Laura Adams RANKING question.

An elderly patient on the ward has RR 16, HR 65, temp 37.5 degrees C. His blood gases are pH 7.35 (7.35-7.45), pCO2 9.0 (4.7-6 kPa), pO2 8.1(10.0-13.3 kPa),  HCO3 45 (22-30). Rank the underlying diseases below in order of likelihood, going from most to least likely:

Pulmonary embolism
Tension pneumothorax
COPD
Hyperventilation
Pneumonia

Answer:
1. COPD
2. Pneumonia
3. Pulmonary embolism
4. Tension pneumothorax
5. Hyperventilation

Explanation: this is a picture of respiratory acidosis with metabolic compensation. Hyperventilation would cause alkalosis so is least likely. A tension pneumothorax would not have time to establish compensation so is next least likely. The carbon dioxide is high and the oxygen is low so this is type 2 respiratory failure with no v/q mismatch. while a number of small PEs might result in compensation over time they would give a type 1 picture with low oxygen and normal carbon dioxide. Both pneumonia and COPD might give this blood gas picture but this patient's vital measurements show no sign of infection so COPD is most likely.