The majority of patients admitted to an intensive care unit require mechanical ventilation and consequently they are vulnerable to a number of airway complications. In these circumstances, airway emergencies such as airway obstruction, failed airway instrumentation, airway device failure or postextubation problems are life threatening situations.
In general, the management of the airway in the intensive care unit is inherently more complex than in the operating theatre, and complications of airway management are disproportionately higher. There are multiple patient, staffing and environmental factors that contribute to the higher complication rate. These factors may include the following: (i) patients are physiologically compromised and frequently unstable; (ii) airway management is usually time critical; (iii) it often occurs out-of-hours; and (iv) it is initially managed by junior medical staff.
The recognition of a compromised airway is the crucial first step in managing an airway emergency. Clinical features of significant airway compromise often involve increased work of breathing, inspiratory stridor, obstructed breathing pattern, desaturation and agitation. Untreated, the rapid development of hypoxia, hypercapnia, acidosis and cardiovascular collapse may ensue.
Rapid assessment of the situation and prompt management is critical to achieve a successful outcome. Airway emergencies are dynamic and often complex situations. The initial treatment priorities are to seek help and establish adequate oxygenation, while preparation for deterioration or airway difficulty is being arranged. In this chapter we will overview the challenges associated with the instrumentation of the airway in critically ill patients, the prevention and management of their airway complications, and the organisational aspects of airway safety in intensive care.
Airway obstruction is a blockage of the airway resulting in reduced or impeded gas flow. The exact incidence of airway obstruction in the cardiothoracic ICU is unknown and it remains one of the most challenging clinical scenarios for anaesthetists and intensivists.
There are many causes of airway obstruction (see Table 26.1). Anatomically, the obstruction may be supraglottic, glottic or subglottic. The clinical presentation depends on both the location of the obstructing lesion and the time course of its development. Inspiratory stridor suggests a significant upper airway obstruction with a reduction in airway diameter of at least 50%, whilst an expiratory wheeze indicates lower airway pathology.
|Obstructive sleep apnoea|
|Vocal cord palsy|
Clinical Presentation and Assessment
A focused history and examination allows rapid assessment of the patient. Important indicators of imminent airway compromise include hypoxia, agitation, inability to lie flat, failure to manage airway secretions and nocturnal symptoms. Importantly, any distress experienced by the patient may exacerbate the severity of the airway obstruction.
After initial assessment, the suspected site of the airway obstruction, the severity of the airway obstruction and the overall condition of the patient will guide further investigations. Initial tests may include a full blood count, inflammatory markers, blood cultures and a chest X-ray. In cases of suspected upper airway obstruction, computed tomography is ideal to delineate the lesion. However, in patients unable to lie flat, nasendoscopy exploration is the procedure of choice. In those with suspected lower airway obstruction due to a mass lesion, computed tomography of the chest and neck is indicated.
Initial Management of the Obstructed Airway
Acute or severe airway obstruction is a critical emergency. Initial supportive measures must include supplemental oxygen, sitting the patient upright and establishing intravenous access and appropriate monitoring. Deteriorating patients and those in extremis will need their airway secured. The definitive treatment should focus directly on the cause of the airway obstruction and is tailored to the individual patient. Antibiotics, corticosteroids and nebulised adrenaline may be effective for the treatment of upper airway swelling and infections, including epiglottitis or croup. Anaphylaxis should be managed with intravenous or intramuscular adrenaline in accordance with local and national guidelines. Foreign bodies may be dislodged by coughing or postural changes. Some patients can require urgent surgical assistance that may include ear, nose and throat, thoracic or cardiac surgery.
Airway management in patients with severe obstruction is a complex and high-risk process. All management decisions should be formulated after consultation between a senior anaesthetist and surgeon. The procedure is ideally performed in theatre and it is critical that the airway plan is well prepared and communicated, with all team members ready and the appropriate equipment in the room.
However, there is no universal management plan for securing the obstructed airway. Patients with upper airway obstruction should be assessed as to whether intubation is possible or a tracheostomy under local anaesthetic is required.
In patients who are considered possible to intubate, the airway plan may include awake fibreoptic intubation or gas induction. Caution should be exercised when using awake fibreoptic intubation – the procedure is often difficult and complete airway obstruction may be caused by the fibreoptic scope or loss of airway tone due to sedation or local anaesthesia. Regardless, an experienced surgeon, tracheostomy tray and rigid bronchoscope should be immediately available in the event of failure to intubate.
In patients with subglottic airway obstruction, the exact site of obstruction should be identified prior to embarking on intubation, unless the patient suffers an acute deterioration. The most important considerations are whether a tracheal tube can be safely passed beyond the obstruction and identification of an appropriate rescue plan. An awake fibreoptic intubation may be an appropriate plan A, allowing placement of the endotracheal tube beyond the site of obstruction. More distal tracheal obstruction precludes the use of tracheostomy as a rescue technique and requires the use of rigid bronchoscopy. In significant tracheobronchial obstruction, venovenous extracorporeal membrane oxygenation may be considered prior to securing the airway.
Failed airway management is a leading cause of morbidity and mortality in intensive care. The Fourth National Audit Project (NAP4) identified ten events in 2009 of failed endotracheal intubation in the intensive care unit and five of these deteriorated into a ‘can’t intubate, can’t oxygenate’ (CICO) situation, requiring cricothyroidotomy or emergency tracheostomy.
The incidence of a ‘can’t intubate, can’t oxygenate’ scenario was estimated to be less than 1/10,000 in 1991, and has probably fallen since then due to the advent of laryngeal masks. A thorough airway assessment will identify most patients with difficult airway, however, the positive predictive value of these tests is poor.
Factors identified in NAP4 as associated with failed intubation include patient obesity, known or predictable difficult airways, trainees with limited advanced airway experience, poor judgement and lack of equipment.
Prevention of a ‘can’t intubate, can’t oxygenate’ scenario requires proper airway assessment and planning. Every intubation should have a plan A, B, C and D as per the Difficult Airway Society (DAS) guidelines, with appropriate equipment ready, the patient position optimised and experienced personnel present.
‘Can’t intubate, can’t oxygenate’ exists when there have been failed attempts at intubation, failed attempts at oxygenation (facemask and supraglottic airway device) and low or falling oxygen saturations. Identification of a CICO situation is imperative to good outcomes. Repeated failed attempts at endotracheal intubation risk further airway trauma whilst delaying appropriate management. The reluctance to perform a surgical airway has been identified as a contributor to mortality in CICO situations.
The Difficult Airway Society published guidelines for management of unanticipated difficult intubation, including CICO. Failure to intubate necessitates that oxygenation, rather than intubation or ventilation, becomes the priority. Rapid development of severe hypoxaemia, hypoxic brain injury and cardiovascular collapse ensues if oxygenation is not re-established. Help should be sought as soon as intubation is recognised as difficult or failed.
Oxygenation must be obtained emergently via front of neck access (FONA), usually through the cricothyroid membrane. The DAS guidelines recommend the scalpel-bougie technique as first-line approach for FONA. This technique uses a cricothyroid incision with a scalpel, insertion of a bougie and rail-roading of a small cuffed endotracheal tube. This technique has higher success rates than a cannula technique and may be more acceptable to anaesthetic and intensive care specialists.
Cannula cricothyroidotomy and surgical tracheostomy are alternative techniques for emergency tracheal access. Cannula cricothyroidotomy involves the insertion of a large-bore cannula through the cricothyroid membrane and use of a high pressure oxygen delivery device. This technique can provide rapid rescue oxygenation; however it is not appropriate for ventilation and clearance of CO2. Further, the technique has reported high rates of failure, and inability to obtain a cannula cricothyroidotomy within five attempts requires an alternative technique. The risks of the technique include cannula displacement with potential to create significant surgical emphysema, barotrauma and volutrauma. A cannula cricothyroidotomy is an emergency and temporary oxygenation technique that allows stabilisation of the patient. A definitive airway should be established as a matter of priority by percutaneous or surgical tracheostomy.
Emergency surgical tracheostomy is less familiar to intensive care and anaesthetic specialists and risks inadvertent endobronchial intubation. It may be performed by those with suitable expertise and experience, particularly in failed FONA.Percutaneous tracheostomy is a technique familiar to intensive care specialists, and presents a viable alternative to establishing an emergency surgical airway. The technique utilises a cannula cricothyroidotomy initially. A wire is then inserted into the trachea, followed by a dilator and then a tracheostomy tube. Various tracheostomy sets exist, including single dilation sets. Current guidelines recommend scalpel-bougie as the initial technique as it is fast, has few steps and it establishes a definitive airway. The alternative techniques may be considered when the scalpel-bougie approach has failed and suitable expertise is available.
Figure 26.1 www.das.uk.com/guidelines/icu_guidelines2017. Reproduced from Guidelines for the management of tracheal intubation in critically ill adults, Higgs et al. (2017).
A variety of oxygen delivery techniques are available, but a detailed discussion is included in Chapter 17. An established surgical airway utilising a cuffed endotracheal tube allows direct connection to most ventilators or bag-valve-mask devices via a 15 mm connector; however, the use of a cannula presents a number of limitations. In a CICO scenario, the upper airway is obstructed, and the main route of exhalation is via the cricothyroidotomy cannula. Many oxygen delivery techniques, including jet ventilation devices, fail to allow exhalation and continue to deliver oxygen to the patient, risking significant and rapid volutrauma. Specially designed devices have an adequate exhalation valve. In the absence of these devices, the oxygen delivery device should be disconnected whenever the patient is not actively ventilated through the cannula cricothyroidotomy. Regular training and familiarisation with local cricothyroidotomy equipment is essential to maintain high standards for the rescue of CICO patients.
Tracheostomy is commonly performed in the intensive care unit for prolonged mechanical ventilation, upper airway obstruction and management of respiratory tract secretions. It may also be performed for rescue airway management or electively in theatre for major airway surgery or laryngectomy. The EPIC study estimated approximately 16% of patients in UK intensive care units have a tracheostomy at any one time.
Tracheostomies accounted for 50% (18/36) airway events in the intensive care unit in NAP4. Fourteen patients had their tracheostomy dislodged, resulting in seven deaths and four hypoxicbrain injuries (see Table 26.2). In two-thirds of these cases, the dislodgement occurred on moving or turning. Two further patients had failure to place an elective tracheostomy in intensive care and two had major haemorrhage post decannulation. Obesity was identified as a significant risk factor for tracheostomy complications and capnography was used infrequently. The high morbidity of tracheostomy complications led to the development of current national guidelines.
|Cricoid cartilage damage|
|Misplacement of tracheostomy|
|Tracheal tube complications|
|Fistula to surrounding structure|