Intraluminal measurement probe increases resistance of pediatric endotracheal tubes

Introduction

During mechanical ventilation the resistance of the endotracheal tube (ETT) causes a noticeable pressure drop between the airway pressure and the tracheal pressure. Analysis of lung mechanics requires knowledge of the tracheal pressure.

Besides methods for calculation of the tracheal pressure [1, 2], direct measurement of the tracheal pressure was suggested [3]. We hypothesized that the measure probe significantly increases the ETT's resistance and therefore is inappropriate for continuous monitoring of the intratracheal pressure in the presence of pediatric ETTs. In a laboratory study we investigated the pressure drop across pediatric ETTs with and without an intraluminal sensor probe.

Methods

A physical model consisting of a special tube connector for insertion of the sensor probe (Samba Preclin 420 LP; Samba Sensors, Västra Frölunda, Sweden), the anatomically curved ETTs of inner diameter 2.0–4.5 mm, and an artificial trachea was ventilated with sinusoidal gas flow with an amplitude of 240 ml/s and a ventilation rate ranging from 20 to 50 cycles/min. The airway pressure (proximal to the ETT) was measured at the proximal end, and the tracheal pressure at the distal end of the ETT.

Results

We found that placement of the intraluminal sensor significantly increased the pressure drop across the ETT (P < 0.05) for all sizes of ETT. Figure 1 shows the pressure-flow relationship of a 2-mm-ID tube. The relative increase of this pressure drop caused by the intraluminal sensor was more prominent for smaller ETTs.

Figure 1

Conclusion

Measurement of tracheal pressure using intraluminal sensors results in an increased ETT resistance and thus in an additional increase of work of breathing. We conclude that direct tracheal measurement is inappropriate for continuous bedside monitoring of tracheal pressure in small children.