The Science Journal of the American Association for Respiratory Care

2011 OPEN FORUM Abstracts


John Rendle1, Lori Alturo1, Thomas Blackson2, James Hertzog1; 1Respiratory Care, Nemours, A. I. duPont Hospital for Children, Wilmington, DE; 2School Of Respiratory Therapy, Christiana Care Health System/Delaware Technical and Community College, Newark, DE

Background: The use of Non-Invasive Ventilation has increased greatly over the years. In an effort to improve the efficacy of this therapy we transitioned from smooth bore, non-heated circuits to heated wire circuits. A major concern of the Respiratory Care Department was the potential for a varying Vt dependent on the tubing type. An initial uncontrolled bench study showed a difference between the volumes delivered on an external monitor and the display of the Phillips V-60 ventilator. This prompted us to add a fixed volume control to the evaluation. Purpose: We created a bench model to evaluate the effect of pressure changes and tubing design on Vte displayed by the V-60. Materials & Methods: A calibrated 100 mL super syringe (SS) was used for all test conditions to simulate a patient breathing at a fixed Vt of 100 mL. The SS was attached at the patient connection of a V-60. An independent volume monitor (CO2SMO, Philips) was inserted between the SS and the ventilator circuit to verify inhaled and exhaled volumes were unaffected by CPAP and BIPAP adjustments made during the trial. Test conditions included ventilator settings of: CPAP 5 cm H2O, BIPAP 10/5, 20/5, 30/5 and 30/10 cm H2O. Ten sequential breaths were evaluated at each ventilator setting and the display of Vt was recorded from the V-60 and CO2SMO simultaneously. The test was repeated using (3) separate tubing designs: Fisher Paykel wide bore, heated wire circuit (RT 219), Philips smooth bore, non-heated wire circuit (312118), and Fisher Paykel standard bore, heated wire circuit (RT-202). Results: The COSMO flow sensor was unaffected by pressure changes (p < 0.05). The V-60 volume display had significant error that increased as the pressure difference (delta P) increased (P < 0.01). The type of tubing used for gas delivery affected the degree of error displayed by the V-60 independent of delta P. Conclusion: The V-60 display provides an estimate of Vte and the magnitude of error of displayed Vte may be as high as 65% in cases of large inspiratory to expiratory pressure differences. Tubing design compounded the exhaled volume display error. The Vte displayed on the V-60 is not accurate and clinicians should be cautious when using this value for purposes other than trending the direction of volume change when CPAP/BIPAP settings are adjusted. Further research is warranted to determine if the results observed in this bench study produce comparable results in a patient model.
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Comparison of Vt readings from the Philips V-60 with 4 separate pressure settings and 3 different types of tubing.
Pressures displayed in cm H2O and volumes displayed in mL.
*= p < 0.01 ()=+/- SD