A term baby that weighs around 3 kg has a length of approximately 50 cm.
The trachea of a preterm baby that is roughly half the weight of a term baby and approximately 80% of the length of a term baby, is much shorter.
Cuffed neonatal endotracheal tubes
The pressure in the mucosal capillaries of a baby’s airway is approximately 20 cm H2O.
In a full term baby, if the pressure in the endotracheal cuff exceeds 20 cm H2O, the blood flow in those capillaries will be impeded (i.e., because the blood vessels are compressed), causing ischemia, necrosis, and scarring to the tissue supplied by those blood vessels. When scarring forms (typically around one to three weeks after injury), it significantly narrows the airway which then impedes the baby’s breathing. This situation is called subglottic stenosis.
Cuffed ETs stay in place by use of a cuff that is inflated while inside the trachea, causing the cuff to make an airtight or nearly airtight seal so the gases traveling in the tube don’t leak between the tube and the trachea.
The way in which cuffed tubes stay in place in place is by inflating a small chamber surrounding the ET thereby applying prolonged, constant pressure to the inside of the trachea.
The inside of the trachea has small blood vessels that can be compressed to the point of not allowing blood flow if the pressure of the endotracheal cuff is too high. To account for size of the cuff upon inflation, a cuffed ET should be 0.5 mm smaller than an uncuffed ET.
When a cuffed ET may be used, “[it] is as safe as an uncuffed tube for infants beyond the newborn period and in children.” However, this statement does not apply to Isaiah because of his size and prematurity. (emphasis added) 2005 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care
Cuffed ETs start at size 3.0, are indicated for babies of term ≥ 3 kg, and are not designed to be used in babies less than 3 kg and approximately 50 cm in length.
The main reasons cuffed ETs are not to be used in < 3 kg babies are because the margin for error is very small due to the short distance between the vocal folds and the carina--so the cuff could too easily be accidentally placed where it could cause damage; and the pressure of the inflated cuff is too great and too difficult to manage safely in a baby smaller than 3 kg.
The primary risk of using a cuffed ET on a baby below the 3 kg minimum is that it will cause subglottic stenosis, which results from such prolonged excessive pressure to the (small blood vessels on the) inside of the trachea.
Oversized outer tube diameters, inadequately designed cuffs, improperly positioned ETs, missing depth marks, and cuff overinflation have been identified as causes of airway damage in children managed with a cuffed tube. When sizing a cuffed ET, it is not only important to consider the diameter of the trachea but also the length of the trachea.
Tracheas of preterm and full-term babies medical expert witness specialties include neonatology, neonatal nursing, pediatric surgery, pediatric otolaryngology, pediatrics, and pediatric neurology.