Key words: Anatomy: oropharyngeal axes. Anesthetic techniques: tracheal intubation. Equipment: laryngeal mask airway.
THE laryngeal mask airway (LMA) has been used widely for airway management during general anesthesia in the last decade. There have been reports in which the LMA successfully secured the airway as an alternative and as an aid to anticipated difficult tracheal intubation in patients with ankylosing spondylosis of the cervical spine or atlantooccipital joint due to severe rheumatoid arthritis. [2-4]However, Pennant and White suggested that the use of the LMA is contraindicated in patients who are unable to extend the neck because of ankylosing spondylitis, severe rheumatoid arthritis, or cervical spine instability. This controversy remains unresolved.
In this report, we describe anesthesia for a patient with advanced rheumatoid arthritis in whom LMA insertion was impossible. The reason was thought to be the acute angle between the oral and the pharyngeal axes at the back of the tongue. We investigated the correlation between the angle and difficulty of LMA insertion in an attempt to resolve the controversy.
A 65-yr-old, 39-kg woman, diagnosed with rheumatoid arthritis at age 30 yr, was admitted to our hospital for right total knee replacement.
On admission, her mouth opening was greater than 4 cm but her upper airway Mallampati classification was grade 4. The patient requested general anesthesia and refused awake intubation. General anesthesia combined with spinal block was planned.
Twenty five milligrams pirenzepine and 0.25 mg brothizolam were given orally 90 min before surgery. The patient was monitored with a continuous electrocardiogram, a pulse oximeter, and blood pressure. Spinal puncture was performed, and 10 mg tetracaine was injected. After confirming development of a sensory block to the T7 dermatome, 150 mg thiopental was administered, and inhalation of 4% sevoflurane with 50% N sub 2 O in oxygen was initiated via mask. The lungs could be manually ventilated easily. Laryngoscopy revealed a grade 4 laryngoscopic view, as defined by Cormack et al. We chose the LMA as an alternative airway to an endotracheal tube because it has been used for the anticipated difficult intubation. [7-10]However, insertion of the LMA (Intavent, size #3, Henley-on-Thames, England) was unsuccessful despite three attempts using the standard technique recommended by Brain.# We ensured the mask tip remained flattened against the hard palate and avoided the tongue, but the cuff tip of the LMA faced the posterior pharyngeal wall and was curled. Even with the alternative technique, [11,12]using a laryngoscope, or with Guedel technique, insertion of the LMA was impossible. We tried to flatten the mask tip and press the LMA forward into the posterior hypopharyngeal wall, using fingers, a spoon, a Magil's forceps, and a self-maintaining retractor. All these attempts, however, followed the same course, in which the mask tip folded over or the mask tube kinked against the posterior pharyngeal wall. Also, the LMA could not be advanced further downward onto the posterior pharyngeal wall.
Surgery was started under general anesthesia with sevoflurane and nitrous oxide in oxygen via a face mask. Her intraoperative course was uneventful.
The roentgenogram of her neck was compared with those of five normal patients in whom the LMA had been successfully inserted. A series of roentgenograms of the neck at maximal head extension revealed the following: The angle between the oral and the pharyngeal axes at the back of the tongue was 105 plus/minus 2 degrees in five normal patients (Figure 1(a)), whereas that angle was 70 degrees in this patient (Figure 1(b)). The narrow angle between the oral and the pharyngeal axes at the back of the tongue was considered a reason for impossible LMA insertion in our case. We further investigated the relationship between LMA insertion and the degree of this angle as follows.
An aluminum plate was bent to an angle corresponding to the 70 degrees angle between the oral and the pharyngeal axes at the back of the tongue in this patient's roentgenogram. After lubrication of the deflated cuff with lidocaine jelly (Xylocaine jelly, Astra, Sweden), we slid the LMA along the curvature of this model. However, it jammed against the wall at the corner (Figure 2(a)). By the same method, LMA insertion was tested with the plate bent at a 105 degrees angle, corresponding to the angle between the oropharyngeal axes in patients in whom the LMA was successfully positioned (Figure 2(b)). Finally, we tested LMA insertion using the same procedure and changing the angle at which the aluminum plate was bent, in 5 degrees increments from 110 degrees to 75 degrees. These results showed that, (1) at an angle greater than 90 degrees, the LMA successfully slid along the curvature at the corner of this model, (2) at approximately 90 degrees, the LMA could not be advanced without kinking at the corner, (3) at an angle less than 90 degrees, the LMA jammed against the wall at the corner.
LMA insertion appeared to be easier when the angle between the oral and the pharyngeal axes was greater than 90 degrees at the back of the tongue. [13-15]The angle in a patient in whom the LMA was successfully inserted is usually 105 degrees when the neck is flexed and head extended, the maneuver considered necessary for successful LMA insertion. There have been few reports that refer in detail to difficult LMA insertion because of narrowing in this angle. The current findings suggest that successful LMA insertion requires the angle to be greater than 90 degrees.
In conclusion, we presented a case of anesthesia for a patient in whom LMA insertion was impossible. An angle between the oral and the pharyngeal axes of less than 90 degrees at the back of the tongue may make LMA insertion impossible.
* Brain AIJ: The Intavent Laryngeal Mask Instruction Manual. 2nd edition. Henley-on-Thames, Intavent International, 1991.