Fluids Flashcards
Why do fluids should be prescribed? (3) - general indications)
- resuscitation
- maintenance
- replacement
General/ key considerations to remember before we prescribe fluids?
- aim of the fluid -> resuscitation, maintenance, or replacement
- weight and size of the patient
- co-morbidities -> e.g. heart failure or chronic kidney disease
- underlying reason for admission (e.g. sepsis or bowel obstruction will require aggressive fluid treatment)
- most recent electrolytes levels
Fluid distribution around the body
(total body weight, intracellular, extracellular and transcellular)
- around 2/3rd of total body weight is water -> around 2/3 of this distributes in to the intracellular fluid -> the remaining 1/3 will distribute in to the extracellular fluid
- Of that fluid in the extracelular space -> around 1/5th stays in the intravascular space -> 4/5th of this is found in the interstitium + a small proportion in the transcellular space
What fluid compartments we want the fluid to stay in:
- general hydration purposes
- fluid resuscitation
- Maintenance of hydration -> all compartments
- Resuscitation -> we want to increase perfusion to the organs so we want most of the fluids in intravascular space
What happens to the fluid in intravascular compartment in sepsis?
Sepsis -> thigh junctions between capillary endothelial cells break -> vascular permeability increases -> fluid leaves the vasculature and enters the tissues
What’s required in terms of the fluids in sepsis?
As the fluid will escape intravascular compartment -> we need to give large amounts of IV fluids to maintain intravascular volume
- need to monitor fluid balance
What population groups (2) and why should we take caution in while replacing the fluids?
Elderly and if HF -> due to risk of pulmonary oedema
What are insensible fluid loses?
- insensible fluid loses -> loss of fluids in the patient that do not come from the urinary output (e.g. respiration, sweating and faeces)
- insensible fluid loses raise in unwell patient as they may be: febrile, tachypnoeic or have increased bowel output -> need to take it into account while planning fluid replacement
Where does a fluid input come from?
- 3/5 of fluid input comes from an enteral route input
- the rest come from metabolic and food processes
*if pt NBM we need to replace or sources via parenteral route
Why does a patient may excessively urinate in the post-op period?
As patient will be recovering, they vascular permeability may return to normal -> therefore if an excess of fluid (e.g. by fluid replacement) they may urinate more to correct the levels to their baseline
- allow it to happen but monitor their electrolytes
Signs of the fluid depletion in a patient
In a fluid-depleted patient:
- dry mucous membrane
- reduced skin turgor
- orthostatic hypotension
- decreased urine output (<0.5 ml/kg/hr)
In worsening stages: tachycardia, hypotension, increased cap refill
Signs of fluid overload in a patient
- peripheral and sacral oedema
- pulmonary oedema
- raised JVP
What to monitor in case if a patient is fluid depleted/ overloaded?
- start daily fluid input/output balance chart
- daily weight measurement
- monitor urea and electrolytes (U&Es) -> to check for kidney hypoperfusion, dehydration, electrolyte abnormalities
What are the components that need to be replaced in the fluids daily (apart from water) ? (4)
- water
- Na+
- K+
- glucose
How much needs to be replaced in the fluid daily? (NICE guidelines)
- water
- Na+
- K+
- glucose
- water -> 25 ml/kg/day
- Na+ -> 1.0 mmol/kg/day
- K+ -> 1.0 mmol/kg/day
- glucose -> 50g / day
- 2 main categories of fluids used (setting use and name of category)
- which one would give a faster fluid replacement effect
A. Crystalloids -> used widely in acute settings, theatres and as maintenance fluids
B. Colloids -> use in many hospital is decreasing (as significantly more expensive)
*there is no evidence that any of the categories is superior in terms of speed of fluid replacement
Example of crystalloid fluid (just names)
- saline 0.9%
- dextrose 5%
- Dexterose saline
- Hartmann’s solution
- Dexterose 50%
What’s the purpose of giving saline 0.9%?
It expands extravascular compartment (75% interstitial and 25% plasma)
*only 25% o plasma expansion so need a lot of crystalloid t expand plasma
What’s the purpose of giving dextrose 5%?
Dexterose 5%
Aim: It is mostly to replace water deficit
- it contains 50g/L of glucose
- glucose will be readily metabolised by the liver -> water is left
Hartmann’s solution
- what are the advantages
- what happens in excess administration
Hartmann’s solution
- Advantage: it is more physiologically similar -> as it contains Na+, K+, Cl-, Ca++ and lactate
*however once given it behaves like 0.9% saline -> expands extravascular volume
- Excess administration: may cause lactic acidosis
What are the colloids?
What are they usually used for?
Colloid - a substance that is unable to pass through the semi-permeable membrane -> it remains in extracellular compartment (they have greater osmolarity than plasma)
Use: extracellular volume replacement (e.g. haemorrhage or hypotension)
*not used as a general fluid replacement as stay only in extracellular compartment
Examples (3) of colloids
- gelatin derivatives (e.g. Haemaccel, Gelofusin) - made from animal gelatine; anaphylactic reactions possible
- Human albumin solution (HAS)- only used at consultant’s/ expert’s request
- Starch (e.g. Hetastarch, Pentastarch)
How to manage initially a reduced urine output (in terms of fluid)
Reduced urine output (<0.5 ml/kg/hr)
- commence fluid challenge
- then, re-check clinical parameters and urine output
- check that no urinary retention; no obstructed catheter
How to do a fluid challenge?
250 ml or 500 ml over 15-30 mins
