Anaesthesia for ENT, Maxillofacial and Dental Surgery
Ear, nose and throat (ENT), maxillofacial and dental surgical procedures account for a significant proportion of work in most anaesthetic departments. Recent cost-benefit and evidence-based analyses have reduced the number of common procedures performed such as tonsillectomy, insertion of grommets and removal of impacted wisdom teeth. Bodies such as the National Institute for Health and Clinical Excellence (NICE) have reviewed the evidence relating to many procedures and developed rigorous guidelines for referral and intervention.
Other trends in surgical practice have offset this reduction, e.g. the prevalence of alcohol-related facial trauma and the increasing use of surgery in the treatment and palliation of cancer of the head and neck. The incidence of these cancers, particularly of the oral cavity, presents a significant and increasing global burden of disease.
The development of anaesthetic practice in these areas has therefore been concentrated on increasing the use of day-case surgery for more minor procedures and facilitating long and technically challenging operations to remove tumours and reconstruct defects. The effect of surgical pathology on the upper airway continues to require meticulous attention to airway management and has led to the proliferation of new devices and techniques to overcome difficult intubation.
Special problems are caused when the airway is shared by both anaesthetist and surgeon (Table 29.1). If bleeding is anticipated, the airway must be protected and the oropharynx may be packed to avoid contamination of the larynx with blood, pus and other debris. If a pack is used, it should either be labelled or the tail left obviously emerging from the mouth as a reminder that it must be removed at the end of the operation. The anaesthetic circuit connections are usually hidden under the drapes and may well be ‘knocked’ by the surgeon during the procedure. Anaesthetic disconnections are, therefore, a constant threat. It is important to realize that disconnections on the machine side of the capnograph sampling tube, in a patient who is breathing spontaneously, does not lead to a loss of the capnograph trace and so careful observation of the reservoir bag is mandatory.
Disconnection of tracheal tube
Dislodgement of tracheal tube
Access for surgeon or anaesthetist
Tube damage, e.g. laser
Lack of visual confirmation of ventilation
At the end of the procedure, the pack, if present, must be removed and the pharynx cleared of blood and debris before the trachea is extubated with the patient in a head-down lateral position. The fact that a pack was used and has been removed should be recorded.
The number of tonsillectomy operations has decreased by about a third since 1996, but there are still approximately 50 000 procedures performed annually in England, just under half of which are in children. Almost all are performed under general anaesthesia, with 34% undertaken as day-case surgery.
Premedication is frequently impractical with modern admission practices but robust preoperative assessment is mandatory, in particular to obtain any history of obstructive sleep apnoea or other airway problems. Often, the patient is young and otherwise fit, and routine investigations are unnecessary.
Surgical access to the pharynx requires the insertion of a Boyle Davis gag. To facilitate this, a secure airway is usually maintained with a ‘south-facing’ moulded tracheal tube (Fig. 29.1). Alternatively, a reinforced laryngeal mask airway (LMA) can be used successfully provided that the surgeon carefully avoids displacement of the LMA during the insertion and removal of the gag.
FIGURE 29.1 Various tubes used in ENT and oromaxillofacial surgery. Clockwise from top left: armoured tracheal tube, south-facing moulded tracheal tube, north-facing moulded tracheal tube, microlaryngoscopy tube, armoured LMA, laryngectomy tube, laser tube.
Spontaneous ventilation following the use of a short-acting muscle relaxant can be used to facilitate deep extubation in the lateral head-down position to protect the airway from soiling during emergence. Alternatively, positive pressure ventilation can be maintained throughout the procedure, with extubation fully awake in the sitting position. Various surgical techniques can be employed including cold steel dissection, electrodiathermy, laser and coblation. Blood loss can be significant and vigilance must be maintained regarding fluid replacement; however, blood transfusion is rarely necessary.
Tonsillectomy is painful and requires adequate postoperative analgesia. This frequently involves a multimodal approach with an initial dose of intravenous morphine together with paracetamol and a non-steroidal anti-inflammatory drug (NSAID). The latter can be given orally before surgery or parenterally during the procedure. Some evidence may point towards an increased risk of bleeding associated with the use of NSAIDs, but this is not clear-cut and most centres use this combination of drugs to facilitate early discharge. Multimodal antiemetic therapy should also be used because postoperative nausea and vomiting is a frequent cause of delay in discharge. There is also evidence to support the use of steroids for control of emesis and pain, usually as a single dose of dexamethasone. Some evidence supports the use of topical or locally infiltrated local anaesthetic. The early establishment of oral intake of food, fluids and analgesia encourages early discharge and should enable most operations to be performed as a day-case.
This is a commonly performed operation in children to improve the symptoms of otitis media with effusion, and chronic rhinosinusitis. It is often combined with tonsillectomy and insertion of grommets. Recent systematic reviews have questioned the evidence of efficacy of adenoid surgery and therefore the frequency is decreasing. Adenoidectomy is also performed occasionally in adults for glue ear.
As in tonsillectomy, good access to the pharynx is required, usually with a Boyle Davis gag, and therefore airway control with a ‘south-facing’ tracheal tube or reinforced LMA is employed. Adenoidectomy as a sole procedure is usually rather quicker and less painful than tonsillectomy and may not require long-acting opioid pain control.
General anaesthesia is required, usually with tracheal intubation to provide a safe airway during surgery. Provided that no difficulty with intubation is predicted, intravenous or gaseous induction is followed by the administration of a muscle relaxant dependent on the anticipated duration of the procedure. In general, a small cuffed (microlaryngoscopy) tube with internal diameter 4–6 mm is inserted into the trachea to allow the surgeon greater access to the pharynx. This should be placed in the left side of the mouth to allow passage of the rigid endoscope down the right.
Examination, with or without biopsy, is usually of a short duration and mivacurium or suxamethonium is often used. Increasingly however, the operating microscope is used to resect neoplasms of the upper airway, especially laryngeal carcinoma, allowing less invasive damage to voice function. These operations may be prolonged, requiring attention to normothermia and fluid balance. Microlaryngeal tumour resection is often carried out using a precision laser cutting tool which requires either a tube specifically designed to tolerate lasers or extreme care on the part of the surgeon to avoid the risk of damage to the tube and potential airway fire. Short-acting opioids provide balanced anaesthesia but morphine may be required for longer operations. Blood loss is not usually significant and is often controlled by the topical application of adrenaline with or without local anaesthetic. Safe extubation is normally achieved with full emergence and recovery of airway reflexes, and careful pharyngeal suction prior to the removal of the tube.
Occasionally, the surgeon requires access to the larynx without the presence of a tracheal tube. In this situation, oxygenation can be provided by jet insufflation of the lungs via a subglottic catheter or an attachment to the endoscope (Fig. 29.2). The catheter can be inserted into the trachea either down the endoscope or through the cricothyroid membrane. Anaesthesia is maintained using an intravenous agent, usually propofol.
Preoperative assessment of the anatomy of any goitre, usually by computed tomography, is vital to predict any impact on the ease of intubation of the trachea or ventilation of the lungs. Preoperative assessment also allows the surgical access route to be planned; this is usually via the neck, but may require intrathoracic access such as a sternal split if significant retrosternal extension of the tumour exists. Medical management of thyroid disease must be optimized preoperatively because abnormalities such as a thyroid storm can cause gross physiological problems intraoperatively.
For routine thyroid surgery via the neck, it is sufficient to provide balanced general anaesthesia usually, using a reinforced tracheal tube to allow the operative area to be draped safely without risking occlusion of the tube. If the goitre is causing significant subglottic stenosis without stridor, a small tube must be available which will pass easily through the stenosed area. If the stenosis extends into the chest towards and beyond the carina, specialized thoracic techniques such as bronchial intubation may be required. If any difficulty is anticipated in securing ventilation or if stridor exists, intravenous hypnotics and muscle relaxants are contraindicated until a definitive airway has been established.
Surgical tracheostomy is usually performed in a sedated or anaesthetized intubated patient. Occasionally, emergency tracheostomy is required in the unintubated patient, for example in stridor, and may even take place under local anaesthetic if general anaesthesia with a secure airway cannot be performed (see ENT emergencies below). Many procedures now take place percutaneously on the intensive care unit. If surgical tracheostomy is required, the patient is stabilized and the lungs ventilated in the operating theatre with the head and neck extended to allow access. When the surgeon has dissected down to the trachea, the lungs are ventilated with 100% oxygen and the tracheal tube is withdrawn carefully into the proximal trachea to allow the tracheal window to be excised without perforating the cuff. At this point, positive pressure ventilation of the lungs becomes impossible but in the event of surgical failure to insert the tracheostomy tube, the anaesthetic tracheal tube can be advanced back down the trachea past the defect to allow ventilation to be reinstituted. After the tracheostomy tube has been inserted, the breathing system is connected to it and ventilation confirmed with visualization, auscultation and capnography. The anaesthetic tube may be removed and discarded after the tracheostomy tube has been secured.
Various operations are performed on the nose and sinuses to treat and prevent epistaxis, to improve the nasal airway, to reduce the symptoms of chronic rhinosinusitis or to improve the external appearance of the nose. Nearly all can be performed as day-case procedures. Major invasive access to the nasal sinuses such as the Caldwell Luc procedure have largely been replaced by the use of endoscopic sinus surgery which is more cost-effective in terms of symptom relief.
Most nasal procedures in the UK are performed under general anaesthesia and range from simple diathermy of the inferior turbinates to prolonged cosmetic external rhinoplasty. The application of a mixture of topical local anaesthetic agents and other adjuncts (e.g. Moffat’s solution, which is a mixture of cocaine, adrenaline and bicarbonate) provides vasoconstriction before surgery. The airway must be secured to allow the delivery of oxygen and a volatile anaesthetic agent and also to protect the trachea from soiling by blood from the operative site. This can be achieved satisfactorily by the use of a reinforced LMA if there are no specific indications for tracheal intubation such as obesity or the expectation of a prolonged operation. Special attention must be paid to avoid disconnection or occlusion of the breathing system by the surgeon, or soiling of the trachea. Balanced anaesthesia is achieved using increments of a short-acting opioid or a longer-acting drug for prolonged or painful procedures. Careful pharyngeal suction is performed at the end of surgery to ensure the removal of blood and other debris which may have accumulated. The use of a pharyngeal pack is generally unnecessary but, if used, it is vital to ensure that it has been removed before emergence. Serious complications, including death, have been reported after failure to remove a throat pack. The usual principles applying to day-case anaesthesia are adhered to including preoperative assessment and postoperative care (see Ch 26).
Examination under anaesthetic, suction clearance and myringotomy with insertion of grommets are extremely common operations, particularly in children, and are performed to relieve the symptoms of chronic otitis media with effusion and to improve hearing. They may be combined with adenoidectomy and tonsillectomy for recurrent tonsillitis or chronic rhinosinusitis. Recent guidance published by NICE may reduce the prevalence of surgical management of these conditions. In general, these are quick operations requiring attention to the principles of paediatric day-case anaesthesia. Postoperative pain is usually managed with a combination of paracetamol and an NSAID to allow early discharge.