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Featured Articles: Original Clinical Research Report

McGrath MAC Videolaryngoscope Versus Optiscope Video Stylet for Tracheal Intubation in Patients With Manual Inline Cervical Stabilization: A Randomized Trial

Yoon, Hyun-Kyu MD; Lee, Hyung-Chul MD, PhD; Park, Jung-Bin MD; Oh, Hyongmin MD; Park, Hee-Pyoung MD, PhD

Author Information
doi: 10.1213/ANE.0000000000004442

Abstract

KEY POINTS

  • Question: Is the clinical performance of tracheal intubation better when a videolaryngoscope, rather than a video stylet, is used in patients with manual inline cervical stabilization who were scheduled for elective cervical spine surgery?
  • Findings: The McGrath MAC videolaryngoscope showed a higher first-attempt success rate for tracheal intubation and a shorter intubation time than the Optiscope video stylet in elective cervical spine surgery patients with manual inline stabilization.
  • Meaning: The McGrath MAC videolaryngoscope may be a better option than the Optiscope video stylet for tracheal intubation in these patients.

See Article, p 869

Special attention is required when performing tracheal intubation in patients with a cervical spine injury, because excessive cervical motion during tracheal intubation may induce secondary neurologic insult.1 Manual inline stabilization of the head and neck has been recommended to prevent further neurologic injury in this situation.2 However, applying manual inline stabilization to patients with an unstable cervical spine inevitably restricts neck flexion and head extension, resulting in a lower first-attempt success rate of tracheal intubation using direct laryngoscopy.3,4 Therefore, alternative intubation devices, such as the videolaryngoscope, video stylet, lighted stylet, and fiberoptic bronchoscope have been used for successful tracheal intubation in patients with manual inline stabilization.5–11

Videolaryngoscopes can be useful for tracheal intubation in patients with cervical immobilization as they allow indirect visualization of the larynx even with restricted neck movements.7 Among various videolaryngoscopes, the McGrath MAC videolaryngoscope (McGrath MAC; Medtronic, Dublin, Ireland), which has a Macintosh-type blade, provides familiarity to practitioners with the experience of direct laryngoscope (Figure 1). In a prior investigation for tracheal intubation in patients with cervical immobilization, the McGrath MAC videolaryngoscope showed the highest first-attempt success rate of tracheal intubation among 6 different videolaryngoscopes.12

Figure 1.
Figure 1.:
Study devices used in this study. A, The McGrath MAC videolaryngoscope. B, The Optiscope video stylet.

Video stylets, which are portable and easier to prepare than flexible fiberoptic bronchoscopes, could be another option for tracheal intubation in patient with cervical immobilization. Previous studies have shown the usefulness of video stylets for tracheal intubation in cervical immobilized patients.13–17 Especially in a recent study, the Optiscope video stylet (Optiscope; Clarus Medical LLC, Minneapolis, MN) produced less cervical spine motion, measured on sagittal radiographic images during tracheal intubation, than the McGrath MAC videolaryngoscope in patients with a cervical collar.17 However, the sample size of the study was not sufficient to compare differences in success rate of tracheal intubation, the intubation time, or severity of sore throat between the techniques.

In patients with a cervical collar, previous studies have shown similarly high first-attempt success rates of tracheal intubation using the McGrath MAC videolaryngoscope and the Optiscope video stylet.15,17 However, there have been no studies to compare tracheal intubation using these 2 devices in patients with manual inline stabilization.

In this study, we compared the clinical performance of the McGrath MAC videolaryngoscope versus the Optiscope video stylet in terms of the first-attempt success rate of tracheal intubation, the intubation time, and the incidence of postoperative airway complications in patients undergoing cervical spine surgery with manual inline stabilization during tracheal intubation. Our hypothesis was that the first-attempt success rate of tracheal intubation using the McGrath MAC videolaryngoscope would be higher than that using the Optiscope video stylet.

METHODS

Patient Population

This study was approved by the institutional review board (IRB) of Seoul National University Hospital (IRB No.: 1603-129-751), and the study protocol was registered before patient enrollment at ClinicalTrials.gov (NCT02769221, Principal investigator: Hee-Pyoung Park, Date of registration: May 11, 2016). This study was conducted under Good Clinical Practice Guidelines and adhered to the applicable Consolidated Standards of Reporting Trials (CONSORT) guidelines. Written informed consent was obtained from all patients before enrollment in the study. Adult patients aged 20–80 years with American Society of Anesthesiologists (ASA) physical status classification I–III and who were scheduled for elective cervical spine surgery from June 1, 2016 to August 31, 2018 at a single tertiary teaching hospital (Seoul National University Hospital) were recruited into this study consecutively. Patients who had a history of aspiration pneumonia, gastrointestinal obstruction, coagulopathy, history of gastroesophageal reflux disease, radiation therapy on the neck and airway surgery, and upper airway lesions (ie, tumor, polyp, inflammation, trauma, abscess, or foreign body) were excluded.

Randomization

Using a computer-generated program, block randomization with a mixture of blocks of size 4 and 6 was performed by an investigator blinded to the study. The patients were randomly assigned to 2 groups: McGrath MAC videolaryngoscope group (group M) or Optiscope video stylet group (group O). All enrolled patients were evenly allocated to the 2 anesthesiologists who performed all tracheal intubation alternately. The patients did not know which group they had been assigned to. The allocation order was concealed in an opaque envelope and was disclosed by an anesthesia nurse immediately before the induction of anesthesia.

Study Protocol

Airway evaluation was performed in the operating room. The modified Mallampati classification,18 which categorizes patients as 4 classes based on the pharyngeal structures seen, and interincisor distance were measured in the sitting and neutral neck positions. Thereafter, standard monitors (3-lead electrocardiogram, noninvasive blood pressure, and pulse oximetry) were used for all patients, and anesthesia was induced with target-controlled infusions of propofol and remifentanil (target effect-site concentrations of 4 µg/mL and 4 ng/mL, respectively). After confirming the loss of consciousness, 0.6 mg/kg of rocuronium was administered to facilitate tracheal intubation, and the patient’s radial artery was cannulated for continuous blood pressure monitoring.

While manual inline stabilization was being performed, the patient’s head was firmly grasped by an anesthesiology resident to prevent head and neck movements during the tracheal intubation. Only mouth opening and jaw lifting were allowed. Under these conditions, tracheal intubation was performed by 1 of 2 attending anesthesiologists, each of whom had performed at least 50 successful tracheal intubations using the McGrath MAC videolaryngoscope and the Optiscope video stylet.

In group M, tracheal intubation was performed using the McGrath MAC videolaryngoscope with a 60°-angled malleable aluminum stylet. In group O, the Optiscope video stylet with a preloaded endotracheal tube was inserted into the posterior pharynx at the midline. Once the epiglottis was identified on the display, the tip of the Optiscope video stylet was advanced between the vocal cords and the endotracheal tube was introduced into the trachea. Mallinckrodt-reinforced tubes (Medtronic) with an internal diameter of 7.0 mm for women and 7.5 mm for men were used in both groups.

The success of tracheal intubation was confirmed by end-tidal carbon dioxide monitoring with capnography. Hemodynamic changes, such as mean arterial pressure and heart rate, were recorded just before and 1 minute after tracheal intubation. The intubation time, which was defined as the interval between insertion of the device into the oral cavity and withdrawal of the device from the oral cavity, was also recorded by an anesthesia nurse who did not know about this study.

Attempted tracheal intubation taking >180 seconds was regarded as failed intubation. If the first attempt failed, one more chance was given to the same anesthesiologist after 1 minute of mask ventilation. In each case, a maximum of 3 attempts was allowed for the same anesthesiologist. If all attempts failed, fiberoptic bronchoscopic intubation assisted by direct laryngoscopy was performed to complete the procedure. Rescue mask ventilation was applied whenever the pulse oximetry was below 90%. After tracheal intubation, the cuff pressure of the endotracheal tube was measured and maintained at 25 cm H2O using a Posey 8199 Cufflator (Posey Company, Arcadia, CA).

At the end of surgery, the presence of blood in the oral cavity and blood staining on the endotracheal tube were evaluated after extubation. In addition, postoperative sore throat and hoarseness were evaluated at 1 and 24 hours after surgery. The severity of throat pain was assessed using a numeric rating scale (0, no pain; 10, the worst pain imaginable). The postoperative neurologic complications defined as newly developed or aggravated neurological status (paresthesia, paresis, and paralysis) at hospital discharge were collected from the electronic medical records by an investigator who was blinded to the group assignment.

Study Outcomes

The primary outcome of this study was the first-attempt success rate for tracheal intubation. Secondary outcomes were intubation time, hemodynamic variables (mean arterial pressure and heart rate before and 1 minute after intubation), the incidence of postoperative airway complications (sore throat, hoarseness, blood in the oral cavity, and blood staining on the endotracheal tube), and postoperative neurologic complications.

Statistical Analysis

For comparison of discrete variables, including the first-attempt success rate of tracheal intubation and the incidence of postoperative sore throat and hoarseness, blood in the oral cavity, and blood staining on the endotracheal tube, the χ2 test or Fisher exact test was performed. For comparison of continuous variables, the Student t test or the Mann-Whitney U test was performed depending on the results of the Kolmogorov–Smirnov test. All statistical analyses were performed with SPSS software (version 25.0; IBM Corp, Armonk, NY). In all analyses, P < .05 was taken to indicate statistical significance.

Sample Size Determination

In a previous study, the first-attempt success rate of tracheal intubation using the McGrath MAC videolaryngoscope in patients with cervical immobilization was 97.5% and the first-attempt success rate of <90% was considered clinically significant.12 Therefore, we defined a difference of >7.5% in the first-attempt success rate of tracheal intubation between the McGrath MAC videolaryngoscope and the Optiscope video stylet as clinically significant. Sample size calculations using G*Power software (version 3.1.9; Franz Faul, University of Kiel, Germany) indicated that 163 patients were needed per group for 2-tailed χ2 test to obtain 80% power and an α value of .05. Considering a possible dropout rate (10%) and missing data (2%), a total of 370 patients were enrolled in this study.

RESULTS

Among 435 patients eligible for this study during the study period, 65 patients were excluded (Figure 2). The remaining 370 patients were randomized, and 3 patients were additionally excluded from data analysis due to the withdrawal of consent (Table 1).

Table 1. - Comparisons of Demographics and Airway-Related Variables Between the 2 Groups
Group M
(n = 183)
Group O
(n = 184)
Mean Difference (95% CI)
Demographic variables
 Age (y) 54.2 ± 14.5 55.3 ± 13.6 1.1 (−1.8 to 4.0)
 Male 111 (60.7%) 124 (67.4%) 6.7% (−3.1 to 16.3)
 BMI (kg/m2) 24.6 ± 3.5 25.1 ± 3.5 0.5 (−0.2 to 1.2)
 ASA physical status
  I 84 (45.9%) 78 (42.4%) 3.5% (−6.6 to 13.5)
  II 91 (49.7%) 89 (48.4%) 1.3% (−8.8 to 11.4)
  III 8 (4.4%) 17 (9.2%) 4.8% (−0.5 to 10.3)
 Comorbidities
  Hypertension 49 (26.8%) 56 (30.4%) 3.6% (−5.6 to 12.7)
  Diabetes mellitus 26 (14.2%) 31 (16.8%) 2.6% (−4.9 to 10.1)
  Cardiac disease 4 (2.2%) 7 (3.8%) 1.6% (−2.2 to 5.7)
  Respiratory disease 8 (4.4%) 5 (2.7%) 1.7% (−2.4 to 6.0)
  Neurologic disease 15 (8.2%) 10 (5.4%) 2.8% (−2.5 to 8.3)
  Renal disease 1 (0.5%) 5 (2.7%) 2.2% (−0.7 to 5.7)
  Hepatic disease 5 (2.7%) 9 (4.9%) 2.2% (−2.0 to 6.6)
  Thyroid disease 3 (1.6%) 2 (1.1%) 0.5% (−2.5 to 3.7)
  Malignancy 4 (2.2%) 7 (3.8%) 1.6% (−2.2 to 5.7)
  Rheumatoid arthritis 2 (1.1%) 7 (3.8%) 2.7% (−0.7 to 6.6)
Airway-related parameters
 Modified Mallampati classification
  I 40 (21.9%) 45 (24.5%) 2.6% (−6.0 to 11.2)
  II 88 (48.1%) 78 (42.4%) 5.7% (−4.4 to 15.7)
  III 50 (27.3%) 52 (28.3%) 1.0% (−8.1 to 10.1)
  IV 5 (2.7%) 9 (4.9%) 2.2% (−2.0 to 6.6)
 Interincisor distance (mm) 43.9 ± 9.2 42.4 ± 8.1 1.5 (−3.3 to 0.3)
 Use of oral airway 6 (3.3%) 9 (4.9%) 1.6% (−2.8 to 6.1)
Surgical variables
 Diagnosis
  Degenerative 128 (69.9%) 140 (76.1%) 6.2% (−2.9 to 15.2)
  Tumorous 47 (25.7%) 36 (19.6%) 6.1% (−2.5 to 14.6)
  Trauma 2 (1.1%) 1 (0.5%) 0.6% (−2.0 to 3.4)
  Vascular 2 (1.1%) 0 (0.0%) 1.1% (−1.1 to 3.9)
  Congenital 4 (2.2%) 7 (3.8%) 1.6% (−2.2 to 5.7)
 Site of operation 7.8% (−0.9 to 16.4)
  At or above C2 51 (27.9%) 37 (20.1%)
  At or below C3 132 (72.1%) 147 (79.9%)
 Surgical approach
  Anterior 22 (12.0%) 30 (16.3%) 4.3% (−2.9 to 11.5)
  Posterior 161 (88.0%) 155 (84.2%) 3.8% (−3.4 to 10.9)
  Both 0 (0.0%) 1 (0.5%) 0.5% (−1.6 to 2.9)
 Anesthesia time (min) 211.4 ± 105.5 193.8 ± 92.6 17.6 (−2.8 to 38.0)
 Operation time (min) 153.8 ± 101.4 137.8 ± 89.2 16.0 (−3.6 to 35.6)
Values are mean ± standard deviation or number (proportion). In the group M and O, tracheal intubations were performed using the McGrath MAC videolaryngoscope and Optiscope video stylet, respectively.
Abbreviations: ASA, American Society of Anesthesiologists; BMI, body mass index; CI, confidence interval.

Figure 2.
Figure 2.:
Consolidated Standards of Reporting Trials (CONSORT) flow diagram.

The first-attempt success rate of tracheal intubation was significantly higher in group M than in group O (92.3% vs 81.0%; risk difference [95% confidence interval], 0.11 [0.05–0.18]; P = .002; Table 2). In addition, the intubation time was significantly shorter in group M than in group O (35.7 ± 27.8 vs 49.2 ± 43.8 seconds; mean difference [95% confidence interval], 13.5 [5.9–21.1]; P = .001). Group O included 5 patients whose trachea could not be intubated within 3 attempts. Each had a long and lax epiglottis that sat toward the posterior pharynx. In these patients, the trachea was intubated successfully by fiberoptic bronchoscopy with assistance from direct laryngoscopy. There were no significant differences in the hemodynamic variables, including mean arterial pressure and heart rate measured just before and 1 minute after tracheal intubation, between the 2 groups.

Table 2. - Comparisons of Intubation-Related Variables Between the 2 Groups
Group M
(n = 183)
Group O
(n = 184)
Mean Difference
(95% CI)
P
Successful tracheal intubation
 Overall 183 (100.0%) 179 (97.3%) 2.7% (0.1–6.2) .061
 At first attempt 169 (92.3%) 149 (81.0%) 11.3% (4.5–18.3) .002
 At second attempt 12 (6.6%) 19 (10.3%) 3.7% (−2.1 to 9.6) .267
 At third attempt 2 (1.1%) 11 (6.0%) 4.9% (1.1–9.4) .020
Intubation time (s) 35.7 ± 27.8 49.2 ± 43.8 13.5 (5.9–21.1) .001
Mean arterial pressure (mm Hg)
 Before intubation 72.7 ± 18.2 71.8 ± 15.0 0.9 (−4.3 to 2.5) .597
 1 min after intubation 87.6 ± 22.1 85.4 ± 21.4 2.2 (−6.7 to 2.3) .326
Heart rate (beats/min)
 Before intubation 64.0 ± 11.8 64.8 ± 12.0 0.8 (−1.6 to 3.2) .510
 1 min after intubation 80.1 ± 54.4 76.5 ± 13.6 3.6 (−11.7 to 4.5) .398
Values are number (proportion) or mean ± standard deviation. In the group M and O, tracheal intubations were performed using the McGrath MAC videolaryngoscope and Optiscope video stylet, respectively.
Abbreviation: CI, confidence interval.

Table 3. - Comparisons of Postoperative Complications Between the 2 Groups
Group M
(n = 183)
Group O
(n = 184)
Mean Difference
(95% CI)
P
Postoperative airway complications
 Sore throat
  Postoperative 1 h 38 (20.8%) 46 (25.0%) 4.2% (−4.4 to 12.7) .400
  Postoperative 24 h 20 (10.9%) 27 (14.7%) 3.8% (−3.1 to 10.7) .359
 Throat pain (NRS)
  Postoperative 1 h 6.0 (5.0–7.0) 6.3 (5.0–8.0) NA 1.000
  Postoperative 24 h 3.0 (2.0–4.5) 3.0 (2.0–4.0) NA .424
 Hoarseness
  Postoperative 1 h 16 (8.7%) 13 (7.1%) 1.6% (−4.1 to 7.4) .687
  Postoperative 24 h 8 (4.4%) 7 (3.8%) 0.6% (−3.8 to 5.1) .991
  Blood in the oral cavity 9 (4.9%) 15 (8.2%) 3.3% (−1.9 to 8.7) .297
  Blood staining on the endotracheal tube 4 (2.2%) 4 (2.2%) 0.0% (−3.6 to 3.6) 1.000
Postoperative neurologic complications
 Overall 14 (7.7%) 9 (4.9%) 2.8% (−2.3 to 8.1) .382
 Paresthesia 11 (6.0%) 8 (4.3%) 1.7% (−3.1 to 6.6) .629
 Paresis 7 (3.8%) 4 (2.2%) 1.6% (−2.2 to 5.7) .380
 Paralysis 0 (0.0%) 0 (0.0%) 0.0% (−2.1 to 2.0) 1.000
Values are number (proportion) or median (interquartile). In the group M and O, tracheal intubations were performed using the McGrath MAC videolaryngoscope and Optiscope video stylet, respectively. Sore throat was evaluated with numeric rating scale from 0 to 10 (0: no pain, 10: the worst imaginable pain). The postoperative neurologic complications were defined as newly developed or aggravated neurological status (paresthesia, paresis, and paralysis) at hospital discharge.
Abbreviations: CI, confidence interval; NA, not applicable; NRS, numeric rating scale.

Comparisons of postoperative airway complications between the 2 groups are presented in Table 3. The incidences of postoperative sore throat and hoarseness at 1 (20.8% vs 25.0%; P = .400 and 8.7% vs 7.1%; P = .687, respectively) and 24 (10.9% vs 14.7%; P = .359 and 4.4% vs 3.8%; P = .991, respectively) hours after surgery were comparable between the 2 groups. In addition, the incidences of blood in the oral cavity and blood staining on the endotracheal tube did not differ significantly between the 2 groups. The overall incidence of postoperative neurologic complications was 6.3% (23/367), and there was no significant difference in the incidence of these complications between the 2 groups (7.7% vs 4.9%; risk difference [95% confidence interval], 2.8% [−2.3 to 8.1]; P = .382).

DISCUSSION

In this study, the first-attempt success rate was significantly higher, and the intubation time was significantly shorter when tracheal intubation was performed using the McGrath MAC videolaryngoscope than with the Optiscope video stylet in patients with manual inline stabilization. The incidence of intubation-related postoperative airway complications was not significantly different between the 2 intubation devices.

Both the videolaryngoscope and the video stylet have been used in clinical practice for tracheal intubation in patients with an unstable cervical spine. However, in this study, the McGrath MAC videolaryngoscope showed significantly better performance of tracheal intubation than the Optiscope video stylet. The possible mechanisms of these results may be as follows. First, manual inline stabilization allows wider mouth opening than cervical collar application. Although the blade of the McGrath MAC videolaryngoscope is bulkier than the Optiscope video stylet, this may not impact the performance of tracheal intubation in patients with manual inline stabilization. This may also explain why our results were inconsistent with those of a previous study using a cervical collar, which reported longer intubation times in patients using the Airway Scope videolaryngoscope (Nihon Kohden, Tokyo, Japan) than those using the Clarus Video System video stylet (Clarus Medical LLC).15 Second, intubating devices with the lens at the tip, such as optical stylet or video stylet, have been reported to be susceptible to contamination by oral secretions.19,20 In a previous study using Bonfils video stylet (Karl Storz Endoscope, Tuttlingen, Germany), oral secretions reduced the view during tracheal intubation in 30% (18/60) of the patients.20 This may also explain why the optical or video stylets showed excellent performance in mannequin studies, but the results could not be reproducible in the living subjects.21–24 In contrast, for the McGrath MAC videolaryngoscope, the camera lens is located proximally and covered by the blade, which can be advantageous in preventing the contamination by oral secretion (Figure 3). Finally, without cervical motion, the hooking or scooping motion below the epiglottis, which is essential for intubation using the Optiscope video stylet, was extremely difficult in some patients with a long and floppy epiglottis. Meanwhile, the McGrath MAC videolaryngoscope can lift the epiglottis directly even in patients with a long and floppy epiglottis.

Figure 3.
Figure 3.:
Different mechanisms of tracheal intubation. A, The McGrath MAC videolaryngoscope. B, The Optiscope video stylet. Arrows indicate the direction of force applied during manipulation of the device. Asterisks indicate the location of the camera lens.

Increasing the first-attempt success rate of tracheal intubation is clinically relevant because repeated attempts to intubate the trachea can result in intubation-related postoperative airway complications. However, the McGrath MAC videolaryngoscope and Optiscope video stylet showed similar and acceptable profiles with regard to postoperative airway complications in this study. The incidence rates of sore throat measured at 1 hour after surgery were 20.8% and 25.0% in group M and group O, respectively (risk difference [95% confidence interval], 0.04 [0.04–0.13]). These results can be ascribed to the following reasons. First, the force applied to the mucosa, which was generated by direct contact of the videolaryngoscope blade, might be minimal. Previous studies reported that lifting force and soft tissue trauma were significantly reduced with the videolaryngoscope than the direct laryngoscope with a Macintosh blade.25,26 Second, other clinical risk factors affecting the development of postoperative sore throat, such as the duration of anesthesia, size of the endotracheal tube, endotracheal tube cuff pressure, and sex were randomized or controlled by the study protocol.26–28 In addition, most tracheas were intubated within second attempts in both groups.

This study had several limitations. First, the operators were not blinded to the group assignment, and this inevitable bias could have affected the results. Second, as the operators were all skilled in using both the McGrath MAC videolaryngoscope and the Optiscope video stylet, the results of this study are not equally generalizable to practitioners unfamiliar with either device. However, previous studies revealed that only 6 and 10 attempts were sufficient for novice users to achieve high success rate of tracheal intubation using the McGrath videolaryngoscope and Optiscope video stylet, respectively.29,30 Third, there may be some differences in clinical performance of tracheal intubation with other types of videolaryngoscope and video stylets. Every airway device has its own distinctive features with regard to the shape and the size of their blades, body curvature, camera location, and guidance of the endotracheal tube. Although devices of the same type usually share similar structures, care must be taken while generalizing the results. Finally, the cervical spine motion during tracheal intubation was not measured in the present study. Therefore, the relationship between tracheal intubation and postoperative neurologic outcome was uncertain, although there was no difference in the incidence of postoperative neurologic complications between the 2 groups.

In conclusion, the McGrath MAC videolaryngoscope showed better clinical performance in terms of the first-attempt success rate of tracheal intubation and intubation time than the Optiscope video stylet in patients undergoing cervical spine surgery with manual inline stabilization during tracheal intubation. In addition, the incidence of postoperative airway complications was similar between the 2 intubation devices. These results suggest that the McGrath MAC videolaryngoscope may be a better option for tracheal intubation in such patients.

DISCLOSURES

Name: Hyun-Kyu Yoon, MD.

Contribution: This author helped in the design of the study, data acquisition, data analysis and interpretation, drafting of the manuscript, and approval of the submitted version of the manuscript.

Name: Hyung-Chul Lee, MD, PhD.

Contribution: This author helped in the design of the study, data acquisition, data analysis and interpretation, drafting of the manuscript, critical revision of the manuscript, and approval of the submitted version of the manuscript.

Name: Jung-Bin Park, MD.

Contribution: This author helped in the data acquisition, data analysis and interpretation, and approval of the submitted version of the manuscript.

Name: Hyongmin Oh, MD.

Contribution: This author helped in the data acquisition, data analysis and interpretation, statistical analysis, and approval of the submitted version of the manuscript.

Name: Hee-Pyoung Park, MD, PhD.

Contribution: This author helped in the design of the study, data acquisition, data analysis and interpretation, critical revision of the manuscript, and approval of the submitted version of the manuscript.

This manuscript was handled by: David Hillman, MD.

FOOTNOTES

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