Study of postoperative laryngopharyngeal discomfort: protocol for a single-centre cohort study

Introduction

Postoperative laryngopharyngeal discomfort is a common clinical complication of extubation during routine elective surgery. General symptoms include throat pain, dysphagia and tongue oedema, which may delay water and food intake and affect postoperative daily activities. On average, one in three patients may experience the above symptoms after extubation.1 2 The most severe manifestations may be postextubation stridor, macroglossia, and airway obstruction, resulting in prolonged mechanical ventilation, unplanned tracheotomy, postoperative pneumonia and increased postoperative mortality.3–5 The incidence of pharyngeal complications after extubation under general anaesthesia has been demonstrated; even after a short elective surgery (median time of tracheal intubation: 132 min), the incidence of dysphagia and sore throat and cough after extubation was 43% and 32%, respectively.6 Possible preventive and therapeutic methods include avoiding prolonged exposure to dangerous positions, using glucocorticoids to reduce airway oedema, and dehydration treatment.1 7 However, quantitative metrics that can provide objective guidance to anaesthesiologists and surgeons are lacking.

There is a lack of clear risk factors, effective clinical indicators and diagnostic methods for postoperative laryngopharyngeal discomfort. According to previous studies, the three pathophysiological mechanisms are as follows: (1) gravity, intrathoracic pressure or intra-abdominal pressure increase the hydrostatic pressure and cause fluid redistribution; (2) surgical or aesthetic procedures lead to soft-tissue damage to the airways and oropharynx; and (3) systemic stress and inflammation contribute to tissue oedema.

From a clinical perspective, there are different contributions to the above mechanisms in specific perioperative aetiologies, which can be divided into three categories: surgical, aesthetic and patient factors. (1) Surgical factors: (a) surgical position that causes gravity to be distributed to the mouth and face; (b) head and neck flexion position, such as the prone position or posterior fossa surgery in the beach chair position, which leads to blockage of venous and lymphatic return8; (c) surgical trauma that changes the permeability of vascular endothelial cells in the inflammatory state of the body and causes water retention; and (d) some surgical procedures that involve potential compression of the airway wall (cervical spine, thyroid, etc). (2) Aesthetic factors: (a) repeated or unskilled intubation9; (b) compression of the tracheal tube on the intraoral tissue and airway during the operation10 11; (c) method of endotracheal intubation, catheter type, tube size and material6 12; (d) additional mechanical compression such as those caused by teeth, intraoral instruments, ultrasound probes, oropharyngeal airways, or throat packs12; and (e) fluid overload.13 (3) Patient factors: (a) duration in high-risk positions and (b) difficult airway (narrow oropharyngeal cavity or conditions that cause difficulty in intubation).13

The three clinical factor categories described above were considered in this trial. Based on current clinical procedures, the contact force of the tracheal tube on the tongue may be a measurable index.14 15 The T-scan pressure distribution system is a non-invasive technology that is used to measure the tracheal tube–tongue contact force in real time during surgery. This study attempted to analyse the catheter–tongue pressure distribution, resultant force position, contact area and pressure values at different surgical positions.14–16 Combined with patient anatomical measurements, airway management, fluid therapy, intraoperative medication, and other factors, this study comprehensively analysed clinical monitoring indicators to identify the risk factors for postoperative laryngopharyngeal discomfort in routine elective surgery under general anaesthesia.

Objectives

This study aims to determine the incidence of postoperative laryngopharyngeal discomfort in different surgical positions during general anaesthesia with tracheal tube intubation. We aim to explore the distribution and duration of the tracheal tube–tongue contact force during routine surgeries. We summarise the risk factors in patients with postoperative laryngopharyngeal discomfort undergoing routine elective surgery under general anaesthesia.

Methods and analysis

Study design

This study was designed in accordance with the Strengthening the Reporting of Observational Studies in Epidemiology statement.17 This is a single-centre, prospective, parallel-group, observational study protocol to be conducted from 1 July 2023 to 30 June 2024 (trial registration: NCT05987293). This study was approved by the Ethics Committee of Clinical Research of China-Japan Friendship Hospital (application number: 2023-KY-219, approved on 14 September 2023).

Settings and participants

This study will be performed at the Department of Anesthesiology of China-Japan Friendship Hospital, Beijing, China. This single-centre study will be conducted in a tertiary general hospital, with 1400 beds, 50 operating rooms and 90 anaesthesiologists, which annually conducts more than 15 000 operations under general anaesthesia. The research group collaborates with the Departments of Otolaryngology, Spine Surgery, General Surgery, Neurosurgery and Medical Engineering.

Fifty-four patients undergoing elective surgery under general anaesthesia for more than 2 hours with an endotracheal tube at the China-Japan Friendship Hospital will be enrolled (see ‘Sample size’). Patients will be divided into two groups according to the surgery: supine position (Supine group) and high-risk position (Flexion group), which includes the prone, cervical traction and beach chair positions. Patients with existing oral or airway problems, or other factors influencing postoperative dietary recovery, will be excluded.

Hypothesis

We assume that the incidence of postoperative laryngopharyngeal discomfort in the Supine group is different from that in the Flexion group and that tongue compression and pressure distribution differ between the two groups.

Patient enrolment

The inclusion and exclusion criteria are shown in box 1. Patients with difficulties in endotracheal intubation, limitations in routine surgical position and delayed oral water intake after surgery will be excluded. After enrolment, demographic data, medical history related to surgery and airway assessment results will be collected. During surgery, the tracheal tube–tongue pressure distribution and dynamic changes from different positions before extubation will be monitored. Patients with unplanned changes in surgical position, unplanned changes in strategy for establishing an artificial airway, unexpected difficult airway, intraoperative airway injury, delayed extubation due to non-airway factors and aggressive fluid therapy administration will be withdrawn from the study. Participants will be followed up for 1 week after the operation. The incidence of postoperative laryngopharyngeal discomfort will be compared between the two groups. Airway measurements, operation duration, mechanical ventilation time, recovery of water and solid food intake, and other airway-related events will be recorded. Figure 1 shows the timeline of this study protocol.

Box 1

Study eligibility

Inclusion criteria

  • ASA class I–III

  • Aged 18–85 years

  • Scheduled for elective surgery with tracheal intubation under general anaesthesia, with operation duration ≥2 hours

  • The intended surgical position is supine, prone, cervical traction, or beach chair position

  • Informed consent is obtained

Exclusion criteria

  • Informed consent is not obtained

  • Maxillofacial surgeries or other surgeries involving the oral cavity and upper airway

  • History of head and neck radiotherapy

  • Deformity, trauma, infection and active bleeding exist in the mouth and tongue

  • Airway hyperresponsiveness, active asthma, acute exacerbation of chronic obstructive pulmonary disease or laryngeal osteomalacia

  • Respiratory insufficiency, moderate-to-severe ventilation or diffusion dysfunction

  • Existing chronic sore throat, recurrent laryngeal nerve injury, dysarthria, dysphagia, severe gastroesophageal reflux, upper oesophageal sphincter dysfunction, cardiac stenosis and other basic diseases

  • Postoperative total parenteral nutrition therapy is planned

Figure 1
Figure 1

Strengthening the Reporting of Observational Studies in Epidemiology flow chart of the trial. BMI, body mass index; POD, postoperative day; VAS, Visual Analog Scale.

Data collection

Tracheal tube–tongue pressure is measured using a computerised occlusal analysis system based on the T-scan technique, suitable for multipoint real-time monitoring of intraoral pressure.18 A flexible film sensor with a thickness of 0.11 mm is placed between the tongue and tracheal tube to measure the pressure distribution, contact force and dynamic changes in pressure at different sites of the tongue. A sensor placed between the tongue and tracheal tube is extensively used to measure the contact force of the tracheal tube on the tongue. The marker line on the tracheal tube used to locate the glottis during intubation is used as the standard position of our T-scan sensor to ensure that it covers the base, middle and tip of the tongue. Through preliminary experiments, we will verify that the pressure measurement range and sensitivity of this technology are suitable for measuring the force of the tracheal tube on the tongue.

Five channels of pressure values will be recorded separately: Channel (Ch) 1, tip of the tongue; Ch2, middle of the tongue; Ch3, base of the tongue; Ch4, right side at the base of the tongue; and Ch5, left side at the base of the tongue. The pressure values will be recorded at the following points during the operation: t1, after intubation; t2, highest pressure during patient positioning; t3, after position fixation; t4, at the end of surgery; and t5, before extubation.

Preoperative information

Demographic characteristics, such as age, sex, height, body weight, body mass index (BMI), and airway measurements, including neck circumference, Mallampati classification, mouth opening, nail–chin distance and mandibular angle, will be recorded. Having a suspicious difficult airway is determined based on baseline data and airway measurements: BMI≥30 kg/m2, neck circumference>40 cm, Mallampati grade≥3, mouth opening<3 transverse fingers, nail–chin distance<3 transverse fingers, mandibular angle length<6 cm, and one or more of them will be identified as having a suspicious difficult airway.

Intraoperative information

After entering the operating room, vital sign monitoring, anaesthetic administration, tracheal intubation and mechanical ventilation will be routinely established. Laryngoscope/video laryngoscope/rigid bronchoscope-assisted tracheal intubation will be performed. The tracheal tube cuff will be inflated after confirming its position. A manometric sensor will be placed intraorally between the tracheal tube and tongue. Mechanical ventilation will be set with conventional parameters (tidal volume, 6–8 mL/kg; respiratory rate, 10–14 beats/min; positive end expiratory pressure, 2–10 cm H2O), and respiratory parameters will be adjusted according to the intraoperative ventilatory status.

Body position and maintenance time (top), duration of mechanical ventilation with an endotracheal tube (ttube), type of endotracheal tube (inner diameter, pressure-resistant tube/normal tube/nasal tube), intraoperative intake and output volume (I/O), glucocorticoid use, visible intraoral injury on video laryngoscopy before extubation, and tracheal tube-related events, including tube kinking, abnormal airway pressure and ventilatory dysfunction, will be recorded.

Postoperative information

Patients will be followed up until postoperative day 7. Patients will be asked if they experience a ‘burning throat’, ‘dry throat’, ‘tingling tongue’, ‘tightness in the throat’, or any head, neck and throat discomfort. The first successful postoperative intake of water and solid food will be recorded. Obvious oedema of the head and face, glucocorticoid use and self-rated scores of patient satisfaction (1–10/10) will be recorded. Airway-related events including bronchospasm, aspiration, unplanned reintubation, pulmonary infection, ventilation insufficiency and prolonged oxygen therapy will be recorded. Table 1 shows the collected data and follow-up data.

Table 1

Data collection and follow-up

Outcome measurement

Primary outcome: the primary composite endpoint is assessed as the incidence of postoperative laryngopharyngeal discomfort, which is either the state of severe sore throat (Visual Analog Scale score≥4), dysphagia after extubation, or any of the symptoms of tongue oedema. Secondary outcomes include the time of first smooth water intake (tliguid), time of first smooth solid food intake (tfood) and airway-related events (bronchospasm, aspiration, secondary intubation, respiratory tract infection, respiratory insufficiency and prolonged oxygen therapy).

Sample size

According to the literature, the incidence of postoperative laryngopharyngeal discomfort in the high-risk positions is approximately 78%,19 and the incidence in the supine position is approximately 33%.20

The sample size was estimated using PASS 2021 software (NCSS Statistical Software, USA). We assumed a two-sided hypothesis, power=0.8, α=0.05, G (group)=2, allocation ratio 1:1, using the formulae for t-tests for proportion ratios for two samples. Considering an allowable dropout rate no higher than 20%, the total sample size will be 54 (n=27 in each group).

Missing data

Attrition bias may influence our results. The participants’ characteristics between the completed and dropout cases will be compared and analysed. The reason for the data default will be published in detail. We will evaluate whether the characteristics of the population with missing data differ from those of other patients and whether they have an impact on the research results. The reasons for withdrawal, loss to follow-up, or missing data, as well as the validity of the study, will be fully discussed.

External validity

The results of this study can be applied to non-critically ill patients undergoing conventional general anaesthesia and routine elective surgery. Our study does not change the intraoral pressure, nor does it influence the surgical or aesthetic protocols. We will analyse the demographic characteristics of the participants and perioperative indicators to further statistically analyse the external validity.

Statistical analysis

Based on the primary and secondary outcomes, the prognostic factors for postoperative laryngopharyngeal discomfort will be compared between the two groups. The distribution characteristics and dynamic changes will be described and compared between the two groups, and the aetiological factors will be analysed. A single-factor analysis will be used to screen the risk factors for postoperative laryngopharyngeal discomfort using the primary outcome as the dependent variable, whereas airway-related and surgery-related factors will be used as the independent variables. Logistic multivariate analysis will be performed to determine independent and significant risk factors. Statistical significance will be set at p<0.05.

Patient and public involvement

The patients and public will not be involved in this study

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