Author:

Dr A.I.J Brain  FFARCSI, FRCA(Hon)

Hon Consultant Anaesthetist

Royal Berkhire Hospital

Reading, UK

Title:

Use of the LMA in the Unstable Cervical Spine

Text:

The problem

General anaesthesia is frequently required in patients suspected or known to have instability of the cervical spine.  Many of these patients will also be emergency admissions to hospital and therefore must be presumed to be at risk from aspiration of gastric contents.  The same is true for victims of trauma involving the head and neck who require immediate airway management at the scene to treat airway obstruction associated with loss of consciousness.  The standard of care in managing these patients’ airways is to perform tracheal intubation, while simultaneously taking measures to reduce both the risk of inadvertent spinal cord damage associated with movement of the unstable spine and the risk of aspiration of gastric contents associated with loss of protective reflexes. 

It is unfortunate that the three standard procedures required to (1) visualise the glottis, (2) stabilise the neck and (3) prevent aspiration of regurgitated gastric contents respectively, all tend to compromise each other’s efficacy.  Visualisation of the glottis using a laryngoscope is facilitated by extending the head while flexing the neck.  This manoeuvre involves significant angular movement of the cervical vertebrae, even when such movement is limited by the presence of a rigid cervical collar, as a recent study showed [i] .  Using either a McCoy or a Macintosh laryngoscope, the authors demonstrated mean angular changes of 7.5 and 6.5 degrees between the first and third cervical vertebrae with each type of blade respectively in ten patients with normal necks.  The correct application of Cricoid Pressure necessarily involves significant force being transmitted to the cervical vertebrae. In addition, if applied at the recommended force of 44 Newtons, Cricoid Pressure has been shown to obstruct [ii] or even occlude [iii] the airway at cricoid level, making ventilation and fibreoptic intubation more difficult [iv] .

Avoidance of cervical vertebral displacement after injury involving the neck is clearly desirable in order to prevent further injury to the vulnerable spinal cord.  Any technique of airway management which threatens the integrity of the cord should be avoided.  An obvious solution is to achieve intubation using a fibreoptic scope.  A recent study [v] in 10 cadavers with destabilised C3 vertebrae using continuous lateral fluoroscopy compared cervical movement for six different airway management techniques.  Manual in-line stabilisation was applied for all techniques. The authors found the only technique associated with insignificant neck movement was fibrescope-guided nasal intubation.  Laryngoscopic intubation was associated with greater movement (2.6 +- 1.6mm, P < 0.0001) than standard LMA insertion or fibreoptic intubation through the ILMA (1.7 +-1.3mm). The Combitube produced the largest movement (3.2 +-1.6mm).  

However, like laryngoscopic intubation, fibreoptic techniques require skill, training and ongoing practice.  The procedure may be prolonged, making hypoxic episodes more likely. A French study [vi]   comparing fibreoptic intubation with ILMA intubation in 100 patients with predicted difficult airways found similar success rates and intubation times, but significantly more hypoxic episodes in the fibreoptic group (P<0.05).  In a comparitive study in normal patients, Joo [vii]   found that the time to intubation was faster using the ILMA alone than when the ILMA was used in combination with a fibrescope.

Clearly, in choosing an appropriate method of securing the airway in this situation, a judgement has to be made as to which is the greater risk – loss of the airway with the attendant risk of hypoxia, soiling of the lungs with aspirated vomit, or possible further damage to the spinal cord.  The standard LMA has an established role as an airway rescue device and can be inserted with a rigid collar in place [viii] .  However it cannot be regarded as offering protection against aspiration, in spite of recent cadaveric evidence suggesting that, in the absence of inadequate anesthesia, a correctly placed LMA can prevent reflux of gastric contents up to 40 cm H2O [ix] .  On the other hand, the risk of aspiration of gastric contents may have been overstated.  It is often forgotten that Mendelson’s original description of the syndrome [x] failed to demonstrate associated mortality, the only deaths in his series being secondary to obstruction from asphyxia due to blockage of the trachea with semi-solid vomit.  Patients developing pneumonitis secondary to liquid aspiration all survived.  A multcentre trial in  which the LMA was used for in-hospital cardio-pulmonary resuscitation [xi] documented one case of aspiration (0.4%), but this patient was one of the survivors.  Another study focussing on the incidence of aspiration in severe trauma found that aspiration of blood was much commoner than aspiration of vomit [xii] .  To prevent the aspiration of secretions or blood from the oropharynx, it appears to be unnecessary to resort to tracheal intubation.  A number of studies have shown that the less-invasive measure of LMA insertion is effective in shielding the larynx from contamination from above [xiii] ^, [xiv] ^, [xv] ^, [xvi] .  The gradual accumulation of anecdotal reports and studies on use of the LMA in emergency situations has led to its acceptance as an alternative to intubation in this arena by the European Resuscitation Council [xvii] and more recently the American Heart Association [xviii] .

Clearly, the use of the LMA outside hospital can no longer be said to be controversial. Whether the LMA should be used in the presence of cervical instability needs more careful evaluation.

The LMA in the Unstable Neck

The first reported use of the LMA in the unstable neck was in a letter to Anaesthesia in 1991 [xix] .  Although the standard LMA insertion technique requires positioning the neck in flexion with extension of the head, it was shown by Pennant et al [xx] that insertion was easily possible with the head and neck held in a rigid cervical collar.  However, the inventor felt that the standard LMA was not ideally suited to this situation, because most patients with an unstable neck were likely to require tracheal intubation and the standard LMA was not designed as an intubation guide, although it remained useful as an airway on its own [xxi] .

The Role of the Intubating LMA

 One of the major reasons for developing the Intubating LMA (ILMA) was to create a means of ventilating the patient while intubating the trachea without moving the head and neck from the neutral position [xxii] .  The design included a rigid, curved wide-bore metal tube mounted on the mask and extending round an arc of 128 º at a radius of 4cm, a shape derived from studying sagittal section nuclear magnetic resonance images of patients whose head and neck were held in a neutral position.  Using this tube as a guide, a tracheal tube would emerge at the correct angle to enter the glottis, provided a straight tube was used.  To facilitate device insertion and removal of the metal tube once intubation had been accomplished, a handle was attached to the proximal end.  An epiglottic elevating bar replaced the two bars across the mask aperture to eliminate the problem of the epiglottis or the bars obstructing the passage of the tube.  The device proved to have a success rate for intubation of about 95% [xxiii] ^, [xxiv] ^, [xxv] ^, [xxvi] and a number of case reports documented success when using it in difficult airways [xxvii] ^, [xxviii] ^, [xxix] ^, [xxx] . 

Studies using cervical collars or manual in-line stabilisation

However, evidence of efficacy of the ILMA in the unstable neck was not immediately forthcoming.  Several studies have been carried out in an effort to evaluate the ILMA’s potential by simulation.  Wakeling reported failure to intubate using the ILMA in 7 out of 10 patients with normal necks who were fitted with a rigid “Stiffneck” collar and had cricoid presure applied [xxxi] .  Asai, on the other hand, studying 25 patients, reported easier and faster placement of the ILMA than the LMA in the presence of manual in-line neck stabilisation [xxxii] and went on to show in a comparative study of 40 paralysed patients with manual in-line stabilisation but without cricoid pressure, that intubation through the ILMA was more successful (P <0.01), easier (P<0.001) and faster than intubation performed with a Macintosh laryngoscope and gum-elastic bougie [xxxiii] .  Another study [xxxiv] compared fibreoptic intubation with fibreoptic-aided ILMA intubation in 84 patients without neck pathology, half of whom were placed in the neutral position while half had manual in-line stabilisation.  Use of the ILMA produced equal success rates for both groups while use of the fibrescope alone was more successful in the neutral group than in the in-line stabilisation group. In addition, ILMA intubation was judged easier and the time to intubation was shorter. Yet another study [xxxv] . using cadavers looked at ease of placement of either the LMA or ILMA by 75 untrained personnel. The authors showed that insertion of the ILMA was faster than LMA insertion (P< 0.05) and produced more effective ventilation (P< 0.05).  Participants also reported a preference for the ILMA as they found it easier to use. Their intubation success was only 67% however and the cadavers were not fitted with rigid collars, nor was the neck manually stabilised.  A study [xxxvi]   by Avidan et al comparing the success rate of inexperienced operators with ILMA intubation and standard laryngoscopic intubation found no advantage using the ILMA .

Clinical Reports and Surveys

When we examine use of the ILMA in patients suspected of having or known to have unstable cervical spines however, the picture is somewhat different.  Schuschnig et al, reporting their first experience of using the ILMA in two patients with suspected cervical spine fracture, were not only successful at securing the airway by intubating through the device but also demonstrated, using lateral fluoroscopy, that the procedure could be accomplished without significant movement of the cervical spine [xxxvii] , providing at least some indication that Brimacombe’s suggestion, that  ILMA insertion  might displace unstable cervical bony fragments, was probably unfounded [xxxviii] .  The first patient was intubated in about 25 seconds, the second in about 35 seconds, as measured with a stopwatch from the time of insertion of the ILMA to the moment of tracheal tube cuff inflation.  Both patients were fitted with rigid cervical collars.  A valuable study from Japan [xxxix] addressed the utility of the ILMA in 40 patients requiring surgery for cervical spine pathology. Of these, 34  presented likely intubation problems, 32 had limited neck extension, 10 wore stabilising devices, and 4 had a cervical fracture or dislocation.  ILMA insertion was successful in all patients and all were intubated successfully through the ILMA, 24 at the first attempt. All 10 patients with stabilising devices were intubated blindly. Four patients required use of the fibreoptic scope. An important finding was the occurrence of severe pharyngeal oedema in three patients, which might be related to the fact that the ILMA was left in place after intubation had been accomplished, probably an unwise strategy in view of the rigid nature of the ILMA tube and Brimacombe’s demonstration in cadavers that the metal tube of the ILMA may cause higher pressures than the silicone tube of the LMA, though without producing significant movement of unstable vertebrae [xl] .  The authors had previously used a prototype ILMA and a polyvinylchloride tracheal tube in a less successful pilot study and they comment that the dedicated silicone tracheal tube with mid-line bevel designed for use with the ILMA produced a more anatomical alignment with the glottis and may have contributed to their success in this study.  This has been independently confirmed in a comparative study of the two types of tube by Murashima et al [xli] .

The only out-of-hospital study [xlii] on use of the ILMA in accident victims is from Barcelona, where doctors forming part of an ambulance service used the ILMA for a period of one year whenever intubation failed using laryngoscopy.  They collected 12 such cases, all of which were ventilated successfully through the device while 8 out of 9 attempted intubations were carried out successfully at the scene of the accident.  Probably the most important in-hospital study on use of the ILMA to intubate patients with cervical spine pathology is a multicentre study from America by Ferson et al, currently awaiting publication.  The authors describe use of the ILMA in 257 difficult airway situations, amongst which they document 84 cases in which the ILMA was successfully used to facilitate intubation of patients with immobilised necks.  It seems likely that this publication will provide sufficient data to enable guidelines to be established with respect to appropriate ILMA use. The authors used both blind and fibrescopic-aided intubation through the ILMA.  Others have investigated the use of the Light-wand instead of the fibrescope to assist ILMA-guided intubation, with encouraging results [xliii] ^, [xliv] .  It may be of some relevance to note that the authors of the American study all underwent training in ILMA use from the inventor prior to commencing the study.

Conclusion

From the available literature on the use of supra-glottic airway devices in patients presenting with instability of the cervical spine, it is at present still difficult to provide hard and fast guidelines.  However, the interest in the use of the ILMA in this arena shows no sign of abating and it is already clear that this approach to intubating the patient with neck pathology is better than using the standard LMA and offers at least comparable advantages to established techniques.  Much still remains to be done, not only in terms of investigation, but also in establishing appropriate teaching to optimise efficacy.  Finally, the inventor is conscious of the need to develop a paediatric range of ILMA devices, for which preliminary data has already been obtained [xlv] .

References