Question 30

College Answer

(A) List 2 causes for this end-tidal CO2 pattern.

♦  Kinked/partially occluded tube
♦  Foreign body in airway
♦  Obstruction of expiratory limb of breathing circuit
♦   Bronchospasm

(B) List 2 causes for this end-tidal CO2 pattern

♦  Decreased respiratory rate
♦  Decreased tidal volume
♦  Increasing metabolic rate (fever, shivering, etc)

(C) Draw and label a pressure-time ventilator waveform showing- (i) normal followed by
(ii) increased airway resistance.

(D) Draw and label a pressure-volume loop (volume targeted ventilation) showing-

(i) normal lung compliance
(ii) decreased lung compliance
(iii) increased lung compliance.

(E) Draw and label the following for a patient with a large cuff leak-

(i) Flow-time waveform
(ii) Volume-time waveform

Discussion

Helpfully, the college answer provides us with some model diagrams. Unhelpfully, the college question omits the EtCO2 curves. I have tried to put together some EtCO₂ curves to remedy this. So long as everybody is aware that this is not the college image.

Though this is a simple pattern recognition question, some references seem in order. The following local chapters discuss waveform interpretation:

• End-tidal capnometry waveform interpretation
• Analysis of ventilator waveforms
• Pressure-volume and flow-volume loops

End-tidal CO₂ patterns are also discussed on this website by Carefusion.