Ultrasound compared to Age Related Formulas for prediction of Pediatric Endotracheal Tube Size
Authors: Abdelghany A , Nasr N , Talaat S , Mansour M , Shabana T 
Published: May 2020

Abstract

Background
In pediatric patients, having proper size of endotracheal tube (ETT) is crucial. The practice of using age-based formulas to calculate the ETT size is easy, practical and commonly used today. However, the incidence of inappropriate tube size is still judicious, hence increasing risk from changing tube such as trauma and aspiration. Recent studies found that measuring the narrowest transverse subglottic diameter may guide the proper tube size

Aim
This study was aimed to proof that selecting ETT size using ultrasound measurement of subglottic diameter is a reliable method and lead to less frequency of changing tube size than age-based formula especially in older children

Materials and Methods
60 children aged between 2 to 12 years, of both genders, American society of anesthesiologists (ASA) I or II physical status scheduled for day case surgery under general endotracheal anesthesia. Children were divided randomly according to age into three groups: group I included children aged between 2 to &lt; 5 years, group II included children aged between 5 to &lt; 9 years, and group III included children aged between 9 to 12 years. In all childern, the size of the ETT was determined according to both ultrasonography and modified cole's formula. The size of the ETT initially inserted was based on ultrasonographic calculation. Ultrasonography is done using high–resolution linear ultrasound probe. The probe was positioned at the anterior aspect of neck in the midline with the head extended and neck flexed (sniffing position). The minimal transverse diameter of the subglottic airway (MTDSA) was estimated at the level of cricoid cartilage at zero cmH2O airway pressure. After measurement of the subglottic diameter, uncuffed ETT with the nearest outer diameter (OD) corresponding to the measured subglottic diameter was selected for intubation. If there was resistance to ETT passage into the trachea, or there was no audible leak when the lungs were inflated to a pressure of 20–30 cm H2O, the tube was exchanged with one that is 0.5 mm smaller. In contrast, the ETT was exchanged for one that is 0.5 mm larger if leaks occurred at an inflation pressure less than 10 cm H2O. Optimal tube size was clinically determined by leakage at airway pressure of 10-20 cmH2O.

Results
Linear correlation study showed that Ultrasonography was a better predictor for optimal ETT size in pediatrics than Cole's formula for all studied groups especially in older age groups (although both were significant); being 0.669 Vs. 0.613 among group I; 0.955 Vs. 0.808 among group II and 0.863 Vs. 0.707 among group III. Multi-regression analysis showed that both Ultrasonography & Cole's formula were highly sensitive independent predictors that can predict Optimal ETT size in pediatrics (F-Ratio = 524.7, p &lt; 0.001); The prediction formula is: Optimal ETT size ID = -0.091 + 0.814(ID obtained by US) + 0.192(ID obtained by Cole's formula).

Conclusion
Ultrasound is a safe, reliable, non-invasive tool for selection of appropriately sized endotracheal tube for clinical use. Our study validates the reliability of ultrasound to measure subglottic diameter which avoids intubation related complications of either trauma or inefficient ventilation.