Intravenous versus topical lidocaine gel administered at intubation for prevention of peri-extubation airway complications in adults undergoing orthopaedic surgery: protocol for a randomised controlled trial

Abstract

Introduction

Peri-extubation airway complications such as coughing, laryngospasm and oxygen desaturation remain common during emergence from general anaesthesia and may contribute to postoperative morbidity. Lidocaine is widely used to reduce airway reactivity during extubation; however, evidence comparing intravenous and topical administration routes in adults remains limited. In particular, little evidence exists regarding topical lidocaine gel applied at the time of endotracheal intubation. This trial aims to compare intravenous lidocaine with topical lidocaine gel for prevention of peri-extubation airway complications in adults undergoing elective orthopaedic surgery.

Methods and analysis

This is a prospective, single-centre, randomised, observer-blinded, parallel-group controlled trial. A total of 120 adult patients undergoing elective orthopaedic surgery under general anaesthesia with endotracheal intubation will be randomly allocated in a 1:1 ratio to receive either intravenous lidocaine 1.5 mg/kg before intubation or topical 2% lidocaine gel applied to the endotracheal tube before intubation. The primary outcome is a composite of severe cough, laryngospasm or oxygen desaturation within 10 min after extubation. Secondary outcomes include assessment of individual airway complications, postoperative sore throat, dysphonia, haemodynamic responses and recovery characteristics in the postanaesthesia care unit. Data will be analysed according to the intention-to-treat principle.

Ethics and dissemination

Ethical approval has been obtained from the Ethics Committee of Tehran University of Medical Sciences (approval number: IR.TUMS.SPH.REC.1404.293) and the Institutional Review Board of Al-Hussein Teaching Hospital, Iraq. Written informed consent will be obtained from all participants before enrolment. The results of the study will be disseminated through peer-reviewed journal publication and presentation at national and international scientific conferences.

Trial registration number

IRCT20260209068811N1.

STRENGTHS AND LIMITATIONS OF THIS STUDY.

• This randomised controlled trial directly compares intravenous lidocaine with topical lidocaine gel administered during endotracheal intubation.

• The study evaluates topical lidocaine gel rather than spray formulations used in most previous comparative studies.

• The composite primary outcome captures clinically important peri-extubation airway complications, including severe cough, laryngospasm and oxygen desaturation.

• The protocol incorporates concealed randomisation, blinded outcome assessment and a standardised anaesthesia protocol to strengthen internal validity.

• The study focuses on elective orthopaedic surgery, providing a relatively homogeneous non-airway surgical population.

Background

Airway complications during emergence from general anaesthesia remain an important source of perioperative morbidity.¹ Among these complications, postextubation coughing, laryngospasm and oxygen desaturation are particularly clinically significant because they may rapidly compromise ventilation, destabilise haemodynamics and adversely affect postoperative recovery.^{2 3} Emergence from anaesthesia represents a physiologically vulnerable period in which airway protective reflexes transition from pharmacological suppression to incomplete recovery,⁴ rendering the airway increasingly susceptible to mechanical and chemical stimulation.⁵ Endotracheal intubation and extubation are major contributors to peri-extubation airway reflex activation, as mechanical interaction between the endotracheal tube and the laryngo-tracheal mucosa can induce epithelial microtrauma, local inflammation and sensitisation of airway sensory receptors.⁶ Postextubation cough is among the most common airway adverse events and may provoke clinically important physiological consequences, including hypertension, tachycardia, wound dehiscence, postoperative bleeding and increased intracranial or intraocular pressure.^{7 8} Although laryngospasm occurs less frequently in adults, it remains one of the most serious peri-extubation complications. Even transient glottic closure can rapidly precipitate hypoxemia, negative-pressure pulmonary oedema, arrhythmias or cardiac arrest if not promptly recognised and managed.⁹ Oxygen desaturation after extubation further reflects clinically meaningful impairment of airway patency or ventilatory adequacy and is associated with increased perioperative risk.¹⁰

Given the clinical importance of these complications, multiple pharmacological strategies have been investigated to attenuate airway reflex responses during emergence from anaesthesia. Lidocaine is among the most widely used agents for this purpose. As an amide local anaesthetic, lidocaine suppresses neuronal conduction through blockade of voltage-gated sodium channels, thereby reducing activation of airway sensory afferents and airway reflex pathways.¹¹ Intravenous lidocaine may additionally exert systemic antitussive and anti-inflammatory effects, whereas topical lidocaine primarily acts locally at the airway mucosa by decreasing sensory receptor stimulation induced by the endotracheal tube.^{12 13}

Evidence supporting perioperative intravenous lidocaine is relatively well established. A recent systematic review and meta-analysis demonstrated that intravenous lidocaine significantly reduced postextubation cough and postoperative sore throat compared with placebo without increasing adverse events.¹⁴ In contrast, evidence regarding topical lidocaine remains more heterogeneous and technique-dependent. Previous studies have evaluated multiple topical delivery approaches, including sprays, intracuff alkalinised lidocaine, nebulised preparations and mucosal applications, with considerable variation in timing, dose, anatomical target and formulation.^{15 16}

Direct comparisons between intravenous and topical lidocaine in adult surgical populations remain limited and have produced inconsistent findings. Some studies suggest that topical lidocaine may provide cough suppression comparable to intravenous administration and may reduce severe cough intensity or postoperative hoarseness,¹⁷ whereas other investigations have demonstrated no significant difference between routes or have favoured intravenous administration in selected populations.¹⁸ Interpretation of the available evidence is further complicated by substantial methodological heterogeneity across studies, including differences in patient populations, airway devices, timing of administration and importantly, the type and formulation of topical lidocaine used. Most adult comparative studies have evaluated lidocaine spray administered shortly before extubation, while evidence regarding lidocaine gel applied at the time of endotracheal intubation remains scarce. This distinction may be clinically relevant because gel formulations may provide more prolonged mucosal contact throughout surgery and potentially attenuate airway irritation initiated during intubation itself. In addition, adult patients undergoing non-airway surgery, including orthopaedic procedures, remain under-represented in existing comparative trials. Because airway mucosal injury and sensory receptor sensitisation begin at the time of airway instrumentation,¹⁹ prophylactic interventions administered during intubation may influence subsequent peri-extubation airway reflex responses despite differences in pharmacological mechanisms and duration of action between administration routes.

Another important limitation of previous studies is their reliance on isolated airway outcomes such as cough alone. Clinically significant peri-extubation airway morbidity, however, frequently involves overlapping manifestations including severe cough, laryngospasm and oxygen desaturation. Evaluation of these events as a composite outcome may therefore provide a more comprehensive and clinically meaningful assessment of airway complications during emergence from anaesthesia while also improving statistical efficiency.

Accordingly, this protocol describes a randomised controlled trial designed to compare the effectiveness of intravenous lidocaine versus topical lidocaine gel, both administered at the time of endotracheal intubation, in reducing peri-extubation airway complications among adult patients undergoing elective orthopaedic surgery under general anaesthesia. The primary objective is to evaluate the incidence of a composite airway outcome consisting of laryngospasm, severe cough or oxygen desaturation occurring within 10 min after extubation. Secondary objectives include comparison of individual airway complications, cough severity during extubation, postoperative airway morbidity including sore throat and dysphonia in the postanaesthesia care unit, extubation-related haemodynamic responses and time to discharge readiness following extubation. It is anticipated that both administration routes may attenuate peri-extubation airway reflexes, while topical lidocaine gel may provide enhanced local suppression of airway stimulation through sustained mucosal contact during endotracheal intubation and the intraoperative period.

Methods and analysis

Study design and setting

This study protocol describes a prospective, randomised, observer-blinded, parallel-group superiority trial designed to compare intravenous lidocaine with topical lidocaine gel for the prevention of peri-extubation airway complications in adult patients undergoing elective orthopaedic surgery under general anaesthesia. The trial is designed to determine whether topical lidocaine gel is superior to intravenous lidocaine in reducing the incidence of a composite airway outcome after extubation. The protocol was developed in accordance with the Standard Protocol Items: Recommendations for Interventional Trials (SPIRIT) statement²⁰ (online supplemental file 1), and reporting of the final trial results will follow the Consolidated Standards of Reporting Trials (CONSORT) 2010 guidelines.²¹

The study will be conducted at Al-Hussein Teaching Hospital, Samawa, Al-Muthana Governorate, Iraq. Participant recruitment, intervention delivery, perioperative monitoring and postoperative assessments will be performed within the orthopaedic operating rooms and postanaesthesia care unit. Orthopaedic procedures were selected because they commonly require endotracheal intubation and relatively prolonged operative duration while avoiding the confounding airway manipulation associated with head, neck or airway surgery.

The overall schedule of participant enrolment, intervention allocation and follow-up assessments is summarised in figure 1.

Figure 1. Study flow diagram. ETT: Endotracheal Tube; PACU: Post Anaesthesia Care Unit.

Eligibility criteria

Participants will be enrolled if they meet all inclusion criteria and none of the exclusion criteria is listed in table 1.

Table 1. Eligibility criteria.

Inclusion criteria	Exclusion criteria
Adult patients aged 18–65 years Elective orthopaedic surgery under general anaesthesia with endotracheal intubation ASA physical status I or II Ability to provide written informed consent	Known hypersensitivity to lidocaine or amide-type local anaesthetics History of asthma or chronic obstructive pulmonary disease Predicted difficult airway or anticipated awake intubation Upper respiratory tract infection within the past 2 weeks Pregnancy or breastfeeding

ASA, American Society of Anesthesiologists.

Interventions

All participants will receive a standardised anaesthesia protocol. Anaesthesia induction will be performed using intravenous fentanyl (2 µg/kg), propofol (2 mg/kg) and atracurium (0.5 mg/kg). Following adequate muscle relaxation, endotracheal intubation will be performed by an attending anaesthesiologist with a minimum of 3 years of clinical experience using a standard high-volume low-pressure cuffed endotracheal tube of appropriate size. Intra-cuff pressure will be standardised to 20–30 cmH₂O using a manometer. Intubation will be performed with a Macintosh laryngoscope (or video laryngoscope if clinically indicated; device type recorded as a covariate).

Anaesthesia maintenance will consist of isoflurane (1–1.2 minimum alveolar concentration) in a 50% oxygen/nitrous oxide mixture. Additional intraoperative analgesia and muscle relaxant administration will be standardised according to institutional practice. At the end of surgery, residual neuromuscular blockade will be reversed using neostigmine (0.05 mg/kg) and atropine (0.02 mg/kg). Extubation will be performed when predefined extubation criteria are fulfilled, including adequate spontaneous ventilation, purposeful response to verbal command, protective airway reflex recovery and sustained head lift for at least 5 s.

Participants will be randomised in a 1:1 ratio into one of the following intervention groups:

Group IV (intravenous lidocaine)

Participants allocated to the intravenous group will receive 2% lidocaine at a dose of 1.5 mg/kg diluted with normal saline to a total volume of 10 mL. The solution will be administered intravenously over 60 s, approximately 90 s before endotracheal intubation.

Group topical (topical lidocaine gel)

Participants allocated to the topical group will receive 2% lidocaine gel. A thin, standardised layer of approximately 0.5–1 g of 2% lidocaine gel (≈10–20 mg lidocaine) will be applied to the entire outer surface of the endotracheal tube cuff and the distal 3 cm of the endotracheal tube immediately before intubation. No additional topical lidocaine will be administered intraoperatively or before extubation.

Both interventions are administered at the time of endotracheal intubation to evaluate prophylactic airway reflex attenuation strategies initiated during airway instrumentation itself. This approach is based on the rationale that airway mucosal irritation and sensory receptor sensitisation begin at the time of intubation and may contribute to peri-extubation airway hyperreactivity during emergence from anaesthesia.¹⁹ Thus, the intervention targets the initiation of airway sensitisation rather than solely providing a pharmacological effect at the moment of extubation. While acknowledging pharmacokinetic differences between routes, the intravenous bolus provides both early systemic coverage and sustained pharmacodynamic effects (including antitussive and anti-inflammatory actions) that persist beyond simple plasma decay.^{12 14}

Outcomes

Primary outcome

The primary outcome is the incidence of a composite adverse airway event occurring within 10 min after tracheal extubation. The composite outcome will be considered present if at least one of the following events occurs:

1. Laryngospasm (partial or complete).

2. Severe cough.

3. Oxygen desaturation

Severe cough will be assessed using a standardised 4-point cough grading scale:

0=no cough.

1=mild cough (single cough).

2=moderate cough (≤5 cough episodes).

≥2 severe cough (>5 cough episodes or sustained coughing).

Severe cough for the primary outcome definition will correspond to a cough severity score of 2 or higher (ie, moderate or severe cough).

Oxygen desaturation will be defined as peripheral oxygen saturation (SpO₂) <90% persisting for longer than 15 s.

Laryngospasm will be defined as partial or complete airway obstruction associated with inspiratory stridor, paradoxical chest movement or inability to ventilate requiring airway intervention.²²

Secondary outcomes

Secondary outcomes include:

• Individual components of the composite primary outcome.

• Cough severity during intubation.

• Cough severity during extubation using the predefined 4-point scale.

• Postoperative sore throat at 30 min and 1 hour after extubation using a 4-point Likert scale: 0=none, 1=mild, 2=moderate, 3=severe.

• Postoperative dysphonia at 30 min and 1 hour after extubation using a 4-point Likert scale.

• Haemodynamic parameters including heart rate, systolic blood pressure, diastolic blood pressure, mean arterial pressure and peripheral oxygen saturation recorded at: baseline (pre-induction), after induction before intubation, 1 min after intubation, immediately before extubation, immediately after extubation, 5 min postextubation, 10 min postextubation.

Sample size calculation

The sample size was calculated based on the primary composite outcome of peri-extubation airway complications. Previous studies evaluating lidocaine interventions for attenuation of airway events during emergence from general anaesthesia have reported heterogeneous event rates depending on patient population, airway outcome definitions, timing of administration and route of lidocaine delivery.^{14 16} Given the variability of the existing literature, the sample size estimation was based on a clinically meaningful absolute risk reduction considered relevant for peri-extubation airway management in adult surgical patients.

Assuming an estimated incidence of the composite outcome of 25% in the intravenous lidocaine group and 10% in the topical lidocaine gel group, with a two-sided alpha level of 0.05 and statistical power of 80%, a minimum of 49 participants per group are required to detect an absolute risk reduction of 15% using the χ² test. The assumed effect size was selected to reflect a clinically relevant reduction in peri-extubation airway complications while remaining feasible for a single-centre trial design.

To account for potential attrition, protocol deviations and incomplete outcome assessment, the calculated sample size was increased by 15%, resulting in a target enrolment of 58 participants per group. To ensure adequate statistical power, a total of 120 participants (60 participants per group) will be enrolled. Sample size calculations were performed using PASS software V.15.0 (NCSS, LLC, Kaysville, Utah).

Recruitment

Potentially eligible patients will be identified from the daily orthopaedic surgery schedule. A trained research assistant will approach eligible patients during the preoperative period, provide verbal and written study information and answer any study-related questions. Written informed consent (online supplemental file 2) will be obtained before any trial-related procedures are initiated.

Patient recruitment is expected to begin on 1 September 2026 and be completed by 28 February 2027 (6 months thereafter).

Randomisation and allocation concealment

An independent statistician not involved in participant recruitment, anaesthesia management or outcome assessment will generate the allocation sequence using computer-generated simple randomisation with a 1:1 allocation ratio. Allocation assignments will be placed into sequentially numbered opaque sealed envelopes.

After eligibility confirmation and informed consent acquisition, the next envelope in sequence will be opened by a study coordinator not involved in outcome assessment. The attending anaesthesiologist will then be informed of group allocation immediately before induction of anaesthesia.

Blinding

This trial is designed as an observer-blinded (single-blind) study.

Because the interventions differ substantially in route and administration technique, the attending anaesthesiologist cannot be blinded to group allocation. Participants will remain unaware of allocation because both interventions are administered after induction of anaesthesia.

Outcome assessors responsible for postoperative airway evaluations and data collection will remain blinded to group allocation and will not be present during intervention preparation or intubation procedures. Data analysts will remain blinded to treatment allocation until completion of the primary statistical analysis.

Data collection and management

Data will be collected using a standardised case report form developed specifically for this trial. The form includes demographic data, perioperative variables, surgical duration, airway outcomes, postoperative airway morbidity assessments and serial haemodynamic measurements.

All data will be entered into a password-protected electronic database with restricted investigator access. Double data entry and periodic range and consistency checks will be performed to ensure data accuracy and completeness. Any discrepancies will be resolved through review of source documentation.

Participant confidentiality will be protected through assignment of unique study identification codes. No directly identifiable patient information will be included in the analytical dataset. Study data will be stored securely for 5 years following study completion.

Participant timeline

The schedule of enrolment, interventions and assessments is presented in table 2.

Table 2. Participant timeline.

Activity	Screening	Baseline (preinduction)	Intraoperative	Postextubation (0–10 min)	PACU (30 min)	PACU (1 hour)
Informed consent	X
Eligibility screening	X
Demographics and baseline data		X
Randomisation		X
Intervention (intravenous or topical)			X
Haemodynamic monitoring		X	X (7 time points)
Surgical duration recording			X
Cough during intubation			X
Cough during extubation				X
Laryngospasm assessment				X
Desaturation assessment				X
Composite primary outcome				X
Sore throat/dysphonia					X	X

PACU, postanaesthesia care unit.

Statistical analysis

Analysis populations

Intention-to-treat population: all randomised participants analysed according to assigned allocation.

Per-protocol population: participants completing the study without major protocol deviations.

Safety population: all participants receiving at least one study intervention.

Primary analysis

The primary composite outcome will be compared between groups using the χ² test or Fisher’s exact test, as appropriate. Effect estimates will be presented as risk difference, relative risk and 95% CIs. Number needed to treat will be calculated if a statistically significant treatment effect is observed.

Secondary analyses

Continuous variables will be assessed for normality using the Shapiro-Wilk test. Normally distributed continuous variables will be analysed using independent-samples t-tests, whereas non-normally distributed variables will be analysed using the Mann-Whitney U test.

Categorical secondary outcomes will be compared using the χ² test or Fisher’s exact test.

Repeated haemodynamic measurements over time will be analysed using linear mixed-effects models with treatment group as a fixed between-subject factor and time as a repeated within-subject factor. Participant-level random intercepts will be included to account for within-subject correlation.

Sensitivity analyses

The primary outcome will be analysed in subgroups stratified by surgical duration (<90 min, 90–150 min, >150 min) to assess the consistency of treatment effects across different exposure times. Duration of anaesthesia will also be included as a covariate in adjusted regression models, if baseline imbalance exists between groups.

All statistical tests will be two-sided, and p values <0.05 will be considered statistically significant. No interim analysis is planned. Statistical analyses will be performed using SPSS V.26.0 (IBM, Armonk, New York).

Missing data

Because the primary outcome occurs during a short peri-extubation observation period, missing data are expected to be minimal. If missing primary outcome data exceed 5%, multiple imputation using chained equations will be performed under the missing-at-random assumption. Sensitivity analyses will be conducted to evaluate the robustness of findings under alternative missing-data assumptions.

Informed consent

All participants will receive a clear verbal and written explanation of the study’s purpose, procedures, potential benefits and possible risks. Written informed consent will be obtained from each participant before enrolment. Participants will be informed that their participation is voluntary and that they may withdraw at any time without affecting their medical care.

Confidentiality

Participant confidentiality will be strictly maintained. Personal identifiers will be removed from the data and replaced with unique study codes. Only authorised members of the research team will have access to the data.

Patient and public involvement

Patients and members of the public were not involved in the design, conduct, reporting or dissemination planning of this study.

Discussion

This protocol outlines the rationale and methodological design of a randomised controlled trial comparing intravenous lidocaine with topical lidocaine gel administered at the time of endotracheal intubation for prevention of peri-extubation airway complications in adults undergoing elective orthopaedic surgery under general anaesthesia. The protocol was developed to address ongoing uncertainty regarding the optimal route and timing of prophylactic lidocaine administration for attenuation of airway responses during emergence from anaesthesia. The study will evaluate a clinically relevant composite outcome consisting of laryngospasm, severe cough and oxygen desaturation occurring within 10 min after extubation.

Summary of key design features

Several methodological aspects of this trial warrant emphasis. First, the study uses a composite primary outcome incorporating laryngospasm, severe cough and oxygen desaturation. Because individual airway complications, particularly laryngospasm, occur relatively infrequently in non-airway surgery,²³ evaluation of clinically related airway events as a composite outcome improves feasibility for detecting clinically meaningful differences between interventions while preserving direct clinical relevance. Each component represents a peri-extubation airway event associated with impaired airway patency, increased intervention requirements or potential postoperative morbidity.

Second, both interventions are administered at the time of endotracheal intubation rather than immediately before extubation. This design reflects a prophylactic strategy targeting airway irritation and sensory receptor activation initiated during airway instrumentation itself. Mechanical contact between the endotracheal tube and airway mucosa may induce epithelial microtrauma, local inflammation and airway reflex sensitisation that persist throughout the intraoperative period and subsequently influence airway responsiveness during emergence from anaesthesia.^{23 24}

Third, the methodological design incorporates several features intended to strengthen internal validity, including concealed randomisation, blinded outcome assessment, predefined outcome measures and a standardised anaesthesia protocol. Although the attending anaesthesiologist cannot be blinded because of the distinct nature of the interventions, outcome assessors and data analysts remain blinded to allocation throughout the trial.

Comparison with the existing evidence

Existing evidence supports the use of intravenous lidocaine for reducing postextubation cough and postoperative sore throat compared with placebo.¹⁴ However, direct comparisons between intravenous and topical lidocaine in adult surgical populations remain limited and methodologically heterogeneous. Interpretation of previous studies is complicated by variation in topical formulations, timing of administration, airway devices, patient populations and definitions of airway outcomes. Furthermore, most available comparative studies have evaluated lidocaine spray administered shortly before extubation, leaving uncertainty regarding the potential role of lidocaine gel applied at the time of intubation.^{15 16}

The present trial is designed to address this gap by evaluating a gel formulation that may provide prolonged mucosal contact throughout surgery and potentially attenuate airway irritation initiated during intubation itself. In addition, the study focuses on adults undergoing orthopaedic surgery, a non-airway surgical population that remains under-represented in previous comparative studies. Elective orthopaedic procedures provide a relatively homogeneous non-airway surgical population with predictable anaesthetic characteristics and minimal direct airway manipulation. Consequently, findings from this trial may be relevant to a broad range of routine non-airway surgical procedures performed under general anaesthesia.

If topical lidocaine gel demonstrates comparable or improved effectiveness relative to intravenous lidocaine, the findings may support a simple prophylactic airway management strategy based on local mucosal anaesthesia. Topical administration may reduce systemic exposure while providing targeted airway reflex suppression at the site of airway instrumentation. Conversely, if no clinically meaningful difference is identified between routes, selection of administration strategy may depend on considerations such as clinician preference, drug availability, cost and perioperative workflow.

Strengths

This study has several important strengths. The randomised parallel-group design with concealed allocation and blinded outcome assessment reduces the risk of selection and detection bias. The use of predefined outcome measures and a standardised anaesthesia protocol further enhance methodological consistency and internal validity. The study additionally evaluates multiple clinically relevant secondary outcomes, including postoperative sore throat, dysphonia and haemodynamic responses, thereby providing a broader assessment of perioperative recovery beyond the primary airway endpoint. Furthermore, the sample size calculation is based on a clinically meaningful effect estimate and incorporates an allowance for attrition and incomplete outcome assessment.

Limitations

Several limitations should be acknowledged. First, the attending anaesthesiologist cannot be blinded to treatment allocation because the interventions differ procedurally and visually. Although this may introduce performance bias, outcome assessment and statistical analysis remain blinded, and the primary outcome consists predominantly of objective clinical events rather than subjective clinician impressions.

Second, the study is conducted at a single centre, which may limit generalisability to other healthcare systems, surgical populations or anaesthesia practice environments. Nevertheless, single-centre comparative effectiveness trials provide important preliminary evidence before larger multicentre investigations.

Third, although the composite primary outcome improves feasibility for detecting clinically meaningful differences, the individual components differ in frequency and clinical severity. In particular, severe cough is expected to occur more frequently than laryngospasm, potentially contributing disproportionately to the composite endpoint. The selected composite outcome reflects clinically related manifestations of peri-extubation airway instability rather than equivalent clinical severity across individual components. To address this limitation, all individual components of the composite outcome are prespecified secondary outcomes and will be analysed separately.

Fourth, the primary outcome observation period is restricted to the first 10 min after extubation. Although this interval captures the period of greatest airway vulnerability and aligns with previous peri-extubation studies, delayed airway complications occurring beyond this timeframe will not be evaluated.

Fifth, postoperative sore throat and dysphonia are assessed using patient-reported Likert scales and may, therefore, be influenced by subjective variability in symptom perception and reporting. However, such measures are widely used in perioperative airway research and reflect clinically relevant patient-centred outcomes.

Sixth, the exclusion of patients with asthma, chronic obstructive pulmonary disease, recent upper respiratory tract infection or predicted difficult airway enhances internal validity but limits applicability of findings to higher risk airway populations.

Finally, the pharmacokinetic characteristics of intravenous lidocaine and topical lidocaine gel differ substantially, and the duration of pharmacological activity may not be directly comparable between routes. Following a 1.5 mg/kg intravenous bolus, therapeutic plasma concentrations (1.5–5 µg/mL) for antitussive effects are achieved within 1–2 min and remain clinically relevant for 20–45 min, with peak effect at approximately 5–10 min. Importantly, the residual membrane-stabilising, antitussive and anti-inflammatory effects on airway nerves persist beyond simple plasma decay, and meta-analyses have confirmed the efficacy of intravenous lidocaine administered at induction for reducing postextubation cough.¹⁴ For very prolonged procedures (>2–3 hours), a supplemental intravenous dose near the end of surgery could be considered in future protocols. However, the current single-bolus approach reflects common clinical practice and is supported by level 1 evidence demonstrating efficacy with this timing.¹⁴ We will collect and adjust for surgical duration to account for this potential confounder and will perform sensitivity analyses stratified by procedure duration.

Implications for clinical practice and future research

Peri-extubation airway complications remain common during routine non-airway surgery. Identification of a simple and effective prophylactic strategy may, therefore, have important implications for patient safety, recovery quality and perioperative resource utilisation. If topical lidocaine gel demonstrates favourable effectiveness and tolerability, it may represent a practical alternative to intravenous administration in routine anaesthesia practice.

Future studies should evaluate these interventions in higher risk populations, including patients with obesity, reactive airway disease or those undergoing airway and head-and-neck procedures. Additional research may also examine longer postoperative observation periods, alternative topical formulations and multicentre study designs powered to detect differences in individual airway complications.

Ethics and dissemination

Ethical approval has been obtained from the Ethics Committee of Tehran University of Medical Sciences (approval number: IR.TUMS.SPH.REC.1404.293) and the Institutional Review Board of Al-Hussein Teaching Hospital, Iraq. The study will be conducted in accordance with the Declaration of Helsinki (2013) and Good Clinical Practice guidelines.

The findings of this study will be disseminated through publication in a peer-reviewed journal and presented at national and international anaesthesia conferences. Preliminary results will be made available to participating hospitals and healthcare providers. The final dataset will be made available on reasonable request to the corresponding author.