Effect of Paratracheal Pressure on the Glottic View During Direct Laryngoscopy: A Randomized Double-Blind, Noninferiority Trial : Anesthesia & Analgesia

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Original Research Articles: Original Clinical Research Report

Effect of Paratracheal Pressure on the Glottic View During Direct Laryngoscopy: A Randomized Double-Blind, Noninferiority Trial

Won, Dongwook MD*; Kim, Hyerim MD*; Chang, Jee-Eun MD*; Lee, Jung-Man MD, PhD*; Min, Seong-Won MD, PhD*; Ma, Seoyoung MD†; Kim, Chanho MD†; Hwang, Jin-Young MD, PhD*; Kim, Tae Kyong MD, PhD*

Author Information

From the *Department of Anesthesiology and Pain Medicine, Seoul Metropolitan Government-Seoul National University Boramae Medical Center and

†Department of Anesthesiology and Pain Medicine, Seoul National University Hospital, Seoul National University College of Medicine, Seoul, Republic of Korea.

Published ahead of print 01 June 2021.

Accepted for publication April 26, 2021.

Funding: None.

The authors declare no conflicts of interest.

Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s website.

ClinicalTrial.gov, identifier: NCT03908411, registry URL: https://clinicaltrials.gov/ct2/show/NCT03908411.

Reprints will not be available from the authors.

Address correspondence to Tae Kyong Kim, MD, PhD, Department of Anesthesiology and Pain Medicine, Seoul Metropolitan Government-Seoul National University Boramae Medical Center, Seoul National University College of Medicine, 20 Boramae-ro 5-gil, Dongjak-gu, Seoul 07061, Republic of Korea. Address e-mail to [email protected].

Anesthesia & Analgesia 133(2):p 491-499, August 2021. | DOI: 10.1213/ANE.0000000000005620

Abstract

KEY POINTS

  • Question: Is paratracheal pressure noninferior to cricoid pressure with respect to the effect on glottic view during direct laryngoscopy?
  • Findings: Paratracheal pressure was noninferior to cricoid pressure regarding the incidence of deteriorated glottic view during direct laryngoscopy.
  • Meaning: If proven to be effective in preventing passive regurgitation/aspiration, then paratracheal pressure might be used instead of cricoid pressure during rapid sequence induction and intubation technique without worrying deterioration of the glottic view.

The aspiration of gastric contents is a major cause of anesthesia-related fatality and complications.1 Its reported incidence ranges from 0.7 to 4.7 per 10,000 general anesthesia inductions with a mortality rate of 3.8% to 4.6%.2,3 Usually, gastric regurgitation and aspiration can be prevented by preoperative fasting in surgical patients.3,4 However, some patients continue to exhibit risk factors for gastric regurgitation that cannot be attenuated by preoperative fasting.5 To avoid pulmonary aspiration in such patients, the rapid sequence induction and intubation (RSII) technique has been used.

Cricoid pressure has been used as a component of the RSII technique.6,7 The main mechanism of cricoid pressure is indirect occlusion of the esophagus between the cricoid cartilage and the bodies of the cervical vertebra.6,8 However, cricoid pressure has been noted to have suboptimal effectiveness, because the esophagus might not be directly behind the cricoid cartilage.9,10 Notably, the esophagus is not fixed to the cricoid cartilage or the cervical vertebrae. Therefore, if they are not aligned in parallel, the esophagus can be displaced laterally by cricoid pressure, resulting in incomplete obstruction of the esophagus.9,11 Furthermore, cricoid pressure itself may decrease the tone of lower esophageal sphincter.12,13 Indeed, there have been reports of aspiration of gastric contents, regardless of cricoid pressure application.14,15

Also, cricoid pressure can interfere with tracheal intubation by worsening the glottic view during direct laryngoscopy.16,17 In a recent large randomized controlled trial, cricoid pressure caused longer intubation time and worsened Cormack–Lehane grade during direct laryngoscopy compared to a sham procedure, suggesting an increased difficulty in tracheal intubation by cricoid pressure.18 Other studies have shown that cricoid pressure can compromise airway patency, thus interfering with mask ventilation and tracheal tube advancement.19–21

Recently, alternatives to cricoid pressure have emerged based on ultrasonographic anatomical observations.22,23 Paralaryngeal or paratracheal pressure was more effective than cricoid pressure in occluding the esophagus or preventing the entrance of air into the stomach during mask ventilation.22,23 Still, there remains uncertainty concerning its widespread acceptance. Further efficacy and safety studies are required to determine whether paratracheal pressure is effective in preventing gastric reflux or aspiration, and whether any adverse effects are not greater compared to cricoid pressure.24 Similar to cricoid pressure, paratracheal pressure may deteriorate the laryngoscopic view because the maneuver is applied to an adjacent region of the airway. Therefore, we tested the hypothesis that paratracheal pressure would not deteriorate the glottic view during direct laryngoscopy, compared to cricoid pressure.

METHODS

Study Design and Patient Selection

F1
Figure 1.:
CONSORT flow diagram. CONSORT indicates Consolidated Standards of Reporting Trials.

This was a prospective, randomized, double-blind, noninferiority clinical trial. This study was approved by the Institutional Review Board of Seoul Metropolitan Government-Seoul National University Boramae Medical Centre, Seoul, South Korea (no. 10–2019–16), and written informed consent was obtained from all subjects participating in the trial. The trial was registered before patient enrollment at clinicaltrials.gov (NCT03908411, principal investigator: T.K.K., date of registration: April 9, 2019). The study protocol followed the ethical guidelines of the Declaration of Helsinki. Reporting of the study conformed with the Consolidated Standards of Reporting Trials statement. From September 2019 to February 2020, patients who were ages ≥18 years and scheduled for general elective surgeries were enrolled (Figure 1). Patients who were at risk for gastric regurgitation or with a history of operation on the neck or esophagus, known stenosis or bruit of the left carotid artery, and/or history of stroke or acute coronary syndrome in the preceding 3 months were excluded. Written informed consent was obtained from all patients before surgery.

Randomization and Blinding

All enrolled patients were randomly allocated to 1 of 2 groups: those in whom paratracheal pressure was applied and those in whom cricoid pressure was applied. To this end, block randomization (block size of 10) was applied using a web-based random sequence generator (http://randomizer.org), and the results were printed and kept in an opaque envelope. A reproducible randomization seed was not utilized. The sequence was managed by a research assistant who was not otherwise involved in the study. Anesthesiologists who performed mask ventilation and tracheal intubation were blinded from patient allocation by an opaque drape covering the patient’s neck and the maneuver provider’s hand. The drape was maintained until the tracheal intubation was completed. Mask ventilation, tracheal intubation, and glottic view grading were all performed by attending anesthesiologists with more than 10 years of experience in anesthesiology.

Anesthesia Procedure

A researcher was trained in the application of paratracheal and cricoid pressure before the study period. We used a 50 mL syringe model to train for applying the correct force.25 Force compressing the volume of a syringe filled with air from 50 to 33 mL was measured as 30 N by scale. The training was repeated at 2-month intervals throughout the study period to maintain the skill.26

All patients entered the operating room without premedication. Routine monitoring included electrocardiography, noninvasive blood pressure, and pulse oximetry. Anesthesia was induced after adequate preoxygenation, using intravenous lidocaine (30 mg), fentanyl (1–2 μg·kg−1), propofol (1.5–2 mg·kg−1), and rocuronium bromide (0.6 mg·kg−1). A Guedel airway was placed in each patient and maintained during manual and mechanical mask ventilation period. During mask ventilation using 6% sevoflurane with oxygen, the transverse spatial relationship of the esophagus with the trachea and cricoid cartilage in the patient was examined with a 5 to 12 MHz linear ultrasound transducer (CX50 ultrasound machine; Philips Healthcare, Andover, MA). The examination focused on the lower-left paratracheal region and the cricoid cartilage-containing region.23 Based on the ultrasound examination, the position of the esophagus in relation to the trachea and the cricoid cartilage was categorized into 5 categories: (1) left (the esophageal lumen deviated to the patient’s left side and did not overlap the trachea or cricoid cartilage), (2) partial left (the esophageal lumen partially overlapped the left side of the trachea or cricoid cartilage), (3) middle (the esophagus fully overlapped behind the trachea or cricoid cartilage), (4) partial right (the esophageal lumen partially overlapped the right side of the trachea or cricoid cartilage), or (5) right (the esophageal lumen deviated to the patient’s right side and did not overlap the trachea or cricoid cartilage).

After the ultrasound examination, the effect of the allocated maneuver on manual bag-mask ventilation was evaluated. In the paratracheal group, a pressure of 30 N against the vertebral body was applied by the researcher’s thumb, at the left side of patient’s trachea, immediately above the left clavicle and medial to the sternocleidomastoid muscle.23 In the cricoid group, cricoid pressure was applied with a single-handed 3-finger maneuver (Figure 2).6,27 The group allocation was maintained throughout the study period. In both groups, the chosen maneuver was initiated based on viewing real-time images of the target area. While applying the allocated intervention, ease of manual bag-mask ventilation was graded using a 4-point scale: (1) easy (manual ventilation achieved easily while the allocated maneuver was applied), (2) moderate (adequate manual ventilation achieved by increasing fresh gas flow or adjusting the adjustable pressure limit valve), (3) difficult (inadequate ventilation volume with increased airway pressure), or (4) impossible (patient could not be ventilated during the application of allocated intervention and expiratory carbon dioxide could not be detected).

F2
Figure 2.:
Diagrams showing paratracheal and cricoid pressures. A, Paratracheal pressure. B, Cricoid pressure.

Thereafter, after the allocated maneuver was released, mechanical ventilation was applied with a facemask. Change in expired tidal volume and peak inspiratory pressure (PIP) was recorded to evaluate airway obstruction. Mechanical ventilation was set in volume-controlled ventilation mode with a tidal volume of 8 mL·kg−1, respiratory rate of 12 breaths per minute, positive end-expiratory pressure of 5 cm H2O, and an inspiratory-to-expiratory ratio of 1:2, with 6% sevoflurane with oxygen. The facemask was held using a 2-handed technique. After baseline expired tidal volume and PIP had been recorded, the ventilatory parameters were recorded while applying the allocated intervention. All ventilatory parameters were recorded once they had reached a steady state.

Subsequently, the effect of the maneuver on the laryngoscopic view was evaluated. The effect of each maneuver was defined as the incidence of deteriorated glottic view during direct laryngoscopy using the allocated maneuver, compared to the view without the maneuver. Initially, sequential glottic views with and without an allocated maneuver were evaluated using the modified Cormack–Lehane grade for the primary end point, which subdivides grade 2 of the original Cormack–Lehane grade into grades 2a and 2b (2a, partial view of glottis; 2b, only arytenoid cartilages evident) and percentage of glottic opening (POGO) score for a secondary end point, to increase the sensitivity for laryngoscopic view deterioration (Figure 3).28–30 As a primary end point, the change in modified Cormack–Lehane grade was categorized into binary values for noninferiority assessment: “worsened” and “not worsened.” “Worsened” Cormack–Lehane grade was defined as a decrease of glottic exposure, for example, grade 1 to grade 2a, 2b, 3, or 4, or grade 2a to 2b, 3, or 4. We used a binary outcome because we were interested in whether the maneuvers deteriorate laryngoscopic view or not. In addition, the change in POGO score was also recorded.30 As POGO score was recorded by a 10% interval, a decrease of POGO score ≥10% was recorded as “worsened.” After evaluating the laryngoscopic view, tracheal intubation was conducted during the application of each intervention. Tube resistance while advancing the tracheal tube through the glottis was evaluated on a 4-point scale: slight, moderate, severe, and obstructed. The ease of tracheal intubation was also evaluated using a 4-point scale: easy (tracheal intubation was achieved with a single trial), moderate (tracheal intubation was achieved with multiple tracheal tube attempts or increased laryngoscopic force), difficult (tracheal intubation was achieved only by tracheal tube modification, such as with a stylet), or impossible. Also, duration of intubation was recorded. Duration of intubation was defined as the time interval between insertion of the tracheal tube into the oral cavity and the confirmation of the capnography. If the allocated maneuver was released to complete tracheal intubation, the case was recorded along with the reason for release of the maneuver.

F3
Figure 3.:
Diagram of POGO score. POGO indicates percentage of glottic opening.

The esophagus positions relative to the cricoid cartilage and trachea were categorized into binary variables to compare the anatomical suitability of compression in both regions: suitable (partial left or left in the lower-left paratracheal region; mid, partial left, or partial right in the cricoid region) or unsuitable (mid, partial right, or right in the lower-left paratracheal region; left or right in the cricoid region).

Statistical Analyses

Continuous data including are expressed as mean ± standard deviation or median [interquartile range], according to variable normality, which was determined using graphical methods such as histogram and Q–Q plot, and the Kolmogorov–Smirnov test. Categorical data are expressed as number (proportion).

Balance of the 2 groups regarding patient demographics and baseline characteristics were compared using absolute standardized differences. If absolute standardized difference exceeded 0.2, the result was interpreted in the clinical context for imbalance.

Deterioration of laryngoscopic view, which was assessed by the modified Cormack–Lehane grade and POGO score, was tested for noninferiority, while all other secondary end points were tested for superiority with a 2-sided significance level of 0.05. Noninferiority was assessed in a 1-sided test with the use of a 2-sided 95% confidence interval (CI) for differences of the incidence of deteriorated laryngoscopic view. If the upper limit of the 95% CI of the difference was <15%, then paratracheal pressure would be deemed noninferior to cricoid pressure. The noninferiority margin was set at absolute 15% difference that was assumed to be clinically acceptable given the incidence of deterioration of glottic view during cricoid pressure application, which had been reported from 12.5% to 45%.16,17,31

Among secondary outcomes, duration of intubation and changes in PIP before and after the maneuvers were assessed using an independent t test or Mann-Whitney U test, according to the variable normality. Ordinal data, such as ease of mask ventilation or tracheal intubation, and resistance encountered while advancing the tube into the glottis, were examined using the ordinal logistic regression analysis. Proportional odds assumption was checked with a graphical technique and Brant’s test. The odds ratio calculated the odds of having a worse outcome in the paratracheal group compared to the cricoid group. The incidence of release of the maneuvers was evaluated using the χ2 test or Fisher exact test.

The anatomical suitability of each region for esophageal compression was also compared. In the same patient, the anatomical position of the esophagus was evaluated by ultrasound in the paratracheal region and cricoid region, respectively. As both measurements were gained in the same patient, and 2 regions are anatomically close to each other, we used the generalized estimation equation method with independent work correlation structure to analyze correlated data, by taking the within-subject correlation into account.

All statistical analyses were performed using R software, version 3.6.2 (R Foundation for Statistical Computing, Vienna, Austria).

Sample Size Calculation

Based on a previous study in which the glottic view during direct laryngoscopy was deteriorated in 12.5% of patients due to cricoid pressure,17 we assumed that paratracheal pressure might be clinically noninferior to cricoid pressure if the difference in the incidences of deteriorated laryngoscopic view between the paratracheal group and cricoid group was <15%. Noninferiority was assessed in a 1-sided test at a significance level of 0.025 with the use of a 2-sided 95% CI for differences of the incidence of deteriorated laryngoscopic view. We originally designed the study to have 80% power at the .05 1-sided α level to detect noninferiority of paratracheal pressure to cricoid pressure. Allowing for a 10% dropout rate, we included 140 patients in the study. However, in the review process, we were guided to test noninferiority using a 1-sided α of .025 and the corresponding 95% CI, as this is more standard practice.

RESULTS

Between September 2019 and February 2020, 140 patients were enrolled. The paratracheal and cricoid groups consisted of 70 patients each. Among the enrolled patients, none met any exclusion criteria. Patient and anatomical characteristics are summarized in Table 1.

Table 1. - Patient Demographics and Baseline Characteristics
Characteristics Paratracheal group (n = 70) Cricoid group (n = 70) Absolute standardized difference
Age, y 57.2 (15.5) 56.7 (16.0) 0.034
Height, cm 160.3 (8.6) 160.2 (8.6) 0.013
Weight, kg 62.4 (11.1) 62.9 (11.6) 0.039
BMI, kg·m−2 24.3 (4.0) 24.4 (3.6) 0.029
Female 43 (61.4%) 40 (57.1%) 0.087
ASA physical status, I/II/III 33/29/8 30/28/12 0.166
Interincisor gap, cm 4.5 [4.0–4.5] 4.5 [4.0–5.0] 0.117
TMD, cm 7.0 [7.0–7.5] 7.3 [7.0–8.0] 0.265
SMD, cm 15.0 [13.5–16.5] 15.5 [14.0–16.5] 0.007
NC, cm 36.0 [34.0–39.0] 37.0 [33.4–40.0] 0.162
Mallampati score, 1/2/3 25/37/8 27/32/11 0.162
Data are presented as the mean (SD), number (proportion), or median [interquartile range].
Abbreviations: ASA, American Society of Anesthesiologists; BMI, body mass index; NC, neck circumference; SMD, sternomental distance; TMD, thyromental distance.

Paratracheal pressure was noninferior to cricoid pressure regarding the effect on the laryngoscopic view. The laryngoscopic view, when evaluated with the modified Cormack–Lehane grade, did not deteriorate in any patient in the paratracheal group, but deteriorated in 2 patients in the cricoid group (0% vs 2.9%; absolute risk difference, −2.9%; 2-sided 95% CI, −9.9 to 2.6; P < .0001). Paratracheal pressure was also noninferior to cricoid pressure in terms of POGO score (1.4% vs 5.7%; absolute risk difference, −4.3%; 2-sided 95% CI, −12.9 to 2.6; P < .0001). The results are summarized in Figure 4.

F4
Figure 4.:
Comparison of the incidences of deteriorated laryngoscopic view between paratracheal and cricoid pressures. C–L indicates Cormack–Lehane; CI, confidence interval; POGO, percentage of glottic opening.

Manual bag-mask ventilation graded with a 4-point scale was significantly easier in the paratracheal group than in the cricoid group (OR, 0.41; 95% CI, 0.21–0.79; P = .008). Mask ventilation using mechanical ventilation was also affected by the maneuvers. The increase in PIP was significantly less in the paratracheal group than in the cricoid group during mechanical mask ventilation (median [min, max], 0 [−1, 1] vs 0 [−1, 23]; P = .001). By contrast, ease of intubation did not significantly differ between the 2 groups (OR, 1.64; 95% CI, 0.68–3.94; P = .270). The duration of intubation was not different between the 2 groups (28.2 [19.0–52.2] vs 28.6 [19.7–47.2]; P = .793). Resistance encountered by the intubator while passing the tracheal tube into the glottis did not differ between the groups (OR, 0.83; 95% CI, 0.41–1.68; P = .607). The effects of both maneuvers on mask ventilation and intubation are summarized in Table 2.

Table 2. - Effects on Mask Ventilation and Intubation
Outcomes Paratracheal group (n = 70) Cricoid group (n = 70) Effect estimate OR (95% CI) P value
Ease of mask ventilation, easy/moderate/difficult/impossible 44/24/2/0 37/27/11/1 0.407 (0.211–0.788) .008
Ease of intubation, easy/moderate/difficult/impossible 55/10/5/0 60/7/3/0 1.641 (0.683–3.943) .270
Resistance during intubation, easy/moderate/difficult/impossible 48/21/1/0 48/12/8/2 0.360 (0.410–1.688) .607
Difference in medians (95% CI)
Duration of intubation, s 28.2 [25.1–32.8] 28.6 [24.6–33.1] −0.4 (−2.9 to 2.1) .793
Difference in proportions (95% CI)
Release of the maneuvers 0 (0%) 3 (4.3%) −4.3% (−10.5 to 1.9) .245
Data are presented as the number (proportion) or median [interquartile range]. Continuous and ordinal variables were tested and calculated for P values with Mann-Whitney U test and ordinal logistic regression analysis, respectively. Release of the maneuvers was tested with χ2 test.
Abbreviations: CI, confidence interval; OR, odds ratio.

Release of paratracheal pressure was never required, whereas 3 patients in the cricoid group required release of the maneuver. This difference was not statistically significant (0% vs 4.2%; P = .245). In 2 patients, cricoid pressure was discontinued due to severe resistance during tracheal tube advancement. In 1 patient, the maneuver was released because tracheal intubation was achieved after reduction of cricoid pressure and movement of the thyroid cartilage to the patient’s left side.

Regarding anatomical suitability for esophageal compression, the esophagus was visualized at the lower-left paratracheal region and suitable for compression in 97.9% of patients (137 of 140). Cricoid cartilage was completely or partially overlapped the esophagus and suitable for compression in 85.0% of patients (119 of 140). When analyzed with the generalized estimation equation method, the position of the esophagus was more suitable for compression in the paratracheal region than in the cricoid region (odds ratio, 8.1; 95% CI, 2.3–27.7; P = .001).

DISCUSSION

We found that paratracheal pressure is noninferior to cricoid pressure with respect to the effect on the glottic view during direct laryngoscopy in terms of modified Cormack–Lehane grade. When evaluated with POGO score, paratracheal pressure also was noninferior to cricoid pressure with respect to the laryngoscopic view. Mask ventilation was easier with the paratracheal pressure than with the cricoid pressure. However, the ease of intubation did not differ between the 2 maneuvers.

In this study, external laryngeal manipulation to improve the glottic view was not applied during direct laryngoscopy. During the application of cricoid pressure, external laryngeal manipulation might deteriorate laryngoscopic view.17 In addition, external laryngeal manipulation might reduce the efficacy of cricoid pressure by altering the alignment of the cricoid cartilage, esophagus, and vertebral bodies. However, paratracheal pressure may be less affected by external laryngeal manipulation, as manipulation sites are relatively far from each other. Further studies are needed regarding the effects of external laryngeal manipulation on the efficacy or safety of paratracheal pressure.

An additional safety concern has been that cricoid pressure can worsen bag-mask ventilation.32 In this study, paratracheal pressure had a smaller adverse effect on bag-mask ventilation, compared to cricoid pressure. Manual bag-mask ventilation was easier with paratracheal pressure. The increase in PIP during mechanical mask ventilation was significantly less in the paratracheal group. In 9 patients in the cricoid group (12.9%), PIP increased by more than half of the baseline airway pressure. Moreover, a patient in the cricoid group exhibited total obstruction and could not be ventilated during mask ventilation. Although ventilation is typically avoided during the RSII technique, gentle manual ventilation might be necessary in some instances, particularly when tracheal intubation cannot be achieved due to difficult airway or insufficient oxygen capacity to endure the apneic period. In such instances, patients might be ventilated manually with a facemask during the application of cricoid pressure. Airway obstruction during manual ventilation may increase the risk for gastric insufflation, by increasing PIP to overcome airway obstruction. Although there have been some reports that cricoid pressure successfully suppresses gastric insufflation, air might pass through the compressed region when airway pressure exceeds the capacity of cricoid pressure.20,33

Also, if the larynx collapses during the application of cricoid pressure, resistance may increase during tracheal tube advancement. In 2 patients in this study, cricoid pressure was released to advance the tracheal tube through the glottis, due to severe resistance. Conversely, no such events occurred in the paratracheal group.

To occlude the esophagus with paratracheal or cricoid pressure, the esophagus should be located in an adequate location: to the lower left of the trachea for paratracheal pressure and behind the cricoid cartilage for cricoid pressure. When the lower-left paratracheal and cricoid regions were compared for anatomical suitability for esophageal compression, the esophageal location in the lower-left paratracheal region was more suitable for compression, compared to the cricoid region. With cricoid pressure, successful esophageal compression occurs indirectly via the posteriorly directed cricoid cartilage. For this to be effective, the cricoid cartilage must completely or partially overlie the esophagus.6 Furthermore, the esophagus that partially overlaps the cricoid cartilage may not be obstructed by cricoid pressure because cricoid pressure can shift the esophagus laterally.34 In contrast, paratracheal pressure is directly applied to the esophagus in the lower-left paratracheal region, but it is still important to know the consistency of its location. There could be an argument whether the position of the esophagus is a relevant factor of the effectiveness of cricoid pressure. In a magnetic resonance imaging–based study, cricoid pressure compressed the postcricoid hypopharynx, which is an anatomical unit with the cricoid cartilage, rather than the esophagus.35 In this study, the postcricoid hypopharynx was compressed by cricoid pressure against the vertebral body or longus colli muscle group regardless of the location of the esophagus. However, still paratracheal pressure might be useful as paratracheal pressure compressed the esophagus directly against the vertebral body and occluded it.23

In 2 patients, the esophagus was found on the patient’s right side in the lower paratracheal region. In one of these patients, it was repositioned after tracheal intubation, then found in the lower-left paratracheal region (Figure, Supplemental Digital Content, https://links.lww.com/AA/D575). This suggests that when pressure is applied to surrounding structures, the position of the esophagus can change. Therefore, the exact location of the esophagus can be determined with ultrasound examination. However, in the absence of ultrasound, the lower-left paratracheal region is presumably effective for esophageal compression in most patients.

There were several limitations to our study. First, we calculated the sample size for a 1-sided noninferiority test with an α of .05. However, noninferiority should be assessed with an α of .025 on the indicated side with the use of a 95% CI. Second, we did not evaluate intubation success rate as a primary end point. A randomized controlled trial of the 2 techniques for comparing intubation success rates was impractical as they require enormous sample sizes given the high intubation success rates. Third, the noninferiority margin of 15% might have been high and there was a risk for type I error. Fourth, we used a same block size for block randomization. Although anesthesiologists were not aware of the randomization sequence, different block sizes should be used to ensure optimal blinding. Fifth, among the baseline patient characteristics, thyromental distance showed a relatively large standardized difference of 0.265. However, median difference between 2 groups was only 0.3 cm, we considered this to be clinically insignificant and statistical analysis was performed without adjustment. Finally, the effects of paratracheal and cricoid pressures were only evaluated in patients with normal airways undergoing elective surgery. The results might be different in patients with difficult airways.

In conclusion, paratracheal pressure was noninferior to cricoid pressure with respect to the effect on the glottic view during direct laryngoscopy. Mask ventilation was easier with the paratracheal pressure than with the cricoid pressure, however, the ease of intubation did not differ between the 2 maneuvers.

ACKNOWLEDGMENTS

We thank the Medical Research Collaboration Centre of Seoul Metropolitan Government-Seoul National University Boramae Medical Centre (Seoul, Korea) for the assistance with statistics and supervision.

DISCLOSURES

Name: Dongwook Won, MD.

Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.

Name: Hyerim Kim, MD.

Contribution: This author helped design the study, conduct the study, and analyze the data.

Name: Jee-Eun Chang, MD.

Contribution: This author helped design the study, conduct the study, and analyze the data.

Name: Jung-Man Lee, MD, PhD.

Contribution: This author helped design the study, conduct the study, and analyze the data.

Name: Seong-Won Min, MD, PhD.

Contribution: This author helped design the study, conduct the study, and analyze the data.

Name: Seoyoung Ma, MD.

Contribution: This author helped conduct the study and analyze the data.

Name: Chanho Kim, MD.

Contribution: This author helped conduct the study and analyze the data.

Name: Jin-Young Hwang, MD, PhD.

Contribution: This author helped design and conduct the study and analyze the data.

Name: Tae Kyong Kim, MD, PhD.

Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.

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

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