Fluid Management Flashcards
Roughly how much water is in a 70kg adult?
42 litres (60%)
How is water distributed in the body?
2/3 intracellular (28 litres)
1/3 extracellular
- interstitial fluid (10.5 litres)
- plasma (3.5 litres)
Which component of water should be most carefully considered and why?
Plasma –> carries blood (oxygen) to the tissues
How does interstitial fluid support plasma?
Interstitial fluid is a reservoir for plasma –> can move quickly into vessels if blood is lost
Which 3 things must be considered when planning fluid management?
Basal requirements
Existing deficit
Predicted losses
What is the basal requirement of water for a 70kg adult?
30-40ml/kg —> 2100-2800ml
What is the basal requirement of sodium + potassium?
1-2mg/kg of each per day
What might be seen on examination of a dehydrated patient?
Dry mouth
Loss of skin elasticity
Cold peripheries
Increased HR + decreased BP tend to be late signs
Which investigations are helpful in a patient who may be dehydrated?
Fluid balance chart (records input + output)
Urine output
Urea + creatinine (if increased may indicate dehydration or pre-renal failure due to hypovolaemia)
What is the minimum acceptable urine output?
- 5ml/kg/hour
- -> about 30ml/hour
What are the different types of fluid available?
Cystalloids
Colloids
5% glucose
What do crystalloids contain and give two examples?
Contain water + electrolytes –> isotonic with extracellular fluid
- Sodium chloride (0.9% saline)
- Hartmann’s solution (Ringer’s lactate)
How does 0.9% saline compare to plasma and what effect does this have?
Slightly more sodium and much more chloride than plasma
–> high chloride means that H+ comes out of cells so risk of patient becoming acidotic
What are the advantages of 0.9% saline?
Cheap and widely available
Good for both resuscitation and maintenance
What are the risks if going large quantities of 0.9% saline?
Hypernatraemia
Metabolic acidosis
How is Hartmann’s different to saline?
Much closer to plasma in terms of ion concentrations
What happens when 5% glucose is given IV?
Effectively like giving free water as all of the glucose is metabolised by the liver
Water goes into all the compartments, mainly intracellularly
What are the clinical uses of 5% glucose?
Good for pure hydration (replacement of water) and maintenance fluids
Useless for resuscitation (as doesn’t stay in plasma)
What do colloids contain?
Big molecules exerting oncotic pressure (fluid follows them)
0.9% saline (so causes same problems with acidosis)
Theoretically, why would colloids be better than crystalloids?
Big molecules stay in intravascular space, attracting water due to oncotic pressure –> volume expanders
What are the disadvantages of colloids?
No proven benefit over crystalloids in resuscitation
More expensive
May interfere with clotting
Small risk of anaphylaxis
What are the general principles of fluid maintenance for a patient who will be nil by mouth for 24 hours?
3 bags of fluid (1 salty, 2 sweet) equally daily required volume of water –> 1x 0.9% saline, 2x 5% glucose
Add 20mg potassium to each bag
–> give over 24 hours
Why does potassium need to be added to bags of maintenance fluid?
Crystalloids do not contain enough potassium for maintenance
What are the signs of fluid overload?
Raised JVP
Peripheral, sacral or pulmonary oedema
Which group of patients are most at risk of fluid overload?
Elderly –> compensation mechanisms less efficient
How is response to a fluid challenge monitored?
Increasing BP and slowing HR
Central venous pressure (CVP) monitoring (in more complex patients)
If CVP remains unchanged or rises then falls after a fluid challenge, what does this indicate?
Patient is dry
If CVP rises and stays up following a fluid challenge, what does this indicate?
Patient is adequately filled
If CVP rises by >4cmH2O following a fluid challenge, what does this indicate?
The patient is overfilled or has heart failure
