Anaesthesia for ENT, maxillofacial and dental surgery

Tonsillectomy

The number of tonsillectomy operations has decreased, but there are still approximately 50,000 procedures performed annually in England, just less than half of which are in children. Almost all are performed under general anaesthesia, with one third undertaken as day-case surgery. Premedication is often impractical with modern admission practices, but robust preoperative assessment is mandatory (see Chapters 19 and 33 ), 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 ( Fig. 37.1 ). To facilitate this, a secure airway is usually maintained with a south-facing Ring, Adair and Elwyn (RAE) moulded tracheal tube ( Fig. 37.2 ). Alternatively, a reinforced supraglottic airway device (SAD) ( Chapter 23 ; see Fig. 23.5C ) can be used successfully provided that the surgeon carefully avoids displacement of the SAD during the insertion and removal of the gag.

Spontaneous ventilation after the use of a short-acting neuromuscular blocking agent (NMBA) can be used to facilitate deep tracheal 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 tracheal 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 often involves a multimodal approach with an initial dose of i.v. morphine together with paracetamol and an 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 (PONV) is a common 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.

Adenoidectomy

Adenoidectomy 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 of the procedure is decreasing. Adenoidectomy is also performed occasionally for glue ear in adults.

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 SAD 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.

Rigid endoscopy and microlaryngoscopy

Rigid endoscopy is performed commonly in ENT to facilitate examination, biopsy and treatment of abnormalities of the upper aerodigestive tract. General anaesthesia is required, usually with tracheal intubation to provide a safe airway during surgery. Provided that no difficulty with tracheal intubation is predicted, i.v. or gaseous induction is followed by the administration of an NMBA, depending on the anticipated duration of the procedure. Examination, with or without biopsy, is usually short, and mivacurium or suxamethonium are often used (see Chapter 8 ). Increasingly, however, the operating microscope is used to resect neoplasms of the upper airway, especially laryngeal carcinoma, allowing less damage to voice function. These operations may be prolonged, requiring attention to normothermia and fluid balance. In general a small cuffed (microlaryngoscopy) tracheal tube (ID 4–6 mm) ( Fig. 37.3 ) 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.

Microlaryngeal tumour resection is often carried out using a precision laser cutting tool. The use of laser in airway surgery creates the risk of airway fire, which can be catastrophic where flammable material exists in combination with oxygen and a means of ignition. The use of a metallic tracheal tube with cuffs inflated with saline ( Fig. 37.4 ) can minimise the risk but may not always be practical. All laser safety protocols must be implemented, such as eye protection, access to extinguishers, laser smoke masks and the use of reduced oxygen concentrations in the ventilating mixtures if possible. 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 tracheal extubation is normally achieved with full emergence and recovery of airway reflexes and careful pharyngeal suction before the removal of the tracheal 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 ( Chapter 23 ; see Fig. 23.52 ). The catheter can be inserted into the trachea either down the endoscope or through the cricothyroid membrane. Anaesthesia is maintained using an i.v. agent, usually propofol.

Thyroid and parathyroid surgery

Thyroid surgery is increasingly performed by specialist ENT surgeons, although some general surgeons still undertake the operation. Thyroidectomy may be partial or total and is performed for indications including thyroid cancer, toxic thyroid nodule, multinodular goitre and Graves’ disease. Safe anaesthesia for thyroid surgery requires preoperative assessment accounting for specific hazards, an effective plan for intraoperative care and an awareness of the potential postoperative complications. Specific issues include the following:

• Thyroid function. Patients should be prepared so they are euthyroid both clinically and biochemically (as indicated by thyroid function testing) before surgery (see Chapter 20 ). Resting tachycardia and poorly controlled atrial fibrillation may indicate inadequate control of hyperthyroidism.

• Airway compression and displacement. A large goitre may displace or compress the trachea. The central position of the trachea above the sternal notch should be confirmed. Hard goitres are suggestive of malignancy. Infiltrating thyroid carcinoma may make neck movement and tracheal intubation difficult. An inability to feel below an enlarged thyroid may be due to retrosternal extension of a goitre. In severe cases the upper end of the sternum may have to be split at surgery to enable resection. Stridor and an inability to lie flat suggest airway compression. A chest radiograph may show tracheal narrowing or deviation. If there is more than 50% narrowing of the trachea, then a CT scan to fully explore the extent of airway compromise is advisable.

• Superior vena cava obstruction. This is uncommon but may be seen with extensive disease. The neck veins are distended and do not collapse on sitting up.

• Vocal cord palsy. Nasendoscopy to identify pre-existing vocal cord palsy is advisable before surgery.

• Blood tests. Preoperative tests should include thyroid function and corrected serum calcium concentrations.

Thyroidectomy is generally performed under general anaesthesia. Although most cases are uneventful the anaesthetist should be prepared for airway problems, and the patient's lungs should be preoxygenated before induction. If there are particular concerns regarding the airway, anaesthesia may be induced with the patient in a semirecumbent position. In cases where there is evidence of incipient airway obstruction, tracheostomy under local anaesthesia may be performed. Where there is obstruction of the mid-trachea after induction of anaesthesia the situation may be rescued with ventilation of the lungs through a rigid bronchoscope.

For surgery the patient is positioned supine with a sandbag between the shoulders to extend the neck. Particular care must be taken to protect the eyes where there is exophthalmos. Tracheal extubation should be performed with the patient awake. Rarely, prolonged compression by a large goitre may cause tracheomalacia leading to tracheal collapse and postoperative airway obstruction.

The surgeon often infiltrates the operative site with local anaesthetic and adrenaline. This may be supplemented with a superficial cervical plexus block for postoperative pain relief. Thyroidectomy is associated with a number of potential postoperative complications. Postoperative haemorrhage may lead to neck swelling and airway compromise. Clip removers or stitch cutters should be kept by the patient's bedside to allow expeditious release of a neck haematoma in the event of airway obstruction. Unilateral or bilateral recurrent laryngeal nerve injury may lead to vocal cord palsy, stridor or airway obstruction. With modern surgical techniques and fastidious identification of the nerves this is uncommon, but with severe airway obstruction, tracheal reintubation may be required. Temporary hypocalcaemia may be seen, especially after surgery for a large goitre. It may present with twitching, facial tingling, tetany and prolongation of the QT interval. Mild hypocalcaemia may be treated with oral calcium supplements, whereas severe hypocalcaemia requires i.v. calcium.

Parathyroid surgery is most often performed for primary hyperparathyroidism caused by adenoma. The traditional operation of exploration of all four parathyroid glands requires general anaesthesia, and surgery may be protracted. Technetium-99m or sestamibi scanning now allows the preoperative localisation of the adenoma in most patients, allowing surgery through a small incision to be performed under local anaesthesia.

Tracheostomy

The indications for tracheostomy include:

• loss of upper airway;

• prolonged mechanical ventilation;

• tracheobronchial toilet; and

• airway protection.

Tracheostomy may be performed percutaneously, usually in the ICU, or surgically in the operating theatre. Patients are usually already sedated or anaesthetised, although upper airway emergency management may require a tracheostomy to be placed under local anaesthetic (see airway emergencies section later). If surgical tracheostomy is required the patient is stabilised 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 visualisation, auscultation and capnography. The anaesthetic tracheal tube may be removed and discarded after the tracheostomy tube has been secured. Early complications of tracheostomy include bleeding, loss of airway as a result of malposition, pneumothorax/pneumomediastinum and injury to surrounding structures. Later complications such as blockage of the tube as a result of secretions, infection, secondary haemorrhage and accidental decannulation; postoperatively patients require careful nursing and monitoring in an appropriate environment. Delayed complications can occur, such as stoma stenosis and tracheomalacia. Patients with tracheostomies should be managed by a multidisciplinary team including expert physicians, physiotherapists and speech/swallowing therapists. Many different types of tracheostomy tube may be encountered, including double lumen, which incorporate an outer and inner tube to facilitate speech and cleaning, adjustable flange for the obese patient and various long-term tracheostomy tubes. These should be regularly cleaned and changed according to the type of tube. The National Tracheostomy Safety Project has developed guidelines and resources for the management of tracheostomy emergencies, which should be embedded in organisations that care for these patients ( Fig. 37.5 ).

Nasal and sinus surgery

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.

Most nasal procedures in the UK are performed endoscopically under general anaesthesia as a day case 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. Moffett's solution, a mixture of cocaine, adrenaline and bicarbonate) provides vasoconstriction before surgery. The airway must be secured to protect the trachea from soiling by blood from the operative site. This can be achieved satisfactorily by the use of a reinforced SAD 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. The usual principles applying to day-case anaesthesia are adhered to, including preoperative assessment and postoperative care (see Chapter 34 ).

Ear surgery

Examination under anaesthetic, suction clearance and myringotomy with insertion of grommets are 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. 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 NSAIDs to allow early discharge.

More complex procedures performed on the structures of the ear using a microscope, such as tympanoplasty, mastoidectomy and stapedectomy, are performed under general anaesthesia. Deliberate hypotension has been employed to minimise bleeding in the operative field, but agents such as β-blockers and vasodilators have largely been superseded by the use of short-acting narcotic agents given by intermittent bolus or infusion. These provide smooth anaesthesia without variations in blood pressure associated with surgical bleeding, which can obscure the surgeon's view through the microscope. If hypotensive anaesthesia is to be used, care should be taken to maintain vital organ perfusion and keep the MAP above the lower limit of autoregulation of about 55 mmHg. In general, these techniques require positive pressure ventilation and neuromuscular blockade. A south-facing moulded tracheal tube or reinforced SAD can be used. Nitrous oxide is avoided because it can increase the pressure in the middle ear, thereby increasing the risk of graft failure. Postoperative pain is not usually severe and can usually be managed using oral analgesia, often allowing same-day discharge.

ENT emergencies