Canadian Journal of Anesthesia, Vol 19, 217-226, Copyright © 1972 by Canadian Anesthesiologists' Society

The Effects of Adding a Positive Expiratory Pressure Plateau (P.E.P.P) with Controlled Ventilation with a Bird Mark 7 Or Mark 8 Ventilator

¹ Department of Anaesthesia, University of Toronto

The effects of adding a P.E.P.P. to controlled ventilation of a test lung with a Bird Mk 7 and Mk 8 ventilator, with the air-mix venturi in use, have been studied.

P.E.P.P. causes

(1) Increased resistance to the bleed-off pressure of the expiratory time cycling mechanism and

(2) Increased resistance to venturi flow.

These effects induce the following changes:

1. A gross change in percentage of oxygen delivered

2. A decrease in tidal volume

3. An increase in expiratory time

4. A decrease in inspiratory time

5. An alteration of flow characteristics.

The effects vary in magnitude with the amount of P.E.P.P. and the characteristics of the individual machine. The effects range from moderate disturbance of ventilator function to complete non-function. Even by making adjustments to the machine to produce the original tidal volume, the expiratory time effects and inspired gas percentage effects cannot be overcome.

Therefore, to use P.E.P.P with controlled ventilation with a Bird Mk7 or Mk8, the ventilator must be driven with a pre-mixed gas of required oxygen concentration without use of the venturi. Even so, detrimental changes in the performance of the expiratory time cycling mechanism are to be anticipated.

Note:

Presented at the Annual Meeting, Canadian Anaesthetists' Society, Quebec, June 1971.