Anesthesia Considerations for Patients with Hemifacial Microsomia
Hemifacial microsomia is a congenital disease that can result in abnormal structural changes in the lower half of the face, most commonly the ears, mouth, and mandible. If severe, this condition can compromise the trachea and result in difficulties breathing. It is thought to occur in the early stages of development due to lack of blood supply to the first and second brachial arches,[1] and is the second most common birth defect of the face.[2] Given that individuals with hemifacial microsomia often have an anatomically distinct mandibular and tracheal structure, putting them under anesthesia can be significantly more complicated, particularly when it comes to airway management and intubation.
There are two methods for improving tracheal intubation success rates in patients with hemifacial microsomia: video laryngoscopy, in which a camera is inserted to assess the tracheal area, and direct laryngoscopy, in which a laryngoscope is used to create direct visual access to the larynx. It was found that video laryngoscopy, though useful for rescuing around 74 percent of failed intubations in individuals with hemifacial microsomia, also resulted in prolonged intubation times and increased chances of failed intubation.3 Therefore, direct laryngoscopy should remain the standard technique for tracheal intubation in cases of patients with unilateral hemifacial microsomia. Bilateral hemifacial microsomia, on the other hand, leads to a three-fold increase in incidences of difficult intubation, and in those cases, video laryngoscopy may be preferred.3
In 1992, McCarthy et al. reported success with lengthening the pediatric mandible by gradual distraction, a process that is now known as mandibular distraction osteogenesis (MDO).[3] This method allows for stable expansion of the mandible, as well as the surrounding muscle and soft tissue. It has since been traditionally practiced in children with difficult laryngoscopic view (DLV), though for a long time the effectiveness of MDO remained unknown. A 2020 study later found that MDO improved visualization in 43 percent of children with DLV.[4] Hence, MDO may be considered in patients with more extreme cases of hemifacial microsomia.
Mandibular anesthesia can similarly be more difficult in individuals with hemifacial microsomia. Though the approach can vary drastically with each unique patient, Ranalli et al. sought to create a comprehensive guide to administering regional mandibular anesthesia to individuals with this condition.[5] The authors use a classification method first established by Murray et al. in 1984 to create distinctions between the varied mandibular characteristics that can arise due to hemifacial microsomia. In this way, standardized techniques for delivering regional mandibular anesthesia can be altered to accommodate these patients.
In conclusion, there are a number of anesthetic considerations for patients with hemifacial microsomia. By considering the needs and characteristics of each individual, physicians can improve both procedural efficacy and patient experience.
[1] Hemifacial Microsomia. The National Craniofacial Association. 2011; http://www.faces-cranio.org/Disord/Hemi.htm.
[2] TMJ Surgery in India. Balaji Dental and Craniofacial Hospital, Chennai, India. 19 January 2019.
[3] McCarthy JG, Schreiber J, Karp N, Thorne CH, Grayson BH. Lengthening the human mandible by gradual distraction. Plast Reconstr Surg. 1992;89:1–08 9-10.
[4] Xu, J., Deng, X. & Yan, F. Airway management in children with hemifacial microsomia: a retrospective study of 311 cases. BMC Anesthesiol 20, 120. 2020.
[5] Ranalli DN, Bennett CR, Mundell R. Anatomical considerations for mandibular anesthesia in patients with hemifacial microsomia. J Pedod. 1989 Summer;13(4):345-54. PMID: 2638397.