mouth to the larynx. This is accomplished using approximately 30° of cervical flexion using pillows/blankets along with extension of the atlanto‐occipital joint, the classic ‘sniffing position.’
Positioning obese patients may be particularly challenging. This can be accomplished by forming a ramp, elevating the upper back and shoulders in order to accommodate adequate cervical flexion. Confirming horizontal alignment of the external auditory meatus with the sternal notch can be a useful guide.
Preoxygenation
Adequate preoxygenation should be provided in all but the most emergent situations.
The aim is to replace nitrogen in the lungs with oxygen. This increases the length of time before desaturation when the patient is apneic (‘apnea time’), providing a margin of safety in case ventilation and intubation become difficult.
Preoxygenation can be performed using a facemask, continuous or bilevel positive airway pressure, or a high flow nasal cannula (HFNC) providing 100% oxygen at flows of at least 10 L/min. It typically requires approximately 3 minutes of normal tidal volume breathing to achieve an end‐tidal oxygen concentration of approximately 90%.
Given normal functional residual capacity (FRC) of about 2 L, and an oxygen consumption rate of about 200–250 mL/min, a properly preoxygenated adult should have an apnea time of about 5–8 minutes before significant desaturation. Reductions in apnea time should be expected in conditions in which FRC is decreased (i.e. obesity, pregnancy, tense ascites) or conditions of increased oxygen consumption (i.e. sepsis, pregnancy, hyperthyroidism).
Bag and mask ventilation
The ability to ventilate a patient using a bag and mask is by far the most important skill for any airway provider to master. The inability to intubate the trachea is not fatal if mask ventilation is possible, making it a vital component of the ASA difficult airway algorithm.
Relative contraindications to mask ventilation are full stomach/regurgitation risk, severe facial trauma, and unstable cervical spine fractures.
Mask ventilation is performed with the provider holding the mask in his or her left hand with the mask over the patient’s nose and mouth with the third, fourth, and fifth digits holding the mandible and lifting the face into the mask while the thumb and index finger form a ‘C’ shape around the collar aspect of the mask near the connection to the circuit. As the bag is squeezed one should note chest rise and condensation in the mask, and should hear no air escape which would indicate a leak due to an inadequate seal. Care should be used not to compress the submandibular tissue as this can collapse the airway and make ventilation more difficult.
If mask ventilation proves difficult, one can employ a two‐handed technique in which one provider holds the mask in both hands with their thumbs on top of the mask and remaining digits on the mandible lifting the face into the mask while an assistant squeezes the bag. Oral and nasal airways can also be useful as they pull the tongue and epiglottis away from the posterior wall of the pharynx, allowing more airflow.
Laryngoscopy and confirmation of placement
After ensuring proper preparation, equipment set‐up, functioning monitors, positioning and preoxygenation, the patient is typically administered an apnea‐inducing medication as well as a paralytic agent, both of which are chosen based on patient conditions as well as the clinical situation. It should also be noted that in certain conditions such as cardiac arrest, induction agents may not be necessary.
When the patient is deemed appropriately anesthetized, the laryngoscope is held in the provider’s left hand while the right hand opens the patient’s mouth using his or her thumb and index finger in a scissoring motion. The laryngoscope is then inserted into the mouth using care not to damage the patient’s lips or teeth. In the case of the curved MAC blade, the tongue is swept to the left and the tip of the blade placed in the vallecula just anterior to the epiglottis, while the straight Miller blade is inserted in midline position beneath the epiglottis. The handle of the laryngoscope is lifted upwards and anteriorly, exposing the vocal cords. The handle should never be tilted backwards as this can result in dental damage. The ETT is then inserted through the vocal cords under direct visualization. After ETT insertion, the stylet (if used) is removed as is the laryngoscope. The pilot balloon is then inflated with air using a 10 mL syringe to no more than 30 mmHg of pressure.
To confirm tracheal placement, the ETT is connected to a bag ventilation circuit and ventilated, observing bilateral chest rise, condensation in the ETT, and, most importantly, continuous end‐tidal CO2 via capnography – considered the gold standard. If continuous end‐tidal CO2 is not detected, esophageal intubation should be suspected and laryngoscopy should be reattempted.
The distal tip of the ETT should lie beyond the vocal cords but above the carina, avoiding mainstem intubation. In adults this typically correlates to 21–23 cm at the patient’s lip. A CXR should be ordered immediately after placement to confirm proper position.
Video 1.1 demonstrates a successful endotracheal intubation of a morbidly obese patient. Note the ready availability of all necessary equipment including suction, laryngoscope, ETT, and oral airway. Also, note the proper patient positioning, including approximately 35° cervical flexion aided by the use of multiple blankets to ramp the shoulders as well as slight head extension. This combination allows for a nearly straight line of sight from the open mouth to the trachea. A MAC blade is used in the left hand and it sweeps the tongue to the side after the right hand scissors the mouth open. The blade is placed in the vallecula. Force is applied in a 45° direction to visualize the glottis opening, not rocked back against the upper incisors. The ETT is directly visualized as it passes between the vocal cords. The laryngoscope is then removed, and the ETT cuff is inflated with no more than 10 mL of air. While bilateral breath sounds and presence of fog in the ETT should indicate proper placement, the gold standard for proper placement is continuous end‐tidal CO2 waveform capnography.
Rapid sequence induction
This is a specialized method of induction used when the risk of pulmonary aspiration is particularly high.
The goal is to achieve optimal intubating conditions in the fastest time possible.
After preoxygenation, cricoid pressure is held by an assistant while induction agents (see Chapter 2 for agents and dosages) are given followed by 1.5 mg/kg of succinylcholine or 1 mg/kg of rocuronium, and laryngoscopy is attempted without mask ventilation. Cricoid pressure is maintained until confirmation of tracheal intubation is observed.
Difficult airway
Most difficult airways can be anticipated, and care should always be taken to recognize them with proper assessment, as unanticipated airway difficulties subject the patient to potential hypoxia, cardiovascular collapse, and neurologic damage.
A distinction should be made as to whether the potential difficulty lies in the ability to mask ventilate, to intubate, or both.
A good rule of thumb is to never intentionally make a patient apneic unless one is certain that ventilation will be possible.
Proper planning and set‐up, availability of equipment, positioning, and adequate preoxygenation
