A child, seizures and sodium

A case, many questions, and hopefully a few answers…
Chris NicksonEmergency Registrar, PMH19 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 x5, but clinically euvolemic
CT head was normal
After the scan he had another self-limiting seizure (2 min)

Lab results
UECNa 125K 4.1Urea 3.7 Cr 49
FBC normal
LFTs normal
VBGpH7.37 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 125SYMPTOMS
A SLOW drop in Na of 130 to 115NO 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 hyponatremiaregardless 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 by1-1.5 mmol/h for 2 or 3 hours
a small rise can markedly improve symptoms
Sodium should not be increased by more than:12mmol/Lover 24h18 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 translocatefrom 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 daysprior 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 ENDhttp://lifeinthefastlane.com

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A child, seizures and sodium

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