Accuracy of Ultrasound in Identification of Cricothyroid Membrane: A Randomized Clinical Trial

Inability to secure the airway remains the most frequent cause of anesthesia-related mishaps.Difficult airway management continues to be the major challenge in anesthesia as it is responsible for a third of anesthesia-related claims and is the single largest class of closed claim injury suits. Difficulties in tracheal intubation is the most frequent cause of anesthesia-related morbidity and mortality.

Repeated attempts of tracheal intubations can result in serious soft tissue injury and rapidly deteriorate into a life threatening "cannot intubate-cannot ventilate" (CICV) crisis. The guidelines suggested by the American Society of Anesthesiologists and the Difficult Airway Society for managing the unanticipated difficult airway recommend the performance of a cricothyrotomy(CTY) as the next step for a CICV scenario.

Cricothyrotomy is an infrequently performed life saving procedure when facing a difficult CICV airway.Previous studies quote, the incidence of the CICV scenario to be in the range of 0.01-2 per 10,000 cases. It is therefore imperative that anesthesiologists have the necessary knowledge and skills in successfully managing this life-threatening airway crisis. However, several studies demonstrated that many practicing anesthesiologists and anesthesia trainees (residents/fellows) are uncomfortable with the management of a CICV situation because it is such a rare event. A recent Canadian survey shows that only a quarter of the residents and 40% of practicing anesthesiologists were comfortable with performing a cricothyrotomy. Similar findings were reported in a German national survey of academic teaching hospitals where difficult airway situations, particularly a CICV crisis, were poorly managed and were postulated to have contributed to adverse patient outcomes.Complications of emergency CTY by physicians are common, with rates ranging from 9% to 40%.These complications include failure to cannulate the trachea, false airway passage, severe bleeding, posterior tracheal wall injuries, pneumothorax and esophageal laceration. All of these major complications may be related to improper identification of anatomical landmarks used to identify the correct position of cricothyroid membrane (CTM). The current method of CTY relies solely on digital palpation of these landmarks to accurately identify the CTM.

Several studies have identified independent predictors for patients with difficult airway. These include characteristics such as high body mass index, presence of beard, short bull neck, distorted neck anatomy either due to congenital or acquired pathology such as goiters or radiation to the neck. These are the same factors which may lead to improper identification of neck landmarks for the CTY.

The outcome and accuracy of CTY may be improved with better preparedness and pre-procedural identification of the neck landmarks for CTY before deciding the method of anesthetic. This is especially true in patients with anatomical features of difficult airway, who may be the ones more likely to have a difficult airway or require an emergency CT. In this patient population, incorrect localization of the CTM may lead to significant airway morbidity or failure to quickly establish an airway.

The role of ultrasound in airway management:

Bedside ultrasound is increasingly being used to assist anesthesiologists in performing various procedures.The use of ultrasonography (US) has been shown to significantly reduce complications and improve outcomes. Diagnostic application of US for upper airway anatomy and its role for the performance of CTY and bedside tracheostomy has been previously described. However, little is known on the reliability and validity of the US when compared to the gold standard CT scan in identifying the CTM.

The methods used to identify CTM are based on identification of anatomical landmarks and digital palpation. This may be difficult in patients with poorly defined anatomy, the very same population in which the likelihood of a difficult intubation/emergency surgical airway are higher.

The trachea and paratracheal soft tissues of the neck can be examined at the highest resolution with US probes of high frequency due to their superficial position. The anterior tracheal wall, thyroid and cricoid cartilages, tracheal rings, and pre-tracheal tissue may all be well visualized , which allows the clinician to select the optimal space for CTY tube placement. The use of US for assisting with airway management in anesthesia and in the intensive care unit is directly related to the availability of low-cost and portable US capabilities. Clinicians initially described US-guided central venous catheterization, followed by US-guided regional anesthesia techniques. Recently, a few studies examined the role of US for emergency airway procedures. Nichollas et al developed a standardized US technique to identify the CTM. The findings in this study suggest that the CTM and relevant structures can be quickly identified by emergency physicians using US technique. However this study was limited to patients with normal airway and mainly focused to the standardization of technique. it did not validate the technique against a gold standard. In another study Muhammad et al, reported four cases in which ultrasound was successfully used to perform percutaneous tracheostomy in the ICU. Cricothyroid membrane can easily be located on CT scan.

In summary, inability to secure the airway remains the most frequent cause of anesthesia-related morbidity and mortality. CTY is highly dependent on proper identification of anatomical land-marks.