Use of the ProSealTM laryngeal mask airway for airway maintenance during emergency Caesarean section after failed intubation

A. Bullingham1, T. M. Cook2, R. Awan2 and J. P. Nolan2

1 Sydney, Australia 2 Bath, UK

{dagger}LMA® is the property of Intavent Ltd.

Editor—I read with interest the case report1 regarding the use of the ProSealTM laryngeal mask airway (PLMA) (Intavent Orthofix, Maidenhead, UK) in a patient undergoing an emergency lower segment Caesarean section (LSCS). I think this case illustrates the urgent need for review of the recommendation that only in the most urgent cases should an LSCS be continued after a failed intubation when the airway has been secured with an LMA®.{dagger} My experience with failed intubation is that if good airway control can be secured with either a classic LMA (cLMA) or a PLMA, the balance of risks favours proceeding with the LSCS. There is some supporting evidence in the form of the study by Han and colleagues2 of the use of the cLMA in 1067 patients undergoing LSCS. The PLMA has added weight to this argument in that it is designed (although not proven) to provide superior airway protection over the cLMA.3 To provide further evidence, my colleagues and I have obtained ethics committee approval for a cohort-controlled study involving the use of the PLMA in elective LSCS in 100 patients. We hope to complete this within the next 12 months. Further information about this study can be obtained from the Blacktown anaesthetic department website (www.badgasser.com).

A. Bullingham

Sydney, Australia

Editor—We thank Dr Bullingham for his interest in our case report. It is important to note that in the case we reported,1 not only did intubation fail, but ventilation of the lungs was difficult and hypoxia developed. Dr Bullingham’s comments raise two different questions. First, after rescuing an airway during Caesarean section with a supraglottic airway, is it appropriate to complete the operation? Second, in these circumstances, does the PLMA offer advantages over the cLMA?

Both questions are controversial and a definitive answer is probably not possible. In practice, it is impossible to prove the safety of use of a supraglottic airway after failed rapid sequence induction, as the incidence of aspiration, even in these circumstances, is very low. Successful use of a supraglottic device in the one case we report,1 or the several cases Dr Bullingham implies he has dealt with, does not mean that the technique is safe.

Dr Bullingham refers to the study of Han and colleagues2 and to his own planned study as sources of data to support the safety of maintaining the airway with a cLMA or PLMA after failed rapid sequence induction. Despite the potential interest of both studies they demonstrate efficacy, not safety, of the airway devices. Dr Han’s large study reported successful airway maintenance with the cLMA in elective LSCS in over 99% of cases.2 Failure of the technique occurred in 0.7%, and airway leak or partial obstruction in 21%. The absence of major complications in 1067 patients provides some reassurance of safety. Even if Dr Bullingham’s study were to show effective airway maintenance with the PLMA, and no complications in 100 patients, this would not be adequate, on its own, to conclude that the technique is safe.

There are two important reasons for this. First, in a study of n subjects, if an adverse event does not occur, the upper limit of the 95% confidence interval for the incidence of that event is approximately 3/n.4 Therefore in Han’s study we can conclude that the incidence of pulmonary aspiration with his technique has a confidence interval of approximately 1 in 355. In Dr Bullingham’s study, assuming no adverse airway events occur, the upper limit of this confidence interval will be 1 in 33.

The second point is that both studies examine the use of the cLMA/PLMA as a primary airway in elective surgery. Neither study addresses management of failed rapid sequence induction. The patient undergoing elective LSCS is routinely starved, has drugs given to raise gastric pH and reduce volume, and patients are not in pain before or during induction of anaesthesia. Obese patients and those with reflux were excluded from Han’s study. While rapid sequence induction is widely used for elective LSCS, it is not universal,5 and the necessity for its routine use has been questioned.6 In contrast, during emergency LSCS many of the above factors are present and all these patients must be considered at high risk of regurgitation. Safety data taken from a study of primary airway management of patients undergoing elective LSCS cannot be extrapolated to rescue airway management during emergency cases.

Similarly, difficult questions about the safety of the use of the cLMA or PLMA during controlled ventilation,7 or during laparoscopic surgery,8 have been the subject of editorials, on either side of the Atlantic, in the last 2 years. The difficulty in proving safety (or absence of harm) in these clinical scenarios is similar to the difficulty in conclusively comparing the relative safety of the cLMA and PLMA. Based on normal power calculations, prospective comparative trials addressing either of these questions require more than 2 million patients and are therefore impractical.9

In our opinion, for the reasons stated in the case report,1 the PLMA does have clinically important advantages over the cLMA when used in a patient with a full stomach. These advantages include improved airway seal, reduced gastric inflation, and the ability to vent oesophageal gases/fluid and drain the stomach. Data supporting the greater efficacy of the PLMA in protecting the airway from pulmonary aspiration comes from design features, laboratory studies, or are based on extrapolation of surrogate measures from clinical studies. Like the questions referred to above, this question cannot be answered by a randomized controlled trial because an adequately powered study would be impractically large. Therefore the data we now have from laboratory and surrogate measures is the best evidence currently available. There is little evidence to suggest that the cLMA has any significant capacity to protect from pulmonary aspiration if gastric regurgitation occurs and the weight of evidence suggests that the PLMA does increase the margin of safety. The probable improved level of protection offered by the PLMA must be balanced against the fact that the PLMA takes a few seconds more than the cLMA to insert, has lower first time insertion rates,10 and experience with the PLMA is generally less than with the cLMA.

In the event of a rare but life-threatening emergency complication, such as failed rapid sequence induction, we must act quickly and decisively. When ventilation of the lungs is possible, in most cases it would seem prudent to wake the patient unless surgical urgency precludes this option. However, in the case of failed rapid sequence induction with difficult airway maintenance or difficult ventilation, an airway must be secured rapidly or life-threatening hypoxia is inevitable.11 12 In our view, there is now enough evidence to support the early use of the PLMA in this circumstance, in those experienced with its use.

T. M. Cook

R. Awan

J. P. Nolan

Bath, UK

References

1 Awan R, Nolan JP, Cook TM. Use of the ProSealTM laryngeal mask airway for airway maintenance during emergency Caesarean section after failed intubation. Br J Anaesth 2004; 92: 144–6[Abstract/Free Full Text]

2 Han TH, Brimacombe J, Lee EJ, Yang HS. The laryngeal mask airway is effective (and probably safe) in selected healthy parturients for elective Caesarean section: a prospective study of 1067 cases. Can J Anaesth 2001; 48: 1117–21[Abstract/Free Full Text]

3 Brian AJ, Verghese C, Strube PJ. The LMA ‘Proseal’ a laryngeal mask with an oesophageal vent. Br J Anaesth 2000; 84: 650–4[Abstract]

4 Hanley JA, Lippman-Hand A. If nothing goes wrong, is everything all right? Interpreting zero numerators. JAMA 1983; 249; 1743–5[CrossRef][ISI][Medline]

5 Thwaites AJ, Rice CP, Smith I. Rapid sequence induction: a questionnaire survey of its routine conduct and continued management during a failed intubation. Anaesthesia 1999; 54: 376–81[CrossRef][ISI][Medline]

6 Benhamou D. Cricoid pressure in unnecessary in obstetric general anaesthesia. Int J Obstet Anaesth 1995; 30: 3

7 Sidaras G, Hunter JM. Is it safe to artificially ventilate a paralysed patient through the laryngeal mask? The jury is still out. Br J Anaesth 2001; 86: 749–53[Free Full Text]

8 Cooper RM. The LMA, laparoscopic surgery and the obese patient—can vs should. Can J Anaesth 2003; 50: 5–10[Free Full Text]

9 Cook TM. cLMA and PLMA for laparoscopic surgery. Can J Anaesth 2003; 50: 965–6[Free Full Text]

10 Cook TM, Nolan JP, Verghese C, et al. Randomized controlled trial of the ProSealTM with the classic LMA in unparalysed patients. Br J Anaesth 2002; 88: 527–33[Abstract/Free Full Text]

11 Benumof JL, Dagg R, Benumof R. Critical hemoglobin desaturation will occur before return to an unparalyzed state following 1 mg/kg intravenous succinylcholine. Anesthesiology 1997; 87: 979–82[CrossRef][ISI][Medline]

12 Heier T, Feiner JR, Lin J, Brown R, Caldwell JE. Hemoglobin desaturation after succinylcholine-induced apnea: a study of the recovery of spontaneous ventilation in healthy volunteers. Anesthesiology 2001; 94: 754–9[CrossRef][ISI][Medline]