19 - Clinical Problem Solving: Electrolytes Flashcards
What should I know
- IV fluid management
- Types of fluid
- Fluid assessment
What should you ask before giving IVF?
- is my patient euvolaemic, hypovalaemic, hypervolaemic
- do they need IV fluid i.e. can they just drink? Why?
- how much do they need?
- what type of fluid do they need?
If they are hypovolaemic they are…
Dehydrated (low fluid vol)
Fluid overload?
- weight gain
- high BP
- swollen ankles and puffy eyes
- breathless
Dehydrated
weight loss, dry mouth, low bp, dizzy
When does a patient NOT need IV fluids?
They are already drinking enough, they are on enteral feeding, fluid overloaded/not dehydrated
When DOES a patient need IV fluids?
They are not drinking and has lost or is losing fluids (nil by mouth and can’t keep up orally)
3 reasons someone may need IV fluids
- Mainenance (keep eurovolaemic if nil by mouth)
- Replace losses
- Rescuscitation
What is a good level of maintenance fluids?
2-3L a day (how much we lose a day)
How do you lose fluid?
- (pee - not enough to get dehydrated)
- sweat (not much), diarrhoea, vomit, breathing
What fluid might you be replacing?
blood
diarrhoea
vomitting
third spacing (third spacing is fluid in a space where it shouldn’t be i.e. ascites! Although over all there is a lot of fluid in the body it is not in the right place to do any good)
In what situation is third spacing more likely to occur
When there is low albumin.
Fluid replacement summary
- need 2-3L a day to replace losses
- constantly assess fluid status i.e. weight and JVP
- patient record of losses (fluid balance charts)
When may you need IVF to rescuscitate?
- shocked patient i.e. sepsis, dehydration, bleeding
What do you need to consider when deciding what type of fluid?
- look at the patient’s fluid status
- what is their serum sodium (hyponatremic?)
What is generally the safest fluid
Isotonic (0.9% saline or plasmalyt)
> this assumes that there is free flow/passage of water from the cells into the ECF
When may you not use isotonic fluid?
Unless you are only doing maintenance fluid and you’re worried about overloading them (pul odema) or the sodium is very HIGH
When may you use a hypotonic solution? Eg?
5% dextrose (isotonic but metabolised)
> doing a little bit of maintenance but patient is on the verge of being overloaded
> if drugs need to be given to an overloaded patient
> hypotonic solutions may be useful if the serum sodium is very high (i.e. not enough water - need fluid but don’t want to make more salty. Need to do carefully don’t want to change sodium levels quickly!!)
What IVF do you give a patient that is overloaded i.e. doesn’t pee and has odema?
DON’T GIVE THEM FLUID
Will make worse
Hypertonic saline e.g.
3% saline
When do you use hypertonic solutions
- severe hyponatraemia as it makes water go into cells and make ECF conc of sodium increase
Hyponatraemia
- problem is water excess (BUT can still be dehydrated)
- low sodium conc
Fluid compartments?
(MALE)
60% fluid
2/3 ICF
1/3 ECF
20% plasma 80% interstitialWhat fluid compartment does IVF go into
ECF
How does water absorption work?
- osmoreceptors detect increased osmotic pressure and baroreceptors detect decreased BP
- both stimulate ADH release from post pit
- ADH causes aquaporin insertion and vasoconstriction
- increase BV and BP
what plays the major role in determining how much water we hold on to?
ADH!! And so osmolality and to a lesser extent bp
What are the 3 causes of hyponatraemia?
- Sodium loss
- Water excess
- Pseudohyponatraemia (abnormal tests but actually normal)
Vast majority are due to water excess.
How can you lose sodium?
- GI loss (vomit/diarrhoea)
- hypo-aldosteronism (ENaC reabsorption)
- sweat (unusual)
- diuretics (pee more sodium)
Aldosterone?
- reabsorbs NA+ into blood
- low means more is excreted
What does low Na+ reabsorption mean for K+?
Na is reabsorbed by Na/K ATPase. Means that if less Na+ is being reabs, less K+ is being secreted and K+ in the blood will increase.
What can cause pseudohyponatremia?
hypertriglyceridemia/proteinemia
What are 3 syndromes that are associated with water excess?
- cirrhosis
- heart failure
- nephrotic syndrome
> SIADH (increased ADH when not needed)
polydipsia
How do you sort out hyponatraemia?
History (are they vomiting, diarrhoea, dehydrated, medications, drinking lots, IVF?
Examine fluid status
Check osmolality
Are people who have water excess hypervolaemic?
Not always they CAN be euvovolaemic
Can be fluid overloaded i.e.
> heart failure, nephrotic syndrome, cirrhosis
(doesn’t take a lot of fluid to change salt con but does to become fluid overloaded)
What do you most commonly see with hyponatraemia?
Water excess with euvolaemia.
- means there are no signs of dehydration, odema, JVP changes,
What can cause water excess with euvolaemia?
- SIADH
- polydipsia
- overhydration with hypotonic fluids
- diuretics
What is the urine osmolality like in people that drink too much?
Low osmolality
In other cases of hyponatraemia the urine osmol is usually high?
SIADH?
Produce ADH even when euvolaemic and sodium levels are normal
What can cause SIADH
- tumours
- CNS (being unconcious, seizures, menigingitis)
- drugs (anticonvulsants)
- lung disease
- infection
- chronic lungdisease
- diuretics can cause hyponatraemia
Diuretics and hyponatraemia?
Thiazide diuretics cause the loss of sodium. They cause a shift in ADH/osmol curve so that more ADH is released at the same osmol so more water is retained for the amount of salt you’re losing causing hyponatraemia
What is the most common cause of low Na in the hispital
Bad IVF selection i.e. hypotonic fluids
How do you treat a dehydrated patient with sodium loss?
Isotonic fluid (saline)
How do you treat a patient with water excess hyponatraemia?
Fluid restriction (1L a day) resets the ADH and fixes Na+. Rapid correction is unadvisable.
