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

Abstract

Abstract Purpose: Anesthesiologists often shorten endotracheal tubes (ETTs) because the resistance of the ETT (RETT) is believed to be a major contributor to total airway resistance (Rtotal) in children intubated with ETTs of smaller inner diameter. However, the effectiveness of ETT shortening for mechanical ventilation in the clinical setting has not been reported. In this work, we performed a prospective clinical study and a laboratory experiment to assess the effectiveness of shortening a cuffed ETT for increasing tidal volume (TV) and decreasing Rtotal during constant pressure-controlled ventilation, and to estimate the RETT/Rtotal ratio in children. Method: In anesthetized children in a constant pressure-controlled ventilation setting, TV and Rtotal were measured with a pneumotachometer before and after shortening a cuffed ETT. The pressure gradient curves for the original length, shortened length, and the slip joint alone of the ETT were measured in vitro to determine the RETT/Rtotal ratio. Results: The clinical study included 22 children. The median ETT percent shortening was 21.7%. Median Rtotal was decreased from 26 to 24 cmH2O/L/s, and median TV was increased by 6% after ETT shortening. Additionally, approximately 40% of the pressure gradient across the ETT at its original length was generated by the slip joint. Median RETT and median RETT/Rtotal before ETT shortening were calculated as 17.7 cmH2O/L/s and 0.69, respectively. Conclusions: The increase in TV caused by ETT shortening was small because the resistance of the slip joint was very large, limiting the effectiveness of ETT shortening.