Voice Disorders after Intubation: The Importance of Intra-Operative Monitoring and Controlling of Endo-Tracheal Tube Cuff Pressure in Reducing Intubation-Related Complications

Abstract
Background: The importance of monitoring and controlling endotracheal tube cuff (ETTc) pressure in reducing larynge-otracheal injuries and intubation-related respiratory compli-cations has been previously investigated by several authors. However, little is known about the role of controlling ETT cuff pressure in minimizing transient voice changes following endotracheal intubation.
Aim of the Study: The aim of this study was to investigate the importance of monitoring and controlling ETTc pressure in reducing voice disorders after endotracheal intubation.
Patients and Methods: Fifty patients in the age between 18-50 years, undergoing middle ear surgery were enrolled into the study. Patients were randomized by means of individ-ually prepared envelopes to either the control group (n=25), without measuring ETTc pressure, or the study group (n=25), with ETTc pressure measurement. All patients were examined pre-operatively to determine baseline values, 24 hours after surgery and 1 week post-operatively. Phoniatric examination included auditory perceptual assessment, videolaryngoscopy and acoustic analysis of voice. Statistical analysis included the arithmetic mean, Standard Deviation (SD), standard error, hypothesis student's "t" and Spearman's rank-order correlation tests. p-values <0.05 were chosen as the level of significance.
Results: Auditory perceptual assessment of voice per-formed one day after extubation indicated the presence of post-intubation dysphonia which was of a mild to moderate grade, an irregular quality, a low pitch and fluctuating loudness. These changes were more pronounced and occurred more frequently in patients of the control group in whom the cuff pressure was adjusted by pilot balloon palpation according to the experience of the anaesthesiologist. One week after surgery, all patients belonging to the study group, in whom a hand-held cuff pressure monitor was used to adjust the cuff pressure, showed improvement in all the perceived parameters, whereas persistent dysphonia was still perceived in two patients of the control group. Videolaryngoscopy performed before intubation showed that all patients were free from any laryngeal lesions. One day after extubation, there was evidence of traumatic laryngeal lesions in the form of vocal fold congestion in 5 patients (20%) of the control group and 3 patients (12%) of the study group. One week after extubation, residual lesions were still present in 3 patients (12%) of the control group in the form of mild vocal fold edema in one patient and vocal fold congestion in two other patients. Acoustic analysis of voice performed 24 hours after extubation showed a highly significant increase in fundamental frequency F0 in both male and female patients of the control group. These changes were accompanied by a significant increase in jitter in only the female patients. By contrast, acoustic analysis of voice recorded both 24 hours and one week after extubation in patients belonging to the study group did not show any significant changes in any of the measured parameters when compared to their corresponding baseline values. An inter-group com-parison of the post-operative parameters recorded by acoustic analysis of voice one day after extubation showed a statistically highly significant (p=0.013) reduction in fundamental fre-quency F0 by 75% among male patients, and a statistically significant (p=0.05) reduction in jitter by 74% in females belonging to the study group when compared to those of the control group. Shimmer and NHR increased to 78% and 47%, respectively, in male patients belonging to the study group, and decreased in females, but these changes were statistically not significant.
Correlation performed between the changes in parameters obtained by acoustic analysis of voice and the duration of intubation showed a statistically significant (p-value=0.023) positive correlation between the changes in fundamental frequency F0 and the duration of intubation. Likewise, a significant (p-value=0.016) positive correlation was found between the changes in jitter and the duration of intubation.
Conclusion and Future Recommendations: General an-aesthesia has multisystem effects, some of which can disturb the fine harmony necessary for voice production. Even short-term intubation is usually followed by a period of dysphonia that may extend after extubation anywhere from 12 hours to more than five days. Proper control of endotracheal tube cuff (ETTc) pressure by a manometer helps reduce ETT-related postprocedural complications. Acoustic analysis may be used to identify and monitor even minor laryngeal trauma resulting from the procedure. Jitter and shimmer are the best indicators of post-intubation phonation changes. For medicolegal reasons, patients scheduled for general anesthesia should be informed about the possible post-operative voice changes that could last longer than one day. We further recommend routine intraoperative monitoring of endotracheal tube cuff pressure, in additition to post-operative phoniatric assessment and follow-up of the patients for early post-operative diagnosis and treatment of dysphonia.