The Science Journal of the American Association for Respiratory Care

2012 OPEN FORUM Abstracts


Nicholas R. Henry, S. Gregory Marshall; Respiratory Care, Texas State University-San Marcos, San Marcos, TX

Background: The apnea test (AT) is used to support the diagnosis of brain death by establishing the absence of a respiratory drive. Previous case reports document the occurrence the spontaneous pneumothoraces while performing the AT with varying sizes of endotracheal tubes (ETT) and insufflation catheters (IC). Furthermore, the most widely accepted guideline for performing the AT does not specify what size of IC to use with different ETT sizes. What pressures and volumes are generated within the lungs when performing the AT with varying IC sizes? The null hypothesis is that there is no significant difference in pressure or volume within the lungs between varying IC size to ETT ratios (IC:ETT) while performing the apnea test. Method: This bench top, IRB approved study used a manikin, RespiTrainer Advance, connected to a QuickLung test lung that provided a measured pressure and calculated volume within the test lung. The test lung was set to a compliance of 50 ml/cmH2O and a resistance of 5 cmH2O/L/sec. Endotracheal tubes with an internal diameter (ID) of 6.0-10.0 were orally intubated into the manikin and advanced to 2 cm above the carina. Insufflation catheters, sizes 10-16 French, and cut oxygen supply tubing were advanced to the end of the ETT. Oxygen was delivered at 6-15 Liters/min into the test lung through the IC. Once the pressure within the test lung stabilized, pressure and volume were recorded. The IC:ETTs were determined by dividing the external diameter (ED) of the IC and the ID of the ETT. The MANOVA and Tukey’s statistical methods were used to analyze data at an alpha level of 0.05. Results: The MANOVA method demonstrated a significant difference with a p value of 0.04 between the varying IC:ETTs. The Tukey’s method identified IC:ETTs > 0.70 had significantly different pressures and volumes within the test lung from IC:ETTs < 0.70 with a p < 0.05 for each delivered oxygen flow rate. Conclusions: As a result of obtaining a MANOVA p value of 0.04 when evaluating the IC:ETTs, the null hypothesis was rejected. The IC:ETTs from 0.5 to 0.70 did not show a significant difference between IC:ETTs < 0.5 for pressure and volume. Selection of an IC with an ED < 70% of the ID of an ETT may prevent excessive pressure and volumes within the lungs while performing the apnea test. The selection of an appropriate sized IC should be included in the guidelines for performing the AT. Sponsored Research - The manikin (RespiTrainer Advance) and test lung (QuickLung) were obtained with financial assistance through an internal institutional research enchancement grant. Texas State University-San Marcos provided the grant.