Brief but high-yield question-based approach to differential diagnosis in hypercapnic failure.
Analyzing the differentials and management options based on the formula of Alveolar Minute Ventilation:
Alveolar Minute Ventilation = Respiratory Rate x (Tidal Volume - Dead Space Volume)
VA = RR x (Vt-Vd)
DDxing of hypercapnia includes low RR (e.g. opiate use), Low Vt (e.g restrictive lung disease) or high Vd (COPD).