Fluid Management

Question 1

What are the main reasons for fluid prescriptions?

Answer 1

Resuscitation - improving tissue perfusion by raising intravascular volume)
Maintenance
Replacement

Question 2

What must you consider before prescribing fluids?

Answer 2

Aim of fluid: rests, maintenance, replacement
Weight and size of patient
Co-morbiditis - HF/CKD
Underlying reason for admission - some surgical patients are deliberately run on the dry side
What was their most recent electrolytes

Question 3

Describe the body fluid compartments.

Answer 3

Total body water (42L)

2/3 of body water distributes to ICF (28L)
1/3 of body water distributes to ECF (14L)

1/5 of ECF stays in intravascular space (plasma) (3L)
4/5th in interstitial water (11L)

Question 4

What is the circulating blood volume? Made up of?

Answer 4

5L
3L plasma
2L red cells

Question 5

What is the difference of fluid distribution required for maintenance and resuscitation?

Answer 5

For general maintenance - fluid to distribute into all compartments
For resuscitation - fluid to stay within intravascular space

Question 6

Why is it necessary to give lots of fluid in sepsis?

Answer 6

Capillary junctions become leaky and vascular permeability increases so lots of fluid required to maintain intravascular volume

Question 7

What is haematocrit?

Answer 7

Proportion of blood that consists of RBCs
Usually 2L/5L so 40%
At rest the HR is 70 bpm and SV is 70ml so CO at rest is 4900ml/min ~ 5L/min
So total blood volume circulates once per minute

Question 8

How is fluid gained and lost from the body? How much?

Answer 8

Intake:
Drinking (1.5L)
Food (0.5L)
Metabolic (0.5L)

Output:
Urine (1.5L)
Respiration (0.4L)
Sweating (0.5L)
Faeces (0.1L)

Actual amount varies depending on physiological status and body weight

Question 9

What are insensible losses of fluid?

Answer 9

Losses from non-urine sources - faeces, sweating respiration.
This will rise in unwell patients - febrile, tachypnoeic, increased bowel motions

Question 10

OE, what should you look for in fluid depleted patients?

Answer 10

Dru mucous membranes
Reduced skin turbot
Urine output (should be 0.5ml/kg/hr)
Thirst
Increased cap refill time
Tachycardia
Hypotension

Question 11

What should you look for in a fluid overloaded patients?

Answer 11

Raised JVP
Peripheral oedema
Pulmonary oedema
Tachycardia
Tachypneuoa/hypoxia

Question 12

What are essential tools to monitor fluids?

Answer 12

Input/output chart
Daily weight
U&Es regularly checked

Question 13

What are the daily requirements for water sodium, potassium and glucose?

Answer 13

Water - 25ml/kg/day
Na - 1mMol/kg/day
K - 1mMol/kg/day
Glucose - 50g/day

Question 14

What is osmolality?

Answer 14

The concentration of particles in a solution
The higher the osmolality, the greater the concentration of particles in a solution.
Particles move from areas of higher osmolality to lower osmolality (due to osmotic pressure)

Question 15

What causes increased urine osmolality?

Answer 15

More concentrated urine
Dehydration
Renal disease
Congestive hear failure
DM/hyperglycaemia
Hypernatraemia
Addison's

Question 16

What causes decreased urine osmoliaity?

Answer 16

Diabetes insipidus - large amounts of dilute urine and increased thirst due to lack fo ADH (Central), kidneys not responding to ADH (nephrogenic)

Question 17

What causes decreased serum osmoliaity and increased urine osmolality

Answer 17

Syndrome of Inappropriate ADH secretion
Excessive release of ADH from posterior pituitary
Urine is not dilute - water is retained
Serum less concentrated

Question 18

What causes decreased serum osmolality and urine osmolality

Answer 18

Overhydration

Hyponatraemia

Question 19

What are the 2 groups of IV fluids?

Answer 19

Crystalloids:
Cheaper and more commonly used
Colloids:
Have high colloid osmotic pressure so theoretically should raise intravascular volume faster than crystalloids but no benefits demonstrated

Question 20

What are the 3 main types of colloid? Crystalloids?

Answer 20

Colloids:
Gelatins
Albumin
Blood products

Crystalloids:
0.9% NaCL saline
5% dextrose
Hartmann’s solution

Question 21

How much sodium and chloride in 1L of 0.9% NaCl?
How much glucose in 1L of 5% dextrose?
What does dextrose-saline contain?

Answer 21

150mmol of sodium, 150mmol of chloride
50g of glucose in 1L dextrose
1/5th normal saline: 1L water, 40g dextrose, 30mmol of sodium and 30mmol of chloride

Question 22

How much water/sodium/potassium/glucose is required for a 70kg normal healthy male?

Answer 22

1750ml water
70mmol Na
70mmol K
50g glucose

Question 23

Give a maintenance fluid regimen for a 70kg man who has adequate renal function and is not overloaded

Answer 23

1: 500ml of 0.9% saline with 20mmol/L K over 8 hours
All Na, 1/3rd of K and 1/4 of water

2: 1L of 5% dextrose with 20mmol/L K over 8 hours
1/3rd K and half of water and all glucose

3: 500ml of 5% dextrose with 20mmol/L K over 8 hours
Remaining 1/3rd of K and 1/4 of water as well as glucose

Question 24

Which patients cannot be safely prescribed typical maintenance regimens?

Answer 24

Renal impairment - normal kidneys correct any minot errors of fluid/electrolyte administration. However patients with renal compromise must be planned

Cardiac impairment

Elderly, frail, cachectic patients

Question 25

What is reduced urine output? How should this be managed?

Answer 25

<0.5ml/kg/hour
Fluid challenge and urine output subsequently rechecked, also checking catheter is not blocked or patient is not in retention

Question 26

What is a fluid challenge for decreased urine output?

Answer 26

250ml/500ml Hartmann’s over 1 hour depending on patient size and comorbidities

Question 27

What are reasons patients may be in fluid/electrolyte deficit?

Answer 27

Vomiting, fistulae, bleeding, perotinitis

Question 28

What should be assessed for excess fluid loss?

Answer 28

Third space losses - to bowel lumen (obstruction) or retroperitoneum (pancreatitis)
Diuresis?
Tachypneoic?
Febrile so sweating more?
Passing more stool/high output stoma
Losing electrolyte rich fluid?
Dehydration? Raised haematocrit and raised Urea:creatinine ratio (raised serum urea)
Vommitting (Low K, low Cl and alkalosis)
Diarrhoea (Low K and acidosis)