Question 1:

PH = 7.56, that is moderate alkalaemia

PO2 = 55, slightly high for a venous gas. However, venous PO2 is not a reliable figure.

PCO2 = 26 (<40), so we have respiratory  alkalosis.

Next we calculate the compensation. The compensation for respiratory alkalosis is different between acute and chronic cases.

For acute respiratory alkalosis, HCO3 will drop by 2 for every 10 PCO2 below 40

For chronic respiratory alkalosis, HCO3 will drop by 5 for every 10 PCO2 below 40.

We know pregnancy is on of the causes of respiratory alkalosis due to progesterone stimulation of the respiratory centre, also the growing fetus produce extra CO2 that the mother body need to exhale.

Accordingly, we are going to assume that the patient has chronic respiratory alkalosis.

According to that, expected HCO3 should be 24 – (40 – 26) x 0.5 = 17. The number that we have here is 20 (lower than expected).

For acute respiratory alkalosis, expected HCO3 should be 24 -(40-26) x 0.2 = 21.2. This number is higher than what we have.

Accordingly this patient has combine Acute and chronic respiratory alkalosis.

Other findings

The only other abnormal finding on this blood gas is K = 3.3 mmol/L. This is mild hypokalaemia. Hypokalaemia is usually happens with alkalosis due to K shift inside the cells (H+ outside and K+ inside the cells).

Question 2

For Respiratory Alkalosis, we follow the mnemonic (CHAMPS).

C = CNS causes

H = Hypoxia (pulmonary causes).

A = Anxiety or Pain

M = Mechanical ventilation

P = Pregnancy/Progesterone

S = Salicylate or sepsis.

This patient had chronic respiratory alkalosis due to her pregnancy the she developed acute respiratory alkalosis as she was anxious and hyperventilating.