Continuing Education Activity

Hemifacial microsomia is the second most common congenital defect of the head and neck, second only to cleft lip/cleft palate, with an incidence of 1 in 3500 to 1 in 4000. This activity explains and describes the considerations for a general anesthetic in patients diagnosed with hemifacial microsomia undergoing surgical procedures in the operating room setting.

Objectives:

• Describe the pathophysiology of hemifacial microsomia.
• Review the classification and stratification of hemifacial microsomia.
• Outline the anesthetic considerations based on the extent of the disease.
• Summarize peri-operative considerations taken by the interprofessional team for hemifacial microsomia.

Introduction

Hemifacial microsomia is a continuum of congenital deformities involving genetic disruption of the first and second branchial arches.[1] There are many disorders and syndromes linked to hemifacial microsomia. However, the basic theme of the issue is one side of the face being underdeveloped (in rare cases, both sides can be affected). With the spectrum of disease, this can manifest as a slight deviation all the way up to extremely underdeveloped and noticeable, even resulting in severe airway compromise requiring a tracheostomy early in life.[2]

Hemifacial microsomia is the second most common birth defect of the head and neck, second only to cleft lip/cleft palate, with an incidence of 1:3500 to 1:4000.[3] Due to the significant variability and spectrum of the disease, there are numerous and confusing classifications. Generally, they are characterized by the O.M.E.N.S. classification; orbital, mandibular, ear, facial nerve, soft tissue, with each item given a score of zero to three depending on the severity.[4] The Pruzanksky and Kaban classification is commonly used to assess the mandible and is broken down into three grades with several subtypes that help delineate the recommended surgical interventions needed.[3] These patients also often manifest with auricular issues, both cosmetically and functionally, with impaired hearing that requires surgical intervention. Though more uncommon, this process can be bilateral, resulting in marked facial issues and failure to develop. Also rare but reported is other internal organ systems being affected, making a comprehensive medical workup necessary in severe cases to rule out further issues.[5]

It is critical to understand the pathogenesis of hemifacial microsomia to understand the surgical therapies (generally) and what will be asked of the anesthesia team to best anticipate potential issues and difficulties, especially with airway concerns. A 2020 retrospective review looked at the anesthetic management of 311 hemifacial microsomia pediatric cases to better elucidate these issues. They found that facemask was possible for all except one child, a bilateral case, that required a two-handed mask technique. The success of intubation with video laryngoscopy and fiberoptic techniques was 100%, but the success of direct laryngoscopy was only 79.5%.[6] This illustrates the need to treat these cases as difficult airways and prepare accordingly.

Anatomy and Physiology

Hemifacial microsomia results from trauma or blood supply disruption to the first and second brachial (also known as the pharyngeal) arches.[7] This is thought to possibly occur secondary to a blood supply disruption at approximately four weeks gestational age.[8] Although there is a possibility of a genetic component, no evidence has been found to support it. The first pharyngeal arch, known as the mandibular arch, becomes the maxilla and palate, the mandible, the muscles of mastication, and Meckel's cartilage which forms structures of the middle ear (incus and malleus).[9] 

The second pharyngeal arch, known as the hyoid arch, is responsible for forming the neck and many of the muscles and structures associated between the head and neck.[10] An important association is that it is associated with the seventh cranial nerve and is responsible for developing all facial expression muscles.

Understanding the anatomy involved provides the basis for understanding potential issues when providing an anesthetic to these patients. The mandible, temporomandibular joint, and neck can all be underdeveloped or affected to varying degrees, leading to a potentially difficult airway.

Indications

In order to understand the anesthetic indications, one must first delineate the surgical interventions.[10] In rare but severe cases, the disorder can be bilateral and to such a degree that the airway is compromised immediately upon birth and requiring surgical intervention with a tracheostomy. In these cases, pediatric anesthesia specialists should work closely with the surgeon (generally an otolaryngologist or oral and maxillofacial surgeon) to plan and prepare accordingly.[11]

More commonly, as the patients age, they will receive several potential surgeries depending on their manifestation of the syndrome. In general, the surgical goal is to wait for the facial skeleton and tissues to finish normal development before intervention.[12] Starting with the earliest indications, if indicated, the ear can undergo external reconstruction at about the age of 7, as the ear is fully developed around this time.[7] 

If the temporomandibular joint fails to develop, early surgical intervention can be indicated between 6 and 12 years of age (normal development finishes between 16 and 20 years of age).[13] This usually occurs in the form of a costochondral graft, that is, harvesting a piece of rib and placing it into the mandible to aid in growth and development.[14] Distraction osteogenesis also plays a large role in treatment where custom bone lengthening devices are inserted and expanded in the post-operative period to help correct the bony deficiency.[15]

The majority of patients will undergo any needed major surgery when they reach skeletal maturity. Determining this age is often a team undertaking with serial radiographs and measurements done to determine when growth is finished, with females generally finishing earlier than males. Generally, it will be between 16 and 20 years of age.[16] This is a critical requirement, as outgrowing a corrective facial surgery can be a disaster, though it is unlikely in cases where the problem is under development, as opposed to a hyperplastic or overgrowth problem. These patients will often require major facial surgery with orthognathic surgery (cutting and moving the maxilla and mandible), surgically moving the zygomatic arch and orbit in extreme cases, and temporomandibular joint surgery to include full replacement.

Contraindications

Except for immediate airway issues, the surgeries for these patients will fall into a more elective category.[17] Therefore, contraindications include medically unstable patients who should wait until medical optimization can be achieved. Active infections, sepsis, gross global homeostatic dysregulation due to concurrent medical conditions, or other urgent surgical needs would all constitute reasons to delay care with an appropriate interdisciplinary discussion between the medical specialties.

Equipment

The equipment armamentarium will use a basic anesthetic operating room setup. This will include an anesthesia machine with ventilator and gas capabilities, monitors and machines for heart rate, blood pressure, pulse oximetry, 3 or 5 lead EKG, and temperature, a drug cart or storage device with the normal array of medications, and normal ancillary supplies for things like IV lines, gauze, Tegaderm, etc.[18] 

For the airway, depending on the surgical case, surgeon preference, and surgery, a mix of oral and nasal tube sizes, Mac and/or Miller blades, video laryngoscope if desired, and Magill forceps if nasal intubation is a choice.[19] It is recommended to have a fiberoptic scope available as backup due to the higher chance of a difficult airway.[20] 

If the team is performing nasal intubation, serial dilations with increasing sizes of nasopharyngeal airways or the use of a red rubber catheter are recommended, along with the application of Afrin spray and a lubricant[21]. Depending on the extent of the surgery and anticipation duration and blood loss, consider an arterial line, a second IV for use if needed, a foley catheter, and temperature regulation with an air warming blanket or system.

Personnel

The anesthesia team should consist of the provider or providers. Depending on the age, a pediatric anesthesiologist should be considered. It is recommended to have at least 2 or 3 anesthesia providers due to the high likelihood of a difficult airway.[22] The operating surgeon or surgical team should be present for the intubation and ready to intervene surgically if needed, depending on the examination and predication of the airway. Another personnel present would be a normal operating room team with an OR nurse and surgical techs.

Preparation

Preparation for the airway is paramount in the anesthetic management of hemifacial microsomia patients.[3] The pre-operative assessment will give a lot of information that will help the providers with the case. Carefully note the maximal incisal opening of the temporomandibular joint, thyromental distance, modified Mallampati score, neck circumference, and correlate their manifestations of hemifacial microsomia to help identify problems.[23]

Reviewing of the difficult airway algorithm and discussions about plans and backup plans must be done prior to the case to maximize success and patient safety.[24] A majority of the facial corrective surgeries will require nasal intubation. This will require an appropriately sized nasotracheal tube; a common mistake is not considering that size correlates with length, i.e., an 8.0 tube is longer than a 7.5. Try to get as large a tube as possible to prevent superior supraglottic displacement during surgery.[25] 

Nasal dilation equipment should be prepared with either serial nasopharyngeal airways as dilators or a red robin catheter placed on the end of the ET tube, then removed through the mouth. This author recommends a video laryngoscope for tube placement for two reasons; it allows a most consistent placement without using a McGill forceps which reduces the chances of puncturing the cuff balloon, and it allows the entire team and surgeons to visualize the tube placement. If severe retrognathia or neck deformities are present, consider an awake nasal fiberoptic intubation with adjunctive anesthesia and blocks (numbing the airway with inhaled 4% lidocaine, lidocaine-soaked gauze placed in the tonsillar pillars, trans-tracheal lidocaine, glossopharyngeal, and/or superior laryngeal nerve blocks.[26] If unfamiliar with the head and neck block techniques, discuss with the surgical team as they may be able to assist.

The team and setup should anticipate and be ready to handle a difficult airway up to and including a cannot intubate cannot ventilate situation with surgical instrumentation laid out and a surgeon scrubbed in ready to assist.

Other preparation includes a standard operating room set up with machine checks, ventilation equipment, airway equipment including backups, and all drugs and emergency drugs available.

Preparation for the intra-op portion should include a workup as dictated by the institution and preference, but likely include a basic metabolic panel, a complete blood count, and possibly a coagulation panel. Depending on the surgery, estimated blood loss, and time, a type and screen or type and cross should be considered.[27]

Another paramount consideration is what will be done after the case regarding extubation or leaving the patient intubated.[28][29] Even though most of these surgeries are done in the head and neck, it is unusual to have airway swelling, and these patients can be extubated as a normal case would be. This needs to be balanced against the time of day and length of the case. If the case is long and ends in the evening or night, strong consideration should be given to leaving the patient intubated overnight with a planned test and extubation in the morning.

Finally, the anesthesia team must discuss with the surgical team whether the patient will be wired shut into maxillomandibular fixation at the end of the case. Though this is less common currently due to the advancement of bone hardware and bony fixation techniques, it is still possible and sometimes is necessitated by unpredictable surgical outcomes; therefore, it may become necessary during a case.[30] The patient may have rubber elastic bands at the end of surgery restricting movement as well. This should be carefully discussed with the surgical team.

Technique or Treatment

Chief techniques involved involve nasal intubation and difficult airway management.[31] The anesthetic itself should be routine and can be run with volatile anesthetic agents or as a total intravenous anesthetic, based on anesthesia and surgeon preference.

Complications

The main complication associated with anesthesia on this type of patient is getting into a cannot intubate cannot ventilate pathway on the difficult airway algorithm necessitating a surgical airway.[32] This can be avoided with meticulous planning and preparation.

Clinical Significance

The clinical significance is the summation of the aforementioned material. This deformity causes under development and problems with the maxilla, mandible, temporomandibular joint and greatly can affect the mechanics of the airway.[6] Thus, all aspects of the particular patient's disease manifestation should be evaluated and calculated in the anesthesia plan and management.

Enhancing Healthcare Team Outcomes

The most important part about performing an anesthetic on a hemifacial microsomia patient is the preparation. A discussion with the surgical staff before the day of surgery can be extremely helpful in conveying the anatomic variations and potential airway difficulties. The surgeons can give input on potential airway issues, what they are doing, the length of time and estimated blood loss, any potential surgical issues or considerations, their pre-operative assessment, anticipated post-operative care, and maxillomandibular fixation or elastics.

The anesthesia team can discuss their concerns and thoughts on the airway and plans for managing the difficult airway, labs, intraoperative anesthetic and drugs, and other considerations. The nursing staff and techs should be brought on board during a team steps huddle with verification of equipment and a comprehensive case review.

Nursing, Allied Health, and Interprofessional Team Monitoring

Post-operative care should be carefully discussed between the anesthesia team, surgical team, and nursing staff to ensure careful and safe management in the recovery period.