One hundred percent oxygen should be adminis-tered prior to intubation to increase patient safety during the obligatory period of apnea prior to and during intubation. For awake intubations in neonates or infants, adequate pre-oxygenation and continued oxygen insufflation dur-ing laryngoscopy (eg, Oxyscope) may help prevent hypoxemia.
The infant’s prominent occiput tends to place the head in a flexed position prior to intubation. This is easily corrected by slightly elevating the shoulders with towels and placing the head on a doughnut-shaped pillow. In older children, promi-nent tonsillar tissue can obstruct visualization of the larynx. Straight laryngoscope blades aid intuba-tion of the anterior larynx in neonates, infants, and young children (Table 42–6). Endotracheal tubes that pass through the glottis may still impinge upon the cricoid cartilage, which is the narrowest point of the airway in children younger than 5 years of age. Mucosal trauma from trying to force a tube through the cricoid cartilage can cause postoperative edema, stridor, croup, and airway obstruction.
The appropriate diameter inside the endotra-cheal tube can be estimated by a formula based on age:
4 + Age/4 = Tube diameter (in mm)
For example, a 4-year-old child would be pre-dicted to require a 5-mm tube. This formula provides only a rough guideline, however. Exceptions include premature neonates (2.5–3 mm tube) and full-term neonates (3–3.5 mm tube). Alternatively, the practi-tioner can remember that a newborn takes a 2.5- or 3-mm tube, and a 5-year-old takes a 5-mm tube. It should not be that difficult to identify which of the three sizes of tube between 3 and 5 mm is required in small children. In larger children, small (5–6 mm) cuffed tubes can be used either with or without the cuff inflated to minimize the need for precise sizing. Endotracheal tubes 0.5 mm larger and smaller than predicted should be readily available in or on the anesthetic cart. Uncuffed endotracheal tubes tradi-tionally have been selected for children aged 5 years or younger to decrease the risk of postintubation croup, but many anesthesiologists no longer use size 4.0 or larger uncuffed tubes. The leak test will mini-mize the likelihood that an excessively large tube has been inserted. Correct tube size is confirmed by easy passage into the larynx and the development of a gas leak at 15–20 cm H 2O pressure for an uncuffed tube. No leak indicates an oversized tube that should be replaced to prevent postoperative edema, whereas an excessive leak may preclude adequate ventilation and contaminate the operating room with anesthetic gases. As noted above, many clinicians use a down-sized cuffed tube with the cuff completely deflated in younger patients at high risk for aspiration; minimal inflation of the cuff can stop any air leak. There is also a formula to estimate endotracheal length:
12 + Age/2 = Length of tube (in cm)
Again, this formula provides only a guideline, and the result must be confirmed by auscultation and clinical judgment. To avoid endobronchial intu-bation, the tip of the endotracheal tube should pass only 1–2 cm beyond an infant’s glottis. We favor an alternative approach: to intentionally place the tip of the endotracheal tube into the right mainstem bron-chus and then withdraw it until breath sounds are equal over both lung fields.