Cricoid pressure: a review of the literature.
Although RSI is universally carried out in medical institutes, the effectiveness of CP is questioned due to the continued incidence of pulmonary aspiration despite application of CP (Beavers et al 2009). Brimacombe and Berry (1997) recognises that insufficient information is available regarding CP and that confirmation of the appropriate mode and the force necessary is required within the clinical environment.
It is vital to establish if the practice of applying CP is beneficial to the patient, or if it is a ritual carried out with no regard to the evidence available. The advantages and disadvantages should be identified, as well as the barriers preventing effective application of cricoid pressure. Patten (2006) implies that nurses routinely applying CP do not always do so correctly and that this results in sub optimum intubating conditions and ineffective pulmonary protection from aspiration.
This article details a comprehensive literature review that was carried out using a cross-search of online databases including CINAHL, British Nursing Index, MEDLINE, Biomedical Reference and Pubmed.
History of cricoid pressure
Cricoid pressure was originally described by Monro in 1774 as a manoeuvre to prevent air from entering the stomach by occluding the oesophagus during resuscitation of near-drowning victims (Patten 2006). In modern anaesthesia it was first proposed by Sellick in 1961 as a method for preventing regurgitation and aspiration of stomach contents during induction of and emergence from general anaesthesia (Sellick 1961).
Cricoid pressure, also referred to as Sellick's manoeuvre, is routinely used during induction of anaesthesia to prevent pulmonary aspiration of gastric contents in patients identified as being at high risk of aspiration (Neelakanta 2003, Landsman 2004, Walker et al 2010). The acidic gastric fluid is identified as causing lung damage resulting in loss of surfactant and the development of pneumonitis within hours of aspiration (Pescod 2005). This is supported by Aitkenhead et al (2007) who state that if aspiration occurs it can have clinical consequences leading to fulminating aspiration pneumonitis and acquired respiratory distress syndrome; this is recognised as the most common and most devastating of anaesthetic hazards. In contrast Prazeres (2010) and Neilipovitz and Crosby (2007) state that aspiration and its consequences are not common complications in modern anaesthetics procedures and the incidence is approximately between one and seven cases of significance in 10,000 anaesthetics.
Sellick (1961) states that a suitable external force needs to be appropriately conveyed through the cricoid ring arch resulting in occlusion of the oesophagus against the fifth cervical vertebrae body to achieve successful application of CP. Smith et al (2003) acknowledges that the cricoid cartilage is the only complete ring in the trachea and applying pressure at this point compresses and occludes the oesophagus at the C5 - C6 level. Landsman (2004) confirms this stating that mistakenly applying pressure on any other cartilaginous structures of the trachea can be ineffective and can lead to sub-optimal intubation situations. This is still considered best practice by Garrard et al (2004) and Turgeon et al (2005) who describe CP as the application of firm backward pressure on the cricoid cartilage by the first three fingers of the anaesthetic assistant against the sixth cervical vertebra resulting in a decrease of the oesophageal lumen.
[FIGURE 1 OMITTED]
According to Clayton and Vanner (2002), Hein and Owen (2005) and Patten (2006), CP is a commonly practised technique in the prevention of pulmonary aspiration and is fundamental to RSI. Lerman (2009) supports this stating that CP is 'the quintessential cornerstone' of RSI. Walz et al (2007) recognise that the application of CP is established practice in the teaching of RSI. According to El-Orbany and Connolly (2010) 44 Newton's (N) was traditionally the recommended force but this has been revised and is now considered excessive. Hein and Owen (2005), The Difficult Airway Society (2007) and Parry (2009) argue that for CP to be protective it must provide an occlusion pressure excessive to oesophageal or gastric pressure, and they advocate a force of 20-30N to achieve this. This force is also recommended in a study by Cook et al (2000) who state that, even during emergency obstetric surgery, gastric pressure averages remain below 25mmHg. Although Beavers et al (2009) state that pressure from 20-30N is sufficient for effective CP, they recommend 44N as a reasonable force to protect the patient's airway.
Physiology related to gastric reflux and pulmonary aspiration
The three stages which result in pulmonary aspiration can be outlined as follows:
* reflux of stomach contents into the oesophagus
* regurgitation of these contents into the pharynx and finally
* pulmonary aspiration of the pharyngeal contents (Vanner 1993).
Ng and Smith (2001) state that the physiological mechanisms involved in preventing reflux and regurgitation are:
* the lower oesophageal sphincter (LOS)
* the upper oesophageal sphincter and
* the laryngeal reflexes.
Aitkenhead et al (2007) identifies regurgitation as a passive process and it is often described as 'silent', or occurring without the practitioner's knowledge. According to Vanner (1993) gastric reflux is due to an incompetent LOS and regurgitation occurs when the upper airway pressures fall below that of the oesophagus. This situation is likely to take place during induction of anaesthesia as the upper oesophageal sphincter is relaxed. The most important mechanism for protecting the airway from aspiration is the LOS which is normally closed and is located at the distal end of the oesophagus where it joins the top of the stomach (Peterson 2007). The closed LOS maintains a resting pressure (10 to 15mmHg) and prevents reflux of the stomach contents into the oesophagus (Peterson 2007). Aitkenhead et al (2007) state that many anaesthetic drugs affect the resting tone of the LOS therefore reducing its capacity to act as the main barrier in preventing reflux.
High risk patients
Certain pre-existing factors are common to increased risk of regurgitation and pulmonary aspiration. Usually these factors are related to a patient's condition which predisposes to delayed gastric emptying or regurgitation (Table 1). Lockey et al (1999) and Hein and Owen (2005) recognise that patients suffering severe trauma may have full stomachs and impaired airway reflexes, increasing their risk of pulmonary aspiration. Vanner (1993) points out that gastric reflux caused by an incompetent lower oesophageal sphincter is found in pregnant women and further states that, prior to cricoid pressure becoming a fundamental component of rapid sequence during tracheal intubation, the leading cause of maternal death was pulmonary aspiration (Vanner 2009).
Lockey et al (1999) declare that aspiration is also commonly associated with neurological trauma and a subsequent Glasgow Coma Scale (GCS - a record of
Table 1 Patients at high risk of pulmonary aspiration during anaesthesia Severe trauma Pregnant women Glasgow Coma Scale < 8 History of hiatus hernia accompanied by reflux Critical illnesses and extremes of age Extremes of age Obesity Gastric obstruction Difficult intubation Underlying neurological diseases
monitoring of the state of consciousness of a person) of 8 and below. Other factors associated with a higher incidence of aspiration include a history of hiatus hernia accompanied by reflux, obesity, gastric obstruction, difficult intubation, underlying neurological diseases, critical illnesses and extremes of age (Neilipovitz & Crosby 2007, Hein & Owen 2005, Prazeres 2010, Spoors & Kiff 2010).
Management of 'high risk' patients
Aitkenhead et al (2007) and Mellor (2004) state that if a risk of gastric aspiration is anticipated RSI should be performed as it facilitates expeditious intubation of the trachea leading to prompt protection of the airway. Ellis et al (2007) support this, maintaining that the main goal of RSI is to minimise gastric insufflation and to provide prompt endo-tracheal intubation conditions. El-Orbany and Connolly (2010) state that, although RSI is considered standard care for patients with full stomachs requiring induction of anaesthesia, no standard protocol has yet been established.
The process of RSI involves pre-oxygenation of the patient, administration of a fastacting induction agent followed by a rapidacting muscle relaxant, and application of CP at the time of administration until confirmation of the correct placement of endo-tracheal tube by the anaesthetist (Morrison & Cook 2001, Spoors & Kiff 2010). The Difficult Airway Society (2010) advocate the application of light pressure, no more than 10N, on the cricoid cartilage on induction of anaesthesia, increasing to 30N once loss of consciousness is achieved. Aitkenhead et al (2007) recommend that a skilled assistant performs CP but, as Patten (2006) suggests, this role is often carried out incorrectly.
Controversy surrounding cricoid pressure
Brimacombe and Berry (1997) argue that concerns have been expressed regarding the safety and efficacy of CP despite it appearing to be a simple and anatomically appropriate manoeuvre. They note that the application of CP is detrimental to patient safety, and that there are few studies which confirm the clinical benefits of cricoid pressure.
A study by Allman (1995) demonstrates that the use of CP, even by experienced anaesthetists, can cause a degree of airway obstruction and can even result in complete airway occlusion. More recently Hartsilver and Vanner (2000) suggest that CP possibly contributed to events of difficult ventilation and that the degree of airway obstruction correlated with the force applied to the cricoid cartilage. Smith et al (2003) conducted an observational study using magnetic resonance imaging (MRI) to determine the anatomical relationship between the oesophagus, the cricoid cartilage and the vertebral body. This study concluded that in over 50% of the subjects the anatomy was not aligned and the application of CP increased the frequency and degree of oesophageal and airway displacement, therefore reducing optimum laryngoscopy conditions.
Gobindrum and Clarke (2008) argue that this questions the concept described in Sellick's original paper (1961) where occlusion of the oesophageal lumen is demonstrated in X-ray images at the level of the 5th cervical vertebra body as a result of pressure being applied to the cricoid cartilage. Furthermore, a study by Garrad et al (2004) demonstrated that application of cricoid pressure resulted in a significant reduction in lower oesophageal pressure in 30 anesthetised volunteers, leading to a decline of oesophageal barrier pressure. Garrad et al (2004) further state that any manoeuvre which results in the reduction in barrier pressure potentially increases the risk of gastro-oesophageal reflux. Contrary to this, Neelakanta (2003) states that several studies demonstrate the effectiveness of CP in identified high risk patients. In fact, a study by Schwartz et al (1995) demonstrates that in 75% of oral intubations CP was applied, with only 4% resulting in an unexplained pulmonary infiltrate present on post intubation chest radiographs. A more recent study on the effectiveness of CP using MRI by Rice et al (2009) challenges Smith et al's (2003) findings and supports Sellick's (1961) original proposal that CP is effective in reducing pulmonary aspiration by occluding the oesophagus. This investigation illustrates that the hypopharynx and cricoid cartilage move together acting as an anatomical unit which is essential for the efficacy and reliability of CP.
Neilipovitz et al (2007) claim that no published randomised controlled trials comparing the outcome of patients with and without application of CP after RSI exist, though as Ellis et al (2007), Lerman (2009) and Vanner (2009) suggest that this is because such a trial would be unethical. According to Lerman (2009) guidelines in anaesthesia endorse CP and its omission legally represents poor practice (M. v East Hertfordshire Health Authority 1991).
Priebe (2005) maintains that CP is still considered an essential technique in RSI in many parts worldwide and that failure to provide CP for high risk patients may be considered negligent. It is appropriate in this context to reflect upon the phrase, 'primum non nocere' or 'first, do no harm' an expression attributed to Aristotle (Parry 2009) . This is a fundamental principle of healthcare ethics: do good and do no harm. In line with this, anaesthetic assistants, who are very often nurses, must ensure that their practice is up to date in order to provide clients with high standard safe and effective evidence based care, in accordance with the Nursing and Midwifery Council's code of conduct (NMC 2008).
Future of cricoid pressure
According to El-Orbany and Connolly (2010) the use of cricoid pressure during rapid sequence induction continues to be contentious. Some believe in its efficacy in preventing pulmonary aspiration, whereas others believe it should be discarded due to the potential complications and lack of scientific evidence of its benefit. A study by Cook et al (2000) found that 11% of anaesthetic assistants had experienced regurgitation despite application of CP, and these authors maintain that the risk of aspiration is in fact increased through the application of CP (El-Orbany & Connolly 2010) . Fenton and Reynolds (2009) argue that its efficacy in saving lives is difficult to
[FIGURE 2 OMITTED]
establish. Their study observing cricoid pressure and maternal outcome in Malawi supports the practice of preoperative emptying of the stomach instead of the practice of CP application.
Hein and Owen (2005) state that CP is a technical procedure which requires constructive education, continual practice and the monitoring of competencies. In a study by Clark and Trethewy (2005) assessing the application of CP, 75% of the participants applied incorrect force, which often resulted in inadequate protection against regurgitation. Both authors recommended training using a model which integrates the concept of force. This is supported by Allman and Wilson (2007) who claim that CP is a skilled and practised technique. Allman (1995) states that correct application of force on the cricoid cartilage is essential; a lower force may result in insufficient oesophageal occlusion whereas excessive force can compress the airway and impair laryngeal visualisation.
In a large study by Meek et al (1999) regarding the standards of practice of practitioners applying CP, it was found that their knowledge was poor and that only one third of the study subjects knew the appropriate pressure to apply. In more recent studies by Stanton (2006) and Nafiu et al (2009) the evidence continues to indicate that anaesthetic assistants often do not possess the knowledge or skills required to correctly identify the cricoid cartilage and apply CP accurately. As recognised by Patten (2006), registered nurses in the operating department frequently perform the cricoid pressure during RSI but they may not possess adequate skills or knowledge to do so competently. This suggestion is further supported in a study by Beavers et al (2009) which reveals significant deficiencies in the knowledge and application of CP amongst anaesthetic assistants. In a pre-test - post-test study by Patten (2006), which looked at the influence of an education programme on cricoid pressure application, a significant post-test improvement was evident.
It is vital that the practitioner must ensure that unnecessary harm to the patient is avoided. The NMC code of conduct (NMC 2008) states that a professional nurse must have the knowledge and skills for safe, effective practice; participating in relevant learning and practice activities to ensure optimum competence and performance in the clinical area. If the concept of nonmaleficence is to be upheld and optimal care offered, it is vital that the practitioner makes certain that his or her knowledge and skills are current and practised, therefore maintaining best standards in practice.
Butler (2005) recognises that, even though CP is widely accepted as standard practice during emergency RSI of anaesthesia in the UK, the USA and many other parts of the world, there are no studies that confirm the alleged clinical benefit of CP in reducing the incidence of pulmonary aspiration in high risk patients. Letters to medical journals indicate that the debate on cricoid pressure continues.
'As a profession we invest a great deal of importance in a technique that is inadequately researched, poorly taught and badly performed' (Haslam & Duggan 2004).
Within the literature there appears to be a lack of consensus concerning the safety and value of CP, although all authors do agree on one point: the knowledge and skills demonstrated by personnel responsible for applying CP in the clinical area are lacking. Parry (2009) recognises from the literature that inconsistencies exist in the knowledge and practice of CP, as well as conflicting opinions on the optimal force required to ensure safe and effective occlusion of the oesophagus. The author concludes that education is essential in ensuring best practice. Matthews (2001) suggests that a structured approach to the training of CP would benefit all staff, particularly those carrying out this role infrequently in the clinical area. It is vital that evidence based practice is demonstrated appropriately throughout the management of RSI and that the application of CP is not performed as a traditional ritual with insufficient consideration given to the rationale behind it (Ewart 2007). All nurses working within the anaesthetic arena have a duty of care to demonstrate the ability to perform effective cricoid pressure, and to equip themselves with a working knowledge of the subject if patient safety is to be maintained and the principle of 'primum non nocere' is to be upheld (Parry 2009).
Provenance and Peer review: Unsolicited contribution; Peer reviewed; Accepted for publication April 2011.
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Correspondence address: Norah Holmes, Anaesthetic Nurse, Royal Hospitals, Grosvenor Road, Belfast, BT12 6BA, Northern Ireland.
About the authors
Norah Holmes RN, BSc Hons
Anaesthetic Nurse, Royal Hospitals, Belfast
Daphne Martin RN, RNT, MSc
Nurse Lecturer/Pathway Leader Specialist Practice in Anaesthetic Nursing, School of Nursing and Midwifery, Queen's University, Belfast
Ann Marie Begley RN, RNT, PhD
Lecturer, School of Nursing & Midwifery, Queen's University, Belfast
No competing interests declared
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|Title Annotation:||CLINICAL FEATURE|
|Author:||Holmes, Norah; Martin, Daphne; Begley, Ann Marie|
|Publication:||Journal of Perioperative Practice|
|Date:||Jul 1, 2011|
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