The figure below illustrates a  airway pressure waveform of a single breath during volume controlled ventilation, incorporating an end inspiratory pause and an auto-PEEP manoeuvre.

a)  What do the variables A, B, C & D indicate?

b)  What will determine the slope of the pressure curve between points Aand B?

c)  What are the factors which determine variable B?

d)  If the delivered tidal volume was 600 ml, what is the calculated static compliance?

e) List 2 adverse consequences of an increase in the value of variable D?  .

f) List the change(s) you would make to the ventilator settings to treat an increase in the value of variable D.

a)  What do the variables A, B, C & D indicate?

A- PEEP, B- PIP, C- Plateau pressure, D- Auto PEEP

b)  What will determine the slope of the pressure curve between points Aand B?

Inspiratory flow pattern

Inspiratory flow rate

c)  What are the factors which determine variable B?

Resistance, compliance, tidal volume, PEEP, insp flow rate and flow pattern

d)  If the delivered tidal volume was 600 ml, what is the calculated static compliance?

30 ml/cm water  [TV/(Plateau-PEEP)]

e) List 2 adverse consequences of an increase in the value of variable D?  .

Decrease in cardiac output, barotrauma

f) List the change(s) you would make to the ventilator settings to treat an increase in the value of variable D.

Increase expiratory time

Decrease I:E ratio, decrease RR, reducing MV

## Discussion

This question is identical to Question 17.3 from the first paper of 2010.

a) Variable B is the peak airway pressure. This variable is determined by the lung compliance, tidal volume, airway resistance and PEEP.

To some extent the flow patern also matters (the higher the inspiratory flow, the greater the contribution from airway resistance)

b) The calculation of compliance is not something we do every day, but people should probably be at least dimly aware of the equation which is involved. Compliance is pressure required per volume of lung distension; thus one can calculate it by dividing the tidal volume by the diference between the pleateau pressure and PEEP.

c) Variable D is the Auto-PEEP. This patient is gas-trapping.

In order to address this one, one can

• minimise PEEP
• decrease the I:E ratio to 1:4 or so
• increase the inspiratory rise time
• decrease the respiratory rate
• decrease the tidal volume

### References

References

Dubbert, Patricia M., et al. "Increasing ICU staff handwashing: effects of education and group feedback." Infection Control and Hospital Epidemiology(1990): 191-193.

Panhotra, B. R., A. K. Saxena, and Al-Ghamdi AM Al-Arabi. "The effect of a continuous educational program on handwashing compliance among healthcare workers in an intensive care unit." British Journal of Infection Control 5.3 (2004): 15-18.

Mayer, Joni A., et al. "Increasing handwashing in an intensive care unit."Infection Control (1986): 259-262.

Naikoba, Sarah, and Andrew Hayward. "The effectiveness of interventions aimed at increasing handwashing in healthcare workers-a systematic review." Journal of Hospital Infection 47.3 (2001): 173-180.

Kaplan, Lois M., and Maryanne McGuckin. "Increasing handwashing compliance with more accessible sinks." Infection Control (1986): 408-410.

WHO have this statement: A Guide to the Implementation of the WHO Multimodal Hand Hygiene Improvement Strategy (2009)