Anesthetic Considerations for Orthognathic Surgery

In: Anesthesia

23 Feb 2010

Anesthetic Considerations

Orthognathic surgery is a type of orthopedic surgery that has gained wide popularity in maxillofacial surgery. Here the maxilla, mandible, or both are sectioned into pieces and are reassembled with plates or wires to improve the facial appearance, to improve the occlusion of the teeth, or for both. The maxilla, mandible, or both may be brought forward, taken back, made smaller by removing bone, or made larger by bone grafting, or the maxilla or the mandible may be brought forward while the other is moved in the opposite direction. Usually, the patients undergoing these operations are young adults; thus, most are of American Society of Anesthesiologists (ASA) Classificaiton I. The main problems of these operations are the airway management and control of bleeding.

AIRWAY ASSESSMENT

Proper airway assessment is of great importance for management of these patients. It includes the assessment of the degree of mouth opening, movements of the jaw and neck, and patency of the nasal passages, the latter being of concern because the intubation has to be carried out nasally. If the osteotomy is in a patient with a cleft palate, the location of the cleft is determined since the osteotomy may involve the opening of the cleft, in which event it is preferable for the endotracheal tube to be inserted through the opposite nasal passage. Further, it may be difficult to pass the endotracheal tube through the nasal passage on the side of the cleft.
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Table 1. Difficulty of Intubation

Class Visible Structures Difficulty of Intubation
I Soft palate, fauces, uvula, Intubation with laryngo
pillars visible scope easy
II Soft palate, fauces, uvula May encounter some diffi-
visible culty (35%)
III Soft palate, base of uvula Mostly difficult
visible
IV Soft palate not visible at Very difficult
all

There are certain markers that indicate that intubation would be difficult. Limited opening of the mouth, a small mouth, bucked teeth, a receding chin, and a short neck are some such markers.

There are a number of classifications for airway assessment. Of these, the most useful bedside assessment is the classification of Mallampati et al as modified by Samsoon and Young. Here the difficulty in intubation is graded according to the visibility of structures in the pharynx when a seated patient opens the mouth (see Table 1).

However, it must be noted that patients with overpro-jection of the maxilla and restricted neck movements may be classified as easy intubations with this classification though in practice they may be extremely difficult to intubate.

The test of Patil et al, measuring the thyromental distance, is also useful at bedside. With the head fully extended, if the distance from the prominence of the thyroid cartilage to the bony point of the chin is greater than 7 cm, intubation should be easy. If less, intubation will be difficult.

Table 2. Risk score

Factor Risk Score
0 1 2
(1) Body weight (kg) <90 90-110 >110
(2) Head and neck movements above 90° about 90° ± 10° below 90°
(3) Jaw movements IG > 5 cm IG < 5 cm IG < 5 cm
SLux > 0 SLux = 0 SLux < 0
(4) Mandibular recession Normal Moderate Severe
(5) Buck teeth Normal Moderate Severe

The test of Wilson et al is another test that can be carried out at bedside. However, it is more complicated than the other two assessments since a risk score has to be calculated. The risk score is based on 5 factors. For each factor, a score of 0-2 is allocated, as shown in Table 2.

Radiological assessments of anatomical factors that may indicate difficult intubation were described by White and Kander as follows:

(1)    the ratio of the effective mandibular length to the posterior depth of the mandible being less than 3.6,

(2)    an increased depth of the mandible,

(3)    a reduced distance between the occiput and the spinous process of CI (atlanto-occipital distance) and, to a lesser extent, the C1-C2 interspinous gap, and

(4)    reduced mobility of the mandible.

The problem with this classification is that it cannot be carried out easily at bedside.
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Evans and Cormack have described a computer-generated equation as

Y = 27.1 – 12.2^ + 1.3X2,

where Хг = posterior depth of the mandible (cm) and X2 = atlanto-occipital distance (cm), both measured from X-rays of the patient. If Y is negative, there may be difficulty with laryngoscopy and intubation.


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Blog invites submissions of review articles, reports on clinical techniques, case reports, conference summaries, and articles of opinion pertinent to the control of pain and anxiety in dentistry.

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