12 Oral and maxillofacial related injuries and hazards during anaesthesia

Major catastrophic sequelae such as death or permanent injury following general anaesthesia are thankfully rare. However, inadvertent damage to teeth, intraoral soft tissues, and morbidity associated with throat packs and nasal intubation represent some of the most commonly reported oral and maxillofacial related injuries. This chapter will be limited to discussion of these injuries. For a wider discussion of the hazards and complications of anaesthesia, the reader should consult the literature^{1  ,2}.

Less serious complications of anaesthesia, such as damage to teeth, can be of major significance to the individual patient. Inadvertent dental damage represents the single most commonly reported anaesthetic related injury, accounting for over a third of all compensatory claims against anaesthetists. Although often individually fiscally moderate, the cumulative cost is substantial.

The reported incidence of dental damage during anaesthesia has been retrospectively reported as 0.05–12%^{3  ,4}. This, however, may be a substantial underestimate⁵. Obvious damage to teeth during anaesthesia will be noted by the anaesthetist at the time of injury. Alternatively, the patient may report damage to their teeth postoperatively. In a prospective study of 745 patients who underwent general anaesthesia, preoperative and postoperative examination by a dentist reported an incidence of oral trauma as high as 18%, of which two-thirds was damage to natural or prosthetic teeth⁴. The implication is that, without expert examination, minor injuries such as enamel microfractures may pass unnoticed^{6  ,7}.

An appreciation of normal developmental dental anatomy is necessary for an understanding of the mechanism of dental injury during anaesthesia. Humans have 20 deciduous teeth, also known as ‘milk’ or ‘baby’ teeth, which are replaced by 32 permanent teeth by the second decade of life. The deciduous teeth in each quadrant are identified by the letters A to E, working outwards from the midline. Permanent teeth are identified by the numbers 1 to 8 in a similar manner. To reduce the likelihood of misidentification of teeth during treatment, the World Dental Federation has proposed an alternative international nomenclature system in which the tooth number is prefixed by a 1, 2, 3, or 4, corresponding to upper right, upper left, lower left and lower right quadrants, respectively (Chapter 13, Figure 13.8).

Anatomically, each tooth is divided into two distinct parts, an exposed crown and a hidden embedded root (Figure 12.1). The boundary between the two parts is known as the cementoenamel junction. Depending on their functional role and the intended axis of applied force, teeth can have single or multiple roots. Within each tooth is a central pulp cavity covered in dentine, a hard elastic avascular mineralized tissue composed of collagen and water. The pulp cavity contains blood vessels and nerves. The dentine of the crown is protected by an outer layer of enamel of varying thickness which extends from the tip of the tooth to the cementoenamel junction. Enamel, which is thickest at the biting edge of the tooth and thinnest near the gingival margin, is the hardest substance in the body and is composed of tightly packed rods or prisms containing crystalline calcium phosphate known as hydroxyapatite. Although of considerable integral strength, enamel is brittle and is susceptible to shatter under abnormally applied shearing forces.

Below the cementoenamel junction the dentine of the anatomical root is covered with cementum, a specialized bony substance composed of collagen and hydroxyapatite. Adherent to the cementum is the collagenous periodontal ligament which suspends each tooth independently within a socket of alveolar bone. The ligament facilitates a slight degree of movement during mastication, so allowing adjacent touch and pressure receptors to relate sensory information critical to the masticatory process via central mechanisms.

Overlying the alveolar bone is the keratinized epithelium of the jaws, or gingiva, in contrast to the non-keratinized oral mucous membrane. Inflammation and infection of this soft tissue caused by bacterial plaque is an important coexisting factor in anaesthetic related dental damage, particularly when associated with underlying bone loss as seen in periodontitis (see below).

In a patient with normal dentition, when the teeth are brought together the lower mandibular teeth will lie symmetrically and slightly lingually to the upper maxillary teeth. A slight incisor overbite is normal, with about one-third of the upper incisors covering the lower incisors. The upper and lower teeth are designed to meet during mastication. Molars, which have up to three roots, are in the position of maximal mechanical advantage adjacent to the powerful muscles of mastication. Teeth tolerate substantial applied axial forces in the intended physiological vector better than lesser abnormally applied lateral forces. For further detail the reader should consult the literature⁸.

Whilst the majority of dental injuries during anaesthesia are reported following laryngoscopy, endotracheal or nasotracheal intubation^{3  ,4  ,9}, about 25% occur on emergence when injury is most commonly associated with extubation or the use of oropharyngeal airways^{3  ,10  ,11}, laryngeal masks, bite blocks, or suction catheters. Emergence dental injuries are more likely to involve the lower teeth^{12  ,13} and often pass unnoticed by the anaesthetist⁴. Diagnostic laryngoscopy or the instrumental assisted passage of a nasogastic tube in an anaesthetized patient can also result in sustained abnormally applied forces leading to dental or soft tissue trauma.

The upper left central incisors are the most vulnerable teeth to damage during anaesthesia^{12  ,15} (Figure 12.2). The preponderance of left-sided injuries is thought to reflect the fact that most anaesthetists are right-handed. Typically, although not exclusively, dental damage is usually limited to a single tooth^{9  ,16}.

Teeth have different dental axes depending on their function. Incisors are mono-rooted teeth with a forward dental axis and small cross-sectional area designed to withstand considerable biting forces along their axis. Upper premolar and molar teeth have two or three roots, respectively, and are designed to withstand substantial aligned forces along a vertical dental axis. Lower premolar and molar teeth have one or two roots, respectively. Any alteration in the vector of the force applied, such as strong vertical forces applied to incisors, makes them more vulnerable to damage^{10  ,17}.

Dental injuries during general anaesthesia are typically caused by direct contact of the upper anterior teeth with the rigid blade of the laryngoscope. In addition to predisposing patient factors (see below), dental injury is associated with the characteristics of the laryngoscope blade¹⁸ in use and the skill of the anaesthetist. The proximity of the upper anterior incisors to the laryngoscope blade during optimal view of the vocal cords has been studied. The forces exerted on the upper teeth vary with the design of the laryngoscope¹⁹. In consequence, modifications to laryngoscope blades with the intention of minimizing contact with the upper teeth have been proposed^{20  –22}. Alternative protective strategies have included the application of compressible adhesive tape²³ and foam cushions²⁴ to the upper surface of the laryngoscope blade²⁵. The use of plastic-bladed scopes may confer some protective advantage²⁶. Electronic warning devices for the prevention of dental injury during laryngoscopy have been developed²⁷ but have not been widely accepted.

The inadvertent use of the upper incisors as a fulcrum during difficult intubation is a well recognized pre-sequel to dental injury, although when intubation is difficult this is regarded as inevitable by some²⁸. Forces of 30–65 Newtons (N) or greater exerted on the maxillary incisors during laryngoscopy have been recorded^{18  ,28  ,29} but the sensitivity of the measuring devices was questioned following subsequent reports of mean axial forces of 20 N^{21  ,30}. Regardless, the applied forces are substantial. Putting this into perspective, a gallon of water exerts a force of 37 N. The patient's body mass index, height, weight^{21  ,30  ,31}, and Mallampati Score appear to correlate with the overall force applied when using a MacIntosh blade, but less so with the McCoy modified blade^{21  ,30}. Patients of increasing age required less applied force for intubation.

Oropharyngeal airways have been implicated in 20% of anaesthetic related dental injuries³². Masseter spam and teeth clenching are not uncommon following anaesthesia with volatile agents^{13  ,33}. During emergence, the masseter muscles can exert considerable forces (of up to 80 N)⁹ which are normally absorbed by the multi-rooted molar and premolar teeth. In the presence of a midline placed oropharyngeal airway, the molar teeth are unable to meet, resulting in the transfer of the vertical jaw clenching forces forward through the anterior mono-rooted incisors¹³. The common practice of using an oropharyngeal airway as a bite guard to protect an endotracheal tube or laryngeal mask airway may therefore put incisor teeth at an increased risk of fracture or impaction^{10  ,13  ,17}. A similar mechanism of injury could also result from biting hard on a midline placed suction catheter. Placing a bite block between the premolar or molar teeth, rather than adjacent to the incisor teeth, would in theory be less likely to result in dental damage.

Healthy teeth are robust and capable of withstanding considerable force and pressure. Although factors predisposing to dental injury during anaesthesia are multifactorial, a prime contributory factor is pre-existing dental or intraoral disease, which increases the risk of injury fivefold^{3  ,4  ,11}. Dental caries resulting in enamel loss, dentine softening, cavity formation, and previous injury can all weaken teeth, making them susceptible to fracture or dislodgement even with minimal applied force.

After dental caries, periodontal and gingival disease are the most prevalent worldwide diseases in adults. Bacterial plaque which has accumulated in the crevices between the teeth and gums can give rise to inflammation of the gums and loss of the supporting underlying alveolar bone. Patients with abnormal dentition are especially prone to plaque accumulation. If left unattended plaque can thicken, become mineralized, and provide a localized anaerobic environment in which bacteria can proliferate. Periodontitis, which is invariably painless, is caused by an aggressive immune and inflammatory response to the bacteria resident on the tooth's surface. Released collagenases destroy the adjacent bony support, predisposing to dental avulsion. Avascular root-filled teeth become brittle and devitalized, making root fracture or dislodgement, even with minimal force, more likely. Associated risk factors include poorly controlled diabetes, osteoporosis, arteriosclerosis, smoking, and an individual genetic predisposition. Patients whose anterior segments have significant decay, advanced periodontitis, or are shedding deciduous teeth (see below) are the most prone to anaesthetic related damage⁴ (Table 12.1).

Many systemic diseases have intraoral manifestations which can exacerbate periodontal disease, so weakening the teeth and gums, and making them susceptible to damage during anaesthesia^{34  –36} (Table 12.2). The mechanisms by which systemic disease can influence the pathogenesis of periodontal disease are unclear but may involve a modification of the host's normal immune response. Adequate saliva production is a prerequisite for optimal dental health. Conditions in which saliva production is diminished or absent are often associated with dental disease and a vulnerability to injury during anaesthesia.

Chronic medication can result in dental discoloration, structural damage or intraoral manifestations that predispose to dental injury during anaesthesia. The drugs most implicated are those formulated in sugar-containing vehicles and drugs which lower the intraoral pH such as aspirin and powdered antiasthmatic medication. Anticholinergics, antidepressants, and antipsychotics all result in decreased saliva secretion, predisposing to periodontitis. Over one-third of patients on the immunosuppressant cyclosporin, nifedipine, and anticonvulsants such as phenytoin will experience gingival overgrowth which may undergo subsequent local inflammatory changes. Localized irradiation can also result in a loss of bony support.

Patients who chronically misuse illegal drugs have a high incidence of periodontal disease. Cocaine and methamphetamine mixed with saliva creates a highly acidic environment, resulting in erosion of enamel and dental caries, often in a very short period of time. Heroin causes a craving for sweet and sugary foods, and ecstasy induces xerostoma, a prerequisite to periodontal disease. Patients on supervised withdrawal programmes are often prescribed methadone. In order to make methadone palatable, it is formulated in concentrated sugary syrup which partly explains why such patients often have very poor dental health and frequently require a dental clearance. For a comprehensive discussion of this topic, the reader should consult Tredwin et al.³⁶.

Between the age of 6 and 12 years, a child's deciduous teeth are progressively replaced by permanent adult teeth and children of this age will have mixed dentition present. Deciduous teeth have shorter roots than adult teeth. As the erupting permanent tooth develops, the root of the overlying deciduous tooth undergoes resorption, leading to a loss of structural bony support. Adult teeth take up to 3 years before they are fully embedded and reach optimal strength⁵. As a result, children between the ages of 5 and 10 are at the greatest risk of inadvertent dental damage during anaesthesia^{4  ,5}. It is a commonly held misconception that because deciduous teeth will be replaced in time, damage to them is of less concern. Injury to a deciduous tooth can easily damage the developing underlying permanent tooth, and loss of the tooth may delay or result in premature eruption of the permanent tooth⁵. This may give rise to crowding and dental misalignment which can require orthodontic treatment in later years. Anaesthetists should therefore treat deciduous teeth with the same respect they would show permanent teeth^{5  ,17}.

Although the elderly are at greater risk of dental injury¹², this is not always reflected in the literature as many patients in the past would have been wholly or partially edentulous. Although the forces applied during laryngoscopy appear to be less with increasing age, the overall incidence of dental injury is high, reflecting the increased incidence of dental and periodontal disease in the elderly. Bony support of teeth declines with age. With greater health education and the availability of dental services, a significant number of elderly patients have retained some or all of their teeth, making them at greater risk than previously.

The anatomical relationship between the upper and lower incisors can have a significant effect on their tolerance to applied forces. Misaligned teeth resulting in malocclusion are more likely to be exposed to abnormal forces³⁷. Traditionally there are three classes of dental malocclusion as described by Angle's classification, the details of which can be found in any standard dental textbook³⁸. Class II relationships, or retrognathia, are of greatest concern to the anaesthetist⁵. Malocclusion, retarded mandibles, prominent anterior teeth, anterior crowding, and high dental arches can all increase the risk of dental damage during anaesthesia. Where the upper incisors are severely proclined or irregular, visualization of the vocal cords during laryngoscopy can be very difficult, encouraging the inadvertent use of the incisors as a lever fulcrum. Patients with malocclusion are also more susceptible to dental and periodontal disease on account of the difficulties in providing effective dental hygiene.

Isolated teeth, which lack the support of adjacent teeth and may also have the same pathological condition as the missing teeth^{37  ,39}, are vulnerable to damage or dislodgement during laryngoscopy by the passage of the endotracheal tube and positioning of a laryngeal mask.

The anaesthetist may encounter several forms of dental restoration, such as single or multiple crowned teeth, fixed bridges, surface veneers, removable partial or complete dentures, and dental implants⁵. Pathologically weakened teeth, either from disease or previous restoration, are unable to withstand the forces tolerated by healthy teeth⁹. Although modern dental resins and porcelain are very robust, excessive pressure from a laryngoscope blade or via an oropharyngeal airway can result in fragmentation. Gold, as a restorative material, seems to be more robust, with fewer patients reporting dental damage following anaesthesia. In one retrospective study, previously filled teeth accounted for 50% of those damaged during anaesthesia⁹.

Whilst the cosmetic result of dental restorations may be pleasing to the patient, the prosthetic tooth is unable to withstand the forces accommodated by a normal healthy tooth. The commonest site for crowned restorations is the upper incisors, further compounding the risk¹³, particularly during recovery from an anaesthetic. Prosthetic dental restorations, such as crowned teeth, involve cavity preparation which removes some of the tooth's original structure and replacement with resins and metal supporting posts (see Chapter 13). The remaining tooth structure, whilst restored, may not be optimally healthy. Prosthetic restorations are designed primarily to withstand axial loading forces along the line of the tooth such as those experienced in chewing. Applied lateral or shearing forces are tolerated poorly (Figure 12.3).

The type of restoration can also influence the consequences of the injury. Where a crowned tooth has a long metal supporting post within the tooth cavity, excessive applied force can result in vertical splitting of the tooth. Crowns with short metal retaining posts are more prone to dislodgement if excessive non-axial force is applied, whilst both restorations are vulnerable to root fractures.

On account of the minimal preparation involved, the cosmetic application of thin veneers to visible teeth has become very popular. Veneers are 0.5–1 mm thick laminates of porcelain, ceramic or a composite of both, the former being the most popular on account of its enhanced strength. The veneer is bonded to either the tooth enamel or underlying dentine, the former creating a much more stable bond⁵. As veneers are bonded only to healthy teeth, abnormally applied forces, especially of a levering nature, will risk chipping the veneer or shearing the comparatively weaker bond between the tooth and the overlying veneer. Bridges, which involve prosthetic teeth being interconnected with supporting bands of metal, are particularly at risk of displacement if excessive shearing force is applied^{5  ,9}.

Dental trauma is divided into six categories⁴⁰ depending on the anatomical site of the injury (Figure 12.1 and Table 12.3). Although all injuries can occur during anaesthesia—Class I, II, and VI are the most common. An understanding of the implications of the nature and site of the injury is important if effective corrective dental treatment is to be provided.

Ideally, prevention of anaesthetic related dental injuries should start with an attempt to attain optimal dental and gingival health. Routine preanaesthetic dental examination of all patients has been proposed^{6  ,41  ,42} but dismissed as unworkable. Whenever possible, any remedial and restorative dental treatment should be undertaken prior to elective anaesthesia and surgery. In reality, this is often unattainable and unrealistic. Patients who present with poor dental health will invariably have a long history of dental neglect and poor intraoral hygiene which is unlikely to be changed during the immediate preoperative period. Concerns have also been raised as to the lack of availability of dental care possibly leading to a greater incidence of anaesthetic related dental damage¹¹. Patients attending anaesthetic preassessment clinics should have their oral cavity and teeth carefully inspected for risk factors such as dental caries, loose teeth, and periodontal disease^{10  ,42}. When risk factors are identified, an explanation of your concerns should be given to the patient and, time permitting, they should be encouraged to attend their dentist for treatment.

The use of a protective mouthguard to minimize dental injury to upper incisors during laryngoscopy and intubation has long been established³. One study claimed that 90% of reported dental injuries were preventable had the patient's dental state been correctly assessed preoperatively and a mouthguard used intraoperatively³. Despite this, the use of protective mouthguards by anaesthetists is still not routine practice^{3  ,9  ,41  ,43} in recognition of the fact that their use can make laryngoscopy and intubation difficult, particularly for less experienced anaesthetists⁴⁴. When the anaesthetist has identified especially vulnerable dentition, the reported usage of mouthguards increases sharply³.

The most commonly used anaesthetic mouthguards are bulky and commercially manufactured to a standard design. A less common but superior alternative is a preformed custom-made mouthguard which fits the patient's dentition precisely. The thinner preformed mouthguards are less like to impede intubation and have been shown successfully to dissipate the forces applied to teeth during laryngoscopy⁴². Unfortunately, the measured protective effect correlated with the increasing bulk of the mouthguard negates any advantage. The use of a mouthguard therefore does not obliterate the risk of dental damage during anaesthesia⁴². Indeed, their efficacy and routine use has been questioned^{39  ,45}. Whilst their use may offer protection against superficial chipping of dental enamel, it will not prevent the avulsion of loose teeth.

When a tooth is damaged during the course of anaesthesia, a full explanation must be given to the patient, the details of which are then recorded in the patient's notes.

The immediate management of teeth damaged during anaesthesia will depend upon the extent of the injury (Table 12.3). For superficial damage, such as chipped enamel (Class I), a routine dental appointment will suffice. As Classes II–VI injuries are at risk of secondary infection, they should receive expert attention within 24 hours. Class II and III injuries can be extremely painful, prompting the patient to present for treatment immediately.

Subluxed deciduous teeth should not be replaced in their sockets as they are prone to fuse with alveolar bone in an abnormal manner. Subluxed or avulsed permanent teeth, however, require urgent treatment if the tooth is to remain viable. Once a subluxed tooth has been repositioned, the tooth socket should be compressed firmly between the thumb and forefinger for 1 minute and the tooth temporarily splinted back into position to avoid further movement⁴⁶. Movement can endanger the blood supply, resulting in an avascular tooth. The patient should be started on oral penicillin and urgently referred to a dental surgeon for definitive stabilization.

No action is necessary if a deciduous tooth has been avulsed other than to inform the parents. In contrast, an avulsed permanent tooth constitutes a dental emergency. Typically, there is coexisting dental caries and/or periodontal disease. Regardless, an attempt should be made to salvage the tooth and preserve the periodontal ligament. A tooth deprived of its blood supply becomes increasingly unviable after 30 minutes, so speed is of the essence.

Reimplantation is only possible if the tooth remains viable. The avulsed tooth and socket should be immediately lavaged in sterile isomolar normal saline (never water) and inspected. Provided the tooth is intact and there are no root fractures, the tooth should be immediately returned to the socket by holding the crown and taking great care to avoid touching the root. When immediate reimplantation is not feasible, the tooth should be stored in sterile isomolar saline or milk and the patient referred urgently to a dental surgeon. Reimplantation of a tooth in a patient partially recovered from a general anaesthetic always carries the risk displacement and aspiration.

An unaccounted for dislodged tooth, or fragment of tooth, can be life-threatening if inhaled on extubation⁴⁹. It is essential to recover the tooth and any fragments. If a tooth, or part of a tooth, is unaccounted for, then X-rays of the head, neck, and chest in two planes should be taken⁴⁵ (Figure 12.4).

Damage or dislodgement to prosthetic teeth and fittings should be attended to within a few days of injury. It is important to ensure that all detached fragments have been recovered. Of concern is the fact that some prosthetic materials are not radiolucent, making the location of fragments difficult.

Damage to intraoral soft tissue as a consequence of general anaesthesia is common and, while rarely life-threatening, there are significant problems that can develop. Trauma is not only associated with the use of a laryngoscope and endotracheal intubation but is also seen with laryngeal mask airways (LMA), Guedel airways, bite blocks, suction catheters, and throat packs. The incidence of oral injuries associated with anaesthesia and endotracheal intubation is as high as 18%⁴, with minor dental injury accounting for the majority. However, over 6% of the 745 cases in this study had soft tissue injuries such as contusions of the lip, gingiva, and edentulous ridge. This figure could be much higher if postoperative sore throat was considered as a form of pharyngeal soft tissue injury; the incidence of this was approximately 40% after intubation, greater than 65% if blood was found on the laryngoscope⁴⁹, and 20–42% after LMA placement⁵⁰.

Lip injuries are most commonly caused by laryngoscopy and include haematomas, lacerations, and generalized oedema which, although usually self-limiting, cause inconvenience and discomfort. A malpositioned or overinflated LMA can compress the lingual artery, resulting in cyanosis of the tongue and loss of taste. Similarly, loss of tongue sensation secondary to compression of the lingual nerve during overzealous laryngoscopy is well recognized. Multiple case reports of gross tongue swelling or macroglossia exist, and some have resulted in life-threatening airway obstruction requiring prolonged intubation⁵¹. Several contributory factors are thought to be involved, including positioning of the patient, prolonged procedures, and anything that causes compression on the base of the tongue resulting in arterial and venous compromise and massive oedema. Thus prolonged intraoral surgery and the use of pharyngeal packs and bite blocks are risk factors^{52  ,53}.

The uvula is also vulnerable to injury which can follow compression by an oral or nasal endotracheal tube, LMA or as a result of a suction injury resulting in oedema and subsequent necrosis. There are several case reports of injury to the uvula secondary to suctioning the tip of the uvula into the Yankauer sucker, which is usually associated with higher suction power^{54  ,55}. These patients complain of a severe sore throat and gagging or choking caused by the uvula touching the back of the tongue. Conservative treatment results in resolution after a few days with the necrosed area sloughing off. Suctioning with a narrower-tipped Yankauer with smaller side holes than the traditional wide-tipped, larger side holed catheter has also been reported to have caused soft tissue injury to the tonsillar pillars, and pharyngeal soft tissue with bleeding and aspiration of small amounts of tissue⁵⁶. Ideally, suctioning would always be under direct vision but this is not practical immediately prior to extubation when airway reflexes and muscle tone have returned. Care should always be taken to use the lowest power of suction that achieves optimal results.

Although rare, several cases of pharyngeal perforation, which can result in death following mediastinitis, have been reported⁵⁷. Laryngoscopy and difficult passage of endotracheal tubes account for most cases, but both nasogastric tube placement and suctioning have been implicated, particularly in the paediatric setting⁵⁸.

Hoarseness postoperatively can be due to damage to the laryngeal muscles and suspensory ligaments or minor lacerations and abrasions to the cords. More severe lesions can result and are usually related to difficult and traumatic intubation with the use of adjuncts such as stylets and bougies. Symptoms usually settle without intervention, but hoarseness can be permanent following unilateral cord paralysis which is thought to be due to compression on the recurrent laryngeal nerve from the cuff of a poorly positioned endotracheal tube in the subglottic larynx⁵⁹. It can be seen that soft tissue injuries can occur during induction, maintenance, and emergence of anaesthesia and a wide variety of pathologies can result.

Throat packs are in common use in dental, maxillofacial, and ENT surgery to pack the oropharynx and nasopharynx. The pack itself usually consists of variable amounts of coarse green gauze which is moistened and supplied in rolls 180 cm long and 10 cm wide (Figure 9.3). The aim of throat packs is to absorb any blood which is not adequately aspirated, thus preventing drainage of this blood into the stomach and leaking of blood around the cuff of an endotracheal tube (ETT) with subsequent contamination of the trachea. It has been shown that a cuffed ETT cannot provide 100% protection from aspiration and so prolonged pooling of blood in the pharynx is undesirable⁶⁰. Methods of inserting pharyngeal packs vary, with some users preferring Magill forceps and others digital insertion. To avoid tearing the frenulum, particularly during blind insertion, the tongue should always be displaced. The placement of throat packs is implicated in grazes to the soft and hard palate, and tears to the frenulum and posterior pharyngeal wall. These injuries are often missed as direct laryngoscopy is not routinely performed. These can occur even after apparently atraumatic insertion and, on occasions, cause bleeding⁶¹. It is thought that this is why some studies have shown a high incidence of sore throat associated with pharyngeal packs. Fine et al.⁶² reported an 80% incidence of sore throat in patients with pharyngeal packs and a zero incidence with no packing. This study was small, with only 25 patients, and a similar study in 62 patients by Tay et al.⁶³ found conflicting results with no difference in the incidence or severity of sore throat when throat packs were used. Basha et al.⁶⁴ prospectively studied 100 patients having nasal surgery and found a higher incidence of sore throat in those with a throat pack, although this did not delay discharge. They also found that the incidence of postoperative nausea and vomiting (PONV) was unaffected by the presence of a throat pack.

Pharyngeal packs can also damage the pharyngeal plexus and have resulted in macroglossia due to compression ischaemia and subsequent oedema as previously discussed⁵³. Potentially the most catastrophic hazard of a pharyngeal pack is in neglecting to remove it on completion of the anaesthetic, which could result in airway obstruction and asphyxiation following extubation. There are sporadic reports in the literature relating to airway obstruction, including a paediatric fatality⁶⁵ and another child presenting with acute respiratory distress in recovery in which the causative throat pack was promptly discovered and removed without consequence⁶⁶. There were three cases of retained throat packs in 2007 reported in the United Medical News Australia, all of which involved a change in anaesthetic personnel and a lack of documentary evidence of pack insertion. In one case the pharynx had been suctioned under direct vision, but the heavily bloodstained pack was unseen. Fortunately, all packs were expelled several hours postoperatively with no morbidity. Retained throat packs may become lodged in the nasopharynx or swallowed and present problems postoperatively. A pack lodged in the nasopharynx for many weeks caused nasal obstruction and bilateral foul discharge, and was discovered on nasendoscopy. Similarly, a swallowed throat pack risks causing bowel obstruction and, potentially, perforation.

Careful thought must always be given to minimize the risk of complications arising from the use of throat packs. It is wrong to assume that all oral, maxillofacial, dental, and ENT cases require a throat pack. The intended benefits of throat pack insertion should always be considered for each individual patient and balanced against the perceived risks. Concern over the lack of uniform practice as regards ensuring removal of packs has recently been discussed at a Royal College of Anaesthetists Safety Conference. Several methods have been advised, including visual checking systems such as labelling or marking the patient's forehead with the mark to be removed when the pack is removed, labelling the airway device, tying the pack to the airway device, or leaving part of the pack protruding. There is no method to suit all situations; for example, intraoral surgery may not allow either tying the pack to the airway or leaving part outside the mouth. Documentary based solutions were also discussed, including a two-person checking system on insertion and removal. One potential solution would be to include the throat pack in the surgical count and introduce a uniformity in practice throughout the country.

Nasotracheal intubation is a common anaesthetic technique which facilitates access during oral, dental, and maxillofacial surgery. There are well described complications of both oral and nasotracheal intubation, some of which have been previously discussed in relation to soft tissue injuries. However, there are some issues particularly pertinent to nasotracheal intubation which need to be considered. In addition, modern dedicated nasotracheal tubes are intentionally made of a softer and more pliable material, making them more prone to extraneous compression and kinking during oral and maxillofacial surgery.

Indications for a nasal ETT include maxillofacial surgery, oropharyngeal, and dental surgery, as well as being useful in rigid laryngoscopy and microlaryngeal surgery. Awake fibreoptic intubation almost invariably involves the nasal route and can be useful in a wide variety of situations when direct laryngoscopy is difficult (Chapter 4).

Assessment of the nasal airway is important if local injury is to be avoided, and attempts should be made to identify any optimal nare. Nasal septal deviations and hypertrophied turbinates are common, but identification of patency problems through patient history, and specifically enquiring about airflow obstructive symptoms, will not reliably predict the best nostril to intubate⁶⁷.

Nasendoscopy can identify asymptomatic nasal abnormalities, but few anaesthetists are sufficiently familiar with this technique to incorporate it into routine practice. Consequently, it may be difficult to predict the best nostril⁶⁸.

Epistaxis is the most common complication encountered during nasal intubation, usually resulting from mucosal tears in the anterior part of the nasal septum—Little's area⁶⁹. Avulsion of polyps, especially in asthmatics, trauma to tonsils, adenoids, or the posterior pharyngeal wall can result in bleeding which, at its worst, can be torrential and life-threatening. The reported incidence of epistaxis varies widely from 18 to 66%^{70  ,71}, although the majority of these cases were minor bleeding, with some classifying blood-tinged saliva as a significant event.

There is a higher risk of epistaxis if too large a nasotracheal tube is used, repeated attempts are required, and if excessive force is applied when difficulty is experienced during navigating the tube through the nasal passages⁷². Various methods to reduce epistaxis have been proposed, including thermosoftening of the tube, alternative tube materials, and the use of vasoconstrictors. It is commonplace to lubricate the tube and apply vasoconstrictors to the nostril such as phenylepehrine, ephedrine, cocaine or oxymetazoline which are usually combined with lidocaine. The literature fails to support any significant difference in efficacy between these agents in reducing the incidence of epistaxis following intubation⁷³.

Introducing sequential nasopharyngeal airways of increasing size to dilate a nasal passage prior to intubation is thought by some to reduce trauma and bleeding⁷⁴, but others believe there is greater potential to damage the delicate mucosa and cause more bleeding than with direct intubation⁷⁵.

Despite attempts to minimize the risks, significant nasal bleeding can still occur. Blood within the airway not only obscures vision but can obstruct the airway, especially if large clots have formed, which can cause bronchospasm, laryngospasm, and impede adequate ventilation. This becomes a particular hazard if direct laryngoscopy is suboptimal. This latter scenario is highlighted in a case report where epistaxis occurred on advancing the nasal ETT through a vasoconstricted nostril⁷⁶. On direct laryngoscopy, there was an unpredicted Cormack and Leherne grade 4 view. The presence of copious blood in the airway made ventilation difficult and negated the use of a fibreoptic scope to facilitate endotracheal intubation. Emergency cricothyroidotomy was necessary to facilitate oxygenation. Visualization of the larynx and fibreoptic intubation was only then achievable after the haemorrhage was brought under control by nasal tamponade. Prior laryngoscopy to assess the adequacy of the laryngeal view before introducing a nasotracheal tube has been proposed as a means of reducing the risk of the aforementioned situation. Having evaluated the airway, fibreoptic devices can then be used if required without the risk of blood obscuring the view. These also allow the anaesthetist to make a judgement that, if nasal haemorrhage does occur, laryngeal intubation will be readily acheivable.

Epistaxis resulting from nasotracheal intubation is usually self-limiting and can invariably be controlled by either the pressure of the nasal tube or through insertion of an absorbent nasal tampon and sitting the patient upright. More persistent haemorrhage may necessitate inserting a Foley catheter and applying a tamponade by means of inflating the cuff.

Avulsion of nasal polyps, inferior and middle turbinates, and tumour have all been reported as resulting in airway and nasotracheal tube obstruction. Less common injuries include submucosal placement and creating false submucosal passages, usually when there have been repeated attempts to pass the tube through the nose. This can lead to retropharyngeal abscess formation, and consideration should be given to the use of antibiotics if a pharyngeal tear is identified⁷⁷. Similarly, use of prophylactic antibiotics in susceptible patients with valve replacements should be considered as nasotracheal intubation can be associated with a bacteraemia⁷⁸.

Prolonged nasal intubation can lead to pressure necrosis of the nostrils and septum, retropharyngeal abscess formation, and paranasal sinusitis.

Although a detailed discussion of eye injuries associated with general anaesthesia is beyond the scope of this chapter, patients undergoing oral and maxillofacial surgery are at an increased risk from such injuries⁷⁹. The eyes, which are often hidden from view by operative drapes, are in close proximity to the surgical field, making them vulnerable to both physical insult and inadvertent instillation of antimicrobial skin preparations. The eyes are at particular risk during laser surgery (Chapter 10). Eye injury has been reported as accounting for 3% of all compensatory claims against anaesthetists, of which 35% are corneal abrasions⁸⁰. Fortunately most, but not all, recover without permanent visual impairment.

In one study, 59% of patients had incomplete eye closure following the induction of anaesthesia⁸¹, so protective measures should always be adopted. Common techniques for protecting the eyes during oral and maxillofacial surgery include taping the eyes shut, with or without protective ointment, protective ointment alone, methycellulose drops, and goggles. There is no evidence that one technique is superior to another.

Injuries to the oral and maxillofacial structures are some of the commonest iatrogenic anaesthetic related injuries reported. Even apparent minor injuries can be a source of considerable discomfort, inconvenience, and expense to the patient. In this respect, damage to teeth and intraoral soft tissues during laryngoscopy are foremost. It is important that anaesthetists are familiar with the risk factors that can predispose to injuries of the oral cavity and maxillofacial region during anaesthesia.

The authors would like to thank Mr James Adams, Consultant in Oral and Maxillofacial Surgery, and Dr Claire Storey for their help and advice in the preparation of this chapter.