The cricoid cartilage is the only cartilaginous part of the upper airway to be a complete ring, and so pressure on its anterior aspect results in compression of the upper oesophagus/ hypopharynx against the vertebral body of C6 posteriorly. First described by Sellick in 1961 (hence ‘Sellick’s manoeuvre’), cricoid pressure is widely used as a means of preventing passive regurgitation (and thus aspiration) of gastric contents during induction of general anaesthesia in at-risk patients. It is thus a standard technique in obstetric anaesthesia, although precisely when the period of risk begins and ends is controversial. In addition, whether cricoid pressure is actually necessary has also been questioned, since it is not routinely practised in many continental European countries without apparent increases in morbidity and mortality, and there is some evidence that it does not completely occlude the oesophagus when applied.
Method
As originally described by Sellick, the assistant’s forefinger is placed over the cricoid cartilage and firm pressure is exerted posteriorly, with the thumb and middle finger supporting on either side. In the two-handed technique, the assistant’s second hand is placed behind the patient’s neck, resisting any flexion of the cervical spine as cricoid pressure is applied. However, it is unclear whether the two-handed technique has any consistent advantage, and it does mean that the assistant has both of his/her hands occupied should the anaesthetist need any more equipment.
The optimal time to start exerting pressure is somewhat controversial, since cricoid pressure is uncomfortable when the patient is awake, whereas regurgitation may occur if it is applied too late. As a compromise, many advocate gentle pressure (10 N) until consciousness is lost, with firmer pressure (30 N) thereafter (as Sellick originally described), although there is evidence that gentle pressure itself may cause relaxation of the lower oesophageal sphincter. Estimates of the force required to prevent regurgitation range from 10 N to over 40 N.
Although the use of cricoid pressure is standard practice, it may hinder tracheal intubation, first because the assistant’s hand may obstruct insertion of the laryngoscope blade into the mouth and second because if incorrectly applied (it has been suggested that this is more likely in obstetrics because of lateral tilt) it may distort the laryngeal anatomy. If pressure is excessive, it may also flex the neck (or hyperextend it if two-handed cricoid pressure is used). It is therefore important that anaesthetic assistants are properly trained in its application; studies have demonstrated considerable variation in assistants’ ability but also considerable improvement following training. Video laryngoscopy may aid the assistant in providing optimum cricoid pressure, and improve the view of the glottis.
In cases of failed intubation, release of cricoid pressure should be considered, especially if mask ventilation or placement of a laryngeal mask airway is considered, as these may be hindered by cricoid pressure. If not hindering ventilation, cricoid pressure should be maintained until the patient wakes (i.e. maintained throughout surgery if the decision is made to proceed with a supraglottic airway). If regurgitation occurs once cricoid pressure has been reduced, the assistant should be ready to reapply pressure if required while oropharyngeal suction and head-down tilt are introduced. Release is also advocated if there is active vomiting, since oesophageal rupture has been reported; however, cricoid pressure should only be released on the anaesthetist’s instruction.
Key points
• Cricoid pressure should be applied as consciousness is lost.
• A force of 10-40 N is required.
• Incorrect application may impede intubation.
• Assistants should be properly trained in its application.
Further reading
Algie CM, Mahar RK, Tan HB, etal. Effectiveness and risks of cricoid pressure during rapid sequence induction for endotracheal intubation. Cochrane Database Syst Rev 2015; (11): CD011656.
Benhamou D, Vanner R. Controversies in obstetric anaesthesia: cricoid pressure is unnecessary in obstetric general anaesthesia. Int J Obstet Anesth 1995; 4: 30-3.
El-Obarney M, Connolly L. Rapid sequence induction and intubation: current controversy. Anesth Analg 2010; 110: 1318-25.
Lerman J. On cricoid pressure: ‘may the force be with you’. Anesth Analg 2009; 109: 1363-6.м