Anaesthesia, 1991, Volume 46, pages 358-360

The Brain laryngeal mask A comparative study with the nasal mask in paediatric dental outpatient anaesthesia

R. BAILIE, M. B. BARNETT

AND

J. F. FRASER

Summary Fifty A S A grade I children, who presented for dental outpatient extraction were studied. They were randomly allocated to two groups after induction: group I had conventional nasal mask anaesthesia andgroup 2 anaesthesia with a laryngeal mask. Group 2 had fewer hypoxic episodes and significantly better arterial oxygen saturations ( p < 0.01). There was no dzflerence between ihe groups as regards surgical access, dificulty of extraction or bleeding. The laryngeal mask appears to provide an alternative to conventional nasal mask anaesthesia, with better overall oxygenation and would seem particularly suitable for prolonged or dificult extractions.

Key words Anaesthesia; dental, outpatient. Equipment; laryngeal mask.

Outpatient paediatric dental anaesthesia requires the provision of a n adequate level of anaesthesia, an unobstructed airway and protection from aspiration of blood and debris whilst allowing the operator adequate access within the oral cavity. Traditionally this has been achieved by the use of a nasal mask and packing. In a number of studies’-’ with this method almost 50% of patients demonstrated a significant degree of hypoxia. In a 10-year review of mortality associated with dental surgery: 50% of deaths were associated with airway problems and it has been postulated that some degree of airway obstruction is inevitable.’ The Brain laryngeal mask airway (LMA)6 has been used to provide good airway control in adults’ and has been successfully used for intra-oral procedures in children.8 The aim of this study was to determine whether the laryngeal mask could be used to provide a viable alternative for airway control for paediatric dental surgery. Method

Fifty patients, ASA grade 1, below the age of 16 years, requiring outpatient dental extraction under general anaesthesia were studied following local ethics committee approval. Those requiring single extractions o r upper incisors only were excluded. All patients were induced according to individual preference either with methohexitone 1.5 mg/kg or with

halothane in 30% oxygen with nitrous oxide. Maintenance was with halothane in 30% oxygen with nitrous oxide delivered from a Bain type coaxial breathing system to a facemask. Patients were randomly allocated to two groups according to hospital number: group 1 nasal mask anaesthesia and group 2 laryngeal mask anaesthesia. When anaesthesia was considered sufficiently deep on clinical grounds in group 1, the facemask was changed for a nasal mask and anaesthesia continued with 30% oxygen in nitrous oxide with halothane, as clinically indicated. In group 2 the LMA was inserted when anaesthesia was judged sufficiently deep. Anaesthesia was continued with halothane as clinically indicated until the end of the procedure. The airway was left in situ until reflexes had returned. All patients had continuous ECG and Sao, monitoring from immediately after induction to the end of the procedure. End-tidal CO, was monitored using a Cardiocap in those patients with a laryngeal mask. Pulse rate, oxygen saturation and, where applicable, end-tidal CO, were recorded at 30-second intervals. The time of induction of anaesthesia, introduction of airway or nasal mask and start and end of surgery were all recorded. Specific intra-operative events such as episodes of obstruction and occurrence of arrythmias were recorded, together with surgical activity at the time. In all cases the surgeon was asked to grade the degree of difficulty in extraction and ease of access on a scale of 1

R. Bailie. MB. FFARCS(1). Senior Registrar. M.B. Barnett. FFARCS. Consultant. DeDartment of Anaesthetics. Guv’s Guy’s Hospital, London Hospital, London SEI 9RT, J.F. Fraser, BDS, House Officer, Department of SEI 9RT. Accepted 21 August 1990. 0003-2409/9 I j050358

+ 03 %03.00/0

@ 1991 The Association of Anaesthetists o f G t Britain and Ireland

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The Brain laryngeal mask Table 1. Demographic data.

Group 1 Mean age; years (SD) Weight; kg (SD) Median number of extractions

5 (2-16)

(range)

Group 2

6.08 (2.34) 23.2 (6.51)

Nasal mask

t

~~~

~~

5.60 (2.32) 21.15 (4.95) 6 (2-13)

Table 2. Mean total anaesthetic time and surgical time in minutes (SD). Group 1

Group 2

p value

.-a,

v

4-

~

Anaesthetic time Surgical time Surgical/anaesthetic %

7.75 (2.22) 2.84 (1.62) 36.64

9.31 (3.12) 4.02 (1.98) 43.18

0.07 0.02

0 a

,

0

I

2

3

A .-

L

Laryngeal mask

a

a

(easy, excellent) to 5 (very difficult, very poor). At the end of surgery the amount of blood on the distal end of the pack was graded on a scale from 1 (very little) to 3 (soaked). Results were analysed using Student’s t-test, Chi-squared and Mann-Whitney U-tests as appropriate. Results Demographic data for the two groups are summarised in Table 1. There was no significant difference between the two groups. Table 2 shows total anaesthetic and surgical time for the two groups and surgical time as a percentage of anaesthetic time. Surgical time was significantly longer (p = 0.02) in the LMA group and was also a larger proportion of anaesthetic time.

Nasal mask ’Oi

Laryngeal mask

0

I

2

3

Number of episodes of oirway obstruction

Fig. 2. Histogram showing the frequency distribution of episodes of obstruction in patients who had either laryngeal mask or nasal

mask anaesthesia.

The lowest recorded saturations in each group after randomisation are shown in Figure 1. One patient in the LMA group had a saturation of 94% or less as compared to five patients in the nasal mask group (Chi-squared, 0.05 < p < 0.1). When all the saturation readings in the two groups were compared, mean saturation in the LMA group (98.4% SD 0.91) was significantly better than in the nasal mask group (97.5 SD 3.03, Mann-Whitney U-test, p < 0.01). The frequency of episodes of obstruction is shown in Figure 2. The nasal mask group tended to have a higher incidence of multiple episodes of obstruction but this did not reach statistical significance. One patient in the nasal mask group had to be withdrawn from the study; after insertion of the pack at the start of surgery total obstruction occurred on two occasions. He was subsequcntly managed easily using a LMA. Only one patient in the LMA group had an episode of obstruction not relieved by simple jaw support; in this case the mask became dislodged upwards and forwards during changing of the pack from

Table 3. Surgical variables as median (range)

Access Minimum arterial oxygen saturation 1%)

Fig. 1. Histogram showing the frequency distribution of minimum oxygen saturation in patients who had either laryngeal mask or nasal mask anaesthesia.

Dificulty Blood

Right Left Right

Left Right Left

Group 1

Group 2

3 (1-5) 3 (2-5) 3 (2-5) 3 (2-4) 2 (1-3) 2 (1-3)

2 (1-4) 2 (1-3) 2 (1-4) 3 (1-5) 2 (1-3) 2 (1-3)

3 60

R . Bailie, M.B. Barnett and J.F. Fraser

one side to the other and required manipulation to correct the obstruction. Table 3 shows the surgical variables. There was no significant difference between the groups with respect to access, difficulty of extraction or bleeding, although access tended to be slightly reduced in the LMA group. There was no difference in frequency of arrythmias o r minimum pulse rate between the two groups. Maximum pulse rate in the nasal mask group was significantly higher (nasal 126 SEM 3.01, LMA 117 SEM 3.18, p < 0.05). Discussion Previous studies'.2 have shown that significant numbers of children undergoing dental extractions are subject to episodes of hypoxia. In our study the use of the LMA was associated with fewer episodes of hypoxia than the nasal mask (p < 0.1). In addition, the LMA led to a significant increase in mean saturation during the study period (p < 0.01). Bone et al.' found that almost 50% of episodes of hypoxia happened during the recovery period and it would be of interest to determine if the LMA also improved oxygenation during this period. It would be expected that the better oxygenation with the LMA was associated with a reduced incidence of airway obstruction. Surprisingly, this study failed to demonstrate a significant difference in the observed incidence of airway obstruction between the two groups. Recognition of obstruction with the LMA, especially in conjunction with end-tidal C 0 2 monitoring, is much easier and earlier and in almost all cases was easily relieved by gentle upwards pressure on the jaw. This earlier recognition and treatment probably led to the improved saturations because of the lag time in Sao, reading. In order for the LMA to be a suitab!e alternative in dental anaesthesia it must allow the surgeon adequate access inside the mouth. The results of this study show that although surgical access was somewhat reduced with the LMA this was not statistically significant and did not increase the difficulty of extraction o r the amount of bleeding. The increased operating time in the LMA group may reflect the reduced access. Alternatively, the apparent

better airway control may reduce the pressure on the surgeon to complete the extractions as quickly as possible. The increased maximum pulse rate in the nasal mask group may be a reflection of mild degrees of hypoxia o r may be because of lighter levels of anaesthesia associated with the dilution of anaesthetic gas mixtures which almost inevitably occurs as a result of mouth breathing. In summary, the LMA provides a suitable alternative to the nasal mask as a means of providing anaesthesia for dental extractions in children. Its use is associated with a significant improvement in overall arterial oxygen saturation during the operative period. Airway obstruction is easily recognised and in most cases requires only jaw support to relieve it. The laryngeal mask may be the method of choice where prolonged or difficult extractions are anticipated. Acknowledgments The authors thank the surgical staff of Guy's Dental Hospital for their permission in allowing us to study their patients and for their assistance and patience during this study. References 1. BONE ME, GALLER D, FLY"

PJ. Arterial oxygen saturation during general anaesthesia for paediatric dental extractions. Anaesthesia 1987; 4 2 879-82. 2. ALLENNA, ROWBOTHAM DJ, NIMMO WS. Hypoxaemia during outpatient dental anaesthesia. Anaesthesia 1989; 44: 509-1 1. MM, CREAN PM, KEILTYSR, BLACKGW. Changes in 3. SAMPAIO oxygen saturation during inhalation anaesthesia in children. British Journal of Anaesthesia 1988; 61: 498P. MP, CURSONI. Deaths associated with dentistry. 4. COPLANS British Dental Journal 1982; 153: 357-62. JA. General anaesthesia and sedation for dentistry. 5. THORNTON In: Hewer CL, Atkinson RS, eds. Recent advances in unaesthesiu and analgesia. 13. Edinburgh: Churchill Livingstone, 1979: 122. 6 . BRAIN AIJ. The laryngeal mask-a new concept in airway management. British Journal qf Anaesthesia 1983; 55: 801-5. NR, NUNNJF. The larygeal mask I. BRODRICKPM, WEBSTER airway. A study of 100 patients during spontaneous respiration. Anaesthesia 1989; 44: 238-241. 8. BEVERIDGEME. Laryngeal mask anaesthesia for repair of cleft palate. Anaesthesia 1989; 44: 656-7.

The Brain laryngeal mask. A comparative study with the nasal mask in paediatric dental outpatient anaesthesia.

Fifty ASA grade 1 children, who presented for dental outpatient extraction were studied. They were randomly allocated to two groups after induction: g...
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