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On-line version ISSN 1806-907X
Rev. Bras. Anestesiol. vol.58 no.6 Campinas Nov./Dec. 2008
Compression of the cricoid cartilage. Current aspects*
Compresión del cartílago cricoides. Aspectos actuales
Eduardo Toshiyuki Moro, TSA, M.D.I; Alexandre Goulart, TSA, M.D.II
pelo CET-SBA da Faculdade de Medicina da PUC/SP; Membro da Comissão Científica
da SAESP (2006-2007)
IIInstrutor do CET-SBA da Faculdade de Medicina da PUC/SP
OBJECTIVES: Sellick described the importance of applying pressure in the
cricoid cartilage during anesthesia induction to prevent regurgitation of gastric
contents. Since then, the maneuver has been widely accepted by anesthesiologists
as a fundamental step during induction with the rapid sequence technique. The
objective of the present report was to discuss the indications, technique, complications,
and reasons why some authors have refuted the efficacy of this technique.
CONTENTS: The indications, technique, and complications of compression of the cricoid cartilage were reviewed. The aspects that have motivated some authors to abandon the Sellick maneuver during anesthetic induction with the rapid sequence technique are also discussed.
CONCLUSIONS: The cricoid cartilage pressure maneuver requires knowledge of the anatomy of upper airways and the correct force to be used. Endoscopic and radiologic studies, as well as patients who developed pulmonary aspiration despite the use of Sellick maneuver, have raised doubts about the usefulness of this technique. Besides, can cause deformity of the cricoid cartilage, closure of the vocal cords, and difficulty to ventilate if it is not used properly. Despite the importance given to Sellick maneuver in preventing pulmonary aspiration, there are no guarantees it will protect the airways of all patients, especially when the technique is not properly used.
Key Words: COMPLICATIONS: pulmonary aspiration, gastric contents; INTUBATION, Tracheal: Sellick maneuver, rapid sequence.
Y OBJETIVOS: Sellick describió la importancia de la presión
aplicada en el cartílago cricoides para la prevención de la regurgitación
del contenido gástrico durante la inducción de la anestesia. Desde
entonces, la maniobra ha sido universalmente aceptada por los anestesiólogos
como un paso fundamental durante la inducción con la técnica de
secuencia rápida. El presente artículo, tuvo el objetivo de discutir
las indicaciones, la técnica, las complicaciones y los motivos por los
cuales algunos autores han refutado la eficacia de la mencionada técnica.
CONTENIDO: Han sido revisadas las indicaciones, la técnica y las complicaciones de la maniobra de compresión del cartílago cricoides. También se analizaron los aspectos que han hecho con que algunos autores abandonen la maniobra de Sellick durante la inducción anestésica con la técnica de secuencia rápida.
CONCLUSIONES: La aplicación de la maniobra de compresión del cartílago cricoides exige el conocimiento de la anatomía de la vía aérea superior y de la fuerza correcta a ser empleada. Estudios endoscópicos y radiológicos, como también pacientes que presentaron aspiración pulmonar pese al uso de la maniobra de Sellick, han colocado en tela de juicio la utilidad de la técnica. Además de eso, cuando se usa mal, puede causar deformidad de ese cartílago, el cierre de las cuerdas vocales y dificultad de ventilación. A pesar del papel de destaque representado por la maniobra de Sellick en la prevención de la aspiración pulmonar, no se garantiza la protección de las vías aéreas para todos los pacientes, principalmente cuando la técnica no está correctamente aplicada.
Compression of the cricoid cartilage was initially described by Monro (1774) 1: "When pulmonary insufflation is done through the mouth, part of the air is directed to the stomach, but it can be prevented by applying pressure in the inferior portion of the larynx. Pressure should be applied on the cricoid cartilage to close the esophagus without interrupting passage of air through the larynx."
In 1961, Sellick described the importance of applying pressure on the cricoid cartilage to prevent regurgitation of gastric contents during induction of anesthesia. Since then, the maneuver has been accepted by anesthesiologists as a fundamental step during the rapid sequential technique. However, after the observation of cases of pulmonary aspiration in patients submitted to compression of the cricoid cartilage 3,4, besides endoscopic 5 and radiologic 6,7 studies that contest the efficacy of the maneuver, several authors have questioned the indication of this procedure 8-10.
How could pulmonary aspiration in cases that compression of the cricoid cartilage was applied be explained?
Anatomical differences among individuals, changes in the anatomy of the airways induced by the maneuver, improper application of the technique, and reduction in the tonus of the inferior esophageal sphincter are the most common reasons suggested to explain the inability of the Sellick maneuver to prevent regurgitation in some cases 8. The objective of the present report was to discuss the indications, technique, complications, and reasons why some authors have contested the indication of this maneuver.
INDIVIDUAL VARIATION IN AIRWAYS ANATOMY
The proximal esophagus begins at the inferior portion of the cricoid cartilage. This is the only cartilaginous structure of the upper airways whose format represents a complete ring. Applying force on the anterior aspect of the cricoid cartilage causes compression of the esophagus against the spine between the fifth and sixth cervical vertebrae (C5 and C6), as long as those structures are aligned in the axial plane. The technique is similar for adults and children, except by the reduced size and the more cephalad placement of the cricoid cartilage in younger patients 1.
The mechanism proposed for Sellick maneuver is based on the supposition that the esophagus is directly behind the cricoid cartilage. Since this structure is a complete ring, its compression against the spine should occlude the esophagus, preventing the passage of stomach contents into the oropharynx.
On the original study of Sellick 2, 26 patients deemed to be at risk for pulmonary aspiration of gastric contents were evaluated. They were placed in the supine position, lowering the torso slightly to avoid aspiration of regurgitated material. The neck was fully extended, which accentuates the anterior convexity of the cervical spine and rectifies the esophagus, preventing the lateral dislocation during compression of the cricoid cartilage maneuver. However, the so-called "olfactory position" (flexion of the neck associated with hyperextension of the atlanto-occipital joint) is currently deemed more adequate for ventilation and tracheal intubation 12.
Two radiological studies (MRI and CT scan) evaluating non-anesthetized volunteers with the head in the "neutral position" demonstrated that in more than 50% of the individuals the esophagus was lateral to the midline of the vertebral body. Comparing with the position of the cricoid cartilage, a 33% incidence of lateral displacement was detected. Smith et al. 6 reported an incidence of 90% and 76%, respectively, after applying the Sellick maneuver. Some cartilaginous structures of the upper airways are "U"-shaped, which is the case of the thyroid cartilage and the trachea. Besides being ineffective, compression of those structures can interfere with tracheal intubation or cause lesions of the airways 1.
In 1970, Fanning was the first author to study the intragastric pressure required to overcome the force generated by cricoid cartilage compression. According to the study, done in cadavers, when the maneuver is properly applied, the intragastric pressure produced (approximately 50 cmH2O) is higher than that of the stomach of individuals fasting (18 cmH2O), during eructation (20 cmH2O), or in cases of increased intragastric pressure caused by fasciculation induced by succinylcholine (> 40 cmH2O). However, during vomiting, when esophageal pressure can be higher than 60 cmH2O, the maneuver should be discontinued due to the risk of esophageal rupture.
Applying pressure on the cricoid cartilage increases the tonus of the upper esophageal sphincter 14, but decreases the tonus of the lower esophageal sphincter 15, suggesting the presence of mechanoreceptors in the pharynx that promote relaxation of this sphincter. However, this effect does not seem to cause gastroesophageal reflux 16.
In his original work 2, Sellick does not mention the force applied on the cricoid cartilage. According to the author: "at the beginning of anesthesia, pressure is applied to the cricoid cartilage"; "even the awake patient can tolerate moderate pressure without discomfort"; "as soon as the patient is unconscious, firm pressure should be used". The force applied on the cricoid cartilage should be enough to occlude the esophagus, without obstructing or hindering ventilation. From the decade of 1990 on, studies on compression of the cricoid cartilage started focusing on the force that should be applied and not on gastric pressure.
Meek et al. 17 used a model of the airways to evaluate the pressure applied on the cricoid cartilage by 135 anesthesiologists, and observed that only one third of them applied the force recommended. Koziol et al. 18 assessed 102 nurses and observed that only 5% of them applied adequate force. Besides, a considerable number of individuals identified the thyroid cartilage as the structure to be compressed.
Vanner e Pryle 19 observed that 30 N (equivalent to 3 kg) was the necessary force that should be applied on the cricoid cartilage to prevent regurgitation of NS in 10 cadavers with esophageal pressure of up to 55 cmH2O.
In awake individuals, applying more than 20 N on the cricoid cartilage can cause pain, cough and nausea. Thus, during anesthetic induction, while the patient is awake, 10 to 20 N should be applied, and 30 to 40 N when the patient is unconscious20.
Sellick maneuver requires knowledge of the anatomy of the upper airways and the correct force to be applied.
According to the Single Hand technique, the thumb and the middle finger are placed on each side of the cricoid cartilage and the index finger is placed above. The objective of this configuration is to control the lateral movement of the cartilage 2. Flexion of the head induced by the force applied indirectly on the cervical spine, decreasing visualization of the glottis, is one of the disadvantages of this maneuver 9.
The Two Hands technique is an alternative for compression of the cricoid cartilage. In this case, an assistant should support the posterior aspect of the neck with his/her hand to oppose the force applied on the cricoid cartilage 21.
Some studies have demonstrated that a considerable percentage of anesthesiologists and other professionals directly involved with anesthesia do not know how or have difficulties to perform this maneuver correctly 17,22. Besides, knowledge of the force to be applied, acquired through training in mechanical models, decreased with time. Flucker et al. 23 used 50 mL syringes, whose bevel was closed, to simulate the force applied on the cricoid cartilage. The authors observed the volume of air compressed by the plunger and transformed the values observed in measures of force. The model was considered an effective training, but the duration of the ability acquired decreased significantly after one month.
Several suggestions have been made to habilitate anesthesiologists to apply the Sellick maneuver properly: cricoid yoke, mechanical simulators, mannequins, and laryngotracheal models 24,25. Unfortunately, those devices are expensive, difficult to be acquired by the majority of anesthesiology services in Brazil, and training for maintenance of the ability should be repeated periodically 26.
According to Kopka and Robinson 27, the 50-mL syringe is an effective training model, even when applied immediately before using the Sellick maneuver. Therefore, it would be an alternative to the proposed periodical training in mechanical models, which is not practical. The use of 20-mL syringes (BD®) is a practical reference for the force to be applied on the cricoid cartilage. The necessary force to compress 10 mL of air when the tip of the syringe is closed is approximately 30 N 28.
SELLICK MANEUVER AND LARYNGOSCOPY
A survey was done in England with questionnaires sent to preceptors and residents revealed that, of the 220 professionals who answered the questionnaires, 100% reported that they use the Sellick maneuver during rapid sequence anesthetic induction, 28% witnessed cases of regurgitation despite the maneuver, and half describe failure of tracheal intubation, at least once, during compression of the cricoid cartilage. The study also evaluated the adequate force to be used according to those professionals. Answers varied from 1 to 44N, for awake patients, and 2 to 80 N, for unconscious patients. Many did not know the force applied or described it as "enough", "enough force to break an egg", or "varies" 29. On the other hand, in a study on the use of Sellick maneuver in children, only 59% of the anesthesiologists interviewed said they use the technique. Considering only school age children, 96% reported the use of the technique 30.
When the Sellick maneuver is not applied properly, it can hinder intubation and ventilation 31. Palmer et al. 32 applied a 20N force on the cricoid cartilage of anesthetized patients, and used fibroscopy to evaluate the incidence of deformity of the cartilage and closure of the vocal cords induced. According to the authors, contact between the anterior and posterior portions of the cricoid cartilage was observed in 24% of the individuals and closure of the vocal cords in 40%. When a 30N force was applied, the incidence of those alterations increased to 43% and 50%, respectively.
In some cases, visualization of the vocal cords is possible only after external manipulation of structures, such as the cricoid cartilage. The BURP maneuver (backward, upward, rightward pressure on the thyroid cartilage) has been considered an interesting option in those cases 33, but it should not be mistaken for the maneuver described by Sellick 2.
The effects on brochoscopy of applying pressure on the cricoid cartilage were evaluated by different authors, with conflicting results 34-36. Anatomical variation of the airways among the individuals evaluated might explain the different results. The BURP maneuver, when used in combination with Sellick maneuver, can hinder visualization of the glottis.
SELLICK MANEUVER IN "I DON'T VENTILATE, I DON'T INTUBATE" SITUATIONS
When the difficult to manage airways is only noticed after general anesthesia induction, ventilation with a face mask would be recommended immediately, but one should be careful with the patient on a full stomach. According to Moynihan et al. 37, applying pressure on the cricoid cartilage is capable of preventing gastric insufflation as long as ventilation is carried out with a pressure lower than 40 cmH2O. In this situation, it is possible to ventilate the patient gently only if Sellick maneuver is used properly.
If visualization of the vocal cords with laryngoscopy or ventilation with a face mask is not adequate, one should reduce the force applied and reevaluate the place where pressure is being applied. Prevention of pulmonary aspiration is fundamental, but permeability of the airways is more important.
Ventilation and oxygenation can be facilitated using the conventional laryngeal mask or the ProSeal®. But according to some studies, Sellick maneuver hinders proper positioning of both devices 38,39. In those cases, the temporary interruption of the maneuver might be necessary, which seems to be reasonable since compression of the cricoid cartilage can become ineffective after being applied for a few minutes 40.
SELLICK MANEUVER AND NASOGASTRIC TUBE
Placement of a nasogastric tube before anesthesia in high-risk patients for pulmonary aspiration, to drain liquid and gases present in the stomach, is a common practice. In his original work, Sellick 2 recommends removal of the tube before anesthesia induction. However, two studies in cadavers demonstrated that the efficacy of the Sellick maneuver is not reduced with the presence of the nasogastric tube 19,41. Thus, the nasogastric tube provides safe passage of gastric contents when effective compression of the cricoid cartilage is applied.
One should not forget that the nasogastric tube is not devoid of risks. Kristensen et al. 42 evaluated the hemodynamic response of 20 non-anesthetized individuals, considered to be on a full stomach, undergoing preoperative drainage of gastric contents. According to the authors, cardiovascular changes were similar to those observed during tracheal intubation in awake patients. It does not seem to be significant differences in the incidence of pulmonary aspiration when different sizes of nasogastric tube are used 43. A balloon to occlude the cardia and prevent gastroesophageal reflux, associated with the nasogastric tube, has been successfully used. This tube with a gastric balloon has been studied in conjunction with the laryngeal mask. It has been observed that the nasogastric tube does not interfere with the insertion of the laryngeal mask and that the mask does not prevent insertion of the tube. This association is a good option for the management of difficult airways in patients at risk for aspiration 45.
Sellick maneuver is not a risk-free procedure. Minor events, such as nausea, vomiting, pain, or hemodynamic changes may occur during compression of the cricoid cartilage. The incorrect use of the maneuver can cause deformity of the cartilage, closure of the vocal cords, and difficulty to ventilate, especially in women. The force applied should be enough to prevent aspiration, but not high enough to cause obstruction of the airways or esophageal rupture in case of vomiting 45.
Cricoid cartilage compression requires knowledge of the anatomy of the upper airways and use of the correct force. Endoscopic and radiological studies, as well as patients who presented pulmonary aspiration, despite the use of the Sellick maneuver, have raised doubts on the usefulness of the technique. Besides, when not used properly, it can cause deformity of the cartilage, closure of the vocal cords, and difficulty ventilating. Despite the importance of the Sellick maneuver in preventing pulmonary aspiration, it does not guarantee protection of the airways in all patients, especially when not used properly.
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Correspondence to: Submitted em 5
de setembro de 2007 *
Received from CET-SBA da Faculdade de Medicina da PUC/SP, Sorocaba, SP
Dr. Eduardo Toshiyuki Moro
Av. Araçoiaba, 85 - Condomínio Lago Azul
18190-000 Araçoiaba da Serra, SP
Accepted para publicação em 28 de julho de 2008
Submitted em 5
de setembro de 2007
* Received from CET-SBA da Faculdade de Medicina da PUC/SP, Sorocaba, SP