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then gently lifted and withdrawn against the anterior wall, elevating the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.