Aspiration pneumonitis and pneumonia are major complications associated with anesthetic management. Indeed, aspiration pneumonia was identified as the largest contributor to deaths amongst all pneumonia etiologies investigated. As many as 15% of all anesthesia malpractice claims in the United States are related to aspiration. Furthermore, it has been shown that of the anesthesia-related reported airway difficulties in one study from the United Kingdom (UK) (n=133), aspiration was associated with the highest mortality rate. It was the second most frequently reported airway complication, surpassed only by difficult intubation.
To avoid aspiration of gastric contents in preparation for intubation, Sellick proposed a method of esophageal compression. The eponymously named “Sellick Maneuver” is now commonly referred to as cricoid pressure. This method has been widely adopted and thoroughly investigated following its introduction in 1961. Arguably one of its most distinctive features is that, along with pre-oxygenation and short induction to intubation interval, it has become an integral part of rapid sequence intubation.
Cricoid pressure has been shown to attenuate the incidence of aspiration mostly through compression of the cricoid cartilage posteriorly. The cricoid cartilage is a hard, ring-like structure inferior to the cricothyroid cartilage at level C6. Sellick documented that this compression occludes the esophagus at C5, whereas other studies, aided by advanced imaging technologies, have specified the post-cricoid hypopharynx as the likely target. The post-cricoid hypopharynx includes the cricopharyngeus as a component of the upper esophageal sphincter.
The cricoid cartilage can be identified by palpating the hard ridge on the inferior border of the cricothyroid membrane. The arch of the cricoid cartilage, the anterior portion of the signet ring shape, is at the level of the body of C6. This is the same level as the carotid tubercle. A moderate agreement was found between these landmarks with a fluoroscopic study, including non-obese patients performing neck extension. However, the study found the cricoid cartilage slightly superiorly placed, between the C5 and C6 vertebral bodies, compared to previous reports.
The inner shape of the cricoid cartilage varies with ovoid, oval, and pear-shaped being the most common types. The shape is similar to a signet ring with the broader end, known as the lamina, found posteriorly.
It was originally hypothesized by Sellick that the cricoid cartilage was directly opposed to the esophagus and that posteriorly directed force would occlude the esophagus between the C5 vertebral body and the rigid cricoid cartilage, thus preventing aspiration of gastric contents. Intragastric pressures up to 40 mmHg have been recorded as being prevented by applying cricoid pressure. In the clinical setting, intragastric pressures rarely exceed 25 mmHg without extenuating circumstances such as obesity, trauma, and other pathological states.
However, it is now believed that the hypopharynx is the target of cricoid pressure as the esophagus begins inferior to the level of the cricoid ring. The cricopharyngeal muscle is a major component of the cricoid pressure unit and is located on the posterolateral hypopharynx at the lower border of the cricoid ring. Additionally, there is an attachment of the tendinous band to the cricoid perichondrium, transverse and oblique aponeuroses of the arytenoid muscles. These structures maintain a fixed relationship between the cricoid ring and hypopharynx with a proffer that the collapse of the musculature resulting in a kidney shape during cricoid pressure is a major factor in impeding regurgitation. Furthermore, occlusion of the hypopharynx may be attributed to the bulkier composition of the anterior tissue of the gastroesophageal tract 1cm below the cricoid.
Despite a substantial proportion of the population having a laterally displaced esophagus and cricoid pressure shown to result in lateral displacement, the technique is thought to be unaffected as the hypopharynx is the target. Paralaryngeal and paratracheal approaches of occluding the esophagus have been proposed due to the ability to maintain a patent airway with limited success of esophageal occlusion in comparison to cricoid pressure.
Cricoid pressure is indicated in patients identified as having an elevated risk of aspiration. Common indications for implementing cricoid pressure include patients who have recently eaten, gastroparesis, gravidity, nausea, recently vomited, hiatal hernia, or known incompetent esophageal sphincter(s), increased intraabdominal pressure, inebriation, impaired neurological, and/or upper respiratory reflexes. Cricoid pressure is commonly used in emergency settings as multiple attempts at intubation, emergent situations, and patients of elevated American Society of Anesthesiology (ASA) status are more prone to aspiration events.
The most emphasized demographic for the use of cricoid pressure is obstetrical patients.
The procedure was initially described employing an assistant's hand. It is possible to attain adequate technique and pressure using only the fingers; however, devices have also been introduced to minimize the equivocal effectiveness of the classicly-described approach.
For example, a tactile feedback device using the same finger placement as Sellick originally instructed has been found to most consistently provide the appropriate pressure and also decrease upward bias in applied force. Similarly, a device that illuminates when the appropriate pressure has been achieved has been described. These devices are claimed to be easier to use and more consistent than the manual approach.
At least two practitioners are required to perform intubation during cricoid pressure. The cricoid pressure should not be released until the patient is intubated with the cuff inflated; therefore, it would be prohibitively challenging for 1 person to perform both tasks simultaneously.
Proper training of all staff who may be involved in providing cricoid pressure is highly recommended. Studies have demonstrated a training gap in regards to consistently and appropriately applied pressure and knowledge of the anatomical location of the cricoid.
The most common technique for cricoid pressure involves at least a 2 person team. As one individual intubates the patient, the other performs the cricoid pressure maneuver.
The patient is classically placed in a supine position with the neck extended. Alternatively, to facilitate the view of the glottis, the patient may have his or her lower cervical spine flexed with the upper cervical spine extended in the “sniffing position.” The benefit of neck extension, as observed by Sellick, is that vomitus is directed away from the airway.
The practitioner who is performing the maneuver will often stand on the right side of the patient. The practitioner will use anatomical landmarks, including the thyroid cartilage and cricothyroid membrane, to identify the cricoid ring. Once identified, the practitioner may use the dominant hand or whichever hand is most able to apply appropriate pressure without impeding the function of the team member performing the intubation. The thumb will remain on the patient’s right side of the cricoid ring with the second digit placed on the contralateral side of the cricoid ring. The practitioner may place the third digit on the same side as the second digit if this is found to be more comfortable. While the patient is awake, a pressure of 10 N or 1 kg is appropriate until induction is complete. Once the patient is unconscious, approximately 30 N or 3 kg will be applied in a posterior direction to the cricoid ring. The constant pressure should be maintained until the endotracheal tube is appropriately placed with the cuff inflated to protect the airway. When applying cricoid pressure in pediatric patients, the pressure should be decreased, considering the increased deformability of soft structures. A pressure of 20 N is effective when the patient is in a head-up position.
A double-handed maneuver may be implemented when there is a concern for cervical spine instability. In such situations, the practitioner will use his or her free hand to support the posterior cervical spine while providing cricoid pressure.
It is generally recommended that gastric tubes are used before intubation in cases of patients who have been identified as having a full stomach. Sellick initially believed that cricoid pressure would be ineffective while a gastric tube was in place. This concern was unsubstantiated as subsequent studies have demonstrated that the tube deviates to the side of the esophagus with occlusion possible.
Cricoid pressure should not be confused with a technique commonly referred to as “BURP” (backward, upward, rightward, pressure on the thyroid cartilage) used to aid in the visualization of the glottis during intubation.
Discomfort, retching, and nausea may be observed in the awake or under-anesthetized patient. More serious complications would include airway compromise, traumatization in the under-anesthetized, esophageal rupture, cricoid fracture, and potential worsening of cervical spine injuries. Some of these complications may be avoided by waiting until induction is complete, applying proper pressure to the cricoid, and effectively supporting the cervical spine while performing the maneuver. There are concerns about arterial compression with some cricoid devices that are being investigated.
One study found that the incidence of significantly longer intubation time and higher Lehane and Cormack scores indicate that intubation may be more challenging in the cricoid pressure versus the sham group. There was no significant difference in traumatic intubations between the sham and cricoid pressure groups. There was no difference in mortality, length of stay, or aspiration. However, the prevalence of aspiration was low in the study at 0.5%, with pregnant patients (emergent cases not included).
The evidence for the wide-spread application of cricoid pressure is equivocal. The American Heart Association removed cricoid pressure from in-hospital and out-of-hospital resuscitation algorithms. This information was based upon practitioner ineptitude at correctly performing the technique on manikins. The Difficult Airway Society, in conjunction with Obstetric Anesthetist's Association, continues to recommend the use of cricoid pressure during rapid sequence intubation in the high risk demographic of parturient patients. The Difficult Airway Society guidelines also continue to recommend its use outside of obstetrics. Much of the debate concerning the effectiveness of cricoid pressure focuses on the inconsistent and improper application of the technique. A study comparing no use of cricoid pressure to a uniformly applied pressure at the confirmed anatomical location in both high risk and low-risk cohorts would be invaluable in putting the controversy to rest.
Increased support of cricoid pressure in the United States compared to the rest of the globe is attributed to higher concern for medico-legal entanglements. There is a low level of evidence by expert consensus for the use of cricoid pressure. Despite its use, aspiration is not fully preventable.
The controversy of cricoid pressure is the result of low-level evidence for its effectiveness and its often incorrect use. Numerous studies have been conducted to assess the knowledge base of various practitioners, including physicians, nurses, respiratory therapists, medical students, paramedics, nurse anesthetists, and anesthesia assistants. Results from these studies often demonstrate a lapse in knowledge regarding effective technique. The most prominent issues include the misidentification of anatomy and improperly applied pressure. One meta-analysis identifies that during emergent intubations, staff members who may lack training in rapid sequence intubations could be asked to assist. The low evidence for cricoid pressure's prevention of aspiration may be attributed to undertraining and inconsistent application.
Tools for improving consistency include regular training and the use of assistive devices. In emergent settings, anesthesia staff who would be expected to have familiarity with cricoid pressure may not be available. Preparation for such scenarios involves regular training of anesthesia staff along with training of support staff commonly present during emergent intubations, such as nurses, respiratory therapists, surgical technicians, and others.
As mentioned previously, there is an indication for all staff who may be involved in rapid sequence intubation to be trained regularly on effective cricoid pressure techniques. Rapid-sequence intubation requires a team of 2 or more individuals. One individual is likely the anesthesia provider for the case, and the other individual could be any other team member involved in patient care when intubation is commonly indicated. Meta-analysis has identified that verbal instruction is inferior to hands-on methods of learning cricoid pressure techniques.
The majority of trainees from a meta-analysis were identified as unskilled in cricoid pressure application; however, an improvement was demonstrated following simulation training. Skill retention following training endures for three weeks as a conservative estimate. Considering contemporary literature documenting the poor retention of these skills and the unlikely nature of most practitioners providing cricoid pressure multiple times daily outside of the obstetrics and trauma units, there is a compelling indication to reassess and retrain team members regularly.
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