Airway Emergency – Management of ‘can’t intubate can’t oxygenate’ scenario

Summary

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.

Introduction

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 [3].  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.

Anatomy

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 [4].

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 [5]. Hence, the incision in the lower half of the cricothyroid membrane is likely to avoid damage to both the vessels and the vocal cords.

Figure 1: Anatomy of cricothyroid membrane.

The width of the cricothyroid membrane varies between 22–33mm (beyond the cricothyroid muscles) and the height is about 9mm [6]. Hence the rationale for selecting a tracheal tube of 6mm internal diameter which has diameter of 8.2 to 8.8 mm (table 1).

Table 1. Various tracheal tubes of 6.0 mm internal diameter and their respective outer diameters.

Technique

Classical teaching involved the cannula and surgical techniques. But more recently in U