Accuracy of 7-8-9 Rule for Endotracheal Tube Placement in Nepalese Neonates

Introduction: Neonatal intubation is done for cardiopulmonary resuscitation, hypoxemia, and hypercapnia, for surfactant therapy or for airway protection. When correctly placed, endotracheal tube (ETT) tip should be at mid tracheal position which is half way between the clavicles and the carina to prevent complications of ventilation. Objective: To assess the accuracy of 7-8-9 Rule in neonates at Kanti Children’s hospital. Methodology: Prospective observational study was conducted in neonates who required oral intubations from July 2009 to December 2009 at NICU of Kanti Children’s Hospital. The initial ETT depth of insertion was determined using admission weight in the 7-8-9 Rule calculation. This depth was compared to the midtracheal depth to determine clinical accuracy of the 7-8-9 Rule. Results: Mean gestation age of the 69 infants was 36.01 weeks (26 to 42 weeks) and weight was 2411 g( 900 g to 3800 g ). 7 (10.1%) neonates weighed 1000 g or less, 19 (27.5%) weighed between 1001 to 2000 g, 31 ( 44.9%) weighed between 2001 to 3000 g, 12(17.4%) weighed between 3001 to 4000 g. The accuracy of 7-8-9 rule in clinical setting with auscultation and Chest x-ray resulted in ETT depth 0.11 cm above midtracheal position. (-1.5 to 1.5 cm). Using this rule ET tube was placed 0.11 cm above the mid tracheal position. Conclusions: The 7-89 Rule appears to be an accurate clinical method for endotracheal tube placement in Nepalese neonates.


Introduction
E ndotracheal intubation means the insertion of endotracheal tube (ETT) into the trachea. Endotracheal Intubation was described more than 2000 years ago 1 . With the development of artifi cial respirations in 1960s and 1970s the endotracheal intubation became an established part of the neonatal intensive care 2 . Endotracheal intubation is either an emergency or an elective procedure for a number of indications like cardiopulmonary resuscitation, airway protection, respiratory failure and administration of surfactant 3 . The correct position of endotracheal tube (ETT) is mid tracheal region or half way between the clavicles and the carina 2,3,4 . The position of ETT should be precise to reduce the complications like atelectasis, hyperinfl ation of the right lung, pneumothorax, tracheal damage, unplanned extubation or post extubation stridor 2,5,6 .
Intubation is a practical skill which cannot be learnt from textbook best way to learn and maintain this skill is in a controlled environment 2 . Since intubation is a very essential life saving procedure every physician should be competent. Intubation can be done orally or nasally. The choice of route depends on the circumstances and the preference of the clinician. Oral intubation in the neonate is faster, more likely to be successful at the fi rst attempt and less traumatic to perform so preferred in emergency intubation 7 . Apart from direct visualization of the tube as it passes through the glottis, there are a number of different methods for estimating the depth of ETT placement. The easiest to remember is rule of 7-8-9 2, 8 .
The simple calculation for determining depth of ETT insertion was described by Tochen in 1979. 9 The predicted estimated insertion of ETT was 1.17 multiplied by infants weight in Kilogram (KG) plus 5.58. According to this an infant weighing 1 kg being intubated to a depth of 7 cm, a 2 kg infant to a depth of 8 cm and a 3 kg infant a depth of 9 cm. The 7-8-9 rule is endorsed by The American Academy of Pediatrics and American Heart Association Textbook of Neonatal Resuscitation. To simplify this rule adds 6 to the weight (i.e. 1 kg + 6 = 7 cm) to estimate the depth of ETT insertion 2, 8, and 10 . This rule is widely used but there is limited data on the accuracy of this test. There is no such study in Nepalese neonates. So this study was conducted at NICU settings at Kanti Children's Hospital.

Material and methods
The study was prospective observational where 69 consecutive neonates admitted to NICU of Kanti Children's hospital who were intubated for various indications during the period of July to December 2009 were the subjects. Neonates already intubated outside NICU and those with congenital anomalies were excluded. After verbal consent intubation was performed by the on duty medical offi cer or pediatric resident in accordance with the protocol. Initial depth of insertion of ET tube was determined using the 7-8-9 rule where the weight taken during admission to NICU was taken as reference. This is important in our setting as exact birth weight is not known in babies delivered at home.
Portable chest x-ray was obtained with neutral head position after intubation and the tip of ET tube was documented. The ideal placement for ET tube placement is defi ned at mid trachea. This is the point halfway between the inferior portion of clavicle and carina as shown in fi gure 1. The distance of ET tube tip from the ideal mid tracheal position was calculated from the each x-ray in centimeters. Help of radiologist was taken while calculating the measurements.
Infants were classifi ed into weight groups of <1000, 1001 to 2000, 2001 to 3000, 3001 to 4000. These weight classes were chosen based on weight categories for appropriate selection of ET Tube 1 . Accuracy was determined using the mean paired differences with 95% confi dence intervals between the initial or predicted ETT depth and the ideal ETT depth. Linear regression was used to adjust for confounding variables and p value <0.05 was considered statistically signifi cant. Statistical calculations were performed using SPSS version 16.

Results
69 neonates admitted at NICU for various reasons and who were intubated for artifi cial ventilation during the study period were enrolled in the study. Among them 49 (71%) were males and 20 (29%) were females. Most of the neonates (78.3%) were > 72 hours of age on admission at NICU.   Neonate's weight on admission ranged from 900 gram to 3800 gram and mean weight was 2411 g (900 g to 3800 g). Seven (10.1%) infants weighed 1000 g or less, Nineteen (27.5%) weighed between 1001 t0 2000 g, Thirty one ( 44.9%) weighed between 2001 to 3000 g, Twelve (17.4%) weighed between 3001 to 4000. The admission weight was counted for the study purpose as there were 13(18.8%) babies delivered at home.
There were neonates of 26 to 42 weeks age calculated from last menstrual period and the mean gestational age was 36.1 weeks.
Out of the 69 babies enrolled in the study ET tube needed adjustment after auscultation and chest x-ray in 6 neonates.ETT size internal diameter ranging from 2.5 to 4 were used and ETT was fi xed at 7 to 9 centimeters in length.
The main indication for admission at NICU was sepsis (53.6%), prematurity (18.8%), birth asphyxia (7.2%), apnea (5.8%) and meningitis (2.9%). The indication for intubation was for mechanical ventilation in neonates. Out of the 69 babies enrolled in the study ETT needed adjustment after auscultation and chest x-ray in 6 neonates. ETTs internal diameters ranging from 2.5 to 4 were used and ETT was fi xed at 7 to 9 centimeters in length.
The overall accuracy of 7-8-9 rule in clinical setting with auscultation and ETT adjustment gave an initial ETT depth 0.11 cm above midtracheal position. (-1.5 cm to 1.5 cm). Using this rule ET tube was placed 0.11 cm above the mid tracheal position. The neonatal resuscitation program 3 uses the 7-8-9 rule to determine ETT depth of insertion. This rule is easy to use, safe, inexpensive and effective. This study provides additional evidence that the 7-8-9 rule is an accurate method for neonatal intubation in Nepalese neonates too. The accuracy improves following clinical auscultation and adjustment when necessary.
In a study done by J Peterson et al 8 in 2004 found that 7-8-9 rule appears to inaccurately position ETT between 0.30 and 0.93 cm too deep in infants weighing <750 g and recommended placing ETT at least 0.5 cm higher than predicted. A revision of the 7-8-9 Rule for the extremely low birth weight neonate may be justifi ed 2,3,8 . This technique of adjustment is also supported in the Neonatal Resuscitation Textbook which states: 'Babies weighing <750 g may require only 6 cm insertion' 3,8 . A prospective study examining the accuracy of this revised equation for ETT insertion depth in infants weighing <750 g is recommended. We in this study were unable to assess this in such neonates as our lowest weight was only 900 g. The adjustments of <1 cm is challenging with tubes have only whole centimeter markings so tubes with smaller markings are needed in lower weight categories. The inaccurate position is concerning as it may increase the neonates risk of pneumothorax and subsequent intraventricular hemorrhage 13,14 . In a study by Kempley ST and colleagues in 2008 15 and Mainie P et al in 2006 16 observed that ETT length was related to gestation in a linear manner and relation with weight was non linear so caution in use of 7-8-9 rule was urged especially those with very low birth weights. Blayney MP and colleague in 1994 17 suggested confi rmation of ETT using a radiograph and alignment of tip of ETT with the fi rst thoracic vertebra is probably the best marker of midtracheal position. However the position of the patient will cause the ETT to move, so if chest radiographs are used to prove correct placement babies' heads should be in a standard position as fl exion of the neck decreases and extension increases oro -carina distances 15,18 .
This was a fi rst of such study done at Nepal and the distance of ETT tip was calculated from mid tracheal point rather than a range for simplicity using a fi xed point rather than a range of distances to defi ne midtracheal position allowed us to obtain a more accurate estimate of placement. Tochen 9 defi ned midtracheal depth at the level of the fi rst or second thoracic vertebral body. This study examined the use of the 7-8-9 Rule as it is most often applied in clinical practice in Nepal too.

Conclusions
The 7-8-9 Rule is an accurate clinical method for endotracheal tube placement in Nepalese neonates. When the 7-8-9 Rule is applied to infants weighing <750 g, caution is warranted. The ETT tip should be confi rmed by auscultation and Chest X-ray after intubation.