Question 22.1
The following ventilator waveforms shown below (Figure 1) are from a female patient, ventilated with a volume preset assist control mode for severe respiratory failure. Her predicted body weight is 55 kg and her arterial oxygen saturation is 97%.
Give the likely lung disease for which the patientis being ventilated. (10% marks)
Give three features from this scenario that supports your diagnosis. (30% marks)
College answer
a) Asthma • COPD (Although pressures of 68 cmH2O unusual in COPD)
b) High peak airway pressure • High peak-plateau pressure difference • Continuing expiratory flow at the end of expiratory time (alternatively, 5 l/min flow at endexpiration) • Oxygen requirements (FiO2 0.4) not very high for a patient who requires mechanical ventilation • PEEP zero
Discussion
That image is not the official CICM image, as they do not publish those. It was from my own collection. A ghostly reflection of the author with his smartphone can be seen in the background of the photograph. The original college image is very similar, but of a better quality (they also took the photo on a Siemens Servo-I). The settings and parameters in the original image were:
- Ppeak = 68 cmH2O
- pPlat = 16 cmH2O
- Pmean = 14 cmH2O
- PEEP = 0 cmH2O
- RR = 16
- FiO2 = 40%
- VT = 360 ml
Overall, the image as shown here illustrates severe obstructive airways disease. One can ascertain this from the very high peak inspiratory pressure and the relatively low plateau pressure. Other features which suggest that the ventilated patient has severe bronchospasm include a zero PEEP setting (which is what you'd do for severe bronchospasm with gas trapping) and a very unusual I:E ratio, with an intenstionally prolonged expiratory phase designed to promote CO2 clearance.