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

BackgroundDuring mechanical ventilation, the airway pressure (P-aw) is usually monitored. However, P-aw comprises the endotracheal tube (ETT)-related pressure drop (P-ETT) and thus does not reflect the pressure in the patients' lungs. Therefore, monitoring of mechanical ventilation should be based on the tracheal pressure (P-trach). We systematically investigated potential factors influencing P-ETT in pediatric ETTs. MethodsIn this study, the flow-dependent pressure drop across pediatric ETTs from four manufacturers [2.0-4.5mm inner diameter (ID)] was estimated in a physical model of the upper airways. Additionally, P-ETT was examined with the ETTs shortened to 75% of their original length and at different curvatures. In nine healthy mechanically ventilated children (aged between 9days and 29months), P-trach was compared to P-aw. ResultsP(ETT) was nonlinearly flow dependent. Low IDs corresponded to high P-ETT. Differences between ETTs from different manufacturers were identified. Shortening of the ETTs' length by 25% reduced P-ETT on average by 14% of the value at original length. Ventilation frequency and tube curvature did not influence P-ETT to a relevant extent. In the pediatric patients, the root mean square deviation between P-aw and P-trach was 2.3cm H2O. ConclusionP(aw) and P-trach differ considerably (by P-ETT) during mechanical ventilation of pediatric patients. The ETTs' ID, tube length, and manufacturer type are significant factors for P-ETT and should be taken into account when P-aw is valuated. For this purpose, P-trach can be continuously calculated with good precision by means of the Rohrer approximation.