A case, many questions,

and hopefully a few answers…

Chris NicksonEmergency Registrar, PMH

19 August 2010

The Case

• 10 year-old boy, previously well except for a history of enuresis

• BIBA after a first episode generalized tonic-clonic convulsion

• tired in the morning but still went to school sports competition

• While getting ready to compete he collapsed and had a self-limiting seizure (5 min)

In the ED

• Afebrile• GCS 13 (E3 V4 M6) (fluctuating) for about 4

hours without improvement • PERL, no focal neurological deficits• vomited x 5, but clinically euvolemic• CT head was normal• After the scan he had another self-limiting

seizure (2 min)

Lab results

• UECNa 125 K 4.1Urea 3.7 Cr 49

• FBC normal• LFTs normal

• VBGpH

7.37 PCO2 42 HCO3 24 Cl

96 glc 7.2 lac 1.9

Question -Is the sodium of 125 mmol/L

likely to be significant?

Symptoms of hyponatremia

• UpToDate says typical symptoms of hyponatremia are:

<125-130 mmol/L – nausea malaise

• <115-120 mmol/L – headachelethargyobtundationseizurescomarespiratory arrest noncardiogenic pulmonary edema

But…

• Symptoms correlate poorly with degree of hyponatremia

• May vary depending on: starting sodium concentration rate of decrease

For instance…

• A RAPID drop in Na of 140 to 125

SYMPTOMS

• A SLOW drop in Na of 130 to 115

NO SYMPTOMS

Question –How can we find out if the Na

125 mmol/L is important in this case?

Fix it and see what happens!

• 3mL/kg of 3% saline over 30 minutes• Immediately following this infusion he was

alert with a GCS 15 and had no further vomiting

• His only complaint was a mild headache that improved after paracetamol

Question -Was it safe to give hypertonic

sodium?

What we fear…Fleming JD, Babu S. N Engl J Med 2008; 359:e29

Weighing the risks

• Most likely acute hyponatremia• The brain adapts

– extrudes intracellular osmolytes to guard against cerebral edema

– Occurs over about 2 days• Risk of osmotic demyelination syndrome is

minimal until adaptation occurs

Weighing the risks

• Give hypertonic saline to patients with significant symptoms of hyponatremia regardless of how low the sodium is– AMS– Seizures– Coma– Noncardiogenic pulmonary edema

Question -How rapidly should

hyponatremia be corrected?

Rate of correction

• Aim to increase sodium by 1-1.5 mmol/h for 2 or 3 hours– a small rise can markedly improve symptoms

• Sodium should not be increased by more than: 12 mmol/L over 24h 18 mmol/L over 48hLower rates are advised for high risk patients

More Lab tests…

• Serum cortisol 1100 nM (60-420)TFTs normalOsmolality plasma 265 mmol/kg L (275-295)Spot urine sodium 209 mMSpot urine osmolality 681 mmol/kg (50-1200)

Question -What do these results suggest?

Syndrome of Inappropriate ADH Secretion

• Low plasma osmolality• urine osmolality > plasma osmolality

(usually >300-400 mosmol/kg)• Urine sodium usually >40 meq/L• Normal acid-base and potassium balance• Normal renal, liver, adrenal & thyroid function• Diuretics are not in use• improves with water restriction

Question -How does ADH cause

hyponatremia?

ADH (aka vasopressin) action

• promotes water reabsorption from the collecting ducts of the kidney

• activates the vasopressin V2 receptor • aquaporin-2 water channels translocate from

intracellular sites to the luminal membranes of the principal cells

• end result is concentrated ‘water-poor’ urine and dilute ‘water-rich’ blood

Question -But SIADH is not a diagnosis…

What is the cause?

Causes of SIADH

• CNS disorders• Pulmonary disorders • Ectopic ADH secretion by a tumour –

lung cancers (especially small cell lung cancers), others less common

• Major surgery • Many drugs

In fact, the patient has none of these!

Question -What can mimic SIADH?

SIADH mimics

• Hereditary vasopressin receptor abnormalities (‘nephrogenic SIADH’)

• Cerebral salt wasting• Exogenously administered vasopressin

agonists – Vasopressin– Desmopressin– Oxytocin

The Answer…

Remember the history of enuresis?

They all lived happily ever after…

• A nightly nasal spray of desmopressin was started 4 days prior for nocturnal enuresis

• His parents encouraged him to ‘drink lots of water’ before competing

• Over the next 12-24 hours he had a large diuresis, his laboratory values all normalized and he remained well

Question -Is hyponatremia a serious risk when treating enuresis with

desmopressin?

Robson WL et al. The comparative safety of oral versus intranasal desmopressin for the treatment of children with nocturnal enuresis. J Urol. 2007 Jul;178(1):24-30.

• Hyponatremia resulting from treatment of enuresis with desmopressin– No reports in 21 clinical trials– 48 case reports (all nasal route)– Post-marketing safety data: 145 nasal, 6 oral cases

• Risk factors– High fluid intake, age <6 years, high dose, other

medications (e.g. anticholinergics)

THE END

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