Journal of Indian College of Anaesthesiologists

: 2022  |  Volume : 1  |  Issue : 2  |  Page : 83--85

Incessant menace of airway obstruction with flexometallic endotracheal tube

Sukhyanti Kerai, Upasana Singh, Vineet Manchanda, Kirti N Saxena 
 Department of Anaesthesiology and Intensive Care, Maulana Azad Medical College and Associated Hospitals, New Delhi, India

Correspondence Address:
Dr. Sukhyanti Kerai
Room No. 413, Bl Taneja Block, MAMC, New Delhi


Flexometallic endotracheal tubes (ETT) are preferred over standard Polyvinyl Chloride ETTs in cases where intraoperatively there is limited airway access to the anaesthesiologist. As they are comparatively expensive, it is common practice to reuse them after sterilization. Here we describe a case where a flexometallic ETT was used in a case of tonsillectomy after a through visual inspection to rule out any structural deformity. Intraoperatively ETT itself led to airway obstruction mimicking bronchospasm.

How to cite this article:
Kerai S, Singh U, Manchanda V, Saxena KN. Incessant menace of airway obstruction with flexometallic endotracheal tube.J Ind Coll Anesth 2022;1:83-85

How to cite this URL:
Kerai S, Singh U, Manchanda V, Saxena KN. Incessant menace of airway obstruction with flexometallic endotracheal tube. J Ind Coll Anesth [serial online] 2022 [cited 2023 Mar 28 ];1:83-85
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Full Text


Flexometallic or reinforced endotracheal tubes (ETTs) are less likely to kink and occlude compared to standard ETT and are therefore preferred for certain head-and-neck surgical procedures and surgeries performed in a prone position when access to the airway is limited.[1] However, flexometallic ETTs are not infallible to kinking, and intraoperatively, there are the reports of these tubes being responsible for airway obstruction.[2],[3] We describe a case of intraoperative airway obstruction in a patient undergoing tonsillectomy due to the dissection of the wall of flexometallic ETT.

 Case Report

An 8-year-old boy (25 kg) was scheduled to undergo tonsillectomy under general anesthesia (GA). Preanesthetic clinic assessment was unremarkable. There was no history suggestive of recent respiratory tract infection or obstructive sleep apnea. Hematological investigations were within the normal limits. The patient was advised fasting period of 8 h for solid food. On the day of surgery, standard anesthetic monitoring including continuous electrocardiogram, noninvasive blood pressure, and pulse oximetry was instituted. GA was induced with an injection of fentanyl 50 μg, propofol 60 mg, and vecuronium 2.5 mg, and the trachea was intubated with cuffed flexometallic ETT ≠ 6.0 using a metal stylet and fixed at 16 cm. The oropharynx was packed with saline-soaked throat pack. Intraoperative, a gaseous mixture of oxygen and nitrous oxide (50:50) in isoflurane and intermittent boluses of vecuronium was used for the maintenance of anesthesia. Volume control mode with the tidal volume of 200 ml, respiratory rate of 14/min was used for intraoperative ventilation. Thirty minutes after the beginning of the surgery, a decrease in expired tidal volume from 200 ml to 60 ml and gradual increase in end-tidal carbon dioxide concentration was observed. The airway pressure was increased to 42 cm of H2O. Surgeons were asked to stop surgery for a while and were asked to remove Boyle–Davis mouth gag. Hand ventilation with the reservoir bag was started, but the patient's chest rise was not observed. The depth of anesthesia was increased with a bolus of injection propofol 20 mg. The anesthesia breathing circuit, tube connector, and proximal portion of ETT which was visible from the outside were found to be unremarkable on visual inspection. Video laryngoscope was introduced to the oral cavity of the patient to confirm the position of black mark just above the cuff of ETT lying above the glottic inlet. A suction catheter was then attempted to pass through the ETT to suction out the possibility of secretions obstructing its lumen. However, the suction catheter could not be negotiated through the lumen of ETT. The flexometallic tube was then replaced with a new ETT of size 6.0. Following this, ventilation with the delivery of adequate TV and chest rise was achieved. The examination of the flexometallic tube revealed intraluminal obstruction due to the invagination of inner polyvinyl chloride (PVC) layer just distal to the point of insertion of inflation line of pilot balloon [Figure 1]. The surgery was resumed and was concluded uneventfully in the next 30 min.{Figure 1}


Flexometallic tubes are designed to resist kinking or compression and are used extensively to secure airway in patients undergoing head-and-neck surgeries. Although these ETTs are used to provide a patent airway, there have been the multiple reports of airway obstruction with the ETT itself being the culprit. The potential etiologies of airway obstruction related to flexometallic ETT can be divided into two categories. First, kinking of the wireless portion of ETT between the end of the embedded spiral wire and the tip of the plastic slip joint. The length of this wireless portion can range from 0.4 to 2.1 mm and it is prone to a kink tube with an angulated force that is not applied directly to the axis of ETT.[4]

Second, airway obstruction could be due to the partial or complete occlusion of the lumen of ETT resulting from the various causes. These include occlusion due to external materials such as blood, secretions or compression of the lumen by surgical devices, and patient bite or due to prone positioning of the patient.[5],[6],[7] While occlusion due to blood or secretions can be cleared using suctioning; in cases, where there is compression of the lumen of ETT, typically a suction catheter cannot be negotiated through it. Reinforced ETTs have a memory effect and hence even when the compressing force is alleviated, it is extremely difficult to rebound back to their original diameter and they remained kinked.

Another important cause of obstruction of the lumen of ETT is due to their reuse. They are single use, but due to cost restraints, they are frequently reused after sterilization. Reuse of these ETTs leads to structural weakening with unfurling of wire spirals or dissection of the wall which have been reported to cause airway obstruction intraoperatively.[8],[9] During the manufacture of flexometallic ETT, a rod is immersed into liquid PVC, creating a thin layer around the rod. The stainless steel or nylon wire spiral is then mounted onto the rod and the dipping procedure is repeated several times, creating the outer coating.[10]

The airway obstruction in the present case occurred due to dissection of inner lining of spiral wires of ETT. In our institution, most of the time, flexometallic tubes are used only once as per the manufacturer's recommendation but sometimes, they are reused after sterilization by ethylene oxide. The flexometallic ETT used in the case was being reused after sterilization and the preuse visual inspection did not reveal any defect or obstruction of the lumen. During sterilization process of ETT, it has been hypothesized that bubbles arise in its wall. Nitrous oxide administered during anesthesia diffuses into preexisting air bubbles of the inner part of the tube wall with consequent enhancement of bubble volume which can lead to dissection of the wall.[11] However, there have been case reports, where wall dissection has been reported even without the use of nitrous oxide.[12] Manufacturing defects, detachment of inner coating of ETT during sterilization, and damage due to stylet aggression (insertion and removal of stylet to ETT for facilitating intubation) are the other factors attributed to flexometallic ETT wall dissection leading to airway obstruction.[13],[14] Of note, when wall dissection is due to the sterilization of ETT, there are discrete points of dissection even when these are multiple whereas if it is due to stylet aggression the dissection runs along the entire length of ETT.


The flexometallic ETTs are not “kink proof” and while using them for airway management, anesthesiologists should be mindful of their factors leading to potential airway obstruction. As the majority of cases of airway obstruction are related to reuse of ETT after sterilization, adherence to manufacturer's recommendation of single use of flexometallic tube is the best option for the prevention.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the legal guardian has given his consent for images and other clinical information to be reported in the journal. The guardian understands that names and initials will not be published and due efforts will be made to conceal identity, but anonymity cannot be guaranteed.

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Conflicts of interest

There are no conflicts of interest.


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