Supraglottic airway (SGA) devices have become popular in airway management.1 Compared with traditional devices, SGAs provide a less invasive and quicker alternative for securing the airway, especially in patients with difficult airways or in situations when securing an urgent airway is necessary.2,3 Moreover, second-generation SGAs offer improved protection against gastric regurgitation and pulmonary aspiration through a gastric drainage channel, which is positioned at the opening of the esophagus after insertion.4 Therefore, the use of second-generation SGAs such as the i-gel® (Intersurgical Ltd., Wokingham, Berkshire, UK) is recommended as a rescue technique in both difficult airways and routine airway management.3,5,6

Despite the established role of SGAs in difficult airways, their usefulness is questionable in patients with an increased risk of gastric regurgitation. Nevertheless, when tracheal intubation is unsuccessful, SGAs can be inevitably used in them. As a standard technique, application of cricoid pressure has been suggested to prevent gastric regurgitation by compressing and occluding the upper esophagus over the cricoid cartilage during rapid sequence induction of anesthesia. Nevertheless, because the cuff of the SGA occupies the hypopharyngeal space and upper esophagus, cricoid pressure might hinder insertion of the SGA and make ventilation via the SGA difficult.7,8,9

Application of paratracheal pressure is a novel technique proposed as an alternative to cricoid pressure. Paratracheal pressure compresses the esophagus immediately above the clavicle and more effectively prevents gastric insufflation during positive-pressure ventilation than cricoid pressure.10,11 In contrast to cricoid pressure, paratracheal pressure is applied to the lower cervical esophagus; therefore, it might have a limited effect on the hypopharynx and allow more successful insertion of SGAs. A recent study showed the noninferiority of paratracheal pressure compared with cricoid pressure in achieving successful insertion of the LarySeal laryngeal mask airway (LMA) (Flexicare, Inc., Irvine, CA, USA).12 An LMA has a longer cuff and tapered tip, allowing it to protrude more deeply into the upper esophageal sphincter. By contrast, the i-gel, a widely used second-generation SGA with unique characteristics such as a thermoplastic noninflating cuff with a round, blunt tip, does not fully occupy the hypopharyngeal space.13 Therefore, insertion of the i-gel may be much less affected by paratracheal pressure than by cricoid pressure; however, this has not yet been investigated. In the present study, we evaluated the effects of cricoid and paratracheal pressures on the success rate of i-gel insertion, the time required for insertion, accuracy of the insertion location, resistance during insertion, and ventilation after insertion.

Methods

Ethics

The study was approved by the Institutional Review Board of SMG-SNU Boramae Medical Center, Seoul, Republic of Korea (approval no. 10-2022-55; date of approval, 4 July 2022) and registered at ClinicalTrials.gov before patient enrolment (NCT05377346; principal investigator, Jin-Young Hwang; date of registration, 17 May 2022). The study protocol complied with the ethical guidelines of the Declaration of Helsinki. We obtained written informed consent from the study participants. This report conformed to the applicable Consolidated Standards of Reporting Trials (CONSORT) guidelines.

Study design and patient selection

This study involved patients aged > 18 yr who were scheduled for surgery under general anesthesia with a supraglottic airway from September 2022 to April 2023. The exclusion criteria were risk factors for pulmonary aspiration (e.g., achalasia or pregnancy), known or predicted difficult airway, anatomic variation or pathology of the upper airway, requirement for postoperative ventilator care, and surgeries requiring positions other than supine. We recorded the following patient characteristics: age, sex, weight, height, body mass index, American Society of Anesthesiologists Physical Status, and airway characteristics (Mallampati score, thyromental distance, sternomental distance, and neck circumference).

Randomization

We randomly allocated the enrolled patients to one of two groups: those who underwent application of cricoid pressure (cricoid group) and those who underwent application of paratracheal pressure (paratracheal group) during and after i-gel insertion. For randomization, we generated a web-based random sequence with block sizes of 4 and 12 (Research Randomizer, Social Psychology Network, Wesleyan University, Middletown, CT, USA; available from URL: https://randomizer.org; accessed January 2024). We sealed the sequence in an opaque envelope, which was kept by an anesthesiologist who was not involved in the study.

Anesthesia procedure

The patients entered the operating room without premedication. Routine monitoring included electrocardiography, pulse oximetry, and noninvasive blood pressure monitoring. After preoxygenation, anesthesia was induced with lidocaine (30 mg), propofol (1–2 mg·kg−1), fentanyl (1–2 μg·kg−1), and rocuronium (0.6 mg·kg−1). After neuromuscular blockade, we covered the patient’s neck with an opaque drape so that the anesthesiologists who performed the i-gel insertion were blinded to the group allocation. We selected the size of the i-gel according to the manufacturer’s recommendation: size 3 for patients with a body weight of < 50 kg, size 4 for those with a body weight of 50–90 kg, and size 5 for those with a body weight of > 90 kg. In the cricoid group, cricoid pressure was applied with a force of 30 N, equivalent to approximately 3.06 kg (9.8 N = 1 kg), using a three-finger maneuver. While applying cricoid pressure, the patient’s head was maintained in the sniffing position and was supported with the other hand of the clinician performing the maneuver to prevent head flexion (bimanual maneuver).14 In the paratracheal group, paratracheal pressure was applied with a force of 30 N against the vertebral body with a 3–12-MHz linear ultrasound transducer (Vscan with Dual Probe; GE HealthCare, Chicago, IL, USA) while observing the esophageal obstruction, and the clinician performing the maneuver also supported the patient’s neck (Fig. 1). Ultrasound was prepared in both groups for blinding. Two anesthesiologists with experience performing more than 300 i-gel insertions performed the i-gel insertion. After inserting the i-gel, the anesthesiologist attempted positive-pressure ventilation with gentle manual bagging under each maneuver. If an adequate tidal volume could not be achieved, the anesthesiologist repositioned the i-gel, and ventilation was re-evaluated. We defined successful insertion as the presence of a square expiratory carbon dioxide curve on capnography and an adequate tidal volume in the absence of a pharyngeal leakage sound with a peak airway pressure of ≥ 12 cm H2O during gentle manual ventilation.15 We allowed two attempts, and each attempt proceeded for 60 sec. If the i-gel could not be inserted within 60 sec, the anesthesiologist ventilated the patient with a facial mask and attempted i-gel insertion again. If the second attempt was unsuccessful, we recorded the case as a failure and the i-gel was inserted without the allocated maneuver. We defined the time required for insertion as the duration of time from picking up the i-gel to detecting the square waveform on capnography, and it was calculated by adding the time taken for each attempt. In successful cases, the allocated maneuvers were maintained, and we recorded the tidal volume and peak inspiratory pressure while the mechanical ventilation was set in volume-control mode with a tidal volume of 8 mL·kg−1 of ideal body weight, respiratory rate of 12 breaths·min−1, and zero end-expiratory pressure. Subsequently, the tidal volume and peak inspiratory pressure without the allocated maneuver were recorded using the same ventilator settings. The resistance felt by the anesthesiologist while inserting the i-gel was evaluated on a 4-grade scale (1, no resistance; 2, moderate resistance; 3, severe resistance; and 4, impossible to insert the i-gel). Finally, we assessed the accuracy of the insertion location by the anatomical alignment of the i-gel in the larynx using a fibreoptic bronchoscope with an outer diameter of 4.1 mm (Olympus LE-P, Olympus Optical Co., Tokyo, Japan) positioned at the end of the tube section of the i-gel. The accuracy was recorded on a five-grade scale (1, only glottis observed; 2, posterior surface of epiglottis and glottis observed; 3, anterior part or tip of epiglottis and > 50% of glottis observed; 4, down-folded epiglottis and < 50% of glottis observed; and 5, glottis completely obscured by down-folded epiglottis).16

Fig. 1
figure 1

Diagram of cricoid pressure and paratracheal pressure

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The primary outcome was the overall success rate of i-gel insertion. The secondary outcomes were the time required for insertion, the accuracy of the insertion location evaluated with a fibreoptic bronchoscope, resistance during insertion, and the tidal volume and peak inspiratory pressure with or without each maneuver after i-gel insertion.

Statistical analysis

All statistical analyses were performed with IBM SPSS Statistics for Windows version 26.0 (IBM Corp., Armonk, NY, USA). We tested continuous variables for normality with graphical methods such as histograms and Q–Q plots, as well as the Kolmogorov–Smirnov test. Values are expressed as mean (standard deviation), median [interquartile range (IQR)], or number (percentage). Point and interval estimates were determined for between-group differences. We tested continuous data with Student’s t test or the Mann–Whitney U test, and categorical data with the Chi square or Fisher’s exact test. In all analyses, P < 0.05 was considered statistically significant.

The sample size calculation was based on a pilot study of 30 patients in our centre. The insertion success rate was 0.93 while applying paratracheal pressure and 0.67 while applying cricoid pressure. With a type I error of 0.05, a power of 0.8, and a dropout rate of 10%, we included 76 patients (38 patients in each group).

Results

In total, we recruited 81 patients from September 2022 to April 2023. Among the recruited patients, two did not fulfill the inclusion criteria and three declined to participate. The remaining 76 patients were enrolled in the study and included in the analysis (Fig. 2). The patients’ characteristics are presented in Table 1.

Fig. 2
figure 2

CONSORT flow diagram of the study

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Table 1 Patient baseline characteristics and airway data
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Data related to the i-gel insertion procedures are presented in Table 2. The overall success rate of insertion was significantly higher in the paratracheal group than in the cricoid group (36/38 [95%] vs 27/38 [71%], respectively; difference, 24%; 95% confidence interval [CI], 8 to 40; P = 0.006). The success rate of insertion on the first attempt was also significantly higher in the paratracheal group than in the cricoid group (36/38 [95%] vs 25/38 [66%], respectively; difference, 29%; 95% CI, 12 to 46; P = 0.002). Repositioning of the i-gel was less frequently required in the paratracheal group than in the cricoid group (14/38 [37%] vs 29/38 [76%], respectively; difference, −39%; 95% CI, −60 to −19; P = 0.001). Resistance during insertion was significantly lower in the paratracheal group than in the cricoid group (P < 0.001). The time required for insertion was significantly shorter in the paratracheal group than in the cricoid group (median [IQR], 18 [15–23] sec vs 28 [22–38] sec, respectively; difference in medians, −10; 95% CI, −18 to −4; P < 0.001). Fibreoptic examination of the anatomical alignment of the i-gel in the larynx revealed no significant difference in the accuracy of the insertion location around the vocal cord between the two groups (P = 0.31). The difference in the tidal volume with or without the maneuvers was significantly lower in the paratracheal group than in the cricoid group (median [IQR], 0 [0–22] mL vs 40 [10–110] mL, respectively; difference in medians, −38; 95% CI, −90 to −8; P = 0.003). The difference in the peak inspiratory pressure with or without the maneuvers was also significantly lower in the paratracheal group than in the cricoid group (median [IQR], 1 [0–2] cm H2O vs 3 [1–7] cm H2O, respectively; difference in medians, −2; 95% CI, −6 to −1; P = 0.003).

Table 2 Data related to i-gel® insertion under paratracheal pressure or cricoid pressure
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Discussion

The present study found that the success rate of i-gel insertion was significantly higher in the paratracheal group than in the cricoid group. Additionally, the insertion time was significantly shorter and easier in the paratracheal group than in the cricoid group. After insertion, the tidal volume and peak inspiratory pressure were less affected by paratracheal pressure than by cricoid pressure. Nevertheless, there was no significant difference in the accuracy of the insertion location between the two groups.

In this study, paratracheal pressure significantly improved both the first-attempt and overall success rates of i-gel insertion compared with cricoid pressure. We did not compare paratracheal pressure to the sham procedure; however, the overall success rate under paratracheal pressure in our study was 36/38 (95%), comparable to the success rate in a multicentre observational study of routine clinical practice (first-attempt and overall success rates of 93% and 96%, respectively).17 In contrast to our results, however, a previous study comparing cricoid and paratracheal pressures for LMA insertion showed no significant difference in the first-attempt and overall success rates between the two maneuvers.12 In that study, the overall success rate of LMA insertion was 76% under paratracheal pressure and 78% under cricoid pressure. Compared with the LMA, the i-gel has a shorter cuff with a round, blunt tip that conforms to the larynx rather than the hypopharynx. A magnetic resonance imaging study of the in vivo position of the i-gel and LMA Supreme™ (Teleflex Inc., Wayne, PA, USA) showed that the tip of the i-gel remained on the upper margin of the upper esophageal sphincter, whereas the LMA Supreme intruded more deeply into the upper esophageal sphincter. These findings indicate that insertion of the i-gel is less affected by paratracheal pressure than insertion of the LMA is.

We also found that the time required to insert the i-gel was significantly shorter under paratracheal pressure than under cricoid pressure. Although the median difference in the insertion time between the two groups was only ten seconds, its clinical significance should not be ignored because our results suggest that insertion of the i-gel can be more rapidly performed in patients with difficult airways during rapid sequence induction.

The i-gel can be used as an intubation conduit, and optimal alignment with the glottic inlet is important for successful tracheal intubation via the i-gel. The i-gel has an epiglottic rest that prevents the epiglottis from down-folding or obstructing the airway. Studies have shown that the i-gel provides an optimal fibreoptic view of the vocal cords (only the vocal cords are visualized) in > 70% of patients.8,18,19 In the present study, however, the glottic view without epiglottic down-folding was observed in eight of 36 (22%) patients in the paratracheal group and five of 27 (19%) patients in the cricoid group. Therefore, when inserted under the application of cricoid or paratracheal pressure, the i-gel may not serve as an effective intubation conduit.

In the present study, cricoid pressure affected the tidal volume and peak inspiratory pressure more strongly than paratracheal pressure. Nevertheless, the accuracy of the i-gel insertion location was similar between the two groups, consistent with a previous study showing that mask ventilation was easier. Peak inspiratory pressure was less affected by paratracheal pressure than by cricoid pressure in anesthetized patients.20 This finding might suggest that airway obstruction is responsible for the deterioration of ventilation during the application of cricoid pressure.

This study had several limitations. First, we did not evaluate laryngopharyngeal damage. Resistance induced by paratracheal pressure or cricoid pressure might lead to laryngopharyngeal damage, thereby causing perioperative complications such as sore throat, hoarseness, and dysphagia. In our study, the resistance felt during insertion was significantly greater during cricoid pressure; therefore, cricoid pressure might result in a higher rate of postoperative laryngopharyngeal complications. Second, this study was conducted in nonobese anesthetized, paralyzed, and fasted patients who were undergoing elective surgery. Therefore, our results may not be generalized to different clinical situations, such as patients with obesity, spontaneously breathing patients, critically ill patients, or nonfasted patients in the emergency setting. Third, as stated above, we did not compare the insertion success rate between paratracheal pressure and a sham procedure. Therefore, further study might be needed comparing the i-gel insertion success rate during paratracheal pressure versus a sham procedure. Fourth, we applied paratracheal pressure with an ultrasound probe because a previous study showed that the esophagus was found on the right side of the lower paratracheal region in 1.4% of patients20 and the actual probability of right-sided esophagus in the paratracheal region has not been accurately investigated. Nevertheless, it might be more reasonable to apply paratracheal pressure with a thumb or index finger instead of the ultrasound probe during an emergency.10 Finally, we did not directly monitor the pressure of 30 N during each maneuver in this study. The investigator who performed each maneuver practiced the application of 30 N based on a previous study showing that 30 N of cricoid pressure is reproducible through proper training.21 Nevertheless, the possibility of errors in the magnitude of a given force cannot be ruled out.

In conclusion, the insertion success rate of the i-gel was higher with the application of paratracheal pressure than with cricoid pressure. Insertion of the i-gel was also significantly easier and faster while applying paratracheal pressure than cricoid pressure. The accuracy of the insertion location was not different between the two maneuvers. When the i-gel is used in patients with an increased risk of gastric regurgitation as a rescue technique for failed intubation, paratracheal pressure can be considered for successful i-gel placement.