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
How much fluid should be given (fluid challenge) may differ from:
A. 30 y old 120 kg lady
B. Frail, 80y old lady with renal disease and IHD
A. May need to give >500ml of fluid to make any difference
B. 250 ml of fluid may be enough
What’s the normal range of serum potassium?
K+ range: 3.5 - 5.5 mmol/L
Routes of potassium replacement in case of hypokalaemia
- oral is preferred
- IV - if unable to tolerate oral or if potassium is really low
- K+ <2.5 mmol/L may require ITU admission and administration via a central line
What are ‘third space loses’?
Loss of fluid ( other than urine, faeces, respiration and sweat) into the non-visible spaces e.g. through bowel lumen (intestinal obstruction) or retroperitoneum (in pancreatitis)
Common electrolyte pattern in dehydration
Dehydration
high urea:creatinineratio and high PCV
*PCV - packed cell volume; proportion of blood that is made up of cells
Common electrolyte pattern in vomiting
Vomiting:
low K+, low Cl–, and alkalosis
Common electrolytes pattern in diarrhoea
Diarrhoea:
low K+ and acidosis
Main use of:
- crystalloids
- colloids
Crystalloids -> general fluid replacement
Colloids -> hypovoluemia (haemorrhage or hypotension)
Initial assessment of a post-op patient with a low urine output
Post-up low urine output => Check/ ensure that there is no:
- ABC assessment
- acute urinary retention -> feel for palpate bladder and positive fluid balance on the fluid chart (should be urinating)
- ensure that a catheter is not blocked
- hypovolemic shock -> check BP, HR, actively bleeding wounds and drains
Case: a patient is post op and low urinary output; no signs of hypovolemia or acute urinary retention
- possible cause?
- what to do?
- reassessment and possible further causes
Possible cause: dehydration
Management: increase IV infusion + reassess
If still low urinary output and positive response to fluid challenge-> AKI may be suspected
Investigations to be done in a dehydrated patient (4)
- U&Es
- FBC
- ABG
- urinealysis
Severity % scale of dehydration (3)
- 15% → mild
- 30% → moderate
- 40% → severe
Why in dehydration there may be mental state changes?
Due to the brain not being perfused
What to give first: crystalloid or colloid?
Crystalloid first then colloid
(better in terms of the fluid movement across compartments)
What fluids are commonly used for a fluid replacement?
Plasmalyte or Hartmann’s
(they contain substances similar to a normal physiological state e.g. K+, Na+, Cl-)
Hyponatraemia
- causes
- presentation
Hyponatraemia
Causes: excess water, TURP syndrome (due to over-irrigation through an intratracheal catheter)
Presentation: impaired consciousness, confusion, clammy
Management of hyponatraemia
- calculation
- what to use
Slow correction!!! (if done too fast → possible pontine demyelination syndrome)
Calculation:
weight (kg) x (pre-post Na) x 0.6
*pre - normal Na level/ level pre TURP
* post - current hyponatraemic level
GIve 1/2 in the first 8 hrs, 1/4 in next 8 hrs, 1/4 in next 8 hrs
Use: NaCL 1.% (infusion pump)
Hypokalaemia
- cause
- presentation
- management
Cause: low intake or excess loss
Presentation: ectopic beats, arrhythmia
Management:
- Slow correction with 20mmol of KCl/hr
- ECG monitoring
What can an excess of 0.9% NaCl cause?
hyperchloraemic acidosis
What are the requirements for maintenance fluid?
- water
- Na, Cl, K
- glucose
- 25-30 ml/kg/day of water
- approximately 1 mmol/kg/day of potassium, sodium and chloride
- approximately 50-100 g/day of glucose to limit starvation ketosis
What is meant by 3rd space fluid loses?
Space Losses = ↓ ECF
• Bowel obstruction → ↓ fluid reabsorption → 3rd space
loss
• Sudden diuresis on day 2-3 post-op = recovery of
ileus
• Peritonitis → ascites → 3rd space loss
What’s Parkland’s Formula? What fluid to use for that?
Parkland’s formula: 4 x wt x %burn = mL in 1st 24hrs
Use Hartmann’s
