Answer for lab case 346
PH = 7.25, that is moderate acidaemia.
PCO2 is 50 mmHg, that is high so we have respiratory acidosis.
HCO3 is 22, that is low so we have metabolic acidosis.
We don’t have enough information about the respiratory condition for this patient. Therefore we are going to consider metabolic acidosis as the primary process.
For metabolic acidosis, we need to calculate the anion gap and check the compensation.
Anion gap = Na – (Cl + HCO3) = 139 – (109 + 22) = 8, so we have NAGMA.
respiratory compensation for metabolic acidosis is calculated with Winter’s formula. That is: expected pCO2 = 1.5 x HCO3 + 8 (+/- 2). Accordingly, expected pCO2 should be between 39 and 43. So we have additional respiratory acidosis (We figured this earlier).
BSL = 21, that is hyperglycemia…
Na = 139, with hyperglycemia we get pseudohyponatraemia. To calculate the corrected Na level we use the following formula:
Corrected Na = Measured Na + (Glucose – 5)/3. Accordingly, the corrected Na level will be 144. Still with in normal range.
K level gets affected by changes in PH. Usually serum K level increase by 0.6 mmol/L for every 0.1 PH below normal (7.35). Accordingly, the corrected K level will be 4.7 mmol/L.
Cl level is high(109), hyperchloraemia.
Urea and creatinine level are elevated. Now we will calculate the Urea/ Creatinine ratio to develop an idea about the location of the renal failure. The equation that we use is:
Urea x 1000/ Creatinine = 20 x 1000/258 = 77.5
Level between 40 – 100 that will be either normal or post renal. (Level less than 40 usually indicates a renal cause while level above 100 indicates pre-renal cause).
Lactate = 2.9 (Can be a feature of poor tissue perfusion).
Also we can calculate serum osmolarity for this patient, that is:
Na x2 + Urea + Glucose = 319. Very high. Normal serum osmolarity level is 285 to 295. This patient is dehydrated.
Final conclusion: Combined NAGMA and respiratory acidosis associated with hyperglycemia and renal impairment.
The cause of NAGMA in this patient. Using the USED CARP mnemonic
- Small bowel fistula
- Excess Chloride, possible.. Cl level is 109.
- Diarrhoea, most likely to be the cause in this patient
- Carbonic anhydrase inhibitors
- Renal tubular acidosis
- Addisson’s disease
Although this patient has hyperglycemia with dehydration and increased serum osmolarity. The numbers don’t the diagnostic criteria for HHS.
- Serum osmolarity > 320mosmol/L
- Serum glucose > 33mmol/L
- profound dehydration (elevated urea:creatinine ratio)
Also ketone level is not provided.
However, the management is the same..
- Stablise the patient, correct vital signs
- Correct fluid deficiency. Expect 6-9 L of fluid deficiency.
- Correct Hyperglycemia, using insulin intravenously.. The dose is depending on Ketones level.. If ketones level is more than 3 mmol/L then we use dose of 0.1 Unit/ kg(Treat as DKA). If ketones level is less than 3 then use 0.05 unit/ Kg.
- look and treat the precipitating cause.