Overview of SIADH and management

1. SIADH
By Hiren Divecha
FY2
Hairmyres Hospital
1/5/2007

2. Sodium
• Needed for:
1. Nerve conduction
2. Co-transport of metabolites
• 135-146 mmol/L
• Regulation
– Thirst
– ADH
– RAAS
– ANP & BNP

3. Euvolaemic
Hyponatraemia
Hypervolaemic Hypovolaemic

4. Hypovolaemic Euvolaemic Hypervolaemic
Extracellular Na ↓ N ↑
TBW Slightly ↓ Slightly ↑ ↑↑
Causes Renal Thiazides CCF
•Diuretics
•Osmotic diuresis SIADH Liver failure
(glucose, urea,
mannitol) Glucocorticoid def Renal failure
•Addison’s
•Salt-wasting neph Hypothyroidism Nephrotic
syndrome
Gut Primary polydipsia
•Vomiting Pregnancy
•Diarrhoea iv dextrose
Other Sodium-free irrigant
•Haemorrhage
•3rd space loss (BO,
burns, peritonitis,
pancreatitis)

5. Causes of SIADH
Neoplastic Pulmonary CNS Drugs Other
Lung Infection Infection AVP analogues Idiopathic
•Small cell •Pneumonia •Abscess •Desmopressin
•Mesothelioma •Abscess •Meningitis •Oxytocin Hereditary
•TB •AIDS •Vasopressin (V2 receptor)
GI •Aspergillosis
•Stomach Bleeds Stimulate AVP
•Pancreas Asthma •Subdural release/action
•SAH •SSRIs
GU Cystic Fibrosis •Antipsychotics
•Bladder CVA •Anti-epileptics
•Prostate PPV •NSAIDs
•Endometrium Head trauma •MDMA
Thymoma MS, GBS
Leukaemia
Lymphoma Shy-Drager
Sarcoma

6. Clinical Features
<120 mmol/l <110 mmol/l
– Dysgeusia • Drowsiness
– Lethargy • Confusion
– Anorexia • Depressed reflexes
– Nausea, vomiting • Extensor plantar responses
– Irritability • Seizures
– Headache • Coma
– Cramps • Death
– Muscle weakness

7. Criteria for SIADH
• Bartter and Schwartz (1967)
– Hyponatraemia
– Clinically euvolaemic
– No diuretic use
– Serum osmolality <275mOsm/kg
– Urine osmolality >100 mOsm/kg
– Urine sodium >40mmol/L
– Normal thyroid, adrenal and renal function

8. Management - acute
• Benzodiapines
• Aim for 1-2mmol/L/hr initially
– Resolution of neurology
– Slow replacement (10 mmol/L/day)
• Frusemide (free water excretion)
• Find and treat cause

9. TBW = weight * 0.5 (girls)
= weight * 0.6 (guys)
Na+ to replace = desired change in Na+ * TBW
Rate of Na+ replacement =
rate of desired change * TBW
Rate infusion =
Rate of Na+ replacement / (conc of infusate)

10. As a rough guide
• To increase Na+ by 1mmol/L/hr
– 1 ml/kg/hr of 3% saline
– 1.7 ml/kg/hr of 1.8% saline
• Max. rate = 70 mmol of Na+/hr
• Monitor U&E 2 – 3 hourly

11. Management - Chronic
• Risk of osmotic demyelination if change is
>12mmol/L/day
• Symptomatic
– Aim for lower rate of correction (0.5mmol/L/hr)
• Asymptomatic
– Fluid restrict
– Demeclocycline
– Oral urea

12. Fluid restriction
(Urinary Na + Urinary K) / Plasma Na
• >1
– <500ml/day
• 1
– 500-700ml/day
• <1
– <1L/day

13. Vasopressin Receptor Antagonists
• RCTs showed sustained increase in plasma Na
compared to placebo
• Risk of hypotension with non-selective
antagonists
• V2 selective antagonists in trials
• No reports of osmotic demyelination

14. Osmotic Demyelination Syndrome
• Central pontine + extrapontine
• Over-enthusiastic correction of Na+
• In chronic hyponatraemia
– Brain tissue losses inorganic and organic solutes
– Takes few days
• Predisposing factors
– Alcoholism
– Malnourishment

15. Osmotic Demyelination Syndrome
• Demyelination
• Pontine symptoms
– Dysarthria, dysphagia, pseudobulbar palsy
– Flaccid quaraparesis
• Extra-pontine
– Tremor, ataxia, mutism
– Parkinsonism, dystonia
• Reversible ?
– 5% dextrose and desmopressin

17. References
1. “The syndrome of inappropriate
antidiuresis”, Ellison et al, NEJM,
2007;356(20):2064-72
2. “Hyponatraemia”, Adrogue & Madias, NEJM,
2000;342(21):1581-89