Evaluation in animals of a system to estimate tracheal pressure from the endotracheal tube cuff

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.