Prediction of Optimal Pediatric Endotracheal Tube Size "Aged Based Formula Versus Ultrasonography"
Condition: Anesthesia Intubation Complication
Study type: Interventional

Summary: 
      Background: Ultrasound (US) imaging technique has recently emerged as a novel, simple,
      portable, noninvasive tool helpful for airway assessment and management. Initial few
      published reports were on soft tissue imaging of neck, focusing on pre-tracheal structure and
      anterior tracheal wall. In our study, we compared the measurement of subglottic diameter
      using ultrasonography and the aged based formula in prediction of endotracheal tube size in
      children underwent elective surgical operation under general anesthesia.

      Methods: Patients were randomly divided in 2 groups (27 patients each) using a
      computer-generated randomization schedule. The first group was aged based group (group AB) (n
      = 27): the endotracheal tube size was determined according to age of the child [inner
      diameter [ID] in mm = (age in yr/4) +4. The second group was ultrasound based group (group
      UB) (n = 27): the endotracheal tube size was determined according to the subglottic
      transverse diameter that was estimated with ultrasonography (the outer diameter of
      endotracheal tube (ETT OD) = 0.55*(subglottic diameter)+1.16) .
    

Detailed description: 
      Introduction:

      Pediatric tracheal intubation requires considerable expertise and can represent a challenge
      to many anesthesiologists(Marciniak et al.,2009). Anatomically; the larynx of a pediatric
      patient assumes a funnel shape with its narrowest part at the level of the cricoid ring,
      which cannot be seen during conventional laryngoscopy (Karsli et al.,2002).

      Choosing the correct endotracheal tube (ETT) size needed for intubation of pediatric patients
      is important because an inappropriately too large tracheal tube can cause upper airway damage
      (e.g., local ischemia, ulceration, scar formation) and the potential for subsequent
      subglottic stenosis. In contrast, an ETT that is too small may result in insufficient
      ventilation, poor reliability of end-tidal gas monitoring, leakage of anesthetic gases into
      the operating room environment, and an enhanced risk of aspiration(Karsli et al.,2002).

      Different algorithms and formula have been proposed to choose the best-fitting size of the
      endotracheal tube. Age-based formulas, such as those of Cole and Motoyama, have been used to
      estimate optimal ETT size for more than half a century (Motoyama,1990) and this formula is
      [inner diameter (ID) in mm = (age in yr/4) +4]. Predictive formulas for appropriate ETT size
      have also been based on patient weight and height as[ID in mm = 2 + height in cm/30] and [ID
      in mm = 2.44 + age in yr ×0.1 + height in cm ×0.02 + weight in kg ×0.016] and other formula
      as the width of the 5th fingernail is used for ID prediction of the ETT [ID in mm = maximum
      width of the 5th fingernail] (Shibasaki et al.,2010). However, these methods are not always
      suitable because the size of the airway varies considerably between patients.

      Ultrasound guided is helpful for evaluate the subglottic transverse diameter which is safe ,
      sample, painless and non invasive modality for prediction of proper endotracheal tube size
      (Jagadish G Sutagatti et al., 2017).

      In this study, we compared the measurement of subglottic diameter using ultrasonography and
      the aged based formula in prediction of endotracheal tube size in children underwent elective
      surgical operation under general anesthesia.

      Patients and methods:

      Study design and participants After getting approval from the institutional research
      board(MS/16.01.143), faculty of medicine , Mansoura University, written informed consents
      were obtained from parents of fifty children aged from 1 to 6 years of either sex scheduled
      for elective surgery not exceeded 90 minutes underwent general anesthesia with uncuffed
      endotracheal tube. This randomized controlled study was conducted in Emergency Hospital,
      Mansoura University between April/2016 to April/2017 .

      Patient exclusion criteria include: an anticipated difficult airway, any respiratory disease
      that might cause airway narrowing, pre-exiting laryngeal or tracheal pathology, any lesion
      that could cause airway deformity due to fibrosis or the presence of a neck anatomical
      pathologies that might have unpredictable effect on the ultrasound assessment of the airway
      and prolonged surgery more than 90 minutes .

      Sample size calculation:

      The appropriateness of ETT size was adopted as a primary parameter for effective size used
      for sample size calculation. A power of 80% was accepted with alpha error of 0.05. fifty four
      patients in both groups were found to be enough to detect a 20% difference between groups.

      Patients were randomly divided in 2 groups (27 patients each) using a computer-generated
      randomization schedule.

      Aged based group (group AB) (n = 27): ETT size was determined according to age of the child,
      inner diameter [ID] in mm = (age in yr/4) +4(Van den Berg and Mphanza, 1997).

      Ultrasound based group (group UB) (n = 27): ETT was determined according to the subglottic
      transverse diameter that was estimated with ultrasonography.

      Technique:

      On arrival to the operating room, basic monitors were applied {ECG, pulse oximetry,
      non-invasive blood pressure (NIBP)}, baseline values were recorded and An intravenous cannula
      (24G) was inserted and secured . General anesthesia was induced by inhalation of sevoflurane.
      Muscular relaxation was achieved with atracurium (0.5mg/kg) to facilitate the endotracheal
      intubation under direct laryngoscopy. The patients were ventilated with sevoflurane in 100%
      oxygen via a facemask before intubation for 3 min for proper muscles relaxation. ETT was
      chosen according to each group. Aged based formula (inner diameter [ID] in mm = (age in yr/4)
      +4) was used in group AB and in group UB, during mask ventilation ultrasound guided
      subglottic transverse diameter was measured with assistant anesthesiologist help. To avoid
      observer bias by anesthesiologist who performs the leak test by the absence of ultrasound
      machine in the operating room, the ultrasound assessment also was done in group
      AB(aged-based).

      Ultrasonography technique:

      The subglottic diameter was estimated with B-mode ultrasonography (Korean, Siemens, Acuson,
      x300) with a 10-13-MHz linear probe positioned on the midline of the anterior neck (figure1).
      The evaluation began by identifying the true vocal folds as paired hyperechoic linear
      structures that moved with respiration and swallowing before patients were paralyzed. The
      probe was then moved caudally to visualize the cricoid arch which appears as an arched,
      rounded and hypoechoic structure (figure2). The transverse air-column diameter was measured
      at the lower edge of the cricoid cartilage after patients were paralyzed (figure3).

      The measurements of the subglottic diameter was used to select the outer diameter of
      endotracheal tube by the equation [ETT OD=0.55*(subglottic diameter)+1.16] (Shibasaki et al.,
      2010), since the outer diameter of endotracheal tube differs among different manufactures, we
      used uncuffed Mallinckrodt tracheal tube with a Murphy's eyes.

      The inner diameter of endotracheal tube that was calculated according to table (1) which show
      the correlation between outer and inner diameter of the endotracheal tube.

      Determination of appropriateness of ETT size:

      Another anesthesiologist who was blinded to the group allocation did the air leak test in all
      patients. The air leak test was done after successful intubation of ETT chosen on the basis
      of either of two methods, The correct tracheal tube size was considered optimal when an
      audible air leak around the tube at an inspiratory airway pressure was detected between 10-30
      cm H2O, with the head and neck in a neutral position. The presence of an air leak was
      assessed by closing off the pop-off valve and allowing pressure to rise slowly until an
      audible leak was heard using a stethoscope on the tube. If there was no audible leak when the
      lung were inflated to a pressure of 30 cm H2O, the tube was exchanged with one that was 0.5
      mm smaller. But if a leak occurred at an inflation pressure of less than 10 cm of H2O, the
      ETT was exchanged for one with the 0.5 mm larger tube.

      The following parameters were monitored:

        1. Primary outcome: Number of optimum tube selection was monitored in both group (group AB
           and group UB).2- Number of reintubation due to large or small tube.

        2. Secondary outcome: 1- Time of intubation. 2- Complication after extubation.

      Statistical analysis:

      All statistical analyses were performed using SPSS for windows version 20.0 (SPSS, Chicago,
      IL). Continuous data we re-expressed in mean ±standard deviation (SD) white categorical data
      were expressed in number and percentage. The differences between two groups were determined
      using Student's t test for variables with continuous data and chi-square test for variables
      with categorical data. The 95% confidence interval (CI) for the frequency of correct size of
      the endotracheal tube (ETT) was calculated. Statistical significance was set at p<0.05.
    

Intervention name(s): ultrasound guided
Intervention type(s): Other
Intervention description(s): Ultrasonography technique:
The subglottic diameter was estimated with B-mode ultrasonography (Korean, Siemens, Acuson, x300) with a 10-13-MHz linear probe positioned on the midline of the anterior neck (figure1). The evaluation began by identifying the true vocal folds as paired hyperechoic linear structures that moved with respiration and swallowing before patients were paralyzed. The probe was then moved caudally to visualize the cricoid arch which appears as an arched, rounded and hypoechoic structure (figure2). The transverse air-column diameter was measured at the lower edge of the cricoid cartilage after patients were paralyzed (figure3).
The measurements of the subglottic diameter was used to select the outer diameter of endotracheal tube by the equation [ETT OD=0.55*(subglottic diameter)+1.16] (Shibasaki et al., 2010), since the outer diameter of endotracheal tube differs among different manufactures, we used uncuffed Mallinckrodt tracheal tube with a Murphy's eyes.
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: Double (Participant, Investigator)
Primary purpose: Prevention
Keywords: pediatric; endotracheal tube; ultrasonography