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From the Department of Anaesthesia, Royal United Hospital, Combe Park, Bath, United Kingdom.
Address correspondence to: Dr. T. M. Cook, Dept of Anaesthesia, Royal United Hospital, Combe Park, Bath, BA1 3NG, UK. Phone: +44 1225 825056; Fax: +44 1225 825061; E-mail: timcook{at}ukgateway.net
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Abstract |
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Clinical findings: The first case involved a 31-yr-old primigravida presenting for emergency Cesarean section for severe fetal distress. She had a grade 3 larynx and airway edema was observed during laryngoscopy. Attempts with a McCoy blade and gum elastic bougie failed to secure the airway. A size 4 PLMA was inserted with good airway control and surgery proceeded uneventfully. The second case involved a 51-yr-old man presenting for appendectomy. Following failed attempts at intubation, a size 5 PLMA was succesful in securing his airway and surgery proceeded uneventfully.
Conclusions: The correctly placed PLMA has potential advantages over the cLMA for airway rescue in the circumstance of failed emergency intubation in a patient with a potentially full stomach. In the two cases reported, the PLMA provided effective rescue of the airway.
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Clinical features |
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Case #2
A 51-yr-old man presented for emergency appendectomy. He weighed 80 kg and was 152 cm tall (body mass index 35 kg•m–2). He was a brittle asthmatic requiring prednisolone 25 mg daily to control his asthma. He had a beard, a full set of teeth, a short neck and his airway was classified Mallampati class III.5,6 A possible difficult laryngoscopy was predicted. Following pre-oxygenation and RSI with cricoid pressure applied (single-handed from the patient’s right with a force of approximately 30N) laryngoscopic view was grade 3,7 and was not improved by airway manipulation or use of a McCoy blade. After two failed attempts to intubate, a classic laryngeal mask (cLMA; Intavent Orthofix, Maidenhead, UK) was inserted, but controlled ventilation of the lungs was not possible due to airway leak and oxygen saturation fell. It was decided to wake the patient and perform awake fibreoptic intubation. However emergence was complicated by severe laryngospasm and further oxygen desaturation, which required additional muscle relaxation. An attempt to pass a 6-mm cuffed tracheal tube through the cLMA into the trachea failed. A size 5 PLMA was inserted (by an anesthesiologist with 20 prior uses). A gastric tube was passed and minimal gastric aspirate appeared. The PLMA enabled ventilation of the lungs to normocapnia without a leak. In view of the potential difficulties of further anesthetic interventions in this patient with reactive airways disease, a decision was made to continue with surgery which proceeded without complication. The patient’s recovery was uneventful.
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Discussion |
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When rescuing the airway after failed RSI, controlled ventilation of the lungs will be required and intragastric volume is likely to be increased. The physionomy of a patient in whom tracheal intubation and mask ventilation have failed may make lung ventilation difficult. Langeron reported a marked increase in the incidence of difficult mask ventilation in patients who were impossible to intubate compared to those who were not.14 The use of the cLMA during controlled ventilation is controversial and the airway seal is below 20 cm H2O in 50% of cases.15 In addition, the risk of gastric inflation increases as airway pressure rises16 and the cLMA is generally regarded as offering no protection against aspiration of regurgitated stomach contents.17 All these factors make it an imperfect rescue device.
The PLMA has potential advantages over the cLMA in these circumstances. It is designed specifically for use during controlled ventilation. Correctly placed, it enables functional separation of the gastrointestinal and respiratory tracts1 and provides a greater than 50% better airway seal than the cLMA.1,15,18,19 The drain tube assists in confirmation of correct placement,1 reduces the likelihood of gastric inflation, enables drainage of the stomach and provides an ‘escape route’ if regurgitation should occur.1 These potential advantages must be balanced against potential disadvantages of the PLMA. Most studies report that the PLMA takes longer to insert than a cLMA and that first time insertion rates are lower (84% PLMA vs 91% cLMA).15,18,19 However, clinicians who have more experience with cLMA insertion generally performed these studies. A recent study of nurses naive to insertion of all laryngeal masks reported equivalent insertion performance with the cLMA and PLMA.20 Partial airway obstruction may occur when using the PLMA21 but is rarely reported outside this one study, and has not been reported in randomized controlled trails. The incidence of obstruction with the cLMA and PLMA is not known. In failed intubation where there is minimal risk of aspiration, the cLMA should probably be the first choice rescue device. However where RSI is undertaken, a high risk of aspiration might be assumed and there is a stronger argument for considering use of the PLMA.
Finally, the PLMA is not a substitute for a tracheal tube and increased protection of the airway occurs only when it is correctly positioned. Pulmonary aspiration has been reported during use of a PLMA which was considered to be placed correctly.22 Further work is needed to determine the extent to which the PLMA protects the airway in the broader clinical setting.
In both cases reported here, cricoid pressure was briefly released to enable passage of the PLMA. The need for cricoid pressure release has not been studied, but both the cLMA and intubating laryngeal mask require reduction or release of cricoid pressure to enable correct placement.23,24 The design of the PLMA, which has a bulkier leading edge than other laryngeal masks, makes the release of cricoid pressure during insertion prudent. When ventilation is difficult and the patient is hypoxic, maintenance of cricoid pressure is a lower priority than prompt establishment of a patent airway and re-oxygenation.
In both cases described, we used either a digital insertion technique or the introducer tool supplied with the PLMA. Recently Brimacombe has reported that the most reliable technique for insertion of the PLMA involves insertion of a gum elastic bougie in the oesophagus and guiding the PLMA over the bougie via the drain tube. In two studies this technique resulted in 100% first-time insertion and the technique intrinsically eliminates the possibility of the PLMA tip folding over.25,26 This insertion technique should be considered in circumstances where accurate first time insertion is essential.
In is notable that four cases (two reported here and two elsewhere)3,4 occurred in one hospital over a period f a little over one year. The cases were managed by several trainee anesthesiologists. The PLMA is a routine tool for elective cases in our hospital and its use is taught to all trainees. The PLMA has been part of our difficult intubation cart for over one year. It is likely that theoretical knowledge and practical familiarity with the PLMA meant that trainees were confident in using the PLMA during these cases.
Our management of these cases might be criticized. In particular the decision to proceed with general anesthesia when the possibility of difficult laryngoscopy was predicted is open to debate. However a class III Mallampati view has been reported to have a positive predictive value of difficult intubation as low as 2%27 and UK and Canadian management of these cases might differ. Importantly, the aim of our report is to consider the role of the PLMA as a rescue device after failed RSI rather than to discuss the relative merits of RSI or awake fibreoptic intubation. Similarly, opinions may differ as to the appropriateness of continuing with surgery once the airway was established.
On the basis of the available evidence, we believe the PLMA has advantages over the cLMA in the circumstance of failed emergency intubation in a patient with a potentially full stomach. We believe the PLMA should be considered in these circumstances, especially by those experienced in its use.
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Footnotes |
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Potential conflict of interest: Dr. T. M. Cook has received a small honorarium from Intavent Orthofix for addressing a company meeting.
Assessed April 7, 2004. Accepted for publication June 22, 2004. Final revision accepted February 8, 2005.
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2 Ovassapian A. Management of failed intubation in a septic patient (Letter). Br J Anaesth 2003; 91; 154–5.
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