53.4.1 How Do You Assess the Airway of This Patient?
Airway evaluation should focus on identifying patient characteristics predictive of difficulty in bag-mask-ventilation, use of extraglottic devices, performance of direct laryngoscopy and endotracheal intubation, and ease of achievement of a surgical airway.
The mnemonic MOANS (see Section 1.6.1) is used to identify predictors of ease of ventilation. This patient has at least two predictors of difficulty in ventilation. She is obese and she has a Mallampati Class IV airway.
Of the four predictors of difficulty in use of an extraglottic device identified by the mnemonic RODS (see Section 1.6.3), this patient has two predictors of difficulties. She has restricted mouth opening and decreased thoracic compliance due to her obesity and the gravid uterus.
The mnemonic LEMON (see Section 1.6.2) is used to identify features which would make direct laryngoscopy and intubation difficult. This patient demonstrates a limited mouth opening and a Mallampati Class IV airway. Restricted mouth opening may also limit the ability to utilize rigid and semirigid fiberoptic devices and video laryngoscopy for tracheal intubation.
The mnemonic SHORT (see Section 1.6.4) describes features that might make a surgical airway a challenge. Apart from obesity, this patient has no other features suggesting difficulty with a surgical airway if needed.
53.4.2 What Preparations Should Be Made Prior to Surgery?
The operating room should be prepared and anesthesia equipment checked. In light of the patient's obesity, limited mouth opening and a Mallampati Class IV airway, a difficult airway situation should be anticipated. Furthermore, the patient is at risk for gastrointestinal stasis, reflux, and aspiration. A difficult airway cart should be brought into the room and appropriately trained assistance should be available.
Prior to proceeding to the operating room, a thorough history and physical examination of the patient must be completed. Specific information regarding previous anesthesia experiences and airway management-related issues should be elicited and previous anesthesia records procured. In this case, the patient has limited mouth opening. The inter-incisor distance should be assessed to determine the potential utility of various devices and techniques available to the anesthesia practitioner.
The patient should be maintained NPO and have intravenous access established. She should receive acid aspiration prophylaxis in the form of metoclopramide 10 mg IV, ranitidine 50 mg IV, and 30 mL of 0.3 N sodium citrate by mouth.
The operating table should be prepared with a ramp to position the patient in anticipation of a difficult airway (see Figure 49-2). In addition, care should be taken to ensure that the patient is positioned appropriately on the operating table with left uterine displacement.
53.4.3 How Should the Airway of This Patient Be Managed?
The specific technique and devices used for airway management under any circumstances should be predicated on the results of the patient's airway assessment and the anesthesia practitioner's skill, proficiency, and confidence with various devices and techniques to secure the airway.
In light of this patient's airway assessment, a rapid-sequence induction followed by direct laryngoscopy would likely be a poor choice. The patient's airway should be secured prior to induction of general anesthesia. The patient should be treated with an antisialogogue in preparation for awake airway management. The patient's airway will need to be anesthetized with topical anesthetics. Specific details regarding the technique of topicalization of the airway may be found in Chapter 3.
While flexible bronchoscopic intubation will be the usual technique of choice for this patient, there are numerous alternative techniques and devices which may be used to secure the airway awake in this patient. The decision will be based on availability of equipment and the inter-incisor distance. For example, the patient can undergo a retrograde intubation with mild sedation. This technique has been used numerous times in patients with very limited mouth opening.14,21 In this patient however, it may be difficult to adequately locate the landmarks for a cricothyroid membrane puncture as a result of her obesity. However, with meticulous technique and adequate experience with the technique, it is possible to secure the airway. This technique has been thoroughly reviewed recently (see Section 11.6).22,23
There are a number of fiberoptic intubating stylets available (see Chapter 10). Shikani performed five awake intubations using the Shikani Optical Scope® during his initial report.24 The Bonfils retromolar fiberscope was used by Corbanese et al25 to successfully carry out awake intubation in 29 or 30 patients with difficult airway. These can be used with either direct laryngoscopy or with a jaw thrust to improve visualization. Most of these devices vary in diameter between 5 mm and 6 mm and can accommodate 5.5 mm ID and larger endotracheal tubes. A number of them have been used successfully to carry out awake intubations in patients with difficult airways or small mouth opening.26-29
Rigid fiberoptic laryngoscopes and video laryngoscopes, such as the Bullard laryngoscope, UpsherScope®, WuScope® and GlideScope®, may be useful in this patient. Cohn30 performed awake intubations using the Bullard laryngoscope in eight patients at risk for neurological injury and requiring awake intubation. However, none of the patients were specifically reported to have limited mouth opening. The Bullard has a spatula-like blade which may be useful in patients with limited mouth opening. Due to its profile, it may be possible to carry out laryngoscopy with an inter-incisor distance of as little as 6 mm. However, it may prove to be difficult to insert or manipulate an endotracheal tube of 6 mm ID or larger size. The WuScope®, due to its design, requires an inter-incisor distance of at least 20 mm to adequately accommodate the scope and endotracheal tube combination.31 The use of the GlideScope® for difficult airway management has increased in recent years. It has been used for awake intubation in patients with a difficult airway,32 and as an adjunct for awake bronchoscopic intubation.33 The GlideScope® provides an improved view of the laryngeal inlet and has been shown to have a high rate of intubation success. The newer model has a 14.5 mm blade flange profile which may be useful in this patient. It must be remembered that all of the optical stylets and video laryngoscopes share the disadvantage of fogging and require some antifogging maneuver prior to their use. In addition, as any blood or secretions in the airway will obscure the view, it is highly recommended that the oropharynx be suctioned prior to the insertion of these devices.
While numerous options to secure the airway of patients with an anticipated difficult laryngoscopic intubation have been discussed, the use of these devices in obstetrical patients is limited. However, it is the author's preference to perform an awake bronchoscopic intubation in this patient. Successful awake intubation will depend upon satisfactory topical anesthesia of pharyngeal and laryngeal structures. Airway edema which accompanies the pregnant state may pose a challenge to topicalization and considerable patience may be required.
Specific details of the techniques of topicalization and bronchoscopic intubation are discussed in Chapters 3 and 9.
53.4.4 What Is the Plan for Extubation of This Patient Following Appendectomy?
No difficult airway management plan is considered complete without a predefined strategy for the safe and successful extubation of the patient following the completion of the procedure. In this case, one must assure that all muscle relaxants have been reversed and the patient is fully awake, following commands, and able to protect her airway prior to extubation. All equipment required for reintubation should be ready and available at the time of extubation. The patient should be extubated in the operating room where access to equipment and medications is assured.