Question 1:
PH = 7.26 that is acidaemia.
HCO3 = 21 (<24) so we have metabolic acidosis. Once we decide it is metabolic acidosis, then we need to calculate the Anion Gap and the compensation.
Anion Gap = (Na – (HCO3 + Cl)) that is (121 – (21 + 84)) = 16 (>12) So, we have high anion gap metabolic acidosis.
Then we calculate the compensation using Winter’s formula, That is: expected PCO2 = 1.5 x HCO3 + 8 +/- 2 = 39.5. PCO2 in this case is 48 So, we have additional respiratory acidosis.
Because we have metabolic acidosis, we need to calculate the delta ratio to exclude additional metabolic process. Delta ratio is calculated as (AG-12) / (24 – HCO3) = 1.333. (ratio between 0.8 – 2, So we have pure HAGMA).
Other abnormal findings on these blood gases:
Na = 121 mmol/L, this is moderate hyponatraemia (between 120 – 125), from the history this lady had normal blood tests 5 days ago. Accordingly it is most likely to be acute hyponatraemia ( Seizure is an uncommon presentation in chronic hyponatraemia).
Lactate = 7.1 mmol/L, that is high. Possibly related to the seizure, however we don’t have enough information to confirm that.
BSL = 9.5 mmol/L, that is mild hyperglycemia.
The final conclusion, We have combined high anion gap metabolic acidosis and respiratory acidosis most likely caused by high lactate level secondary to seizure. The seizure is caused by acute moderate to severe hyponatraemia.
Question 2:
When we are dealing with hyponatraemia we need to consider the following
- Severity
- speed of development (Acute vs Chronic).
- Cause (and treat it)
- complications (prevent and treat them)
Question 3:
Since the seizure has stopped then there is no need to use the rapid reversal therapy, that is 100-150 ml of 3% N/S over 10-15 minutes until seizure stops.
Instead we give the patient 1 ml/Kg/hr. (based on lean body weight). Check Na level every 4 hours. continue with this therapy until symptoms resolve or Na level is 125 mmol/L or more.
We can also add Frusemide 20 mls IV.