The Science Journal of the American Association for Respiratory Care

2004 OPEN FORUM Abstracts

INSPIRATORY RISE TIME affects PEAK inspiratory FLOW AND TIDAL VOLUME delivery

Mark 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)
PB 840 Slow 822 62 20
  Fast 928 80 20
Avea Slow 791 59 19
  Fast 852 66 19
Esprit Slow 779 61 19
  Fast 975 77 20
SV300 Slow 834 69 20
  Fast 935 76 20
Bear 1000 Slow 169 19 10
  Fast 977 91 20

Conclusions: 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.

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