Lecture 18: Clinical problem solving: Hyponatraemia

Question 1

What are the questions to ask before giving IV fluid?

Answer 1

• 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?

Question 2

What is hypotonic fluid?

Answer 2

• Hypotonic solution
• Lower osmolality, more dilute
• Pushes fluid into cell
• Makes cell fat

Question 3

What is hypertonic fluid?

Answer 3

• Hypertonic solution
• More concentrated, usually more Na
• Pushes fluid out of cells
• Makes cells smaller

Question 4

What is isotonic fluid?

Answer 4

• Isotonic solution
• Same osmotic pressure across membrane
• Keeps everything the same

Question 5

Its important to ask if youre patient is euvolaemic, hypovolaemic or hypervolaemic.

How do you assess volume status?

Answer 5

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.

Question 6

Why would ur patient not need IV fluid?

Answer 6

• Drinking enough
• On enteral feeding
• Already fluid overloaded

Question 7

What are the reasons patients need IV fluid

Answer 7

1. Maintenance (nil by mouth)
2. Replacement of losses i.e diarrhoea
3. Resuscitation (i.e shock)

Question 8

If nil by mouth, how much fluid would you need?

Answer 8

You loose 2-3L/D

So 2-3L to maintain

Question 9

How are paediatric needs different when it comes to maintenance?

Answer 9

• 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

Question 10

What would you be replacing when it comes to fluids?

Answer 10

Fluids lost to:
- Diarrhoea
- Vomiting
- Burns
- Effusions i.e ascites

Question 11

How can you determine the volume of fluid lost?

Answer 11

Weight, biggest indicator of rapid weight change // est. of loss/gain

Question 12

Why do you need to give IV fluid for resus?

Answer 12

IV fluids given in shock i.e rapid blood loss etc

Question 13

How do you determine what fluid to give a patient?

Answer 13

• Look at patient fluid status
• What is the serum sodium (osmolality status)

Safest fluid generally isotonic unless specific situation

Question 14

What do you generally give in terms of IV fluid?

Answer 14

Generally give isotonic fluid unless maintenance fluid and overloaded or high Na

Question 15

Describe how hypotonic fluid works? and whats the warning with it?

Answer 15

5% dextrose starts as isotonic but dextrose is metabolised by cells so just becomes free water

Can result in hyponatreamia

Question 16

When is hypotonic IV fluid useful?

Answer 16

Hypotonic solutions useful if high serum sodium i.e not enough water, or if patient needs maintenance fluid but already overloaded

Watch serum sodium!!

Question 17

Why give hypertonic fluid and how does it work?

Answer 17

Hypertonic fluid given in hyponatreamia but risks overcorrecting causing major issues.

Question 18

What is hyponatraemia?

Answer 18

• 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.

Question 19

What are the predominant cations and anions in each of the fluids?

Answer 19

ECF: High Na (Cation) and High Cl (anion)

ICF: High K (Cation) and High PO4 (Anion)

Question 20

Where do IVF fluids go?

Answer 20

1. ICF
2. ECF

Question 21

Describe ADH release:

Answer 21

Brain: Osmoreceptors detect increased osmolarity -> ADH
Baroreceptors: Detect decreased BP -> ADH

ADH
-> Increased reabsorption of Water
-> Vasoconstriction of blood vessels

= Increased BP and BV

Question 22

What are the causes of hyponatraemia?

Answer 22

• Sodium loss
• Water excess
• Psuedohyponatraemia

Question 23

What causes sodium loss?

Answer 23

• GI loss
• Hypo-aldosteronism
• Sweat (not usual)
• Diuretics

Question 24

What is hypoaldosteronism? (Addisons disease)

Answer 24

• Low serum aldosterone
• Usually malfunctioning adrenals
• Low Na -> lost in urine
• Low BP
• Pigmentation
• May have high K

Question 25

Why is there high K in hypoaldosteronism?

Answer 25

• 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)

Question 26

What is pseudohyponatremia?

Answer 26

• Hypertriglyceridemia
• Hyperproteinemia
• Osmolality normal in these conditions but sodium is low.

Question 27

What are conditions with water excess?

Answer 27

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

Question 28

Describe the steps of dealing with a hyponatreamia patient?

Answer 28

History:
- Vomiting/diarrhoea
- Dehydration
- Medication

Examination: Fluid status i.e signs of addisions

Osmolality (true vs psuedohyponatremia)

Question 29

Describe what water excess with euvolaemia? and the potential causes:

Answer 29

No signs of dehydration or oedema; JVP not elevated

No evidence of fluid overload
- SIADH
- Polydipsea
- Hypotonic IV
- Diuretics

Question 30

What is a good indicated of water excess/poldipsea in hyponatremia?

Answer 30

• Urine osmolality becomes very low. Usually is is high in hyponatremia

Question 31

What causes syndrome of inappropriate ADH?

Answer 31

ADH release despite not being dry or hypotensive

Caused by:
- Tumours (brain)
- CNS issues
- Drugs i.e SSRIs, diuretics
- Lung disease

Question 32

How can diuretics lead to hyponatremia?

Answer 32

• Low Na with Thiazides
• Na loss with diuretics
• Activate baroreceptors and osmoreceptors = Inc. ADH

= Low Na

Question 33

How does a change in NaCl change the set point of ADH?

Answer 33

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

Question 34

What is the most common cause of low Na in hospital?

Answer 34

Use of hypotonic IV fluid…

Question 35

What are the treatments of hyponatraemia?

Answer 35

Depends on cause:

Dehydrate pt with Na loss -Give Saline

Water excess = Generally fluid restriction i.e 1L a day. Avoid rapid correction

Question 36

Whats a potential consequence of rapid correction for hyponatremia?

Answer 36

Severe osmotic demyelination: = Quadraplegic, loss of consciousness, brainstem damage