16 Airway Management and Sedation

History and Examination

History

Determine the mechanism of injury and whether there is any associated trauma (craniofacial, thoracic, or pulmonary) or spinal cord injury. If there is a plan for surgery, the patient may need to be intubated for general anesthesia. Assess for previous history of a difficult airway, including a history of prolonged intubation, head or neck radiation or surgery, history of rheumatoid arthritis (associated with atlantoaxial subluxation), Down’s syndrome (associated with abnormal airway anatomy and atlantoaxial subluxation), ankylosing spondylitis (which may limit neck movement), or a history of tracheostomy. A cardiac and pulmonary history should be assessed as well as a history of smoking. A history of last ingestion should be undertaken to ascertain aspiration risk.

Physical Examination

1. Assess difficulty of airway. The pneumonic H-LEMOON can be applied (Table 16.1). In patients in whom the difficult airway may be anticipated, alternative airway devices such as the Rusch FlexiSlip (Teleflex Medical, Research Triangle Park, NC) stylet, the gum elastic bougie, the fiberoptic scope, video laryngoscopes, or an intubating laryngeal mask airway (ILMA) may prove helpful. A laryngeal mask airway (LMA) of the appropriate size should be readily available for the patient in whom intubation is anticipated to be difficult.
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   

   Table 16.1 The H-LEMOON Pneumonic

   	Less Difficult Airway	More Difficult
   History	No history of difficult intubation	History of difficult intubation or tracheostomy
   Look externally	Normal face and neck No facial or cervical pathology	Abnormal facial shape Facial hair Overhanging incisors Narrow mouth Inability to protrude mandible Micrognathia Poor temporomandibular joint mobility Long, high-arched palate Facial or cervical pathology Short, thick neck Tracheal deviation Presence of vomitus or blood in oropharynx
   Evaluate the 3-3-2 rule	Mouth opening >3 finger breadths (4 cm) Hyoid-chin distance >3 finger breadths (4 cm) Thyroid cartilage-mouth of floor <2 finger breadths	Mouth opening <3 finger breadths (4 cm) Hyoid-chin distance <3 finger breadths (4 cm) Thyroid cartilage-mouth of floor >2 finger breadths
   Mallampati classification (best performed with the patient sitting, tongue protruding, and not phonating)	Class I: Fully visible tonsils, uvula, and soft palate Class II: Visibility of hard and soft palate and upper portion of the tonsils and uvula	Class III: Soft and hard palate and base of uvula are visible Class IV: Only hard palate visible
   Obstruction and Obesity	No airway obstruction BMI <30 kg/m2 and/or neck circumference <60 cm	Pathology in or surrounding the upper airway, difficulty swallowing secretions, stridor (ominous and occurs when <10% of airway patent), muffled (hot-potato) voice BMI >30 kg/m2 and/or neck circumference >60 cm
   Neck mobility	Complete flexion and extension of neck	Limited ROM of neck Presence of halo or neck immobilization devices History of cervical instrumentation

   
   

   Abbreviations: BMI, body mass index; ROM, range of motion.

   
   
2. Assess aspiration risk. Pneumonia secondary to aspiration and microaspiration is a common source of infection following intubation. Neurocritically ill patients have potential for aspiration secondary to decreased or altered level of consciousness, decreased gastric motility, increased sympathetic tone, and intermittent feeds. The goal of aspiration preventive measures is to decrease gastric stomach content volume, raise the pH of stomach content to greater than 7.25, and decrease the time of induction of unconsciousness to intubation.
   

   The American Society of Anesthesiology has suggested a period of 2 hours after the ingestion of clear liquids, 6 hours after a “light meal,” and 8 hours after a meal of fried or fatty food be utilized as a guideline for surgical patients undergoing elective surgical procedures.1 The administration of 100% oxygen to preoxygenate the patient, avoidance of positive-pressure ventilation during induction, the use of rapid sequence induction (RSI), and the institution of cricoid pressure have been advocated to decrease the risk of aspiration.

   
   
3. Assess ICP. It is essential for the laryngoscopist to take maneuvers to minimize elevations of ICP, such as to minimize laryngeal stimulation and to use maneuvers to avoid bucking, movement, and vomiting. Lidocaine 1% 1.0 mg/kg IV suppresses the cough reflex, may lower cerebral oxygen demand, reduces bronchospasm, and should be used in patients with suspected elevated ICP.
   
4. Assess hemodynamics. Intubation in the intensive care unit is often complicated by hemodynamic compromise and cardiovascular collapse. As many as a quarter of ICU patients may experience hemodynamic collapse, 10% experience cardiac arrhythmias, and 2% have cardiac arrest coincident with endotracheal intubation. Should multiple attempts at intubation be required, the incidence of cardiac arrest increases 1600%.¹
   

   In the hypovolemic patient who is hypotensive, a bolus of intravenous (IV) fluid is indicated. The judicious use of vasopressor agents may be indicated should hypotension persist. The use of etomidate as an induction agent should be considered in patients who are elderly, critically ill, or have tenuous hemodynamics. Etomidate (even a single dose) can suppress steroidogenesis and cause delayed hypotension after intubation related to relative adrenal insufficiency.

   
   
5. Assess immobilizations and restraints. Neurocritical care patients may sometimes be immobilized to prevent movement, which could be detrimental or dangerous to their condition. Devices such as hard cervical collars and halo frames restrict neck mobility. In patients with C-spine precautions who require emergent intubation, a two-person intubation can be undertaken, with one person providing in-line mobilization once the anterior portion of the cervical collar is removed. In the nonemergent setting, fiberoptic bronchoscopy should be strongly considered.
   

   The halo device provides the most rigid form of external cervical immobilization and prevents proper positioning for laryngoscopy by restricting atlanto-occipital extension. Oral intubation is often possible, but it is a function of other variables, such as mouth opening, tongue size, upper dentition, and ability to prognath the lower jaw forward. Techniques include awake or sedated fiberoptic intubation and the ILMA performed awake or asleep. Video laryngoscopy may be successful, but it requires expertise, and mask ventilation is often possible with the addition of oral airways. It is imperative that clinicians involved have: (1) skills and equipment for alternative intubation techniques, (2) a neurosurgeon or professional who can safely remove the halo if necessary, and (3) a rescue plan in case of failed ventilation in these challenging patients.

1. Equipment and preparation. The most commonly used laryngoscope is a Mac #3 curved blade, and in circumstances of larger patients, a Mac #4. A Miller #3 or #4 (straight blade) can also be used. A Mac blade is placed in the vallecula, while a Miller blade is placed over the epiglottis and lifted. Video-assisted laryngoscopes are gaining popularity and allow for group visualization of the airway. Such devices include the Glidescope (Saturn Biomedical System Inc., Burnaby, BC, Canada), the McGrath (Aircraft Medical, Edinburgh, Scotland), Airtraq (Prodol, Meditec S.A., Vizcaya, Spain), and the AWS (Pentax Corp., Montvale, NJ) (Table 16.2).
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   

   Table 16.2 Equipment Checklist

   Endotracheal tube with a stylet (usually 8.0 in men and 7.0 in women)

   Ambu bag with PEEP device attached to 100% O2

   Suction

   10 mL syringe

   Intubating laryngeal mask airway

   Capnometer/CO2 detector

   Oral and nasal airway

   Tape and tincture of benzoin

   
   

   Abbreviation: PEEP, positive end expiratory pressure.

   
   

   As part of the preparation for intubation, the cuff of the endotracheal tube (ETT) should be checked and lubricated, the light source on the laryngoscope should be confirmed, contraindications to medications should be reviewed, free-flowing IV access should be present, and blood pressure (BP), O₂, and heart rate (HR) continuous monitoring should be applied. In case of hypotension related to induction, the laryngoscopist should have available phenylephrine (mix 10 mg in 250 mL of normal saline (NS), 40 µg/mL; never inject phenylephrine directly from vial without dilution). In patients who are bradycardic and hypotensive, ephedrine is preferred (50 mg in 10 mL; 5 mg/mL).

   
   
2. Positioning. Place the patient in sniffing position (neck flexion and head extension) or neck extension to obtain adequate visualization of the glottic opening. Avoid this in patients with known or suspected C-spine injury.
   
3. Pretreatment. Preoxygenate with 100% O₂ for at least 1 minute prior to attempted intubation, and ensure that the O₂ saturation is at least 95% prior to an attempt. Lidocaine 1% 1.0 mg/kg IV suppresses the cough reflex, may lower cerebral oxygen demand, and reduces bronchospasm. Lidocaine spray can rarely cause methemoglobinemia, but it can be used to blunt coughing and gagging. IV lidocaine should be used in any patient with intracranial pathology, as it may blunt increases in ICP.
   
4. Induction (Table 16.3)²
   
   
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