2004 OPEN FORUM Abstracts
INSPIRATORY RISE TIME affects PEAK inspiratory FLOW AND TIDAL VOLUME delivery
J. Sollars RRT, John D. Davies RRT, Damian M. Craig MS, Michael
A. Gentile RRT, Ira M. Cheifetz MD FAARC. Duke University Medical
Center, Durham, NC.
Background: Inspiratory rise time, a feature available on many mechanical ventilators, allows adjustments in the speed of flow at the initiation of inspiration in pressure targeted modes. However, not all ventilators adjust rise time in the same manner. We hypothesize that altering the inspiratory rise time will affect peak inspiratory flow (PIF) and tidal volume (Vt) delivery.
Methods: Five mechanical ventilators (Puritan Bennett 840, Viasys Avea, Respironics Esprit, Siemens SV300, Viasys Bear 1000) were evaluated. PIF, Vt, and peak inspiratory pressure (PIP) were studied from the slowest to fastest rise time settings available for five minutes on each ventilator. Each ventilator was connected to a test lung (TTL, Michigan Instruments, Grand Rapids, MI.) with a compliance of 0.05 l/cm H2O and a respiratory mechanics monitor (NICO, Respironics-Novametrix, Wallingford, CT). Ventilators were set in the Pressure Control mode: inspiratory pressure 15 cm H2O, PEEP 5 cm H2O, inspiratory time 1.0 seconds, rate 15 bpm, and FiO2 0.40.
Results: PIF and Vt increased with the faster inspiratory rise time for each ventilator studied. A variable range of PIF and Vt was demonstrated. The set PIP was not exceeded even at the fastest inspiratory rise time settings.
|Device||Rise time||Vt (ml)||PIF (l/min)||PIP (cm H2O)|
Under constant conditions (set PIP, inspiratory time, airway
resistance, and respiratory system compliance) a faster rise time
will increase Vt and PIF without affecting the delivered PIP.
However, clinicians should be familiar with the variabile response to
adjusting inspiratory rise time for different mechanical ventilators.