The Science Journal of the American Association for Respiratory Care

2003 OPEN FORUM Abstracts

PRESSURE-TIME PRODUCT AS AN INDICATOR OF INSPIRATORY WORK IN A LUNG MODEL DURING DIFFERENT INSPIRATORY FLOW DEMANDS IN THE RESPIRONICS ESPRITÔ, PURITIAN BENNETT 7200aeÔ AND SIEMENS SERVOiÔ.

RL Joyner PhD RRT, KM Bathgate, JL O'Connell, SR Schneider PhD RRT-NPS RPFT
Respiratory Therapy Program, Department of Health Sciences, Henson School of Science & Technology, Salisbury University, Salisbury, MD


Background:
Non-invasive ventilation is commonplace in patients with certain types of reversible respiratory failure. Because of their ubiquitous presence, it is common to use ventilators designed for invasive ventilation when providing non-invasive ventilation. Ventilator manufacturers now offer ventilators designed with non-invasive and invasive modes in the same ventilator. Using graded inspiratory demands and pressure-time product as an index of inspiratory work, we compared the ability of a ventilator designed for invasive ventilator and a full service ventilator set in a non-invasive mode to limit inspiratory work.

Methods:
Three ventilators (EspritT, Puritan Bennett 7200aeT, and Siemens Servoi), each with two inspiratory trigger mechanisms (Esprit - AutotrakT or flow-trigger, PBT 7200ae - pressure trigger or flow trigger, Servoi - pressure trigger or flow trigger) were evaluated with a lung model that simulated spontaneous breathing at three inspiratory flow rates (40 l/m, 60 l/m, 80 l/m). Pressure was measured at the proximal airway position for each ventilator trigger type at each inspiratory flow rate for five minutes using a data acquisition rate of 100 Hz. For each ventilator and flow setting, five breaths without artifact were used to calculate the pressure-time product. The pressure-time product was defined as the area produced by the pressure waveform below PEEP during onset of the triggered breath. The settings for each ventilator were as follows:

Respironics Esprit PBT 7200ae Servoi
IPAP = 12 cm H2O PSV = 10 cm H2O PSV = 10 cm H2O
EPAP = 2 cm H2O PEEP = 2 cm H2O PEEP = 2 cm H2O
Sensitivity = Autotrak Sensitivity = 0.5 cm H2O (PT) Sensitivity = -1 cm H2O (PT)
Or
IPAP = 12 cm H2O PSV = 10 cm H2O PSV 10 cm H2O
EPAP = 2 cm H2O PEEP = 2 cm H2O PEEP = 2 cm H2O
Sensitivity = (FT - 4/1) Sensitivity = (FT - 5/2) Sensitivity = (FT - most sensitive that did not cause auto cycle)



RESULTS:
In this bench study, these data show that across the flow rates examined the Servoi using flow trigger has the smallest pressure-time product (mean ± SD = 0.94 ± 0.33) and the PBT 7200ae using flow trigger has the largest pressure-time product (mean ± SD = 3.04 ± 1.51) of the ventilator triggers tested (p < 0.05). In addition, across flow rates examined, there was no statistical difference between the PBT 7200ae using pressure trigger (mean ± SD = 1.53 ± 0.70) and the Esprit using Autotrak (mean ± SD = 1.45 ± 0.80) or flow trigger (mean ± SD = 1.48 ± 0.82), or the Servoi in pressure trigger (mean ± SD = 1.40 ± 0.29). 

Conclusions:
These data suggest that of the ventilators tested in this study, the Servoi using flow trigger would have the least ventilator added work of breathing and the PBT 7200ae using flow trigger would have the greatest. With the exception of the PBT 7200ae in flow trigger (which has a pressure-time product twice that of the other ventilator triggers tested) differences between the pressure-time products of the remaining ventilator triggering systems is small and therefore it is difficult to speculate on their clinical relevance.

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