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| REVIEW ARTICLE |
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| Year : 2017 | Volume
: 7
| Issue : 2 | Page : 25-28 |
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Postintubation recurrent laryngeal nerve palsy: A review
R Inita Matta1, B Kanupriya Halan2, Kavita Sandhu3
1 Head of Dept of ENT Mumbai Port Trust Hospital, Mumbai, Maharashtra, India
2 Consultant KBH Bachooali Hospital, Mumbai, Maharashtra, India
3 Director Neuroanaesthesiology and Critical Care, Max Superspeciality Hospital, New Delhi, India
| Date of Web Publication | 26-Sep-2018 |
Correspondence Address:
Dr. B Kanupriya Halan
C 901 Sanjeev Enclave, Seven Bungalows, Andheri (West), Mumbai, Maharashtra
India
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/jlv.JLV_5_16
 Abstract | | |
Endotracheal intubation is one of the most common procedures performed in the Operating Theatre, Intensive Care Unit or wards, either on an elective or emergency basis. Recurrent laryngeal nerve injury leading to vocal cord paralysis is a lesser known but important complication of intubation. It is important to identify and monitor these patients to prevent confusion with regard to etiology and outcome. This article explores the etiopathogenesis of recurrent laryngeal nerve palsy following intubation and the various risk factors and possible mechanisms which contribute to this complication. Techniques to prevent and recognize this injury are also discussed. PubMed was the main database searched for articles related to the topic which were found through the period 1972–2017.
Keywords: Intubation, recurrent laryngeal nerve, vocal cord paralysis, hoarseness
How to cite this article:
Matta R I, Halan B K, Sandhu K. Postintubation recurrent laryngeal nerve palsy: A review. J Laryngol Voice 2017;7:25-8 |
| Introduction | |  |
Endotracheal intubation has witnessed many advancements in both materials and techniques since it was first introduced. It is now a routine and safe procedure, but as it causes some degree of laryngeal injury, it may result in acute and long-term complications.
Vocal cord paralysis is a lesser known, but significant complication of intubation as it may cause diagnostic confusion in the postoperative period or the Intensive Care Unit (ICU). This is more significant in cases undergoing thyroidectomy, cardiac surgery, thoracic surgery, and interventions where the nerve lies in the surgical field.[1] It is also a risk factor for aspiration pneumonia, which in turn increases postoperative morbidity and mortality.[2]
Various factors related to tube size, cuff pressure, and duration of intubation are postulated to be responsible for increased incidence of vocal cord immobility. Santos et al. found that patients intubated with tubes larger than 7.5 mm inner diameter had a greater incidence of vocal fold immobility.[3] The risk of vocal cord paralysis was increased when intubation lasted 3–6 h as found by Kikura et al.[4] Thus, many factors have to be borne in mind while intubating a patient or caring for an already intubated patient. A thorough search of literature regarding vocal cord palsy due to intubation was conducted between 1972 and 2017 and the information was used for this review.
| Discussion | | |
Orotracheal intubation was first described by Macewen in 1878 for the administration of anesthesia using a tube fashioned from brass.[5] Many years later, tubes made of rubber were used. After that, Guedel and Waters added an inflatable cuff.[6] In the 1960s, polyvinylchloride tubes with integrated cuffs were marketed and a few years later, high volume, low-pressure cuffs were introduced.
Intubation injuries to the recurrent laryngeal nerve both in the operating room and in the ICU setting are being increasingly noted. Their incidence ranges from 0.1% to 0.2%.[7] This incidence is probably underquoted as many cases go unnoticed or undiagnosed since intubation is a procedure practiced even in remote and far-flung areas. Usually unilateral, recurrent laryngeal nerve injury can rarely, even be bilateral.[8] However, it contributes to significant distress and morbidity in the form of hoarseness and dysphagia for the extubated patient. The significance of a vocal cord palsy after general anesthesia for thyroidectomy and the ensuing confusion as to the cause cannot be overemphasized.
Recurrent laryngeal nerve paralysis is further subdivided into two patterns – direct injury and indirect injury.[7] The mechanism of recurrent laryngeal nerve paralysis due to tracheal intubation is usually an indirect injury. The factors of indirect injury are said to include tracheal tube size, location of the cuff, fixing side of the tube, cuff pressure, curvature of tracheal tube, and intubation time.[9]
Anatomical analysis of recurrent laryngeal nerve palsy was performed by Ellis and Pallister.[10] They highlighted the fact that the posterior branch of the recurrent laryngeal nerve innervates the posterior cricoarytenoid and the interarytenoid muscles, while the anterior branch supplied most of the adductors. Cavo[9] performed a series of laryngeal dissections which showed that the probable site of injury to the recurrent laryngeal nerve is the subglottic region. In this area, the anterior branch of this nerve is vulnerable to compression between the expanded cuff and the overlying thyroid cartilage on the superoanterior border of the posterior cricoarytenoid muscle, which is about 6–10 mm below the posterior third of true vocal cord. This compression of the recurrent nerve and its peripheral branches in the larynx causes degeneration and subsequent nerve paralysis. Insufficient microcirculatory supply to the nerve and its branches may cause ischemic neuronal degeneration and subsequent paralysis.[4]
Previous studies by Stout et al., Christensen et al., Higgins et al., and Jensen et al. have identified several factors affecting laryngeal injury and postoperative hoarseness, including size of tracheal tube, cuff pressure and quality and duration of tracheal intubation.[11],[12],[13],[14] An inflated cuff may compress the anterior branch of the recurrent laryngeal nerve, therefore, the cuff should be located at more than 15 mm below the vocal cords.[15] Since nitrous oxide diffuses into the cuff more rapidly than nitrogen, intracuff pressure can increase significantly even for a short time of endotracheal intubation. Such increased cuff pressure can cause damage to the mucous membrane of the larynx and the trachea and compress the nerve.[16] Hence, frequent monitoring of cuff pressure intraoperatively may be useful in preventing this complication. It is advisable to use an endotracheal tube with a high-volume low-pressure cuff. Instilling the cuff with preservative-free lignocaine 4% has been shown to decrease the incidence of hoarseness and postoperative sore throat. Lignocaine tends to diffuse across the cuff and provide local anesthetic action and attenuate the cough reflex during extubation.[17] It also helps to maintain a stable intracuff pressure based on the physical principle that liquids do not expand when highly soluble gases dissolve in them.[18] Other tube factors include a diameter of the tube, Santos et al. demonstrated that patients who had prolonged intubation with a tube >7.5 mm had an increased incidence of vocal fold immobility after extubation and thus recommended that prolonged intubation with a larger tube is to be avoided.[3] Shin et al.[19] described unilateral vocal cord paralysis following a short period of endotracheal intubation anesthesia where the surgical procedure lasted only 150 min.
Other types of endotracheal tubes are also known to cause vocal cord paralysis. Sagawa et al.[20] and Jeong et al.[21] reported that double lumen tubes could cause bilateral vocal cord paralysis. Knoll et al.[22] proposed that a double lumen tube could harm a patient during intubation as well as extubation due to its curved endobronchial lumen. Ethylene oxide gas can induce chemical burns and ulceration of the skin and mucous membranes. Holley and Gildea proposed the role of ethylene oxide gas (used for sterilization of medical materials such as ETTs) as a cause of vocal cord paralysis, on the basis of a finding of myelin degeneration of the vagus nerve at autopsy.[23] Star recommended that ethylene oxide-sterilized endotracheal tubes should be aerated for 10 days after sterilization for the desorption of ethylene oxide residues on the tube.[24]
Overextension of the neck causing stretching of both vagus nerves is also believed to be another mechanism for vocal cord paralysis as cited by Nuutinen and Kärjä.[25]
Damage to the left recurrent laryngeal nerve can also occur during insertion of a nasogastric tube through the esophagus. Gastroesophageal reflux disease-causing “acid laryngitis” can create conditions favoring this type of complication. This was shown by Kanski et al.[26]
Also noted by Kikura et al., Mencke et al. and Quick and Merwin was that the left vocal cord was twice as vulnerable to vocal cord paralysis than the right. This may be due to rightward insertion and fixation of the tracheal tube in the right angle of mouth whereby the tube is in contact with the left vocal cord.[4],[27],[28]
There are multiple patient factors which contribute to an increased risk of vocal cord palsy due to tracheal intubation. Kikura et al.[4] have found a clear relationship between aging and an increased risk of vocal cord paralysis. Although the exact mechanism is not known, it is supposed that tissues in the laryngeal system have degenerated with age and may be more vulnerable to acute inflammation and microcirculatory insufficiency due to cuff pressure and mechanical damage by the tube. Age, as a risk factor may be related with increase in comorbidity with increasing age. They have also found the risk of vocal cord palsy to be two times higher in patients with diabetes and hypertension than in patients without these diseases. The proposed mechanism is that diabetics have associated peripheral neuropathy which may increase susceptibility to paralysis.[29],[30],[31] Hypertension is associated with atherosclerotic changes in the arterial vasculature of the larynx, and microcirculatory insufficiency of the laryngeal nerve may be caused by mechanical compression by cuff of the tracheal tube as reported by Kikura et al.[4]
Laryngeal electromyographic monitoring can be helpful in obtaining an index of potential recovery. Obtaining a baseline electromyography (EMG), 30–40 days after injury and a second EMG 1 month later can help in evaluating the recovery status of the vocal cords. This was highlighted by Munin et al. in their article.[32]
In evaluating a patient with bilateral vocal fold immobility, EMG provides the potentially useful information in the following:
- Differentiating between fixation and paralysis
- Differentiating between neurapraxia and axonal transaction
- Determining the presence of neuromuscular disorders or peripheral neuropathy
In adults, any definitive procedure to address vocal cord paralysis, whether unilateral or bilateral, must not be undertaken while a possibility for recovery exists. Recovery can occur as long as 12 months after injury. In addition, laryngeal EMG can be used to evaluate normal action potentials (normal nerve), the absence of potentials (nonfunctioning nerve), defibrillating potentials (worsening nerve), or polyphasic potentials (regenerating nerve). The 12 months wait for the return of function can be shortened by obtaining two laryngeal electromyographs several months apart and by looking for evidence of improved function or stabilized function.[32]
Recurrent laryngeal nerve injury due to endotracheal intubation is a known, but often overlooked cause for vocal cord dysfunction in the operating room and the ICU. It is rare, Vyshnavi and Kotekar[33] found only three such cases over a period of 12 years. Emphasis on prevention and recognition of this condition is important both for the otolaryngologist and other medical staff involved in anesthesia and ICU settings. Early intervention voice therapy in such patients has the potential to significantly improve laryngeal physiology, voice quality, voice stability, voice efficiency, and communication.[34]
| Conclusion | | |
Recurrent laryngeal nerve injury consequent to endotracheal intubation documented since 1975 still remains a comparatively lesser known entity. When following a thyroidectomy, it can cause considerable diagnostic confusion as the nerve is also vulnerable in the surgical field itself. The improvement in intensive care facilities in recent years has translated into more patients being sustained on respiratory facilities using endotracheal intubation. The “ICU doctor” or intensivist being the main caretaker in these situations, must, therefore, be made aware of recurrent laryngeal nerve paralysis due to endotracheal tube pressure. When this injury occurs during intubation for general anesthesia, it can be a worrisome situation in the postoperative period where the cause for vocal cord dysfunction is not readily apparent. It also has medicolegal implications, dissatisfied patients often seek legal redress with costly, time-consuming litigation that has adverse psychological effects on concerned medical professionals.[35] Shaw and Pierce did the closed-claims analysis for the claims involving vocal cord paralysis. Twenty-four of 112 claims were against anesthesiologists. Thyroid and parathyroid surgeries formed a majority of the claims. In this analysis, commonly cited claims were consent issues (19%) and improper performance (61%).[36] Hence, the role of informed consent is very important in all such procedures.
Simple preventive measures should be followed as outlined below:
- Use of endotracheal tubes with high volume low-pressure cuffs
- Avoiding the use of reprocessed endotracheal tube. If ethylene oxide-sterilized endotracheal tube is to be used, it should be aerated for 10 days after sterilization
- Regular monitoring of cuff pressures, cuff position
- Adequate patient sedation to prevent excessive movement while endotracheal tube is in situ
- Avoiding overextension of neck during surgical procedures
- Proper positioning of the tube while suctioning
- Better training of staff so as to decrease the incidence of multiple intubations, or traumatic intubation, which may be caused due to lack of skill.
Failure to recognize this important and often preventable entity could mean voice and extubation problems once the ICU phase is over or when the patient is extubated after general anesthesia.
Recurrent laryngeal nerve palsy due to endotracheal tube pressure is usually temporary and once the condition is recognized and understood, need not be cause for undue alarm. Most of the references to this condition are in journals of anesthesia, while it has found rather less mention in otolaryngology research. Since the otolaryngologist is closely involved in the management of any case of recurrent laryngeal nerve palsy, it stands to reason that familiarity with recurrent laryngeal nerve palsy due to endotracheal intubation would translate into better prevention and care.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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