Effectiveness of substantial shortening of the endotracheal tube for decreasing airway resistance and increasing tidal volume during pressure-controlled ventilation in pediatric patients: a prospective observational study.

The endotracheal tubes (ETTs) used for children have a smaller inner diameter. Accordingly, the resistance across ETT (R) is higher. Theoretically, shortening the ETTs can decrease total airway resistance (R), because R is sum of R and patient's airway resistance. However, the effectiveness of ETT shortening for mechanical ventilation in the clinical setting has not been reported. We assessed the effectiveness of shortening a cuffed ETT for decreasing R, and increasing tidal volume (TV), and estimated the R/R ratio in children. In anesthetized children in a constant pressure-controlled ventilation setting, R and TV were measured with a pneumotachometer before and after shortening a cuffed ETT. In a laboratory experiment, the pressure gradient across the original length, shortened length, and the slip joint alone of the ETT were measured. We then determined the R/R ratio using the above results. The clinical study included 22 children. The median ETT percent shortening was 21.7%. Median R was decreased from 26 to 24 cmHO/L/s, and median TV was increased by 6% after ETT shortening. The laboratory experiment showed that ETT length and the pressure gradient across ETT are linearly related under a certain flow rate, and approximately 40% of the pressure gradient across the ETT at its original length was generated by the slip joint. Median R/R ratio were calculated as 0.69. The effectiveness of ETT shortening on R and TV was very limited, because the resistance of the slip joint was very large.