Department of Anesthesiology, Kanagawa Childrens Medical Center, 2-138-4 Mutsukawa, Minamiku, Yokohama, Japan*Corresponding author
LMA is the property of Intavent Limited.
Accepted for publication: August 21, 2000
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Abstract |
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Br J Anaesth 2001; 86: 1224
Keywords: intubation tracheal; equipment, mask anaesthesia
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Introduction |
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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.
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Methods and results |
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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 manufacturers guideline (size 2 for 1020 kg, and size 2.5 for 2030 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 3060 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 min1. 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 Scheffés procedure. The fibreoptic scores were analysed using the KruskalWallis rank test for comparison among groups and the MannWhitney 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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Comment |
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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.
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References |
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