Bronchoscopic assessment of paediatric laryngeal mask airways
Authors: Wallace CJ , Sticks S , von Ungern‐Sternberg BS 
Published: April 2009

Background:  Laryngeal mask airways (LMA) are commonly used in paediatric anaesthesia. Correct positioning of the LMA determined by adequacy of ventilation does not always indicate optimal anatomical position by either radiographical or fibreoptic assessment. Comparison of fibreoptic views of the laryngeal inlet seen through different sized paediatric LMA's has not been described for all sizes of LMAs.

Aims:  In paediatric patients aged 0–7 years undergoing elective flexible examination of the upper and/or lower airways, we aimed to assess the relationship between LMA's (size 1–2.5) and three measures: (1) Number of attempts required to insert the LMA to achieve acceptable ventilation for anaesthesia; (2) quality of ventilation; (3) fibreoptically assessed glottic aperture view.

Method:  Following approval by the local Ethics Committee, 350 children undergoing elective flexible examination of the upper and/or lower airways under general anaesthesia were included. Anaesthesia management was not standardized and performed at the discretion of the anaesthetist. Two types of LMA were available [LMA –unique (PAC MED Richmond, Vic., Australia) or LMA Pro‐breathe (single use, Well Lead Medical Co Ltd; with vertical bars at the distal outlet removed prior to use)]. Following induction of anaesthesia the LMA was inserted whilst the anaesthetic technician was performing a jaw thrust. All LMA's were tested by auscultation for an audible leak at an inflation pressure of 20 cmH2O and for signs of obstruction by auscultation at the larynx and both lung fields.

We classified quality of ventilation into good (no leak and no sign of obstruction, good bilateral air entry) or acceptable (slight leak but no obstruction of the airway and good bilateral air entry). Glottic view was classified into (1) complete view of glottic aperture (2) Partial glottic view, epiglottis impinging on view and (3) No glottic view, epiglottis completely obstructing glottic aperture.

Results: 

Size 1
Size 1.5
Size 2
Size 2.5

n

44
73
143
90

M : F

25 : 19
39 : 34
75 : 68
44 : 46

Age, months

2.5 (1–5)
7 (2–16)
31 (14–75)
73 (54–94)

Weight (kg)

4.7 (3.5–5.21)
8.46 (4.92–10.1)
14.6 (11.1–20.4)
23.1 (19.8–29.4)

Insertion
1st attempt
36 (81.8%)
65 (89.1%)
127 (88.8%)
79 (87.8%)

2nd attempt
6 (13.6%)
6 (8.2%)
12 (8.4%)
9 (10%)

≥ 3rd attempt
2 (4.6%)
2 (2.7%)
4 (2.8%)
2 (2.2%)

Ventilation
Good
39 (88.6%)
62 (84.9%)
132 (92.3%)
86 (95.6%)

Acceptable
5 (11.4%)
11 (15.1)
11 (7.7%)
4 (4.4%)

Glottic View
Complete
22 (50.0%)
42 (57.5%)
104 (72.7%)
70 (77.8%)

Partial
16 (36.3%)
23 (31.5%))
30 (21.0%)
16 (17.8%)

No view
6 (13.7%)
8 (11.0%)
9 (6.3%)
4 (4.4%)

Conclusion:  Despite adequate ventilation smaller sized LMA's were more likely to have a sub‐optimal glottic view. Size 1 LMA's required more attempts to achieve good or acceptable ventilation, however still having a first attempt rate higher than previously reported (81.8% vs 67% [1]). This was most likely caused by the jaw thrust performed during the insertion of the device enlarging the pharyngeal space easing positioning.

Reference

1 Dubreuil et al. Complications and fibreoptic assessment of size 1 Laryngeal mask airway. Anesthesia and Analgesia 1993; 76: 527–529.