Lecture 18: Clinical problem solving: Hyponatraemia Flashcards
What are the questions to ask before giving IV fluid?
- Is my patient euvolaemic, hypovolaemic or hypervolaemic?
- Does my patient need IV fluid? Why?
- How much?
- What type(s) of fluid does my patient need?
What is hypotonic fluid?
- Hypotonic solution
- Lower osmolality, more dilute
- Pushes fluid into cell
- Makes cell fat
What is hypertonic fluid?
- Hypertonic solution
- More concentrated, usually more Na
- Pushes fluid out of cells
- Makes cells smaller
What is isotonic fluid?
- Isotonic solution
- Same osmotic pressure across membrane
- Keeps everything the same
Its important to ask if youre patient is euvolaemic, hypovolaemic or hypervolaemic.
How do you assess volume status?
Must assess if euvolaemic, dehydrated or fluid overloaded.
Fluid overload: Sudden weight gain, oedema (swollen ankles, puffy eyes), high BP, breathlessness.
Dehydration: Weight loss, dry mouth, low BP, dizziness
Measure JVP for both dehydration and fluid overload.
Why would ur patient not need IV fluid?
- Drinking enough
- On enteral feeding
- Already fluid overloaded
What are the reasons patients need IV fluid
- Maintenance (nil by mouth)
- Replacement of losses i.e diarrhoea
- Resuscitation (i.e shock)
If nil by mouth, how much fluid would you need?
You loose 2-3L/D
So 2-3L to maintain
How are paediatric needs different when it comes to maintenance?
- 4 mL/Kg/hr for the first 10kgs
- +2 mL/Kg/hr for the next 10kgs
- +1 mL/Kg/hr for the remainder of body weight
What would you be replacing when it comes to fluids?
Fluids lost to:
- Diarrhoea
- Vomiting
- Burns
- Effusions i.e ascites
How can you determine the volume of fluid lost?
Weight, biggest indicator of rapid weight change // est. of loss/gain
Why do you need to give IV fluid for resus?
IV fluids given in shock i.e rapid blood loss etc
How do you determine what fluid to give a patient?
- Look at patient fluid status
- What is the serum sodium (osmolality status)
Safest fluid generally isotonic unless specific situation
What do you generally give in terms of IV fluid?
Generally give isotonic fluid unless maintenance fluid and overloaded or high Na
Describe how hypotonic fluid works? and whats the warning with it?
5% dextrose starts as isotonic but dextrose is metabolised by cells so just becomes free water
Can result in hyponatreamia
When is hypotonic IV fluid useful?
Hypotonic solutions useful if high serum sodium i.e not enough water, or if patient needs maintenance fluid but already overloaded
Watch serum sodium!!
Why give hypertonic fluid and how does it work?
Hypertonic fluid given in hyponatreamia but risks overcorrecting causing major issues.
What is hyponatraemia?
- When serum sodium levels are low.
- Can be caused by excess water
- Can be due to low sodium but very unlikely entirely because of Na loss.
What are the predominant cations and anions in each of the fluids?
ECF: High Na (Cation) and High Cl (anion)
ICF: High K (Cation) and High PO4 (Anion)
Where do IVF fluids go?
- ICF
2. ECF
Describe ADH release:
Brain: Osmoreceptors detect increased osmolarity -> ADH
Baroreceptors: Detect decreased BP -> ADH
ADH
- > Increased reabsorption of Water
- > Vasoconstriction of blood vessels
= Increased BP and BV
What are the causes of hyponatraemia?
- Sodium loss
- Water excess
- Psuedohyponatraemia
What causes sodium loss?
- GI loss
- Hypo-aldosteronism
- Sweat (not usual)
- Diuretics
What is hypoaldosteronism? (Addisons disease)
- Low serum aldosterone
- Usually malfunctioning adrenals
- Low Na -> lost in urine
- Low BP
- Pigmentation
- May have high K
