2min read - Hyponatremia

A 75 years old female patient known to have hypertension for 10 years admitted with a progressively deteriorating level of consciousness for one day. There was no history of fever, headache, vomiting, diarrhea or trauma. Her medication included aspirin, losartan, HCT and atorvastatin.

Examination revealed a GCS of 9 with no focal neurological deficits. She was mildly dehydrated. Her blood pressure was 140/90 mmHg. Respiratory and abdominal examinations were unremarkable.


What are the possibilities?

• Intracranial vascular events (Stroke/ hemorrhage) 
• less likely in the absence of focal neurological deficits
• Infections - Meningitis/ encephalitis
• Absence of fever and meningism is against, but elderly patients can present without those symptoms
• Seizures
• Nonconvulsive status epilepticus
• Prolonged postictal drowsiness
• Metabolic derangements
• Hypoglycemia
• Particularly hyponatremia

• List down a few more possibilities.

RBS was 127mg/dl. Urgent non-contrast CT of the brain was ordered.

What are the abnormalities?

CT was reported as multiple lacunar infarctions.

What are you going to do?

• Few cortical lacunar infarctions are unlikely to give rise to loss of consciousness.
• However, this finding raises the possibilities of
• Undetected brain stem infarction
• Infarction associated seizure-related condition

As there was no compatible lesion on CT to explain her symptom other basic investigations were ordered. 

WBC - 8.2

Hb - 11.3

Plt - 188

S.Cr - 0.8

Na - 118

K - 3.9

ECG - Mild LVH, no acute ischemic changes

What is the clinical diagnosis?

• Symptomatic hyponatremia

What is the most likely cause?

• It is important to follow a methodical approach to identify the etiology of hyponatremia, which is complicated!
• Therefore, let's only look at a few common causes and features

• First of all patients hydration should be assessed.
• Dehydration indicates sodium loss 
• Urinary loss - Diuretics
• GI loss - Vomiting/ Diarrhoea
• Edematous patient
• Heart failure
• Cirrhosis
• Normovolemic patient
• SIADH (Syndrome of inappropriate ADH secretion)
• Hypothyroidism

• Correct identification of etiology needs the measurement of
• Serum osmolality
• Urine osmolality
• Urine sodium
• Other supportive investigations
• Thyroid functions, Cortisol

In many instances it is multifactorial. The use of drugs alters most of these investigation values. Therefore, sometimes all that matters is somehow raising the Na level.

In this patient, it is most likely due to the combined effects of losartan and HCT.

How are you going to manage the patient?

First of all, if the culprit is a drug - omit it!

• There are few treatment options available

1. Rapid correction with IV hypertonic saline
2. Fluid restriction
3. Oral salt

Which option are you going to use?

• It depends on two factors
• Whether the hyponatremia is acute or chronic
• Patients symptoms

In acute hyponatremia (less than 48 hours) correction should be rapid. But it's quite rare.

In Chronic hyponatremia assess patients symptoms

• The presence of seizure, confusion, reduced level of confusion demands rapid correction.
• For rapid correction IV 3% saline can be used
• Use of boluses is recommended
• 100-150ml over 20 minutes
• Target is a symptomatic improvement
• A rise of few millimoles (3-5) is adequate to get symptomatic improvement.

The patient was given a bolus of IV 3% saline 100ml. There was no much improvement. ABG showed a Na of 120mmol/l. A second bolus of 3% saline given. With that, there was an improvement in GCS. ABG Na rose to 123mmol/l.

What to do after the acute correction of Na?

• Further correction should be gradual
• Maximum recommended correction is
• 8-10mmol within first 24 hours
• further 8mmol (total 18) during next 24 hours
• Methods that can be used
• Fluid restriction is the mainstay of management
• Generally daily fluid intake of 500ml less than the urine output can be tried.
• Calculation of the exact volume of fluid to be given is complicated and requires a urine sodium level. Get endocrinologist's help. (Or call a medical registrar!)
• Oral salt - remember hyponatremia does not equal oral salt!
• If at all give 1-2 mg of oral salt 2-3 times a day.

What is the problem associated with too rapid correction of chronic hyponatremia?

• Osmotic demyelination syndrome / Central pontine myelinosis
• It develops 2-6 days after rapid correction. The patient and doctor have a few days to enjoy the normonatremia!
• The danger is the neurological deficits may be irreversible!
• They include dysarthria, dysphagia, paraparesis or quadriparesis, movement disorders, seizures, locked in syndrome and coma.

What does the MRI show?

This is just an overview.

REMEMBER TO SUSPECT HYPONATREMIA IN PATIENTS ON DIURETICS/ ACEI and ARB. 
It is very common!

Read about 

1. Causes of SIADH and diagnostic criteria

2. Why normal saline cannot be used for correction of hyponatremia in SIADH.