Anaesthesia for orthognathic surgery—a narrative review

Introduction

Background

Orthognathic surgery is corrective surgery of the jaw and lower face. The term ‘orthognathic’ stems from the Greek word orthos meaning to straighten and gnaqos, meaning jaw. Since its inception over a century ago, advances in surgical and anaesthetic techniques have made orthognathic surgery a largely safe and effective procedure for correction of dentofacial deformity (1). There has been improved post-operative morbidity, particularly with reduction in intra-operative blood loss and infection rates (2-4). The surgery involves manipulation and fixation of the maxilla, mandible or both and it is carried out to treat malocclusion, improve oral health, normalise facial balance, improve airway anatomy, manage obstructive sleep apnoea and in the treatment of congenital craniofacial disorders.

There are some key anaesthetic considerations for orthognathic surgery. Patients are often young adults and may have existing psychosocial issues surrounding self-esteem and self-image. They have often been through a lengthy 2-to-3-year process of investigation and workup for the surgery, with preceding orthodontic treatment (5).

The nature of the surgery necessitates management of a shared airway, and therefore good communication between the anaesthetist and surgeon is important. These patients may present with a challenging airway and this requires thorough pre-operative assessment and planning.

There is growing literature to support the use of orthognathic surgery to treat moderate and severe obstructive sleep apnoea with maxillomandibular advancement (MMA). This patient population may be older and increasingly co-morbid which presents anaesthetic challenges.

There are also considerations for improving surgical conditions and reducing blood loss; i.e., patient positioning, use of tranexamic acid and hypotensive anaesthesia.

Objective

It is estimated that around 5% of patients in the UK and US with a dentofacial abnormality require surgery for correction (6). The incidence of orthognathic surgery worldwide is difficult to estimate due to the differences in population and treatment thresholds. In the UK, the British Orthodontic Society (BOS) estimates that around 3,000 people undergo orthognathic surgery each year, with 90% of patients noting an improvement in their overall health and well-being (7). The aim of this narrative review is to provide a summary of the literature and recommendations currently available on anaesthetic practice in orthognathic surgery. We present this article in accordance with the Narrative Review reporting checklist (available at https://joma.amegroups.com/article/view/10.21037/joma-24-18/rc).

Methods

A literature search was conducted using databases PubMed, Cochrane Library, EMBASE, and Google Scholar. Articles included were in the English language and included randomised control trials, systematic reviews, meta-analyses, cohort studies, case control studies, case reports, cross-sectional studies and expert opinions.

The search included key words shown in Table 1, and their combinations. Articles were selected for inclusion after independent review by the authors, as shown in Table 1.

Discussion/summary

Surgical techniques and considerations

Maxillary osteotomies are based on the Le Fort fracture patterns (4). The most common maxillary orthognathic procedure is the Le Fort I osteotomy, where sectioning occurs above the apices of the teeth, through the lateral wall of the maxillary sinus to the lateral wall of the nose, just at the base of the nasal piriformis. The maxilla is then down-fractured, mobilised in the three planes, and fixed using miniplates and screws. Clear communication between the surgeon and anaesthetist is essential preceding the moment of down-fracturing, as this juncture represents the point of maximal tissue disruption and concomitant risk of surgical bleeding. Another consideration during the time of down fracture is the risk of damage to the nasal tube.

The predominant mandibular orthognathic surgery is the bilateral sagittal split osteotomy (BSSO). The divisions of the mandible are made in a sagittal fashion lingually just above where the inferior alveolar nerve exits, across the external oblique ridge, to end buccally and parallel to the long axis of the teeth to the lower border of the mandible. The mandible is then carefully split and plated in the pre-operatively planned position either using miniplates and screws or bicortical screws.

A bimaxillary osteotomy (bimax) or “double-jaw surgery” involves surgery of both the maxilla and mandible. It provides patients with the greatest degree of jaw correction. These procedures are associated with the greatest surgical duration and the highest degree of blood loss (8). The mean operating time in the UK for a bimax is estimated to be between three to four hours (9,10). It is important to ensure these patients have a valid group and screen prior to surgery in case they require a blood transfusion.

A genioplasty is when surgery involves the bone in the chin itself. This involves osteotomy of the mandibular symphysis, which is plated in the desired position, and is carried out to augment the size and shape of the chin. This is often carried out in combination with maxillary and mandibular surgery.

Pre-operative considerations

Most patients presenting for surgery are young adults, as surgical fixation is usually delayed until bone growth in the jaw is complete, and this occurs in late adolescence. The mean age of patients undergoing orthognathic surgery is estimated to be between 20–40 years (11,12). Many patients typically have no significant medical comorbidities and are seeking treatment for developmental malocclusion. The aim of treatment is to improve function, improve oral health, treat speech problems as well as for aesthetic reasons which may be impacting their self-esteem (13,14).

There is a significant psychosocial impact on patients, as the treatment and recovery time for orthognathic surgery is lengthy and in the initial post-operative stages, patients may find it difficult to adapt to a change in appearance. Patients often have at least 18 months of orthodontics prior to having surgery and require 4–5 months of orthodontics post-operatively. It is important to ensure patients are fully aware and prepared for the challenges they may encounter during treatment. There is a multi-disciplinary team involved in their care, including orthodontics, maxillo-facial surgeons, nurses, anaesthetists, dieticians and psychologists/psychiatrists (15).

Patients requiring orthognathic surgery for congenital craniofacial syndromes; for example, cleft lip and palate, Treacher Collins Syndrome and craniosynostosis disorders; are medically complex (16-19). These patients should ideally be managed in specialised tertiary cleft or craniofacial centres with multi-disciplinary team involvement (19). In the UK, there are four Craniofacial Units where patients born with craniofacial abnormalities are treated (20). This patient population may have associated congenital heart disease, poor nutritional status due to limitations in feeding, upper airway obstruction [obstructive sleep apnea (OSA), apnoeas], and some respiratory restriction (21). These patients may also have challenging airways, and this requires assessment and appropriate airway planning. They are likely to require respiratory support post-operatively and will need admission to a high dependency unit (HDU) or intensive care unit (ICU).

Orthognathic surgery has a growing role in older patients (aged over 40 years), and this may be explained by its growing use in the treatment of OSA (22-26). Literature suggests that MMA surgery, which involves repositioning of the jaw anteriorly, with the goal of expanding the airway and reducing collapsibility has been successful for treatment of OSA, with significant reduction in apnoea-hypopnoea index (AHI). These patients present a challenge to anaesthetists as they are often older, have a raised body mass index (BMI), micrognathia and comorbidities related to OSA. Untreated OSA is associated with cardiovascular disease, hypertension, pulmonary hypertension, cerebrovascular disease and metabolic dysfunction (27). Patients will require sleep study investigations pre-operatively to determine the severity of their OSA. This will impact intra-operative monitoring and anaesthetic techniques used, as well as their post-operative destination. Short-acting anaesthetic agents should be used and opioids should be administered with caution, as these patients are at risk of respiratory depression post-operatively. If patients are using continuous positive airway pressure (CPAP) machines, use of CPAP in the immediate post-operative period may not be suitable as the facemask may disrupt the osteotomy fixation. Humidified high flow nasal oxygen may be an alternative during this stage.

Airway management

Patients presenting for orthognathic surgery may have a challenging airway as they often have mandibular retrognathia. There is also a subset of patients with congenital craniofacial syndromes, and they will have a difficult airway due to anatomical abnormalities, i.e., cleft lip, palate, mandibular prognathism and craniosynostosis. Thorough pre-operative assessment and planning are required (18,28). They may be associated with difficult face mask ventilation, difficult intubation or both and this requires appropriate assessment and planning for intubation and extubation. This will include use of videolaryngoscopy, and consideration for awake intubation.

Surgeons require unobstructed access to the jaw, and this is usually achieved with nasal intubation. Nasal intubation is generally a safe technique which carries minimal risk to the patient. Situations where nasal intubation is contraindicated include suspected epiglottitis, midface instability, coagulopathy and suspected basilar skull fractures. Other situations where nasal intubation may not be possible include congenital craniofacial abnormalities (29,30).

Submental intubation is an alternative that can be used where nasal intubation is not possible or expected to be challenging. It can also be useful in procedures which include combined nasal surgery and avoids the risks of exchanging a nasal tube for an oral tube intra-operatively. This is where standard oral intubation is carried out [using a reinforced endotracheal tube (ETT) to prevent kinking of the tube]. A surgical excision is then made in the submental crease, and a continuous passage created between the floor of the mouth to the mandible. The oral ETT is then pulled through the submental crease and secured. This procedure carries fewer risks than a tracheostomy, and is associated with reduced scarring, providing a better cosmetic result for patients (31-34).

Use of tracheostomy for orthognathic surgery has become increasingly infrequent, and is reserved for patients who have a predicted challenging airway, and where there is concern regarding airway swelling post-operatively.

Discussion with the surgeons is important in deciding the most appropriate intubation technique for the patient.

Intra-operative management

Patient positioning

Orthognathic surgery necessitates a shared airway with surgeons, and there is limited access to the patient’s head once surgery is underway. It is important to ensure the ETT is secured and the breathing circuit and monitoring cables are long enough to reach the operating table, which is positioned at 90–180 degrees to the anaesthetic machine (35).

With prolonged surgical time, the patient may require a urinary catheter. There are also important considerations for patient positioning. It is important to ensure the nasal tube is taped so that it is not compressing the alar margin, which is susceptible to ischaemic injury. Careful positioning of the patient, padding of the eyes and arms to avoid prolonged exposure to cables is important in preventing pressure sores. This is particularly important as hypotensive anaesthesia is frequently employed intra-operatively increasing the risk of skin ischaemia and necrosis. Elevation of the head by 10–15 degrees or reverse Trendelenburg positioning allows venous drainage, improves the surgical view and facilitates intra-operative hypotension.

Temperature regulation

Temperature regulation during surgery is important in orthognathic surgery, given the lengthy surgical time. Inadvertent hypothermia can occur, which may cause shivering post-operatively and this can be uncomfortable for patients (36). Forced-air warming blankets and warmed intravenous fluids can be used intra-operatively, but should be used with caution and with regular temperature monitoring as patients may overheat as only the head is exposed during surgery. Measurement of temperature can be carried out using axillary and urinary catheter probes, as placing an oral or nasopharyngeal probe may not be possible.

Maintenance of anaesthesia

Anaesthesia can be maintained intra-operatively with a volatile agent or total intravenous anaesthetic (TIVA). TIVA with propofol (alongside an opioid agent, see below) may be beneficial as studies suggest it reduces post-operative nausea and vomiting (PONV) and reduces the risk of emergence delirium, which is a prominent feature of orthognathic surgery (37,38). TIVA with propofol has also been associated with reduced haemodynamic changes during emergence and extubation, allowing for a ’smooth extubation’ which is desirable for this type of surgery (38). One study comparing inhalational agent and propofol use in orthognathic surgery found that propofol anaesthesia was associated with an increased requirement for adjunctive agents to control blood pressure (39). However, other studies have showed no significant difference in blood loss or length of recovery between the two techniques (40,41).

Opioids with a rapid onset, i.e., fentanyl, alfentanil and remifentanil can be used intra-operatively—either given as boluses or as an infusion to obtund autonomic responses to painful stimuli. Using a remifentanil infusion has become a popular anaesthetic technique for orthognathic surgery, as it has shown to be superior in providing a consistent plane of analgesia, helping to maintain hypotensive anaesthesia (42). It can be used either as a component of TIVA or alongside volatile anaesthesia. Utilising a target-controlled infusion (TCI) model allows for rapid titration of effect particularly around the time of down fracture (43).

Alternatives to a remifentanil infusion include dexmedetomidine and clonidine, which are alpha receptor agonists that act on the brain and spinal cord as an analgesic and sedative medication. They can be used as an anaesthetic adjunct (as an infusion alongside a volatile agent or propofol) (44). Some studies have shown that dexmedetomidine reduces blood loss and PONV, as well as reducing analgesic requirement in patients undergoing orthognathic surgery (45-47)

The trigeminocardiac reflex

During surgery, stimulation of the trigeminal nerve can cause bradycardia and even asystole via the trigeminocardiac reflex. This is most likely to occur during the down fracture of the maxilla and maxillary and mandibular osteotomies. Early detection of bradycardia and communication with the surgeons is important and often resolves with release of surgical traction or pressure and treatment with anticholinergic agents (28,48).

Intra-operative blood loss

The maxillofacial region is highly vascular, and orthognathic surgery can involve significant bleeding from both soft tissue and bone which is hard to control surgically. Bleeding points in the maxilla include the pterygoid venous plexus, maxillary artery in the pterygopalatine fossa and the maxillary sinus mucosa. Blood loss from surgery can not only have detrimental effects on the patient but can also distort the surgical field and visibility.

Administration of tranexamic acid during orthognathic surgery is a common practice, and multiple studies have shown that this significantly reduces blood loss, improves the quality of the surgical field and may even improve the post-operative haemoglobin (49-52). A meta-analysis of randomised control trials by Olsen et al. showed a reduction of intra-operative blood loss by 30% with a single dose of 10–20 mg/kg of tranexamic acid given intra-operatively (50).

Injection of local anaesthetic with adrenaline either as local infiltration by surgeons or regional blocks has also been associated with reduced intra-operative blood loss (53,54). This may be due the effect of adrenaline as a vasoconstrictor, but may also be due to the pre-emptive analgesic effect of a regional block in countering the sympathetic hypertensive response to painful stimulus during surgery.

Hypotensive anaesthesia

Hypotensive anaesthesia is commonly used in maxillofacial surgery to reduce blood loss. Studies specifically investigating the benefits of hypotensive anaesthesia for reducing transfusion rates, improved surgical conditions and reduced length of surgery have proven inconclusive (50,55,56). However, there does appear to be a consensus opinion that hypotensive anaesthesia reduces blood loss intra-operatively in orthognathic surgery, though this is difficult to quantify. The technique should be considered for patients on an individual basis, with the goal to reduce the patient’s mean arterial pressure (MAP) safely, relative to their starting MAP. Studies considering end organ perfusion suggest that a 20–30% reduction in MAP with a minimum MAP of 50–55 mmHg in American Society of Anesthesiologists (ASA) I patients is considered a safe target (57).

Hypotensive anaesthesia may present risks to patients due to reduced end organ perfusion and this can affect the brain, heart, liver and kidneys. While growing studies highlight the risk of end organ injury with inadvertent hypotension intra-operatively (58-60), there is little conclusive evidence of the risk posed by controlled hypotension. Due to the potential risk of end organ injury, it is not suitable for all patients and should be considered carefully in patients with co-morbidities (55,61). Conditions such as ischaemic heart disease, severe hypertension, hepatic disease, diabetes, renal disease, polycythaemia, anaemia and ischaemic cerebrovascular disease are all contraindications to hypotensive anaesthesia.

The nature of this type of surgery and use of hypotensive anaesthesia does not necessitate the use of invasive arterial blood pressure monitoring. Non-invasive blood pressure monitoring is often sufficient unless there are patient specific concerns which would require invasive arterial blood pressure monitoring (62).

Blood pressure is dependent on cardiac output and systemic vascular resistance. Techniques to lower blood pressure can be achieved by manipulating each of these elements with medications (63) as summarised in Table 2.

Extubation and post-operative considerations

Prior to extubation, careful and thorough suctioning of the oral cavity is important to remove any blood, airway secretions and clots in the post nasal space which may cause airway obstruction. This should be carried out while the patient is in a deep plane of anaesthesia to avoid coughing. If suctioning is carried out under direct vision with laryngoscopy, this should be done gently, to avoid pressure on the jaw is important to avoid any disruption screws or plates used in the osteotomy fixation. Oropharyngeal suctioning is also important to ensure haemostasis and this should be communicated clearly between the anaesthetic team and surgeons, prior to placement of inter-maxillary fixation (IMF) (11).

While rigid IMF (with wires) are rarely required in orthognathic surgery, elastic bands attached to orthodontic brackets to apply traction are often used. Sterile scissors should be available during extubation and in the post-anaesthesia care unit (PACU) environment if emergency access to the mouth is required and the elastic IMF bands need to be cut off.

A smooth controlled emergence is important for this surgery and this can be achieved with a remifentanil or dexmedetomidine infusion. Alternatives which also reduce emergence coughing include lidocaine (either given IV or topically to the vocal cords), fentanyl or alfentanil (64).

Patients should be nursed in a “sitting up” position in PACU and on the wards, as this reduces swelling. They should be carefully monitored for any bleeding post-operatively. Forceful placement of oxygen masks should also be avoided as this may displace the jaw fixation screws and plates.

Patients are typically discharged to a ward setting for a few days. However, studies have shown that orthognathic surgery can be safely carried out as a day case procedure in the UK and this is becoming an increasing practice (65). Patients with congenital craniofacial syndromes, and OSA will often require HDU/intensive therapy unit (ITU) post-operatively.

PONV

PONV is a common complication in orthognathic surgery, with studies reporting the incidence of PONV to be between 40–70% (38,46,66-69).

The highest incidence is often reported in maxillary orthognathic surgery, this includes Le Fort I osteotomy and bimaxillary osteotomy surgery (66,70). This may be explained by the fact that these procedures are prolonged, often associated with hypotensive anaesthesia, have higher blood loss and a higher risk of ingested blood and surgical secretions. These patients also require an adapted soft diet post-operatively while their jaw heals. Patients undergoing orthognathic surgery are often young and female, which is another risk factor for PONV (69,71). Anaesthetic risk factors for PONV in these patients are prolonged anaesthesia time and use of nitrous oxide and volatile anaesthetic agents (72).

PONV can be an extremely unpleasant experience for patients, lead to extended hospital stay and is undesirable for the outcome of the surgical procedure itself as it can cause bleeding and delayed wound healing.

Patients should be identified as high risk for developing PONV pre-operatively based on patient factors and surgical factors. Techniques to reduce PONV include use of TIVA, administration of multiple anti-emetics and using multi-modal, opioid-sparing analgesia. The placement of throat packs to prevent swallowing of blood, and use of nasogastric (NG) tubes to aspirate stomach contents is controversial and there is no evidence to recommend these (73).

Analgesia

Patients undergoing orthognathic surgery are likely to develop moderate post-operative pain. Effective pain relief after the operation is imperative for patients, as it improves their experience, recovery and reduces the duration of hospital stay. With modern surgical techniques and reduced operating time, patients rarely require opioid patient-controlled analgesia (PCA) post-operatively (74,75). Patients should be prescribed regular non-opioid analgesics [i.e., paracetamol, nonsteroidal anti-inflammatory drug (NSAIDs)], with breakthrough opioid analgesia.

Pain relief is known to be improved with pre-emptive analgesia, i.e., introducing pain relief early and before the surgical stimulus to reduce central sensitisation of pain receptors (76). Local anaesthetic infiltration with adrenaline is usually carried out before incision (with the added advantage of reducing bleeding).

Non-pharmacological methods for analgesia including facial cooling masks, targeting the Hegu acupuncture point (between the thumb and index finger) with ice, massage and pressure and low-level laser therapy (LLLT) have also been shown to be effective providing analgesia for orthognathic surgery (75). However, with limited availability and the added cost and training required for LLLT, it is not a practical option for most hospitals.

Regional blocks with a long-acting local anaesthetic, carried out either under ultrasound guidance by the anaesthetist or by landmark technique by the surgeon target the trigeminal nerve branches V2 (maxillary) and V3 (mandibular) and can provide effective post-operative analgesia (54,77-79). Pre-emptive analgesia with regional blocks may also reduce the intra-operative anaesthetic and analgesic requirements by reducing pain response to surgical stimulus (54).

Enhanced recovery after surgery (ERAS)

ERAS is a multi-disciplinary, surgery-specific approach which allows for early recovery and return to health. ERAS has its origins in colorectal surgery, but is increasingly being used in head and neck cancer surgery. There are no formal recommended protocols for orthognathic surgery but some centres have adapted local guidelines (80). ERAS protocols in orthognathic surgery have been shown to be effective at improving outcomes for analgesia, PONV, and decreasing opioid consumption. The protocols involve pre-operative counselling, optimising nutrition, standardised multi-modal analgesia and early mobilisation (80-82). Orthognathic surgery is currently considered to have a low incidence of morbidity and severe complications, and in some centres, BSSO procedures are routinely done as a day case.

Complications from the surgery

Bleeding

Though the conduct of surgery and anaesthesia has reduced haemorrhage in orthognathic patients, significant bleeding can still occur in these patients (8). The incidence of a life-threatening haemorrhage in patients undergoing osteotomy is around 1% (83). Damage to the internal maxillary artery and its branches is the most common cause of major haemorrhage in these patients.

While most instances of bleeding occur and can be managed intra-operatively, delayed bleeding can also occur. Patients presenting with epistaxis can often be managed conservatively with nasal packs. Rarely, severe bleeding can occur which requires intervention and this may be in the form of nasal endoscopy, embolisation and even surgical exploration. Bleeding may be due to the formation of pseudoaneurysms, arteriovenous fistulas and delayed bleeding from surgical injury. Bleeding from a pseudoaneurysm can be severe and life threatening, and may present up to 9 weeks post-operatively (53). Delayed post-operative bleeding can be a challenging situation for the anaesthetist as it involves a management of a bleeding airway, a haemodynamically compromised patient, and risk of aspiration due to ingested blood.

Infection

Routine administration of prophylactic antibiotics, which are given either as a single dose intra-operatively or continued for 3–5 days following surgery, reduces post-operative surgical site infection. The incidence of infection, i.e., cellulitis, maxillary sinusitis, osteomyelitis is around 1% and very rarely requires return to theatre (84,85).

Nerve damage

The inferior alveolar, lingual and infraorbital nerves are at risk of damage as they lie close to the osteotomy incision site. Patients may present with numbness and tingling over their face which is temporary in most cases (lasting less than a year). The incidence of permanent hypoaesthesia has been reported to be between 10–20%, though in many patients they may only have mild symptoms (84,85). This surgical complication may be important to consider for the anaesthetist, especially if they are using nerve blocks intra-operatively which may also result in nerve damage. Avoiding high concentrations of local anaesthetic and repeated doses may be protective in preventing nerve damage from regional blocks (86).

Limitations

This was a narrative review covering an extensive topic, and as a result, it was not possible to include a search of all articles published in the field. The articles were independently selected by the first author based on the key word search strategy and only articles published in English were included. This may have introduced subjectivity in the article. More robust evidence is still required to comment conclusively on the safety and efficacy of controlled hypotensive anaesthesia for orthognathic surgery.

Conclusions

Orthognathic surgery is often a transformative procedure for patients and is a key part of their lengthy treatment journey. The involvement of a multi-disciplinary team working together is crucial and the anaesthetist plays an important role in optimising the patients’ experience and outcomes. Thorough pre-operative assessment and planning should be carried out, especially in patients with craniofacial syndromes and in patients with challenging airways. Communication between the surgical team and knowledge of key surgical steps is vital intra-operatively. The main challenges presented to the anaesthetist involve management of a shared airway, employing techniques to reduce intra-operative blood loss and being vigilant of post-operative complications. The review of literature suggests that hypotensive anaesthesia remains a useful technique which can be safely carried out in select patient groups to reduce intra-operative blood loss. With advancements in the surgical technique and a generally fit and healthy patient population undergoing this procedure, growing literature suggests enhanced recovery may play an important role and day-case procedures can be carried out safely for these patients. There is also growing literature to support the role of orthognathic surgery in the treatment of OSA. Though orthognathic surgery is currently not widely accepted in treatment of OSA in the UK, OSA is a highly prevalent condition and this patient population may be increasingly seen undergoing surgery in the near future.

Acknowledgments

Funding: None.

Footnote

Reporting Checklist: The authors have completed the Narrative Review reporting checklist. Available at https://joma.amegroups.com/article/view/10.21037/joma-24-18/rc

Peer Review File: Available at https://joma.amegroups.com/article/view/10.21037/joma-24-18/prf

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://joma.amegroups.com/article/view/10.21037/joma-24-18/coif). The authors have no conflicts of interest to declare.

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