A ‘can’t intubate can’t oxygenate’ scenario (CICO) is defined as a situation when there is failed intubation and failure to adequately oxygenate using facemask ventilation or supraglottic airway device resulting in increasing hypoxemia in an anaesthetised and paralysed patient. As this occurs unexpectedly, all anaesthetists need to be regularly trained in managing this scenario.
Prior to declaring CICO, difficult ventilation resulting from laryngospasm, which requires different treatment, should be excluded.
The management of such a situation involves prompt decision-making to access the airway through cricothyroid membrane, generally described as front of neck access (FONA). Successful management of such an emergency crisis situation requires sound knowledge of anatomy of front of neck, familiarity with the technique, timely decision making, situational awareness, good leadership skills and a team approach including an experienced assistant.
The incidence of CICO scenario varies form in 1:10,000 to 1 in 50,000 [1,2]. In the recently published Danish anaesthesia database the incidence of emergency surgical airway was 0.06 events per thousand . Difficulty with airway management is often the result of poor assessment and failure to follow a pre-planned airway management strategy. Often, repeated attempts at intubation worsen the scenario and lead to airway complications. The age-old adage of prevention being better than cure perhaps fits the bill best in a CICO scenario. However, one cannot always predict the inevitable. It is in such situations that preparedness and alertness of the anaesthetist and the whole team plays a vital role.
The anatomical landmarks in the midline from the front of the neck superiorly are the mandible, hyoid bone, thyroid cartilage and cricoid cartilage (figure 1). The thyroid cartilage is the largest of the laryngeal cartilages. As the index finger slides down from the laryngeal prominence in the midline, the first indentation felt is that of the cricothyroid membrane. There is a steep incline from anterior to posterior aspect of the superior margin of the cricoid cartilage. This incline leaves an anterior window where the cricothyroid membrane lies .
The cricothyroid membrane is bounded by the cricothyroid muscle laterally, thyroid and arytenoid cartilage superiorly and the cricoid cartilage inferiorly. The common carotid artery and internal jugular vein have a posterolateral relationship while the anterior jugular vein follows a lateral descent in relation to the cricoid cartilage. Hence, it is important to access the front of the neck in the midline. This dense fibro elastic membrane has no major arteries, veins or nerve crossing it, though small blood vessels may pierce it at the superior margin. The right and the left cricothyroid arteries traverse the superior part of the membrane. The vocal cords lie in close proximity to the lower border of the thyroid cartilage . Hence, the incision in the lower half of the cricothyroid membrane is likely to avoid damage to both the vessels and the vocal cords.
The width of the cricothyroid membrane varies between 22–33mm (beyond the cricothyroid muscles) and the height is about 9mm . Hence the rationale for selecting a tracheal tube of 6mm internal diameter which has diameter of 8.2 to 8.8 mm (table 1).
|Tracheal tube manufacturer||Internal
|LMA Fastrach oral||6.0||8.8|
|Mallinckrodt oral/nasal reinforced||6.0||8.4|
|Mallinckrodt microlaryngeal oral/nasal cuffed tube||6.0||8.2|
Table 1. Various tracheal tubes of 6.0 mm internal diameter and their respective outer diameters.
Classical teaching involved the cannula and surgical techniques. But more recently in UK, surgical technique using scalpel, bougie and tube has been taught in preference to cannula techniques.
Cannula versus scalpel technique
A randomised crossover bench study comparing the three cricothyroidotomy techniques on a porcine model (the Melker seldinger technique, the VBM Surgicric 2 set and a scalpel-bougie-tube surgical technique) showed that surgical technique had the fastest insertion time . The reasons for choosing cannula technique includes more familiarity for anaesthetists, less tissue destruction and the ability to use them as a back-up plan in elective scenarios. But they can be associated with increased risks such as barotrauma, kinking, malposition and displacement particularly with narrow bore cannulas.
The surgical technique allows the placement of a cuffed tracheal tube, therefore effective ventilation using breathing system and monitoring of end tidal carbon dioxide. This is the final pathway even when cannula cricothyroidotomy fails.
The recommended technique for FONA in the 2015 Difficult airway society guidelines is scalpel cricothyroidotomy . The perceived benefits of this technique include simplicity of the equipment without a need for a specific kit and therefore the ability in ensuring a standardized training. With appropriate training, this technique is likely to reduce the decision making time and simplify the CICO management pathway. The equipment required for scalpel cricothyroidotomy are presented in figure 2.
In order to access the front of neck the neck, the neck should be extended so that the anterior structures are stretched and made more prominent. This may be achieved by pushing a pillow under the shoulders, dropping the head of the operating table, or by pulling the patient up so that the head hangs over the top of the trolley.
The ‘laryngeal handshake’ helps identify and assess anatomical relationship between the hyoid, thyroid and cricoid . This is performed using the thumb and middle finger of the non-dominant hand while the index finger palpates the
cricothyroid membrane as an indentation just above the cricoid cartilage. The landmarks for cricothyroidotomy are described in figure 3.
If the membrane is palpable, a transverse stab incision through cricothyroid membrane is made and the blade is turned through 90, sharp edge faces caudally to avoid injury to vocal cords. The angled tip of bougie is then slid along the blade into trachea and a lubricated 6.0mm cuffed tracheal tube is then railroaded over the bougie. The cuff is inflated and ventilation commenced. The correct placement of tube is confirmed using capnography. These steps are described in details DAS 2015 guidelines paper .
For an impalpable cricothyroid membrane, it is recommended to make an 8-10cm vertical skin incision, caudad to cephalad. Blunt dissection is then used with fingers to separate tissues and to identify the cricothyroid membrane. The remainder of the technique is similar to that described in the palpable cricothyroid membrane method.
The anticipated difficulty of performing this technique in an impalpable cricothyroid membrane situation yet to be evaluated. The described vertical incision and blunt dissection of front of neck in order to identify cricothyroid membrane in the presence of profuse bleeding may encourage all to manage airway carefully and with a great care to avoid CICO situation. Any anticipated minor degree of difficulty in airway management may caution the operator to use an appropriate airway management strategy such as considering an awake technique instead of inducing general anaesthesia. Nonetheless, all anaesthetists should be regularly trained and be prepared to perform front of neck access when a CICO situation arises.
With careful airway evaluation impalpable cricothyroid membrane should be identified during preoperative airway assessment or at least prior to induction of general anaesthesia. Palpation of cricothyroid membrane should be a part of routine airway assessment. In situations where cricothyroid membrane is not palpable, ultrasound can be used to image the airway .
Ultrasonography visualizes cartilaginous structures, such as the cricoid cartilage as homogeneously hypo echoic structures. The cricothyroid membrane can be identified with ultrasonography by placing the linear transducer transversely on the neck superior to the sternal notch and first identifying the trachea and then scanning the front of neck in the midline in a sagittal plane. One can identify the tracheal rings as hypoechoic oval structures and the most cranial hypoechoic structure is cricoid cartilage . Cricothyroid membrane is located cranial to the cricoid cartilage.
Once the CICO scenario is successfully managed, an immediate airway management plan should be formulated. This may involve waking the patient up following reversal neuromuscular blockade or a formal tracheostomy. Hence expert surgical help should be summoned immediately. In addition, the events and management should be recorded on the patient notes. Subsequently detailed information should be given to the patient and to his general practitioner.
CICO situation is an airway emergency and all precautions should be taken to prevent this situation. In the event of encountering such a situation, a prompt decision making to access the trachea below the level of vocal cords using a well-rehearsed technique and a good team approach can enable successful management of such airway emergency.
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Dr Sunita B Rao, FRCA, Specialty trainee, Department of Anaesthesia, University Hospitals Coventry and Warwickshire, Coventry, United Kingdom
Professor Cyprian Mendonca, FRCA, Consultant anaesthetist, Department of Anaesthesia, University Hospitals Coventry and Warwickshire, Coventry, United Kingdom
Dr Sunita Rao, Department of Anaesthesia, University Hospitals Coventry and Warwickshire, University Hospital, Clifford Bridge Road, Coventry, CV2 2DX, United Kingdom.