Successful surgery is built on a foundation of airway management. While each of surgery's moving parts plays a critical role in a procedure, difficulties faced in establishing a patient's airway can stop it at square one. It's been reported that one in every 2,230 anesthetic administrations involves a failed intubation, but in many cases you can anticipate a difficult airway. Here's what a thorough pre-op evaluation should include to reduce the likelihood of airway trouble.
Defining the difficult airway
What we anesthesia providers mean by the phrase "difficult airway" is a function of the series of tasks we're responsible for during surgery. After we anesthetize the patient, we often employ mask ventilation to keep him breathing. Depending on patient factors and surgical requirements, we can then perform a laryngoscopy to visualize the glottic opening, then intubate the trachea so that the patient can be ventilated by way of a breathing tube.
With regards to this process, a difficult airway situation could refer to one or both of the following types of incidents: either the provider experiences difficulty in maintaining the patient's mask ventilation, which is a very big problem; or he finds it difficult to insert the breathing tube due to poor visualization of the airway's anatomy. Three or four unsuccessful attempts indicates a failed intubation.
In the outpatient arena, most patients selected for surgery particularly those undergoing elective procedures tend to be healthy with few or no previous incidents of difficult ventilation or intubation. But cautious preparation is always a good idea, especially when it can potentially identify otherwise unanticipated obstacles.
If your patient has had surgery before, your anesthesia providers can learn a lot from the past. The most important predictor of difficulty in ventilating or intubating a patient is his medical history, so you should review past experiences with anesthesia. If a difficulty occurred, you may know what to expect.
Interview the patient during the pre-surgical evaluation, if possible, or by telephone. Ask if he was told, following the previous procedure or procedures, that he'd presented airway difficulties of either sort during surgery.
Conduct the interview well in advance of the scheduled surgery. If the patient reports previous difficulties, you'll want to contact the facility that hosted the procedure and request that it fax you copies of its records for review (see "How to Create an Anesthesia Passport" on page 76). Speaking with the anesthesia provider who attended the case may also offer perspective on what to expect.
Known and unknown
The American Society of Anesthesiologists' "Practice Guidelines for Management of the Difficult Airway" provides solid guidance on how to treat a patient who presents problems in the OR. In contrast, we don't have a surefire single test or physical exam finding that will accurately tell us, in and of itself, whether a difficult airway situation will arise. What we do have, however, is a list of factors that, when considered jointly, can give us a fairly good estimate of the likelihood of such an incident.
Potential ventilation difficulties can often be predicted through a patient's visible physical characteristics. But if you don't meet the patient until the day of surgery, you might not recognize these issues unless they're noted in a medical history or discussed during a phone interview.
The most common indicators that a patient may present with mask ventilation difficulties include:
- a full beard or other extensive facial hair (which may prevent the mask from properly fitting the face),
- chronic snoring or obstructive sleep apnea,
- a limited range of cervical motion (for example, the patient can't touch his chin to his chest or extend his neck), whether it results from a short or thick neck, previous head or neck surgery, or trauma,
- dental factors, such as having no teeth, large or irregularly spaced teeth or dentures,
- an oversized or undersized jaw,
- facial structure abnormalities such as a narrow face or high arched palate, and
- a large tongue.
During intubation, a laryngoscope's rigid blade is placed into the mouth of an anesthetized patient. The patient's tongue is displaced with the laryngoscope blade, his neck is extended and the airway is visualized in order that the breathing tube can be placed into the trachea.
The more space that's available to displace the tongue, the better. So patients with small jaws, limited ability to open the mouth or a reduced range of cervical spine motion obviously present problems.
Most anesthesia providers rely on the Mallampati classification, which assesses the size of the tongue relative to the mouth, to predict possible intubation difficulties. The Mallampati classification is determined by examining the patient in a sitting position, with his mouth wide open and his tongue protruding as much as possible, without phonating. The more structures that are seen, the better for intubation, as follows:
- Class I: the soft palate, fauces (palatoglossal and palatopharyngeal arches), uvula and tonsillar pillars are visualized.
- Class II: the soft palate, fauces and a portion of the uvula are visualized.
- Class III: the soft palate and the base of the uvula can be visualized.
- Class IV: only the hard palate can be visualized.
The upper lip bite test assesses a patient's jaw displacement. Ask the patient to bite his upper lip with his lower incisors. A larger range of motion suggests an easier intubation, as detailed below:
- Class I: the lower incisors can bite the upper lip above the vermillion line (where the red of the lip meets the skin of the face).
- Class II: the lower incisors bite the lip below the vermillion line.
- Class III: lower incisors can't bite the upper lip.
Anesthesia providers should also assess the patient's thyromental distance. In normal anatomy, the space between the patient's laryngeal prominence and the mentum at the base of the mandible should fit three of the patient's fingers. Additionally, the patient's mouth opening or interincisor distance should be greater than three fingerbreadths.
As mentioned above, none of these physical exam components are comprehensive on their own, but the presence of several indicates a strong probability that airway difficulties may be encountered.
In the event
Even after reviewing patients' medical histories and conducting physical exams, you're still going to see a small but present incidence of patients with unanticipated airway difficulties. In the same-day surgery field, that will likely require that you factor in the possibility of postponing a case and performing it in another venue. But it also demands that every facility have a difficult airway cart containing the equipment necessary to rescue and secure an airway at each anesthetizing location.
The tools are available and proven. If, for example, we encounter difficulty during mask ventilation with an oral airway in place and a jaw thrust performed, we all reach for a laryngeal mask airway. It's very rare to have an LMA fail to ventilate the patient.
On the Web
Download ASA's "Practice Guidelines for Management of the Difficult Airway" at www.asahq.org/publicationsAndServices/Difficult%20Airway.pdf
The video laryngoscope is turning out to be a valuable instrument as well. Video technology has utterly transformed surgery, but only recently has it been applied to anesthesiology. Similar to the rigid blades we've been using for the past 30 or 40 years, except with the addition of a camera at the tip, a video laryngoscope lets you visualize anatomy that you couldn't see before without having to learn new skills.
The thing to remember about unanticipated airway difficulties is that we can't predict them, so we need to be prepared for them in the event that they occur. To remain sharp, we need to practice our skills, regularly perform rescue techniques and be familiar with equipment that's routinely used.