The influence of head rotation on ProSeal[TM] laryngeal mask airway sealing during paediatric myringotomy.
Myringotomy with ventilation tube insertion in children involves turning the head from neutral to allow surgical access to the ear. In adults, rotation of the head from the mid-line generally increases the oropharyngeal leak pressure when a ProSeal[TM] laryngeal mask airway (PLMA) is used to manage the airway. There are concerns that these manoeuvres may distort or obstruct the paediatric airway. Paediatric sizes (1.5, 2.0 and 2.5) of the PLMA differ from the adult versions in that they do not have a dorsal cuff. This study examines the effect of these head position changes on the seal of the PLMA in children. Twenty-nine children (ASA 1-2, aged 0.9 to 7.5 years) scheduled for myringotomy were recruited. After PLMA insertion, oropharyngeal leak pressure and fibreoptic determined PLMA position scores were measured in the neutral position and with head rotation of 45[degrees] to the left or right. Fibreoptic positioning scores were similar in all positions. Head rotation was associated with a statistically significant but modest increase in oropharyngeal leak pressure versus the neutral position (P <0.05). After rotating the head from neutral, 38% (11 of 29) of subjects had an increase of oropharyngeal leak pressure of at least 2 cm[H.sub.2]O. Only 7% (2 of 29) of subjects had a decrease in oropharyngeal leak pressure with head rotation, the maximum decrease being 2 cm[H.sub.2]O. Airway obstruction did not occur in any of the positions. We conclude that the efficacy of the seal for the pediatric sizes PLMA is improved by head rotation for myringotomy.
Key Words: laryngeal mask airway, middle ear ventilation, paediatric anaesthetic
Myringotomy with tympanostomy tube insertion is one of the most frequently performed procedures in children and the majority of the patients require general anaesthesia. During the procedure, the head is turned to one side to permit access to the ear and the 'sniffing position' cannot be maintained. Anaesthetised children have narrowed upper airways (1) and are susceptible to collapse of the pharyngeal airway with head and neck rotation (2), so upper airway obstruction can occur during myringotomy with tympanostomy tube placement in children (3). Airway management of these cases varies widely around the world. Face mask use is associated with anaesthetic gas pollution of the operating theatre, while endotracheal intubation may be associated with laryngeal injury even during apparently straightforward laryngoscopies (4).
The classic[TM] laryngeal mask airway (cLMA) can be used in paediatric operations requiring rotation of the head (5-7). The adult sizes of the ProSeal[TM] laryngeal mask airway (PLMA) (Laryngeal Mask Company, Henley on Thames, U.K.) have a wedge-shaped dorsal cuff that is designed to push a ventral elliptical cuff to adapt to the contours of periglottic tissues. The paediatric sizes of 1.5 to 2.5 PLMA do not have a dorsal cuff. It has been documented that head rotation improves airway sealing for adult-size PLMAs (8), but no clinical study has been undertaken regarding the sealing effect of paediatric size PLMAs during head rotation.
The aim of this study was to determine whether airway sealing and stability of 1.5, 2.0 and 2.5 size PLMAs are changed by head rotation during myringotomy in children.
MATERIALS AND METHODS
Twenty-nine ASA 1-2 paediatric patients aged between 11 months and 7.5 years and scheduled for elective myringotomy with or without tympanostomy tube placement were studied. Ethics committee approval and written informed parental consent were obtained in all cases. Patients were excluded if they were at risk of aspiration, or had symptoms of respiratory tract disease. PLMA sizes were chosen according to the manufacturer's guidelines (size 1.5 for 5 to 10 kg, size 2 for 10 to 20 kg and size 2.5 for 20 to 30 kg)
Patients were routinely monitored during the procedure (i.e. ECG, pulse oximeter and noninvasive blood pressure, end-tidal C[O.sub.2]) (Datex-Ohmeda S/5[TM], Datex-Ohmeda, Inc., Madison, U.S.A.). Briefly, patients were administered atropine 0.01 mg/kg intravenously (IV) as premedication. Anaesthesia was induced according to the usual practice at our institution. After thiopentone 5 mg/kg IV and rocuronium 0.6 mg/kg IV, 3% sevoflurane and 100% oxygen were delivered at a fresh gas flow rate of 5 l/min via a facemask. After obtaining sufficient anaesthesia depth, a single experienced PLMA user (>100 uses) inserted a PLMA using the introducer tool with the cuff fully deflated. Once inserted into the pharynx, the mask cuff was inflated with air until effective ventilation was established. Patients were maintained with sevoflurane 2 to 3% in nitrous oxide and 50% oxygen at a fresh gas flow rate of 4 l/min using a circle system. The ventilator (Aestiva[R]/5, Datex-Ohmeda, Inc., Madison, U.S.A.) was set to pressure-controlled mode whereby airway pressure, which was limited up to 20 cm[H.sub.2]O, and respiratory rates were adjusted to maintain an end-tidal C[O.sub.2] in the normal range (35 to 40 mmHg). After successful insertion, intracuff pressure was adjusted to 60 cm[H.sub.2]O using a cuff inflator (VBM cuff pressure gauge, VBM Medizintechnik, Germany) with the head and neck in the neutral position. Cuff pressure was not subsequently altered.
Before the surgical procedure was commenced, we determined the effect of head rotation on the efficacy of the airway seal and on airway stability. Oropharyngeal leak pressure (OLP) was measured to evaluate airway seal efficacy. OLP was assessed by closing the expiratory valve of the circle system at a fixed gas flow rate of 3 l/min with ventilation stopped and noting the airway pressure at which the dial on a calibrated aneroid manometer (accuracy [+ or -] 2 cm[H.sub.2]O) reached equilibrium (9). The scoring system for fibreoptic determined airway positioning (FP) described by Brimacombe et al was used to determine airway stability (10). Scores were measured by passing a fibreoptic scope to a position just proximal to end of the airway tube. Positioning of the PLMA was scored as: 4=only vocal cords visible; 3=vocal cords plus posterior epiglottis visible; 2=vocal cords plus anterior epiglottis visible; 1=vocal cords not visualised. In each patient, head and neck positions were changed using the following sequence: neutral and about 45[degrees] rotation to the left or right arbitrarily. Angle of head rotation was defined as a relative angle between the subject's sagittal plane and the imaginary line perpendicular to the floor, and was measured using a levelled protractor. OLP and FP scores were measured 30 to 60 s after each head-neck position adjustment and documented by a trained assistant.
The distribution of data was determined using Shapiro-Wilks W test. Unless otherwise stated, normally distributed data were described by the mean (SD) and skewed data by median values (range). Statistical analysis was performed using the Wilcoxon signed-rank nonparametric analysis and SPSS 13.0 for Window (SPSS Inc., Chicago, IL, U.S.A.); P values of <0.05 were considered statistically significant.
The 29 study subjects comprised 24 males and five females. The age, height and body weight were 4.3 (2.0) years, 107.3 (13.4) cm and 17.3 (4.7) kg, respectively. Two size 1.5 PLMAs, 19 2.0 PLMAs and eight 2.5 PLMAs were used. PLMAs were successfully inserted at first attempts and correctly positioned in all patients. Data are presented in Table 1. Compared with the neutral position, OLP for PLMAs were higher in rotation (P <0.05). After rotating the head, 38% of subjects did not have a leak pressure change, but another 38% had an increase of at least 2 cm[H.sub.2]O above OLP-N (Figure 1). Fibreoptic findings were unaffected by head and neck position. In no case were the vocal cords not visualised by the fibreoptic scope. Mean duration of surgery was 12 minutes (range, five to 20 minutes). Gas exchange was adequate in all patients during the procedure. Unplanned device removal was not required and no accidental dislodgement occurred prior to procedure completion in any patient, and laryngospasm, bronchospasm, desaturation, or clinical evidence of aspiration did not occur in any patient.
[FIGURE 1 OMITTED]
The results of this study indicate that head rotation in the supine position does not detrimentally affect airway stability, but rather that it improves airway seal efficacy in children with the airway managed with a PLMA (sizes 1.5, 2.0 and 2.5). Although paediatric PLMAs do not have a dorsal cuff, the results of the present study concur with the results of an earlier study of adult PLMAs (8). Conversely, studies on cLMAs have yielded different results, suggesting that head rotation does not change OLP for cLMAs in children or adults (7,11).
PLMAs differ from cLMAs inasmuch as they have larger ventral and dorsal cuffs. Several reports have shown that the better sealing pressure of PLMAs is mainly due to the dorsal cuff (12-14), which pushes the ventral cuff more firmly into periglottic tissues. However, the fact that head rotation is associated with an increase in OLP for paediatric sized PLMAs suggests that the dorsal cuff plays only a minor role in improved sealing during head rotation. Moreover, when the pharyngeal airway in children is collapsed by head rotation2, it appears that the ventral cuff shape of the PLMA is better suited to periglottic tissues than that of the cLMA. We postulate that the ventral cuff shape is responsible for the modest OLP elevation observed after head rotation in the present study.
Our sample size was too small to allow meaningful analysis of the outcome according to each size of PLMA used in our study. Wheeler (15) reported that although not statistically significant, OLPs with the head-neck in neutral position were similar between the groups using 1.5 and 2.0 size PLMAs, but are slightly higher for the size 2.5 PLMA compared to the size 1.5 and 2.0 PLMAs. More data will be required to clarify these relationships according to PLMA size.
It has been established that a higher OLP actually allows a larger tidal volume in most children (16). Thus, it is likely that tidal volume is higher than in the neutral position when OLP becomes elevated after rotating the head in the supine position. However, further evaluation is needed to determine whether tidal volume is positively correlated with OLP during head rotation.
This study has the limitation, however, of selecting a different head rotation angle compared with previous studies, which used a 90[degrees] angle (7,8,11). Myringotomies at our hospital are conducted in a position where the chin is slightly rotated to the shoulder in the supine position. In this position, head rotation angle was measured at about 45[degrees]. Nevertheless, it is significant that the improved airway seal was induced by head rotation angle less than 90[degrees] in the present study.
In conclusion, our data supports the hypothesis that rotation of the head to an angle of 45[degrees] for myringotomy is associated with a stable patent airway when paediatric size PLMAs are used. Oropharyngeal leak pressure is usually maintained or increased. In our study, there was no detrimental effect of the head rotation on airway patency during myringotomy. Further work is needed using large numbers of subjects to confirm the safety of the use of the PLMA in procedures requiring head rotation, such as myringotomy.
Accepted for publication on May 29, 2007.
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W. J. CHOI *, Y. H. KIM [[dagger]]
Department of Anesthesiology and Pain Medicine, Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, Seoul, Korea
* M.D., Fellow.
[[dagger]] M.D., Ph.D., Assistant Professor.
Address for reprints: Dr Y. H. Kim, Department of Anesthesiology and Pain Medicine, Kangbuk Samsung Hospital, 108 Pyeong-dong, Jongno-Gu, Seoul 110-746, Korea.
TABLE 1 Oropharyngeal leak pressure (cm[H.sub.2]O) and fibreoptic determined position scores for ProSeal[TM] laryngeal mask airways in different head/neck positions Oropharyngeal leak Fibreoptic scores 4/3/2/1 pressures cm[H.sub.2]O (n) Neutral 22.0 (18.0-26.0) 12/11/6/0 Rotation 22.0 (18.0-31.0) * 10/13/6/0 Data are median (range) or patient numbers. * P <0.05 vs. the neutral position. Fibreoptic determined position scores: 4=only vocal cords visible; 3=vocal cords plus posterior epiglottis visible; 2=vocal cords plus anterior epiglottis visible; 1=vocal cords not visualised.
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|Author:||Choi, W.J.; Kim, Y.H.|
|Publication:||Anaesthesia and Intensive Care|
|Article Type:||Clinical report|
|Date:||Dec 1, 2007|
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