December 2011 Readers Letters
Cricoid pressure: Improving standards
T. Hellyer and J. Duggan
Wansbeck General Hospital, Ashington, UK hellyer.thomas@gmail.com
Figure 1. Set of weighing scales used for auditing and syringe method of self-calibration
We read with interest the recent article regarding the cricoid force bow (CFB) and agree there is a need to improve the application of cricoid pressure (CP).1 However there are concerns about the introduction of new airway devices into practice without full evaluation. The issue here is the protection CFB provides and the risk to the airway when compared to standard technique.
First is the question of whether a device is as good as the ‘trained hand’ at performing the manouvre. Second, with regard to the correct force, our work has suggested that a 30N force is an overestimate.2 Vanner based his recommendation for CP force on the median value of upper oesophageal pressure (UOSP) in awake subjects.3 He initially recommended 40N but revised this to 30N because of oesophageal rupture at high oesophageal pressure in cadavers.4
Vanner has accepted that UOSP has limited relevance to passive regurgitation.5 Intragastric pressure is the key factor in the process of gastro-oesphageal reflux and also the protection generated by CP. We have shown that the range of intragastric pressures in the anaesthetised and paralysed patient likely to be encountered in practice is low (<12mmHg).2 A force of 20N is more than adequate based on this criterion and Vanner’s original data on the range of occlusive oesophageal pressures generated by CP. Furthermore we have shown that practitioners cannot sustain a 30N force for long.6 Release occurred within three minutes due to pain. This finding leads us to question whether this level of force is used in clinical practice. There is some evidence that the adverse effects of CP on the airway and laryngoscopy are related to the force applied (7,8), and that these effects may be significant in some patients at low force >20N, particularly in females (9,10). If, as we suspect, lower force is used routinely in practice use of a device that ensures 30N force is applied may expose patients to greater risk of airway compromise.
Until we have more evidence that CFB is effective and safe can we improve standard technique? Knowledge of the technique and the standard of performance have been shown to be poor amongst practitioners (11,12). We found training was exclusively the ‘see-one-do-one’ method and few could recall the amount of force required. Although we performed this study over a decade ago we doubt that much has changed. In this study, however, we also showed that a marked improvement in performance could be achieved simply by describing the target force in kilograms. We saw further improvement when practitioners were able to practice target force on a model before performing the technique. This can be done without complex equipment. A satisfactory measurement tool can be constructed from a closed 20ml syringe filled with air.
The volume of compressed air in the syringe is related to the force applied to the plunger: 30N -10ml; 20N -12ml. This apparatus can be quickly assembled in the anaesthetic room and allows the practitioner to self-calibrate immediately before performing the technique. We suggest all departments should regularly audit performance of cricoid pressure using a model and a set of weighing scales and have in place robust in-service training programmes (13). Self-calibration prior to performing cricoid pressure could improve standards.
References
Brimacombe J and Berry A. Cricoid pressure in chaos. Anaesthesia 1997; 52: 914-930
Haslam N, Syndercombe A, Zimmer CR, Edmondson L, Duggan JE. Intragastric pressure and its relevance to protective cricoid force. Anaesthesia 2003; 58: 1003-1022
Vanner RG, O’Dwyer JP, Pryle BJ, Reynolds F. Upper oesophageal sphincter pressure and the effect of cricoid pressure. Anaesthesia 1992; 47: 95-100
Vanner RG, Pryle BJ. Regurgitation and oesophageal rupture with cricoid pressure: a cadaver study. Anaesthesia 1992; 47: 732-735
Meek T, Vincent A, Duggan JE. Cricoid pressure: can protective force be sustained? British Journal of Anaesthesia 1998; 80: 672-674
Hartsilver EL and Vanner RG. Airway obstruction with cricoid pressure. Anaesthesia 2000; 55: 208-211
Allman KG. The effect of cricoid pressure application on airway patency. Journal of Clinical Anaesthesia 1995; 7: 197-199
Palmer JH and Ball DR. The effect of cricoid pressure on the cricoid cartilage and vocal cords: an endoscopic study in anaesthetized patients. Anaesthesia 2000; 55: 260-287
Haslam N, Parker J, Duggan J. The effect of cricoid pressure on the view at laryngoscopy. Anaesthesia 2005; 60: 41-47
Walton S. Auditing the application of cricoid pressure. Anaesthesia 2000; 55: 1025-1043
Meek T, Gittins N, Duggan JE. Cricoid pressure: knowledge and performance amongst anaesthetic assistants. Anaesthesia 1999; 54: 59-62
Herman NL, Carter B, Van Decar TK. Cricoid Pressure: Teaching the Recommended Level. Anaesth Analg 1996; 83: 859-863
Anaesthesia and learning difficulties
Dr. John Davies FRCA
Consultant Anaesthetist,
Royal Lancaster Infirmary, Lancaster LA1 4RP
Sir,
Your report of a publication that found an association between children’s risk of learning difficulty and early exposure to anaesthesia was both alarming and alarmist. (US study finds link between early anaesthesia and learning difficulties, JAP, Sept/Oct 2011, p115). You report the results as mere per centages, without the statistical analysis that no doubt is in the original paper, but which we cannot study as the paper will not be published until the November edition of Pediatrics. As you must know, association is not causation, and much more rigorous analysis is necessary than you have given us the opportunity to do. There should be and usually is an embargo on publishing such findings early, which you have breached. Please do not publish premature resumes of papers that include inadequate detail.
At the same time, I congratulate you and the authors on the paper warning of the possible association between aminoglycosides and botulinum toxin. (Watts JC, Mallik M. What is the risk of interaction between gentamicin and intravesical botulinum toxin injection? JAP, 2011, 4 ,122). Original and not pretending to do anything other than raise reasonable concern, it has already added to the practice of my department and our urology colleagues.
Dear Dr Davies,
Thank you for your letter. We’re sorry to hear you were not happy with the points put forward in one of the news stories, ‘US study finds link between early anaesthesia and learning difficulties’, featured in the previous issue of JAP.
At JAP our role is to bring the very latest news to our readers, and although we actively obey all embargo orders, we cannot disseminate each and every finding from a particular study’s results, discussion or conclusion, as we just don’t have the resources to analyse them all.
It was not our intention to print anything which could be interpreted at alarmist or inaccurate, the piece was a summary of the study as put forward by the researchers. The story was not embargoed and had already been published online in early October. To read the article in full visitpediatrics.aappublications.org/content/early/2011/09/28/peds.2011-0351.
Combination of Glidescope and fibre optic scope
Dr. Patrick Martens
Department of Anesthesiology, Intensive Care and Emergency Medicine, AZ St Jon Hospital Bruges, Belgium.
I’d like to respond to the article “Combination of Glidescope and fibreoptic scope - A rescue technique for failed awake tracheal intubation using Glidescope
Authors: Dr Narotham Burri1 and Dr Cyprian Mendonca2
As a videoscope like the Glidescope is designed to be inserted into the midline of the oropharynx I found it interesting to use it as a “left-handed laryngoscope” enabling me to insert the endotracheal tube with my left hand in the left corner of the patient’s mouth. This may be useful not only for left-handed anaesthetists but also for patients in whom the nature of the teeth or maxilla make it undesirable to exert pressure upon a particular area.
This may be due to loose or ill positioned teeth, or the presence of cysts or tumours of the maxilla, to which damage could be caused by pressure of the conventional laryngoscope.
