16 Anaesthesia for oral and maxillofacial malignancy

Oral cancer is the sixth most common cancer worldwide and accounts for approximately 2% of all cancer-related deaths. Approximately 5000 new cases are diagnosed annually in the United Kingdom. In recent years, trends show a significant increase in the incidence of oral cancer in young males (aged under 40 years)¹.

The distribution of head and neck cancer is shown in Figure 16.1. Squamous cell carcinoma accounts for 90% of all malignant head and neck tumours, but a wide variety of other tumours and premalignant states may also present in this region (Table 16.1). Patients with oral cancer have a 10% risk of having a synchronous primary elsewhere in the aerodigestive tract. Almost 60% of patients present with advanced disease. Lesions in the head and neck region spread primarily by the lymphatic system and distal metastasis occur relatively late in the course of the disease. In all, 30–40% of patients with head and neck cancer have persistent or recurrent locoregional disease after completion of definitive treatment. Despite advances in cancer treatment, the overall 5-year survival rates for cancer of the oral cavity and pharynx have remained unchanged at around 55%².

The main predisposing factors are smoking and alcohol, which seem to have a synergistic effect. Chewing betel nut, tobacco, and poor oral hygiene are significant risk factors for oral cancer. In addition, more recent evidence is emerging of a link between viral infection with human papilloma virus 16 and oral cancer. Immunosuppression in solid-organ transplant recipients is also an important risk factor in a small subgroup. Head and neck cancer occurring in transplant patients tends to affect a younger group of patients and is more aggressive with a poorer outcome as compared to the general population. Cancer progression has been associated with loss of tumour suppressor oncogenes p16 and p53 and an increase in epidermal growth factor receptor, which is being investigated as a biomarker for the disease³.

Head and neck cancer is staged on the basis of the tumour, node, and metastases (TNM) system (Table 16.2), which is useful in planning treatment and predicting outcome. Ideally, all cancer patients are seen at multidisciplinary team meeting comprising oncologists, surgeons, and radiologists who objectively assess and agree on the optimum management strategy.

The treatment depends on the patient’s age, general medical condition, and tolerance, acceptance and compliance of the proposed treatment plan. The principal treatment options remain elective surgery and radical radiotherapy.

Traditionally, the primary modality of treatment has been surgery for squamous cell carcinoma of the oral cavity supplemented by adjuvant radiation therapy when indicated (in the majority of Stage III and IV cases). Although surgery with postoperative radiation remains the cornerstone in treatment, with recent advances in chemoradiation protocols and greater understanding of importance of organ preservation, the role of radiotherapy in the management of head and neck cancer is increasing⁴ (see Chapter 17).

Current evidence suggests that results of surgical excision are superior for lesions involving anterior tongue, mandible, and buccal mucosa as compared to those achieved with radical radiotherapy. For cancer of the base of tongue, oropharynx, and hypopharynx the survival figures are broadly similar with both modalities of treatment⁵.

However, the overall medical condition and ability of the patient to tolerate an optimal therapeutic programme are important factors which govern the choice of treatment. The perioperative morbidity and mortality remain uniformly high with advancing age and associated cardiopulmonary conditions with extensive surgical treatment. This is where the anaesthetist should play a vital part in the multidisciplinary team in deciding the treatment plan. The potential benefits of surgical intervention in cancer patients must be weighed against the risks of surgery and alternative non-surgical therapeutic options must be explored.

Surgical management depends again upon the size, location, and type of tumour.

T1 lesions are excised and repaired with local flap reconstruction. Lesions of T2 and higher level require extensive resection. Elective neck dissection is advocated where nodal disease is present on either clinical or radiological examination or where the risk of spread to the nodes exceeds 20%. The majority of head and neck tumours metastasize in a predictable fashion to levels I–IV in the neck and rarely to other levels (Figure 16.2). Traditionally, radical neck dissection used to be performed, where the superficial and deep cervical fascia along with the lymph nodes within it were removed along with the sternocleidomastoid muscle, internal and external jugular vein, submandibular gland, and spinal accessory nerve. However, more recently radical neck dissection has lost favour because of a higher incidence of complications⁶. These include massive facial oedema, cerebral oedema resulting from the removal of internal jugular vein, and severe restriction of shoulder function caused by the excision of accessory nerve. In the 1990s, several studies showed that the integrity of neck dissection and subsequent clinical outcome is not compromised by selective neck dissection; consequently, this approach is preferred for N0 and N1 tumours⁷.

In selective neck dissection, only the nodal tissue from level I to IV is dissected, however, the critical non-lymphatic structures such as the spinal accessory nerve, the internal jugular vein, and sternocleidomastoid muscle are preserved. In extensive nodal disease these structures may have to be sacrificed to remove tumour metastases.

The different methods available for reconstruction following tumour resection are:

Primary closure and skin grafting is only possible in small defects. After extensive resection, pedicled or free flap repair is needed which aims to improve not only the cosmetic appearance but more importantly to restore the complex functions of upper aerodigestive tract, particularly swallowing and speech.

The commonly used pedicled flaps in the head and neck region are pectoralis major, deltopectoral, and temporalis flaps. Skin and muscle is raised from the donor area and rotated with the vascular pedicle as a pivot point to cover the defect. Unlike free flaps, the blood supply comes from its own vascular pedicle. As there is no microvascular anastomosis, the length of the operation is reduced significantly.

The disadvantages of a pedicled flap is that in the majority of cases, the type of tissue that is needed to reconstruct is not available, and contouring of the flap is difficult, which leads to a bulky flap with poor functional results. Furthermore, blood supply at peripheral areas is less robust leading to a high rate of partial dehiscence and flap necrosis. Pedicled flap transfer is technically less demanding and suitable for high-risk patients with significant comorbidity.

A free flap is a composite block of tissue which is removed from the donor site and transferred to a distant recipient site where its circulation is restored by microvascular anastomosis. This is in contrast to a ‘pedicled’ flap in which tissue remains attached to the donor site keeping the ‘pedicle’ intact as a conduit for blood supply. For all free flaps, the artery and vein are reconnected to recipient vessels in the neck.

Free flaps may be soft tissue flaps which have muscle and skin, free visceral flaps, e.g. free jejunum transfer for reconstruction of oropharynx, and composite flap where vascularized bone is grafted, e.g. radius, fibula, iliac, or scapular graft for reconstruction of mandible.

Free flaps are the preferred option in reconstruction because of greater ability to match the resected tissue (like for like), suitable contour to match the defect, and a robust blood supply. The main disadvantage is that the surgery is technically demanding with prolonged operating time. Intensive postoperative monitoring is needed to ensure flap perfusion and additional morbidity of the donor site is also seen. Commonly used free flaps used in head and neck reconstruction are listed in Table 16.3.

The stages during flap transfer include initial dissection, flap elevation and clamping of vessels, period of primary ischaemia when there is no blood flow in the flap and intracellular metabolism is entirely anaerobic, and reperfusion after anastomosis of artery and vein.

Free flaps rely on small vascular anastomosis for perfusion and this makes them extremely vulnerable to hypoperfusion and ischaemia. All flaps undergo a period of primary ischaemia during harvest. This in part triggers a reperfusion injury which results in microcirculatory sludging, release of inflammatory mediators and vasospasm with reduction in blood flow in the initial 8–12 hours⁸. Flap failure is most commonly due to formation of thrombus at the anastomosis site, which in turn is related to the quality of vessels and the technical skill of the surgical team. Duration of primary ischaemia is a critical determinant of ischaemic complications⁹.

Arterial vasospasm and extrinsic compression of the pedicle have also been identified as crucial factors in flap failure. Vessels that are used for anastomosis are generally 1–4 mm in diameter and any vasoconstriction can lead to critical ischaemia. Interstitial oedema from tissue handling and excessive fluids could also contribute to poor perfusion.

Free flaps are different from normal tissues in several respects. There is no lymphatic drainage in the flap tissue. Hence, reabsorption of interstitial fluid is minimal and this makes the flap tissue highly vulnerable to interstitial oedema. Transplanted vessels in a free flap have no sympathetic innervation but are still able to respond to physical stimuli such as cold, handling, and local and humoral factors including circulating catecholamines. The impaired autoregulation in flap tissue also predisposes to vasospasm¹⁰.

Poorly controlled diabetes leads to increased microvascular atherosclerosis, impaired wound healing, and delayed neovascularization of the flap. Patients with significant cardiac disease may not tolerate prolonged surgery with large fluid shifts and these patients may be better served with less ambitious reconstruction.

Collagen vascular disease is a relative contraindication with a high incidence of anastomotic thrombosis especially during active vasculitis. Free flap transfer may not be acceptable to some Jehovah’s Witness patients. The only absolute contraindication for free flap transfer is sickle cell disease and polycythaemia because of high failure rate from a combination of microcirculatory sludging and hypercoagulability.

A basic understanding of the physiology of microcirculation and the unique features of free flap is essential for anaesthetic management¹¹. Hagen–Poiseuille’s law quantitatively relates the laminar flow of a liquid through a rigid tube to the driving pressure. The equation describing this relationship is:

where Δ P is the pressure difference across the tube, i.e. the perfusion pressure, r is the radius of the tube, l the length of the tube and □ the viscosity of the liquid.

Although the microcirculation is too complex for a strict application of the formula, we can see that any change in perfusion pressure, cross sectional area, and viscosity will have an influence on flap flow. Pressure gradient depends on mean arterial blood pressure and pressure in the interstitial space. As the flow depends on the fourth power of the radius, halving the diameter will lead to a 16-fold reduction in flow rate.

In addition, Laplace’s law states that diameter of the vessel also depends on the transmural pressure. Transmural pressure is decreased by a decrease in intraluminal pressure (hypotension, hypovolaemia) or an increase in extravascular pressure (oedema, haematoma).

The relationship between viscosity and haematocrit is non-linear. Viscosity rises steeply when the haematocrit levels rise above 40%. Viscosity also depends on plasma proteins, temperature, and aggregation of cells. A reduction in viscosity is accompanied by an increase in velocity of erythrocytes. This increases the shear stress on the capillary endothelial cells, which is believed to be a crucial local factor in regulating capillary circulation¹².

An additional factor which can affect microcirculation is the pulse pressure. A good pulse pressure in the microcirculation ensures a greater period of capillary patency for the same mean arterial pressure (MAP) because of relaxation of precapillary sphincter. Peripheral vasoconstriction produces a damping of the pressure wave and in addition to reduction in total flow makes the flow less effective.

These physiological principles are the rationale of haemodynamic interventions taken to improve blood flow in both pedicle and free flap transfer. Basic principles of patient management in free flap transfer are to maintain the patient warm and vasodilated, with a well filled circulation, adequate pulse pressure, free from pain and shivering which may lead to sympathetic stimulation and vasoconstriction, and with a haematocrit around 0.30 to optimize microcirculation through optimal rheology.

The patient may present for initial examination under anaesthetic and panendoscopy as part of diagnostic workup or for definitive surgery for excision of tumour with immediate or delayed reconstruction.

The aims of preassessment are to detect potential difficulty in intubation because of the tumour or its treatment, coexisting medical problems, and decide on suitable options for surgery.

Preoperative evaluation should aim to assess the site and extent of the tumour and to detect any symptoms of obstruction, which may be indicative of significant distortion of airway (Figure 16.3) or direct laryngeal involvement with tumour with implications for safe induction of anaesthesia (Figure 16.4). Patients should be asked about recent change in voice, hoarseness, dysphagia, and dyspnoea on lying flat. Old anaesthetic charts and notes of previous operations should be reviewed. Stridor, recent onset of snoring, or obstructive sleep apnoea are ominous signs and may indicate airway obstruction.

The tongue may be fixed and immobile in cancer arising from the base of tongue and floor of mouth potentially leading to airway obstruction and difficult intubation (Figure 16.5). Large pedunculated and mobile supraglottic lesions can obstruct the laryngeal inlet with loss of muscle tone after induction of general anaesthesia¹³. Infiltration of hyoepiglottic ligament and stylohyoid ligament by hypopharyngeal tumour can cause fixation of epiglottis. Among the effects of radiotherapy in the head and neck region (Table 16.4) is fibrosis, which produces thick woody non-compliant tissue which is very difficult to elevate during direct laryngoscopy as well as severe limitation in mouth opening (Figure 16.6) (see Chapter 17).

Radiological investigations such as CT scan and MRI should be reviewed for information about the location of tumour and severity of airway obstruction. Awake nasal endoscopy is a simple bedside (or anaesthetic room) test which gives vital information about the size, mobility and site of lesions and degree of airway obstruction. The real time view of the supraglottis and the laryngeal inlet obtained is useful in planning the approach to airway management. However, it must be remembered that air passages visible in an awake patient in the sitting position via the bronchoscope, may narrow or disappear altogether as muscle tone is lost with general anaesthesia

Patients are often malnourished from dysphagia caused by the tumour per se, dietary habits (e.g. alcoholism), systemic effects of chemotherapy, and radiation mucositis. Preoperative malnutrition has been shown to correlate with impaired wound healing and infection. Nutritional status should be corrected in the time preceding surgery and the enteral route is preferred if feasible. A specialist dietician should be involved wherever possible. With history of alcohol abuse, a detoxification regimen should be commenced if possible, in order to avoid postoperative withdrawal¹⁴.

Patients with head and neck cancer are usually elderly with a history of smoking and alcohol abuse. There is a high prevalence of smoking-related respiratory disease, coronary artery disease, and peripheral vascular disease. Old age per se is not a contraindication for free flap surgery; however, coexisting cardiac and respiratory disease increases the incidence of complications and flap failure¹⁵.

With a history of heavy smoking, cardiorespiratory assessment is necessary. Although functional capacity may be assessed clinically, formal cardiopulmonary exercise testing is more accurate for stratification of risk. Patients with an anaerobic threshold lower than 11 ml/min/kg are at high risk of postoperative cardiac complications after major surgery and alternative treatment options may have to be explored.

Routine preoperative tests include full blood count and chemistry profile including liver function tests, clotting studies, chest radiography, and an electrocardiogram. If the patient is elderly or has a history of smoking it is advisable to obtain pulmonary function tests, perform cardiopulmonary exercise testing, and a nutritional assessment including determination of total serum protein, albumin, and transferrin levels.

A north preformed nasal endotracheal tube (Figure 9.1) is commonly used to facilitate surgical access to the oral cavity for the majority of oral and maxillofacial cancer operations. The tube should be carefully secured to avoid dislodgement during surgery.

These patients present significant airway challenges and intubation and even mask ventilation may be difficult. Decisions regarding airway management in these patients is often between asleep induction, intravenous if no loss of airway is anticipated, inhalational spontaneously breathing if there is a potential to lose controlled ventilation, or awake fibreoptic intubation. If there are any markers to suggest that conventional direct laryngoscopy or mask ventilation is likely to be difficult then an awake technique should be considered, which is the standard method for management of an anticipated difficult airway (see Chapter 4). However, it is worth remembering that awake fibreoptic intubation is a relative contraindication in the presence of significant airway stenosis and severe stridor, particularly if the larynx is not visible on diagnostic nasal endoscopy.

In patients with severe upper airway distortion or impending obstruction, awake surgical tracheostomy under local anaesthesia may be the safer option. Note that extubation and re-intubation can also present significant problems in this patient population and will be discussed later.

Elective tracheostomy at the start of surgery under general anaesthesia is critical if postoperative airway compromise is anticipated¹⁶. The indications for elective tracheostomy include possibility of postoperative airway oedema and prevention of aspiration.

Significant oedema with potential to cause airway obstruction is likely after resection of the posterior two-thirds of the tongue, mandible, and oropharynx. This is from a combination of tissue handling and impaired venous and lymphatic drainage. The airway can also be compromised by large bulky flaps. Aspiration of blood and secretions is likely with mechanical difficulty in swallowing, after excision of base of tongue, total glossectomy, and oropharyngeal resection. Damage to lower cranial nerves during neck dissection or from compression by the tumour also causes impairment in swallowing¹⁷. Therefore, elective tracheostomy is indicated for airway protection.

In major head and neck cases, tracheostomy has several advantages: the airway is secure; oral hygiene is improved with more effective bronchial toilet. The reduction in dead space and airway resistance assists in weaning from mechanical ventilation in the typical head and neck cancer patient with a history of heavy smoking and associated chronic obstructive airway disease. Additional benefits are decreased requirement of sedation, improved patient comfort with better mobility, and communication. Tracheostomy enables safe transfer to theatre and the airway is secure in the event of flap failure or haemorrhage in the immediate postoperative period¹⁸.

However, tracheostomy carries its own risks and should not be a blanket policy for all major head and neck resections^{19  ,20}. Recent studies show that it is not needed after uncomplicated maxillectomy unless a bulky flap is used for reconstruction²¹. Postoperative oedema after bilateral modified neck dissection is not significant and tracheostomy is generally not required¹⁷. Kruse-Lösler and colleagues have proposed a scoring system to predict need of tracheostomy in the postoperative period based on tumour size, location, coexisting respiratory disease, and alcohol consumption, but this has not been validated²².

Postoperative ventilation for a short period through an oral or nasal endotracheal tube is an option if tracheostomy is to be avoided²³. Submental intubation (Figure 14.8) is an absolute contraindication in cancer cases because of high incidence of orocutaneous fistula²⁴.

Head and neck cancer resection carries risk of major blood loss so large-bore venous access is needed.

In addition to standard monitoring, invasive arterial and central venous pressure, urine output, and temperature monitoring is also indicated. Arterial pressure monitoring is recommended to allow safe manipulation of blood pressure and facilitate sampling for serial blood gas analysis and haematocrit measurement. Central venous pressure (CVP) reflects cardiac filling pressure and is useful in assessing response to fluid therapy. Appropriate access site should be discussed with the surgeon in order to avoid using the ‘flap donor site’ for access. Femoral venous line is used if surgical access to the neck and chest is needed. Long lines placed from peripheral veins (e.g. antecubital fossa) are frequently poorly positioned and may not give accurate CVP readings.

Core temperature can be measured through the rectal route or by urinary catheters with built-in temperature measurement probe. Bladder temperature is preferred as rectal temperature frequently lags behind core temperature, especially with large fluid shifts²⁵. Peripheral skin temperature is also measured to calculate the core to peripheral gradient in free flap transfer.

Careful positioning is essential for the long length of operation to avoid well-recognized problems (e.g. pressure sores, nerve injury). Pressure points should be padded and the pulse oximeter probe should be moved frequently to prevent pressure necrosis. Almost all head and neck operations need supine positioning with the exception of latissimus dorsi and scapular flap surgery where the patient is turned intraoperatively to the lateral position for harvesting the flap. Head-up tilt and adjustment in the operating table are required to keep the limbs at the heart level which helps to decrease blood loss. Eyes are covered with eye shields and all pressure points should be padded. TED (thromboembolus deterrent) stockings and pneumatic compression boots should be used to reduce the risk of deep venous thrombosis.

Anaesthesia is usually maintained with a combination of remifentanil and a volatile agent. In animal models, isoflurane has been shown to be superior to halothane in maintaining flap perfusion²⁶. This was attributed to maintenance of adequate cardiac output accompanied by mild vasodilation with isoflurane. Desflurane or sevoflurane is preferred if extubation is planned at the end of surgery, as both are haemodynamically stable with rapid offset of action.

Remifentanil analgesia provides intense analgesia with good intraoperative conditions. It also reduces the need for muscle relaxation and allows nerve monitoring or muscle twitch testing for isolation of nerves during neck dissection. The short half-life of 9 minutes enables titration of dose to match the surgical stimulation, during the operation which may vary from periods of minimal to intense stimulation²⁷. It also enables rapid emergence and return of protective airway reflexes as well as having the advantage of a smooth transfer to an Intensive Therapy Unit (ITU) if indicated. It may be used in ITU to facilitate overnight ‘light’ sedation, minimizing inotrope requirements and allowing a quick wake up, extubation, and return of reflexes the following morning.

Total intravenous anaesthesia or target-controlled infusion with propofol or remifentanil can also be used. Nitrous oxide is best avoided in major resections with negative intravenous pressure in head-up tilt. Moreover, risk of postoperative nausea and vomiting and concerns regarding bone marrow suppression during prolonged surgery, do not justify its routine use, especially in the presence of suitable alternatives²⁸.

Surgical management can be divided into two phases as the principal problems and management goals are very different for the two. The first phase involves resection of tumour, neck dissection, and harvest of the flap. This is followed by transplantation of flap and microvascular anastomosis. The main problems of phase 1 are intense stimulation and blood loss whereas maintenance of adequate blood pressure and flap perfusion are the main concerns in phase 2.

During tumour resection significant blood loss may occur. The risk of bleeding is increased with previous radiotherapy, bilateral radical neck dissection, and craniofacial resection. Raising of large myocutaneous and some bone flaps, e.g. iliac crest, can also cause blood loss. With radial forearm and fibular flaps, blood loss is minimal as tourniquet is used.

Blood transfusion is reportedly required in 14–30% of head and neck cancer operations. In addition to the inherent risks, blood transfusion is independently associated with increased perioperative complications. An additional reason for avoiding blood transfusion in patients with cancer is its reported effect of immunosuppression with increased rate of recurrence. Specific to head and neck cancer, there are a small number of studies which looked at recurrence with allogenic blood transfusion. The results have been conflicting, primarily because of a range of variables that account for recurrence^{29  ,30}. Despite this, the risks and cost of blood transfusion mandate that blood conservation strategies are used. We shall briefly examine the different methods that can be used to achieve this.

Hypotensive anaesthesia has been shown to improve the surgical field, decrease duration of surgery, and reduce blood loss (see Chapter 20). In the past, a wide range of hypotensive agents and anaesthetic drugs have been used to reduce blood pressure. Currently, remifentanil is the most commonly used agent in head and neck cancer surgery. Remifentanil infusion reduces neurohumoral stress response and provides an excellent operative field by controlled reduction of blood pressure without causing tachycardia. Its metabolism by tissue esterases and short context-sensitive half-life provides greater control and haemodynamic stability in the event of major haemorrhage

MAP is typically reduced by 20% of preoperative baseline pressure. Extreme caution should be exercised in patients with fixed stenosis, e.g. in coronary and carotid atherosclerosis, as blood flow distal to the stenosis may be compromised with the reduction in pressure. Deliberate hypotension should be avoided in uncorrected hypovolaemia and severe anaemia.

Additional methods that help to reduce blood loss are avoiding hypothermia, meticulous surgical technique, and use of ultrasonic harmonic scalpel (Table 16.5).

Venous drainage is improved by head-up tilt and adjusting the operating table so that the legs are at heart level.

Acute normovolaemic haemodilution has been shown to reduce the need for allogenic blood in major head and neck cancer surgery. Typically, after induction of anaesthesia 10 ml/kg of blood is withdrawn and stored in CPDA-1 buffer. This is transfused back to the patient after surgical haemostasis is achieved. On a physiological basis, less red cell mass is lost per millilitre of blood lost during operation because of the dilutional effect. In addition, the whole blood that is returned to the patient has all the clotting products and platelets. Acute normovolaemic haemodilution should be considered where massive blood loss is expected^{31  ,32}.

Until recently, the consensus view on the use of cell salvage in cancer surgery was that the risk of viable cancer cell dissemination rendered its routine use too risky. In 2008 the National Institute for Health and Clinical Excellence (NICE) approved use of cell salvage in urological cancer surgery³³. However, until further evidence is available of its safety in head and neck cancer, use of intraoperative cell salvage is probably best reserved for major blood loss in patients who refuse allogenic blood.

The principal goals of anaesthetic management for free flap transfer are to provide a full, hyperdynamic circulation with increased cardiac output, peripheral vasodilation, wide pulse pressure, and maintenance of normothermia to ensure optimum flap perfusion³⁴. The evidence base in anaesthetic management of free flaps is limited because of the relatively low failure rate of vascularized free flap transfer. Much of what we know today is extrapolated from research on animal models.

The key to adequate flap perfusion is the maintenance of normothermia, especially during long operations with extensive exposure involving the flap donor and tumour site. Hypothermia has been shown to cause vasoconstriction, a rise in plasma viscosity, and increased platelet aggregation with resulting reduction in blood flow to the free flap³⁵.

Normothermia is maintained by active warming of intravenous fluids, using forced air warming systems, an under-heating mattress, humidification of anaesthetic gasses, low fresh gas flow rates, and raising ambient temperature.

Hypothermia must be avoided by minimizing exposure and starting active warming in the anaesthetic room at induction. This prevents the initial anaesthesia-related redistribution hypothermia by decreasing the core-to-periphery temperature gradient. Forced air warming is continued during the pre-incision period while invasive monitoring lines are being inserted and surface marking for surgery is carried out. The ambient theatre temperature is raised to around 22–24°C, a level sufficient to reduce patient heat loss, without being too uncomfortable for the theatre staff.

It is recommended that normothermia should be achieved prior to anastomosis and maintained for at least 48 hours postoperatively. Both the core and peripheral temperature should be monitored and the gradient should ideally be less than 1.5°C. A larger gradient indicates peripheral vasoconstriction.

Perioperative fluid management has a significant impact on outcome from free flap surgery. The insensible loss from the two exposed sites of surgery, i.e. donor and recipient site of the flap is often underestimated. Hypovolaemia with resulting vasoconstriction causes a reduction in flap perfusion. Fluid therapy is aimed at correcting hypovolaemia and reducing viscosity in order to improve microcirculatory flow (combined with haematocrit 0.30). Transfusion is required only if significant blood loss occurs during the resection and regular bedside haematocrit measurement may assist in this determination. Fluid management is aimed at keeping CVP 2–4 mmHg above baseline and urine output of 1–1.5 ml/kg/hour.

The role of hypervolaemic haemodilution is contentious³⁶. There is no clinical evidence that this is beneficial despite the theoretical advantage of reduction in viscosity. On the contrary, there is some evidence that the resulting extravasation in flap tissue could be detrimental. Moreover, patients with ischaemic heart disease and left ventricular dysfunction may not tolerate hypervolaemic volume load. The resulting cardiac failure almost always guarantees flap failure.

The current knowledge base favours the use of colloids as large volumes of isotonic crystalloids predispose to interstitial oedema in the flap. The use of crystalloids is limited to replacement of insensible losses and preoperative deficit to minimize interstitial oedema. Hartmann’s solution is preferred as fluids with high chloride content may lead to hyperchloraemic acidosis.

Colloids (starches or gelatine solutions) are used for volume expansion and haemodilution. Gelatin solutions remain in the intravascular compartment for a relatively short period, as compared to other colloids. There is some experimental evidence of beneficial effect of both tetrastarch and pentastarch on microcirculation. Starch solutions (Voluven or Haesteril) have been shown to reduce endothelial permeability and minimize reperfusion injury. The potential disadvantage is prolonged bleeding time in large doses and pruritus.

Dextran decreases platelet aggregation and adhesion and reduces platelet polymerization. Low-molecular-weight dextran (dextran 40 and 70) was routinely used after free flap transfer for its antithrombotic effect. Recent studies have shown that there is no benefit in terms of preventing microvascular thrombosis with prophylactic use of dextran³⁷. Hypertonic saline has been used in severe flap oedema and after prolonged ischaemia time with variable success.

Table 16.6 gives a practical and logical regimen for fluid management in these cases.

Indicators of optimally filled circulation are increasing CVP trend, urine output greater than 1 ml/kg/hour, cardiovascular stability, and a narrow core to peripheral temperature gradient. Several recent studies have demonstrated the benefit of goal-directed fluid therapy over conventional fluid regimens. The titration of fluid administration to measured and dynamic physiological endpoints, such as stroke volume variation or cardiac output via the LiDCO system (LiDCO Ltd., Cambridge, United Kingdom), PiCCO system (Pulsion Medical Systems AG, Munich, Germany), or transoesophageal Doppler, may reduce morbidity, decrease length of stay, and improve gut function in surgical patients. Optimizing perioperative balance by calculating the variations in pulse pressure and stroke volume using LiDCO in patients undergoing free flap transfer is currently under investigation³⁸.

The haematocrit is generally maintained at 30–35%. Haemodilution is accompanied with a marked increase in red cell velocity in the microcirculation. The product of haematocrit and erythrocyte velocity determines the erythrocyte flux, which reaches its maximum at this haematocrit. Consequently, the capacity to transfer oxygen is maximum at this level³⁹. Extreme haemodilution should be avoided as it prolongs bleeding time and adversely affects oxygen-carrying capacity.

Free flaps are different from pedicled flaps in that they are denervated with complete sympathectomy of all vessels, whereas the feeding artery and the draining vein, on which the flap vessels are anastomosed, have intact innervation. Our understanding of the exact effects of vasoactive agents on the blood vessels in free flaps is limited and based largely on animal experiments.

Theoretically using vasodilators to improve microvascular perfusion is an attractive option, but in practice the resultant reduction in MAP may adversely affect blood flow. Intravenous sodium nitroprusside has been shown to markedly reduce blood flow in free flaps⁴⁰. There is some evidence that local intravascular injection of vasodilators such as papverine, verapamil and prostacyclin prevent vasospasm and improve flow. Topical vasodilators are routinely used by the surgeons during the operation to minimize vasospasm.

Inotropes are generally avoided in free flap surgery, despite there being little evidence to show that systemically administered inotropes reduce flap perfusion because of vasoconstriction. The exact effect of different inotropes on flap perfusion is uncertain. Interestingly, it has also been speculated that when the vessels in the flap are maximally constricted after handling and drop in temperature, an increase in mean arterial blood pressure with adrenaline may improve perfusion. The role of inotropes on flap flow is currently being investigated³⁸.

Shafik et al.⁴¹ have shown that dobutamine increases cardiac index and flap blood flow in a small group of patients. This was accompanied by a decrease in systemic vascular resistance⁴¹. Milrinone has been shown to have no effect on flap flow, arterial spasm, or flap survival⁴². In animal models, vasopressors like systemic phenylephrine appear to reduce the blood flow⁴⁰.

In practice, small incremental doses of ephedrine or metaraminol are often used if required to correct hypotension intraoperatively and if an inotrope is required, it is logical on current evidence base to use dobutamine; however, it is essential that hypotension is addressed by optimizing cardiac preload through adequate fluid resuscitation to optimize flap flow before inotropes are commenced.

Intraoperatively remifentanil infusion provides excellent analgesia as part of a balanced anaesthetic technique. 0.15mg/kg of morphine may be given towards the end of the surgery for postoperative analgesia. Patient-controlled analgesia (PCA) containing morphine and regular paracetamol is usually adequate for most patients postoperatively. Non-steroidal anti-inflammatory drugs (NSAIDs) are generally avoided because of the risk of postoperative bleeding and haematoma. Pain in the head and neck region is surprisingly moderate and relatively easy to manage. In fact, majority of the pain after major head and neck surgery is from the flap donor and skin graft site. Amongst the commonly used flaps, severe postoperative pain is frequent in iliac crest bone flap.

The role of epidural analgesia for donor site pain in flap surgery is contentious. Epidural anaesthesia reduces vasospasm and improves blood flow. However, in microvascular free flap transfer, because the flap is denervated, a chemical sympathectomy produced by an epidural may decrease blood flow. This is caused by reduction in mean arterial blood pressure and a steal phenomenon resulting from reflex vasoconstriction, which diverts blood away from the flap to normal tissues⁴³. Animal studies have shown a reduction in blood flow in flaps with epidural analgesia especially with concurrent hypovolaemia.

However, regional analgesia has several advantages. These include reduction in the neuroendocrine stress response to surgery, reduced postoperative opioid requirement, reduced respiratory complications, reduction in deep vein thrombosis, and improved recovery. Interestingly, preliminary studies suggest that immunomodulation from better pain relief by regional anaesthesia may reduce recurrence after cancer surgery^{44  ,45}. It remains to be seen whether further research in this field changes management of perioperative pain in cancer surgery.

We currently use epidural analgesia only for iliac crest flaps. The osteotomy of iliac bone and division of internal oblique, transversus abdominis, and iliacus muscles cause severe postoperative pain. Poor pain relief in the postoperative period is linked with chronic pain and gait problems. We use low thoracic (T10–11, T11–12) epidural for continuous infusion of bupivaciane 0.125% with fentanyl 2 mcg/ml in these patients. Some centres use multilumen catheters placed by the surgeon in the wound for continuous infusion of local anaesthetic. If epidural analgesia is used it is essential that hypovolaemia is avoided and vasopressors are used appropriately to correct hypotension, so that flap perfusion is not compromised.

Paravertebral block has been shown to be effective for latissimus dorsi flaps. Fibula donor site rarely causes significant pain and most patients can be controlled on day 3 with simple analgesics alone. Similarly, there is no clinical need for catheters for brachial plexus blockade in radial forearm free flaps as the pain responds well to paracetamol and morphine PCA.

Extubation and any need for emergency re-intubation presents specific challenges in these patients. Patients undergoing limited resection and uncomplicated pedicle flap surgery may be extubated at the end of surgery. Extubation carries risk of laryngeal spasm, surge in blood pressure, or airway obstruction because of oedema and bleeding. Therefore, awake extubation in a semi-sitting position after recovery of neuromuscular function and normal breathing pattern is advisable to maximize airway protection and return of reflexes. Intravenous lidocaine or esmolol may be needed to suppress the surge in blood pressure on extubation. Prior to extubation, it is essential to examine the airway to detect oedema and bleeding, and to check for air leak on deflation of cuff. If the initial intubation was difficult, extubation over airway exchange or jet ventilation catheter should be considered to optimize oxygenation and facilitate re-intubation in case of loss of airway.

If the patient requires re-intubation in the immediate postoperative period, this may be challenging. Specific problems include difficult controlled ventilation and anticipated difficult intubation because of airway bleeding, flap or laryngeal oedema, limited mouth opening, or poor visualization of the larynx due to bulky intraoral flaps. In addition, attempts at laryngoscopy may cause damage to an intraoral free flap or its vascular pedicle leading to disruption of vascular supply. For these reasons awake fibreoptic intubation is the commonly preferred technique; this may be difficult if the patient is symptomatically short of breath or there is bleeding in the airway where the view may be poor and inhalational induction may also be considered. Each case is different and relative merits of preservation of airway reflexes and degree of anticipated difficulty in intubation needs to be considered. However, difficult intubation should be anticipated and planned for in the presence of the surgeon, if there is a chance of loss of the airway and need for emergency tracheostomy or cricothyroidotomy.

The majority of patients undergoing major resection or free flap surgery are transferred to the intensive care unit for individual nursing care: monitoring and optimization of cardio respiratory function, care of tracheostomy, and management of free flap⁴⁶. Patients are usually ventilated overnight to provide a still head in order to reduce the shear stress on the anastomosis. It is important that the patient’s head is maintained in neutral position to avoid mechanical distortion of the vascular pedicle. Nursing in 30° head-up position helps to reduce airway oedema. Any pressure on the flap or its pedicle from tube ties, dressings, or elastic bands of the oxygen mask should be avoided.

In essence, postoperative management for free flap surgery involves continuation of all the measures taken intraoperatively to ensure adequate flap perfusion, i.e. maintenance of normothermia, adequate filling with good postoperative analgesia. It is essential to avoid peripheral vasoconstriction caused by hypothermia, shivering, hypovolaemia, pain, and sympathetic stimulation (Table 16.7). Administration of fluids is aimed at maintaining a urine output between 1–1.5 ml/kg/hour. Conversely, caution is warranted to avoid overzealous fluid replacement which risks both fluid overload and flap oedema.

After the patient is awake, PCA with morphine and regular paracetamol is usually adequate for pain relief. In iliac crests flap, epidural or infusion through the wound catheter is commenced prior to stopping the sedation.

Intravenous antibiotics, antiemetics, and dexamethasone are continued for 48 hours.

Subcutaneous low-molecular-weight heparin is given for deep vein thrombosis prophylaxis. Low-molecular-weight heparin has also been shown to reduce anastomotic thrombosis and improve flap survival. In the absence of clinical proof of efficacy, aspirin and dextran are no longer used routinely following free flap surgery. Nutritional support through the fine bore nasogastric, percutaneous endoscopic gastrostomy (PEG) or jejunostomy is commenced as soon as possible. After reconstruction of oropharynx, videofluroscopic study of oesophagus and assessment of swallowing is carried out at day 5 and oral intake is started if no abnormalities are seen. Chest physiotherapy is continued in the postoperative period to improve clearance of secretions. Patients are then transferred to the ward and tracheostomy decannulated, after the oedema has settled.

Flap perfusion is monitored hourly for the first 3–5 days with decreasing frequency of monitoring thereafter, as free flaps rarely fail after that⁴⁷. The clinical signs to assess are colour, turgor, capillary refill, and temperature gradient. Additional information on the condition of the flap can be obtained from percutaneous Doppler and dermal bleeding on pin prick.

Clinical evaluation is not possible in ‘buried’ free tissue transfers which have no visible external surface. Such transfers are commonly used for reconstruction of oropharynx and skull base. Regular nasal endosocopy is preferred in some head and neck units for free jejunum transfer. A small portion of buried flaps may be exteriorized to allow clinical monitoring. Implantable Dopplers and laser Doppler flow monitoring can also be used for monitoring buried flaps.

Clinical signs when present either singly or in combination, suggest a problem in perfusion. These include pale flap colour, reduction in flap temperature, loss of capillary refill, and loss of flap turgor, all of which indicate arterial insufficiency. Venous insufficiency, on the other hand, can result in a purple or blue hue in the flap, congestion, swelling, and rapid capillary refill in the initial stage followed by loss of capillary refill.

Simple measures like improving blood pressure, increasing fluid input, warming, and repositioning of external dressings may improve perfusion in an ischaemic flap. The threshold for triggering re-exploration of a flap for suspected arterial or venous thrombosis should be low as salvage rates are considerably higher with early identification and treatment.

Seventy per cent of all adult salivary gland tumours are seen in the parotid gland, 15% in the submandibular, and the remaining in sublingual and minor salivary glands. The only known predisposing factor is therapeutic external irradiation. Surgery remains the mainstay of initial definitive treatment for nearly all tumours of the major and minor salivary glands.

Only the specific features regarding anaesthetic management of salivary gland surgery will be discussed further. In parotid surgery, monitoring of the facial nerve is required to preserve the nerve. This is carried out by inserting two subdermal platinum electrodes in the upper and lower face which record facial muscle activity on stimulation. An audiovisual response is evoked on stimulation of the nerve.

If neuromuscular blocking agent is to be used to facilitate intubation a suitable dose should be administered so that full recovery takes place before monitoring begins. A remifentanil infusion reduces the need of subsequent doses of relaxants. Peripheral nerve monitoring (e.g. train of four) is essential to establish recovery of neuromuscular function, so that monitoring of nerve function can begin. A spontaneously breathing technique with reinforced laryngeal mask airway (LMA) has also been described for parotid surgery but the potential drawback is that the LMA is easily displaced during surgical manipulation and neck movement.

Limited mouth opening and trismus is seen if the parotid cancer involves temporomandibular joint. Direct laryngoscopy may be difficult if malignant lesions of the sublingual and submandibular gland invade the floor of mouth and fix the tongue.

Re-exploration in the immediate postoperative period following major head and neck surgery may be needed for several reasons, including salvage of an ischaemic flap, to control postoperative bleeding, and debridement of an infected flap. Airway management can be a challenge in these patients unless there is a tracheostomy in situ as discussed earlier^{48  ,49}.

Subsequent general anaesthesia may be required for insertion of osteointegrated implants, change of surgical obturator, panendoscopy for suspected recurrence, and contouring of flap. These patients present in an elective setting well after the original operation. As life expectancy improves with advances in management, it is foreseeable that many of these patients will undergo surgery for unrelated medical problems in the future.

In the immediate postoperative period, airway management is complicated by abnormal anatomy with severe distortion of the upper airway. In the initial postoperative period, oedema may be extensive from tissue handling, and reduced venous and lymphatic drainage. Moreover, inflamed and oedematous tissues in the postoperative period bleed on minimal trauma with instrumentation.

There are some specific technical difficulties in this group of patients. Postoperative pain and loss of supporting tissue may preclude tight mask seal for inhalational induction. Rarely, one may have a significant air leak on controlled ventilation, for example if an extensive maxillectomy has been performed. Awake fibreoptic intubation is technically challenging as identification of familiar anatomical structures may be difficult after reconstruction in the presence of oedema and blood⁵⁰. It is also difficult to achieve adequate topical anaesthesia in the presence of excessive secretions. It is also worth noting that some recovery of sensory function does take place in free flaps following sensory re-innervation so topical anaesthesia of the flap tissue is also essential if awake intubation is planned.

Supraglottic devices (see Chapter 4) such as the intubating LMA (ILMA) and the i-gel, are essentially designed for a normal airway and a tight ‘seat and seal’ may not be achieved in the presence of severe airway distortion. Giraud and colleagues describe their inability to ventilate or view the glottic aperture by fibrescope passed through an LMA, in patents who had received cervical radiotherapy because of distorted anatomy⁵¹. While video laryngoscopes and rigid intubating stylettes have been successfully used in patients with difficult airways, and may provide a useful addition to the practitioner’s repertory of airway devices, there is limited evidence of their use in this setting⁵². Moreover, limited mouth opening may also preclude the use of ILMA and video laryngoscopes. Blind nasal intubation has two major limitations: infrequent success on first pass and increased risk of trauma with multiple attempts.

Table 16.8 lists potential problems that may be encountered after fibrosis and scarring following surgery^{53  –55}. When evaluating these patients, it is essential to consider the potential for such dynamic changes, even if initial airway management was straightforward.

On airway examination the anaesthetist must be able to assess⁵⁶ difficulty in mask ventilation, aspiration risk, ability to ventilate using supraglottic devices, difficulty in awake fibreoptic intubation, and access for cricothyroidotomy and tracheostomy.

It is also crucial to detect impending obstruction because if the patient is rendered apnoeic, total obstruction can rapidly ensue.

A clear understanding of the problem and a calm, logical approach is essential in formulating a management plan. There should be a primary plan with clear and anticipated back-up plans in case the first plan encounters difficulties. This depends not only on anticipated problems, but also on the experience and training of the anaesthetist and the availability of equipment. Management of the airway should be a joint decision between the anaesthetist and surgeon in this situation.

Management depends on each individual case. The gold standard technique is usually that of an awake nasal endoscopy followed by awake fibreoptic intubation if possible. If potential loss of airway is anticipated, one approach is to insert a cricothyroid cannula for jet ventilation before the procedure, this serves as a back-up plan in case of failure. In some circumstances, tracheostomy under local anaesthesia may be the only option, particularly in the presence of significant narrowing of any part of the airway that cannot be navigated with a flexible scope or endotracheal tube, and with active bleeding in the upper airway, where the view on fibreoptic endoscopy is obscured.

In all cases where the balance of evidence suggests that an attempt at awake intubation or inhalational induction is justified, the personnel and equipment for an emergency surgical airway (in the form of rigid bronchoscopy and a double set-up) should be on standby. Injecting the soft tissue over the cricothyroid membrane with 1% lidocaine and 1:100 000 epinephrine will result in vasoconstriction and a much drier operative field if emergency cricothyroidotomy or awake tracheotomy becomes necessary.

If there is uncertainty about the ability to maintain the airway following induction of anaesthesia, premptively placing a cricothyroid cannula, e.g. Ravussian jet ventilation catheter under local anaesthesia, should be considered⁵⁷. Insertion of a transtracheal jet ventilation catheter prior to induction, under controlled circumstances, secures the ability to ventilate the lungs following induction. This allows safe, unhurried, and comfortable airway instrumentation and can be crucial for rescue ventilation in an emergency.

Craniofacial resection for maxillofacial tumours extending into the anterior cranial fossa is done as a joint case by the neurosurgeons and maxillofacial surgeons. The intracranial part of the tumour is resected through a bicoronal incision or transnasal route.

A standard neuroanaesthetic is provided and the principal goals of anaesthetic management include: preservation of adequate cerebral perfusion pressure and oxygen delivery; avoidance of large and sudden swings in intracranial pressure; providing conditions that allow optimal surgical exposure with least brain retraction; and allowing rapid awakening of the patient, e.g. remifentanil–sevoflurane with invasive monitoring. Oral intubation is needed if a transnasal approach is used or excision of floor of anterior cranial fossa is planned. The extensive resections can cause significant bleeding. Other complications of skull–base surgery include cerebrospinal fluid (CSF) leak, neurological and ocular complications, vascular injury, and thrombosis. Broad-spectrum antibiotic cover is needed as the dura is breached and risk of contamination from sinuses, nasal and oral cavity is high. The defect is reconstructed by either pericranial, galeal, or free flaps. These flaps provide watertight separation of the intracranial space from the nasopharynx, preventing CSF leak and ascending infection.

The perioperative management of neurosurgical patients differs significantly from the management of patients with free flaps. In neurosurgical anaesthesia, vasodilation is avoided and fluid administration aims to maintain a slightly negative fluid balance. Diuretics and steroids may also be needed. The ideal perioperative conditions for free flaps are exactly the opposite and these may have to be compromised⁵⁸. It is, therefore, important to appropriately select the ideal method for reconstruction and have an experienced microsurgical team.

Carotid blowout syndrome (CBS) remains one of the most devastating complications of head and neck cancer and its treatment. The clinical severity of CBS ranges from threatened haemorrhage following asymptomatic exposure of the artery to small repeated bleeds and acute massive haemorrhage.

CBS is caused by invasion of the carotid artery by the tumour in advanced cancer or following infection in the surgical wound. This is more likely after wound dehiscence following radical neck dissection where the sternocleidomastoid muscle cover over the artery is removed. Radiotherapy by causing damage to vasa vasorum of the artery predisposes to CBS.

Historically, treatment of CBS was emergency surgical ligation of the artery. This led to a high incidence of postoperative stroke and death as the patency of collateral circulation was not tested. In addition, operation on an unstable patient in an irradiated and often infected neck is difficult. Currently with advancement of endovascular techniques, stent insertion is the mainstay of treatment⁵⁹.

In the presence of advanced cancer with significant residual disease and where the prognosis is poor, palliative management should be considered. In potentially curable conditions, such as postoperative wound infection, management follows an ABC approach. The wound is packed with gauze, airway secured, and fluid resuscitation is started while interventional radiology treatment or surgical repair is carried out.

Treatment of patients with maxillofacial cancer present significant problems for the anaesthetist. An understanding of the anatomy and surgical techniques, operative conditions required, and postoperative complications and their management is essential. Airway management may be challenging and require a primary management plan and appropriate back-up plans. Each individual patient presents their own problems and working in liaison with the surgeons and as part of a multidisciplinary team is essential to optimize outcome for these patients; this includes being part of the team to plan the specific treatment options for individual cases in assessing perioperative risk and survival with non-surgical techniques.