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IAAC > IV Fluids > Flashcards

IV Fluids Flashcards

1
Q

What are the two principle body fluid compartments and and what are their respective volumes

A

Intracellular fluid and Extracellular fluid

Total body water is ~60% of weight with 1/3 being ECF and 2/3 being ICF

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2
Q

What are the major components of ECF

A

~1/4 is plasma (intravascular volume) and 3/4 is interstitial fluid

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3
Q

What are crystalloids

A

Solutions of sodium chloride, glucose or both in water

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4
Q

What are the major crystalloids used in clinical practice

A 
0.9% Saline
Hartmanns (Compound sodium lactate)
5% Dextrose
3% Dextrose + 0.3% Saline
4% Dextrose + 0.18% Saline
Plasmalyte 148
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5
Q

What is the chemical composition of 0.9% Saline

A

Na 154 mmol

Cl 154 mmol

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6
Q

What is the Osmolarity and pH of 0.9% Saline

A

308mOsm/L

pH 5.5-6

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7
Q

What is the chemical composition of Compound Sodium Lactate

A 
Na 130 mmol
Cl 110 mmol
K 5 mmol
Ca 2 mmol
Lactate 30 mmol
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8
Q

What is the Osmolarity and pH of CSL

A

279mOsm/L

pH 6.5

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9
Q

How is 1L of normal saline/CSL distributed after IV administration and why

A 
Sodium concentration is similar to ECF hence the fluid will remain in the ECF
The electrolytes in these solutions are small molecules that pass freely across the semi-permeable capillary membrane (and others).  Therefore the distribution in ECF will approximate the divisions of ECF
ie 250mLs (1/4) will remain in IVF and 750mLs (3/4) will move into ISF
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10
Q

How much crystalloid is required to replace 1L of blood loss

A

~3-4L as only 1/3 to 1/4 of their volume will remain in the intravascular space

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11
Q

What is the effect of administering 1L of 5% dextrose?

A

The glucose in 5% dextrose is rapidly taken up by cells.
The net effect is of administering pure water, so it is distributed throughout TBW.
Each compartment receives fluid in proportion to its contribution to TBW (~2/3rd ICF, ~1/3 ECF)
ICF 670mLs, ECF 330mLs with 250mLs to ISF and 80mLs to plasma
Intravascular volume will increase from 5L to 5080mLs (insignificant), but osmolarity of plasma (3.2L) will decrease by ~7mOsm/L. This is detected by osmoreceptors and ADH release is decreased with renal water excretion rising

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12
Q

What is the Osmolarity of 5% Dextrose

A

278mOsm/L

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13
Q

What is the chemical composition of Plasmalyte 148

A 
Na 140mmol
Cl 98mmol
K 5mmol
Mg 1.5mmol
Acetate 27mmol
Gluconate 23mmol
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14
Q

What is the Osmolarity and pH of Plasmalyte 148

A

294mOsm/L

pH 4.0-6.5

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15
Q

How is plasma Osmolarity calculated

A

2(Na + K) + glucose + urea

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16
Q

What are the benefits of Crystalloid

A

Cheap, readily available, no reports of anaphylaxis, promotes urine output, less interstitial oedema

17
Q

What is the effect of administering 1L of 4% Albumin

A

Plasma protein solution will only be distributed to the intravascular fluid (if capillary membrane is intact)
Tonicity is unaltered, but volume increases from 5L to 6L which will be detected by volume receptors which will trigger a fall in ADH levels and the excretion of water commences
Water loss increases plasma oncotic pressure and water moves from ISF to IVF

18
Q

What is the chemical composition of 4% Albumin

A

Albumin 40g/L
Na 140mmol
Cl 128mmol
Octanoate 6.4mmol

19
Q

What is the Osmolarity, MW and pH of 4% Albumin

A

250mOsm/L
MW 70kDa
pH 7.0

20
Q

What are colloid fluids

A

IV fluids that contain high molecular weight molecules suspended in saline
They are plasma expanders because the exert osmotic pressure and hence retain the fluid in the IVF

21
Q

What are the disadvantages of colloids

A

Cost
Anaphylactoid reactions (esp gelatins and dextrans)
Coagulopathy (HES)
Pruritis (HES)
Renal failure (HES)
Not proven to change outcome - SAFE trial

22
Q

What are gelatins

A

Semi-synthetic polypeptides with MW 30kDa prepared by hydrolysis of chemically modified bovine collagen

23
Q

What are the disadvantages of gelatins

A

Lower molecular weight with poor intravascular retention
Plasma half life only 1-2hrs
Previously linked to significant risk of anaphylactoid reactions

24
Q

What are dextrans

A

Semi-synthetic highly branched polysaccharide molecules produced by bacterial action on sucrose
MW 40-70kDa

25
Q

What are the advantages/disadvantages of dextrans

A 
Duration of action 6-8hrs
Improve microcirculatory flow
Antiplatelet, antifibrin activity
More severe anaphylactic reactions
Induce an acquired Von Willebrand's state by reducing components of factor VIII
May obstruct renal tubules
Max dose 20mLs/kg in adults
26
Q

What are hydroxyethyl starches

A

Semi synthetic colloids produced by hydroxythetyl substitution of amylopectin - highly branched starch
MW 70-450kDa

27
Q

What are the advantages/disadvantages of HES

A

Duration of plasma expansion can be upto 24hrs with large molecules (most are comparable to 4% Albumin)
Affect platelet function and coagulation
Cause a Von Willebrand’s like syndrome
Can be deposited in the reticuloendothelial system leading to debilitating pruritis
Renal impairment

28
Q

How is 4% Albumin prepared

A

Human albumin is heated at 60’C for 10hrs and incubated at low pH to inactivate viruses
Once prepared shelf life is short unless refrigerated

29
Q

What is the effect of infusing 1L of 3% Saline into a 70kg male

A

The Na content limits distribution of infused fluid to the ECF. The hypertonic solution will also draw water out of cells, decreasing ICF
ECF volume will increase by ~2.1L with ~1/4 being intravascular (500mLs)
Plasma osmolality will increase by ~4.8%
ICF volume will decrease by ~1.1L
The increased Osmolality leads to inc ADH to cause water retention in the kidneys. This is balanced against the inc in blood volume that inhibits ADH and causes water excretion.
Volume expansion stimulates ANP to drive a natriuresis
Secretion of Aldosterone is inhibited by decreased Renin and Angiotensin II
Overall effect is natriuresis and slow excretion of excess water

30
Q

What is the daily sodium, potassium, chloride and water requirements for an adult

A

Sodium 1-2mmol/kg/day
Chloride 1-2mmol/kg/day
Potassium 0.5-1mmol/kg/day
Water ~35mLs/kg/day to replace insensible losses or 4/2/1 rule (~37mLs/kg/day for a 70kg adult)

31
Q

Define tonicity

A

Osmolality due to effective osmoles

32
Q

Which patients in particular are likely to present to OT with fluid deficits

A

Emergency cases, prolonged fasting, bowel prep, inappropriate fluid prescription pre-op

33
Q

How do you determine IV fluid requirements in the intra-operative period

A

Calculate basal fluid (maintenance) requirements using a 4/2/1 guide +
Replace existing deficits +
Replace body fluid losses +
Replace blood losses

34
Q

How do you calculate degree of existing fluid deficit (dehydration)

A

Clinically & weight change

Mild dehydration 7% - delayed CRT with mottling, signs of shock, deep acidotic breathing, dec tissue turgor

35
Q

How should fluid deficit be replaced

A

TBW deficit as calculated percentage of weight
Multiply by weight
Time course for replacement is variable - consider replacing over 24hrs
Probably best to limit to 20mLs/kg bolus

36
Q

Which conditions necessitate more restrictive fluid replacement

A 
Congestive cardiac failure
Cardiac disease
Renal failure
Dilutional hyponatraemia
Oedema
Ascites
37
Q

What is the primary determinant of ECF volume

A

Sodium content (not concentration)

38
Q

What is the primary determinant of ICF volume

A

Tonicity

39
Q

What is the normal Osmolar gap and what alters it

A

IAAC (10 decks)

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