Editorial I
Variant Creutzfeldt±Jakob disease and disposable anaesthetic equipmentÐ balancing the risks
New variant Creutzfeldt±Jakob disease (vCJD) was ®rst reported in the UK in 1996.1By August 2002, a total of 125 cases of de®nite or probable vCJD had been identi®ed in the UK, six in France, one in Italy, one in Florida and one in the Republic of Ireland.2 vCJD is one of a class of diseases known as transmissible spongiform encephalopathies (TSEs), which include scrapie in sheep and bovine spongi- form encephalopathy (BSE) in cattle. TSEs are fatal degenerative brain diseases that are characterized by rapidly progressive dementia and a spongy macroscopic appearance of brain tissue. The infective agents appear to be misshapen prion proteins. It is thought that the misshapen prion proteins (PrPSC) can cause further distortion of the normal form of the prion protein (PrPC), leading to a chain reaction that propagates the disease and generates new infectious material.3 This infectious agent is resistant to methods of sterilization currently used, including autoclaving (121°C for 15 min), high-dose ionizing radiation, and ultraviolet radiation.5 Creutzfeldt±Jakob disease (CJD) occurs in the UK in three other forms: a sporadic form of unknown cause (responsible for 73% of cases since 1990), a familial form associated with a single gene mutation, and an iatrogenic form where infection is associated with contamination from a medical procedure. In the UK, iatrogenic CJD has resulted exclusively from treatment with human-derived pituitary growth hormone or dura mater grafts.2However, transmis- sion has occurred following use of a medical electrode that had been previously inserted into the brain of a patient with CJD and was subsequently inserted into the brain of another patient.5 This cross-infection occurred despite routine cleaning and sterilization of the electrode between uses.
vCJD differs from sporadic CJD in a number of important ways.6It typically affects younger people (average age of death 29 yr, compared with 65 yr for sporadic CJD). The early symptoms are mainly psychiatric or behavioural (particularly depression), and the disease duration is slightly longer (median of 14 months between onset and death).
However, whilst in both sporadic CJD and BSE, PRPSCcan be detected only in neural or ocular tissue, in vCJD the distinct type-4 PrPSChas also been identi®ed in lymphoid tissue. Prion expression in lymphoreticular tissue appears to occur from a very early stage in the disease, with detection
in tonsil, spleen, lymph nodes7 and appendix.8 This lymphoid tissue is thought to be highly infectious, having an infectivity of 106ID50g±1(i.e. 1 mg of tissue has a 50%
chance of causing an infection).9for BSE, the oral ID50is approximately 1 g of neural tissue. vCJD therefore creates a new and signi®cant risk to patients undergoing surgical procedures. The unique dif®culty with this illness is that contamination can occur in procedures that do not involve neural or ocular tissue. Almost all general anaesthesia performed in the UK today involves the use of some form of airway device. Whilst disposable tracheal tubes have been widely used for at least 15 yr, the majority of laryngoscopes are reused between patients, as are laryngeal mask airways (LMA²). The presence of lymphoid tonsil tissue in the oropharynx means that all anaesthetic airway equipment is at risk of contamination and hence of providing a vector for transmission of vCJD.
The government's Spongiform Encephalopathy Advisory Committee (SEAC) advised that rigorous implementation of washing, decontamination and general hygiene procedures were key steps in minimizing the risk of transmission of vCJD via surgical instruments. In January 2001, the Department of Health announced its strategy for minimizing the risk, which included providing £200 million to improve decontamination services.10However, the only completely safe way to prevent the transmission of vCJD via this route is to use disposable (single-use) instruments. The SEAC further advised that, where discrete procedures could be identi®ed as suitable, and provided patient safety would not be compromised, single-use equipment should be con- sidered. Adenotonsillectomy was one such procedure and was used as a pilot to test the practicality of this approach. It was considered to be suitable because the patients involved were young (median age 9 yr), with a postoperative life expectancy greater than 65 years. Furthermore, the oper- ation required only a relatively limited number of instruments that were reused frequently. Disposable tonsill- ectomy equipment, along with disposable anaesthetic equipment, was introduced into use in the summer of 2001. Soon after the introduction of this equipment, the
²LMAâis the property of Intavent Limited.
``I would have everie man write what he knowes and no more.''ÐMontaigne
BRITISH JOURNAL OF ANAESTHESIA
Volume 90, Number 1, January 2003
Ó
The Board of Management and Trustees of the British Journal of Anaesthesia 2003Medical Devices Agency began to receive an increased number of reports of adverse incidents following tonsil and adenoid surgery. These continued to be received following two hazard notices, and were attributed to a range of factors, including the diathermy forceps, the general single-use instruments set, and a surgical technique involving diathermy dissection. Morbidity included an increased incidence of bleeding, and one death was associated with the use of single-use equipment. As a result, the Department of Health directive was reversed in December 2001.11The Royal College of Anaesthetists subsequently issued a press release con®rming that this return to reusable equipment also applied to anaesthetic equipment, including the LMA and laryngoscopes.12 However, in a rather bizarre volte- face, the Department of Health subsequently decided that this change did not apply to anaesthetic equipment used during tonsillectomy, and that all anaesthetic equipment placed in the mouth or respiratory tract during tonsillectomy should be disposable or covered by a disposable protective sheath.13We are thus left with the present state of affairs in which surgical equipment used during an operation may be reused, whereas anaesthetic equipment placed in the same mouth during the same operation must be disposable.
In order to ascertain appropriate policies with respect to disposable equipment, a number of issues must be con- sidered. First, the risk associated with continued use of reusable equipment must be ascertained. In order to evaluate this we must consider the number of infective (i.e.
PrPSC-expressing) patients, the infectivity of the tissues involved in the procedures, the ability of decontamination and sterilization procedures to reduce the mass of infective tissue present on equipment used in subsequent procedures, and the transfer of this lymphoid tissue directly onto the lymphoid tissue of subsequent patients.14 If we assume a moderately pessimistic 60 000 (0.1%) infected patients and 10 mg of tissue on the (single) reused instrument, then if full decontamination and sterilization procedures (as for surgi- cal instruments) are performed, we might expect cross- infection in 1±10 per 100 000 anaesthetics involving reused airway equipment. However, if decontamination alone is used then, because a smaller proportion of the infective tissue is removed from the instrument, cross-infection might be expected to increase to a completely unacceptable 1 per 1000.
In this edition of the British Journal of Anaesthesia, Twigg and colleagues15 present data evaluating the per- formance of a number of single-use laryngoscopes. They demonstrated that, in their simulator model, the use of either single-use laryngoscopes or disposable sheaths over a Macintosh laryngoscope blade led to signi®cant increases in both the Cormack and Lehane grading and POGO scores when compared with a standard Macintosh laryngoscope.
Furthermore, potential differences between the various models of single-use laryngoscope blade could be identi®ed in their study, and whilst it was not their objective to assess the blades relative to one another, their results suggest that it
may be possible to identify the best single-use laryngoscope blade.
In assessing this study, it is important to consider whether the use of a simulator is valid. This simulator allowed the introduction of neck rigidity and pharyngeal swelling to increase the dif®culty of glottic visualization. It is likely that the use of simulation equipment designed for intubation training should be a reasonable model of intubation.
However, whether it is an accurate model of a dif®cult intubation is not so certain and hence may be open to criticism. Importantly, the model allows a substantial increase in the likelihood of intubation dif®culty, and hence increases the power of a study designed to assess intubation equipment. A large Canadian audit16 of over 18 000 direct laryngoscopies identi®ed dif®cult intubation in only 1.8% of cases. If we were to assume that a doubling of the incidence of dif®cult intubation was signi®cant, then a controlled clinical study would require 3300 patients. Thus, it is not surprising that the previously published work on single-use laryngoscopes did not demonstrate any increase in the incidence of dif®cult intubation.17 Indeed, this crossover study of 100 patients would have required an eightfold increase in the incidence of dif®cult intubation to demonstrate a difference.
The importance of Twigg and colleagues' study15is that it demonstrates a potential increase in the risk of dif®cult intubation in patients undergoing surgery where intubation is performed using either single-use laryngoscopes or plastic sheaths over reusable blades. Of course, the patient's life is only at risk when intubation is dif®cult if it is also dif®cult to maintain the airway. The incidence of failed intubation and associated loss of the airway is dif®cult to de®ne. In the Canadian audit,16intubation failed in 54 (0.3%) patients. Of these, two required tracheostomy, and anaesthesia was discontinued in 29, requiring cancellation of proposed surgery in 10 (5.5 per 10 000 cases). This incidence of failure or life-threatening sequelae is comparable with 16/
198 000 identi®ed in a prospective French study.18 One might hypothesize that the 1.5-fold increase in dif®cult (Cormack and Lehane grade III or IV) intubation in the dif®cult airway might be associated with an increase in life-threatening sequelae of approximately 2 per 10 000 intubations. This therefore suggests that the use of dispos- able equipment for anaesthesia goes against the original SEAC recommendation that single-use equipment should be used in suitable procedures where patient safety would not be compromised. The Department of Health should there- fore be encouraged to review the present directive on the use of only disposable anaesthetic equipment for patients undergoing tonsillectomy. However, whilst this is an appropriate short-term response it does not deal with the longer-term issues of how we should modify our anaesthetic practice in order to minimize the risk to patients. It is evident that the current approach to cleaning of anaesthetic equipment in many hospitals is inadequate; indeed 34% of senior operating department practitioners would not be
Editorial I
2
prepared to put a laryngoscope cleaned in their units into their own mouths.19The presence of proteinaceous material has been identi®ed in 20/20 used (and autoclaved) LMAs, and 50/61 laryngoscope blades after routine cleaning,20 demonstrating that the current practice would not be adequate to prevent the substantial numbers of cross- infections occurring in patients undergoing anaesthesia with reusable anaesthetic equipment.
The Working Party of the Association of Anaesthetists of Great Britain and Ireland is currently investigating methods to reduce the risk of cross-infection in patients undergoing anaesthesia, ideally by single-use equipment where prac- tical. They have also identi®ed the need for effective decontamination and sterilization processes in order to minimize risk (personal communication, Peter Wallace, July 2002). This approach would allow the use of reusable equipment whilst reducing the risk to levels that are probably acceptable, but it would mean that anaesthetic equipment would have to be tracked in the same way that will soon be expected for surgical instruments.21 This process allows identi®cation of the instruments used on a patient subsequently found to be infectious, and of the patients who have been put at risk. The process involves recording both the details of the instruments used on each patient and the patients that each instrument is used on. The administrative rami®cations of this are obvious when these instruments are used not only in the relatively controlled surgical environment but also in critical care, accident and emergency departments and other wards.
The alternative is to identify single-use equipment that functions adequately and therefore does not increase the risk to patients. There will be a cost implication in adopting this equipment for all airway manipulation, but this may be reasonable in preventing what is a particularly unpleasant form of death, occurring mostly in younger people.
M. C. Blunt*
K. R. Burchett
Department of Anaesthesia and Critical Care Queen Elizabeth Hospital
Gayton Road
Kings Lynn PE30 4ET
UK*E-mail: [email protected]
References
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DOI: 10.1093/bja/aeg006 Editorial I
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