A randomized trial of three lubrication strategies on sore throat after insertion of the LMA® Classic™ supraglottic airway

  • William P. S. McKayEmail author
  • Jurgen Maslany
  • Edward P. Schubert
To the Editor,

Patient characteristics and outcome data


Control group

Muko group

Lidocaine jelly group

P values

Age (yr)

46 (15)

40 (15)

47 (15)


Gender (M|F)





Height (cm)

165 (8)

167 (8)

162 (7)


Weight (kg)

80 (15)

77 (15)

74 (16)







Throat pain day 0

0 [0-0.5]

(0 to 0)

0 [0-1]

(0 to 0)

0 [0-0]

(0 to 0)


Throat pain day 1

0 [0-0.9]

(0 to 0)

0 [0-0.5]

(0 to 0)

0 [0-0]

(0 to 0)



0 [0-0]

(0 to 0)

0 [0-0]

(0 to 0)

0 [0-0]

(0 to 0)


Insertion attempts

One: 55

Two: 5

Three: 0

One: 62

Two: 9

Three: 1

One: 52

Two: 4

Three: 1

Abandoned: 1


Range of cough scores in PACU

0 to 3

0 to 2

0 to 2


ASA = American Society of Anesthesiologists; PACU = postanesthesia care unit

Mean (standard deviation) if normally distributed; median [interquartile range] (95% confidence interval for median) if non-normally distributed

The laryngeal mask supraglottic airway (SGA) is commonly used in anesthesiology and is often lubricated for easy insertion. We studied sore throat (primary outcome), cough, and laryngospasm after insertion of the LMA® Classic™ (Teleflex Inc.; Morrisville, NC, USA) comparing three lubricating strategies: water-soluble medical lubricant (M) (Muko™; Source Medical, Mississauga ON, Canada) or 2% lidocaine jelly (L) (Lidodan™; Odan Laboratories, Montreal QC, Canada) vs no lubricant control (C).

After institutional ethical approval,1 consenting American Society of Anesthesiologists physical status I-II adult patients having elective surgery where an LMA was planned were recruited. Those with asthma, sore throat, cough, or allergy to lidocaine or Muko were excluded.

Participants were randomly assigned after anesthesia induction by opening an opaque envelope, prepared by the research pharmacist, that contained a 3-mL syringe with Muko, lidocaine jelly, or nothing, with instructions to apply the lubricant to the entire inflatable surface of the LMA. Patients, investigators, and other caregivers were blinded to group assignment. The anesthesiologist was blinded to the lubricants, but not to lubricant vs. controls.

Anesthesia was induced with 1 ug·kg−1 fentanyl and propofol and maintained with sevoflurane in air-oxygen with additional fentanyl as needed (up to 4 µg·kg−1·hr−1). Antiemetics were given according to guidelines by Gan et al.1 Morphine was used in the postanesthetic care unit (PACU) as needed. Patients were assessed for coughing and laryngospasm as well as for sore throat in the PACU and on the first postoperative day.

Demographics, concurrent diseases, cigarette use, medications, number of attempts to insert the LMA, and any complications were recorded. The anesthesiologist graded severity of coughing on emergence on the validated five-point Breathlessness, Cough, and Sputum Scale (where 0 is no cough and 4 is a prolonged distressing coughing spell resulting in breathlessness), so for simplicity we used a similarly rated scale for throat pain in PACU.2,3

Continuous variables were compared using Kruskal-Wallis analysis of variance on ranks; categorical variables using Chi-squared. An intention-to-treat analysis was used, with removal of one patient from analysis whose surgery was cancelled and one where the pharmacy was unable to provide the envelope in time.

Two hundred participants were recruited from 4 June 2004 to 28 February 2007 (see Table). Pain scores on day zero and day one were low and not different (Table). One participant in group M had severe throat pain (score = 4) in PACU; no one had severe throat pain on postoperative day 1. There was no significant difference in difficulty with LMA insertion. Laryngospasm on LMA removal occurred in two controls and once in each lubricated group.

We were surprised to find no benefit of lubrication of an LMA. We are uncertain as to why, but speculate that first difficult insertion may increase mucosal trauma, and lubricants made no difference to ease of insertion as measured by number of attempts. Second, once in place, the LMA, with pressure spread over a wide area, produces little mucosal trauma. Literature on this issue is sparse; a pediatric study of LMA lubrication showed that lidocaine decreased coughing on emergence.4 A strength of the study is its pragmatic conduct during usual clinical practice. A weakness is the study of only one brand of SGA. While allergy or other complications of lubricating the LMA are rare, this study suggests that routine lubrication of the LMA provides no benefit and could be potentially abandoned.


  1. 1.

    Trial registration was not available at the time, but the protocol and Research Ethics Board approval are available as online Electronic Supplementary Material.


Conflicts of interest

No author has any commercial or non-commercial affiliations other associations, such as consultancies, that are or may be perceived to be a conflict of interest with the work.

Editorial responsibility

This submission was handled by Dr. Hilary P. Grocott, Editor-in-Chief, Canadian Journal of Anesthesia.


Department of Anesthesia, University of Saskatchewan.

Supplementary material

12630_2018_1132_MOESM1_ESM.pdf (24 kb)
Supplementary material 1 (PDF 24 kb)
12630_2018_1132_MOESM2_ESM.pdf (100 kb)
Supplementary material 2 (PDF 99 kb)


  1. 1.
    Gan TJ, Meyer T, Apfel CC, et al. Consensus guidelines for managing postoperative nausea and vomiting. Anesth Analg 2003; 97: 62-71.CrossRefPubMedGoogle Scholar
  2. 2.
    Leidy NK, Schmier JK, Jones MK, Lloyd J, Rocchiccioli K. Evaluating symptoms in chronic obstructive pulmonary disease: validation of the Breathlessness, Cough and Sputum Scale. Respir Med 2003; 97 Suppl A: S59-70.Google Scholar
  3. 3.
    Breivik H, Borchgrevink PC, Allen SM, et al. Assessment of pain. Br J Anaesth 2008; 101: 17-24.CrossRefPubMedGoogle Scholar
  4. 4.
    O’Neill B, Templeton JJ, Caramico L, Schreiner MS. The laryngeal mask airway in pediatric patients: factors affecting ease of use during insertion and emergence. Anesth Analg 1994; 78: 659-62.CrossRefPubMedGoogle Scholar

Copyright information

© Canadian Anesthesiologists' Society 2018

Authors and Affiliations

  • William P. S. McKay
    • 1
    Email author
  • Jurgen Maslany
    • 1
  • Edward P. Schubert
    • 1
  1. 1.Department of AnesthesiaUniversity of SaskatchewanSaskatoonCanada

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