The Science Journal of the American Association for Respiratory Care

2010 OPEN FORUM Abstracts


John S. Emberger, Joel M. Brown; Respiratory Care, Christiana Care Health System, Newark, DE

BACKGROUND: Identifying partially occluded endotracheal tubes (ETT) is a key factor to patient safety in the ICU. Current methods for identifying partial ETT obstructions may not be sensitive enough to notify caregivers that action is necessary to maintain a patent airway. Normal airway resistance (Raw) is expected to be < 15 cmH2O/L/s1 as monitored on a ventilator with a plateau pressure. A new airway monitoring system (SonarMed Inc, Indianapolis IN) may be able to quickly and accurately identify partial ETT obstructions. This device is a handheld monitor that uses an audio waveform echo algorithm (also known as acoustic reflectometry), and can give continuous measurements during conventional mechanical ventilation. We wanted to compare the SonarMed Airway Monitoring System (AMS) with Raw measurements typically used to identify partial ETT obstructions. METHODS: We performed a bench study using a ventilator (Drager Evita 4, Lubeck Germany), ETT and training test lung model for all readings. We created partial ETT obstructions with 1 minute epoxy. ETTs (size 7.0 and 8.0) had partial obstructions created in 3 different positions. Obstruction positions: near the top of the ETT (Proximal), near the middle of the ETT (Middle) and near the far end of the ETT (Distal). We calculated the airway resistance (Raw) by performing a plateau pressure using a peak inspiratory flow of 50 LPM while ventilating with a tidal volume of 500 ml. We also collected the Raw displayed on the ventilator and the % obstruction reading on the AMS. After bench testing, we cross-sectioned each ETT obstruction and took a digital image. Then we superimposed the enlarged image of the partially obstructed lumen over a square counting grid, to calculate actual % obstruction. RESULTS: See table for the data. The AMS accurately displayed the position of the obstruction in each different ETT. CONCLUSIONS: The AMS identified every partial ETT obstruction. Raw measurement would only identify the 2 largest of the 6 partial ETT obstructions (Raw > 15 cmH2O/L/s). Raw measurements trended in the direction of the severity of the obstructions, but the threshold of normal Raw may fail to show partial obstructions that may have clinical significance. The new Airway Monitoring System could be a useful adjunct for patient safety in monitoring patientÂ’s endotracheal tubes. REFERENCES: 1) Respiratory Care, January 2002, vol 47, Evidence-Based Guidelines for Weaning and Discontinuing Ventilatory Support Sponsored Research - None Detecting Partial ETT Obstructions: Raw Measurements Versus AMS