Comparison of full-dose succinylcholine and rocuronium for rapid sequence intubation in an academic emergency department: a retrospective cohort study

Abstract

BACKGROUND Succinylcholine and rocuronium are the principal neuromuscular blocking agents used for rapid sequence intubation (RSI). Prior studies comparing these agents have shown conflicting results, although a Cochrane review suggested that succinylcholine may provide superior intubating conditions. This study aimed to compare the first-pass success rate, intubating conditions, and peri-intubation safety between full-dose succinylcholine (1.5 mg/kg) and rocuronium (1.2 mg/kg) during RSI.

METHODS This retrospective cohort study was conducted in a single academic emergency department between 2017 and 2021. Adult patients who underwent RSI with either succinylcholine or rocuronium were included. The primary outcome was the first-pass success rate. The secondary outcome was clinically acceptable intubating conditions, and exploratory safety outcomes included hypoxia, hemodynamic change, vasopressor use, and post-intubation adverse events. Logistic regression was performed to identify independent predictors of the first-pass success rate.

RESULTS A total of 342 patients were included, with 201 receiving succinylcholine (1.5 mg/kg) and 141 receiving rocuronium (1.2 mg/kg). There was no statistically significant difference detected on the first-pass success rates between succinylcholine and rocuronium (81.6% vs. 79.4%; absolute risk difference 2.2%; 95% confidence interval [95% CI] −6.4 to 10.7; P=0.31). No statistically significant differences were observed in exploratory peri-intubation safety outcomes, including hypoxia, hemodynamic changes, or adverse events between the groups. Rocuronium was more frequently used in patients with endocrine comorbidities, which is consistent with confounding by indication (30.5% vs. 13.9%; P=0.03). Independent predictors of the first-pass success rates included the use of video laryngoscopy (adjusted odds ratio [aOR] 1.59; 95% CI 1.22-4.09, P=0.02) and greater physician experience (aOR 2.12; 95% CI 1.09-5.21, P=0.04).

CONCLUSION In this single-center retrospective cohort study, there was no statistically significant difference observed in the first-pass success rates, intubation conditions, and peri-intubation safety outcomes between succinylcholine and rocuronium during RSI in the emergency department. However, clinically relevant differences cannot be excluded because the study was not designed to establish equivalence.

INTRODUCTION

Rapid sequence intubation (RSI) is a cornerstone of airway management in the emergency department (ED), where rapid airway control is often required to secure ventilation and oxygenation. Neuromuscular blocking (NMB) agents are integral to RSI because they optimize intubating conditions and may increase the first-pass success.^[1-3] Succinylcholine and rocuronium remain the two most widely used paralytics in emergency airway management.^[3] Succinylcholine has a rapid onset and short duration, but its use is limited by contraindications such as hyperkalemia risk, neuromuscular disease, burns, and prolonged immobilization.^[4,5] Rocuronium is a nondepolarizing alternative with fewer contraindications, although it has a longer and dose-dependent duration of action.^[6] Contemporary RSI practices commonly use 1.0-1.5 mg/kg succinylcholine or 1.0-1.2 mg/kg rocuronium, with higher rocuronium doses used to optimize onset and intubating conditions.^[4-8]

Previous studies comparing first-pass success rates between succinylcholine and rocuronium have reported conflicting results.^[9,10] It is likely that different dosing strategies may have led to these differences. A Cochrane review published in 2017 reported superior intubating conditions with succinylcholine compared with low-dose rocuronium (0.6 mg/kg), although outcomes were similar when higher-dose rocuronium was used.^[11] In 2018, the National Emergency Airway Registry (NEAR) group did not detect an association between paralytic choice and the first-pass success rates in EDs.^[12] These differences may be partly explained by variations in dosing regimens, as suboptimal or non-equivalent doses can affect onset time and the depth of neuromuscular blockade. In turn, adequate dosing may improve intubating conditions by producing more rapid, complete paralysis; reducing coughing or bucking; and facilitating laryngoscopy and endotracheal tube passage.

This study aimed to compare the first-pass success rate, intubating conditions, and peri-intubation safety between full-dose succinylcholine (1.5 mg/kg) and rocuronium (1.2 mg/kg) during RSI in an academic ED. Based on prior registry data, we hypothesized that there would be no large difference in the first-pass success rate or peri-intubation safety outcomes between groups.

METHODS

Study design and setting

We conducted a single-center retrospective cohort study in the ED of the King Abdulaziz University Hospital, an academic center in Jeddah, Saudi Arabia, with an annual census of approximately 60,000 visits. The department is staffed by board-certified emergency physicians and emergency medicine residents, with the majority of intubations performed by residents under direct supervision.

Study population

All adult patients (≥18 years) who underwent RSI between January 2017 and December 2021 were eligible. We included patients who received either succinylcholine (1.5 mg/kg) or rocuronium (1.2 mg/kg) as the NMB agent. Patients younger than 18 years, pregnant women, intubations during cardiac arrest, and those undergoing awake intubations were excluded. Patients with incomplete documentation were also excluded.

Intubation procedure

RSI was performed according to departmental protocols. All patients were monitored with continuous electrocardiography, pulse oximetry, non-invasive blood pressure, and respiratory rate monitoring. Preoxygenation was provided using either a non-rebreather mask at 15 L/min or non-invasive ventilation, according to patient physiology, clinical indication, tolerance, and contraindications. Non-invasive ventilation was preferentially used when clinically indicated for hypoxemic or hypercapnic respiratory failure and when not contraindicated. Bag-valve mask ventilation was reserved for patients who were apneic or for whom oxygen saturation declined to <90% after paralytic administration. Two large-bore intravenous lines were placed before induction. Induction agents—etomidate (0.3 mg/kg), ketamine (1 mg/kg), or propofol (1 mg/kg)—were selected at the discretion of the attending physician. Medication doses were calculated using estimated total body weight. Because measured body weight was usually not available before emergency RSI, total body weight was estimated at the bedside by three clinical staff members involved in the resuscitation, typically including the treating physician, assisting nurse, and another bedside clinician or nurse. The average of the three estimates was used for weight-based dosing during medication preparation. Hemodynamic parameters were optimized prior to induction, targeting a systolic blood pressure >100 mmHg (1 mmHg=0.133 kPa) and an oxygen saturation >98% when feasible. Intubation was typically attempted approximately 60 s after paralytic administration per the departmental protocol. The standard practice in our ED is to use succinylcholine for RSI; however, paralytic selection in this cohort was clinician-directed and was influenced by perceived contraindications or precautions to succinylcholine (e.g., concern for hyperkalemia risk), with rocuronium used when succinylcholine was avoided. Airway devices included either direct laryngoscopy (Macintosh or Miller blades) or video laryngoscopy with a hyperangulated blade. All endotracheal tubes were preloaded with a stylet, and placement was confirmed using capnometry or capnography.

Data collection

Data were obtained from the department’s local airway database, which was initially developed to support a continuous improvement in airway quality. For each intubation, the treating physician and assisting nurse completed a standardized paper-based airway procedure form within 10 min of the attempt. The form captured patient demographics, comorbidities, indications for intubation, and presenting diagnosis, which were categorized as cardiovascular, pulmonary, neurologic, hepatic, renal, infectious, traumatic, endocrine, or toxicologic. Pre-induction vital signs were recorded within 10 min prior to induction agent administration, and post-intubation vital signs were recorded within 30 min after endotracheal tube confirmation. The form also captured difficult airway predictors (blood or vomiting in the airway, a cervical collar, immobility, airway edema, facial or neck trauma, a small mandible, a short neck, a large tongue, restricted mouth opening, and obesity), medications and dosages, the Cormack-Lehane grade, operator experience, and complications. Intubation conditions were assessed using the Goldberg scale,^[11] with clinically acceptable conditions defined as easy tracheal intubation with immobile open vocal cords and no reactive cough or open vocal cords with only mild reactive cough; clinically unacceptable conditions included moderate reactive cough, resistance at the vocal cords, uncontrolled coughing with closed vocal cords, or resistance to endotracheal tube passage. Additional data were retrieved from the electronic health records.

As part of the quality improvement process, completed forms were reviewed regularly for completeness and internal consistency before entry into the database. Information on the procedure form was cross-checked against the electronic health records. Any discrepancies between the airway form and electronic health records were resolved through review of the source documentation; when clarification was still needed, the involved clinical staff were contacted to verify the event details before database entry. Cases with incomplete airway documentation that precluded ascertainment of the primary outcome were excluded from the final analysis.

Definitions

Intubation attempt

An intubation attempt was defined as a single insertion of the laryngoscope blade into the oral cavity with an associated attempt to pass the endotracheal tube. If the laryngoscope blade was withdrawn and reinserted, this was considered a new attempt. If the laryngoscope remained in the mouth but more than one endotracheal tube passage attempt was made, this was also counted as more than one attempt.

Experienced operator

At least 50 intubations were required. This threshold was supported by previous evidence indicating that under mostly elective circumstances, at least 50 endotracheal intubations with no more than two attempts are required to achieve a >90% success rate.^[13] Inexperienced operators should perform endotracheal intubations less than 50 times.

Glottic view

Good glottic view was Cormack-Lehane grades I and II, and poor glottic view was Cormack-Lehane grades III and IV.

Outcomes

Primary outcome

The first-pass success was defined as successful endotracheal tube placement, confirmed by capnometry or capnography, after one laryngoscope blade insertion and one endotracheal tube passage attempt.

Secondary outcome

The secondary outcome included clinically acceptable intubation conditions (per Goldberg scale), as documented in the airway procedure form.

Exploratory safety outcomes

Peri-intubation safety outcomes included hypoxia, hemodynamic change, vasopressor use, esophageal intubation, pneumothorax, hyperthermia, and post-intubation cardiac arrest. These outcomes were analyzed descriptively as exploratory endpoints.

Statistical analysis

Continuous variables are summarized as medians with interquartile ranges (IQRs), and categorical variables are summarized as frequencies and percentages. Group comparisons were performed using the Chi-square test for categorical variables and the Mann-Whitney U test for continuous variables. Logistic regression was performed to evaluate the association between the use of paralytic agents and the first-pass success while clinically relevant predictors of intubation success were adjusted. Candidate variables were selected a priori based on biologic plausibility, clinical relevance, and prior emergency airway literature rather than through automated statistical selection alone. Variables were included if they were considered potential confounders of the relationship between the paralytic agent and the first-pass success or were known predictors of intubation outcome. The prespecified covariates were age, sex, induction agent, paralytic agent, indication for intubation, presence of difficult airway predictors, device type, and operator experience. To improve model parsimony and avoid sparse categories, indications for intubation and induction agents were analyzed using clinically meaningful categories, and difficult airway features were collapsed into a binary variable indicating the presence or absence of at least one difficult airway predictor. No automated stepwise selection procedure was used. Model diagnostics included assessment of collinearity using variance inflation factors, discrimination using the area under the receiver-operating characteristic curve, and calibration using the Hosmer-Leme-show test and a calibration plot. The results are reported as adjusted odds ratios with 95% confidence intervals (95% CI). The secondary outcome and exploratory peri-intubation safety endpoints were compared between paralytic groups using unadjusted absolute differences with 95% CI. Multivariate logistic regression was performed for the primary outcome only. Analyses were conducted using SPSS Statistics version 26 (IBM Corp., USA).

Sample size

This retrospective study included a consecutive sample of all eligible adult RSI cases; therefore, no a priori sample size calculation was performed. Because the final sample size was limited by the number of eligible patients with complete airway documentation, the study may have been underpowered to detect small or moderate between-group differences in the first-pass success or uncommon adverse events. Rather than reporting post-hoc power, we emphasize estimation and precision by presenting the primary outcome as an absolute risk difference with 95% CI. The observed difference in the first-pass success was small; however, the CI around the absolute risk difference should be interpreted as the plausible range of between-group differences compatible with the data.

RESULTS

Study population

Among the 496 total intubations, cases were excluded for missing data (n=56), non-RSI techniques without paralytic administration (n=59), or pediatric patients (n=39), yielding 342 intubations in the final analytic cohort: 201 received succinylcholine, and 141 received rocuronium. No statistically significant difference was observed in age or sex between the groups (Table 1).

Table 1.

Selected baseline and peri-intubation characteristics by paralytic agents

Characteristics	Succinylcholine (n=201)	Rocuronium (n=141)	Absolute difference	P-value
Age, years, median (IQR)	64 (55-78)	66 (54-81)	+2 years	0.45
Male sex, n (%)	116 (57.7)	82 (58.1)	+0.4%	0.12
Estimated body weight, kg, median (IQR)	68 (64-75)	75 (65-89)	+7 kg	0.10
Endocrine diagnosis, n (%)	28 (13.9)	43 (30.5)	+16.6%	0.03
Hypoxic respiratory failure, n (%)	82 (41.7)	63 (44.6)	+2.9%	0.32
Hypercapnic respiratory failure, n (%)	60 (29.8)	39 (27.6)	-2.2%	0.22
Preoxygenation method, n (%)				0.62
Non-rebreather mask preoxygenation	139 (69.2)	94 (66.7)	-2.5%
Non-invasive ventilation preoxygenation	62 (30.8)	47 (33.3)	+2.5%
Difficult airway predictor present, n (%)	52 (25.8)	31 (21.9)	-3.9%	0.44
Video laryngoscopy, n (%)	183 (91.0)	126 (89.3)	-1.7%	0.90
Experienced operator, n (%)	58 (28.8)	42 (29.7)	+0.9%	0.10
Estimated weight-based paralytic dose, mg/kg, median (IQR)	1.5 (1.4-1.6)	1.2 (1.1-1.3)	-	NA

Absolute differences are calculated as rocuronium minus succinylcholine for categorical variables and as median rocuronium minus median succinylcholine for continuous variables. The full baseline and peri-intubation characteristics are provided in supplementary Tables 1 and 2. IQR: interquartile range.

Baseline and peri-intubation characteristics

Baseline and selected peri-intubation characteristics are shown in Table 1, with detailed baseline and procedural variables provided in supplementary Tables 1 and 2. Endocrine disorders were more prevalent in the rocuronium group, with an absolute difference of 16.6%. Indications for intubation were predominantly respiratory failure, reflecting the local ED case mix. Hypoxic respiratory failure accounted for 41.7% of the succinylcholine cases and 44.6% of the rocuronium cases, whereas hypercapnic respiratory failure accounted for 29.8% and 27.6%, respectively. There was no significant difference in difficult airway features, preoxygenation method, device type, or operator experience between groups. No significant difference was observed in the peri-intubation systolic or diastolic blood pressure trajectories between the groups, with an early post-intubation decline followed by partial recovery by 30 min (supplementary Figures 1 and 2).

Primary, secondary, and exploratory safety outcomes

There was no significant difference in the first-pass success rates between succinylcholine and rocuronium (81.6% vs. 79.4%; absolute risk difference 2.2%; 95% CI −6.4 to 10.7; P=0.31). Although the observed difference was small, the CI does not exclude clinically relevant differences. In unadjusted comparisons, clinically acceptable intubating conditions and exploratory safety endpoints, including hypoxia, vasopressor use, and post-intubation cardiac arrest, were also similar between groups (Table 2). In multivariable analysis, difficult airway predictors were associated with lower first-pass success, whereas video laryngoscopy and operator experience were associated with higher success. Paralytic agents were not independently associated with the first-pass success (Table 3; full model in supplementary Table 3).

Table 2.

Clinical outcomes by paralytic agent, n (%)

Outcomes	Succinylcholine (n=201)	Rocuronium (n=141)	Absolute difference, percentage points	P-value
First-pass success	164 (81.6)	112 (79.4)	2.2 (95% CI -6.4 to 10.7)	0.31
Clinically acceptable intubating conditions	166 (82.6)	118 (83.7)	-1.1 (95% CI -9.1 to 6.9)	0.28
Oxygen saturation <90%	106 (52.7)	70 (49.6)	3.1 (95% CI -7.7 to 13.8)	0.89
Vasopressor use	30 (14.9)	18 (12.8)	2.2 (95% CI -5.2 to 9.5)	0.76
Post-intubation cardiac arrest	10 (5.0)	8 (5.7)	-0.7 (95% CI -5.6 to 4.2)	0.77

95% CI: 95% confidence interval.

Table 3.

Key adjusted predictors of first-pass success

Adjusted predictor	aOR (95% CI)	P-value
Rocuronium vs. succinylcholine	0.61 (0.49-1.21)	0.38
Difficult airway predictor present	0.79 (0.61-0.89)	0.03
Video laryngoscopy	1.59 (1.22-4.09)	0.02
Experienced operator	2.12 (1.09-5.21)	0.04

aOR: adjusted odds ratio; CI: confidence interval. The full multivariable regression model is provided in supplementary Table 3.

DISCUSSION

No statistically significant difference was observed in the first-pass success, intubating conditions, or safety outcomes between succinylcholine and rocuronium. Compared with paralytic choice, airway difficulty, operator experience, and device selection appeared to be more important determinants of success. Given the predominance of respiratory failure in this cohort, the findings should be generalized cautiously to EDs with different airway case combinations.

Prior comparisons of succinylcholine and rocuronium have shown mixed results, likely reflecting differences in dosing, setting, and operator factors.^[14-16] Our findings align with this literature because both groups received full-dose RSI regimens, reducing bias from non-equivalent or subtherapeutic dosing. ED data similarly suggest that first-attempt success is dose-dependent and comparable between agents when rocuronium is administered at higher contemporary RSI doses.^[10]

Although 1.2 mg/kg rocuronium is a commonly recommended full RSI dose, some systems use higher doses. A retrospective prehospital and retrieval system study reported that rocuronium doses >1.5 mg/kg were associated with lower odds of inadequate paralysis compared with doses ≤1.5 mg/kg.^[17] This, however, did not reach statistical significance, presumably because of the low event rate. Our findings therefore should not be interpreted as excluding a potential benefit of higher-dose rocuronium over either standard-dose rocuronium or 1.5 mg/kg succinylcholine. This represents an important area for future comparative effectiveness research.

Induction agents provide hypnosis and blunt airway reflexes, whereas NMB agents optimize laryngoscopy and endotracheal tube passage by improving intubating conditions.^[18] Thus, intubation success reflects both induction depth and neuromuscular blockade. Inadequate induction may cause sympathetic activation or movement, although effective paralysis may attenuate motor responses.^[19] Conversely, excessive induction can worsen peri-intubation hypotension in physiologically unstable patients. A multicenter ED study found RSI with a sedative and paralytic was associated with higher first-attempt success than non-RSI techniques were, supporting neuromuscular blockade as an important determinant of procedural success.^[20] In our cohort, induction agent type was balanced between groups and was not independently associated with the first-pass success, suggesting that procedural factors and operator experience were more influential within our standardized RSI approach.

Although this study was conducted in a Saudi Arabian academic ED, the airway practice pattern observed in our cohort—frequent video laryngoscopy use and predominantly supervised resident-performed intubations—is likely shared by many contemporary academic EDs. Therefore, these features may strengthen the applicability of our findings to teaching hospitals with similar supervision structures and device availability. Our practice pattern differs from that of some prior registries in which direct laryngoscopy was more common and attending physicians performed more intubations.^[21] In our cohort, video laryngoscopy and operator experience were associated with higher first-pass success, which is consistent with evidence supporting video laryngoscopy and structured training in critically ill patients.^[22] These findings suggest that airway expertise and device selection may be more influential than paralytic choice in contemporary ED airway management.

Secondary and exploratory safety outcomes, including clinically acceptable intubating conditions, hypoxia, vasopressor use, and post-intubation cardiac arrest, showed small absolute between-group differences with CIs that were not significantly different. This finding is consistent with prior work suggesting that both agents are safe when appropriately dosed and administered under controlled conditions.^[12] The higher prevalence of endocrine disorders in the rocuronium group likely reflects confounding by indication, as clinicians may have avoided succinylcholine in patients with perceived hyperkalemia risk.

This study has several limitations. First, as a retrospective observational study, it is subject to selection bias, information bias, and residual confounding. Although standardized airway forms were reviewed before database entry, missing or incomplete documentation may have affected internal validity through outcome misclassification, under-ascertainment of adverse events, or exclusion of eligible cases. The sample size was not determined a priori, and exclusions for incomplete documentation may have reduced statistical power, widened confidence intervals, and introduced selection bias. Second, the first-pass success is a procedural quality metric rather than a patient-centered outcome. Third, this was a single-center academic ED study with frequent video laryngoscopy use, supervised trainee-performed intubations, and a predominance of respiratory failure; therefore, the findings may not be generalizable to EDs with different airway practices or case mixes. Fourth, the interval between paralytic administration and laryngoscopy was not consistently time-stamped, limiting the assessment of adherence to the intended timing protocol. Fifth, dosing weight was estimated using the average of three bedside staff estimates, which may reduce reliance on a single estimate but does not eliminate dosing misclassification. Finally, although covariates were selected a priori and the model was kept parsimonious, treatment allocation was clinician-directed and not randomized, and the study was not prospectively registered or supported by a public statistical analysis plan.

CONCLUSION

In this single-center retrospective cohort study, no statistically significant difference was observed in the first-pass success rates, intubation conditions, or peri-intubation safety outcomes between succinylcholine and rocuronium during RSI in the ED. However, the study was not designed or powered to establish equivalence, and clinically relevant differences cannot be excluded. The first-pass success was lower in the presence of difficult airway features and higher with video laryngoscopy use and experienced operators, whereas paralytic selection was not independently associated with the first-pass success.

Funding: This study received no external funding.

Ethical approval: This study was conducted in accordance with the ethical principles outlined in the Declaration of Helsinki and its later amendments. Ethical approval for this study was obtained from the Unit of Biomedical Ethics, Faculty of Medicine, King Abdulaziz University, Jeddah, Saudi Arabia (Reference No. 47-21) on February 3, 2021. The requirement for individual patient consent was waived due to the retrospective nature of the study.

Conflicts of interest: The authors declare no conflicts of interest.

Contributors: AAB: conceptualization, methodology, data curation, formal analysis, supervision, writing, editing, and manuscript reviewing. DAT: writing, editing, and reviewing manuscript, supervision, methodology, investigation, and formal analysis.

All the supplementary files in this paper are available at http://wjem.com.cn.