Comparision of fibreoptic bronchoscopy with trans-laryngeal ultrasound for functional assessment of vocal cords post-extubation in thyroid and parathyroid surgeries - a prospective observational study

Functional vocal cord (VC) maintenance is essential in thyroidectomies1. Nerve injury is a significant complication during thyroidectomy2, leading to vocal cord palsy. So, assessing the vocal cord function before and after surgery is mandatory. Direct visualisation of vocal cords using laryngoscopy at the time of extubation is routinely done, but at the same time, it is associated with higher sympathetic stimulation, leading to hypertension, tachycardia, and patient discomfort. So, visualisation of vocal cords using the fibreoptic bronchoscope (FOB), though semi-invasive, is considered the reference standard3-5 but sparingly used for perioperative detection of VC palsies due to various reasons. Other methods for assessment of vocal cord function include indirect laryngoscopy (IDL), laryngeal muscles electromyography (LME), computed tomography (CT), and magnetic resonance imaging (MRI). Trans laryngeal ultrasonography (TL-USG) is a valuable non-invasive method for assessing VC anatomy and functionality. More literature is needed comparing FOB with TL-USG to assess VC morphology and mobility. The efficacy and non-inferiority of TL-USG over FOB-guided VC assessment have not been evaluated. We hypothesise Trans laryngeal ultrasonography(TL-USG) is comparable to FOB in identifying post-operative vocal cord palsy in real-time view.

nclusion criteria: Patients belonging to ASA1-3 between ages 18 and 70 who are posted for thyroid and parathyroid surgeries.

Exclusion Criteria: Patients with coronary artery disease (CAD), history of cerebrovascular accident (CVA), and pregnant patients will be excluded from the study.

Methodology: After institutional ethics committee approval and informed consent, patients posted for thyroid and parathyroid surgeries belonging to ASA class 1-3, aged 18-70 years, will be enrolled in the study. As a part of the routine preoperative surgical work up, these patients will be evaluated for vocal cord movements using indirect laryngoscopy (IDL)  by a well experienced surgeon. All those patients with preoperative vocal cord palsy will be excluded from the study. The patients will be explained about coughing, phonation like making a continuous sound like aaa for easy assessment of VC movements and the same will be asked to be reproduced post extubation on the operating table on request. TL-USG will be performed preoperatively under the domains like Visualisation of vocal cord, Symmetry, position, and mobility of vocal cords, Paresis: decreased movements of vocal folds, Paralysis: complete loss of mobility of vocal cord/s, Time to visualize VC mobility by an experienced anesthesiologist. TL-USG will be done on the anterior neck in thyroid view6 with a high-frequency linear probe (frequency: 8–12 MHz). Patients will lay supine with their necks slightly extended and the ultrasound transducer will be positioned transversely over the anterior aspect of the middle portion of the thyroid cartilage, serving as acoustic window. Vocal cords will be assessed by scanning transducer caudo-cranially. Image will be optimised so that false cords will be seen as hyperechoic structures, while true cords seen as hypoechoic structures. VC mobility will be evaluated during passive spontaneous breathing, active phonation with a sustained vowel ‘‘aaa”. Normal mobility of the true vocal cords will be characterized by symmetrical movement in adduction and abduction. Preoperative VCDV will be noted and compared with the post operative VCDV.

All patients will receive premedication with tab alprazolam 0.25 mg and tab ranitidine 150 mg in the morning of surgery. In the operating theatre, intravenous access will be secured and intravenous fluids started; the patient will be connected to standard American Society of Anesthesiologists monitors (electrocardiogram, pulse oximeter, non-invasive blood pressure). Patient will be induced with fentanyl 2 mcg/kg, propofol 2 mg/kg and atracurium 0.5 mg/kg. Patients will be preoxygenated with 100% oxygen for 3 minutes with a fresh gas flow of 6 L/min in closed circuit. Patients will be intubated with an appropriately sized endotracheal tube using a standard Macintosh laryngoscope. Anaesthesia will be maintained with oxygen and air in a ratio of 50:50, with fresh gas flow of 2 L/min and sevoflurane to maintain a minimum alveolar concentration (MAC) around 1. Intermittent boluses of atracurium were used to maintain muscle paralysis in the intraoperative period.

At the beginning of skin closure MAC will be maintained at 0.3 with Sevoflurane. An anesthesiologist with adequate bronchoscopy experience introduces a flexible fibreoptic bronchoscope into one of the nostrils, and the tip of the scope is just positioned where the glottic view is best obtained. After completion of skin closure, sevoflurane will be switched off. When the patients are awake, obeying commands, arousable, and having attained regular spontaneous breathing, are adequately reversed with neostigmine 0.05 mg/kg and glycopyrrolate 0.01 mg/kg. immediately after the endotracheal tube has been removed, the vocal cord movements will be assessed, and the following findings are noted. Visualisation of vocal cord, Symmetry, position, and mobility of vocal cords, Paresis: decreased movements of vocal folds, Paralysis: complete loss of mobility of vocal cord/s, Time to visualize VC mobility.

The anesthesiologists performing FOB and TL-USG are blinded to each other’s findings and also to preoperative IDL findings. A third anesthesiologist will compare the findings of preoperative IDL, FOB-guided VC assessment findings, and TL-USG-guided VC assessment findings. IDL will be performed routinely for all patients undergoing thyroid and parathyroid surgeries at discharge and two-month follow-up. These findings will be compared with those of FOB and TL-USG findings done immediately after extubation.

Sample size calculation:

As per a study by Shetmahajan et al., who compared trans laryngeal ultrasonography with flexible laryngoscopy and Hopkins endoscope for vocal cord assessment, Cohen’s Kappa Coefficient was 0.69 for flexible laryngoscopy in concordance with TL USG. To detect a discordance (kappa of 0.8) between TLUSG and FOB at 80% power, the expected sample size is 149. Using the previous institutional data, a 30% incidence of postoperative vocal cord palsy was used for sample size calculation. For a dropout rate of 5%, a total of 157 patients will be enrolled in the study.