Influence of head and neck position on cuff position and oropharyngeal sealing pressure with the laryngeal mask airway in children

K. Okuda, G. Inagawa, T. Miwa and K. Hiroki*

Department of Anesthesiology, Kanagawa Children’s Medical Center, 2-138-4 Mutsukawa, Minamiku, Yokohama, Japan*Corresponding author

{dagger} LMA is the property of Intavent Limited.

Accepted for publication: August 21, 2000


    Abstract
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 Abstract
 Introduction
 Methods and results
 Comment
 References
 
We studied how head and neck position affect the cuff position and oropharyngeal sealing pressures of the laryngeal mask airways (LMAs) in children. We studied 39 non-paralyzed healthy children aged 1.5–8.0 yr, weighing 10.3–27.0 kg, managed with size 2 or 2.5 LMAs during elective surgery. Head and neck movements did not adversely affect airway patency in 97% of patients. One child developed apparent airway obstruction with head and neck flexion, which was relieved in the neutral position. Oropharyngeal sealing pressure was significantly greater during neck flexion compared with the neutral position (P<0.02). Fibreoptic examination revealed that the epiglottis covered a larger area of the LMA aperture during neck flexion, compared with the neutral position (P<0.02).

Br J Anaesth 2001; 86: 122–4

Keywords: intubation tracheal; equipment, mask anaesthesia


    Introduction
 Top
 Abstract
 Introduction
 Methods and results
 Comment
 References
 
The laryngeal mask airway (LMA{dagger}) is used for paediatric surgery with different head and neck positions, such as extension of the neck for adenotonsillectomy,1 and rotation of the head for myryngotomy.2 Studies of children with their head and neck in neutral position, assessing the position of the LMA fibreoptic35 or radiological6 examination, found that well functioning LMAs were not necessarily ideally anatomically, placed. Fibreoptic examination of the LMA position showed that the epiglottis occupied a larger area within the LMA aperture in children than in adults.4 5 These observations suggest that head and neck movement could distort the oropharyngeal space, and affect anatomical position and function of the LMA more in children than in adults.

A study of adult patients7 showed little influence of head and neck position on cuff position and oropharyngeal leak pressure of the LMA, but no studies have been done in children.

We measured how head and neck movement changed the cuff position and oropharyngeal sealing pressure of the LMA in children patients.


    Methods and results
 Top
 Abstract
 Introduction
 Methods and results
 Comment
 References
 
After obtaining Ethics Committee approval and informed consent from the parents, we studied ASA physical status I paediatric patients who were managed with size 2 or 2.5 LMAs during elective urological surgery.

Anaesthesia was induced via a facemask with 5% sevoflurane and nitrous oxide in 65% oxygen. After obtaining sufficient depth of anaesthesia, LMAs were inserted by well-trained anaesthesiologists using the technique recommended by the manufacturer without the use of neuromuscular blocking agents. The size of LMA was chosen according to the manufacturer’s guideline (size 2 for 10–20 kg, and size 2.5 for 20–30 kg). The intra-cuff pressure was adjusted to 60 cmH2O using an ergonomic pressure gauge (Hi-LoTM Hand Pressure Gauge, Mallinckrodt Medical, Germany). General anaesthesia was maintained with oxygen, 65% nitrous oxide, and sevoflurane. Patients breathed spontaneously through the LMA for the duration of surgery. In all patients regional anaesthesia (caudal block or epidural block) was performed.

At the end of surgery, the intra-cuff pressure of the LMA was adjusted to 60 cmH2O again with the head and neck in the neutral position. Anaesthesia was maintained with sevoflurane 2%, nitrous oxide 65%, and oxygen. The head and neck position was then changed successively to the following positions; neutral, maximal flexion, maximal extension (about 45°, each) and about 90° rotation to the left and right. In each position, after 30–60 s of a stable period, oropharyngeal sealing pressures and fibreoptic images were recorded. To assess sealing pressure, the expiratory valve of the circle breathing system was closed and fresh gas flow adjusted to 3 litre min–1. Pressure in the breathing circuit increased until airway pressure reached equilibrium. The airway pressure was measured with an aneroid manometer attached to the breathing circuit and recorded as oropharyngeal sealing pressure.8 During these measurements the position of the head and neck was hidden from the observer. After this the expiratory valve was re-opened and a fibreoptic scope was passed to a position just proximal to the mask aperture bars and the view was recorded on videotape. A second anaesthetist, not aware of the position of the head and neck, scored the views on videotape as follows; 1: the view through aperture bars completely covered with anterior epiglottis, but LMA function adequate; 2: anterior epiglottis covering more than 2/3 of the view in diameter; 3: anterior epiglottis covering more than 1/3, but less than 2/3 of the view in diameter; and 4: anterior epiglottis covering less than 1/3 of the view in diameter.

A factorial analysis of variance was used to assess the differences in the oropharyngeal leak pressure among groups. Post-hoc testing of multiple comparisons was performed with Scheffé’s procedure. The fibreoptic scores were analysed using the Kruskal–Wallis rank test for comparison among groups and the Mann–Whitney U test for the comparison between neutral position and other groups. P<0.05 was accepted as statistically significant.

Thirty-nine patients, ages from 1.5 to 8.0 yr (mean 4.0 yr) and weighing between 10.3 and 27.0 kg (mean 15.7 kg) were enrolled in this study. Thirty-one size 2 LMAs, and eight size 2.5 LMAs were used.

The movement of the head and neck did not adversely affect the airway patency in 38 of the 39 patients and these patients could breathe spontaneously in all head and neck positions. One 3-yr-old child weighing 14 kg, managed with a size 2 LMA developed airway obstruction during neck flexion, which was relieved in the neutral position. The results are summarized in Table 1.


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Table 1 Oropharyngeal sealing pressure and fibreoptic score in the five head and neck positions. *P<0.05 vs neutral position
 

    Comment
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 Abstract
 Introduction
 Methods and results
 Comment
 References
 
In agreement with previous reports,36 we also found that the epiglottis occupied a considerable area of the aperture of the LMA, and that airway patency was well maintained in most patients with any head and neck position, during breathing.

The fibreoptic score proposed by Brimacombe9 has been used for the assessment of LMA positioning in many studies, mainly with adult patients. However, this score did not seem suitable for the assessment of LMA positioning in paediatric patients. As the epiglottis occupied a considerable area in the LMA aperture in the majority of children, such fibreoptic findings would be classified into the same score if this method were used. We used an alternative scoring system to express the extent that the epiglottis occupied the LMA aperture.

In the current study, the fibreoptic score was less during neck flexion than in the neutral position, with the epiglottis filling more of the aperture view. Neck flexion could increase the posterior deflection of the epiglottis. Sealing pressure with neck flexion was greater than in the neutral position in agreement with previous studies of adults.7 Neck flexion could reduce the longitudinal tension in the anterior pharyngeal muscles, allowing them to settle down onto the mask to form a better seal.

One child developed an apparent airway obstruction with neck flexion, which could be relieved in the neutral position. Together with the fact that the epiglottis fills the aperture of the LMA more in this position, head flexion may possibly jeopardize LMA function, but further study of this is needed.


    References
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 Abstract
 Introduction
 Methods and results
 Comment
 References
 
1 Williams PJ, Bailey PM. Comparison of the reinforced laryngeal mask airway and tracheal intubation for adenotonsillectomy. Br J Anaesth 1993; 70: 30–33[Abstract]

2 Watcha MF, Garner FT, White PF, Lusk R. Laryngeal mask airway vs. face mask and Guedel airway during pediatric myryngotomy. Arch Otolaryngol Head Neck Surg 1994; 120: 877–80[ISI][Medline]

3 Rowbottom SJ, Simpson DL, Grubb D. The laryngeal mask airway in children—a fibreoptic assessment of positioning. Anaesthesia 1991; 46: 489–91[ISI][Medline]

4 Mizushima A, Wardall GJ, Simpson DL. The laryngeal mask airway in infants. Anaesthesia 1992; 47: 849–51[Abstract/Free Full Text]

5 Dubreuil M, Laffon M, Plaud B, Penon C, Ecoffey C. Complications and fiberoptic assessment of size 1 laryngeal mask airway. Anesth Analg 1993; 76: 527–9[Abstract]

6 Goudsouzian NG, Denman W, Cleveland R, Shorten G. Radiologic localization of the laryngeal mask airway in children. Anesthesiology 1992; 77: 1085–9[ISI][Medline]

7 Keller C, Brimacombe J. The influence of head and neck position on oropharyngeal leak pressure and cuff position with the flexible and the standard laryngeal mask airway. Anesth Analg 1999; 88: 913–6[Abstract/Free Full Text]

8 Keller C, Brimacombe JR, Keller L, Morris R. Comparison of four methods for assessing airway sealing pressure with the laryngeal mask airway in adult patients. Br J Anaesth 1999; 82: 286–7[Abstract/Free Full Text]

9 Brimacombe J, Berry A. A proposed fiber-optic scoring system to standardize the assessment of laryngeal mask airway position. Anesth Analg 1993; 76: 457