Stroboscopy and acoustic analysis of voice following endotracheal intubation in otological surgeries

Abstract

Background

Stroboscopy is an endoscopy that is performed with intermittent light at a frequency that approximates the frequency of a moving object so that it appears in slow motion or motionless. It is used to analyze the structure and motion of the vocal fold.

Aim and objective

To compare the stroboscopic findings of various vocal parameters such as symmetry, amplitude, periodicity, mucosal wave of vocal folds, and glottis closure before and after elective endotracheal intubation and to compare acoustic analysis of voice using fundamental frequency, intensity, maximum phonation time, and dysphonia severity index in patients before and after elective intubation, who were undergoing otological surgeries. It also assesses the correlation between changes in these vocal and acoustic parameters and the size of the endotracheal tube, duration of intubation, and number of attempts made during intubation. This study creates awareness and provides insights to avoid intubation-related vocal fold injury.

Methods

This was a prospective cohort study involving 31 patients done in a Tertiary Care Centre. All patients who underwent otological surgeries by elective endotracheal intubation were included. All of them underwent stroboscopic and acoustic evaluation preoperatively, 24 h, and 7 days postoperatively.

Results

Statistically significant changes in mucosal wave pattern score were observed in the 1st postoperative day that reverted to normal by the end of 7th postoperative day and in GRBAS which was significant at the end of both 1st and 7th POD. Other parameters like fundamental frequency, intensity, DSI, MPT, amplitude, symmetry, periodicity, and glottis closure remain unaltered. There was a moderate positive correlation between the duration of intubation (minutes) and mucosal wave 1st POD (P-value: 0.003).

Conclusion

The majority of the patients (61%) had normal laryngeal structures. A total of 39% had evidence of injury, the most common being right vocal fold hemorrhage improved by the end of 7th postoperative day and became normal.

Background

The production of human voice involves a complex process that extends beyond the mere oscillation of the vocal folds since it requires the coordination of various systems. To commence voice production, it is imperative to have adequate respiratory support and control while also ensuring the presence of resonance for optimal sound amplification and projection [1]. Videostroboscopy has emerged as the predominant technique for assessing vocal fold vibration, and it has become widely acknowledged as an integral component in the comprehensive evaluation of voice disorders [2].

The utilization of stroboscopic imaging to observe the vibratory behavior of the vocal folds during phonation remains essential in the process of making diagnostic, therapeutic, and surgical determinations [3]. The present discourse encompasses comprehensive data about glottis closure pattern, amplitude, mucosal wave, the presence of non-vibrating segments, phase symmetry, and regularity. The progression of innovative laryngeal imaging techniques, such as high-speed video endoscopy (HSV), magnetic resonance imaging (MRI), and optical coherence tomography, has substantially augmented our understanding and capacity to quantify intricate phonatory mechanisms [4].

In the context of general anesthesia, the process of endotracheal intubation is generally considered to be a procedure that carries a relatively low risk, resulting in a low occurrence of post-intubation complications such as sore throat and hoarseness [5]. Laryngeal injuries resulting from intubation have been extensively documented in the worldwide literature, with reported occurrence rates ranging from 63 to 94%. Furthermore, persisting sequelae caused by prolonged intubation have been reported in around 10 to 22% of cases [6]. Vocal complications have been associated with many variables during endotracheal intubation, including unilateral fold paralysis or paresis, the formation of scar tissue or granulomas, and the displacement of arytenoid cartilage [7].

Vocal injuries have the potential to manifest as either transient or enduring conditions. Transient complications encompass laryngotracheal infection, vocal fold hemorrhage, ulceration, scabs, laryngeal edema, and granulations, whereas enduring complications comprise vocal fold paralysis, vocal fold scarring, laryngotracheal stenosis, tracheomalacia, and tracheo-esophageal fistula. In several instances, the structural integrity of the larynx remains unaffected; however, dysphonia can arise due to modifications in vocal fold biomechanics and histological changes underneath the epithelial layer. The occurrence of postoperative dysphonia after elective endotracheal intubation varies between 21 and 71.8% and is associated with various laryngeal pathologies including vocal folds erythema, edema, ulceration, temporary or permanent vocal folds paralysis or paresis, subglottic stenosis, laryngeal scar, fibrosis, and glottic web granuloma [8, 9].

The primary objective of this study was to conduct a comparative analysis of stroboscopic observations about different vocal parameters, including symmetry, amplitude, periodicity, mucosal wave of vocal folds, and glottis closure and acoustic parameters like fundamental frequency, intensity, DSI, and MPT. This analysis was performed before and after elective endotracheal intubation in patients undergoing otological procedures. Additionally, this study evaluates the relationship between alterations in these vocal parameters and acoustic parameters and the size of the endotracheal tube, the duration of intubation, and the number of intubation attempts. This study aims to raise awareness and offer valuable insights into the prevention of vocal fold injuries associated with intubation.

Methods

Study design

A prospective cohort study was performed in the Otorhinolaryngology Department at the Tertiary Care Centre on 31 patients who underwent otological surgeries.

Study duration

This study was conducted for a period of 1 year from April 2022 to April 2023.

Subject selection

The patients who were undergoing otological surgeries under general anesthesia.

Inclusion criteria

• 1. Patient aged 18 to 60 years belongs to both sexes.

• 2. American Society of Anesthesiologists (ASA) category I and II patients

Exclusion criteria

• 1. Patients who are not willing to give consent for participation in the study

• 2. Patients with a previous history of endotracheal intubation

• 3. Patients diagnosed to have benign/malignant lesions of the larynx

• 4. Smokers and are addicted (substance abuse) and obesity (BMI more than 30) and chronic obstructive pulmonary disease

• 5. Previous history of surgeries in the aerodigestive tract (endoscopy, direct laryngoscopy, bronchoscopy)

• 6. Patients who vomited within the 1st 24 h following endotracheal intubation

These factors may potentially exert a direct influence and increase the susceptibility to vocal fold injuries during the process of endotracheal intubation. Evaluating stroboscopic parameters presents challenges in the presence of preexisting pathology and does not provide conclusive evidence on the causation of harm by endotracheal intubation.

Method

The selection of patients for this study was conducted by rigorous inclusion and exclusion criteria, following the approval of the Institutional Human Ethics Committee of Sri Ramachandra Medical College and Research Institute (CSP-MED/15/Aug 24, 2022). Following the acquisition of duly informed written consent, a comprehensive assessment encompassing a meticulous medical history and a thorough clinical examination was conducted. The study encompassed individuals who were scheduled to undergo surgical intervention for conditions affecting the ear. Various ear surgeries include tympanoplasty both endoscopic and open approaches and cortical mastoidectomy. As surgeries to the nose and throat can cause some amount of voice change, we identified and analyzed those patients who underwent ear surgeries. The surgeons who performed surgery and the surgeons who analyzed the stroboscopic parameters were different, and both were kept blinded.

Preoperative assessment

Patients were assessed preoperatively using the following:

• 1. Mallampati classification — In order to foretell the difficulty of the airway, the Mallampati score compares the size of the oropharyngeal opening to the base of the tongue. Patients were categorized into one of three classes based on visible structures. These classes were as follows:

  • Class I — Complete visualization of the faucial pillars, soft palate, and uvula.

  • Class II — Complete visibility of the faucial pillars and soft palate and unable to visualize the uvula as it is obscured by the base of the tongue.

  • Class III — Only the soft palate could be visualized.

• 2. ASA grading — The American Society of Anesthesiologists (ASA) physical status classification system was developed to provide perioperative clinicians with a straightforward way to categorize a patient’s physiological condition to anticipate operative risks. Patients were categorized into the following:

  • I. The patient is a completely healthy fit patient.

  • II. The patient has mild systemic disease.

  • III. The patient has a severe systemic disease that is not incapacitating.

  • IV. The patient has an incapacitating disease that is a constant threat to life.

  • V. A moribund patient who is not expected to live 24 h with or without surgery. VI A declared brain dead patient whose organs are being removed for donor purposes.

Timing of stroboscopy

Patients were subjected to stroboscopy and acoustic analysis of voice on the following:

• 1. Day before surgery

• 2. First postoperative day (24 h)

• 3. End of 7th postoperative day

Technique of stroboscopy

Stroboscopy was done using ATMOS Media stroboscope II system REF: 507.3170.0, 512 MB RAM instrument which consists of 90-degree rigid laryngoscope, camera, voice level meter, contact microphone (collar mic), airborne microphone (scope mic), monitor, light source, mouse, and fiber-optic cable (Fig. 1).

Fig. 1

Atmos media stroboscope unit

Stroboscopy procedure

Following the acquisition of duly informed and documented consent, the patient was instructed to be in a seated position in an examination chair, adjusted to a height conducive to the comfort of the examiner. The patient exhibits a forward inclination, accompanied by flexion of the neck and extension of the head at the atlanto-occipital joint. A contact microphone was strategically positioned atop the thyroid lamina, ensuring optimal placement for accurate acoustic detection and analysis.

• Fundamental frequency: Measured before stroboscopy by asking the patient to say “i” vowel.

The synchronized emission of luminous flashes from the stroboscope was meticulously coordinated with the vocalizations of the patient, thereby facilitating the assessment of the fundamental frequency. A 10% solution of xylocaine was administered via spray application onto the posterior aspect of the tongue, as well as the posterior pharyngeal wall. After defogging the stroboscope, the patient’s tongue protruded out and was held at the middle 1/3rd by the examiner; the stroboscope was introduced to visualize the vocal folds (Fig. 2).

Fig. 2

Technique of stroboscopy

Once the vocal folds are visualized, the patient was asked to phonate the vowel “i,” soft phonation of “i,” loud phonation, intermittent phonation, gliding of “i” from low pitched to high pitch and then from high pitch to low pitch, normal cough, and phonate on inhalation.

Voice analysis was performed by speech pathologist, when patient is asked to phonate a vowel “i,” soft phonation oh “i,” loud phonation, intermittent phonation, gliding of “i” from low pitched to high pitch, and then from high pitch to low pitch, normal cough, and phonate on inhalation. It is recorded and saved in “Lingware” software (Fig. 3).

Fig. 3

Technique of voice analysis

Parameters assessed the following:

• 1. Preoperative assessment: Mallampati classification, ASA grade, stroboscopic parameters: vocal fold symmetry, amplitude, periodicity, glottis closure, mucosal wave pattern, acoustic parameters: fundamental frequency, intensity, maximum phonation time, and dysphonia severity index.

• 2. Intraoperative assessment: Duration of intubation and number of attempts used at intubation

• 3. Postoperative assessment: Vocal fold symmetry, amplitude, periodicity, glottis closure, and mucosal wave pattern were assessed, and acoustic parameters are as follows: fundamental frequency, intensity, maximum phonation time, and dysphonia severity index.

• Symmetry: The level of coordination exhibited by the two vocal folds in terms of their vibratory motion, characterized by their balanced and synchronized convergence and divergence during phonation and coughing. The grading system assigned a value of 0 for symmetrical and 1 for asymmetrical.

• Amplitude: The lateral excursion of the vocal folds refers to their movement away from the midline during oscillation. The determination of pitch frequency and loudness in speech is contingent upon factors such as vocal fold tension and subglottic pressure. The grading system included three distinct categories: a score of 0 designated as normal, a score of 1 indicated less than normal, and a score of 2 represented a level greater than normal.

• Periodicity: The regularity of consecutive vocal vibratory cycles. The assessment utilized a grading system comprising three distinct categories: 0, denoting the lack of deviance; 1, denoting a minor degree of deviance; and 2, denoting a substantial amount of deviance.

• Glottis closure: To assess the vocal folds if there is complete glottis closure during adduction. The grading system used for this assessment consisted of three categories: 0, indicating complete closure; 1, indicating intermediate closure; and 2, indicating broad opening.

• Mucosal wave: The propagation of the mucosal wave is contingent upon the rheological characteristics of the phonatory mucosa, which encompasses the epithelium and superficial lamina propria, during particular vocal activities. The evaluation of the mucosal wave’s existence or the absence was conducted utilizing a grading system, in which a score of 0 denoted its presence and a score of 1 denoted its absence.

GRBAS

Five parameters are used by the GRBAS score: The overall level of hoarseness or voice irregularity is represented by a grade (G). A psychoacoustic sense of the irregularity of vocal fold vibrations is represented by the rough (R). It is associated with the erratic variations in the glottal source sound’s loudness or fundamental frequency. A psychoacoustic impression of the degree of air leaking through the glottis is represented by breathy (B). It has to do with turbulence. Asthenic (A) indicates a voice that is feeble or lacks strength. It has to do with either a lack of higher harmonics or a weak glottal source sound. A hyperfunctional condition of phonation is represented by the psychoacoustic sensation of a restrained (S) state. It is associated with noise in the high-frequency range, richness in high-frequency harmonics, or an unusually high fundamental frequency. GRBAS is graded as 0 = slight degree, 1 = medium degree, and 2 = high degree of hoarseness. One of the main benefits of the GRBAS system is its ease of use which can be done quickly.

Acoustic parameters

• Fundamental frequency: It is defined as the frequency of vibration of the vocal fold during phonation.

• Maximum phonation time: Maximum phonation time is the longest duration of sustained phonation of a vowel sound; typically, “ah” is measured.

• Intensity: Vocal intensity is examined in accordance with fundamental frequency and lung pressure.

• Dysphonia severity index: The dysphonia severity index (DSI) is an established evaluation technique that calculates a weighted combination of maximum phonation time, highest frequency, lowest intensity, and jitter (%) of a person.

The preoperative and postoperative stroboscopic parameters and acoustic analysis were assessed by surgeons and speech pathologists who were blinded, unaware of patient demographics, procedure, size of endotracheal tube, duration of intubation, and number of attempts made at intubation. The results were documented and statistically analyzed.

Statistical analysis

The data was assessed utilizing the Statistical Package for Social Sciences (SPSS)-Version 22, a widely recognized software tool employed for statistical analysis in various research domains: (1) SPSS I, IBM SPSS Statistics Version 22 Statistical Software: Core System Users’ Guide, SPSS Inc. 2014.

The key explanatory variable in this study was the size of the endotracheal tube, measured in millimeters, and the duration of intubation, measured in minutes.

Statistical methods

The present study employed a descriptive analysis approach to examine the quantitative and categorical variables. The mean and standard deviation were computed to summarize the central tendency and variability of the quantitative variables, respectively. On the other hand, the frequency and proportion were utilized to summarize the distribution and relative frequencies of the categorical variables. The comparative analysis of mean values for normally distributed quantitative parameters was conducted between distinct research groups utilizing an independent sample t-test. This statistical test involved the examination of two groups to evaluate any potential differences. The investigation into the association between quantitative explanatory variables and outcome variables was carried out through the calculation of the Spearman rank correlation coefficient (rs).

The Spearman rank correlation coefficient is commonly used to assess the strength of the relationship between two variables. A weak correlation is defined as falling below 0.5, indicating a limited association between the variables under consideration. When the correlation coefficient ranges from 0.5 to 0.7, it is classified as moderate, suggesting a moderate level of association and > 0.7 suggesting strong association. A statistical significance level of p < 0.05 was determined to be of statistical significance.

Results

The mean age was 36.68 ± 12.35 years (range 18 to 57). A total of 29% were aged 46 and above. A total of 25.80% were aged between 18 to 25 years and 36 to 45 years each. Out of the 31 participants in the study, 23 (74.19%) were female, and 8 (25.81%) were male.

The majority of the patients (16) had left chronic otitis media—mucosal, while 14 patients had right chronic otitis media—mucosal, and 1 participant had bilateral disease. Fourteen participants underwent a left, type 1 tympanoplasty, and 13 patients underwent a right, type 1 tympanoplasty. Thirty participants were classified as Mallampati Class I, while only 1 patient was classified as Mallampati Class II. Twenty-two participants were classified as ASA Grade I, with the remaining 9 participants were classified as ASA Grade II. Duration of endotracheal intubation ranged from 45 to 270 min with an average of 153.55 min. The endotracheal tube size used was around 7.5 mm on average. Number of attempts average was 1.93, ranging from 1 to 3. The majority of the patients (19) had normal vocal folds (Fig. 4), while the rest had various vocal fold abnormalities with different specific conditions and percentages. Postoperatively, one patient had subglottic hemorrhage and posterior commissure ulcer (Fig. 5), two patients with posterior commissure ulcer (Fig. 6), and one patient with left vocal fold hemorrhage (Fig. 7) (Table 1).

Fig. 4

Showing still image of normal stroboscopic status of vocal folds done in the immediate preoperative period

Fig. 5

Showing still image of subglottic hemorrhage and posterior commissure ulcer in the 1st postoperative day

Fig. 6

Showing a still image of posterior commissure ulcer on 1st postoperative day

Fig. 7

Showing a still image of left vocal fold hemorrhage on 1st postoperative day

Table 1 Summary of demographic parameters (N = 31)

After surgery, the fundamental frequency of voice increased from an average of 282.46 Hz to around 287.72 Hz on the first day and eventually around 289 Hz by the 7th postoperative day, but it was not statistically significant. Seventeen patients had mucosal wave abnormality on the first postoperative day. Of the 17 patients who had mucosal wave abnormality, only 12 patients had gross vocal fold changes (Table 2).

Table 2 Summary of baseline parameters (N = 31)

The study findings indicate that there is no statistically significant disparity in fundamental frequency observed between male and female individuals both before undergoing surgery (p-value 0.396) and during the initial day (p-value 0.322) and 7th day (p-value 0.272) following the surgical procedure. This was compared to see if any specific gender is more prone to contracting injury from intubation (Table 3).

Table 3 Comparison of mean of fundamental frequency pre-op between gender (N = 31)

The study noted a significant change in the mucosal wave 24 h after surgery (p < 0.001). By day 7, the mucosal wave had returned to its original state before the operation in all patients (p = 1.000) (Table 4).

Table 4 Comparison of mucosal wave in the preoperative and postoperative follow-up periods (n = 31)

Comparison of GRBAS , MPT , Io, and DSI in the preoperative and postoperative follow-up periods (Table 5 )

Table 5 Comparison of GRBAS, MPT, Io, and DSI in the preoperative and postoperative follow-up periods (n = 31)

The study noted a statistically significant change in GRBAS score 24 h after surgery (p < 0.001). By 1 week, the change still remained became significant. Whereas with regard to maximum phonation time, intensity, and dysphonia severity index, there was no change at any point postoperatively as compared to the preoperative evaluation.

Fundamental frequency 1st POD (24 h)

A negative correlation was observed (rs = − 0.375, p = 0.038), indicating an inverse association between these variables. Further exploration is warranted to elucidate the underlying mechanisms and clinical implications of this finding. There exists a positive correlation between the duration of intubation and the observed variable, as indicated by a correlation coefficient of rs = 0.425 (p = 0.017). The present study also aimed to investigate the potential correlation between the number of intubation attempts and relevant clinical outcomes. Our findings revealed no significant correlation between these variables (rs = − 0.065, p = 0.727).

Fundamental frequency end of 7th POD

A negative correlation was observed between the size of the endotracheal tube and the measured coefficient of (rs − 0.428, p = 0.018). A positive correlation was observed between the duration of intubation and the variable of interest (rs = 0.407, p = 0.023). The analysis revealed no statistically significant correlation between the number of intubation attempts and the observed variable (rs = − 0.093, p = 0.620) (Table 6).

Table 6 Correlation between size of endotracheal tube (mm) and FO (Hz), MPT, IO, DSI, GRBAS parameters in the study population (n = 31)

Maximum phonation time

There was a weak correlation between maximum phonation time and size of endotracheal tube at the end of 1st POD which was statistically significant. There was also a weak correlation at the end of 7th POD but was statistically insignificant. Correlation of MPT with duration of endotracheal intubation and number of attempts made at intubation was not significant.

Intensity, dysphonia severity index, GRBAS score

Size of endotracheal tube had a negative correlation with intensity at the end of both 1st and 7th POD. DSI had a positive correlation with it at the end of 1st POD but had a negative correlation at the end of 7th POD. There was negative correlation between GRBAS score and size of endotracheal tube at the end of 1st POD which were 0 statistically insignificant (Table 6).

Mucosal wave 1st POD (24 h)

The results revealed no significant correlation between the size of the endotracheal tube and the mucosal wave abnormality (p = 0.761). The present study reveals a statistically significant correlation between the duration of intubation and the variable of interest (p = 0.003). No correlation was observed between the number of intubation attempts and the outcome variable (p = 0.449) (Table 7).

Table 7 Comparison of mean of size of endotracheal tube between mucosal wave 1st POD (N = 31)

Discussion

The vibratory motion of the human vocal folds surpasses the perceptible range of the human ocular faculties, akin to the rapid oscillation observed in the flapping of hummingbird wings. Multiple scales exist for the evaluation of vocal characteristics. A perceptual analysis was conducted using the GRBAS scale, developed by the esteemed Japan Society of Logopedics and Phoniatrics. This scale assigns scores ranging from 0 to 3 to assess the various grades of hoarseness, namely roughness, breathiness, asthenia, and strain. A score of 0 indicates normal vocal characteristics, while a score of 1 represents a slight degree of hoarseness. A medium degree of hoarseness is denoted by a score of 2, whereas a score of 3 signifies a high degree of hoarseness. There are also other scores like the Consensus Auditory-Perceptual Evaluation of Voice (CAPE-V), Roughness, Breathiness, and Hoarseness (RBH) scale, the CAV scale (a modified version of the CAPE-V scale), and the Voice Handicap Index (VHI) for analysis of vocal characteristics.

The advantages of stroboscopy include diagnostic, sensitive, simple, reliable, less time-consuming, office-based procedure, does not require admission, and is easily acceptable by the patient. Disadvantages are mainly observed in patients with strongly breathy, irregular or spasmodic voice signals, and expensive. Vocal fold morphology varies greatly between different species [10]. Mechanism of injury is set in motion during intubation causing damage to structures, and injury occurs in specific conditions only related to scarring of posterior commissure [11]. The endotracheal tube exerts pressure on the posterior commissure of the larynx (arytenoids, posterior commissure, cricoid cartilage). Many variables influence the development and magnitude of a post-intubation sequel like the material with which the endotracheal tube is made, the size and shape of the tube, cuff pressure, and the drugs used for anesthesia purposes [12].

In the year 2019, a study was conducted by Sharannya et al. involving a cohort of 100 patients. The objective of this study was to evaluate the condition of the vocal folds after endotracheal intubation, utilizing stroboscopic assessment techniques. A video stroboscopy was conducted 1 day before the surgical procedure, as well as 1-day post-surgery and 1 week thereafter. The study findings revealed a notable disparity (p = 0.0001) in video stroboscopic parameters between preoperative and day 1 postoperative scores. Similarly, a significant distinction (p = 0.3197) was not observed in the comparison of preoperative and 1-week postoperative scores [2]. The present study revealed the presence of an abnormality in the mucosal wave, which was found to be statistically significant (p = 0.001) on the first day following the surgical procedure. However, the fundamental frequency did not exhibit a statistically significant difference (p > 0.005) during the same period. It is worth noting that both the mucosal wave abnormality and the lack of significance in fundamental frequency were observed to resolve by the 7th day after the operation. The observed parameters remained within normal ranges during both the preoperative and postoperative periods.

Satoshi Kitahara et al. in 2005 evaluated the case of a vocal fold polyp who underwent laryngeal surgery and was assessed for vocal folds injury following endotracheal intubation. They used the GRBAS scale for voice assessment and graded it as G2R2B1A1S0 before operation. Postoperatively, vocal folds wound defect was resolved completely on the 69th day (G0R0B0A0S0), and on the 97th day, mucosal wave pattern was restored [13]. The current study showed voice change and changes in mucosal wave pattern and fundamental frequency on postoperative day 1, which were completely resolved on postoperative day 7.

In the year 2007, a study conducted by Hamdan et al. delved into the investigation of vocal symptoms and acoustic alterations experienced by a cohort of 35 individuals after the process of endotracheal intubation. The study also aimed to establish a correlation between the aforementioned changes and various parameters associated with the endotracheal tube. The patient underwent preoperative, postoperative 2-h, and postoperative 24-h examinations. Within 2 h following the surgical procedure, a notable exacerbation in vocal symptoms was observed, exhibiting a significant correlation with both the number of attempts made during intubation and the augmentation in cuff volume. In light of a diminished maximum phonation time (MPT), the acoustic properties exhibited minimal alterations. The resolution of all vocal complaints was observed within 24 h following the surgical procedure, exhibiting no significant deviation from the initial baseline measurement [14]. The current investigation aimed to evaluate the association between stroboscopic parameters and the dimensions of the endotracheal tube, duration of intubation, and the frequency of intubation attempts. The present study aimed to investigate the correlation between stroboscopic parameters (mucosal wave) and various factors related to endotracheal intubation. The results revealed no correlation (p-value: 0.761) between the mucosal wave and the size of the endotracheal tube (measured in millimeters) and mucosal wave and the number of attempts (p-value: 0.449). Conversely, a statistically significant correlation (p-value: 0.003) was observed between the mucosal wave and the duration of intubation. These correlations were consistent across postoperative day 1.

In 2011, Ha I. W. et al. investigated the frequency and causes of voice changes that persist for longer than 72 h following a general anesthetic endotracheal intubation. Eighty participants who were planned for surgery under general anesthesia were included in the trial. Before surgery as well as 3 days later, the patients were assessed using stroboscopic imaging and speech analysis. Voice changes that lasted longer than 3 days in 7.5% of the patients had a strong correlation with patient age, anesthesia duration, and cuff pressure [15]. In the current study, 96.80% of participants experienced transient voice change after 24 h of intubation. The voice change was resolved by the 7th postoperative day.

Fifty-one patients who had been intubated for more than 24 h in a critical care unit were assessed for laryngeal lesions by Rangachari et al. in 2006. A laryngeal video endoscopy was performed on the patient the day following extubation and 3 weeks later. On the day of extubation, 41 patients had laryngeal abnormalities. There were only 10 patients with aberrant laryngeal findings at the end of the third week following extubation. Laryngeal problems on the day of extubation were more likely to occur with larger tubes, prolonged intubations, and emergency intubations [6]. The present study showed stroboscopic parameter (mucosal wave) had no correlation (p-value: 0.761) with the size of the endotracheal tube (measured in millimeters) and with the number of attempts (p-value: 0.449). Conversely, a statistically significant correlation (p-value: 0.003) was observed between the mucosal wave and the duration of intubation in postoperative day 1.

In 1999, Zimmert et al. compared the impact on voice function and incidence of laryngeal problems in 56 individuals when using a laryngeal mask airway and endotracheal tube. Both before surgery and 18–24 h afterward, video endoscopy and video strobolaryngoscopy were performed. Six patients in the ETT group and one patient in the LMA group had vocal tract lesions that were not life-threatening, according to the study. Between the two groups, there was not a significant difference in any stroboscopic parameters [12]. The current study assessed vocal injuries only with elective endotracheal intubation and showed changes in a mucosal wave pattern (statistically significant, p = 0.001) and fundamental frequency (statistically not significant, p > 0.005) on postoperative day 1, which were completely resolved on postoperative day 7. Other parameters (amplitude, periodicity, symmetry, and glottis closure) were normal in both the pre- and postoperative periods.

On comparing the GRBAS scores pre- and postoperatively, there was found to be a statistically significant difference between preoperative and 1st and 7th postoperative day evaluation, whereas there was no statistically significant difference in maximum phonation time, intensity, and dysphonia severity index between the pre- and postoperative period. There was also a statistically significant correlation between maximum phonation time and size of endotracheal tube at the end of 1st POD. This is one of the very few research studies that has assessed how endotracheal intubation affects variables such as intensity, maximal phonation time, fundamental frequency, and dysphonia severity index.

In the developing world with the advent of cuff pressure monitors, and C-MAC where controlled cuff pressure in the former and video-assisted intubation is possible in the latter, the incidence of laryngeal injury following endotracheal intubation can be reduced.

Limitations

The present study is deficient in terms of follow-up stroboscopic evaluation data for patients who had persisting gross vocal folds alterations beyond the 7th day following surgery. The long-term consequences of intubation leading to intubation granuloma were not evaluated as well. This would facilitate the identification of the point at which the vocal functions returned to their previous state. The study was limited by the use of small sample numbers and the absence of a single anesthetist performing endotracheal intubations. Auditory perceptual evaluation if performed along with stroboscopy would have added benefit in the study.

Conclusion and recommendation

The findings of this study indicate that the presence of endotracheal intubation on the first postoperative day leads to a statistically significant and transient alteration in the stroboscopic parameters, specifically the mucosal wave pattern. Based on these results, it is recommended that further research be conducted to explore the long-term effects of endotracheal intubation on vocal fold function and to develop strategies for mitigating these temporary changes. A significant proportion of patients achieved recovery within 7 days. Minor injuries were observed, which were solely attributed to elective endotracheal intubation. It is recommended to provide patients with counseling regarding voice-related concerns, even for procedures that do not involve the larynx, when they are scheduled to undergo endotracheal intubation.

To enhance comprehension of the phonatory processes, the study additionally recommends the utilization of advanced laryngeal imaging techniques, including high-speed video endoscopy (HSV), magnetic resonance imaging (MRI), and optical coherence tomography.