Cricoid pressure: are we doing it right?
Abstract: I am an operating department practitioner (ODP) who routinely applies cricoid pressure under the direction of an anaesthetist in order to prevent gastric aspiration. This article examines the current use of cricoid pressure in anaesthetics.

KEYWORDS Cricoid pressure / Mendelsohns syndrome / Sellick / Anaesthetics
Subject: Perioperative care (Analysis)
Medical personnel (Practice)
Anesthetics (Health aspects)
Author: Chewter, Michelle
Pub Date: 10/01/2011
Publication: Name: Journal of Perioperative Practice Publisher: Association for Perioperative Practice Audience: Academic Format: Magazine/Journal Subject: Health; Health care industry Copyright: COPYRIGHT 2011 Association for Perioperative Practice ISSN: 1750-4589
Issue: Date: Oct, 2011 Source Volume: 21 Source Issue: 10
Topic: Event Code: 200 Management dynamics
Product: Product Code: 8010000 Medical Personnel; 2834280 Anesthetic Preparations NAICS Code: 62 Health Care and Social Assistance; 325412 Pharmaceutical Preparation Manufacturing SIC Code: 2834 Pharmaceutical preparations
Geographic: Geographic Scope: United Kingdom Geographic Code: 4EUUK United Kingdom
Accession Number: 272168042
Full Text: During a recent learning experience I had an opportunity to perform cricoid pressure on an electronic training aid which measured the efficiency and the accuracy of the pressure applied. I found that it was difficult to maintain the correct amount pressure and to apply this in the correct position. Wayne-Conroy (2007) states that this is not unusual and that practitioners are often surprised by the force that is required. This startling discovery directed the choice of topic for this article. Furthermore, the examination of the author's personal practice lead to the questioning of the practice of colleagues. The application of cricoid pressure is a technical skill and as such needs to be practiced regularly to ensure correct position and pressure and thereby patient safety.

Brisson & Brisson (2010) suggest that perioperative practitioners often apply cricoid pressure incorrectly and this renders it ineffective. Furthermore, Ewart (2007) states that the use of cricoid pressure is indiscriminate and that there is little evidence to show that it is beneficial to patient care. In this article I explore the relevant research to establish current best practice, and to identify the correct amount of pressure and the hazards which may occur when the procedure is performed incorrectly. I also make recommendations which aim to enhance professional practice.

Gastric aspiration or Mendelson's syndrome occurs when gastric acid comes into contact with the lungs due to the absence of a cough reflex (Ewart 2007). Patients undergoing a general anaesthetic are predisposed to this as they have no protective mechanisms because their state of consciousness is affected (Pattern 2006). When a patient is conscious the epiglottis ensures that food is passed down the oesophagus and not the trachea. In anaesthetised patients these laryngeal reflexes are lost due to the administration of drugs such as induction agents and muscle relaxants. If gastric contents are aspirated into the lungs it may result in aspiration pneumonitis leading to extended ventilation and admission to intensive care (Farman 2004).

Risk of gastric aspiration during anaesthesia

Whilst all patients who are receiving general anaesthesia are at increased gastric aspiration (Pattern 2006), some patients fall into a higher risk category. Any patient who suffers from increased gastric volume or delayed gastric emptying is at risk from Mendelson's syndrome (Kozial et al 2000). Simpson and Popat (2001) describe patients at risk of aspiration as those that have experienced trauma which may mean that they do not know when they last ate or drank, and patients who suffer from hiatus hernias or reflux. Obstetric patients are at particular risk due to an enlarged uterus and the physiological changes that take place during pregnancy.

Cricoid pressure to prevent aspiration of gastric contents

Owen et al (2002) remarked that cricoid pressure can be seen in medical literature from the 18th century. However, Sellick (1961) first described its use in The Lancet. Prior to this the aspiration of stomach contents was often fatal and in 1956 as many as 110 deaths during anaesthesia were attributed to the aspiration of gastric content (Wayne-Conroy 2007). Cricoid pressure or Sellick's manoeuvre is used at induction of and occasionally at emergence from a general anaesthetic. Prior to the introduction of Sellick's manoeuvre anaesthesia was induced with the patient in an upright position (Sinclair & Luxton 2005).

Cricoid pressure should only be applied by a skilled practitioner (Enkin et al 2000). However, Sellick himself described the procedure as a 'simple technique' and this description may well have lead to a relaxed approach to teaching the skill. My personal opinion is that this is not a simple skill to develop. Wayne-Conroy (2007) concurs that it is a difficult technique to perfect and comments that in the past there has not been enough training in this area of anaesthesia.

The aim of applying cricoid pressure is to exert pressure on the cricoid cartilage to occlude the oesophagus, which then prevents the regurgitation of stomach contents into the pharynx. The cricoid cartilage can be found by locating the first firm bulge beneath the Adam's apple (Stanton 2006). This is often easier to identify in a male than a female because it is well defined however, if not obvious it can be located by asking the patient to swallow before the anaesthetic is commenced. This shows the Adam's Apple clearly and subsequently the cricoid cartilage can be located.

Application of cricoid pressure

Cricoid pressure can be applied either with one hand - which allows the assistant to aid the anaesthetist, or two handed - which is known as Sellick's manoeuvre. Sellick's manoeuvre is performed by the application of the left hand behind the patient's neck to prevent the pressure undoing the flexion of the neck and allowing for laryngoscopy. Farman (2004) comments that Sellick's manoeuvre must be used in cervical spine injuries due to the support provided by the second hand.

The right hand is normally used by practitioners in the UK due to the design of the majority of anaesthetic rooms (Wayne- Conroy 2007). However, in practice the author has an airway trolley which is mobile, enabling pressure to be applied with either hand. Stanton (2006) comments that researchers have found that practitioners can better judge the amount of pressure that has been exerted with their right hand and concluded that the right hand should be favoured.

By using one hand to perform this technique the practitioner is performing a modification of Sellick's manoeuvre. As previously mentioned, without the support of the other hand flexion is undone, however in the author's experience it is rare that a second practitioner is available to give support. It is evident there is a theory practice divide.

Walsh and Ford (1998) suggest that there is a wide chasm between how care should be carried out and how it actually is. The HPC (2008) states that practitioners should adopt an evidence-based approach to practice. This is defined as the use of the best clinical evidence to make decisions for the care of patients with emphasis placed on evidence which is obtained from disciplined research (Polit & Beck 2006). Greenhalgh (2001) suggests that this is not merely the reading of papers but it is the 'systematic framing' of questions relating to the care of a patient and the ability to convert new evidence in relation to sound patient care.

The cricoid cartilage is used because it is the only complete ring of cartilage in the respiratory tract. The pressure is applied with the right hand with the practitioner's thumb and fore finger (see Figure1). However, there is debate about which fingers should be used. Sellick (1961) advocated the use of the thumb and second finger, to avoid deviating the trachea. Alternatively, Farman (2004) suggests that the thumb and first two fingers should be used to apply an even pressure. The information available is conflicting and there is no definitive answer.

[FIGURE 1 OMITTED]

The use of pressure during Sellick's manoeuvre

The pressure should be applied in a downward motion without lateral tracheal deviation (Farman 2004) and is maintained until the tracheal tube is in place and the cuff is inflated. A force of 30 Newtons (N) is applied and this is enough to prevent regurgitation (Kumar 2000). However, the recommended amount of force which should be applied has been a source of debate (Schmidt & Akeson 2001). Sellick originally recommended as much force as was necessary, but it was later suggested that the amount of pressure should be similar to that which would cause pain across the bridge of the nose. Since the 1960s when Sellick carried out his research, practitioners now view pain and respond to patients differently. Pain is subjective: it is what the patient says it is.

Communication with the patient is paramount when applying cricoid pressure due to the discomfort experienced by the patient. A clear explanation of the procedure is also important as this can reduce patient anxiety and panic.

The debate relating to the amount of pressure applied to the cricoid cartilage is mainly due to one of the complications of cricoid pressure which is the rupture of the oesophagus. Although this is a rare event it can be fatal (Ewart 2007, Landsman 2004). Vanner et al (1992) recommended a force of 40 N. However, further studies found that the recommended force varied depending on the level of consciousness of the patient (Farman 2004). Studies carried out using both live patients and cadavers showed that in a conscious patient a force of 20 Newtons was sufficient to protect against aspiration. In an unconscious patient this could be increased to 30N or above (Haslam et al 2003). The type of drugs used to induce anaesthesia are also a factor influencing how much pressure should be exerted, and practitioners are advised to use a common sense approach (Farman 2004). Farman (2004) comments that if excessive pressure is exerted on a conscious patient then the gag reflex is triggered.

Wayne-Conroy (2007) states that the pressure required should be between 20 and 40N. Due to the large variation in recommended pressure it is difficult for a practitioner to know what is the appropriate amount of force to be exerted.

During the cricoid pressure training session I found that it is difficult to maintain 30N of pressure and also to know how much pressure is being applied. This can have implications for the patient: too little pressure and the risk of gastric aspiration is increased but too much pressure could cause unnecessary pain for the patient or a potential risk to the oesophagus. The concern relating to the application of pressure is echoed by Clayton and Vanner (2002). They found that in a study of 40 experienced health practitioners only three were able to maintain the correct amount of pressure for a period of one minute. In the author's experience, difficult intubations can often take longer than a minute.

I have found it difficult to ascertain exactly how much pressure is being exerted. Stanton (2006) alluded to practitioners having difficulties in converting the measurement of Newtons into actual practice. What is perceived to be 30N by one practitioner might feel entirely different to another. The measurement is not objective and therefore, after review of current literature, the use of training devices is advocated in order to allow practitioners to determine what 30N feels like and to correctly locate the cricoid cartilage.

Standardising practice

Stanton (2006) commented that there is a no standardised approach to cricoid pressure and that this is due primarily to the amount of debate on the correct amount of pressure that is needed for success. In an age where standardisation and benchmarking are necessary for a gold standard approach to practice, this should be paramount. Wayne-Conroy (2007) remarks that there should be a priority for standardisation in teaching this technique. Such standardisation could be developed through the use of training aids to allow practitioners to develop competence in the application of cricoid pressure.

Due to the lack of a definitive method of performing this technique it is assumed that mentors pass on poor techniques to their students and thereby perpetuate poor practice (Stanton 2006). Pattern (2006) introduced an education programme which aimed to assess and improve practitioners' skills in the application of cricoid pressure. It was found that, before the programme, only two out of 51 anaesthetic practitioners could locate the cricoid cartilage and maintain the correct amount of pressure. However, after completing the course the number was increased to 35. Pattern (2006) recommended that regular updates were essential in maintaining this skill.

Effectiveness of Sellick's manoeuvre

The effectiveness of the application of the correct pressure in reducing and preventing gastric aspiration has been questioned by Gobindram and Clarke (2008). Ewart (2007) supported this opinion and commented that Sellick based his study on assumptions. Wayne-Conroy (2007) reinforced this view and commented that, even if cricoid pressure is applied correctly, aspiration may still take place.

Sellick (1961) stated that the oesophagus is occluded between the cricoid cartilage and cervical vertebra. However, studies that have been carried out using CT and MRI imaging have shown that, instead of occluding the oesophagus, it is displaced laterally (Smith et al 2003). Ewart (2007) concluded that this may account for cricoid pressure being unsuccessful.

Furthermore, Ewart (2007) commented that Sellick based his study on the theory that pressure exerted on the cricoid cartilage increased upper oesophageal sphincter pressure. However, this is not the case. Regurgitation is prevented due to the lower oesophageal sphincter pressure being lower than stomach pressure (Ewart 2007). The original study was based on evidence that was up to date at the time, but the procedure has not been updated since new evidence has been published (Gobindram & Clarke 2008).

Although the effectiveness of Sellick's manoeuvre has been questioned, Farman (2004) advocated the use of cricoid pressure and commented that this is the leading method of preventing acid aspiration in the UK. Although it is commonly used in the UK this is not the case in France. The French neutralise the stomachs acid with the use of antacids prior to theatre. The reduction of the pH of the stomach acid is believed to reduce harm (Farman 2004).

Cricoid pressure can make laryngoscopy difficult due to altered larynx anatomy (Arthurs 2001). Gobindram and Clarke (2008) commented that often it causes airway obstruction and affects the success of intubation. They further commented that, when cricoid pressure is applied successfully, the anaesthetist will ask for less pressure to pass the endo tracheal tube. In the experience of the author this has often been the case and it is questionable to whether this negates the success of the pressure as it is altered.

If indeed cricoid pressure is ineffective, as has been suggested, then should there be an alternative method of preventing acid aspiration? Wayne-Conroy (2007) commented that currently there is no alternative. However, Gobindram and Clarke (2008) highlighted a study carried out by Snow and Nun (1959) which looked at inductions using a 40[degrees] head tilt in place of the application of cricoid pressure. The rationale for this position is that gastric contents could not reach laryngeal level. It was found that in 606 high risk cases, only one resulted in regurgitation and this was attributed to a low administration of muscle relaxant. Although this research is dated there are reasonable alternatives to cricoid pressure which are less painful and are suggested to be more effective. By adopting Sellick's manoeuvre as a protocol for rapid sequence induction, and with so little importance being placed on doing it correctly, anaesthetic practitioners could be accused of a blase attitude towards aspiration. Sellick (1961) commented that the procedure could be taught to an assistant in a matter of minutes (Lerman 2009).

Conclusion

It is evident that there is much debate concerning this area of clinical practice. Furthermore, there is doubt regarding its validity in protection against Mendelson's syndrome. However, it is the opinion of the author that if the medical profession continues to use this form of practice, then standardisation and training should be a matter of priority due to the potential risk to the patient if the manoeuvre is performed incorrectly.

The author found the use of an electronic cricoid pressure training device to be a beneficial experience.. The primary recommendation of this article is that more training is required in relation to this technique and the use of the aforementioned device is highly recommended. There are alternatives to the electronic trainer which are viewed to be more cost effective. Matthews (2001) used a 5ml Luer-lock syringe. It was found that compression of the syringe to the 17mm point was found to be the equivalent to 30N of pressure.

The debate and subsequent doubt regarding the effectiveness of cricoid pressure leads to the questioning of the decisions made regarding patient care. The author is not the first after viewing the current literature to suggest that it could be an out dated practice. From this limited view there appears to be much debate surrounding the practice and its correct application and that it requires development and standardisation. The Health Professions Council (2008) requires ODPs to adhere to standards of proficiency which ensure that the professional interprets new information in order to make professional judgments and change practice. This article is by no means exhaustive, however from analysing the literature we are duty bound to influence a change in practice by questioning what we are asked to do.

No competing interests declared

Provenance and Peer review: Unsolicited contribution; Peer reviewed; Accepted for publication July 2011.

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Correspondence address: c/o RCDM, K Block, Selly Oak Hospital, Birmingham, B29 6JD Email: michelle.chewter@uhb.nhs.uk

About the author

Michell Chewter

BSc (Hons), Dip HE ODP

Military ODP, Queen Elizabeth Hospital, Birmingham
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