Intubation

11 Intubation

John W. Liang, Elena Solli, and David A. Wyler

Abstract

Endotracheal intubation is a key skill in the neurointensivist toolbox. The neurocritical care patient demands additional attention to blood pressure and carbon dioxide control. It is important to be able to properly assess the patient’s airway, have all essential equipment ready, and anticipate any potential difficulties during the procedure.

Keywords: airway, respiratory failure, intubation, endotracheal, oxygenation

11.1 Introduction

Securing and maintaining an airway is one of the most important components of resuscitation and critical care medicine. This chapter focuses on evaluation and management of the airway. While endotracheal intubation is typically the end goal, one must keep in mind that the skill of manually ventilating a patient is more important and often more difficult. Inability to ventilate a patient will bring panic to even the most seasoned practitioner. Therefore, all trainees should practice and develop good ventilation techniques (i.e., obtaining good seal with bag-valve mask) taught in Advanced Cardiac Life Saving courses before attempting intubation.

11.2 Relevant Anatomy/Physiology

Endotracheal intubation can be achieved orally or nasally. The oral route is more common and preferred. The nasopharynx joins the oropharynx near the base of the tongue. The vallecula is a cavity formed by the base of the tongue and the epiglottis and is used as a landmark for placing intubation blades/scopes. Best practice is to avoid lifting force while visualizing these landmarks as lacerations to the soft tissues may otherwise occur. The epiglottis is a cartilaginous flap attached to the larynx entrance and serves as a protective mechanism covering the larynx during swallowing to prevent food from entering the trachea and lungs ( Fig. 11.1). The larynx ends and the trachea begins at the level of the cricoid cartilage. The trachea continues down into the carina and bifurcates in the left and right main stem bronchi. The left bronchus is more angulated due to space taken up by the heart whereas the right bronchus is shorter and more vertical; thus the endotracheal tube, if advanced too far, is more likely to be in the right bronchus. Most providers perform intubations by positioning themselves at the head of the bed and often obtain a view as seen in Fig. 11.2.

Fig. 11.1 Oral cavity. Artist’s drawing of a midsagittal section of the oral cavity and pharynx. (Reproduced with permission from Schuenke et al., Atlas of Anatomy, © Thieme 2012, Illustration by Karl Wesker.)

Fig. 11.2 Laryngoscopic view.

11.3 Indications

The primary indications for intubation can be broken down broadly into three categories: airway, lung, and tissue.

11.3.1 Airway

Airway management is the first priority in the time-honored “ABC” protocol of emergency resuscitation. Maintaining airway patency is essential for oxygenation. Issues that can lead to airway obstruction in patients with impaired consciousness or bulbar dysfunction include vomit or inability to clear secretions and mechanical blockage of the pharynx by the tongue, or laryngeal edema. In the Neuro-ICU population, intubation is mandatory to protect the airway when treating patients with refractory intracranial pressure (ICP) crises or refractory status epilepticus with general anesthetics.

11.3.2 Lung

Respiratory failure, either hypercapnic or hypoxic, requires intubation for invasive mechanical ventilation. Signs of impending respiratory failure include increased work of breathing with use of accessory muscles, difficulty speaking in full sentences, rapid shallow breaths, and nasal flaring. Common causes of hypoxic respiratory failure include atelectasis, aspiration, pneumonia, pulmonary edema, and pulmonary embolism. Patients with neuromuscular disease such as Guillain-Barré syndrome (GBS) or myasthenia gravis may require elective intubation in anticipation of impending respiratory failure as part of the disease course. The “20–30–40 rule” (vital capacity < 20 mL/kg, negative inspiratory force < 30 cm H₂O, maximal expiratory force < 40 cm H₂O, respectively) is a commonly cited pulmonary function threshold for intubation in GBS. As with all critically ill patients, the bedside clinical assessment should take precedence over these generic cutoff values in intubation decisions.

11.3.3 Tissue

The mantra of the Neuro-ICU is to prevent secondary brain injury. Recent trials have shown a potential benefit in avoiding brain hypoxia (brain tissue oxygen tension < 20 mm Hg).1 Intubation plays an integral part in optimizing oxygen consumption in patients with brain injury. Intubation and sedation should be considered for patients with Glasgow coma score (GCS) < 8 as this will decrease energy expenditure and lead to improved brain oxygenation. Additionally, patients with ICP crises may require intubation for hyperventilation purposes.

11.4 Contraindications (and Precautions)

Aside from a “Do Not Intubate” (DNI) order, there are no true contraindications to intubation. There are situations in which the technique of intubation needs to adjusted and extra precautions taken. Therefore, proper assessment for a difficult airway is recommended in nonemergent cases.

11.4.1 General Assessment for Difficult Airway

Presence of the following physical characteristics should prompt consideration for potential difficult airway. Depending on the practitioner’s comfort and skill level, consider alternate routes of intubation such as awake intubation by direct or video laryngoscopy, nasotracheal intubation, and flexible fiber-optic intubation.

•Cervical spine: The presence of possible neck instability (i.e., trauma) or limited mobility (i.e., short neck, prior surgery, rheumatoid arthritis) will restrict the ability to adequately position the patient and obtain a good view of the airway

•Patients with excessive facial hair, facial trauma, absence of teeth, and active oral or nasal bleeding may make it difficult to achieve a proper face-mask seal for effective ventilation

•Patients with limited mouth opening (typically less than three finger breadths)

•Patients with large tongue (i.e., Down syndrome) and poor visualization of the pharynx; a high Mallampati score is associated with difficult intubation ( Fig. 11.3)

•A short thyromental distance, from the Adam’s apple to the chin, of less than three finger breadths is associated with an anterior airway and poor visualization during laryngoscopy ( Fig. 11.4)

Fig. 11.3 Mallampati score.

Fig. 11.4 Thyromental distance.

11.5 Equipment

Proper preparation is of utmost importance for successful intubation. It is essential to have all necessary equipment ready and easily accessible in anticipation of encountering a difficult airway. The mnemonic SOAP ME is useful as an initial equipment check 2

•S – Suction turned on and ready to go

•O – Oxygen with bag-valve mask and nasal cannula @ 15 LPM

•A – Airway

○Glidescope or laryngoscope (Mac or Miller blade)

○Endotracheal tube (typically size 7 mm for adult women and 7.5–8.5 mm for adult men)

○Stylet

○Syringe (used to inflate cuff)

○Oral airway, nasal airway

○Supraglottic airway device (SAD)—laryngeal mask airway, esophagealtracheal double-lumen airway

•P – Pharmacology (see Table 11.1)

○Pretreat

○Induction

○Paralytic

•M – Monitoring

○SpO₂

○Blood pressure

○Electrocardiogram (ECG)

•E – End tidal CO₂

11.6 Technique

•Evaluate the patient for a potential difficult airway: As discussed in the preceding section, it is always best to have a backup plan if a difficult airway is anticipated.

•Pre-oxygenate/Ventilate: The ability to ventilate a patient is key and will bring ease of mind to the intubation team as this buys you time to wait for advanced backup to arrive (if needed). Inability to ventilate the patient is an emergency as this severely limits the time and number of intubation attempts before life-threatening hypoxia sets in.

In conscious patients, passive breathing of 100% oxygen for 5 minutes should provide adequate reserve for intubation. In unconscious patients, insertion of an oral or nasal airway is advised to help prevent the tongue from blocking air flow. Provide ventilation via face mask with good seal. Ensure good chest rise with appropriate oxygen saturation.

•Medicate: Once the patient is pre-oxygenated, proceed to pharmacological sedation followed by paralysis.

In patients with no cervical neck restriction, perform a head-tilt/chin-lift maneuver to place the head into a sniffing position ( Fig. 11.5). This helps prevent the tongue from obstructing the airway and aligns the airway for direct visualization.