Hypernatremia

HOSP # WARD Red Cross Children’s Hospital ICU
CONSULTANT Dr. S
Prof. G		 DOB/AGE 14 day old Neonate

Abnormal Result

Sodium = 198 mmol/L (H) (136-145)

Presenting Complaint

1 day of poor feeding.  Child passing very hard/ dark brown stool for the preceding 10 days.

History

Birth weight @ term: 3.380kg.  Delivered vaginally after induction of labour because of spontaneous rupture of membranes at 40 weeks gestation. Discharged home without any problems after 1 day.

Examination

On arrival at district hospital: Temp: 38oC, Sats 96% on Nasal O2, Finger prick glucose: 10mmol/L, Capillary refill time: 6 seconds,

HR: 140bpm. 

Blood gas:

pH: 7.26,

BE -16.3,

pCO­2 3.2 kPa,

Na 190.

Weight: 2.2kg (birth weight: 3.380 kg, thus 35% weight loss)

Laboratory Investigations

Other Investigations

Urine organic acid analysis by GCMS demonstrates elevation of the liver markers 4-OH-phenyllactate and 4-OH-phenylpyruvate together with lactaturia. Succinylacetone, a marker for tyrosinaemia type 1 is absent. Moderate ketonuria with elevated dicarboxylic acids C6, C8, and C10 is also present, these changes suggest a lipolytic response to catabolic or fasting stress or hypoglycaemia together with underlying hepatic dysfunction with lactataemia but are non-specific for an IMD per se. 

Final Diagnosis

Patient was pure water depleted with a sodium concentration of 198 mmol/L.  The mother was not lactating adequately despite the infant sucking well, evidenced by the fact that when expressed breast milk was tried, there was too little milk for the baby to drink.  The nurses’ notes confirmed this finding.  This finding also confirms the failure to produce stool volume and the normal urine organic acid profile with evidence of starvation / fasting stress.

Take Home Messages

When considering a patient with high plasma sodium concentration it is
important to bear in mind:

  1. Hypernatremia does not necessarily indicate an excess of extracellular sodium.  Except in rare cases of salt overload most patient with hypernatremia have a deficiency of both water and sodium, with the water deficiency being proportionally higher than that of sodium.
  2. Patients become hypernatremic because the water lost from the body exceed the intake and there is negative fluid balance.  The amount of water which a person can drink generally exceeds by far the amount lost from the body in most pathological fluid-losing disorders, eg. Diarrhoea, sweating.  Patients thus become hypernatremia due to:
    1. Too old, young or sick to drink
    2. Obstruction of oesophagus
    3. Disorders of thirst centre
    4. No access to water                          

Ref: Walmsley – Cases in Chemical Pathology 4th
ed.

It is also important:

  1. To calculate the Osmolar gap( difference between calculated and measured osmolarity)
  2. U:P osmol (>1 = hypotonic fluid depletion, pure water loss or salt gain; ~1 = osmotic diuresis; <1 = diabetes insipidus ~the various causes of nephrogenic and neurogenic DI)