SIADH in Heart Failure

Question 1

2020 stem: A 75yo gentleman with a background of biventricular failure presents to the ED. Investigations are performed and no abnormalities are demonstrated besides a sodium of 125mmol. He is on prazosin, metoprolol and aspirin. Discuss the reason for this investigation finding and the management plan.

You are asked to see an 89 year old male admitted to the hospital with biventricular heart failure. His results from ED show a plasma sodium of 128 mmol/L. The other results are normal. His medications include metoprolol, prazosin, and aspirin. How would you approach and manage this situation?

Answer 1

This likely represents hypotonic, hypervolaemic hyponatraemia in the context of heart failure.

This is likely to have occurred in the setting of fluid overload secondary to congestive cardiac failure (get increased ADH release due to impaired cardiac output)

DDx for hyponatraemia;

• Hypovolaemic: mineralocorticoid deficiency (Addison’s disease), diarrhoea, vomiting, 3rd spacing
• Euvolaemic: SIADH, medications, beer potomania, reduced salt intake (tea and toast diet).
• Hypervolaemic: Renal failure, liver failure, heart failure, albumin-losing enteropathy

Goals of management:

• ascertain whether chronic or acute hyponatraemia
• assess for serious complications of hyponatraemia
• correct electrolyte deficiencies in safe manner
• treat underlying heart failure

Question 2

Hyponatraemia - History

Answer 2

History:

• PC: distinguish between mild to mod - severe: LOC, seizures, fatigue, muscle cramps, weakness, nausea/vomiting
• sx of heart failure: nocturnal dyspnoea, orthopnoea, lower limb oedema, chest pain/angina, other potential causes of heart failure decompensation
• assoc: HTN sx, palpitations/irregular heart rate,
• RED FLAGS: LOC, confusion, gait ataxia (severe)
• PMHx, Surgical Hx
• Medications: non-compliance, anticholinergics (bradycardia), CCBs (peripheral oedema), anti-inflammatories/steroid medications - can lead to fluid retention but also cardiac/renal complications
• Fluid status: Inputs, outputs

Question 3

Hyponatraemia - Examination

Answer 3

Exam:

• ABCDE approach
• Fluid status: Weights, urine output, HR, BP, skin turgor, mucous membranes - assess whether hyper/hypo/euvolaemic
• Cardiovascular examination
• Neurological examination

Question 4

Hyponatraemia - Investigations

Answer 4

Investigations:
Bedside: Urine osmolality, urine sodium UA, VBG, BSL, ECG for features of acute cardiac changes, CXR
Bloods: serum osmolality, UEC, CMP, TSH, FBC, trops, BNP, iron studies
Imaging: Consider MRI brain

HF investigations: TOE/TTE

Question 5

Hyponatraemia - Management

Answer 5

Management:
Disposition
- Determined by clinical severity, ICU if critical, otherwise cardio for HF management

Heart failure
- POND
- add fluid restriction;
   o gentle diuresis + fluid restriction should not worsen hyponatraemia as there is greater water excretion than salt excretion.
- further optimisation of 

Supportive

• daily weights
• regular obs, neuro obs for deterioration

Hyponatraemia
Hypovolaemic
- Fluid restriction (<500mL/day)
- Electrolyte replacement (3% hypertonic saline), aim for SLOW particularly if chronic hyponatraemia (risk of demyelination and chronic neurology)

Euvolaemic
- fluid restriction (500mL less per day)

Hypervolaemic

• fluid restriciton
• diuresis (frusemide - gentle)