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Featured Articles: Meta Analysis

Comparison of Supraglottic Airway Devices With Endotracheal Intubation in Low-Risk Patients for Cesarean Delivery: Systematic Review and Meta-analysis

White, Leigh D. MBBS*,†; Thang, Christopher MD, BE*,†; Hodsdon, Anthony MBBS‡,§; Melhuish, Thomas M. MBBS∥,¶; Barron, Fiona A. MBChB, FANZCA; Godsall, M. Guy MBBS, BChemEng, BSc, FANZCA, MclinTRes; Vlok, Ruan MBBS#,**

Author Information
doi: 10.1213/ANE.0000000000004618

Abstract

See Article, p 1090

KEY POINTS

  • Question: What is the first-attempt success and adverse event rate of supraglottic airways (SGAs) compared to endotracheal intubation in the context of an elective cesarean delivery?
  • Findings: There was no significant difference in first-attempt success rate or major adverse event rates with an SGA compared to endotracheal intubation.
  • Meaning: Despite the reasonable insertion success rate and safety profile of SGAs compared to endotracheal intubation, the results of this meta-analysis remain underpowered.

There are numerous protocols and guidelines that aim to provide optimal conditions for cesarean delivery (CD) intubation success and thus minimize associated maternal morbidity and mortality.1,2 These include measures such as aspiration prophylaxis, rapid sequence intubation, and apnoeic oxygenation.3,4 Despite this, pulmonary aspiration occurs in approximately 0.1% of patients.5 Furthermore, failed intubation is not an uncommon scenario, with an incidence of 2.3 per 1000 general anesthetics.6 The more alarming statistic is that for every 60 failed intubations, there will be 1 maternal death.6

There are several options when a failed intubation for CD is encountered. These include waking up the patient for neuraxial blockade or inserting a supraglottic airway (SGA) to continue with the operation.1,6 There is still hesitancy by some clinicians to continue on with the surgery and instead reattempt intubation.7,8 The persistence in further intubation attempts may come with significant consequences such as airway trauma, aspiration, and delayed time to delivery.7,8

Currently, there are no published trials comparing the use of SGA devices with endotracheal intubation in the setting of emergency CD. There are, however, several studies published demonstrating a reasonable safety profile with an SGA device in the context of a low-risk, elective CD.7,8 To date, there are no meta-analyses comparing the efficacy of supraglottic devices with endotracheal tube intubation in CD.

The primary aims of the present systematic review with meta-analysis were to determine if the first-pass success rate was higher and insertion time was faster for SGA than endotracheal intubation in the context of elective CD. The secondary aim was to determine the airway-related adverse event rate associated with SGA use compared to endotracheal intubation in elective CD under general anesthesia (GA).

METHODS

Search Strategy

A systematic search was performed by 2 independent reviewers (L.D.W. and C.T.). The search included SCOPUS, PubMed, Medline, Cochrane Central Register of Controlled Trials, China Academic Journals Full-text Database, and Web of Science. The search was conducted from the inception of the databases until September 2019. The search was performed using Medical Subject Headings (MeSH) terms, which included “airway management” plus “cesarean section.” The term “Airway Management” consists of MeSH terms “intubation,” “laryngeal mask” OR “supraglottic airway,” and “positive pressure respiration.” “Cesarean section” consists of MeSH terms “c-section” and “abdominal delivery.” For completeness, a manual reference and citation check of included articles was performed to identify any additional studies.

Eligibility Criteria

For a study to be included in this review, the authors were required to report on (1) CD, (2) placement of an SGA device (eg, classic laryngeal mask airway [LMA®], Supreme [Teleflex] LMA, ProSeal [Teleflex] LMA, etc), and (3) compared to endotracheal intubation. Clinical outcomes of interest were required to be presented (no systematic review or meta-analysis). Only cesarean deliveries, not obstetric surgeries, were eligible for inclusion. Two reviewers (L.D.W. and C.T.) assessed and agreed on each study for inclusion in this systematic review. Any disagreements were settled by a third reviewer (R.V.). All study designs were eligible for inclusion.

Exclusion Criteria

Manikin and simulation studies were excluded. Studies of minor operations in pregnancy were excluded. Studies investigating the use of an SGA without an endotracheal intubation control group were also excluded. There were no language exclusion criteria. Any studies written in languages other than English were translated using Google Translate and reviewed by a translator fluent in both languages.9

Outcomes

The primary “a priori” outcomes were first-attempt success and time to successful insertion. The secondary outcomes of interest were difficult insertion, insertion failure, peak airway pressures required to achieve adequate ventilation, aspiration, bronchospasm, hypoxia at time of induction, laryngospasm, blood on the device at time of removal, and sore throat. Difficult insertion was defined as >1 attempt required to secure the airway. All included studies were screened for additional common outcomes for post hoc analysis, as well as commonalities between studies amenable to sensitivity analysis (eg, high-quality studies).

Data Collection and Extraction

Two reviewers (L.D.W. and C.T.) independently extracted data from each article that met the inclusion criteria. The data extracted from each study included the study design, sample size, CD urgency category, American Society of Anesthesiologists (ASA) physical status, patient body mass index (BMI), airway device, fasting status, induction and SGA insertion procedure, intraoperative management, and outcome measures. The data collected by each reviewer were then compared for homogeneity. If any data were not readily available in the article, the corresponding authors were emailed for clarification.

Risk of Bias

Two independent reviewers assessed each comparative study for risk of bias. Randomized controlled trials (RCTs) were assessed for risk of bias and methodological quality using the Cochrane Collaboration tool for assessing the risk of bias.10 Nonrandomized trials were evaluated using the Risk Of Bias In Non-randomised Studies - of Interventions (ROBINS-I) tool for assessing risk of bias.11 A study was deemed to be of “high quality” if it scored ≥4 low-risk criteria on the risk of bias tools.

Statistical Analyses

The combined data for comparative analysis were performed using RevMan 5.3 software (The Nordic Cochrane Centre, Copenhagen, Denmark). The results for dichotomous outcomes were reported using an odds ratio (OR) with 95% confidence interval (CI). The Mantel–Haenszel random-effects model was used. The results for continuous outcomes were reported using a weighted mean difference (WMD) with 95% CI. This was done using the random-effects inverse variance model. Heterogeneity was assessed using the I2 statistic, with an I2 >50% indicating significant heterogeneity. For any dichotomous outcomes with included studies with no event or 100% event rates, a continuity correction of ±0.5 events was applied using MetaXL 5.3 software (Epigear, Brisbane, Australia).

Subgroup Analysis

Several subgroup analyses based on SGA type were planned before the performance of the statistical analysis.

Assessment of Quality of Evidence

Publication bias and small-study effects were assessed via funnel plots of standard errors versus effect estimates if there were >10 studies as part of the analysis.12 Each outcome in the SGA versus endotracheal intubation meta-analysis was assessed for the quality using the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) criteria.13 This study was written in accordance with the Preferred Reporting Items for Systematic reviews and Meta-analyses (PRISMA) checklist.14

RESULTS

Literature Search

The systematic review of the literature identified 14 studies for inclusion in this review (Table). The initial electronic search identified 2885 studies, and a further 16 were identified on manual reference and citation searches (Figure 1). Following the removal of duplicate records and title screening, 83 abstracts were reviewed (Figure 1). Thirty-six full-text articles were reviewed to identify the 14 included studies (Figure 1; Table).15–28 Twenty-three articles were excluded with reasons (Supplemental Digital Content, Table S1, https://links.lww.com/AA/C998). There were 14 studies with 2236 patients eligible for an SGA versus intubation meta-analysis (Table). Of these, there were 7 high-quality RCTs, 5 low-quality RCTs (Figure 2A), and 2 low-quality cohort studies (Figure 2B). A colleague fluent in both Chinese (Simplified) and English assisted with data extraction where required.

Table. - Characteristics of Studies Comparing the Use of an LMA Versus Endotracheal Intubation
Study Design Country of Study Origin SGA Used Number of Patients (SGA/TT) ASA Mean BMI (SGA/TT) Cesarean Delivery Category Fasting Status Induction of Anesthesia SGA Insertion Technique Maintenance NMB Used? Outcome Measures
Ahmed and Hasan15 (2015) RCT Egypt I-gel 40/40 1–2 30.8.3/30.2 Elective Fasted RSI with thiopentone, rocuronium, and CP. Lubricated I-gel inserted with continuous introduction into the mouth against the hard palate until resistance was felt, as recommended by the manufacturer. In case the airway and ventilation were not established properly, gentle pushing, pulling, head extension, jaw thrust, or neck flexion manipulations were tried before considering failed attempt. Gastric tube was lubricated and inserted down the gastric drainage port of the I-gel. Yes Insertion time
First-attempt success
Peak airway pressure
Difficult placement
Aspiration
Laryngospasm
Blood on device
Sore throat
Hypoxia
Bronchospasm
Geng and Wang16 (2017) Retrospective cohort China Supreme 56/124 1–4 28.1/28.6 Elective and emergency Unclear RSI with propofol, suxamethonium, and CP. No details provided. Unclear Difficult placement
Aspiration
Laryngospasm
Hypoxia
Bronchospasm
Mu17 (2014) RCT China Classic 60/60 2–3 27.1/27.6 Elective and emergency Fasted RSI with midazolam, fentanyl, etomidate or propofol, and suxamethonium. Head in a neutral position, a pen-like grip of the classic laryngeal mask was used. It was pushed back firmly until resistance was met. Hand ventilation was used to confirm ventilation with auscultation of the chest and stomach. A gastric tube was then inserted and stomach suctioned. Unclear Aspiration
Sore throat
Panneer et al18 (2017) RCT India I-gel 40/40 2 20.6/20.8 Elective Fasted RSI with propofol, fentanyl, and suxamethonium. No details provided. Yes Insertion time
Difficult placement
Aspiration
Laryngospasm
Blood on device
Sore throat
Saini et al19 (2016) RCT India ProSeal 30/30 1–2 20.5/20.9 Elective Fasted RSI with thiopentone and suxamethonium. Inserted with gentle pressure until resistance was met. A gastric tube was then inserted and the stomach contents aspirated. Yes Insertion time
Difficult placement
Aspiration
Blood on device
Sore throat
Wu et al20 (2016) RCT China Supreme 50/50 1–2 27.6/28.4 Elective and emergency Mixed Non-RSI with propofol TCI, remifentanil TCI, and rocuronium. Inserted with gentle pressure until resistance was met. A gastric tube was then inserted and the stomach contents aspirated. Unclear Peak airway pressure
Aspiration
Sore throat
Yan21 (2014) RCT China Variety 20/20 Unclear 26.4/27.1 Elective Fasted Non-RSI with ketamine, propofol, and atracurium. No details provided. No Aspiration
Yan22 (2017) RCT China I-gel 34/34 Unclear 24.1/25.1 Elective Fasted Non-RSI with midazolam, etomidate, fentanyl, and cisatracurium. Weight-based I-gel sizing as per manufacturer. I-gel was lubricated and inserted to bottom of pharynx until pressure met. Unclear Insertion time
First-attempt success
Aspiration
Blood on device
Sore throat
Hypoxia
Yao24 (2016) RCT China Supreme 100/100 Unclear Unclear Elective Unclear RSI with propofol and suxamethonium. No details provided. Unclear Insertion time
First-attempt success
Peak airway pressure
Aspiration
Blood on device
Sore throat
Yao et al23 (2016) RCT China Tuoren 80/80 1–2 28.2/27.1 Elective and emergency Mixed Non-RSI with remifentanil TCI and propofol TCI with rocuronium. No details provided. Unclear Peak airway pressure
Aspiration
Sore throat
Yao et al25 (2019) RCT China Supreme 460/460 1–2 26.0/25.7 Elective Fasted RSI with propofol, suxamethonium, and CP. Supreme laryngeal mask with a size 14 gastric tube preloaded was inserted using a rotational technique. Following successful placement, the gastric tube was advanced and suctioned. Yes Insertion time
First-attempt success
Peak airway pressure
Difficult placement
Aspiration
Blood on device
Sore throat
Zhao et al26 (2014) RCT China Guardian 30/30 1–2 29.2/28.8 Elective and emergency Unclear Non-RSI with remifentanil TCI and propofol TCI with rocuronium. No details provided. Gastric tube inserted after operation. Yes First-attempt success
Insertion time
Peak airway pressure
Aspiration
Sore throat
Zhiyu27 (2015) Retrospective cohort China Variety 33/75 1–3 Not stated Elective Fasted Variety of methods for both induction and insertion. Variety of methods for both induction and insertion. Unclear Difficult placement
Aspiration
Laryngospasm
Hypoxia
Bronchospasm
Zhou et al28 (2013) RCT China ProSeal 30/30 Unclear Not stated Elective Fasted Non-RSI with remifentanil TCI and propofol TCI with vecuronium. The supreme laryngeal mask was lubricated with lignocaine gel and inserted until resistance was met. Placement was confirmed with capnography. Yes Peak airway pressure
Sore throat
Abbreviations: ASA, American Society of Anesthesiologists; BMI, body mass index; CP, cricoid pressure; LMA, laryngeal mask airway; NMB, neuromuscular blocker; RCT, randomized controlled trial; RSI, rapid sequence intubation; SGA, supraglottic airway; TCI, target controlled infusion; TT, endotracheal tube.

Figure 1.
Figure 1.:
Literature search flow diagram.
Figure 2.
Figure 2.:
Risk of bias summary. A, Randomized controlled trials. B, Nonrandomized studies.

One study reported on the use of a classic LMA (Telflex, Westmeath, Ireland),17 3 studies used the I-gel (Intersurgical, Berkshire, UK),15,18,22 2 studies reported use of the ProSeal (Telflex),19,28 and 4 studies used the Supreme (Telflex) SGA.16,20,23,25 The rest of the studies used a variety of SGAs.

Based on the reasonable number of high-quality RCTs, the decision to perform a post hoc high-quality study sensitivity analysis was made. The GRADE certainty for each outcome is included in Supplemental Digital Content, Table S2, https://links.lww.com/AA/C998.

Primary Outcomes

Five studies showed no significant difference in first-attempt success rate (OR = 1.92; 95% CI, 0.85–4.32; I2 = 0%; P = .44; Figure 3; GRADE very low certainty).15,22,23,25,26 There was no significant difference in the Supreme subgroup (OR = 0.84; 95% CI, 0.23–3.01; P = .79).23,25 A subgroup analysis for the ProSeal SGA could not be performed. On sensitivity analysis for the I-gel subgroup, there was a significantly higher first-attempt success rate with SGA (OR = 3.95; 95% CI, 1.09–14.25; I2 = 0%; P = .04).15,22 On sensitivity analysis of the high-quality RCTs, there was no significant difference in first-attempt success rate (OR = 2.20; 95% CI, 0.73–6.65; I2 = 21%; P = .16).15,22,25

Figure 3.
Figure 3.:
First-attempt success of supraglottic airway versus endotracheal tube intubation. CI indicates confidence interval; OR, odds ratio.
Figure 4.
Figure 4.:
Time to successful insertion with SGA versus endotracheal tube intubation. CI indicates confidence interval; ETT, endotracheal intubation; IV, inverse variance; SD, standard deviation; SGA, supraglottic airway.

Similarly, 7 studies investigated time to device insertion showing a small but statistically significant difference between SGA and intubation (WMD = −15.80 seconds; 95% CI, −25.30 to −6.31 seconds; I2 = 100%; P = .001; GRADE very low certainty; Figure 4).15,18,19,22,24–26 This difference remained nonsignificant for the I-gel (P = .29)15,18,25 and ProSeal (P = .13).19 There was a significantly faster time to insertion in the Supreme subgroup (WMD = −23.00 seconds; 95% CI, −23.75 to 22.25 seconds; P < .001) compared to intubation.25 On sensitivity analysis of high-quality RCTs, there was no significant difference in time to secured airway (WMD = −7.44 seconds; 95% CI, −18.56 to 3.69 seconds; I2 = 100%; P = .19).15,18,19,22,25

Secondary Outcomes

Six studies investigated difficult insertion rate, showing no significant difference (OR = 0.44; 95% CI, 0.12–1.67; I2 = 37%; P = .23; GRADE very low certainty).15,16,18,19,25,27 On subgroup analysis for I-gel, there was a significantly reduced incidence of difficult placement (OR = 0.07; 95% CI, 0.01–0.54; I2 = 0%; P = .01).15,18 There was no significant difference for the Supreme subgroup (P = .80).18,25 Subgroup analyses for classic and ProSeal subgroups were unable to be performed. On sensitivity analysis of high-quality RCTs, there was no significant difference in the rate of difficult placement in the SGA group (OR = 0.32; 95% CI, 0.07–1.41; I2 = 41%; P = .13).15,18,19,25

Following successful device placement, there was no significant difference in peak airway pressure required to achieve adequate ventilation(WMD = 0.29 cmH2O; 95% CI, −0.81 to 1.39; I2 = 92%; P = .60; GRADE very low certainty).15,20,23–26,28 There was no difference for the Supreme subgroup (P = .36).20,23,25 This difference remained nonsignificant on sensitivity analysis of high-quality RCTs (WMD = 1.01 cmH2O; 95% CI, −0.36 to 2.38 cmH2O; I2 = 94%; P = .15).15,20,23,25 Subgroup analyses for classic, I-gel, and ProSeal use were unable to be performed.

Of the studies that investigated aspiration, bronchospasm, and hypoxia, there was zero incidence for all 3 outcome measures in both the SGA and intubation groups. Therefore, no statistical analysis was performed. There was no difference in the incidence of laryngospasm (OR = 0.64; 95% CI, 0.10–4.09; I2 = 21%; P = .64; GRADE low certainty)15,16,18,27 or blood on the device at time of removal (OR = 0.73; 95% CI, 0.48–1.13; I2 = 0%; P = .16; GRADE moderate certainty).15,18,19,21,24,25 On sensitivity analysis for high-quality RCTs, there was still no significant difference (P > .05) for laryngospasm15,18 or blood on the device.15,18,19,21,25

There was, however, a significantly lower rate of sore throat with SGA (OR = 0.16; 95% CI, 0.08–0.32; I2 = 53%; P < .001; GRADE moderate certainty).15,17–20,22–26,28 This remained significantly lower with I-gel (P < .001),15,18,22 ProSeal (P = .003),19,28 and Supreme (P = .004)20,23,25 subgroups. There was no change to the significantly lower rate of sore throat with SGA on sensitivity analysis for high-quality RCTs (P < .001).15,18–20,22,23,25

There were only a sufficient number of studies investigating sore throat to inspect its associated funnel plot (Supplemental Digital Content, Figure S1, https://links.lww.com/AA/C998). This was asymmetrical, which indicated reporting bias.

DISCUSSION

This was the first systematic review with meta-analysis on the topic with 14 studies and 2236 patients. Overall, no evidence for a difference in success rate was observed between SGA and endotracheal intubation for airway management in a GA for CD. There was no difference in adverse event rates except of sore throat which was significantly less in the SGA group.

The primary outcomes of interest assessed first-attempt insertion success and time to successful insertion. Overall, the SGA insertion success rate of 98.1% reported in the present review was similar to those reported in prior obstetric SGA studies.29–36 The first-attempt success rates presented were associated with a high degree of heterogeneity and a very low GRADE level of certainty. One significant contributor toward the observed heterogeneity was the SGA device variation. On an exploratory subgroup analysis, the I-gel device without heterogeneity (I2 = 0%) was associated with a significantly increased first-attempt success rate compared to endotracheal intubation (OR = 3.95). The 3 studies that contributed to this result were all deemed to be high-quality RCTs. There are several possible contributors to the high success rates demonstrated in the included studies. Most studies utilized rapid sequence induction techniques before the insertion of the SGA. The majority of studies also adhered to recommended insertion techniques from manufacturers, and these studies took place in centers with likely significant experience in the placement of an SGA for CD.

The overall results were similar for time to successful insertion and the incidence of difficult placement with no clinically significant difference demonstrated. The present study demonstrated that once the airway is secured, SGAs are able to provide ventilation using airway pressures generally under 20 cmH2O (Supplemental Digital Content, Figure S2, https://links.lww.com/AA/C998). When compared to endotracheal intubation, there was no significant difference (P = .60) in peak airway pressures required to provide adequate ventilation.

Patients having a GA for CD are considered high risk for aspiration. The incidence of aspiration can increase with coexisting obesity and labor-related pain. These comorbid factors were not present in the patients included in this review. Overall, there was no incidence of aspiration in the present meta-analysis. In addition to the results of this review, a number of cohort large studies have been performed investigating the use of an SGA without an endotracheal intubation control group for GA CD. Between these studies, there are >8000 parturients with only 1 reported aspiration event.15–36 In addition, in the National Audit Project 4 (NAP4) study, there was 1 reported aspiration during CD associated with the use of an SGA.8 This aspiration occurred following 3 failed intubation attempts. There are several possible reasons for such low aspiration rates reported in the literature. These include the use a nasogastric tube, minimal fundal pressure, and the use of a rapid sequence intubation (RSI) technique to insert the SGA without bag-mask ventilation.

Two observational studies of parturients at a higher risk of aspiration have been performed demonstrating similar results to those reported in elective parturients.32,36 Between these 2 studies, there were 1596 patients requiring a category 2 or 3 emergency CD. All included patients were fasted; however, a large proportion were in active labor. There were no reported aspirations, and the first-attempt insertion success rate was 98%–99.8%. Therefore, there is a growing body of evidence to support the use of an SGA in the context of CD.

In the largest study of elective CD to date, Halaseh et al31 reported an aspiration rate of 1 in 3000 with an SGA. Therefore, there is insufficient evidence presented in this review to confirm that an SGA has the equivalent safety profile compared to endotracheal intubation. This meta-analysis review adds support to the Difficult Airway Society obstetric guidelines, which advocates for the early use of a second-generation SGA rather than persisting with numerous intubation attempts.1

Limitations

There are several limitations to the study, the first being the lack of available studies in high-risk emergency patients, especially as a rescue technique following failed intubation. However, for obvious reasons, a large study of SGA use following failed intubation would be difficult or near impossible to design in a safe manner. In addition, the majority of included patients were well fasted and not in active labor. This differs from the commonly encountered emergency CD population. Therefore, the results of this study, particularly aspiration risk, do not apply to patients having an emergency CD. There was also a lack of obese parturients, which is likely to make up a sizable proportion of the difficult and failed intubations, as well as aspiration events.8 The BMI of a large proportion of patients included in this study was in the overweight (BMI 25–30) category.15–17,20–23,25,28 However, the results of those studies are unlikely to be applicable to the morbidly obese population.

There were also several limitations related to the studies included in the review. The present review was limited by the number of outcomes measured. Only airway-related outcomes were assessed by the primary studies, and, therefore, we are unable to comment on any longer-term maternal or neonatal outcomes. There was also a limitation in the quality of several studies included. A large number were deemed low quality and published in unranked journals. To compensate for the inclusion of these studies, a sensitivity analysis using only high-quality RCTs was performed for all outcomes.

The overall results presented for each outcome produced a low or very low level of GRADE certainty. This is largely related to the low patient numbers and significant heterogeneity in SGA devices, cohorts, and clinician familiarity with SGA device use in the obstetric population. This was reflected in the overall I2 values and to skewing of the sore throat funnel plot. For each outcome, there were sensitivity analyses performed including only high-quality RCTs that often resulted in low levels of heterogeneity. The results of these sensitivity analyses included were underpowered for a large number of outcomes.

CONCLUSIONS

Despite the reasonable insertion success rate and safety profile of SGAs demonstrated in this meta-analysis, the analysis remains underpowered and therefore inconclusive. At present, further studies are required before the use of an SGA as the first-line airway for an elective CD can be recommended. Given the high first-attempt success rate demonstrated, the use of an SGA following failed intubation is likely to be more effective and potentially safer than repetitive intubation attempts.

ACKNOWLEDGMENTS

We would like to thank Yi Lynn Ooi for her assistance in translation and data extraction.

DISCLOSURES

Name: Leigh D. White, MBBS.

Contribution: This author helped with concept design, review of current literature, literature search, data extraction, data analysis, and proofing.

Name: Christopher Thang, MD, BE.

Contribution: This author helped with concept design, review of current literature, referencing, and proofing.

Name: Anthony Hodsdon, MBBS.

Contribution: This author helped with concept design, referencing, and proofing.

Name: Thomas M. Melhuish, MBBS.

Contribution: This author helped with concept design, review of current literature, data analysis, and proofing.

Name: Fiona A. Barron, MBChB, FANZCA.

Contribution: This author helped with concept design and proofing.

Name: M. Guy Godsall, MBBS, BChemEng, BSc, FANZCA, MclinTRes.

Contribution: This author helped with concept design and proofing.

Name: Ruan Vlok, MBBS.

Contribution: This author helped with concept design, review of current literature, data extraction, and proofing.

This manuscript was handled by: Jill M. Mhyre, MD.

FOOTNOTES

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