The efficiency of USG and  age related formula to determine the endotracheal tube diameter in pediatric patient
 A Cigdem Tutuncu, Meltem Kanar, Pinar Kendigelen, Guner Kaya
IU Cerrahpasa Tip Fakultesi Anesteziyoloji ve Reaniamasyon AD, Istanbul
Determination of the correct sized endotracheal tube (ETT) is frequently challenging. Although the age or height  based formulas are used, repeated laryngoscopic procedures are often necessary to identify the appropriate tube for individual patients to obtain sufficient ventilation with the accurate size. In this study we aimed to compare efficiency of USG measurement and age based formula to determine the correct uncuffed endotracheal tube diameter according to established tube diameter in clinically.  
Method
After the obtaining ethics comitee and parenteral informed consent. The patients from 2 to 10 years of age who were planned various type of surgeries were prospectivelly included this study. Exclusion criteries were patients weighted less than 10 kg or more than 50 kg and suspected laringeal and upper airway abnormalities. After the general anesthesia was induced by inhalation or intravenous way, the maintanance was provided with remifentanyl and sevoflurane with mask ventilation. 
During the mask ventilation and end of the inspration, internal transverse diameter of cricoid level was measured with ultrasonography in B mode with a linear probe placed on the midline of the anterior neck. The tube diameter was also calculatad with Cole formula and noted for  same patient.  The neuromuscular blocker was administered and patients were entubated with the best fit endotracheal tube in clinically. The endotracheal tube which was providing less than 30 ml leakage with the 25 cmH20 peak airway pressure and 6-8 ml/kg  tidal volume during the ventilation was accepted the convienent diameter and size. All patient characteristics, results from measurements, and the predicted OD calculated according to the formulas ‘ID [mm] = 4 + age [years]/4’ for the specific tube models were noted.
Results
The one hundred patients were enrolled the study. Mean age was 4.24±1.85 years. The succesful intubation rate at the first attempt was 87 %,  the second attempt rate was 12 %, and only 1 % pateint need the third attempt.  The mean diameter  obtained with Cole formula (4.95±0.53mm) were smaller than  the clinically fitted endotracheal tube  diameters (5.66±0.5 mm). The mean cricoid diameter obtained with USG measurements (8.32±0.98mm) were higher than  the clinically fitted endotracheal tube diameters (7.82±0.72mm). 
Bland Altman analysis showed a mean bias of 0.71 mm with the limits of agreement (bias± 0.36 SD) 0.0012 to 1.42 for formula and a mean bias of 0.5 mm with limits of agreement (bias±0.73 SD) -0.93 to 1.93 for ultrasound.

The efficiency of USG measurement and age related formula to determine the endotracheal tube diameter in paediatric patient