Metabolic acidosis or Metabolic Alkalosis?

Question

A 61 year-old female was admitted to the St. Joseph’s Mercy Hospital with pneumonia. She had been taking a thiazide diuretic for several months. The results of blood tests on admission are given below (reference ranges are given in brackets):

Potassium 2.2 mmol/L (3.5–5.0)

HCO3- 31 mmol/L (24–29)

pH 7.65 (7.35–7.45)

PCO2 4.3 kPa (4.7–6.0)

PO2 10 kPa (12–14.6)

(a) Is an acid-base disorder present, if so what type?

(b) Is there any compensation?

Answer 1

I would argue this is a mixed alkalosis, and it is decompensated. First, the pH is significantly high (alkalosis). We call something decompensated when the pH is significantly out of normal range, along with abnormal other values. We note a relatively low PCO2; this is common for alkalosis that is caused by something respiratory in nature (say, hyperventilation). However, the bicarbonate level is also high, which is a common feature for alkalosis being driven by a metabolic process.

If this were purely respiratory, the bicarbonate levels would be normal. If this were purely metabolic, the PCO2 levels would be normal. Given both are out of whack, we can call it a mix of both.