Acta Anaesthesiol Scand 1990: 34: 669-672
The use of a laryngeal mask airway in spontaneously breathing patients V. J. SARMA Pitel General Hospital, Pitel, Sweden
The Laryngeal Mask Airway (LMA) is a new type of oropharyngeal airway that provides an alternative to endotracheal intubation and standard mask anaesthesia in certain cases. Once the patient is adequately anaesthetised, it can be inserted blindly, without recourse to laryngoscopy or muscle relaxants. Anaesthetists of all grades, given minimum instruction, were able to provide a clinically satisfactory airway in 49 out of 50 spontaneously breathing, anaesthetised patients. The advantages over standard mask anaesthesia are: better airway control, minimal leakage of anaesthetic gases, secure airway during transport to the recovery ward, and it frees the anaesthetist’s hands, as no mandibular support is needed. Postoperative problems were minimal and 97.6% of our patients said that they would prefer a similar anaesthetic in future. LMA does not guarantee against the risk of aspiration and it is not recommended for use in patients who may have a full stomach. Received 25 June, acceptedfor publication 2 August 1990
K q words: Anesthesia, spontaneous ventilation; equipment, laryngeal mask.
Maintenance of a clear airway under general anaesthesia can be achieved by endotracheal intubation or by the use of a face mask. The use of a face mask is often dificult and occupies the anaesthetist’s hands. Good approximation is not possible in edentulous patients and its use is not without risks. Endotracheal intubation has its own problems, and damage to teeth, pharyngeal and laryngeal structures has been reported (1). Incorrect placement of an endotracheal tube can have disastrous consequences. In recent years a new device called the Laryngeal Mask Airway (LMA) (Intavent, Colgate Medicals Limited, Windsor, U.K.) (Fig. 1 and 2) has been put onto the market. A full description of a prototype has been given by Brain and his colleagues (2, 3). It consists of a conventional silicone tracheal tube which has been cut diagonally across to remove the cuff. An elliptical cuff, which lies in the hypopharynx, is attached to the distal end. The cuff with an inflatable rim provides an airtight seal over the larynx (Fig. 2). It is manufactured to withstand repeated autoclaving and it is reusable. It can be inserted “blindly” without the use of a laryngoscope and it enables a patient to breathe spontaneously (4) or be ventilated (5). In this study we anaesthetised 50 ASA grade 1 and 2, spontaneously breathing patients and used the LMA to maintain their airway. MATERIAL AND METHODS The Ethics Committee of the University of Umel, Sweden approved the conduct of this study. Formal consent was obtained from all the
patients taking part. Obstetric and paediatric patients and patients with possible risk of aspiration were excluded from the study. Some of the patients were admitted for day-care surgery and others were inpatients. Eight members of the anaesthetic staff performed the intubations. The author was the only member of the team with prior experience of the LMA technique. All the participating staff were instructed in its use and attended demonstrations of the technique prior to using the LMA by themselves. Premedication consisted of 10 mg of diazepam. All patients were induced with propofol2-2.5 mg/kg and fentanyl l-1.5 pg/kg, followed by maintenance with isoflurane or halothane, oxygen and nitrous oxide ( 1 :2) in a circle system with low fresh gas flows (3 I/min). After achieving a satisfactory depth of anaesthesia, i.e. Guedel’s stage 111 plane 2, a LMA, previously lubricated with 2% lidocaine gel, was inserted into the mouth and advanced blindly over the tongue into the hypopharynx until resistance was met (Fig. 3 and 4).The cuff was inflated with air according to the manufacturer’s instructions, and chest and bag movements were observed. A dental bite block was then inserted to prevent the patient from chewing on the tube. If a clear airway was not achieved at the first attempt, the device was withdrawn, the anaesthesia deepened and two further attempts were allowed before changing to an alternative technique. I n no case was laryngoscopy used to aid insertion. All patients continued to breathe spontaneously and no muscle relaxant was used in this series. T h e blood pressure, heart rate, ECG, oxygen saturation and end-tidal carbon dioxide were continuously monitored. At the conclusion of surgery the LMA was left in situ till the patient started to make swallowing movements or responded to verbal commands, whereupon the cuff was deflated and the LMA was removed, followed by the removal of the dental bite-block. After each use the airway was washed with soap and water and autoclaved for re-use. The patient’s demographic data, type of operation (Table I ) , grade of the anesthetist (Table 2), number of attempts (Table 3) and any intra- or immediate post-operative problems were recorded (Table 4). All the patients were visited in the post-operative ward to evaluate the
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Fig. 1 and 2. Laryngeal mask airway: deflated and inflated views. incidence of immediate postoperative complications. A week after the operation, all the patients were sent a brief questionnaire regarding sore throat, difficult in swallowing and their views on the conduct of the anaesthetic (Table 5).
RESULTS The LMA could be correctly sited in 44 patients (88%) on the first attempt and 98% on the second attempt.
Fig. 3. Method of insertion of the laryngeal mask airway.
Laryngospasm occurred in one patient early on in the study when the LMA was introduced before the patient was sufficiently anaesthetised. The technique was abandoned in this case. Forty patients were extubated in the operation theatre and the rest in the recovery ward. The patients often extubated themselves once the cuff was
Fig. 4. Lateral view of correct placement of the laryngeal mask airway.
67 1
T H E LARYNGEAL MASK AIRWAY Table 1 Demographic and operative details of the patients (n =50) involved in the LMA study. Males : females Age in years Weight in kg Duration of anaesthesia (min) Operation: General surgery Orthopaedic Genito-urinary
22 : 28 38.8+ 14 (18-76) 68 & 13 (42-108) 54 35 (20-1 10) 26 21 3
*
released. There were no major problems during extubation. No pharyngeal suctioning was done on extubation in these patients. Forty-two of the 49 patients replied to the questionnaire sent to them a week after the operation. (No questionnaire was sent to the patient in whom LMA anaesthesia was abandoned.) Only one patient reported a severe sore throat pain ( > 24 h) and difficulty in swallowing ( < 12 h). She had a similar experience with endotracheal intubation in the past and was not sure ifshe would consent to a LMA anaesthetic in future. DISCUSSION The LMA has proven to be a welcome addition to the anaesthetist’s armamentarium. Compared to the usual face mask, it has some obvious advantages. It frees the anaesthetist’s hands, as there is no need to support the jaw. Even in edentulous patients it is possible to avoid leakages and obtain a satisfactory airway. The LMA may be left in situ till the patient is fully conscious and regains his laryngeal reflexes. It is possible to maintain a clear airway in most cases. Table 2 Details of anaesthetic staff involved in the LMA study and number of intubations performed by each group. Anaesthetist
Individuals
Intubations
1
Consultant Trainee anaesthesiologists Nurse anaesthetists
2 5
8 10 32
Total
8
50
Table 4 Patient appraisal of the LMA anaesthetic technique and incidence of oostomrative comdications ( n = 42).
Table 3 Details of intra- and post-operative problems associated with LMA use (n=50). Downfolding of the epiglottis Lary ngospasm Abandoned LMA technique Coughing during extubation Sore throat in the postoperative period Anaesthesia of the tongue and lips due to absorption of lidocaine eel i< 2 h)
*
Same patient.
Some of the advantages over endotracheal intubation are: the ease of insertion without recourse to a laryngoscope, succinylcholine or other muscle relaxants. This avoids postoperative muscle pains and other problems that can result in some cases from succinylcholine use, such as hyperkalaemia or malignant hyperpyrexia. There is also little risk of oesophageal or endobronchial intubation as the large size of the LMA makes it hard to misplace. Anaesthesia with LMA is reported to have an attenuated cardiovascular response on insertion compared to endotracheal intubation ( 5 , 6 ) , and this could be advantageous in the management of patients where the avoidance of the pressor response is of particular concern. The incidence of postoperative sore throats has been reported to be lower after LMA use compared to endotracheal intubation (5). The incidence of postoperative sore throats in our patients ( 1 1.9%) compares with the 9% reported by Jensen and his colleagues for anaesthetised unintubated patients (7). The incidence of sore throats in patients who had tracheal intubation has, however, been reported to be about 28% (8). LMA has been used successfully in some cases of anticipated or proven difficult intubation (5,9, 10). Three patients in this study had potential airway problems but LMA was easily inserted in all cases. It has been used during emergency caesarean section when endotracheal intubation was not possible ( l o ) , but it must be stressed that LMA does not guarantee against aspiration as reliably as a cuffed endotracheal tube (1 1). Inflation ofthe stomach can occur ifpositive pressure ventilation is performed via an incorrectly placed LMA (5). The commonest cause of difficulty during insertion has been reported to be due to a downfolding of the epiglottis (4). It is more common in elderly men who tend to have a large, floppy epiglottis and the use of an introducer has been suggested as a means of getting round this problem. We have not used an introducer in any of our cases.
5 I* I* 2 6 1
Sore throat: No sore throat Mild, < I 2 h Moderate, > 12 h Severe, >24 h
36 (85.7%)
5 (11.9%) 0 1 (2.38%)
D i f l c u l ~in swallowing: No difficulty Mild, c: 12 h
41 (97.6%) 1 (2.38%)
Patients’ prejerence f o r a similar anaesthetic in future: Yes Don’t know No
41 (97.6%) 1 (2.38%) 0
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The LMA has been used successfully for all age groups starting from 3-week-old patients (12) to the very old. However, kinking of the LMA has been reported recently in two children (13), a problem apparently isolated to size 2 LMA, according to the authors. None of the children came to any harm as they continued to maintain good oxygen saturations despite the kink. The manufacturers have promised to come up with modifications (14) to rectify this problem. We have not used any size 2 LMA’s in this study. The use of the LMA during transfer to the postoperative ward helps to maintain a free airway during this critical stage. Most of the patients in this study were, however, extubated in the operating theatre. Because of its obvious advantages over endotracheal intubation, it has been recommended that the LMA can be used as an airway in emergency resuscitation (15). We have a set of LM airways in our emergency intubation box, but we have never needed to use them so far. In a previous study at our hospital, we recorded nitrous oxide concentrations in the anaesthetist’s breathing zone during LMA anaesthesia under spontaneous ventilation in seven patients, using a Miran 1A general purpose infrared gas analyser. The mean nitrous oxide concentration, with the LM airway in situ, was 4.5 ppm, way below the permitted 25 pprn limit set by NIOSH (16).The mean top level of27.5 ppm 13 was recorded during less than 18% of the total anaesthetic time, usually just prior to the introduction and after extubation of the airway. Values of up to 280 pprn were momentarily obtained when positive pressure ventilation was applied, indicating that leakage occurs at higher airway pressures ( 17). The mean leak pressure during artificial ventilation was reported to be around 1.7 kPa (4) and 2.0 kPa (3). I n our hospital the bulk of the general anaesthetics are administered, under supervision, by nurse anaesthetics and trainee anaesthesiologists. Given minimal training in the use of the LMA, they could achieve a clinically satisfactory airway in most instances. A similar rate has been reported by Broderick and his colleagues (4).It is thus a technique eminently suitable to be taught to paramedics and emergency room nurses and is definitely easier to master than endotracheal intubation. They can be trained to recognize airway obstruction and gross leakage due to a misplaced LMA, which can be remedied by removal and reinsertion. Though each LMA unit costs around SKR 500 (GBP 50), it is manufactured to withstand repeated autoclaving and with care can be reused up to 150-200 times (5), thus making it 7-8 times cheaper than an endotracheal tube per use. The LMA has bridged a gap between endotracheal
intubation anaesthesia and mask anaesthesia. The ease ofinsertion, the high quality of the airway obtained and the lack of serious intra- or postoperative complications make it a useful technique to add to our anaesthetic repertoire.
REFERENCES I . Atkinson R S, Rushman G B, Alfred-Lee J. A synopsis of anaesthesia, 10th ed. Bristol: Wright, 1987: 219-220. 2. Brain A I J. The laryngeal mask - a new concept in airway management. B7J Anaesth 1983: 55: 801-805. 3. Brain A I J, McGhee T D, McAteer E J, Thomas A, Abu-Saad M A W, BushmanJ A. The laryngeal mask airway. Development and preliminary trials of a new type of airway. Anaesthesia 1985: 40: 356-361. 4. Broderick P M, Webster N R, Nunn J F. The laryngeal mask airway. A study of 100 patients during spontaneousbreathing. Anaesthesia 1989: 44: 238-241. 5. Alexander C A, Leach A B. The laryngeal mask. Experience of its use in a District General Hospital. Today’sAnaesthetist 1989: 4: 20&205. 6. Braude N, Clements E A F, HodgesU M, AndrewsB P. The pressor response and laryngeal mask insertion. A comparison with tracheal intubation. Anaesthesia 1989: 44: 551-554. 7. Jensen P J, Hommelgaard P, Sodergaard P, Eriksen S. Sore throat after operation: influence of tracheal intubation, intracuff pressure and type of cuff. Br J Anaesth 1982: 54: 453-456. 8. Brindle G F, Soliman M G. Anaesthetic complications in the surgical out-patient. Can AnaesthSocJ 1975: 22: 613418. 9. Brain A I J. Three cases of difficult intubation overcome by the laryngeal mask airway. Anaesthesia 1985: 40:353-355. 10. Chadwick I S, Vohra A. Anaesthesia for emergency caesarean section using the Brain laryngeal mask airway. Anaesthesia 1989: 4 4 261-262~. 11. Wilkinson P A, Cyna A M, MacLeod D M, Campbell J R, Criswell J, John R. The laryngeal mask: cautionary tales. Anaesthesia 1990: 45: 167-168. 2. Grebenick C R, Ferguson C, White A. The laryngeal mask airway in pediatric radiotherapy. Anesthesiology 1990: 72: 474-477. 3. Goldberg P L, Evans P F, Filshie J. Kinking of the laryngeal mask airway in two children. Anaesthesia 1990: 45: 487-488. 4. Martin D W. A reply. Kinking of the laryngeal mask airway in two children. Anaesthesia 1990: 45: 488. 5. Calder I, Ordman A J, Jackowski A, Crockard H A. The Brain laryngeal mask airway. An alternative to emergency tracheal intubation. Anaesthesia 1990: 45: 137-139. 6. National Institute for Occupational Safety and Health. Criteria for a Recommended Standard -Occupational Exposure to Waste Anaesthetic Gases and Vapors. Cincinnati: U S . Department of Health, Education and Welfare, 1977: DHEW Publication No. (NIOSH): 77-140. 7. Sarma V J, Lenman J. Anaesthetic waste gas levels during laryngeal mask anaesthesia. Anaesthesia 1990. (In press).
Address: Dr. !I Jayadev Sarma, FFARCSI Department of Anaesthetics Pitei General Hospital 941 28 Pitel Sweden