The pressure drop across the endotracheal tube in mechanically ventilated pediatric patients

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Abstract

Background:

During mechanical ventilation, the airway pressure (Paw) is usually monitored. However, Paw comprises the endotracheal tube (ETT)-related pressure drop (δPETT) and thus does not reflect the pressure in the patients’ lungs. Therefore, monitoring of mechanical ventilation should be based on the tracheal pressure (Ptrach). We systematically investigated potential factors influencing δPETT in pediatric ETTs.

Methods:

In this study, the flow-dependent pressure drop across pediatric ETTs from four manufacturers [2.0–4.5 mm inner diameter (ID)] was estimated in a physical model of the upper airways. Additionally, δPETT was examined with the ETTs shortened to 75% of their original length and at different curvatures. In nine healthy mechanically ventilated children (aged between 9 days and 29 months), Ptrach was compared to Paw.

Results:

δPETT was nonlinearly flow dependent. Low IDs corresponded to high δPETT. Differences between ETTs from different manufacturers were identified. Shortening of the ETTs’ length by 25% reduced δPETT on average by 14% of the value at original length. Ventilation frequency and tube curvature did not influence δPETT to a relevant extent. In the pediatric patients, the root mean square deviation between Paw and Ptrach was 2.3 cm H2O.

Conclusion:

Paw and Ptrach differ considerably (by δPETT) during mechanical ventilation of pediatric patients. The ETTs’ ID, tube length, and manufacturer type are significant factors for δPETT and should be taken into account when Paw is valuated. For this purpose, Ptrach can be continuously calculated with good precision by means of the Rohrer approximation.

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