Question

"You're asked to review a 59-year-old female who has been admitted the acute medical ward of your hospital. The nurse tells you that she appears short of breath despite currently receiving 3 litres of oxygen via nasal cannulae. You take an arterial blood gas with the patient on oxygen and the results are shown below:

PaO_2: 9.1 kPa (68 mmHg)
pH: 7.36
PaCO_2: 8.4 kPa (63 mmHg)
HCO_3-: 29 mmol/L
BE: +4
Does this blood gas suggest an acute or chronic derangement in CO2?"
(A) Acute respiratory acidosis
(B) Chronic respiratory acidosis
(C) Acute respiratory alkalosis
(D) Chronic respiratory alkalosis

Answer 1

The blood gas results suggest chronic respiratory acidosis due to the elevated PaCO2, slightly low pH, and compensated high bicarbonate levels.

Step-by-step explanation:

The arterial blood gas results indicate that the 59-year-old female patient is experiencing respiratory acidosis. This is deduced by looking at her raised PaCO2 value of 8.4 kPa (63 mmHg), which is higher than the normal range for female patients (32-45 mm Hg). The patient's pH is 7.36, which is on the lower end of the normal range and indicates acidemia, but not fully outside the normal pH range of 7.35-7.45. The elevated bicarbonate (HCO3-: 29 mmol/L) and the base excess (BE: +4) suggest the presence of compensatory mechanisms, where the kidneys retain bicarbonate to counterbalance the excess CO2, thus indicating a chronic process rather than an acute event.