Friday, February 20, 2009

All exhalation valves are not created equal.

The new design of ventilator exhalation valves (e.g. active, floating) allows for unhindered spontaneous breathing during APRV. The valve prevents the ventilator from terminating the inspiratory phase and losing mean airway pressure during coughing or exhalation.
  • Can the exhalation valve design influence patient comfort and interaction? 

Each manufacturers exhalation design is different.

Draeger and Maquet uses a type of "pressure threshold resister".
  •  During inspiration a preset degree of force (pressure) against the exhalation valve keeps it seated proportional to the operator desired set pressure.
  • Should the patient want to exhale or cough prior to the inspiratory time being reached, the valve releases any excess pressure. 
Hamilton Medical and Puritan Bennet uses a type of electromagnetic valve for its exhalation valve design.
  • Uses known electrical current (force) relationships, expiratory pressure, flow monitoring, and algorithms to determine when to release excessive pressure. 
Is one design superior than the other in regards to ease of pressure release, expiratory resistance, and pressure over-shoot? 
Some medical device vendors (e.g. Draeger) argue that their product is superior and state that it is more responsive due to that it does not require a feedback loop to determine if excessive pressure should be released. 
  • Researchers reveled no statistical differences when comparing the Evita XL, PB 840, and Servo-I in regards to ease of pressure release and pressure over-shoot. 
  • There are differences when evaluating expiratory resistance. In one bench study (1) researchers discovered that the Evita XL had the highest exhalation resistance. 
  • There are no studies in regards to patient interaction and comfort, at this time. 
Exhalation valve actions are similar when comparing ease of pressure release and pressure over-shoot. There are differences in design and expiratory resistance, however there are no studies identifying if these differences influence patient interaction or comfort. 

  1. Jiao, G-Y. and Newhart, J. (2008). Bench Study of Active Exhalation Valve Performance. Respiratory Care. 53 (12): 1697-1702.