How do we know that we have the endotracheal tube in the center of the trachea
How Do We Know That the Endotracheal Tube Has Been Positioned Correctly in the Trachea?
The correct placement of the endotracheal tube ( ETT) in the trachea is one of many important issues that face the anesthesia care provider daily. The practitioner that manages the care of infants, the issue becomes even more critical. The distance between the laryngeal inlet and the carina is short. In children up to one year of age this distance varies from 5 to 9 cm.
The tolerance for one lung ventilation in infants is limited as the FRC is small relative to the utilization of O2. Our ability to determine placement by listening to breath sounds is limited by the small size and the rounded configuration of the infant chest. Generalized transmission of sound is the norm and unless there is essentially no background noise, a truly accurate assessment rarely occurs.
Many authors have created formulas to determine the placement of the tip of an ETT in the mid trachea of a child. Most, if not all of these formulas apply to children that are more than two years of age. (Age in years/2 + 12; or weight in kg/5 +12) and are not useful for infants. The gold standard, of course, would be direct visual placement of the tip of the ETT in the exact mid trachea as measured via radiograph or bronchoscope. Practically speaking, visualizing the lines on the ETT as it passes through the cords represents a reasonable approximation of the gold standard. However, a view of the glottic inlet that is partially obstructed may inhibit this method to some extent.
A reasonable method for initial placement of the tip of the ETT in infants is the 7-8-9 rule. This rule adds 6 cm. to the infants weight in kg. (A 1000 gram infant would have their ETT taped at 7cm at the lip.) In a recent study utilizing this technique, 25% of infants up to 3 Kg in the nursery at Rainbow Babies and Children’s Hospital required adjustments in the initial placement. In addition, there was substantial variability between the percentages of correct placements with 2. 5 and 3.0 endotracheal tubes. In a recent study published in Anesthesia and Analgesia three methods of positioning were compared – Pulling the tube back from the rt. mainstem while listening, placing the prescribed marks at the level of the vocal cords, or by palpating the ETT in the suprasternal notch. In each the position was validated using fiberoptic bronchoscopy. In this study the visualization of marks at the level of the cords was nearly universally associated with correct placement and there were no associated endobronchial intubations in this group when the head was flexed. Similarly, there were no inadvertent extubations with extension.
So, this is what I think that we can learn.
1. The distance between the cords and the carina in infants less than one year of age is short and variable depending on variables such as the post conceptual age at the time of delivery, the nutritional and growth state of the child after delivery, and the presence of aberrations of growth such as dwarfism.
2. The best method for determining the placement of the tip of the ETT in a clinical situation is to watch the marks on the as they go through the cords and verify your effort using the 7-8-9-rule.
3. A major source of variability is the size of the ETT that is going through the larynx – smaller than is appropriate for the size of the larynx will leave the tube high, and larger than appropriate will risk endobronchial intubation. In some infants that have subglottic stenosis the ETT that would seem appropriate for the size of the child will be inappropriate for the size of the airway.
4. There are rules, and there are rules but airway catastrophes are by far the leading cause of morbidity in small children. No matter what rule you have learned be suspicious of the airway in every infant and vigilant for changes in any ventilatory parameter.
Rae Brown, MD
Professor of Anesthesiology and Pediatrics
University of Kentucky Medical Center
The correct placement of the endotracheal tube ( ETT) in the trachea is one of many important issues that face the anesthesia care provider daily. The practitioner that manages the care of infants, the issue becomes even more critical. The distance between the laryngeal inlet and the carina is short. In children up to one year of age this distance varies from 5 to 9 cm.
The tolerance for one lung ventilation in infants is limited as the FRC is small relative to the utilization of O2. Our ability to determine placement by listening to breath sounds is limited by the small size and the rounded configuration of the infant chest. Generalized transmission of sound is the norm and unless there is essentially no background noise, a truly accurate assessment rarely occurs.
Many authors have created formulas to determine the placement of the tip of an ETT in the mid trachea of a child. Most, if not all of these formulas apply to children that are more than two years of age. (Age in years/2 + 12; or weight in kg/5 +12) and are not useful for infants. The gold standard, of course, would be direct visual placement of the tip of the ETT in the exact mid trachea as measured via radiograph or bronchoscope. Practically speaking, visualizing the lines on the ETT as it passes through the cords represents a reasonable approximation of the gold standard. However, a view of the glottic inlet that is partially obstructed may inhibit this method to some extent.
A reasonable method for initial placement of the tip of the ETT in infants is the 7-8-9 rule. This rule adds 6 cm. to the infants weight in kg. (A 1000 gram infant would have their ETT taped at 7cm at the lip.) In a recent study utilizing this technique, 25% of infants up to 3 Kg in the nursery at Rainbow Babies and Children’s Hospital required adjustments in the initial placement. In addition, there was substantial variability between the percentages of correct placements with 2. 5 and 3.0 endotracheal tubes. In a recent study published in Anesthesia and Analgesia three methods of positioning were compared – Pulling the tube back from the rt. mainstem while listening, placing the prescribed marks at the level of the vocal cords, or by palpating the ETT in the suprasternal notch. In each the position was validated using fiberoptic bronchoscopy. In this study the visualization of marks at the level of the cords was nearly universally associated with correct placement and there were no associated endobronchial intubations in this group when the head was flexed. Similarly, there were no inadvertent extubations with extension.
So, this is what I think that we can learn.
1. The distance between the cords and the carina in infants less than one year of age is short and variable depending on variables such as the post conceptual age at the time of delivery, the nutritional and growth state of the child after delivery, and the presence of aberrations of growth such as dwarfism.
2. The best method for determining the placement of the tip of the ETT in a clinical situation is to watch the marks on the as they go through the cords and verify your effort using the 7-8-9-rule.
3. A major source of variability is the size of the ETT that is going through the larynx – smaller than is appropriate for the size of the larynx will leave the tube high, and larger than appropriate will risk endobronchial intubation. In some infants that have subglottic stenosis the ETT that would seem appropriate for the size of the child will be inappropriate for the size of the airway.
4. There are rules, and there are rules but airway catastrophes are by far the leading cause of morbidity in small children. No matter what rule you have learned be suspicious of the airway in every infant and vigilant for changes in any ventilatory parameter.
Rae Brown, MD
Professor of Anesthesiology and Pediatrics
University of Kentucky Medical Center
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