations of the different ions in the intervascular compartment?

A

1/5 (70kg male: ~3l)

[Na+] = 142mmol/l
[K+] = 4mmol/l
[Cl-] = 103mmol/l
[HCO3-] = 27mmol/l
[glucose] = 5mmol/l
[protein] = 10mmol/l
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6
Q

What are the approximate values for input and output of fluid?

A
INPUT: 40ml/kg/day
- drink = 1500ml
- food = 750ml
- metabolic = 350ml
= 2600ml
OUTPUT: 0.5ml/kg/hr urine
- urine = 1500ml
- faeces = 100ml
- lungs = 400ml
- skin = 600ml
= 2600ml
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7
Q

Give some examples of causes of reduced urine output after surgery.

A

Normal response to fluid loss during surgery

Pre-renal = ?dehydration (insufficient intake or excessive loss before kidneys)

Renal = ?patient known to habe CKD, ?AKI due to nephrotoxic drugs

Post-renal = ?catheter blocked (anuria)

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8
Q

Give some examples of cystalloid fluids and their approximate ion fluids.

A
  1. 9% saline:
    - [Na+] = 154mmol/l
    - [K+] = 0mmol/l (unless added)
    - [Cl-] = 154mmol/l
    - Osm = 308 (hypotonic)

Dextrose (5%):

  • [Na+] = 0mmol/l
  • [K+] = 0mmol/l
  • [Cl-] = 0mmol/l
  • Osm = 278 (hypertonic)

Combination

Hartmann’s:

  • [Na+] = 131mmol/l
  • [K+] = 5mmol/l
  • [Cl-] = 111mmol/l
  • Osm = 275 (hypertonic)
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9
Q

Give some examples of colloid fluids.

A

Gelafusine/Volplex

Starch

Albumin

Blood products

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10
Q

Contrast the duration of plasma volume expansion of 5% dextrose, 0.9% saline, and Hartmann’s.

A

5% dextrose = 1/3 x 1/5 = 1/15 (therefore not good for shocked patients)
- 1l distributes through 42l of total body water, therefore only 3l goes intravascular (14l would need to be given to increase the plasma volume by 1l, 14 x 3 = 42l)

  1. 9% saline = 0.2hrs (1/5 remains)
    - 1l distributes to ECF, therefore only 1/6 goes intravadcular (6l would need to be given to increase the plasma volume by 1l, 1/6 x 6 = 1l)

Hartmann’s = 0.2hrs

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11
Q

What is the maximum safe rate of K+ infusion?

A

5mmol/hr

If more than 1l of 20mmol/l K+ needs to be given then it must be supervised and go through a controlled pump.

K+ is a vein irritant; if given too fast it should it should be given into a central vein.

note: K+ released by damaged tissue so usually no K+ needs to be given 48hrs post-op

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12
Q

Describe the practicalities of giving fluid resuscitation (pre-existing deficit).

A

Req. clinical assessment of patient’s hydration status and CVS parameters

Fluid administered in boluses and titrated to response.

Req. freq. reassessment i.e. every 15min

Give crystalloids or colloids (blood in haemorrhage)
- note: do not give 5% dextrose (only 1/15 stays in intravascular compartment)

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13
Q

Describe the practicalities of replacing ongoing fluid losses.

A

e.g. vomiting, diarrhoea, high output stoma, enterocutaneous fistula

Measure and record fluid losses

Patient assessment:
- peripheral perfusion 
,- pulse rate/BP
- JVP/CVP
- flow based measurements 
- urine output (>0.5ml/kg/hr) 

HYPOVOLAEMIA:

  • consider nature of fluid loss
  • resuscitate with crystalloid, colloid, or blood

EUVOLAEMIA:

  • maintenance req. of 40ml/kg/day H2O, 2mmol/kg/day [Na+]. 1mmol/kg/day [K+]
  • replace ongoing fluid losses
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14
Q

Why is a loss of ECF much more serious than an equivalent loss from the total body volume?

A

1l lost per day from total body volume = ~17%

1l lost per day from functional ECF = 7/12 = 53% (not compatible with life)

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15
Q

What fluid changes occur as a result of surgical trauma?

A

Increased ADH —> reduced fluid output

Increased aldosterone and cortisol —> Na+ retention, loss of K+ and H+

Increased catecholamines

Increased renin

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