IV fluids

Question 1

What are the fluid compartments of the body?

Answer 1

Intracellular fluid (2/3rds) - 28L

Extracellular fluid (1/3rd) - 14L:

• Interstitial fluid (11L)
• Plasma (3L)

Question 2

What is the difference between osmolarity and osmolality?

Answer 2

Osmolarity - number of osmoles of solute/litre

Osmolality - number of osmoles of solute/kg

Question 3

What different fluids comprise our extracellular fluid?

Answer 3

Interstitial fluid

Intravascular fluid

Water in connective tissue

Transcellular fluid

Transcellular fluid - fluid in cavities lined by epithelium (eg CSF, aqueous humor of the eye)

Question 4

What factors determine osmotic pressure?

Answer 4

number of dissociated particles - n

concentration (g/l) - c

molecular weight - M

temperature (K) - T

Osmotic pressure = n x c(c/M)RT

R (universal gas constant)

Question 5

What is normal plasma osmolarity?

What calculation determines this?

Answer 5

298 mosm/L

2([na+] + [k+]) + urea + glucose

2( [140] + [4] ) + 5 + 5

Question 6

When assessing if a patient needs fluid resuscitation - you use an ABCDE approach initially

What are the indications that fluid resuscitation is needed?

Answer 6

Systolic bp < 100 mmHg

HR > 90 bpm

RR > 20

NEWS >/= 5

Cap refill > 2s or peripheries cold to touch

Note - this equally depends on the presentation, history and labratory measurements as well

Question 7

What comprises ‘maintenance’ fluids?

Answer 7

Maintenance IV fluids are based off daily requirements

25-30 mls/kg/day

1 mmol/kg/day of Na+ and K+

50-100 g/day glucose

Question 8

What are the daily requirements for:

Sodium Na+

Potassium K+

Glucose

Answer 8

Sodium = 1-2 mmol/kg/day

Potassium = 0.7 mmol/kg/day

Glucose = 2-4 g/kg/day

Question 9

If you have a solution of 5% glucose - what is the concentration of glucose?

Answer 9

5% glucose = 5g/100ml

Question 10

What is tonicity?

Answer 10

Effective osmolality

Only particles restricted to one of the compartments will determine water distribution

Particles which move freely will not influence water distribution

Question 11

If you were to place RBCs in a Hypertonic and a hypotonic solution - what would happen and why?

Answer 11

Hypertonic - H20 would move out of the RBCs as there is a higher concentration of restricted particles in the ECF

Hypotonic - theres more trapped stuff inside the cells - so water moves into them and they swell up

Question 12

Out of K+ and Na+

Which is more concetrated in the ICF and in the ECF?

Answer 12

ECF contains a lot of sodium Na+ (and accompanying anions)

ICF contains a lot more potassium K+ (and macromolecules)

Question 13

If there are changes in tonicity - the symptoms that arise are largely ________

why is this?

Answer 13

Tonicity changes = neurological symptoms

Hypotonicity:

• cell swelling…
• raised ICP, compromised CBF_{cerebral blood flow}, herniation

Hypertonicity:

• cell dehydration (shrinking)…
• ICH_{intracerebral haemorrhage}, venous sinus thrombosis

Question 14

Whats the difference between a crystalloid and a colloid?

Give examples of each

Answer 14

Crystalloids = aqueous mixtures with lots of soluble stuff

Colloids = water with insoluble stuff in it

Crystalloids:

• dextrose, saline, Hartmann’s solution, plasmalite etc

Colloids:

• gelatins, starch, albumin, blood products, dextrans

Question 15

What are the indications for the use of crystalloids or colloids?

Answer 15

Situations for use of CRYSTALLOIDS:

• fluid resuscitation in the presence of hypovolemia, hemorrhage, sepsis, and dehydration…
• ECF expansion

Situations for use of COLLOIDS:

• anaphylaxis
• renal failure
• coagulopathy
• rheology (investigations of how stuff flows)

Question 16

Should you use 0.9% saline?

What are the problems associated with its use?

Answer 16

No - too much salt

Can cause:

Hypercholaemic acidosis, reduced renal blood flow and reduced GFR

This all exacerbates sodium retention

Question 17

How do you assess a patients volume status?

Answer 17

1 - history:

• previous limited intake, thirst, abnormal losses of fluid, comorbidities

2 - examination:

• pulse & blood pressure
• cap refill, temperature of peripheries
• JVP
• oedema
• postural hypotension

3 - clinical monitoring:

• NEWS, fluid balance, weight monitoring

4 - laboratory assessments:

• FBC
• U&Es
• creatinine

Question 18

How much fluid is given for ‘maintenance fluid’?

At what rate is this given?

Answer 18

30ml/kg/24hrs (20-25ml in frail & elderly)

This means it is usually 1200mls - 2400mls per day depending ofc on the weight of the patient

Rate of 50-100 ml/hr. Never go over 100 ml/hr due to risk of hyponatraemia

Question 19

What fluid is the go-to for maintenance?

In what situations would you give other fluids for maintenance?

Answer 19

0.18% NaCl / 4% glucose / 0.3% KCl

Unless:

• K+ > 5.0 ——– use 0.18% NaCl / 4% glucose
• Na+ < 132.0 ——– use plasmalyte 148

Question 20

How do you calculate how much ‘replacement’ fluid is needed?

What is the link between replacement fluid and maintenance fluid?

Answer 20

Add up losses in the last 24hrs (or sooner if required) - e.g. bleeding, D & V, drain output, fistulae

Give this volume back to the patient

Replacement fluid is in addition to maintenance fluid

Question 21

What is the go to fluid for replacement?

Answer 21

Plasmalyte 148

If there are Upper GI losses (no clue) - then use 0.9% NaCl with KCl

Question 22

How do you assess a patient for fluid resuscitation?

Answer 22

Fluid resucitation indicated for patients with severe dehydration, sepsis or haemorrhage leading to hypovolaemia & hypotension

For a patient who presents with above^:

give fluid challenge of 250-500ml over 5-15 mins and reassess

If adequate response - continue with replacement and maintenance fluids

If no/inadequate response - repeat fluid challenge and reassess

(you can continue to repeat until you reach the daily limit of 2000ml)

Question 23

What fluid is used for fluid resuscitation?

Answer 23

Plasmalyte 148

Colloid

Blood

not sure what indications are for each