perioperative fluids and fluid prescription Flashcards
What is the 4-2-1 rule used for?
Calculating hourly fluid requirements
4ml/kg for the 1st 10kg of body weight
2ml/kg for the 2nd 10kg of body weight
1ml/kg for every further kg of body weight
What is the 100-50-20 rule used for?
Calculating daily requirements of fluid
100ml/kg for the first 10kg
50ml/kg for the next 10kg
20ml/kg for every kg after that
What conditions decrease the need for fluids?
- Oliguric renal failure
- Use of humidified air
- Oedematous states
- Hypothyroidism
- Obesity
It is suggested to use ideal body weight for calculations in obese individuals, seek expert advice for BMI >40
What conditions increase fluid requirements?
- Trauma
- Febrile illness
- Sepsis
- Burns
- Surgical (bleeding, drainage)
- Vomiting
- Diarrhoea
What are some methods to assess fluid status?
- JVP
- Skin turgor
- BP
- Pulse
- Oxygen saturation
- Peripheral oedema
- Mucous membranes
- Breath sounds
- Weight chart
- Fluid chart (input/output)
What is passive leg raise used for?
To assess fluid responsiveness without continuous boluses of fluid
Particularly useful for patients with heart failure.
What is the maximum effect time for passive leg raising?
30-90 seconds
A 10% increase in stroke volume (SV) is assessed during this time.
What type of fluids are used for resuscitation?
Isotonic solutions with sodium in the 130-154mmol/L range
Examples include 0.9% sodium chloride, Hartmann’s, and Plasmalyte.
What is the recommended bolus volume for resuscitative fluids?
500ml in 15 minutes
This is followed by reassessment and possible repeat boluses.
What are maintenance fluids needed for?
Patients unable to maintain oral fluids, especially during fasting for surgery or vomiting
NG fluids or enteral feeding is preferred if maintenance fluids are needed for more than 3 days.
What is the risk associated with saline?
Used commonly, not as good as CSL
Should only give 1L/day
Patients only need one 1L bag to meet daily Na requirements
Can cause non ion gap acidosis with as little as 2L of normal saline
Giving 1L of saline every day can cause metabolic acidosis
Has been shown to have adverse effects on renal perfusion
how much saline can you give per day
you should only give 1L per day
What do CSL/Hartmann’s solutions use to replace NaCL?
Uses K+ and Ca++ to replace Na and lactate to replace Cl-
lactate is good because it can be broken down
what is the downside of lactate in CSL
Lactate can complicate monitoring for increased lactic acid
why can Ca sometimes be problematic
can be an issue with blood products as Ca is a coagulant
hence why citrate is in some blood vials to mopup Ca to stop the blood from clotting
how is plasmalyte different from CSL
It uses acetate and gluconate instead of lactate.
doesn’t have Ca, uses Mg instead
probably the best of the crystalloids but also the most expensive
What is the general guideline for choosing a crystalloid?
CSL should be the go-to fluid
if you’re only giving 1L, it doesn’t really matter
What is a risk associated with colloids?
Risk of anaphylaxis
Colloids are not commonly used except for albumin.
types of colloids
hydroxymethyl starches: considered to be bad and aren’t really used, several contraindications
gelatins eg. gelofusine: made of bovine collagen
albumins: fairly safe, controversial in head injuries
What are the pre-operative fluid needs?
- Maintenance fluids 1.5-3L/day is needed for most surgeries
- Replace specific losses (e.g., vomiting, diarrhoea)
- Replace blood with crystalloid colloid or blood products
Especially important for emergency surgeries.
What is allowed regarding clear fluids before surgery?
clear fluids <400ml up to 2 hours prior
## Footnote
This reduces the aspiration risk compared to overnight fasting.
