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We conclude our discussion of airway management this week. The "Mallampati" classification is commonly used to assess the airway prior to induction of general anesthesia, in order to predict difficult intubation.

1.  Describe the Mallampati classification: how is the test performed, how many classes are there, and what features are visible with each?
2.  How well does the system predict difficult intubation?

Mallampati分级常用于全麻诱导前气道的评估，以预防插管困难。

1.  请叙述Mallampati分级：如何实施？分哪几级？每级可观察到的特点？
2.  预测困难插管的方法效果如何？

参考答案：

1.  请叙述Mallampati分级：如何实施？分哪几级？每级可观察到的特点？

呼吸道的口咽分级最初由Mallampati[1]于1983年提出，随后在1985年通过一前瞻性研究得到证实[2]，从而成为麻醉科医生评估气道标准的基本工具。其优点有实施方便、快捷、可重复、无创。

最初对该方法的描述[2]，假设患者处于坐位，最大程度的张口并伸舌。患者不发声；头位不固定。后来为观察到口咽部的结构进行分级：

Class 1：可见咽腭弓、软腭和悬雍垂；
Class 2：可见咽腭弓、软腭，但悬雍垂被舌根遮挡；
Class 3：只能看到软腭。

[注：最初的Mallampati分级分为三级，但很多麻醉科医生使用Samsoon和Young[3]提出的四级。该分级一级与Mallampati分级相同，二级为可见软腭、咽部和悬雍垂；三级为可见软腭和悬雍垂基底部，四级为不能看到软腭。]

给与患者规范的全麻诱导后，使用Macintosh 3号喉镜片实施喉部暴露，通过下列四种方法评估喉部可见度：

1级：声门暴露充分（可见前、后联合）
2级：声门部分暴露（不能看到前联合）
3级：声门无法暴露（只能看到小角软骨）
4级：声门无法暴露（不能看到小角软骨）

2.  预测困难插管的方法效果如何？

Mallampati等人为目测法3和4级并不合适。如果我们预计困难气道分级为3级，原始数据为：

真阳性（TP）=14，假阳性（FP）=1，假阴性（FN）=14，真阴性（TN）=181

可得出如下结果：

敏感性=TP/(TP+FN)=14/(14+14)=50%
特异性=TN/(TN+FP)=181/(181+14)=99%

这表明通过这些试验对于正常气道的鉴别很容易，但可能漏诊许多典型的困难气道。随后Cohen等[4]研究发现了相似结果：敏感性=42%，特异性=91%。最近，Tse等[5]研究认为该试验可靠性较差：敏感性=66%，特异性=65%，阳性预测率（TP/[TP+FP]）只有22%，意味着相对于真阳性的实际数值而言，有大量的假阳性。而因此对困难气道阳性均采取规范的困难气道处理程序，这样导致很多实际上为正常气道的患者过度治疗。

Describe the Mallampati classification: how is the test performed, how many classes are there, and what features are visible with each?

The oropharyngeal classification of the airway, first suggested by Mallampati in 1983 (1) and subsequently tested in a prospective study in 1985 (2) has become the standard basic assessment tool for anesthesiologists. Its advantages include ease and rapidity of performance, reasonable reproducibility, and noninvasiveness.

In the original description of the method (2), the patient assumes the sitting position, opens the mouth maximally, and extends the tongue. The patient did not phonate; head position (neutral vs. extended) was not specified. The visibility of the oral and pharyngeal structures was then rated according to a three point scale:

1.  Class 1: Faucial pillars, soft palate and uvula could be visualized.
2.  Class 2: Faucial pillars and soft palate could be visualized, but uvula was masked by the base of the tongue.
3.  Class 3: Only soft palate could be visualized. (ref 2, page 430)

[Note the original Mallampati test utilized a three-Class scale. Many anesthesiologists use a four-Class scale popularized by Samsoon and Young (3). This scheme essentially duplicated Mallampati's Class 1, but described Class 2 (soft palate, fauces, uvula), Class 3 (soft palate, base of uvula), Class 4 (soft palate not visible at all).]

Patients were then given a standardized general anesthetic induction and laryngoscopy was attempted in a standardized fashion with a Macintosh #3 blade. The quality of visualization of the larynx was then assessed on a four point scale:

1.  Grade 1: Glottis (including anterior and posterior commissures) could be fully exposed.
2.  Grade 2: Glottis could be partly exposed (anterior commissure not visualized).
3.  Grade 3: Glottis could not be exposed (corniculate cartilages only could be visualized).
4.  Grade 4: Glottis including corniculate cartilages could not be exposed. (ref 2, page 431)

How well does the system predict difficult intubation?

Mallampati et al. defined Grade 3 and 4 visualizations to be "inadequate". If we assume a predicted difficult airway to be Class 3, then the original data was:

True positive = 14
False positive = 1
False negative = 14
True negative = 181

This yields:
Sensitivity=TP/(TP+FN)=14/(14+14)=50%
Specificity=TN/(TN+FP)=181/(181+14)=99%

This means the test successfully identified easy airways, but missed significant numbers of difficult airways. A subsequent study by Cohen et al. (4) found similar results: sensitivity = 42%, specificity = 91%. More recently, Tse et al. (5) found the test to perform even less well: sensitivity = 66%, specificity = 65%. The positive predicted value (TP/[TP+FP]) was only 22%, meaning there were a large number of false positives relative the number of true positives. Treating all positive airways would therefore cause significant overtreating of patients with actually easy airways.

References:

1.  Mallampati SR. Clinical sign to predict difficult tracheal intubation (hypothesis). Can Anaesth Soc J 1983; 30:316-7.
2.  Mallampati SR, Gatt SP, Gugino LD, et al. A clinical sign to predict difficult tracheal intubation: a prospective study. Can Anaesth Soc J 1985; 32:429-34.
3.  Samsoon GLT, Young JRB. Difficult tracheal intubation: a retrospective study. Anaesthesia 1987; 42:487-90.
4.  Cohen SM, Laurito CE, Segil LJ. Examination of the hypopharynx predicts ease of laryngoscopic visualization and subsequent intubation: a prospective study of 665 patients. J Clin Anesth 1992; 4:310-314.
5.  Tse JC, Rimm EB, Hussain A. Predicting difficult endotracheal intubation in surgical patients scheduled for general anesthesia: a prospective blind study. Anesth Analg 1995; 81:254-258.


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