There are numerous methods for selecting the correct endotracheal tube size for a given pediatric patient, including age, height, weight, and diameter of the fifth digit. Endotracheal tube size for premature and full-term infants is usually selected by weight, since, given the rapid growth during this period, age formulas become invalid. The rule usually employed is a 2.5-mm tube below 1.5 kg body weight, a 3.0-mm tube between 1.5 and 2.5 kg, and a 3.5-mm tube above 2.5 kg. The most commonly used formula for age determination of endotracheal tube size in children over 1 year of age is tube size (in millimeters) = 4 + age (in years)/4. 5 However, single-formula methods based on age have been shown to lead frequently to inappropriate tube selection. 6 Resuscitation measuring tapes have been found to be more accurate than age-based formulas, which in turn are superior to the diameter of the fifth digit. 78 The tube should fit sufficiently snugly to prevent any leakage at pressures up to 10 cmH2O but should leak at a pressure lower than 30 cmH2O. An insufficiently snug fit will result in difficulty ventilating, compromised airway protection, and leakage of inhalational agents if the patient undergoes anesthesia. An overly tight-fitting tube risks endotracheal injury with the potential for development of subglottic stenosis due to the anatomic reasons noted above. For the same reason, cuffed tubes are generally avoided in patients 8 years old and under. Clearly, in the care of an unstable patient in the emergency department, a suboptimal tube that provides adequate ventilation is preferable to no airway at all, and exchange for a more appropriate tube can be deferred until the patient has been stabilized. The ideal depth of placement is midway between the glottis and the carina. Because of substantial variability in tracheal length, especially before the age of 1 year, formulas predicting the distance to the lips are unreliable. Since most pediatric tubes have a series of marks at the distal end, one technique is to simply advance the tube so that the second mark is just past the vocal cords. This results in a conservatively high tube that will not risk bronchial intubation. However, inadvertent dislodgement of the tube with head and neck manipulation may occur. A second technique is to initially deliberately perform a bronchial intubation, advancing the tube until breath sounds are heard only unilaterally, and then to back the tube up to a point 1 cm above where the breath sounds are again heard bilaterally. This method results in a conservatively low tube, but with little risk of inadvertent displacement out of the airway.
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