Types of LMA
Different types of LMA currently available are:
Classical LMA is a soft rubber tube with a silicon cuff at the distal end which fits snuggly around the glottic opening and can be inserted blindly. The hazards of laryngoscopy and intubation are thus prevented. It can be sterilized up to 40 times.
Intubating LMA is an advanced form of the standard LMA. It has a shorter tube and a metal handle which permits single handed insertion without moving the head and neck in patients with unstable spine and with limited mouth opening. An 8mm cuffed silicon endotracheal tube and an introducer are available with it.
Proseal LMA has an extra tube which opens at the tip of the cuff at the distal end. The other end opens to the atmosphere. It helps to drain out any regurgitant and prevent aspiration specially in obstetric patients. An orogastric tube may also be passed through it easily.
Reinforced LMA is a non kinckable tube with spirally wound metal wire. It is helpful in minor procedures of the head and neck where the head and face are covered with drapes, and access to airway is difficult.
Disposable LMA is same as Classical LMA but for single use only.
Induction techniques for LMA insertion
1. Intravenous induction: This may be either a single or a two drug method in which a drug is combined with local anaesthetic, with a muscle relaxant or an inhalational agent.
Propofol: Conventionally LMA is inserted with propofol induction. Although this technique has a low failure rate, it has its limitations. There are involuntary movements, pain at injection site, greater cardio-respiratory depression and infection due to egg-phosphatide content, as well as high cost.
Thiopentone: Scanlon2 compared equipotent doses of propofol and thiopentone and reported that thiopentone is associated with adverse response in 76% of cases as against 26% for propofol group. Even when used with narcotics (fentanyl), thiopentone was associated with a higher incidence of gagging.3 Driver4 on the other hand did not find any significant difference between alfentanil-propofol and alfentanil-thiopentone induction when midazolam was added to both drug regimes. Requirement for bolus doses for undesirable responses was higher in the thiopentone group. Thiopentone with muscle relaxants, has been found very economical and effective.
Etomidate: Etomidate alone is far from perfect because of high excitatory phenomenon (up to 40%). Pain at injection site, nausea and vomiting, cortisol suppression and emergence phenomenon is high. In combination with fentanyl or a small dose of succinylcholine insertion becomes smoother with decreased insertion time.5 This combination may be useful in patients in whom cardiovascular stability is required.
Thiopentone -Propofol admixture: Yeo6 compared a mixture of 1.25% thiopentone and 0.5% propofol in a dose of 0.25ml/kg with propofol alone. Both groups received pre-induction fentanyl 1µg/kg. Coughing and gagging was higher in the combination group (32%), but patients had less hypotension and cost was 45% less as compared to propofol. This may be beneficial in patients requiring haemodynamic stability. Combination of midazolam-alfentanil with either propofol 1.25mg/kg or thiopentone 2.5mg/kg produced similar insertion conditions, but propofol group had less undesirable responses.
Lignocaine and Thiopentone: Cook7 found comparable results with 10% (40mg) lignocaine spray 3 minutes before thiopentone induction with that of propofol as against I/V lignocaine 1.5 mg/kg with thiopentone. Pre-induction fentanyl was used. On the other hand Hussain8 found a high incidence of gagging (25% and 30%) in both I/V and local lignocaine spray under thiopentone induction. This less ideal insertion condition may be due to the fact that Hussain used 4% spray as against 10% used by Cook. Moreover Cook used I/V fentanyl as well. A similar incidence of 60% smooth insertion of LMA has been found by Zafar9 and Paracha10 under thiopentone anaesthesia and lignocaine in Pakistani population.
Ketamine: Bhak11 reports successful insertion of LMA in children with addition of 10% lignocain spray under ketamine anaesthesia in a dose of 3-3.5mg/kg. This technique avoids apnoea and airway obstruction associated with propofol.. Goh12 found that pre induction ketamine 0.5mg.kg-1 improved haemodynamics under propofol induction when compared to fentanyl 1µg.kg-1, with less prolonged apnoea, and is associated with better insertion conditions than placebo (saline).
Induction agents with muscle relaxants: Not only propofol, but thiopentone was found to have markedly improved insertion conditions when used with the mini-dose of muscle relaxants. The depolarizing muscle relaxants have a far better effect than non-depolarizing drugs. In a study by Yoshino13 LMA insertion was found to be 90% smoother with 0.5mg/kg succinylcholine and thiopentone as compared to 45% with 0.25% succinylcholine, but with a higher incidence of post-operative myalgia.
Comparing two doses of atracurium (0.05mg/kg and 0.1mg/kg) under thiopentone induction Koh14 found comparable results but with a higher failure rate of 10% with 0.05mg/kg. In the control group Propofol had 100% smooth insertion probably due to pre-induction fentanyl.
Monem15 comparing succinylcholine 0.35mg/kg with atracurium 0.06mg/kg under thiopentone induction found excellent insertion conditions with succinylcholine group in 83% as against 46% for that of atracurium. No pre-induction narcotic was used. There was no failure in the succinylcholine group compared with 17% failure rate with atracurium. Post-operative myalgia was also insignificant with 3.3% in each group. The technique was found to be economical with an additional cost of only $1.2. Combining mivacurium with fentanyl and propofol, Chean16 found comparable results to that of fentanyl and propofol.
2. Inhalational Induction: Khan17 demonstrated technically easy insertion with thiopentone and halothane in 84% of adult patients. Inhalation agents alone are many a times required to induce infants and children in whom I/V access is not possible. The disadvantage of this technique is a longer time to achieve sufficient depth and theatre pollution. Sevoflurane is now often used in such situations with quicker induction, but at a higher cost.
Comparison of sevoflurane with propofol: Ti18 found comparable results with single vital capacity breath of 8% sevoflurane and 3mg/kg of propofol for LMA insertion. LMA was inserted significantly rapidly with sevoflurane than with propofol due to a greater incidence of prolonged jaw tightness. Apnoea was also significantly higher in the propofol group. In a meta-analysis Joo19 concludes that sevoflurane and propofol had similar efficacy for anaesthetic induction. However for routine outpatient surgery, propofol may still be the preferred induction anaesthetic because of its favourable induction of anaesthesia characteristic, high patient satisfaction and less frequent incidence of nausea and vomiting
Combination of sevoflurane and propofol: Sayyid20 found that the induction of anaesthesia with sevoflurane-propofol combination provided a frequent incidence of successful LMA insertion at the first attempt that was associated with less incidence of apnoea.
Sevoflurane and extreme of age: Kirkbride21 found favourable insertion conditions with sevoflurane in the elderly with a higher mean arterial pressure than slow propofol induction. Kihara22 is of the opinion that oxygen in nitrous oxide with sevoflurane suppresses the response to LMA insertion in a linear and additive fashion in children
Insertion techniques for LMA
1. Classical technique: Conventionally LMA is fully deflated and lubricated with water based jelly on its posterior surface and pressed along the palato-pharyngeal curve using the index finger. It is finally pushed further down till resistance is felt. Reported first time insertion rates for standard technique vary between 76 and 96%23 Analysing 1500 cases Brimacombe24 found a first time insertion rate of 95.5%. In another study of paramedics and medical students, Penant found a 94% first time success with classical technique. Many a times difficulties are encountered with the classical technique. Various modifications have been evaluated.
2. 180o rotation (reverse technique): In this technique the LMA is inserted with concavity facing the palate. On reaching oropharynx it is rotated 180o counter-clockwise and pushed to its final position. Soh25 found it as an acceptable technique in 100% of paediatric patients as compared to 90% in the standard technique. Comparing four techniques Brimacombe26 found that the standard technique and 180o rotational techniques are superior to partially or fully inflated cuff techniques in terms of fiberoptic positioning.
3. Fully or partially inflated cuff: According to Walkeling27 insertion of the LMA with the cuff fully inflated is equally successful compared to the standard technique in experienced hands. The inflated technique is associated with less minor pharyngeal mucosal trauma and consequently lesser incidence of post operative sore throat. Navaratram28 also favours partial inflation of cuff with 50% cuff volume in combination with head tilt and jaw thrust.
4. Techniques based on change of head position: Brimacombe29 found smooth LMA insertion in 95% of patients in neutral position as compared to that of 100% in the standard position. Keller30 studied the pressure exerted and its effects on the cervical spine on 20 cadavers (6-24 hours post mortem), comparing classic LMA, Intubating LMA and laryngoscopic intubation. They found that the LMA devises exert greater pressure on the cervical spine than established intubtion techniques and can produce posterior displacement of cervical spine. It is therefore recommended that laryngeal mask devices should only be used in the unstable cervical spine if difficulties are anticipated or encountered with established techniques.
5. Laryngoscopic guided LMA insertion: Koay and Yoong1 compared the classic LMA insertion technique with that of laryngoscpic guided LMA insertion. There was no significant difference as regards to the ease of insertion, haemodynamic instability, local trauma and sore throat. However the ease of insertion was greater in the classical technique with less incidence of blood tinge. It was inferred that the laryngoscopic guided LMA insertion is reasonable option in situations like doubling over of the LMA, increased pharyngeal tone, tonsillar hypertrophy, high arched palate and large floppy epiglottis.
6. Yodfat Technique (Figure 1): Since LMA is a flexible tube its insertion requires force to push it into place. Combined with repeated attempts it is usually found to cause some mucosal trauma with consequent blood tinged tip of the LMA on removal. Yodfat31 found that the insertion of a rigid stylet into a partially inflated LMA and creation of a 90o angle close to the laryngeal portion of the LMA helps significantly to increase the rate of first attempt successful insertion for all practitioners. Care should be taken to lubricate the stylet and avoid pushing it beyond the lumen of the LMA. The Intubating LMA can also serve the same purpose but it adds to the cost.
7. Use of Introducer ( Figure 2): This is a portex spoon like instrument with a blunt tip, which acts as an artificial hard palate to guide the laryngeal mask into correct position. Dingley found a 96% success rate in the hands of unskilled workers as compared to 68% with that of the classical method.
8. LMA insertion in prone position: Although the prone position is not the ideal position for inducing anaesthesia, Alexander32 found successful insertion in fast tracking ambulatory anaesthesia in this position. The patients placed themselves in the prone position before induction. After induction the head ring was removed and the head rotated to one side with the non dominant hand. LMA was inserted with the help of an assistant opening the mouth by holding the chin. In the prone position the tongue falls forwards opening the oropharyngeal space for the LMA. This has been successfully applied in emergency situation like accidental extubation in prone in a neurosurgical patient in a case report by Dingeman33. In another case report Valero34 observed successful insertion of LMA in prone position in a 19 year old with a drill bit penetrating the spinal canal at C1-C2 level after inhalational induction with sevoflurane.
9. Other maneuvers: Maneuvers which may ease insertion include partial removal and reinsertion, jaw thrust, anterior traction on the tongue and superior laryngeal nerve block
1. Koay CK, Yoong CS, Kok P. A randomized trial comparing two laryngeal mask airway insertion techniques. Anaesth intensive Care 2001;29: 613-5.
2. Scanlon P, Carey M, Power M, Kirby F. Patient's response to laryngeal mask insertion after induction of anaesthesia with propofol or thiopentone. Can J Anaesth 1993;40: 816-8.
3. Brown GW, Patel N, Ellis FR. Comparison of propofol and thiopentone for laryngeal mask insertion. Anaesthesia 1991; 46:771-2
4. Alexander R, Fennelly M. Comparison of ondonsetron, metaclopramide and placebo as pre-medicants to reduce nausea and vomiting after major surgery. Anaesthesia 1997; 52: 695-8.
5. Liou CM, Hung WT, Chen CC, Hsu HS, Lau HK. Improving the success rate of laryngeal mask airway insertion during etomidate induction by using fentanyl or succinylcholine. Acta Anaesthesiol Taiwan 2004; 42: 209-13.
6. Yeo KSJ, Kua SW, Teoh GS, Onsiong MK. The use of thipentone/ propofol admixture for laryngeal mask airway insertion. Anaesth Intensive Care 2001; 29: 38-42.
7. Cook TM, Seavall CR, Cox CM. Lignocaine aids in insertion of laryngeal mask airway with thiopentone. A comparison between topical and intravenous administration. Anaesthesia 1996; 51: 787-90.
8. Hussain SM. Laryngeal mask airway insertion with thipentone aided with I/V or topical lignocaine: A comparative study. The Professional 1999; 6: 163- 5.
9. Zafar ME, Ahmed S. Evaluation of the effect of intravenous lignocaine on improving the condition for laryngeal mask airway placement under thiopentone anaesthesia. Pak Armed Forces Med J 2006;56:129-33.
10. Paracha MK. Intravenous lignocaine helps insertion of LMA under thiopentone sodium alone. Med Spectrum 1988;19:47-9.
11. Bahk JH, Sung J, Jang IJ. A comparison of ketamine and lidocaine spray with propofol for the insertion of LMA in children : a double blinded randomized trial. Anesth Analg 2002; 95: 1586-9.
12. Goh PK, Chiu CL, Wang CY, chang YK, Loo PL. Randomized double-blind comparision of ketamine-propofol, fentanyl-propofol and propofol-saline on haemodynamics and laryngeal mask airway insertion conditions. Anaesth Intensive Care 2005;33: 223-8.
13. Yoshino A, Hashimoto Y, Hirashima J, Hakoda T, Yamada R, Uchiyama M. Low dose succinylcholine facilitates laryngeal mask airway insertion during thiopentone anaesthesia. Br J Anaesth 1999; 83:279-83.
14. Koh KF, Chen FG, Cheong KF, Esuvaranathan V. Laryngeal mask insertion using thiopentone and low dose atracurium: a comparison with propofol. Can J Anaesth 1999; 46: 670-4.
15. Monem A, Chohan U. Comparison of low dose succinylocholine with low dose atracurium to evaluate LMA insertion during thiopentone induction. J Anaesth Clin Pharmacol 2004; 20: 39-44.
16. Cheam EWS, Chui PT. Randomized double blind comparison of fentanyl, mivacurium or placebo to facilitate laryngeal mask airway insertion. Anaesthesia 2000; 55: 323-6.
17. Khan FH, Khan FA, Kamal RS. Experience with laryngeal mask airway in Pakistani patients. J Pak Med Assoc 1996; 46: 276-8.
18. Ti LK, Chow MY, Lee TL. Comparison of sevoflurane with propofol for LMA insertion in adults. Anesth Analg 1999; 88: 908-12.
19. Joo HS, Perk WJ. Sevoflurane verses propofol for anaesthesia induction: a meta-analysis. Anaesth Analg 2000; 91: 213-9.
20. Siddik-Sayyid SM, Aouad MT, Taha SK, Daaboul DG, Deep PG, Massoouh FM, et al. A comparison of sevoflurane-propofol verses sevoflurane or propofol for LMA insertion in adults. Anesth Analg 2005;100: 1204-9.
21. Kirkbride DA, Parker JL, William GD, Buggy DJ. Induction of anaesthesia in the elderly ambulatory patient : a double blind comparison of propofol and sevoflurane. Anaesth Analg 2001; 93: 1185-7.
22. Kihara S, Yaguchi Y, Inomata S, Watanabe S,Brimacombe JR, Taguchi N et.al. Influence of nitrous oxide on minimum alveolal concentration of sevoflurane for laryngeal mask insertion in children. Anaesthesiology 2003; 99: 1055-8.
23. John RE, Hill S, Hughes TJ. Airway protection by laryngeal mask airway. A barrier to dye placed in the pharynx. Anaesthesia 1991; 46: 366-7.
24. Brimacombe J. Analysis of 1500 Laryngeal mask uses by one anaesthetist in adults undergoing routine anaesthesia. Anaesthesia 1996; 51: 76-80.
25. Soh CR, Ng AS. Laryngeal mask airway insertion in paediatric anaesthesia: comparison between the reverse and standard technique. Anaesth Intensive Care 2001; 29: 515-9.
26. Brimacombe J, Berry A. Insertion of the laryngeal mask airway. a prospective study of four techniques. Anaesth Intensive Care 1993; 21: 89-92.
27. Wakeling HG, Butler PJ, Baxter PJ. The laryngeal mask airway: a comparison between two insertion techniques. Anaesth Analg 1997; 85: 687-90.
28. Navaratnam S, Tayler S. The laryngeal mask- another insertion technique. Anaesth Intensive Care 1993; 21: 250.
29. Brimacombe JR, Berry AM. Mallampati grade and laryngeal mask placement. Anesth Analg 1996;82: 1112-3.
30. Keller C, Brimacombi RJ, Keller K. Pressure exerted against the cervical vertebrae by the standard and the intubating laryngeal mask airways: a randomized, controlled, cross over study in fresh cadavers. Anesth Analg 1999; 89: 1296-300.
31. Yodfat UA. Modified technique for laryngeal mask airway insertion. Anesth Analg 1999; 89: 1327.
32. Ng A, Raitt DG, Smith G. Induction of anaesthesia and insertion of laryngeal mask airway in the prone position for minor surgery. Anesth Analg 2002; 94: 1194-8.
33. Dingeman RS, Coumnerova LC, Goobie SM The use of laryngeal mask airway for emergent airway management in a prone child. Anesth Analg 2005;100:670-1.
34. Valero R, Serrano S, Adalia R, Tercero J, Blasi A, Sanchez-Elayo GS et al. Anaesthetic management of a patient in prone position with a drill bit penetrating the spinal cord at C1-C2, using a laryngeal mask. Anesth Analg 2004;98:1447-50.
35. Mc Crory CR, Moriarity DC. Laryngeal mask airway positioning is related to Mallampati grading in adults. Anesth Analg 1995; 81: 1001-4.
36. Ishimura H, Minami K, Sata T, Shigematsu A, Kadoya T. Impossible insertion of laryngeal mask airway and oropharyngeal axis, a case report. Anaesthesiology 1995;83: 867-9.