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LETTERS TO THE EDITOR

Sore Throat and Pharyngeal Trauma After Extratracheal Airway Placement: Does the Literature Help Practitioners?

Department of Anesthesiology University of Milan IRCCS H. San Raffaele 20132 Milan, Italy

Brimacombe et al. (1) recently demonstrated that the laryngeal mask (LMA) has a higher success rate and airway stability, and is associated with less pharyngeal trauma and postoperative sore throat, than the cuffed oropharyngeal airway (COPA) (Study 1) whereas results of a previous study (2) reported more frequent blood and postoperative sore throats after LMA than COPA (Study 2). Information from the literature should be always balanced against daily practice, but the practitioner may be perplexed after reading opposite results published at nearly the same time by the same research group. It seems that the COPA would be more difficult to place and require more airway manipulation than LMA, but are these disadvantages balanced by less pharyngeal trauma, or are they further enhanced by the risk of higher postoperative sore throat? In Study 2, they evaluated a large number of COPA placements in different institutions and the severity of sore throat was not assessed, whereas in Study 1, a small number of COPA placements were evaluated in one institution only, and the overwhelming number of sore throats were of mild severity. Moreover, if data from the two studies are pooled together and the incidence of sore throat compared using the ² test, immediate postoperative sore throat is more frequent after LMA than COPA (Table 1). Further, Nakata et al. (3) recently demonstrated that the anesthetic exposure associated with acceptable conditions for COPA placement was shorter than that for LMA, which suggests that COPA insertion could be less stimulating than LMA insertion. However, no one could answer this simple and humble question better than the authors themselves.

1. Brimacombe JR, Brimacombe JC, Berry AM, et al. A comparison of the laryngeal mask airway and cuffed oropharyngeal airway in anesthetized adult patients. Anesth Analg 1998;87:147–52.[Abstract/Free Full Text]
2. Greensberg RS, Brimacombe J, Berry A, et al. A randomized controlled trial comparing the cuffed oropharyngeal airway and the laryngeal mask airway in spontaneously breathing anesthetized adults. Anesthesiology 1998;88:970–7.[Web of Science][Medline]
3. Nakata Y, Goto T, Saito H, et al. The placement of the cuffed oropharyngeal airway with sevoflurane in adults a comparison with the laryngeal mask airway. Anesth Analg 1998;87:143–6.[Abstract/Free Full Text]

Response

Cairns Base Hospital Cairns, Australia

A. M. Berry, MB, ChB, FRCA

Nambour General Hospital Nambour, Australia

C. Keller, MD

Leopold-Franzens University Innsbruck, Austria

Thank you for the opportunity to reply to Drs. Casati and Casaletti. Their main concern seems to be that two trials comparing the laryngeal mask airway (LMA) and cuffed oropharyngeal airway (COPA) produced differing results with respect to pharyngolaryngeal morbidity: the multicenter trial (1) showed that the COPA had a lower incidence, and the single-center trial (2) showed a lower incidence with the LMA. Before suggesting reasons for these differences, we would like to clarify that these studies were only partially conducted by the same research group and that the investigators involved in the single-center study (2) contributed only one third of the cases to the multicenter study (1). In addition, the two trials were not methodologically identical. A notable difference is that postoperative data from the single-center trial were double-blinded and graded, but those from the multicenter trial were unblinded and ungraded. Both studies showed a higher incidence of jaw and neck pain with the COPA, and most other results were similar.

We consider that the differences in pharyngolaryngeal morbidity between trials probably reflects variations in user skill with oropharyngeal airway devices. The multicenter trial involved 62 investigators with variable skill, whereas the single-center trial involved 4 investigators with high skill. Placement of the COPA requires less skill than the LMA, and we postulate that a skilled COPA user will only have a slightly lower trauma rate compared with an unskilled user, whereas a skilled LMA user will have a much lower trauma rate compared with an unskilled user. Thus, a high level of skill favors a lower incidence of pharyngolaryngeal morbidity with the LMA. A further explanation may be related to differences in intracuff pressure. The intracuff pressures for the COPA were similar for the multicenter (93 cm H₂O) and the single-center trial (72 cm H₂O) but were considerably lower for the LMA in the single-center trial (129 vs 59 cm H₂O). We recently studied the pressures exerted by the LMA and COPA against the oropharyngeal mucosa using millimeter-sized microchip pressure transducers and showed that, for a given airway sealing pressure, mucosal pressure is higher for the COPA (3). Our data suggests that the mean (95% confidence interval) overall mucosal pressure for the COPA at 93 and 72 cm H₂O intracuff pressure is 23 (13–30) and 20 (10–30) cm H₂O, respectively; and the overall mucosal pressure for the LMA at 129 and 59 cm H₂O intracuff pressure is 12 (10–13) and 6 (6–7) cm H₂O, respectively. Thus, there may have been a significant reduction in mucosal pressure for the LMA, but not for the COPA, between trials.

We conclude that a higher level of investigator skill and lower intracuff pressures for the LMA may have favored a reduction pharyngolaryngeal morbidity with the LMA in the single-center trial. Further comparative work is needed to resolve this and other issues, such as the depth of anesthesia required for placement (4,5), for which recent studies have provided conflicting results.

References

1. Greenberg RS, Brimacombe J, Berry A, et al. A randomized controlled trial comparing the cuffed oropharyngeal airway and the laryngeal mask airway in spontaneously breathing anesthetized adults. Anesthesiology 1998;88:970–7.
2. Brimacombe JR, Brimacombe JC, Berry A, et al. A comparison of the laryngeal mask airway and cuffed oropharyngeal airway in adult patients. Anesth Analg 1998; 87:147–52.
3. Keller C, Brimacombe J. Mucosal pressures for the cuffed oropharyngeal airway versus the laryngeal mask airway. Br J Anaesth. In press.
4. Nakata Y, Goto T, Saito H, et al. The placement of the cuffed oropharyngeal airway with sevoflurane in adults a comparison with the laryngeal mask airway. Anesth Analg 1998;87:143–6.
5. Versichelen L, Struys M, Crombez E, et al. Haemodynamic and electroencephalographic response to insertion of a cuffed oropharyngeal airway a comparison with the laryngeal mask airway. Br J Anaesth 1998;81:393–7.[Abstract/Free Full Text]

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