18. IV fluids and Hyponatraemia Flashcards
What are the steps to prescribing IV fluids
- Assess volume status: euvolaemic, dehydrated or fluid overload.
- Is drinking enough, enteral feeding or already fluid overloaded- then no. If not drinking, lost or ongoing fluid loss then YES
- Choose an IV fluid based on fluid status, serum Na and urine osmolality- generally isotonic
How is volume status assessed/ signs
Dehydrated: thirsty, excessive vomiting, diarrhoea, quick weight loss, low BP, decreased JVP-2, decreased tissue turgor when young.
Fluid overload: weight gain, high JVP +2 , swelling in ankles, eyes, breathless
What are the reasons for needing IV fluid and the differences between them in application
- Needed for Maintenance of fluid loss through breathing, skin, excretion- small amount for longer- 2/3 L/day
- Replacement of losses- eg after operation
- Rescuscitation: lots of bags, quickly, continue monitoring.
What are the three types of IV fluid, eg, what do and when used
Hypotonic eg. 5% dextrose: moves water from ECF into ICF. Used for cardiac care when high Na+ and HF risk.
Hypertonic: eg. 3% saline, moves water from ICF to ECF (not v used)
Isotonic: eg. 0.9% sod-chlr, plasmalyte. keep same; just add ECF volume.
What is hyponatraemia, causes
<120 mmol/L serum Na+ mostly due to
-Excess water: Cirrhosis, HF, Nephrotic syndrome- hypertension. SIADH and polydipsia. However some ppl still present as euvolemic
-Sodium Loss:
Vomiting, diarrhoea, Diuretics
hypo-aldosteronism : Less Na aborbed- lost in urine (along with water) using Na/K xchanger so Hyperkalaemia, hyperpigmentation is expected.
-Pseudohyponatraemia: lab anomaly for normal Na+ caused by hypertriglyceridemia or hyperproteinemia.
What is the expected K+ and Na+ in ICF vs ECF
Na+ is the dominant cation in the ECF which is the driver of serum osmolality while K+ is dominant in ICF with concentrations of the other low viceversa.
How is Hyponatraemia cause narrowed down so that it can be treated by addressing the underlying cause
Warning no rapid correction - can lead to osmotic demyelination, quadraparesis, loc.
- History: vomiting, diarrhoea, dehydration, and medication
- if due to Na+ loss: saline replacement - Examination fluid status and signs of addisons disease
- Check that serum osmolality and Na+ match- if normal could be pseudohyponatremia bc osmolality not affected by hyp3glyc or hypprotein.
- If presenting as excess fluid then look at history for causes- treat with fluid restriction
If presenting as Euvolaemia could be
-SIADH - more ADH despite not dry or hypotensive
-Polydipsia: low urine osmolarity
-Over hydration with low Na IV fluids- eg. dextrose - hypotonic fluids
-Diuretics: Thiazide, causes Na+ loss but also activates baro-receptors and osmoreceptors to increase ADH- shifting the ADH curve lower set point so ADH released in high amounts at even lower osmolarities