5 The surgical airway

A surgical airway is an airway created by an invasive technique, as opposed to an airway maintained via an anatomical route such as the oropharynx or nasopharynx. The circumstances prompting the use of a surgical airway are extremely varied, ranging from the desperate emergency where oxygenation cannot be achieved by any other means, to the airway fashioned in a controlled manner as part of an elective surgical procedure or to facilitate weaning from ventilatory support. A number of surgical approaches to the airway exist, including needle cricothyroid puncture and cricothyroidotomy, surgical and percutaneous dilatational tracheostomy, and the submental airway. Each of these will be discussed in turn, focusing on technique, indications, contraindications, and complications.

Needle cricothyroid puncture and surgical cricothyroidotomy are emergency surgical airway procedures that are most commonly performed in the situation in which oxygenation cannot be achieved by any other means. Both procedures gain access to the airway via the cricothyroid membrane. One of the most difficult aspects of these techniques is recognizing that they need to be performed, and that further attempts to either intubate or ventilate by conventional means may be potentially catastrophic.

Indications are fortunately rare, but include the patient who is impossible to both intubate and ventilate and the patient with impending or actual complete airway obstruction.

An inability to intubate and ventilate a patient may ensue following a failed intubation, where the priority is to maintain oxygenation until such time as the patient regains spontaneous ventilation and consciousness. If it becomes impossible to maintain a patent airway to enable either spontaneous ventilation or hand ventilation by ordinary means, then an emergency airway must be created.

Needle cricothyroid puncture or surgical cricothyroidotomy may be necessary in patients with impending or actual complete airway obstruction in whom there is no time to reverse the underlying problem, or to attempt either conventional intubation or time-consuming surgical procedures such as a tracheostomy. The underlying problems might include severe maxillofacial trauma, epiglottitis, anaphylaxis, and laryngeal pathology such as tumour.

Needle cricothyroid puncture and surgical cricothyroidotomy would not usually be performed in anything other than the absolute emergency. If time allows, then an airway should be achieved by other means where possible. This may be via the conventional orotracheal or nasotracheal route, or if this is found to be, or is likely to be, impossible then via a surgical tracheostomy.

A surgical cricothyroidotomy is contraindicated in the paediatric patient under the age of about 12 years of age. These patients have extremely small, pliable, and mobile laryngeal and cricoid cartilages, making the procedure extremely difficult in this age group. In these patients a needle cricothyroidotomy should be performed or, if time allows, a surgical tracheostomy under direct vision.

In a situation in which there is complete upper airway obstruction, a needle cricothyroid puncture should not be performed, as this relies on exhalation of gases through the upper airway. In complete obstruction, air trapping and barotrauma will ensue on attempted insufflation of gas, as discussed below. In such a situation, a surgical cricothyroidotomy would be the emergency technique of choice.

As these techniques are generally performed in a desperate emergency where other means to create an airway have failed, most other contraindications are relative. These include situations which might make the procedure more difficult such as previous neck surgery or scarring, obesity, haematoma, coagulopathy, overlying infection, and neck trauma.

Both techniques access the cricothyroid membrane. This membrane has the advantage over the trachea in the emergency setting in that it is more anterior than the trachea with less overlying tissue, easier to fix to facilitate puncture or incision, and generally a less vascular area and there is therefore less danger of significant bleeding.

Of the two techniques, needle cricothyroid puncture is simpler, quicker, and associated with less bleeding. The needle cricothyroid puncture is a more temporary solution, however, and simply buys time during which a more definitive airway must be achieved.

It should be noted that, with this technique, although oxygenation may be achieved, ventilation will be poor. This is particularly the case when using high-flow oxygen, and the patient will become rapidly and progressively hypercapnic. Jet ventilation using the Sanders injector will usually achieve better ventilation, but may perform less well in situations of increasing upper airway obstruction^{1  ,2}. In addition, the needle cricothyroidotomy offers no airway protection. This manoeuvre is therefore only a temporary solution which buys about 30–40 minutes, during which a more definitive airway which will facilitate both oxygenation and ventilation must be achieved.

Complications of needle cricothyroidectomy are included in Table 5.1.

Compared to needle cricothyroidotomy, surgical cricothyroidotomy is the method of choice in adults if skills allow as it will facilitate both oxygenation and ventilation²

Commonly, the emergency surgical cricothyroidotomy will be revised within the first 24 hours to a surgical tracheostomy, as this has traditionally been thought to be associated with lower longer term airway morbidity. This is controversial, however, and some would argue that continued ventilation via the cricothyroidotomy is not associated with an increased incidence of complications^{3  ,4}.

The complications associated with surgical cricothyroidotomy are given in Table 5.2.

A number of complete commercial cricothyroidotomy kits are available for use in the emergency setting. These are useful if both immediately available and familiar to the user. Examples of these kits include the following:

CricKit® is marketed by North American Rescue Incorporated and contains sachets of antiseptic solution, a scalpel, a tracheal hook, a size 6.0 mm cuffed cricothyroidotomy tube, a syringe with which to inflate the cuff, and a tie to secure the tube after insertion.

Mini-Trac® II is manufactured by Portex and contains a scalpel, a size 4.0 mm uncuffed cannula loaded onto a curved introducer to aid insertion, a neck tape, and a suction catheter.

The PCK® kit is manufactured by Portex and contains a scalpel, a size 6.0 mm cuffed cricothyroidotomy tube mounted on a Veress needle designed to reduce the chances of injury to the posterior wall of the trachea, a tube tie, a suture, and a heat and moisture exchanger.

Tracheostomy refers to the creation of a surgical airway through the wall of the trachea. The indications for a tracheostomy range from the emergency to the elective. There are two principal techniques, namely surgical and percutaneous dilatational. The surgical tracheostomy (ST) may be done as an emergency or as a more elective procedure, whilst the percutaneous dilatational tracheostomy (PDT) is usually performed in an elective manner, and is usually to facilitate longer term intubation and/or ventilation in the critically ill patient. These techniques will be discussed in turn below.

Tracheostomy may be indicated to relieve impending or anticipated upper airway obstruction due to pathology such as airway tumour, infection, oedema, trauma, or congenital malformation. A tracheostomy may also be part of an elective surgical procedure to ensure a patent airway. This may be permanent in the case of laryngectomy, or temporary following other major maxillofacial procedures where transient airway swelling is anticipated.

In critical care patients requiring protracted intubation and ventilation, tracheostomy is an alternative to orotracheal or nasotracheal intubation. A surgical airway facilitates weaning from mechanical ventilation in the patient with reversible respiratory failure and allows tracheobronchial toilet in the patient with insufficient ability to clear respiratory secretions. Patients on long-term ventilation, such as those with irreversible respiratory failure owing to a high cervical spinal injury or neuromuscular disease, benefit from a tracheostomy. It may also provide airway protection in the patient with impaired airway reflexes because of reduced conscious level or bulbar disorders.

The advantages of a tracheostomy over endotracheal intubation are most apparent in the critically ill population. These include the following: patient comfort, reduction in sedation requirements, reduced resistance to breathing through a shorter tracheal tube, possibly more rapid weaning from mechanical ventilation, improved tracheal toilet, better oropharyngeal hygiene, and an ability to eat and speak.

There are few contraindications to a ST although certain conditions such as morbid obesity, limited neck extension or severe kyphoscoliosis, large thyroid goitres, or overlying infection may make the procedure technically more difficult.

There are few absolute contraindications to percutaneous dilatational tracheostomy, and many of the contraindications that have previously been felt to have been absolute have been challenged⁵. The need for emergency airway access is generally considered an absolute contraindication to PDT. In such a situation cricothyroidotomy or ST are usually the techniques of choice, depending on the time and skills available. The technique is also considered to be contraindicated in children below the age of 12 years, in whom an open ST would be the technique of choice in the more controlled setting, or needle cricothyroidotomy in the emergency situation.

Relative contraindications to PDT include morbid obesity, anterior neck masses such as goitres, previous neck surgery, limited neck extension or unstable neck injury, coagulopathies, high ventilatory requirements such as high positive end expiratory pressure (PEEP) dependency or high inspired oxygen concentration. In such patients, if a tracheostomy were considered to be indicated, an open ST might be favoured over a PDT.

Although there are definite logistical advantages to PDT at the bedside in critical care patients, the short- and long-term advantages and disadvantages of percutaneous versus ST are less clearcut. There have been many studies performed, including a number of randomized controlled trials attempting to address this question. There have also been several published meta-analyses, the two largest of which have looked at around 1000 patients each. The conclusions drawn include that PDT is associated with a lower incidence of wound infection and unfavourable scarring, and that there is no difference in terms of bleeding, late stenosis or mortality. PDT may have a cost benefit and is faster to perform^{6  ,7}.

A surgical or open tracheostomy (ST) is most commonly performed in the operating theatre, although may less commonly be undertaken at the bedside in the intensive care unit.

Tracheostomy is commonly used in critical care as an alternative to translaryngeal endotracheal intubation in the patient expected to require protracted periods of mechanical ventilation.

Although in the past the majority of tracheostomies were performed surgically in the operating theatre, over time the technique of PDT has become increasingly popular. This latter technique may be performed quickly and simply at the bedside, without the need to transport the patient, and by non-surgical doctors.

The earliest dilatational tracheostomies were performed by a serial dilatational method developed by Ciaglia¹⁰. A number of other dilatational techniques have also been described, including a modification of the Ciaglia method employing a single dilator (e.g. Blue Rhino, Cook)¹¹, dilatational forceps (e.g. Griggs)¹², a screw-action dilator (PercuTwist)¹³, and a translaryngeal method of placement (Fantoni)¹⁴. The technique currently most commonly used in the UK is that using a single dilator and this will be described in detail below.

This was described by Ciaglia in 1985¹⁰. It is a technique broadly similar to that outlined above, but using a series of dilators of gradually increasing gauge to create the stoma. In comparison to single dilator techniques, this method is slower, with greater potential for deterioration in oxygenation.

One version of this was developed by Griggs in 1990¹². A Seldinger technique is used to locate and pass a guidewire into the trachea as in the tapered dilator technique. A pair of customized forceps is then threaded over the wire, firstly through the skin and subcutaneous tissue. The forceps are then opened up to stretch up these tissues. The forceps are advanced further along the wire into the trachea itself, and opened up a second time to stretch up a hole in the tracheal wall. A tracheostomy tube is then passed over the wire through the passage created.

A technique developed by Rusch known as PercuTwist¹³ involves a single-step dilatation of the tracheal wall. In this case the dilator is a screw-like device that actually lifts the anterior wall of the trachea during its use. This is in contrast to the posterior displacement of the anterior tracheal wall commonly observed with the use of the Blue Rhino dilator. This has the advantage of ensuring an unobstructed bronchoscopic view of the procedure, and may potentially be associated with a lower incidence of tracheal ring fractures and posterior tracheal wall injury.

This was developed by Fantoni in 1993¹⁴. In this method, the guidewire placed in the trachea is directed superiorly through the larynx. A specially designed tracheostomy tube is then threaded over the guidewire and passed through first the larynx and then through the anterior tracheal wall. This technique may theoretically reduce the risk of damage to the posterior tracheal wall, but is possibly more complicated than other techniques with a high incidence of technical difficulties¹⁵.

There are many potential complications associated with both surgical and percutaneous tracheostomy (Table 5.3), and so the risk:benefit ratio must be carefully considered in every patient before proceeding, particularly in the critical care setting. The complications may be divided into immediate (procedural), early, and late. Any complications more specific to PDT or ST are indicated.

The size of a tracheostomy tube is expressed in millimetres, and generally corresponds to its internal diameter (ID). The actual internal and outer diameter (OD) of the tube will usually be displayed on the packaging or on the tube itself and will vary depending on the design and manufacturer of the tube. When selecting a tube, both internal and external diameters must be considered. A tube with too small an internal diameter will provide an increased resistance to respiration and may be difficult to clear secretions through. If it is a cuffed tube, a smaller tube will require an increased pressure to create a seal within the trachea. A tube with too large an OD will be difficult to pass into the trachea, and may hinder the ability of the patient to breathe around the tube through the upper airway with the cuff deflated.

A tube with an OD that is approximately three-quarters of the diameter of the patient's trachea should be selected. A size 8.0 mm ID tube (11 mm OD) will usually be appropriate for the average adult male, and a 7.0 mm tube (10 mm OD) for the average adult female.

Many tubes are preformed to fit the average adult patient, such that the outer flange will lie comfortably and flush with the anterior neck wall, whilst the distal end of the tube sits within the trachea parallel to the tracheal walls. Preformed tubes may create problems, however, particularly in the obese patient or patient with more extensive pretracheal tissues. In these patients, the tube may be too short, such that the end of the tube abuts the posterior tracheal wall. This may lead to ulceration, formation of granulation tissue on the posterior wall of the trachea, and obstruction of the tube. In the very large patient, the tube cuff may not sit completely within the tracheal lumen. In larger patients a tube with a variable flange position may therefore be suitable. Conversely, in the very small patient, a preformed tube may be too long, and the tube may curve forward and ulcerate or even erode through the anterior tracheal wall.

Metal tubes are usually only used in patients with permanent tracheostomies. These are silver-coated which is bactericidal and non-irritant. Metal tubes are uncuffed, and do not have a standard 15 mm connector and so are unsuitable for providing positive pressure ventilation. They are also extremely rigid. Plastic tubes are more flexible and may be made from polyvinyl chloride (PVC) or silicone. PVC tubes tend to soften at body temperature, conforming to patient anatomy. Silicone tubes are the most flexible and naturally soft regardless of temperature.

Tubes may be cuffed or uncuffed. The uncuffed tube is useful for clearance of secretions but provides no airway protection. Although an uncuffed tube may be used to provide a degree of mechanical ventilation, positive pressure ventilation is much more effectively provided with a cuffed tube, particularly with incompliant lungs. A large volume low pressure cuff is desirable as this will dissipate pressure over a wider surface area. This will reduce the incidence of tracheal wall erosion and ulceration, and longer term stenosis.

The fenestrated tube is similar in construction to the standard tracheostomy, but has one or more holes in the posterior wall, above the level of the cuff. With the cuff deflated and the tracheal tube occluded at its outer end, the patient may breathe via the upper airway. This will allow phonation, and may also be a useful step in the assessment of a patient prior to decannulation, as discussed below.

Some tracheostomy tubes are designed to be used with a coaxial inner tube. Occasionally the 15 mm universal connector is part of the inner tube, and so a ventilator circuit may not be attached without the inner tube in place. The advantage of an inner tube is that it may be removed for cleaning or replaced at intervals. A non-fenestrated inner tube placed within a fenestrated outer tube may convert a fenestrated tube to one which is effectively non-fenestrated.

Decannulation decision-making will depend on the reason for which the tracheostomy was performed. In the case of a tracheostomy performed for upper airway obstruction, the tracheostomy may be removed if and when the underlying airway obstruction has sufficiently resolved and a patent upper airway is restored. Endoscopic examination of the upper airway may assist in confirming this. Prior to decannulation, the cuff of the tracheostomy may be deflated and, on occlusion of the tracheostomy tube, the patient should be observed to breathe comfortably, without respiratory distress through their upper airway and around the tracheostomy tube.

In the case of a tracheostomy tube performed to facilitate prolonged mechanical ventilation, decannulation is usually considered once the patient has successfully weaned from mechanical ventilation, including PEEP. The patient will usually have demonstrated stable gas exchange on no mechanical support for at least 24 hours.

The patient should also be able to demonstrate an effective cough such that he or she will be able to expectorate secretions adequately. Occasionally, where the secretion load is still very high, or the patient's cough strength borderline, a mini-tracheostomy may be placed as an interim measure to assist with secretion clearance.

Prior to formal decannulation, a ‘physiological decannulation’ is sometimes performed by occluding the tracheostomy tube with a tracheostomy button and deflating the cuff. This will allow additional time to assess the patient for respiratory distress, stable gas exchange, and cough effectiveness prior to actually removing the tube. To reduce the resistance to breathing around a large tracheostomy tube during such a trial, some physicians would advocate first exchanging the tube for a fenestrated tube, or a smaller diameter tube.

When a tracheostomy is performed in the critical care setting, the procedure is generally carried out in a planned and controlled manner, and the patient will usually already be intubated. If the patient is not already anaesthetized, anaesthesia should be induced and maintained with an appropriate agent. In the critical care setting this would usually involve an intravenous induction and maintenance with a short-acting agent such as propofol. If the procedure is to be carried out in the operating theatre, the option of a volatile anaesthetic will be available. A short-acting opiate administered either as an infusion or in the form of boluses will be useful to obtund the sympathetic response to airway manipulation. The patient should be paralysed with a muscle relaxant of intermediate duration to prevent coughing during the procedure.

The urgent tracheostomy performed for airway obstruction will require more careful consideration and preparation. The patient will not uncommonly present with a variable, sometimes severe, degree of respiratory distress and stridor. They may be extremely frightened and uncooperative, agitated, using their accessory muscles of respiration, and will often adopt a position in which airflow is maximized such as sitting upright. Depending on the pathology, the patient may also be unable to swallow, and may be drooling and have pooled secretions in the airway. In the emergency setting, the patient may also have a full stomach.

In addition to the usual assessment, the anaesthetist must focus in particular on the airway to formulate an appropriate management plan (Chapter 4).

In broad terms the choice lies firstly between performing the procedure under either local or general anaesthesia. If the procedure is performed under general anaesthesia, then the anaesthetist must decide how best to secure the airway, and how to induce anaesthesia.

Only very rarely will it be necessary to undertake a tracheostomy under local anaesthesia. This will usually only be required in the situation where it is felt that attempting to secure an airway via the oral or nasal route will either be impossible or unduly hazardous, and that the safest option is to have a patient who is conscious and maintaining his or her own airway until a surgical airway has been created.

Performing a tracheostomy under local anaesthesia will avoid the risk of losing the airway completely under general anaesthesia with potentially catastrophic consequences. It will also avoid the need for a potentially difficult awake fibreoptic intubation. The disadvantages of performing the procedure under local anaesthesia are that it may prove to be extremely distressing for the patient, particularly in the patient with severe respiratory embarrassment. In the patient with a critically obstructed airway the patient may be unable to lie flat with the neck extended, and the surgeon may have to attempt the procedure with the patient sitting or semi-recumbent. The patient's respiratory rate may be high, and the excursion of the trachea may be increased as the patient attempts to overcome the obstruction. This will clearly add to surgical difficulty.

Local anaesthesia per se will usually be achieved by simple infiltration of the tissues with a mixture of lignocaine and adrenaline. An injection of lignocaine into the trachea itself injected via the cricothyroid membrane may help to reduce coughing during airway manipulation.

In the majority of cases the tracheostomy will take place under general anaesthesia with the airway having been first secured via the oral or nasal route. General anaesthesia offers the advantage of greater control over the surgical field, and removes the risk of patient distress or lack of cooperation during the procedure itself. However, securing the airway and administering anaesthesia may prove hazardous and technically challenging. For this reason, an experienced anaesthetist should always be involved in the planning and management of such a case.

A number of options will be available to the anaesthetist, and these will depend on the individual patient's circumstances and pathology. A detailed description of all potential techniques that may be employed is beyond the scope of this chapter, but the basic principles will be discussed below.

Factors influencing the decision are multiple. If the patient's mouth opening is severely restricted and unlikely to improve under anaesthesia (Chapter 11), then direct laryngoscopy will not be an option. Local pathology can distort the normal anatomy and obscure an adequate view of the vocal cords. A nasendoscopy performed by the ENT surgeon may give valuable information in this regard. The patient may not be able to cooperate with an awake fibreoptic intubation and in some circumstances an awake fibreoptic intubation may actually precipitate complete airway obstruction or the size of the scope may be too large to traverse a narrowed larynx. The patency of the nostrils or presence of a base of skull fracture may influence whether the nasal route may be used. Other factors to consider are the patient's fasting status and the skills of the anaesthetic team and the equipment available to them.

A decision must first be made as to whether or not it is necessary to secure the airway prior to induction of anaesthesia; in other words, whether or not an awake fibreoptic intubation is indicated. An awake fibreoptic intubation might be appropriate in the patient in whom direct laryngoscopy is unlikely to provide a view of the larynx, for example due to pathology such as tumour or swelling in the supraglottic region. In addition, the patient might either be unfasted, or there may be concern about the ability to maintain an airway following induction of anaesthesia, such that asleep fibreoptic intubation is precluded.

A fasted patient in whom direct laryngoscopy is unlikely to be successful, but is not expected to present undue difficulties in maintaining an airway following induction of anaesthesia, can be managed with an asleep fibreoptic intubation. Induction of anaesthesia may be achieved by the intravenous or inhalational route. However, an intravenous induction will run the risk of rendering the patient apnoeic with the potential for the situation of not being able to ventilate an un-intubatable patient. A gaseous induction with a non-irritant volatile agent such as sevoflurane will facilitate the induction of deep anaesthesia in the spontaneously breathing patient. If the airway becomes impossible to maintain adequately at any stage, then the volatile may be turned off and the patient allowed to regain consciousness, and an alternative plan followed. Once the patient is deeply anaesthetized, an assessment of the ability to hand-ventilate may be made. If this is easy, a muscle relaxant may be administered, but if there is any doubt as to the adequacy and ease of hand-ventilation, then spontaneous respiration should continue. A fibreoptic intubation may then be undertaken via either the nasal or oral route as clinically indicated.

In the patient in whom direct laryngoscopy is likely to provide a view of the larynx, albeit a distorted one, and there is no major concern over the ability to maintain an airway following induction of anaesthesia, the inhalational induction of anaesthesia is an acceptable technique. With the patient breathing spontaneously under deep inhalational anaesthesia, laryngoscopy may be attempted, and the patient intubated if possible. The anaesthetist should have a range of endotracheal tubes available, and be prepared to use one of a very small diameter if necessary.

Submental intubation is an alternative to tracheostomy where both nasal and oral intubation is contraindicated, and protracted intubation and ventilation not anticipated. Such an airway was first described by Hernandez Altmir in 1986¹⁶, and has proved useful in areas such as complex craniomaxillofacial trauma, and oncological cranial base surgery^{17  ,18}. The submental airway facilitates surgical access to the base of skull, facial bones, and oropharynx, and allows control over dental occlusion. It has the potential advantage of avoiding breach of the tracheal wall, and the complications of tracheostomy.

There are few complications of submental intubation reported in the literature. However, potential complications include haemorrhage, injury to the sublingual glands, Wharton's duct or lingual nerve, fistulas, infection, and submental or oral scarring.

Securing a surgical airway is a potentially hazardous procedure. It is important for the anaesthetist to understand the dangers and pitfalls associated with the various surgical approaches and the complications that can arise.