N A Wilder1, J Orr, D Westenskow. 1. Department of Anesthesiology, University of Utah, Salt Lake City 84132, USA.
Abstract
OBJECTIVE: Flow through an endotracheal tube (ETT) causes a pressure loss across the tube. This loss results in a difference between pressure measured at the airway and pressure measured in the trachea. This difference can lead to errors when calculating pulmonary mechanics and when setting ventilators. We have tested a method of estimating tracheal pressure from the pressure in the ETT cuff. METHODS: Pressure transducers were placed in the proximal ETT connector, in the trachea, and in the ETT cuff (through the inflation port). Instantaneous periods of zero flow, detected with a flow meter, were used to calculate the slope and offset of the line relating cuff pressure to tracheal pressure. The system was tested on the bench using a ventilator and lung simulator and in 2 dogs and 5 pigs. Tests were performed at various cuff pressures, trachea diameters, ETT sizes, respiratory rates, tidal volumes, and airway obstructions. RESULTS: In bench tests, our estimate of tracheal pressure was within -4.0 +/- 2.6% of the actual tracheal pressure (mean +/- standard deviation [SD]). In animal tests, our estimation of tracheal pressure was within -0.6 +/- 5%. In all bench test measurements and in 40 of 42 animal measurements, the error was less than 1 cm H2O. CONCLUSIONS: The cuff estimation technique gives real-time, continuous, noninvasive tracheal pressure measurements in intubated animals with cuffed ETTs.
OBJECTIVE: Flow through an endotracheal tube (ETT) causes a pressure loss across the tube. This loss results in a difference between pressure measured at the airway and pressure measured in the trachea. This difference can lead to errors when calculating pulmonary mechanics and when setting ventilators. We have tested a method of estimating tracheal pressure from the pressure in the ETT cuff. METHODS: Pressure transducers were placed in the proximal ETT connector, in the trachea, and in the ETT cuff (through the inflation port). Instantaneous periods of zero flow, detected with a flow meter, were used to calculate the slope and offset of the line relating cuff pressure to tracheal pressure. The system was tested on the bench using a ventilator and lung simulator and in 2 dogs and 5 pigs. Tests were performed at various cuff pressures, trachea diameters, ETT sizes, respiratory rates, tidal volumes, and airway obstructions. RESULTS: In bench tests, our estimate of tracheal pressure was within -4.0 +/- 2.6% of the actual tracheal pressure (mean +/- standard deviation [SD]). In animal tests, our estimation of tracheal pressure was within -0.6 +/- 5%. In all bench test measurements and in 40 of 42 animal measurements, the error was less than 1 cm H2O. CONCLUSIONS: The cuff estimation technique gives real-time, continuous, noninvasive tracheal pressure measurements in intubated animals with cuffed ETTs.