Peri-op & Anaesthesia : Fluid Prescription Flashcards
What are the 3 types of fluid prescription?
Resuscitation
Maintenance
Replacement
What should you be considering when prescribing fluids for an individual pt?
- Is the aim of the fluid for resuscitation, maintenance, or replacement?
- What is the weight and size of the patient?
(fluid requirements of a frail 45kg 80yr female and a healthy 100kg 40yr male will be v different) - co-morbidities present e.g. heart failure or CKD?
- What is their underlying reason for admission?
- What were their most recent electrolytes?
Fluid compartments AR
Around 2/3rd of total body weight is water (‘total body water’). Around 2/3 of this distributes in to the intracellular fluid and the remaining 1/3 will distribute in to the extracellular fluid.
Of that fluid in the extracellular space, around 1/5th stays in the intravascular space and 4/5th of this is found in the interstitium, with a small proportion in the transcellular space.
Fluid output: what are insensible losses?
Losses from non-urine sources are termed insensible losses; insensible losses will rise in unwell patients, who may be febrile, tachypnoeic, or having increased bowel output.
What signs are you looking for in a fluid depleted pt?
- Dry mucous membranes and reduced skin turgor
- Decreasing urine output (should target >0.5 ml/kg/hr)
- Orthostatic hypotension
In worsening stages:
* Increased capillary refill time
* Tachycardia
* Low blood pressure
What signs would you look for if you suspected a pt was fluid overloaded?
- Raised JVP
- Peripheral or sacral oedema
- Pulmonary oedema
Pts fluid status: what else would you like to implement if monitoring pts fluid status?
hint ask nursing team
- Ask nursing team to start fluid input-output chart and daily weight chart commenced
- monitor U&Es regularly, for evidence of dehydration, renal hypoperfusion, or electrolyte abnormalities.
Daily fluid / electrolyte requirements for adults
- Water: 25 mL/kg/day
- Na+: 1.0 mmol/kg/day
- K+: 1.0 mmol/kg/day
- Glucose: 50g/day
IV fluids can be broadly categorised in to two groups, crystalloids and colloids
what are they?
Crystalloid = solution containing small molecules e.g. sodium, chloride (most commonly used)
Colloid = solution containing larger molecules e.g. albumin
Maintenance fluid prescribing example: A 70 kg male (no co-morbidities) needs maintenance fluids : work out prescription for 24 hours
In total, we need to prescribe fluids over 24 hours that provide 1750mL of water (70kg x 25mL/kg/day), 70mmol of Na+ (70kg x 1.0mmol/kg/day), 70mmol of K+ (70kg x 1.0mmol/kg/day), and 50g (50g/day) of glucose. Consequently, a typical fluid maintenance regimen is as follows:
- First bag: 500mL of 0.9% saline with 20mmol/L K+ to be run over 8 hours
This provides all of their Na+, ~1/3rd of their K+, and a quarter of their water - Second bag: 1L of 5% dextrose with 20mmol/L K+ to run over 8 hours
This provides a further 1/3rd of their K+, and half of their water, as well as glucose - Third bag: 500mL of 5% dextrose with 20mmol/L K+ to run over 8 hours
This provides the remaining 1/3rd of their K+, and a quarter of their water, as well as glucose
example from teach me surgery
What should you do if a pt has a Any reduced urine output (<0.5ml/kg/hr)
should be managed aggressively, giving a fluid challenge and the clinical parameters, including urine output, subsequently rechecked (also ensuring any catheter is not blocked or patient not retaining urine)
How much should a fluid challenge be?
should be either 250ml or 500ml over 15-30mins, depending on the patient’s size and co-morbidities.
Fdor example a 120kg 30yr male may need >500 ml to make any difference to their intravascular volume, whereas in a frail 80yr lady with ischaemic heart disease and renal disease, 250ml may be more appropriate.
What is the aim of resuscitation fluids?
To improve tissue perfusion - will stay in intravascular space.
