|
By William Rosenblatt, MD,
Professor of Anesthesiology and Surgery
Yale University School of Medicine
Awake intubation (AI) remains a cornerstone of difficult airway management. The airway algorithms published by many national and international advisory groups have emphasized this.
Unfortunately, many clinicians steer away from awake intubation for a variety of reasons unrelated to patient risk and conditions, including lack of confidence in the skills required, time pressure, and fear of patient annoyance, discomfort, and cardiovascular stimulation. Much of this was recognized in the recent Fourth National Audit Project of the Royal College of Anesthetists (NAP 4) study.
AI is chosen based on an evaluation of patient safety. Once this decision is made, the clinician is obliged to follow this course as long as safety is maintained. Though analgesia of the airway is often the primary (if not the only) concern of most clinicians employing AI, I find it to be only one of 6 facets to success.
Six ingredients for a successful Awake Intubation
1.Explanation
The first critical aspect of AI is gaining the confidence and cooperation of the patient. By explaining your decision to pursue AI you gain the patient's trust. You will find that the majority of patients are willing to cooperate with AI once they understand its necessity. This explanation should take place outside the operating room, where you can have a calm discussion with the patient who is not distracted and may have the support of family, who may have their own questions.
2. Desiccation
The second key to success is to give a desiccant (drying agent) as soon as possible. A mistake often observed is the injection of an antisialogogue after the patient has entered the operating room. These drugs may require 15 minutes or more to have the desired effect. Beginning airway analgesia prior to effective drying can be counterproductive. There are four reasons a desiccant is used – 1) to remove the barrier of saliva to topical local anesthetic action on the mucosa, 2) to reduce dilution of topical anesthetics as oral manipulation stimulates saliva production, 3) to improve visualization during the intubation and 4) to reduce airway reflexes (coughing, laryngospasm) which excess saliva will encourage. Relative contraindications to anticholinergics include known atrial arrhythmic disease and closed angle glaucoma.
3. Nasal preparation
While waiting for the desiccant to take affect, preparation of the nose begins. Unless contraindicated (e.g., choanal atresia, pregnancy, coagulopathy, anticoagulation, propensity for epitaxis) the nose should always be prepared for two reasons: anesthetic agents in the nasal cavity will begin the anesthetic preparation of the oral and pharyngeal cavities via block of the lateral nasopalantine nerves, and should there be a plan change to nasotracheal intubation, the field is ready for manipulation. In general, orotracheal intubation is preferred to avoid traumatic nasal bleeding. But, if during attempts at awake orotracheal intubation, excessive gagging or hindrance to securing the airway is encountered, the anesthetic team may choose to intubate via the nasal route. Failure to have the nasal cavity prepared in advance may lead to patient discomfort, bleeding, and intubation failure. Preparation of the nose can be as simple as using a vasoconstrictor (e.g., oxymatazoline, phynelephrine) and is done immediately after desiccant administration.
4. Topical anesthesia
We next turn to airway analgesia. Though many invasive techniques have been described, most patients can be managed with topical anesthetic application. Though the choice of blocks may seem confusing, the clinician need only remember that three distinct regions of the airway require attention: the nasal cavity, the oral pharynx, and the hypopharynx-larynx-trachea. The nasal cavity is blocked by simple application of local anesthetic (LA). Though any LA may be used, I prefer to use an agent, which is available in multiple formulations so that I can choose the correct viscosity, yet easily calculate total dose. Lidocaine is such an agent. It is commonly available in 1%, 2%, 4% and 5% concentrations and as a solution, viscous solution, jelly, or petroleum based ointment. We often forget that local anesthetics can be a toxic when misused 7. A popular agent, benzocaine, is rapid-acting but has a narrow therapeutic window in patients susceptible to methemoglobinemia. The nasal passage is easily anesthetized with topical application of as little as 100mg of lidocaine. One-half inch per nostril of 5% lidocaine ointment placed on cotton swabs, or 2.5 cc of viscous solution injected via a plastic intravenous catheter, are effective techniques. These are placed gently and unrushed – if begun just after the injection of a desiccant, there is no need to hasten their application.
Once the patient is subjectively dry in the mouth, our attention is turned to the oropharynx block. The glossopharyngeal nerve travels through the base of the palatoglossal arch – the arch of tissue, which reaches from the uvula to the base of the tongue. A swab of lidocaine (50mg each side) is placed against the arch and held in place for 3 to 5 minutes. Holding the patient's tongue with a gauze pad will facilitate your finding the arch. A gag reflex when the arch is touched is a good sign that the mark has been reached.
To anesthetize the hypopharynx-larynx-trachea, the key is to apply a bath of LA that the patient then aspirates into the lower airway. Still holding the tongue, 100mg of viscous lidocaine solution is "dripped" onto the back of the tongue, or sprayed into the hypopharynx. By holding the tongue out of the mouth during this procedure, the patient is unable to swallow and will aspirate some of the agent.
The procedures above have used 300mg of lidocaine. A large margin of safety exists with the use of 400mg or even more lidocaine in the adult. If a fiberscope with a working channel is to be employed, the clinician may elect to apply another 100mg into the airway during the intubation attempts. Techniques that atomize or nebulize lidocaine, though often effective, may come close, or produce toxic serum levels.
5. Sedation
Another important aspect of AI is sedation. Sedation can be a key to a comfortable procedure. There are many sedatives that can be used, but certain basic cautions should be observed. First, pharmacologic agents should be judiciously titrated. Not only do we wish for the patient to maintain spontaneous ventilation, but also to continue to protect their own airway from obstruction and aspiration and to cooperate with procedures. Though it may be tempting to sedate a patient to the point where they are unaware of the procedures though spontaneously breathing, this may not be safe in many circumstances. Second, limit the number of agents used. Typically, no more than two sedatives will be needed. Though the clinician may be tempted to use separate drugs to cover all aspects of hypnosis, analgesia, amnesia, and suppress cough, this is rarely necessary or wise. In AI, over sedation must not be used as a substitute for good anestheitc block techniques.
6. Time management
Lastly, time management should be considered. Though this discussion began with the caveat that when the safety of the patient is of concern, little else matters, we must be aware of the constraints of time. Beginning our preparation early and in an unrushed atmosphere is key to success. Enlisting colleagues, timing other procedures and having equipment available in anticipation of need will all contribute to efficiency. Explanation of the reasons for AI, injection of a desiccant, preparation of the nose, and non-invasive airway blocks can all be accomplished before the patient enters the operating room. Once in the OR, proceeding with the intubation can be expeditious.
Please note that Dr. Rosenblatt is an uncompensated consultant to Ambu A/S.
|
