Choice of the correct size of endotracheal tube is fundamental. The average man will accept a cuffed tube with an inner diameter of 8.0 or 8.5 mm. For women, the tube diameter is 0.5 to 1.0 mm smaller. Smaller tubes have more resistance to airﬂow and may not allow passage of a bronchoscope, but larger tubes may increase injury to the glottis and lower airway.
It is always best to be fully prepared with the necessary personnel and equipment before attempting endotracheal intubation. If a patient can be adequately oxygenated and ventilated with a bag-valve-mask, emergent intubation is not required. Necessary equipment includes an oxygen source and bag-valve-mask, suction, several sizes of endotracheal tubes and laryngoscopes, and any necessary medications. The light on the laryngoscope and the cuff of the endotracheal tube should always be tested before use.
Familiarity with various laryngoscopes is required. Whereas the curved McIntosh blade is positioned in the vallecula, the space between the base of the tongue and the epiglottis, laryngoscopes with straight blades (Miller) are designed to be placed posterior to the epiglottis. Proper positioning with the patient’s neck ﬂexed and head tilted slightly backward (the “snifﬁng position”) is essential to provide a straight line from the oral cavity into the trachea.
To expose the larynx, the laryngoscope is held with the left hand, and the blade is ﬁrst placed in the right side and then moved to the middle of the mouth, sweeping the tongue to the left. A straight blade is advanced along the posterior wall of the pharynx, distal to the epiglottis, and then gently lifted and withdrawn against the anterior wall, elevating the epiglottis until the larynx is clearly seen. A curved blade is moved along the base of the tongue until the tip is in the vallecula, and the tongue and epiglottis are lifted forward until the cords are in view. The laryngoscope should not be used to ﬂex or extend the head by wrist movement because this may result in injury to the teeth. Introduction of an endotracheal tube should not be attempted unless the larynx is adequately exposed. A soft-metal stylet may facilitate intubation but should be removed after the tube passes the glottis so as not to injure the trachea.
Nasotracheal intubation is performed in a similar fashion except that the tube is inserted through the larger nostril, and a stylet cannot be used. When the tube reaches the pharynx, it may be grasped with a pair of curved forceps (Magill), with the balloon cuff being carefully avoided, and guided into the larynx and trachea.
After the tube has passed the vocal cords, it is advanced to a point approximately 2 to 3 cm proximal to the main carina. The low-pressure cuff is inﬂated with sufﬁcient air to overcome any leak during forced ventilation. It should be tested intermittently with a gauge to ensure that the cuff pressure does not exceed 20 mm Hg. Adequate placement should be conﬁrmed by auscultation of the lungs and epigastrium, visualization of chest rise, and the use of an end-tidal CO2 detector. After the tube is correctly positioned, it should be adequately secured. It is sound practice to follow intubation with chest radiography to determine the tube’s position.