College Answer

What pathological process is revealed by this flow time trace?

- The trace reveals the commencement of inspiration before expiratory flow returns to zero, thus setting the scene for dynamic hyperinflation/ small airway obstruction. (Importantly, the trace does not reveal Auto-PEEP as that is a pressure measurement performed after an expiratory pause)

b)  List 4 other features (both clinical and adjunctive tests) may support the diagnosis of this pathological process?

• Clinical: On auscultation, commencement of inspiration before end of expiration
• Evidence of obstructive lung disease, the typical scenario in which this happens
• Increased Auto PEEP
• Increased Plateau pressure
• Ventilator settings such as short exp time f) VEI > 20 ml /Kg

c)  List 2 therapeutic measures you will undertake on observing this phenomenon.

•  Bronchodilators
•  Increase exp time

Discussion

This is another in the long line of questions which ask the candiate to interrogate the flow/time waveform and make the diagnosis of airflow limitation.

Yes, yet again the flow curve fails to return to zero, demonstrating incomplete emptying and possibly gas trapping.

Again, 4 features of this are asked for. One could produce many more.

• wheeze
• prolonged expiratory phase
• increased chest distension
• decreased chest expansion
• bilaterally decreased air entry
• increased autoPEEP in the expiratory hold manoeuvre
• increased peak airway pressures
• increased plateau pressures
• short expiratory time setting on the ventilator

Again, suggestions for management are asked for.

Apart from adjusting the ventilation (decreasing the I:E ratio and respiratory rate) one may consider using bronchodilators and steroids.