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
Why is there high K in hypoaldosteronism?
- Less Na reabsorbed, thus Na lost in urine down gradient.
- Low Na results in high K in the blood (as no Na/K ATP action)
What is pseudohyponatremia?
- Hypertriglyceridemia
- Hyperproteinemia
- Osmolality normal in these conditions but sodium is low.
What are conditions with water excess?
FLuid overload: Syndromes with water overload - Cirrhosis (liver failure + Ascites) - HF - Nephrotic syndrome (Oedema) SIADH Polydipsia
Can be euvolaemic:
- Excess H2O, but not enough to cause oedema
Describe the steps of dealing with a hyponatreamia patient?
History:
- Vomiting/diarrhoea
- Dehydration
- Medication
Examination: Fluid status i.e signs of addisions
Osmolality (true vs psuedohyponatremia)
Describe what water excess with euvolaemia? and the potential causes:
No signs of dehydration or oedema; JVP not elevated
No evidence of fluid overload
- SIADH
- Polydipsea
- Hypotonic IV
- Diuretics
What is a good indicated of water excess/poldipsea in hyponatremia?
- Urine osmolality becomes very low. Usually is is high in hyponatremia
What causes syndrome of inappropriate ADH?
ADH release despite not being dry or hypotensive
Caused by:
- Tumours (brain)
- CNS issues
- Drugs i.e SSRIs, diuretics
- Lung disease
How can diuretics lead to hyponatremia?
- Low Na with Thiazides
- Na loss with diuretics
- Activate baroreceptors and osmoreceptors = Inc. ADH
= Low Na
How does a change in NaCl change the set point of ADH?
NaCl loss -> reduced ECF volume
Shift ADH curve to lower setpoint
ADH system now allows decreased [Na] , i.e decereased ECF osmolarity
Adaptation favors Na instead of K (aldosterone), i.e relative wasting of K
What is the most common cause of low Na in hospital?
Use of hypotonic IV fluid…
What are the treatments of hyponatraemia?
Depends on cause:
Dehydrate pt with Na loss -Give Saline
Water excess = Generally fluid restriction i.e 1L a day. Avoid rapid correction
Whats a potential consequence of rapid correction for hyponatremia?
Severe osmotic demyelination: = Quadraplegic, loss of consciousness, brainstem damage
