The Science Journal of the American Association for Respiratory Care

2008 OPEN FORUM Abstracts


Roger W. Reichenbach1, Nik Pamukov1, ONeal Sanders1

Background: Ventilator graphic analysis has come to the forefront of patient care. Patient-ventilator dysynchrony can be detected on physical exam,careful review of ventilator graphics allows for greater definition of the underlying cause .Variables can effect how the waveform appears, one is the use of expiratory filters.We hypothesized an expiratory filter reaching its saturation limit will have an increased resistance changing the graphics during mechanical ventilation.

Methods: This in vitro study examined two expiratory filters (n=20) for the Draeger Evita 4 XL and SERVO I in two controlled conditions (Dry vs. 100% saturated).The Airlife(#851 ) filters(n=10)and(n=10) Airlife(#852) filters placed on the expiratory limb proximal to the exhalation valve. Resistance known and measured via a calibrated pressure manometer/flow meter system. "Dry circuit" defined as having no humidity, and "wet circuit" 100% humidity added via a Fisher Paykel 850 heated wire circuit. Trend data collected for resistance, flow, and graphics displayed over serial time points.

Results: With little differences in baseline variables(# 851 Resistance 17.6 cm H2O/L/s vs. # 852 Resistance 17.6 cm H2O/L/s).At 6 hours, the #851 "dry circuit" filters had a consistent resistance of 17.6 cm H20/L/s vs. 17.6 cmH20/L/s for the #852.At 6 hours the #851 and #852 filters were measured at 100% saturation in the "wet circuit". The #851 had an increased resistance of 14.7 % from baseline (17.6 cm H20/L/s (dry) vs. 20.2 cm H20/L/s (wet). #852 had a notably reduced resistance of 0% from baseline. An obvious change in the flow/volume loops noted from dry to wet states, with a circular "sine wave appearance" vs. the more dampened linear appearance. Flow volume loops however appeared unchanged at the other serial time points.Both the Draeger and SERVO I displayed graphics equally.

Conclusion: The #852 had significantly less resistance over time when placed on the expiratory limb of a wet circuit than the #851.Increased expiratory resistance of #851 manifested an obvious change in the flow/volume loop yielding a dampened linear pattern, appearing less area under the curve though difficult to quantify. However, there was little change in the flow/volume loop with the increase in resistance over the duration the study. This study identifies the need for additional measures of displayed graphics (i.e.retrievable trended/graphics data) due to the subjective nature of bedside interpretation.