Mallampati Classification, an Estimate of Upper Airway Anatomical Balance, Can Change Rapidly During Labor

Mallampati Classification, an Estimate of Upper Airway Anatomical Balance, Can Change Rapidly During Labor

᭜ EDITORIAL VIEWS Anesthesiology 2008; 108:347–9 Copyright © 2008, the American Society of Anesthesiologists, Inc. Lippincott Williams & Wilkins, Inc. Mallampati Classification, an Estimate of Upper Airway Anatomical Balance, Can Change Rapidly during Labor THE Mallampati classification is a rough estimate of the More surprisingly and significantly, half of the parturi- tongue size relative to the oral cavity.1 Although the ents demonstrated Mallampati class 3 or 4 by the end of single usage of the Mallampati classification has labor, predicting a further increase in difficulty of airway limited discriminative power for difficult tracheal in- management during labor or immediately after delivery tubation,2 it is a simple, reproducible, and reliable upon medical interventions such as general anesthesia. Downloaded from http://pubs.asahq.org/anesthesiology/article-pdf/108/3/352/366713/0000542-200803000-00005.pdf by guest on 25 September 2021 preanesthetic airway assessment method when per- The risk of emergency cesarean delivery and surgery for formed properly. In addition to difficult tracheal intu- postpartum hemorrhage is particularly high in obese bation, Mallampati class 3 or 4 is an independent parturients, presumably because of their higher inci- predictor for difficulty of mask ventilation during an- dence of maternal complications and fetal growth retar- esthesia induction and presence of obstructive sleep dation.7–9 Hood et al.8 reported that 48% of laboring apnea.3,4 Increase of the Mallampati class during labor morbidly obese parturients required emergency cesar- 5 and delivery reported in this issue of ANESTHESIOLOGY ean delivery compared with 9% of control laboring par- provides insight for exploring and understanding the turients. Considering the high prevalence of obstructive mechanisms of difficulty in perioperative airway man- sleep apnea in obese subjects and the growing problem agement of pregnant women, particularly during or of obesity among industrial countries, the finding of immediately after labor. In the article, the authors Kodali et al. is not trivial and carries particular impor- thoroughly discuss the clinical implications of their tance to practitioners when anesthetizing obese parturi- findings on difficult tracheal intubation; therefore, I ents. In fact, a recent survey of anesthesia-related maternal would like to assess their data focusing on periopera- deaths in Michigan identified obesity and African-Ameri- tive upper airway obstruction of pregnant women. can race as common characteristics of these cases.10 Noticeably, there were no deaths during anesthesia in- duction, and five of eight anesthesia-related deaths re- Clinical Significance of Upper Airway sulted from hypoventilation or airway obstruction dur- Changes during Pregnancy and Labor ing emergence, endotracheal extubation, or recovery. Although safety of airway management during anesthesia Kodali et al.5 did not directly test the clinical signifi- induction seems to have greatly improved as a result of cance of the increased Mallampati class because none of development of the airway algorithm and various intu- the women underwent general anesthesia; however, bation devices, an unsolved and significant problem in careful interpretation of their data reveals noticeable obstetric anesthesia is how to assess and manage the features of the upper airway structures in pregnant upper airway upon emergence and endotracheal extu- women. First, Mallampati class 3 and 4 seem to be more bation. The data of Kodali et al. suggest the labor is a prevalent in parturients at the beginning of labor (28%) potential risk factor for perioperative airway catastrophe than in the general adult population (7–17%), suggesting in parturients in addition to obesity, craniofacial abnor- that tongue volume increases even during normal preg- malities, and sleep-disordered breathing. Pregnancy and nancy as previously reported.6 Increased tongue volume labor are inevitable and physiologic processes for human presumably due to fluid retention during pregnancy may beings that significantly burden the respiratory system be partly responsible for increasing both prevalence of by decreasing lung volume and thoracic compliance and obstructive sleep-disordered breathing in pregnant narrowing the upper airway. Labor potentially makes women and incidence of difficult tracheal intubation in some parturients more susceptible to pathologic upper obstetric anesthesia.7 airway narrowing. This Editorial View accompanies the following article: Kodali Upper Airway Anatomical Imbalance in ᭜ B-S, Chandrasekhar S, Bulich LN, Topulos GP, Datta S: Airway Parturients changes during labor and delivery. ANESTHESIOLOGY 2008; 108:357–62. The pharyngeal airway is a collapsible tube whose pa- tency is precisely regulated by upper airway dilating mus- cles such as the genioglossus. Increase in the dilating mus- Accepted for publication December 3, 2007. The author is not supported by, nor maintains any financial interest in, any commercial activity that may be cle activity acts to maintain the narrowed pharyngeal associated with the topic of this article. airway during wakefulness in patients with obstructive Anesthesiology, V 108, No 3, Mar 2008 347 348 EDITORIAL VIEWS sleep apnea.11 Similar neural mechanisms presumably com- Assuming similar changes of the Mallampati class in pensate the progressive upper airway narrowing in partu- both study groups, e.g., a 26-point increase of the rients. Preservation of these neural regulatory mechanisms Mallampati class in 61 subjects leads to a 10-ml reduc- is, therefore, crucial for parturients with a high Mallampati tion of upper airway volume on average, it can be class to maintain their breathing. Regional anesthetic tech- roughly estimated that a 1-point increase of the Mal- niques have only minimal influence on the neural mecha- lampati class approximately corresponds to a 20-ml nisms; however, the neural compensatory mechanisms be- increase of the tongue volume in women with Mallam- come weaker during general anesthesia, sedation, and pati class 3 or 4 before labor. Upper airway volume sleep with residual anesthetics. The pharyngeal airway pa- differed between patients with and without difficult tency entirely depends on its structural stability in parturi- tracheal intubation by 30–40 ml.14 Tongue volume ents undergoing emergency cesarean delivery during gen- was significantly larger in patients with obstructive Downloaded from http://pubs.asahq.org/anesthesiology/article-pdf/108/3/352/366713/0000542-200803000-00005.pdf by guest on 25 September 2021 eral anesthesia. sleep apnea, by approximately 20–25 ml, than in non- Structurally, the pharyngeal airway is surrounded by apneic persons.15 For every 1-point increase of the soft tissues such as the tongue and soft palate, which Mallampati class, the relative risk of obstructive sleep are enclosed by bony structures such as the mandible apnea doubles and apnea hypopnea index increases and spine. Size of the airway space is determined by by5hϪ1.4 Accordingly, a 20-ml increase of the tongue the balance between the bony enclosure size and soft volume during labor potentially results in difficult tissue volume (anatomical balance) when pharyngeal tracheal intubation and upper airway obstruction un- muscles are inactivated by general anesthetics and der influence of general anesthetics and sedatives. muscle relaxants.12 Pharyngeal edema, presumably due The Mallampati classification allows us to instanta- to fluid retention during pregnancy, and pharyngeal neously identify such small but significant increases in swelling acutely developed during labor increase the soft the tongue volume at the bedside without using sophis- tissue volume surrounding the airway, narrowing the ticated apparatuses. The Mallampati classification origi- pharyngeal airway in parturients. Recent extensive re- nated in our specialty, and recently, clinicians and re- search on the pathophysiology of upper airway obstruction searchers in other specialties have recognized its revealed a significant role of the lung volume reduction in usefulness for assessment of upper airway anatomical pharyngeal narrowing. Tagaito et al.13 demonstrated that balance. We anesthesiologists should be proud of the lung volume dependence of pharyngeal airway patency is Mallampati classification and are encouraged to use this more pronounced in obese patients. Accordingly, obese classification to assess the upper airway anatomical bal- parturients, a high-risk group for perioperative airway ca- ance with it before every general anesthesia induction. tastrophe, are prone to develop progressively narrower The article by Kodali et al.5 reminds us that the Mallam- pharyngeal airways due to increase of soft tissue volume pati classification is not static, but can change over hours surrounding the pharyngeal airway and decrease of lung with processes such as labor, and we should assess it just volume during pregnancy. Lung volume reduction during before instrumentation, rather than relying on an assess- general anesthesia is known to be more prominent and ment even a few hours earlier. prolonged in obese patients. General anesthesia for emer- Shiroh Isono, M.D., Department of Anesthesiology (B1), Graduate gency cesarean delivery in obese parturients during or School of Medicine, Chiba University, Chiba, Japan. [email protected] immediately after labor may tend to exaggerate upper air- way swelling and lung volume dependence, in addition to impairment of neural compensatory mechanisms,

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