Anaesthesia for goitre surgery: A review

Introduction

The term ‘goitre’ is derived from the Latin phrase tumidum gutter (swollen throat) and refers to an abnormal enlargement of the thyroid gland. The prevalence of goitres varies from 80% in areas of severe iodine deficiency (such as South East Asia, South America and Africa) to 1–4% in iodine-replete areas of developed countries.^1,2 The nature of the goitre dictates whether a patient requires medical and/or surgical treatment. Thyroidectomy for goitre was first described in 1170 by Robert Frugardi, but historically it was considered a dangerous undertaking such that the French Academy of Medicine banned it in 1850, and in London in 1877 the mortality rate was 44.4%. ³ Modern day thyroid surgery is now commonplace and is associated with a low mortality rate (0.16%) ⁴ due to improved surgical and anaesthetic practices, and better management of complications.

Goitre pathology

Morphologically, goitres may be diffuse smooth or nodular, and their aetiology includes: neoplasm (benign or malignant), autoimmune disease (Grave’s or Hashimoto’s), inflammation, infection, iodine deficiency (worldwide this is the most common cause of goitre), and certain foods and drugs (‘goitrogens’). Functionally, most cases are euthyroid, but they can present with either hyper- or hypothyroidism. Indications for thyroidectomy include: malignancy (proven/suspected), obstruction/mass effect, retrosternal goitre (early surgery is easier and has fewer complications), hyperthyroidism (recurrent or unresponsive to medical treatment), Hashimoto’s disease or cosmetic reasons. The ‘mass effect’ may impact on structures in the neck (airway, oesophagus and nerves) or in the thorax (mostly in the anterior mediastinum). Retrosternal goitre (RSG) may be classified depending on the location of the goitre: grade 1, above the aortic arch; grade 2, between the aortic arch and pericardium; and grade 3, below the right atrium. ⁵ A surgical approach is usually via a cervical incision but, depending on the presence of any intra-thoracic extension, it may necessitate manubriotomy, sternotomy or thoracotomy (3.1, 6.6 and 4%, respectively) ⁵ which exposes the patient to the risk of pneumothorax (pleural tear) and haemorrhage (from the inferior thyroid and innominate veins).

Anaesthesia: Pre-operative considerations

History taking and assessment focuses on the patient’s thyroid status, predictors of difficult airway, and symptoms and signs secondary to the goitre. The latter group include dyspnoea, dysphagia, and features of superior vena cava (SVC) obstruction and nerve compression (Horner’s syndrome, and recurrent laryngeal and phrenic nerves). Pemberton’s sign is elicited when the patient elevates both arms until they touch the sides of the head, resulting in facial congestion, flushing and cyanosis due to the ‘thyroid cork’ effect at the thoracic inlet. ⁶ Predictors of difficult face mask ventilation (FMV) ⁷ and difficult intubation (mouth opening, Mallampati score, ⁸ mandible luxation score, thyromental distance, neck movement) have only low to moderate predictive values. ⁹ Additional assessment of the larynx with a flexible nasendoscope can detect anatomical distortion (by large goitres), confirm accessibility to the glottis (should intubation using direct laryngoscopy be attempted) and determine vocal cord function.

Investigations include thyroid function tests and serum calcium levels (baseline values for comparison in case of post-operative hypocalcaemia). Imaging (e.g. X-ray, computerized tomography (CT) scan and magnetic resonance imaging (MRI)) identifies the location and extension of a goitre, and any tracheal deviation, narrowing and luminal wall invasion. A virtual bronchoscopic movie of the 3D reconstruction from a multi-slice CT can help in the pre-operative evaluation and planning of the management of tracheal stenosis or deviation. Flow volume loops depend on patient effort and co-operation, and have poor correlation with the patient’s symptoms and degree of tracheal deviation and stenosis as determined on a CT scan. ¹⁰ This is due to the flow volume studies being performed in the sitting position and at maximal inspiratory and expiratory volumes (dynamic picture). CT scans, on the other hand, are usually done in the supine position and during apnoea (static picture).

Elective surgery

Anaesthesia for thyroid surgery is well described in the literature and the basic principles follow the ABCDE approach ¹¹ (further details in the decision-making process are described below). ‘Airway’ involves the placement of an endotracheal tube, for example a flexible, reinforced tube (to prevent kinking), a pre-formed north facing Ring, Adair and Elwyn (RAE) tube or a Neural Integrity Monitor (NIM) tube. The latter is an electromyogram tracheal tube recommended by the National Institute for Health and Care Excellence to detect and avoid damage to the recurrent laryngeal nerve (RLN). ¹² It is not universally used due to the lack of conclusive evidence of its benefit over traditional visualization techniques, its costs, its set-up time, associated false negative results and concerns of nerve damage. ¹³ As such, it is recommended for surgery which is considered high risk for RLN damage (e.g. thyroidectomy for malignant goitres or re-do thyroidectomy). A laryngeal mask airway (LMA) is rarely used except at the end of an operation, when it is inserted into the airway to act as a conduit for flexible fibreoptic bronchoscope insertion and subsequent assessment of vocal cord and tracheal function. ‘Breathing’ is accomplished by positive pressure ventilation. ‘Circulation’ is well maintained as blood loss is approximately 135 ml. ¹⁴ Establishing a large-bore intravenous cannula is recommended for RSG due to the potential for massive haemorrhage. ‘Disability’ is provision of an adequate depth of anaesthesia (using volatile agents or an intravenous infusion of propofol) and analgesia (opioids, paracetamol and non-steroidal analgesics). Intravenous remifentanil infusion provides intra-operative analgesia, controls the patient’s blood pressure to facilitate a bloodless surgical field, and obtunds the laryngeal reflexes reducing coughing and straining during emergence. ‘Exposure’ of the patient encompasses placing the patient in a head-up tilt position (promoting venous drainage), placing a shoulder roll and extending the head and neck (maximising surgical exposure of the goitre), padding the eye (especially if exophthalmos is present) and using skin infiltration with local anaesthetic with adrenaline (minimising surgical stimulation and bleeding).

Post-thyroidectomy, hypocalcaemia is relatively common (transient in 8.3% and permanent in 1.7%), ¹⁵ but other complications are rare: haematoma (0.36–2.0%);^16,17 RLN damage (0.5% in benign but 10.6% in malignant disease); ¹⁷ and post-thyroidectomy tracheomalacia (PTTM) (0–1%).^5,18 Findlay et al. went so far as to say that PTTM was ‘almost mythical within modern thyroid surgery in the Western world’, although Bennett et al. found up to 10% in cases of RSG.^5,18,19 Risk factors predisposing to PTTM include goitre for more than five years, pre-operative RLN palsy, significant tracheal narrowing and/or deviation, retrosternal/retrotracheal extension, difficult tracheal intubation and thyroid malignancy. ²⁰ However, these factors have low predictive values and PTTM can occur without tracheal compression. In the authors’ experience a post-operative tracheostomy (and ICU bed) is rarely needed.

Emergency surgery

Emergency thyroidectomy for patients with goitres presenting with acute airway obstruction is rare (<1%) and is due to intra-thyroid haemorrhage, tracheal compression or luminal invasion by tumour, or RLN infiltration.^21,22 Securing the airway under these conditions presents unique challenges to the anaesthetist and has been associated with significant morbidity. ²³ An ABC management plan to secure the airway is formulated after considering four ‘basic management choices’ from the American Society of Anesthesiologists’ (ASA) difficult airway algorithm in a logical manner: use an ‘awake’ or ‘asleep’ technique (securing the airway before or after induction of anaesthesia, respectively); ‘maintain spontaneous ventilation’ or ‘ablate spontaneous ventilation’; use ‘non-invasive or invasive airways’; and use ‘conventional direct laryngoscopy or indirect laryngoscopy’. ²⁴ The reason for keeping the patient ‘awake’ and ‘spontaneously ventilating’ is to avoid the potentially catastrophic ‘cannot intubate, cannot ventilate’ (CICV) scenario (1 in 10,000 anaesthetic cases). ²⁵ Therefore, predicting which patient will be difficult to ventilate and/or intubate (and therefore opting for the safer ‘awake’ options to secure the airway) is important.

Awake techniques for surgery and airway management

Options for keeping the patient ‘awake’ for safety reasons include performing surgery in the awake patient, or securing the airway while awake before the induction of anaesthesia. Awake thyroidectomy under local infiltration of lignocaine with adrenaline^26,27 or regional block (superficial and deep cervical plexus block) ²⁸ is not commonly performed. Awake techniques (see below) to secure the airway includes awake fibreoptic intubation (AFOI), awake tracheostomy and, very rarely, awake direct laryngoscopy and awake rigid bronchoscopy (RB).

Another ‘awake technique’ is to establish cardiopulmonary bypass (CPB) or extracorporeal membrane oxygenation (ECMO) via femoral vessel cannulation under local anaesthesia, although this is only available in specialist hospitals. This is indicated for those at risk of CICV (and those whose airways cannot be safely secured by other means) or mediastinal mass syndrome (MMS). ²⁹ RSG occurs in 6% of patients presenting with a mediastinal mass. ³⁰ In severe cases, MMS may cause compression of the trachea, bronchi, heart and major vessels (SVC and pulmonary artery) leading to cardiac hypotension or arrest, and/or acute respiratory compromise. Risk factors for peri- and intra-operative MMS include: pericardial effusion, tracheal compression >50% on CT scan and cardiopulmonary signs and symptoms. ³⁰ CPB/ECMO is logistically difficult to set up and the timing of femoral cannulation varies. Some authors have established vascular access or even established bypass before securing the airway,^31-34 whereas others have done so only after AFOI.^35,36 It must be noted that it takes several minutes to cannulate the femoral vessels and achieve full bypass, and this delay may result in brain hypoxia. ³⁷ Goh et al. suggest that all patients with trachea with ≥50% reduction of the cross-sectional area on a CT scan ‘should have the femoral vessels cannulated under local anaesthesia in readiness for CPB prior to induction of anaesthesia’. ³⁸ However, this was based on MMS complications in children (who are poor historians and so symptoms are under-appreciated, and also have more compressible tracheas). ³⁹ Furthermore, calculating the tracheal diameters from CT scan studies in normal subjects, results in mean values of 11 and 13 mm (females and males, respectively). ⁴⁰ Most patients with goitres quoted in this article have tracheal diameters considerably less than these values, and have been managed successfully without CPB/ECMO. RSG has not been widely reported to cause MMS and research is needed to establish if it differs (and should be managed differently) from other causes of MMS. Possible reasons are that goitres are more noticeable (and therefore treated earlier than other mediastinal masses) and are usually tethered in the neck, resulting in less intra-thoracic involvement and cardio-respiratory compromise.

Asleep techniques for airway management (including preserving or ablating spontaneous ventilation)

If tracheal intubation is deemed safe after induction of anaesthesia, then full pre-oxygenation is recommended (‘3 minute tidal volume’ or ‘8 deep breaths’ techniques) to prolong the apnoea time. ⁴¹ Induction of anaesthesia is carried out either with a volatile or an intravenous agent. The advantage of gas induction is that it is a slow, gradual process and so preserves spontaneous ventilation; this ‘buys one time’ to intubate as long as the patient continues to breathe. If airway obstruction does occur, then there is automatic cessation of drug delivery and the patient can theoretically wake up. However, gas induction is not widely reported in the literature regarding goitre management, and there are cases of failure of the technique. ⁴² There are reported cases of ‘cannot ventilate’ and CICV, ⁴³ and the 4th National Audit Project (NAP4) report from the UK stated that it may lead to ‘loss of airway and failure to wake up’. ²³ Intravenous induction has been used safely even in patients with large endemic goitres^44,45 but there is not enough data regarding patients with large goitres who are severely symptomatic.

The ability to ‘wake up’ a patient is the reason for avoiding the use of neuromuscular blocking agents (NMBA). However, if they are not used, optimal intubating conditions may not be as rapidly obtained. ⁴⁶ However, there is no strong evidence about their role in patients with large goitres and whether they improve or impede attempts at FMV, laryngoscopy or intubation. There are opposing opinions on this matter, depending on whether the goitre is considered as a fixed, annular tracheal stenosis or as a cause of MMS. In the former, one study showed improved ventilatory dynamics after administration of NMBA and the application of positive pressure ventilation, even in patients with as much as 51–99% luminal obstruction. ⁴⁷ In cases of MMS, authors recommend avoidance of NMBA or, if absolutely required, use of a short-acting NMBA.^29,37 Suxamethonium may be used due to its short duration of 5–11 minutes, although it has rare but serious side effects (anaphylaxis, hyperkalaemia and malignant hyperthermia). ⁴⁸ An alternative is to use the intermediate acting NMBA rocuronium, which has a mean (range) duration time of 73 (38–150) minutes. ⁴⁹ However, when its reversal sugammadex (16 mg/kg) is given within 3 minutes then the train-of-four (TOF) ratio returns to 0.9 by 2.2 minutes, that is, substantially quicker than suxamethonium. ⁵⁰

Non-invasive vs. invasive airway

After induction of anaesthesia, airway manipulation usually involves non-invasive airway techniques, for example FMV, laryngeal mask ventilation and tracheal intubation. One case series reported no difficulties with FMV in patients with goitre but there were no data on patient symptomatology or size of the goitre. ⁵¹ The LMA is rarely used as a primary airway, ⁵² but it can be used as a rescue technique after failed intubation.^51,53,54 The endotracheal tube (ETT) is the airway of choice due to the site, nature and length of surgery. There is an assumption of encountering difficult ETT insertion in the presence of tracheal narrowing secondary to goitre. However, studies have shown that stenotic tracheas can accommodate ETT much larger than indicated on CT scan. Findlay et al. had patients (n=334) with a mean (range) tracheal diameter of 7.6 (2–15) mm on CT scan, but all were successfully intubated with ETT 6.0–8.0 mm internal diameter (approximately 8.0–10.0 mm outer diameter). ¹⁸ Similarly, Dempsey et al.’s patients (n=19) had a mean (range) of 9.6 (5.8–15) mm, but they still allowed passage of ETT with 7.0–9.0 mm inner diameter (9.0–11.0 mm outer diameter). ⁴³ There are a few explanations for this. Firstly, CT scans are usually performed in the supine position but, if in a prone position, the tracheal diameter can double since the weight of the goitre is pulled away. ⁵⁵ Secondly, most goitres do not infiltrate the tracheal wall and so the trachea remains distensible. Thirdly, CT scans are usually done in apnoea and may not be at full inspiration. If AFOI is attempted, using a smaller-sized ETT minimizes tube impingement during railroading. ⁵⁶

In rare (and extreme cases) of airway compromise, an awake tracheostomy may be considered. However, it is technically difficult to perform in the presence of an enlarged and vascular thyroid gland, ⁴³ but it can be lifesaving (performed either awake or asleep).^22,54

Direct laryngoscopy vs. indirect laryngoscopy

Conventional direct laryngoscopy is usually sufficient to achieve tracheal intubation. Swadia et al. reported ‘no difficulties encountered in viewing and intubating larynx’ in 20 patients with endemic goitres who had a mean (range) neck circumference of 60 (47–80) cm. ⁴⁵ Dempsey et al. in a study of 19 patients with massive retrosternal goitre (i.e. one that extends to the aortic arch or beyond), concluded that ‘intravenous induction of anaesthesia and conventional direct laryngoscopy is a safe technique in appropriately experienced hands in a tertiary referral centre’ (although one patient required an emergency tracheostomy after developing into a CICV scenario). ⁴³

The incidence of difficult intubation in patients with goitres is 2–12.7%.^57,58 Two case series comparing patients with and without goitres showed conflicting results: Amathieu et al. showed similar incidences (11 vs. 9.9%, respectively), ⁵⁹ but Voyagis and Kyriakos showed statistically different values (6.8 vs. 0.9%, respectively). ⁵¹ The latter study also showed similar rates of failed intubation in both groups (0.3% vs. 0.5%, respectively), although no details were provided of the methods used.

In cases of predicted difficult tracheal intubation and ventilation, indirect laryngoscopy to secure the airway should be considered. The most reported technique of indirect laryngoscopy for the management of patients with goitre is AFOI but there have been reports of failure, with subsequent successful tracheal intubation using conventional direct laryngoscopy.^42,57,60 AFOI has been successfully used in patients with airway obstruction.^{21,34-36,51,61-64} However, in the severely obstructed airways there are many reasons why this may not be prudent: AFOI requires a calm and co-operative patient but this is not usually seen in patients with severe obstruction; administering sedation, or topicalization with local anaesthetics, may cause further respiratory deterioration or laryngospasm (converting an already partially obstructed airway to a completely obstructed one); passing the fibrescope causes a ‘cork in a bottle’ situation, resulting in failure of the technique and/or complete obstruction.^42,54,55 At present, there is little data on the use of videolaryngoscopy in patients with goitre to determine its role. ⁶⁵

Plan ABC

Each case needs to have a tailored plan ABC after weighing up the risks and benefits of the ASA four ‘basic management choices’ (see above). Cook et al. showed that there is no consensus on the best ‘plan A’ to secure the airway in patients with goitre, even among international airway experts. ⁶¹ However, all agreed that RB should be part of a plan B (or C), and other experts have concurred. ⁶⁶ RB can secure a narrowed airway (if a relatively soft ETT is unable to pass); allows ventilation (using the conventional low-pressure system from the anaesthetic machine or the high-pressure jet ventilation techniques); tamponades any intra-tracheal bleeding; and allows diagnostic and therapeutic procedures to be performed. Should RB fail then plan C involves instigating CPB/ECMO.

Conclusion

In summary, patients with goitre are common and, in extreme cases, may present a unique set of challenges to the anaesthetist. Careful consideration of the disease process (and its secondary effects), the patient’s history and examination, and investigation results are essential. A multidisciplinary team approach with surgical colleagues allows safe management.