Head Rotation Reduces Oropharyngeal Leak Pressure of the i-gel and LMA® Supreme™ in Paralyzed, Anesthetized Patients: A Randomized Trial

Abstract

BACKGROUND: 

Second-generation supraglottic airway (SGA) devices are useful for airway management during positive pressure ventilation in general anesthesia and emergency medicine. In some clinical settings, such as the anesthetic management of awake craniotomy, SGAs are used in the head-rotated position, which is required for exposure of the surgical field, although this position sometimes worsens the efficiency of mechanical ventilation with SGAs. In this study, we investigated and compared the influence of head rotation on oropharyngeal leak pressures (OPLP) of the i-gel and LMA® Supreme™, which are second-generation SGA devices.

METHODS: 

Patients who underwent elective surgery under general anesthesia were enrolled in this study and randomly divided into i-gel or LMA Supreme groups. After induction of anesthesia with muscle relaxation, the i-gel or LMA Supreme was inserted according to computerized randomization. The primary outcome was the OPLP at 0°, 30°, and 60° head rotation. The secondary outcomes were the maximum airway pressure and expiratory tidal volume when patients were mechanically ventilated using a volume-controlled ventilation mode with a tidal volume of 10 mL/kg (ideal body weight), ventilation score, and fiber-optic views of vocal cords.

RESULTS: 

Thirty-four and 36 participants were included in the i-gel and LMA Supreme groups, respectively. The OPLPs of the i-gel and LMA Supreme significantly decreased as the head rotation angle increased (mean difference [95% confidence interval], P value: i-gel; 0° vs 30°: 3.5 [2.2–4.8], P < .001; 30° vs 60°: 2.0 [0.6–3.5], P = .002; 0° vs 60°: 5.5 [3.3–7.8], P < .001, LMA Supreme; 0° vs 30°: 4.1 [2.6–5.5], P < .001; 30° vs 60°: 2.4 [1.1–3.7], P < .001; 0° vs 60°: 6.5 [5.1–8.0], P < .001). There were statistically significant differences in expiratory tidal volume and ventilation score between 0° and 60° in the i-gel group and in ventilation score between 30° and 60° in the LMA Supreme group. There was no statistically significant difference between the 2 devices in all outcome measures. The incidences of adverse events, such as hoarseness or sore throat, were not significantly different between i-gel and LMA Supreme.

CONCLUSIONS: 

Head rotation to 30° and 60° reduces OPLP with both i-gel and LMA Supreme. There is no difference in OPLP between i-gel and LMA Supreme in the 3 head rotation positions.

KEY POINTS

• Question: Does head rotation worsen oropharyngeal leak pressure (OPLP) with the i-gel or LMA® Supreme™ in paralyzed, anesthetized patients?
• Findings: Head rotation to 30° and 60° reduces OPLP with both i-gel and LMA Supreme, with no difference in OPLP between i-gel and LMA Supreme in the 3 head rotation positions.
• Meaning: Head rotation should be avoided when using the i-gel or LMA Supreme to maintain optimal sealing effect of the device.

Supraglottic airway (SGA) devices are useful as an alternative to tracheal intubation for airway management. Various SGAs have been widely used and their efficacy in anesthesiology and emergency medicine investigated. Among them, i-gel (Intersurgical Ltd, Wokingham, UK) (i-gel) and LMA^® Supreme™ (Teleflex, Westmeath, Ireland) are popular as second-generation SGA devices that additionally enable placement of a gastric tube through the devices.

The i-gel is made of a thermoplastic elastomer (styrene ethylene butadiene styrene) and has the advantage that its form is changed by body temperature, providing an anatomical seal of the pharyngeal, laryngeal, and perilaryngeal structures while avoiding compression trauma.^1,2 The use of the i-gel has been expanded to include its use as a conduit for fiber-optic–guided intubation.³ The LMA Supreme is a modified second-generation SGA that is designed to match the shape of the mouth and oropharyngeal inlet, facilitating its insertion.^4,5 The LMA Supreme has an innovative second sealing function that can seal the upper esophageal sphincter and minimize gastric insufflation, minimizing the risk of aspiration. These 2 devices provide enough sealing pressure to allow positive pressure ventilation, although the adequacy of sealing presupposes that the patient’s head is in the neutral position.

The field of application of SGAs is expanding to various clinical settings and head positions. Sanuki et al⁶ investigated the influence of head position on oropharyngeal leak pressure (OPLP) of the i-gel in paralyzed patients and demonstrated that head extension significantly decreases and head flexion significantly increases OPLP. Gupta et al⁷ also reported that head flexion causes a significant increase in leak pressure of both the i-gel and LMA Supreme in a spontaneously breathing pediatric population. Various studies have been conducted to elucidate the effects of head extension and flexion on the OPLP of SGA devices, although few studies have investigated the influence of head rotation on OPLP.^8,9 The guidelines for awake craniotomy recommend the use of SGA devices for airway management during the procedure, in which a key element of the anesthetic management is the asleep-awake-asleep procedure, even if the patient’s head is rotated.^10,11 However, in clinical practice, head rotation sometimes worsens the sealing effect of SGAs, making mechanical ventilation more difficult in patients in whom muscle paralysis is induced by muscle relaxants.

In this study, we investigated the effect of head rotation on OPLP of the i-gel and LMA Supreme. Additionally, we investigated differences in OPLP between the i-gel and LMA Supreme with head rotation.

METHODS

This article adheres to the applicable CONsolidated Standards Of Reporting Trials (CONSORT) guidelines. This randomized controlled study was conducted in accordance with the Declaration of Helsinki at Sapporo Medical University Hospital and Takikawa Municipal Hospital between January 2018 and July 2019. This study was approved by the institutional review board of the hospital associated with the Sapporo Medical University School of Medicine (approval code: 302-1017) and that of Takikawa Municipal Hospital (approval code: 18-5), and written informed consent was obtained from all subjects participating in the trial. The trial was registered before patient enrollment in the University hospital Medical Information Network (UMIN)-Clinical Trials Registry (registration code: UMIN000030706, principal investigator: Yasuyuki Tokinaga, date of registration: January 5, 2018).

Eligible participants were males and females aged 18–80 years, American Society of Anesthesiologists physical status (ASA-PS) I–II, who were scheduled to undergo elective surgery under general anesthesia. Exclusion criteria were patients with the risk of pneumothorax, aspiration pneumonia, and cervical spine injury caused by head rotation, or those who were otherwise unsuitable for insertion of SGA devices. Patients were additionally ineligible if endotracheal intubation was imperative for their airway management during general anesthesia.

Participants were assigned to the i-gel or LMA Supreme group by computerized randomization in a ratio of 1:1. Standard American Society of Anesthesiologists monitors, including electrocardiography, pulse oximetry, noninvasive blood pressure, and end-tidal CO₂ were applied, and patients received preoxygenation with 100% oxygen at 6 L/min for 3 minutes in the supine position. After induction of general anesthesia with 2 mg/kg of 1% propofol, muscle relaxation was achieved by intravenous injection of 0.6 mg/kg rocuronium. The i-gel was prewarmed to 42°C in a warming cabinet with automatic temperature control for 30 minutes before its use in the i-gel group.¹² After application of a water-based gel for lubrication, the allocated SGA device was orally inserted 3 minutes after rocuronium administration. Determination of the size of the SGA device to be used was based on the patient’s body weight, as per the manufacturer’s instructions. An i-gel size 3 was chosen for individuals weighing 30–60 kg, size 4 was chosen for individuals weighing 50–90 kg, and size 5 was chosen for individuals weighing >90 kg. The LMA Supreme size 3 was used for patients weighing 30–50 kg, size 4 was used for patients weighing 50–70 kg, and size 5 was used for patients weighing >70 kg. Appropriate placement of the SGA was assessed by observation of the end-tidal CO₂ waveform and chest movements caused by squeezing the reservoir bag. The inserted SGA device was fixed by taping the device to the center of the upper lip. When the LMA Supreme was used, the intracuff pressure was adjusted to 60 cm H₂O using a cuff pressure gauge (Covidien, Dublin, Ireland) according to the manufacturer’s instructions. Five minutes after insertion of the i-gel or LMA Supreme, evaluations of the effectiveness of the SGA device were performed in all participants under a flow of 100% oxygen at 3 L/min, with the head in 3 head-rotated positions in the order of 0° (neutral), 30°, and 60°. The neutral head position was defined as the posture when the external ear canal line and the shoulder line were horizontal, and 30° and 60° head rotations were determined using a goniometer. In the LMA Supreme group, the intracuff pressure of the LMA Supreme was readjusted to 60 cm H₂O after rotation of the head. The depth of anesthesia was maintained using 0.1–0.25 μg·kg⁻¹·minute⁻¹ remifentanil and a target-controlled infusion of propofol during anesthesia, including at the time of end point measurements. The infusion rate of propofol was adjusted to achieve a bispectral index value of 40–60. Additionally, muscle relaxation was monitored using a train-of-four (TOF) monitor, and rocuronium was intermittently administered to achieve a TOF of <2 during anesthesia. During measurement of the study end points, TOF was maintained at 0.

The primary outcome was OPLP at 0°, 30°, and 60° head rotation. The secondary outcomes included maximum airway pressure and expiratory tidal volume when the patients were mechanically ventilated using a volume-controlled ventilation mode with a tidal volume of 10 mL/kg ideal body weight, ventilation score, and fiber-optic views of the vocal cords.^6,13–15 OPLP was measured by closing the expiratory valve of the circular breathing system at a fixed gas flow of 3 L/min, and noting the airway pressure at which the dial on a calibrated aneroid manometer reached equilibrium.^16–18 The OPLP was measured in 1 cm H₂O increments and in the 0–40 cm H₂O range. The maximum allowed airway pressure during this evaluation period was 40 cm H₂O, to prevent severe cardiovascular and respiratory complications.¹⁹ Ventilation was scored from 0 to 3 based on 3 criteria: no leakage with an airway pressure of 15 cm H₂O, bilateral chest excursion with a peak inspiratory pressure of 20 cm H₂O, and a square wave capnogram, each item scoring 0–1 point. If the criterion was met, the score was recorded as 1.^20,21 The positions of the i-gel and LMA Supreme were determined by passing a fiber-optic scope (Olympus, Tokyo, Japan) through the airway lumen to a position 1 cm proximal to the end of the tube and scored as 4: only vocal cords visible, 3: vocal cords and posterior epiglottis visible, 2: vocal cords and anterior epiglottis visible, and 1: vocal cords not seen.^22,23 All the above outcome measures were assessed in each head position by 1 independent observer at each institution. Thus, the outcome measurements were performed by a total of 2 observers who did not know about the purpose, design, and protocol of this study. In addition, the following data were collected as patients’ characteristics: age, height, weight, ASA-PS, anesthetic time, and operation time. The presence of sore throat and hoarseness after removal of the SGA were recorded as adverse events.

Statistical Analysis

Statistical analysis was performed with SPSS 23.0 for Windows (IBM, Chicago, IL). For within-group analysis of OPLP, maximum airway pressure, and expiratory tidal volume, repeated-measures 1-way analysis of variance (ANOVA) followed by the paired t test with Bonferroni correction as a post hoc test were used. For within-group analysis of ventilation score and fiber-optic views of the vocal cords, Friedman analysis followed by Wilcoxon signed-rank test with Bonferroni correction for 3 comparisons as a post hoc test was used. The unpaired t test was used for between-group analysis of OPLP, maximum airway pressure, and expiratory tidal volume, and Mann-Whitney U test was used for the between-group analysis of ventilation score and fiber-optic views of the vocal cords. The incidence of sore throat and hoarseness was analyzed by Fisher exact test. A 2-tailed P value of <.05 was considered a statistically significant difference. In multiple pairwise comparisons, a 2-tailed P value of <.017 (0.05/3) with Bonferroni correction was considered a statistically significant difference. Data are presented as the absolute numbers, means ± standard deviations or medians (interquartile ranges), and mean difference or Hodges-Lehmann estimator, including the confidence interval and Bonferroni-adjusted confidence interval set to 95%.

Sample size was calculated using G*power 3.1 (Heinrich-Heine-University, Düsseldorf, Germany). According to appropriate sample size calculations, a total of 64 participants were required (2-tailed, α = .017 with Bonferroni correction, 1 − β = 0.9), based on a 3.6 cm H₂O difference in OPLP, which is considered a clinically meaningful difference, and a standard deviation of 3.8, according to a previous study.²⁴ Considering an anticipated dropout rate of 10%, we determined that a total of 70 participants was necessary.

RESULTS

A total of 70 patients were enrolled in this study and were randomized into i-gel or LMA Supreme groups according to computerized randomization. None of the participants met any of the exclusion criteria. Finally, 34 and 36 participants were allocated to the i-gel and LMA Supreme groups, respectively. All of the participants were successfully followed-up and their outcomes were analyzed (Figure 1). An overview of the patients’ characteristics is presented in Table 1. The 2 groups were balanced at baseline.

Table 1. - Characteristics of the Participants

Biometric Data	i-gel (n = 34)	LMA Supreme (n = 36)	Standardized Mean Difference
Age (y)	57 ± 17	55 ± 17	0.05
Sex (F/M)	26/8	24/12	0.22
Height (cm)	158 ± 9	160 ± 8	−0.24
Weight (kg)	61 ± 14	58 ± 10	0.23
ASA-PS (I/II)	18/16	20/16	0.05
Anesthetic time (min)	126 ± 64	114 ± 50	0.20
Operation time (min)	80 ± 56	71 ± 42	0.17

Data are presented as means ± standard deviations and absolute numbers. Standardized mean difference was calculated as the difference in means or proportions divided by the standard deviation.

Abbreviation: ASA-PS, American Society of Anesthesiologists physical status.

Figure 1.: CONSORT flow diagram of this study. CONSORT indicates CONsolidated Standards Of Reporting Trials.

None of the patients’ OPLPs exceeded the upper limit of 40 cm H₂O. Ventilation score was marked as 2 or 3 in all participants. In the i-gel group, repeated-measures 1-way ANOVA revealed that there was a statistically significant difference in OPLP among the 3 head positions (F_2,33 = 33.21; P < .001) and the results of pairwise comparisons by the paired t test revealed that there were statistically significant differences in OPLP between the 3 head positions, that is between 0° and 30°, 30° and 60°, and 0° and 60° (Figure 2A; Supplemental Digital Content, Table 1, https://links.lww.com/AA/D182). Moreover, there were statistically significant differences in expiratory tidal volume (repeated-measures 1-way ANOVA; F_2,33 = 5.28; P = .008) and ventilation score (Friedman test; P = .012) between 0° and 60° positions in the i-gel group (Tables 2–3). There were no statistically significant differences in other secondary outcomes in the i-gel group (Tables 2–3).

Table 2. - Expiratory Tidal Volume and Maximum Airway Pressure During Head Rotation With the i-gel and LMA Supreme

	Measured Value	Mean Difference	95% Confidence Interval	P
Expiratory tidal volume
i-gel (within group at 3 head positions)				.008a
0° (cm H2O)	9.6 ± 1.3
30° (cm H2O)	9.1 ± 1.8
60° (cm H2O)	8.9 ± 1.7
0°–30°		0.52	−0.06 to 1.09	.030
30°–60°		0.18	−0.32 to 0.69	.364
0°–60°		0.70	0.09–1.31	.007
LMA Supreme (within group at 3 head positions)				.364a
0° (cm H2O)	9.5 ± 1.3
30° (cm H2O)	9.5 ± 1.2
60° (cm H2O)	9.3 ± 1.3
i-gel–LMA Supreme (between groups)
0°		0.14	−0.46 to 0.74	.634
30°		−0.40	−1.12 to 0.33	.278
60°		−0.37	−1.06 to 0.33	.296
Maximum airway pressure
i-gel (within group at 3 head positions)				.378a
0° (cm H2O)	15.6 ± 2.6
30° (cm H2O)	15.4 ± 3.2
60° (cm H2O)	15.6 ± 3.4
LMA Supreme (within group at 3 head positions)				.039a
0° (cm H2O)	17.2 ± 4.9
30° (cm H2O)	16.6 ± 4.7
60° (cm H2O)	16.3 ± 4.6
0°–30°		0.56	−0.22 to 1.33	.082
30°–60°		0.28	−0.23 to 0.78	.177
0°–60°		0.83	−0.11 to 1.78	.033
i-gel–LMA Supreme (between groups)
0°		−1.55	−3.45 to 0.35	.108
30°		−1.26	−3.20 to 0.67	.199
60°		−0.72	−2.64 to 1.21	.460

Data are presented as means ± standard deviations. For within-group analysis, repeated-measures 1-way ANOVA followed by the paired t test with Bonferroni correction for multiple pairwise comparisons were used. For between-group analysis, the unpaired t test was used. A P value of <.05 was considered as a statistically significant difference in repeated-measures 1-way ANOVA and unpaired t test analysis. In multiple pairwise comparisons of the 3 head positions, a P value of <.017 (0.05/3) with Bonferroni correction was considered a statistically significant difference. The multiple pairwise comparisons were performed in cases in which the P values of repeated-measures 1-way ANOVA indicated statistical significance.

Abbreviation: ANOVA, analysis of variance.

^aP value of repeated-measures 1-way ANOVA.

Table 3. - Ventilation Score and Fiber-optic View of the Vocal Folds During Head Rotation With the i-gel and LMA Supreme

	Measured Value	Hodges-Lehmann Estimator	95% Confidence Interval	P
Ventilation score
i-gel (within group at 3 head positions)				.012a
0°	3 (3–3)
30°	3 (3–3)
60°	3 (2–3)
0°–30°		0.0	0.0–0.0	.025
30°–60°		0.0	−0.1 to 0.2	.564
0°–60°		0.0	0.0–0.3	.014
LMA Supreme (within group at 3 head positions)				.004a
0°	3 (3–3)
30°	3 (3–3)
60°	3 (2–3)
0°–30°		0.0	0.0–0.0	.705
30°–60°		0.0	−0.5 to 0.0	.005
0°–60°		0.0	−0.5 to 0.0	.052
i-gel–LMA Supreme (between groups)
0°		0.0	0.0–0.0	.511
30°		0.0	0.0–0.0	.557
60°		0.0	0.0–0.0	.490
Fiber-optic view of the vocal folds
i-gel (within group at 3 head positions)				.135a
0°	3 (2–4)
30°	3 (2–3)
60°	2 (2–3)
LMA Supreme (within group at 3 head positions)				.475a
0°	3 (2–3)
30°	3 (2–3)
60°	3 (2–3)
i-gel–LMA Supreme (between groups)
0°		0.0	−1.0 to 0.0	.367
30°		0.0	−1.0 to 0.0	.544
60°		0.0	0.0–0.0	.873

Data are presented as median and interquartile ranges. For within-group analysis, Friedman test followed by Wilcoxon signed-rank test with Bonferroni correction for multiple pairwise comparisons was used. For between-group analysis, the Mann-Whitney U test was used. A P value of <.05 was considered a statistically significant difference in the Friedman test and Mann-Whitney U test. In multiple pairwise comparisons within each group, a P value of <.017 (0.05/3) with Bonferroni correction was considered a statistically significant difference. The multiple pairwise comparisons were performed in cases in which the P values of Friedman test indicated statistical significance.

^aP value of Friedman test.

Figure 2.: OPLP with head rotation with the i-gel and LMA Supreme. OPLP was measured with the patient’s head rotated to 3 positions, in the order of 0°, 30°, and 60°. A, OPLP in the i-gel group. B, OPLP in the LMA Supreme group. Data are presented as means and standard deviations. Repeated-measures 1-way analysis of variance followed by paired t test with Bonferroni correction as a post hoc test are used for data analysis (i-gel: F _2,33 = 33.21, P < .001, LMA Supreme: F _{2 ,35} = 70.20, P < .001). *P < .001, †P = .002. The descriptive data and details of analysis are presented in Supplemental Digital Content, Table 1, https://links.lww.com/AA/D182. OPLP indicates oropharyngeal leak pressure.

In the LMA Supreme group, repeated-measures 1-way ANOVA revealed that there was a statistically significant difference in OPLP among the 3 head positions (F_2,35 = 70.20; P < .001), and the results of pairwise comparisons by the paired t test revealed that there were statistically significant differences in OPLP between the 3 head positions, that is, between 0° and 30°, 30° and 60°, and 0° and 60° (Figure 2B; Supplemental Digital Content, Table 1, https://links.lww.com/AA/D182). Furthermore, there was a statistically significant difference in ventilation score (Friedman test; P = .004) between 30° and 60° head rotation positions (Table 3). There were no significant differences in the other secondary outcomes in the LMA Supreme group (Tables 2–3).

Comparison between i-gel and LMA Supreme groups indicated no statistically significant difference in primary and secondary outcomes between them (Tables 2–3; Supplemental Digital Content, Table 1, https://links.lww.com/AA/D182). Moreover, the incidences of sore throat and hoarseness were not significantly different between the 2 groups (sore throat: i-gel: 4/34 [11.8%] versus LMA Supreme: 6/36 [16.7%], difference of proportion: −0.049, 95% CI, −0.021 to 0.144, P = .736; hoarseness: i-gel: 2/34 [5.9%] versus LMA Supreme 2/36 [5.6%], difference of proportion: 0.003, 95% CI, −0.106 to 0.112; P > .999).

DISCUSSION

In this study, we evaluated the effect of head rotation on OPLP of the i-gel and LMA Supreme. The results indicated that OPLP decreased with head rotation by 30° and 60°, although the decrease was not significantly different between the 2 SGA devices.

In this study, OPLP decreased as head rotation increased. Although many studies have elucidated the effects of head flexion and extension on SGA device performance, only a few reports have evaluated the influence of head rotation on the OPLP of SGA devices. Somri et al²⁵ investigated the effect of head rotation on OPLP of the laryngeal tube suction airway device and LMA Supreme as a secondary outcome. Like our results, their results suggested that maximum head rotation significantly decreases OPLP, although the mechanism of the decrease in OPLP was not elucidated. Nakayama et al²⁶ investigated the effects of head rotation on pharyngeal structure using computed tomography. They revealed that head rotation increased the volume and cross-sectional area of the opposite side of the pharynx, and deepened the opposite pyriform fossa. Considering these structural changes in the pharynx, head rotation seems to worsen the fit between SGA devices and the pharynx on the side opposite to that of head rotation, resulting in a decrease in OPLP. The results of fiber-optic visualization of the vocal folds in our study indicated that head rotation did not induce gross malposition of the 2 SGA devices. Hence, we suppose that the main mechanism of the worsening OPLP was not gross displacement of the i-gel and LMA Supreme, but the anatomical changes induced in the pharynx by head rotation.

Maximum airway pressures at each of the 3 head rotation angles were lower than the OPLP when participants were mechanically ventilated with a tidal volume of 10 mL/kg ideal body weight using a volume-controlled ventilation mode, which seems to be an adequate tidal volume for mechanical ventilation in clinical situations. In the participants of this study, although head rotation significantly reduced OPLP, the 2 devices provided clinically acceptable functionality to allow effective positive pressure ventilation. However, it is possible that the 2 SGA devices might not be able to ensure adequate tidal volume in patients with low thoracic cage compliance (eg, in obese individuals). Hence, we additionally analyzed the data of patients stratified according to their body mass index (BMI) as obese (BMI >30 kg/m²) and nonobese (BMI ≤30 kg/m²) patients. The maximum airway pressure of obese patients was significantly higher than that of nonobese patients, although OPLP was not significantly different between obese and nonobese participants (data not presented). Moreover, maximum reduction in OPLP was seen at a head rotation of 60° in obese patients and the value of OPLP was nearly equal to the level of maximum airway pressure. Thus, we opined that head rotation should be avoided when using the i-gel or LMA Supreme during mechanical ventilation, especially in obese patients who require a high positive airway pressure.

OPLP in our study was lower than that in other reports. Several studies reported OPLP in various head positions, and almost all the results suggested that OPLPs were more than 25 cm H₂O.^7,13–15 The cause of this difference in OPLP might be that the participants in our study were limited to Asian people. Kimijima et al²⁷ used pressure sensors to investigate the pressure exerted by the i-gel on the pharyngeal mucosa of Japanese Thiel embalmed cadavers, and reported that excessive pressures were exerted by certain parts of the noninflatable cuff of the i-gel when they were inserted into female cadavers.²⁷ They also suggested that anatomical differences between Japanese and Caucasian women were the cause of the excessive pressure. In our study, since the majority of participants (50 of 70 participants) were women, we believe that the relatively small pharyngeal space of Japanese females was responsible for the poor fit between the SGAs and pharyngeal wall, inducing the lower OPLP.

Although the superiority of i-gel or LMA Supreme with head rotation could not be clarified in this study, head rotation should be avoided when i-gel or LMA Supreme is used for airway management in paralyzed patients. Some guidelines recommend SGA usage for airway management during awake craniotomy.^10,28 Since head rotation is often required by neurosurgeons when approaching brain tumors in the vicinity of motor and language areas of the cortex, anesthesiologists must provide a suitable patient posture that meets the needs of both the required surgical field and SGA fit. Some studies have revealed that OPLP was maintained when the patient’s posture was changed from supine to lateral.^29,30 Therefore, anesthesiologists should use other measures to achieve the patient position required for exposure of the operative field, including adoption of the lateral decubitus position and bed rotation, rather than head rotation. However, since various factors influence SGA function in clinical settings, we plan to evaluate the function of different SGAs during airway management for awake craniotomy.

Our study has several limitations. First, OPLP in the i-gel group might have been higher if the measurement was performed several tens of minutes after insertion, because the i-gel is made of a thermoplastic elastomer. However, according to a previous report, fitting of the prewarmed i-gel did not change 30 minutes after device insertion.³¹ Thus, we believe that the timing of outcome measurements did not influence our results. Second, blinding about patient allocation was impossible in our study because of its protocol. The observer could easily detect which SGA was being used, which might have caused observer bias. Third, our study outcomes were evaluated in paralyzed patients. Muscle relaxants influence the pharyngeal muscles, which can potentially change the functioning of SGAs under mechanical ventilation. Hence, our study results might not be applicable to nonparalyzed patients.

In conclusion, this study revealed that head rotation to 30° and 60° reduces OPLP with both the i-gel and LMA Supreme. However, there is no difference in OPLP between i-gel and LMA Supreme in the 3 head positions. Further studies should be performed to evaluate the effect of head rotation on the OPLP of various SGA devices.

ACKNOWLEDGMENTS

The authors thank Tomoko Sonoda, DDS, PhD (Department of Basic Medical Science, Department of Public Health, Sapporo Medical University School of Medicine, Sapporo, Japan) for advice regarding the statistical analyses.

DISCLOSURES

Name: Tomohiro Chaki, MD, PhD.

Contribution: This author served as the global chief investigator for the study and helped design the study, develop the protocol, enroll patients, review final data, and critically review the manuscript.

Name: Shunsuke Tachibana, MD, PhD.

Contribution: This author helped design the study, develop the protocol, enroll patients, and review final data.

Name: Sho Kumita, MD.

Contribution: This author helped develop the protocol and enroll patients.

Name: Honami Sato, MD.

Contribution: This author helped enroll patients.

Name: Kosuke Hamada, MD.

Contribution: This author helped design the study and develop the protocol.

Name: Yasuyuki Tokinaga, MD, PhD.

Contribution: This author helped design the study and develop the protocol.

Name: Michiaki Yamakage, MD, PhD.

Contribution: This author served as the study director and helped design the study, develop the protocol, oversee study operational activities, review final data, and critically review the manuscript.

This manuscript was handled by: Narasimhan Jagannathan, MD, MBA.