An elderly man with critical illness, shock and hypoperfusion. His blood test shows:
High anion gap metabolic acidosis
Delta ratio = 1, pure AG metabolic acidosis
Appropriately compensated
corrected Na = Na + (Glucose-10)/3 = 168, patient has severe hypernatraemia (with pseudo hypernatraemia)
Renal failure – check previous, likely a component of acute on chronic
Corrected K for acidosis = 4.5, which is normal
Osmolality = 2XNa + Urea + Glucose = 356 mmol even without the urea result
Patient has all the features of HHS:
altered mental state
acidosis (NAGMA)
Pseudohypernatraemia
Glucose > 15 but not as high as expected with DKA
hyperosmolar state (>320)
in addition – elderly patient, but must check ketones
2.
HHS usually develops over a course of days to weeks, unlike diabetic ketoacidosis (DKA), which develops more rapidly, over the course of a few days. Often, a preceding illness results in several days of increasing dehydration. Adequate oral hydration may be impaired by concurrent acute illness (eg, vomiting) or chronic comorbidity (eg, dementia, immobility).
3.
Fluid – up to 9 litres deficit, give slowly after initial resuscitation, normal saline is ok as it is hyponatraemic with respect to the patient’s sodium
Monitor K an dreplace once below 4
Treat underlying cause
aim for normal pH, gluocose
is it not the case that correcting the sodium involves adding a third of the glucose value rather than subtracting it? that would increase the calculated anion gap too.
Correcting for pseudohyponatraemia involves adding a correction factor to the sodium. Correction factor, based on the glucose is (glucose-10)/3.
Using the corrected sodium in anion gap calculations gives an erroneously high sodium which may then lead to an erroneously elevated anion gap.
Interesting that this patient has a pseudohyponatraemia even though his sodium is elevated.
Thanks for the comment, post has been updated