The Effects of Variations in Flow through an Insufflating Catheter and Endotracheal-Tube and Suction-Catheter Size on Test-Lung Pressures

Abstract

The use of insufflating suction catheters that deliver an oxygen flow either simultaneously or alternately with suction may have definite benefits. However, the potential exists for any inflating flow to cause barotrauma, and this risk has not been addressed. MATERIALS & METHOD: We tested a commercially available single-lumen insufflating suction catheter (VenTech) to determine the factors that affect the insufflating pressures within a test lung, using a variety of flowrates, suction-catheter and endotracheal-tube sizes, and suction pressures. We also attempted to determine the factors that affect the pressure-relief-activation point on the insufflating catheter. RESULTS: Pressure-relief-valve-activation values in this catheter are higher (86-1196 cm H2O) than clinically acceptable and are dependent on flowrate but independent of catheter size. We found that the factors affecting pressures within the test lung include insufflating flowrate and the ratio of the cross-sectional area of the suction catheter to the cross-sectional area of the endotracheal tube (SC:ETT) and the length of time the lung is exposed to the flow (ie, the absolute gas volume added to the lung). CONCLUSIONS: Although our bench study does not allow us to draw specific conclusions applicable to human subjects, we believe that clinicians should assure an SC:ETT of approximately 0.5 and avoid excessive insufflating flows and prolonged insufflating intervals.