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68 Australasian Anaesthesia 2011contraindicated in patients with a foreign body in the oesophagus but is if the foreign body is in the upper airway.It should not be applied if it can’t be applied correctly. 2 Patients with gut obstruction or dysfunction (hiatus hernia, GORD).Cricoid pressure: is there any evidence? 69HOW SHOULD CP BE APPLIED – SINGLE OR BIMANUALLY?There is controversary on how CP should be applied, particularly, in relation to the view obtained at laryngoscopy.Cook concluded that single-handed CP gave a better view, Yentis the opposite – that bimanual gave the betterview, while Vanner et al concluded there was no difference. The author’s opinion is that single-handed CP is easierto apply while bimanual requires the assistant to concentrate solely on the application of CP. 12-14IS CP EFFECTIVE?In a study by Howells et al of a 139 anaesthetists surveyed 10% had witnessed regurgitation despite CP. 15 In anothersurvey by Morris et al 209 anaesthetists reported regurgitation in 99 patients undergoing a rapid sequence induction(RSI) and CP, 15 aspirated and 3 died. 16The application of CP requires that:• it is easily applied and taught;• the force is applied to the cricoid cartilage;• the force must be in the correct direction;• anatomically the oesophagus lies behind the cricoid cartilage;• there must be a correct amount of force; and• the force must be applied for a correct duration of time.There are, however, several fundamental faults in the application of CP, which can be identified. Meek et alCOMPLICATIONS OF CPThere are limited data on reported complications of CP, these are listed in Table 1.Table 1. Reported complications of CPOesophageal rupture (n=2).Fracture of the cricoid cartilage (n=1).Regurgitation.Intrathyroidal bleeding (n=1).Neck soft tissue haematoma.Pharyngo-oesophageal trauma.Traumatic recall due to patient awareness.Airway difficulties.published a study of anaesthesia assistants regarding the application of CP which showed:• that CP was not easily taught prior to anaesthesia;• that there was a lack of knowledge and training on its application;• a lack of knowledge on how much force to apply; and• the majority interviewed used a poor technique. 17The impact on airway management is the most important complication of CP. It not only impairs laryngoscopeinsertion and intubation, but also the passage of a bougie and insertion of a laryngeal mask. It can cause airwayobstruction and decrease the tidal volume during bag mask ventilation; however, it can be used in cardiopulmonaryresuscitation to limit gastric inflation by limiting the tidal volume achieved. If applied incorrectly CP will cause airwaydistortion, pharyngeal compression and misalignment of the larynx and the trachea. 2In a study presented at the Difficult Airway Society meeting in 2010, of 68 anaesthetic assistants showed that32% were unable to identify the cricoid ring, 80% were unable to quantify how much pressure was needed preinduction and 71% were unable to quantify how much pressure was needed post induction. 18The effectiveness of CP has been shown to decrease with time. If the application time is greater than 2 minutesit becomes less effective due to operator fatigue. 6Anatomical variations may make CP ineffective. The cricoid cartilage may be insufficiently rigid to achieveThere are various recommendations proposed if CP interferes with laryngoscopy:1. if it is applied correctly then decrease the pressure and review, if the view is still inadequate release the CP;2. if it is incorrect adjust accordingly and review, if the view is still inadequate release the CP.In the author’s opinion if the view obtained at laryngoscopy is poor then release CP and intubate, to delayintubation to adjust CP is poor clinical practice, because the purpose of a RSI is to intubate as soon as possible.oesophageal occlusion or the cricoid cartilage does not overly the oesophagus. A CT and MRI study of the positionPREVENTION OF ASPIRATIONof the oesophagus published by Smith et al showed in 49% of patients there is a lateral displacement of theMajority of clinicians would agree that prevention of aspiration should not solely rest on the application of CP. Riskoesophagus (92% to left and 8% to right). The oesophagus starts at the inferior border of the cricoid cartilage sofactors for pulmonary aspiration (Table 2) should be identified prior to anaesthesia and appropriate action taken.CP may actually be compressing the inferior hypopharynx and the cricopharyngeus muscle. 19There should be a suitable pre operative fasting regime, although fasting does not guarantee an empty stomach.Finally, CP is known to decrease lower oesophageal sphincter pressure and therefore encourage regurgitation. 20Some studies suggest that safety can be improved by the use of drugs, which reduce gastric volume and increaseTHE PHYSIOLOGICAL EFFECTS OF CPApplication of CP causes a haemodynamic response (an increase in heart rate and blood pressure) and a reductiongastric pH. There has been only one study, from the Mayo Clinic, that assesses the value of using antacids in thepre operative period. 2,10in lower oesophageal sphincter pressure, accompanied by an increase in upper oesophageal sphincter pressure.An application of a pressure of 20 Newtons to an awake patient will activate upper airway reflexes provoking retchingTable 2. Known risk factors for regurgitation and pulmonary aspirationand regurgitation. 2,6,7Pregnant patients greater than 20 weeks gestation.CONTRAINDICATIONS TO CPPatients who have had a recent meal within the last 6 hours.CP should not be applied to patients who are actively vomiting because it may cause oesophageal rupture. It isalso contraindicated in patients suspected of having a fractured cervical spine or laryngeal tracheal injury. It is notPatients who have suffered a recent injury.Patients receiving opioid medication.Patients with head injury and/or a depressed level of consciousness.Obesity.Patients with in-coordination of swallowing.Patients with a tracheostomy.
70 Australasian Anaesthesia 2011Cricoid pressure: is there any evidence? 71PRESENCE OF A NASOGASTRIC TUBESellick originally proposed that a nasogastric (N/G) tube should be removed prior to the application of CP. Hethought that it interfered with oesophageal compression and made the lower and upper oesophageal sphinctersincompetent. This is supported by the clinical view that a N/G tube breaches the integrity of the lower oesophagealsphincter and acts as a capillary tube encouraging regurgitation, particularly in a case of upper gastrointestinalobstruction with raised intragastric pressure with the N/G occluded proximally. However, this is challenged bystudies which show that the efficacy of CP is enhanced by the presence of a N/G tube because it occupies thepart of the oesophagus not obliterated by CP, the raised intragastric pressure can be decreased with suction priorto the application of CP, and that this pressure reduction is maintained if the N/G tube’s proximal end is left openduring induction and the application of CP.18. Patel PN. Effect of education on the application of Cricoid pressure during Rapid sequence Induction. DifficultAirway Society Meeting, Cheltenham UK 2010.19. Smith KJ; Dobransowski J, Yip G et al. Cricoid pressure displaces the oesophagus: an observational studyusing magnetic resonance imaging. Anesthesiology. 2003; 99(1):66-64.20. Toumadre J, Chassard D, Berrada KR et al. Cricoid pressure decreases lower oesophageal sphincter tone.Anesthesiology. 1997; 86(1):7-9.21. Vanner R. A presentation at the Difficult Airway Society Meeting, Cheltenham UK 2010.SUMMARYThere is little evidence to support the view that the application of CP reduces the incidences of aspiration. Thereis a growing body of literature questioning the efficacy of CP. Effective or not it is likely to remain standard practicebecause its efficacy can’t be disproven and there may not be a better option.The majority of the data on aspiration ignores post operative and intraoperative aspiration, of which there arelimited data.New guidelines have been proposed for the application of CP:1. the patient should be placed with a 200 head up tilt; this will make pre oxygenation more effective and willmake intubation easier and decrease the pressure applied to prevent regurgitation;2. is to be maintained during pre oxygenation;3. if there is a poor laryngoscopic view during intubation then CP should be released;4. should be released to allow insertion of a laryngeal mask. 21REFERENCES1. Thwaites AJ, Rice CP, Smith I. Rapid sequence Induction: a questionaaire survey of its routine conduct andcontinued management during failed intubation. Anaesthesia. 1999; 54(4):376-381.2. Brimacoombe J, Berry A. Cricoid pressure. Can J Anaesth. 1997;44(4):414-425.3. Neillipovitz DT, Crosby ET. No evidence for decreased incidence of aspiration after rapid sequence induction.Can J Anaesth. 2007;54(9):748-764.4. Sellick BA. Cricoid pressure to control regurgitation of stomach contents during induction of anaesthesia.Lancet. 1961; 2:404-406.5. Mendelson CL. The aspiration of stomach contents into the lungs during obstetrical anaesthesia. AmericanJ Obs Gynae. 1946;52:191-204.6. Warner MA, Warner ME, Weber JG. Clinical significance of pulmonary aspiration during the peri operative period.Anesthesiology. 1993; 78(1):56-62.7. Maltby JR, Beriault MT. Science, pseudoscience and Sellick. Can J Anaesth. 2002;49(5):443-447.8. Lienhart A, Auroy Y, Pequiqriot F et al. Survey of anaesthesia- related mortality in France. Anaesthiology. 2006;105(6):1087-1097.9. Vanner R. The aspiration problem. In Calder I, Pearce A. eds. Core topics in Airway management. CambridgeUK; Cambridge University Press, 2011.10. Engelhardt T, Webster N. Pulmonary aspiration of gastric contents in anaesthetics. BJA. 1999; 83(3):453-460.11. Palmer JHM, Ball DR. The effect of cricoid pressure on the cricoid cartilage and vocal cords: an endoscopicstudy in anaesthetised patients. Anaesthesia. 2000; 55(3):263-268.12. Cook T. Cricoid pressure: Are two hands better than one? Anaesthesia. 1996; 51(4):365-368.13. Yentis S. The effects of single handed and bimanual Cricoid pressure on the view at laryngoscopy. Anaesthesia.1997; 52(4):332-335.14. Vanner R, Clarke P, Moore WJ et al. Effect of neck support on the view at laryngoscopy. Anaesthesia.1997; 52(9):896-900.15. Howells YH, Chamney Ar, Wraight WJ. The application of Cricoid pressure: assessment and survey of itspractice. Anaesthesia. 1983; 38(5):457-460.16. Morris J, Cook TM. Rapid sequence induction: a national survey of practice. Anaesthesia. 2001; 56(11):1090-1097.17. Meek T, Gittins N, Duggan J. Cricoid Pressure: Knowledge and performance amongst anaesthesia assistants.Anaesthesia. 1999; 54(1):59-62.
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