Cricothyroidotomy forms part of the DAS guidelines in the “can’t intubate, can’t oxygenate” (CICO) scenario once oxygen saturations have fallen below 90% on FiO2 of 1.0 (Plan D), and in the Vortex approach, when optimal attempts have been made at the three non-surgical airway techniques.
There are three basic methods to achieve trans-tracheal oxygenation:1
- Small cannula techniques (2-3 mm) plus a high-pressure gas source. These techniques rely on a patent airway for exhalation. However, inability to inflate the lungs with positive pressure ventilation via a facemask does not mean that the airway will be obstructed in expiration, when positive intraluminal pressure tends to expand and open the upper airway. In one series, 86% of patients with CICV retained a patent expiratory route.2 Gas entrainment is also a feature of these techniques if the upper airway is not obstructed.
- Large cannula techniques (≥4 mm). These enable oxygenation and ventilation with a lower pressure gas source but require either a cuffed cannula or obstruction of the upper airway to achieve adequate driving pressure for prolonged ventilation.
- Surgical technique. This enables placement of a size 6.0 to 7.0 tube and conventional ventilation.
As cricothyroidotomy is performed so rarely in clinical practice, evidence for the superiority of one technique over another is confined to studies in manikins, cadavers, case series and audits. Manikin studies consistently show high success rates, with mean times to successful oxygenation ranging between 23-123 seconds for various methods.3-5 The manikins used in these studies have slim necks the material which needs to be breached to perform a cricothyroidotomy has a limited resemblance to human tissue. A more recent study, in which the manikin was modified with belly pork to simulate a morbidly obese patient, showed a significantly longer median time to successful oxygenation (183.5s), with a low success rate of needle techniques (30%). When the needle technique failed, the majority of participants used a surgical approach as their second choice and succeeded.6
A study in 200 cadavers compared a Seldinger technique with surgical cricothyroidotomy and found similar success rates (84-88%) between the techniques, although mean time to oxygenation was faster with the Seldinger technique (98s vs 119s).7
A group from Western Australia has trained hundreds of anaesthetists to perform needle, Melker™ kit, scalpel-bougie and ‘scalpel-finger-needle’ cricothyroidotomy in anaesthetised sheep.8The latter technique is advocated in cases of difficult neck anatomy, where the cricothyroid membrane cannot easily be palpated. A long, vertical midline neck incision is made, then the soft tissues blunt-dissected away with the fingers until the neck anatomy can be palpated. The group have reported success rates for these techniques, but unfortunately, only for 10 participants for each technique. As might be expected, cannula cricothyroidotomy performed poorly in difficult neck anatomy (40% success rate). Despite this, the algorithm that the group has produced (and which has been adopted by the Australia and New Zealand College of Anaesthetists), advocates a needle cricothyroidotomy as a first-line intervention in all patients, with palpation of neck anatomy only in the event of failure.8
The largest study of airway emergencies in hospitalised patients is the UK National Audit Project 4 (NAP4), conducted by the Royal College of Anaesthetists and the Difficult Airway Society.9,10 In this audit, the anaesthetist attempted to rescue the airway on 25 occasions. In 19 cases, they chose needle techniques, and notably, these failed in the majority of cases (12/19 = 63%). In Emergency Departments (EDs) and Intensive Care Units (ICUs), needle techniques were chosen less often, as the patients more often had facial trauma or known airway pathology. In the ED, there were four attempts at needle cricothyroidotomy, all of which failed, and in the ICU, a needle technique was used only once, successfully. By contrast, in NAP 4, surgical techniques were consistently successful when performed by surgeons, emergency physicians and anaesthetists alike, although not always with a good patient outcome.
In pre-hospital medicine, surgical techniques are chosen more often than needle techniques, and appear to be more successful. One meta-analysis showed success rates of 66% (27 patients) and 90% (485 patients) for needle and surgical techniques, respectively.11 In a British study of 7256 pre-hospital intubations, surgical cricothyroidotomy was performed in 48 patients with a 100% success rate.12 By contrast, a paramedic study, which included 1332 needle and surgical cricothyroidotomies, had a success rate of 34%.13
Complications from attempts at needle cricothyroidotomy and trans-tracheal jet ventilation can be severe, and appear to be commonplace. A 2005 American Society of Anesthesiologists closed claims analysis showed that, in 26 needle cricothyroidotomies, all had a poor outcome, and pneumothorax, pneumomediastinum or subcutaneous emphysema occurred in 89%.14
A 2006 systematic review came to the conclusion that surgical cricothyroidotomy should replace needle techniques as the intervention of choice for the CICO scenario.15 The authors maintained that the surgical technique is easily taught, allows for sustained, adequate ventilation and has relatively fewer complications than needle cricothyroidotomy.
A recent editorial came to the same conclusion, recommending not only that all anaesthetists should be able to perform a surgical technique, but that it should be considered the default technique.16 They have produced an algorithm which can be found in the paper. The Difficult Airway Society CICO algorithm also now advocates that the default technique should be surgical, with cannula techniques reserved for experts only.17 The CCAM CICO Algorithm is based on these two resources, and is shown below. The CCAM approach advocates a long vertical incision and blunt dissection in cases where the cricothyroid membrane cannot be easily identified.16 This is followed by a stab incision through the membrane, then the insertion of a gloved finger to dilate the orifice.18 This allows for controlled dilatation, and provides tactile feedback: the inferior surface of the thyroid cartilage and the superior surface of the cricoid arch should be palpable on the sides of the finger, and the hard anterior surface of the cricoid lamina should be palpable with the fingertip. Finger dilatation should then allow for a tracheal tube to be inserted under direct vision. Alternatively, a digitally guided bougie can be inserted first, followed by a tracheal tube.
In small-bore needle techniques, a high-pressure gas source must be used.1,15 There are two methods available: a specialised jet ventilator, such as the Manujet™, or a wall or cylinder oxygen supply connected via a system in which there is the capacity to vent gas, such as the Rapid-O2™ device. Ventilation is not possible with bag-valve devices or via the common gas outlet of an anaesthetic machine, which is limited by a 40 KPa pressure valve.
When using a wall or cylinder oxygen flowmeter, it has been found that the flow through a trans-tracheal catheter is almost three times higher and the pressure just before the catheter four times higher when the flowmeter is fully opened than when it is opened to the 15 l.min-1 mark.19 Care should therefore be taken when fully opening the flowmeter, just as care is taken to gradually increase the pressure when using the Manujet™.
No formal evaluation of the Melker™ and Rapid-O2™ devices has been undertaken. The developers of the Rapid-O2™ device suggest that is provides better tactile feedback about obstruction to flow, and the large bore vent in the system acts as a safety valve, preventing the dangerous build up of pressure that can occur with a Manujet™.20
If a small bore cannula technique is not chosen, different practitioners may opt for either a large bore cannula or a surgical technique. With the advent of cuffed Seldinger based kits (such as the Melker™), practitioners (especially those familiar with dilational percutaneous tracheostomy) may opt for these techniques.