Endotracheal tube cuff rupture during anesthesia in 2 dogs

Abstract

A 15-year-old intact male dachshund dog weighing 4.3 kg and a 5-year-old intact male mixed-breed dog weighing 13.6 kg were referred for examination because of paraparesis and facial paralysis, respectively. Magnetic resonance imaging (MRI) of the thoracolumbar region and brain was performed. The dogs were premedicated with IV butorphanol, 0.2 mg/kg body weight (BW) and midazolam, 0.2 mg/kg BW. Anesthesia was induced with IV propofol, 4 to 5 mg/kg BW and maintained with sevoflurane in oxygen. The dachshund was orotracheally intubated with a 5.0-millimeter internal diameter endotracheal (ET) tube. During positioning in the MRI room, intermittent positive pressure ventilation (IPPV) was applied. The mixed-breed dog was orotracheally intubated with a 6.0-millimeter internal diameter ET tube. After inflation of the ET tube cuff, a leaking test was done by applying positive pressure ventilation. In both dogs, a distinct “popping” sound was heard when positive pressure was applied, after which air leakage from the cuff was evident. Failure to inflate the pilot balloon led to suspicion of a ruptured cuff. Reintubation was completed, both dogs remained stable during anesthesia, and no postanesthetic complications were observed. Rupture of both cuffs, which was visually confirmed, was thought to be caused by overinflation of the cuff, repeated sterilization of the ET tubes, and positive pressure ventilation. Repeated sterilization of ET tubes with ethylene oxide can alter the physical integrity of cuffs. Care should be taken not to overinflate ET tube cuffs, especially when they have been repeatedly sterilized, as cuff rupture may result in failure to provide adequate IPPV.

Key clinical message:

This report describes 2 cases in which ET tube cuff rupture was noted during anesthesia for MRI.

Endotracheal (ET) intubation is a critical component of anesthesia in both human and veterinary medicine. It serves to maintain a patent airway, reduce aspiration of fluids, deliver volatile anesthetics and oxygen, enable positive pressure ventilation, and limit exposure to waste anesthetic gases (1–3). Despite its many benefits, complications related to ET intubation include laryngeal and tracheal edema and inflammation; laryngeal paralysis; and tracheal stenosis, necrosis, or rupture (3–5). In human medicine, a rare but potentially life-threatening complication related to the use of ET tubes is rupture of the inflatable cuff (6–9). To the authors’ knowledge, this is the first report of ET tube cuff rupture in veterinary medicine.

Case descriptions

Case 1

A 15-year-old intact male dachshund dog weighing 4.3 kg was presented to the Ian Animal Diagnostic Imaging (IAN) Centre (Seoul, South Korea) for further evaluation of suspected intervertebral disk disease. Before presentation, the dog had a 6-day history of hind limb weakness. A complete blood (cell) count (CBC) was within normal limits, whereas a serum biochemistry panel revealed mild elevations in alanine aminotransferase [140 U/L; reference range (RR): 17 to 78 U/L], alkaline phosphatase (476 U/L; RR: 47 to 254 U/L), and gamma-glutamyl transferase (34 U/L; RR: 5 to 14 U/L). The remaining results were within normal ranges. Thoracic radiographs obtained by the primary care veterinarian showed a mild, right-sided cardiomegaly, but no murmur was appreciated on cardiac auscultation and there were no clinical signs associated with heart disease.

On presentation to the IAN Centre, the dog was quiet, alert, and responsive. Physical examination results were within normal limits. On neurological examination, the dog was ambulatory but had proprioceptive deficits in the left hind limb. Magnetic resonance imaging (MRI) of the thoracolumbar spine region was planned. The dog was premedicated with butorphanol, 0.2 mg/kg body weight (BW), intravenously (IV) and midazolam, 0.2 mg/kg BW, IV. Before induction of anesthesia, a previously used, 5.0-millimeter internal diameter (ID) polyvinyl chloride ET tube with a high-volume, low-pressure cuff (Shiley; Covidien, Mansfield, Massachusetts, USA) that had been sterilized with ethylene oxide (EO) gas was tested for air leaks by inflating the cuff and checking for decreases in cuff volume. The tube was lubricated with water-soluble lubricant (Silgreen Cream; Firson Co., Cheonan-si, Republic of Korea). The size of the ET tube was selected based on animal size and the clinician’s experience, and the length of the tube was premeasured such that the distal tip was located at the level of the thoracic inlet. Anesthesia was induced with propofol, 4 mg/kg BW, IV, to effect, and the dog was orotracheally intubated with the aid of a laryngoscope. After inflation of the ET tube cuff, an air-leak test was done by applying a peak pressure of 20 cmH₂O and listening for any audible air leaks. No leakage of air was noted during the leak test, and the dog was subsequently disconnected from the anesthetic machine, transported to the MRI room, and connected to a different circuit. During patient positioning, the dog’s breathing was assisted through intermittent positive pressure ventilation (IPPV) to pressures of 10 to 15 cmH₂O. While the dog was being positioned, a distinct “popping” sound was heard within the MRI room, after which a significant air leak between the ET tube and trachea was noted. Further attempts to inflate the ET tube cuff through insertion of air into the pilot balloon were unsuccessful. The dog was reintubated with a 5.5-millimeter ID ET tube. Upon careful assessment of the extubated ET tube, it was determined that the cuff had ruptured (Figure 1). Anesthesia was maintained with sevoflurane in > 95% oxygen delivered through a circle rebreathing system (Datex Ohmeda N-MRI2-00; GE Healthcare, Helsinki, Finland). Isotonic saline was administered at a rate of 5 mL/kg BW per hour during the procedure. The MRI scan was completed and the dog recovered from anesthesia without complications. The dog was diagnosed with thoracolumbar intervertebral disk disease at multiple sites, with the most severe at the T13-L1 region. The dog was transferred back to the primary care veterinarian for management.

Figure 1.

The cuff of an endotracheal tube that ruptured upon positive pressure ventilation during general anesthesia in a 15-year-old dog (arrows).

Case 2

A 5-year-old, intact male mixed-breed dog weighing 13.6 kg was presented to the IAN Centre for further evaluation of right-sided facial paralysis. The dog had a history of right-sided lip drooping and drooling, as well as a decreased ability to chew solid foods that had started 1 mo before presentation. A CBC and serum biochemistry panel obtained by the primary care veterinarian showed a mild thrombocytosis (platelet count: 49.1 × 10⁴ platelets/μL; RR: 11.7 to 46.0 × 10⁴ platelets/μL). The remaining results were within normal limits. No remarkable findings were observed on thoracic radiography.

On presentation to the IAN Centre, the dog was quiet, alert, and responsive. On physical examination, right-sided lip drooping and drooling were observed. On neurological examination, the dog had a decreased palpebral reflex and an absent menace response of the right eye. Therefore, MRI of the brain was scheduled. The dog was premedicated with butorphanol, 0.2 mg/kg BW and midazolam, 0.2 mg/kg BW, IV. Anesthesia was induced with propofol, 5 mg/kg BW, IV, to effect, and the dog was orotracheally intubated with a previously used, EO gas-sterilized 6.0-millimeter ID ET tube with a cuff that was leak tested before induction. The size of the ET tube was selected based on animal size and the clinician’s experience, and the length of the tube was premeasured to the level of the thoracic inlet. During the initial air-leak test, an audible leak was appreciated before peak airway pressures reached 20 cmH₂O; therefore, additional air was insufflated into the cuff and a subsequent leak test was performed. While positive pressure was applied to the rebreathing system, a distinct “popping” noise was heard and further attempts to inflate the cuff were unsuccessful. The dog was reintubated with a 6.5-millimeter ID ET tube and rupture of the ET tube cuff (6.0 mm ID) was observed. After reintubation and confirmation that no leak was present, the dog was subsequently disconnected from the circuit, transported to the MRI room, and connected to a new circuit. Anesthesia was maintained with sevoflurane and isotonic saline was administered at a rate of 5 mL/kg BW per hour during the procedure. The MRI scan was completed and no complications related to anesthesia or cuff rupture were observed during the perianesthetic period. No abnormalities in the intracranial cavity were noted on MRI to explain the signs of facial nerve paralysis. Therefore, on the basis of these results, the dog was diagnosed with idiopathic facial nerve paralysis. A follow-up discussion with the referring veterinarian 1 wk after the anesthesia episode confirmed that the dog was doing well without any complications related to the event.

Discussion

Rupture of ET tube cuffs has been previously described in human medicine, with some cases resulting in severe complications or fatalities but others having no related complications (6–9). However, to the authors’ knowledge, there have been no reported cases of ET tube cuff rupture in veterinary medicine.

In the present report, ET tube cuff rupture was noted in both cases after a distinct “popping” sound was heard upon positive pressure ventilation. Three contributing factors for the ruptured cuffs were considered. First, the ET tubes used in these cases were repeatedly sterilized with EO gas. In human medicine, to eliminate the possibility of cross-contamination, a new ET tube is used for every patient (10). This option is not economically feasible for many veterinary practices, which ultimately leads to the reuse of ET tubes after disinfection/sterilization. Although there are no official guidelines or regulations for the cleaning and reusing of ET tubes in veterinary medicine, it is recommended that all anesthesia equipment requiring direct patient contact, including ET tubes, should be thoroughly cleaned and disinfected between animals (11). Chlorhexidine or glutaraldehyde may be used for disinfection, but sterilization is the best way to eliminate all potential organisms that can produce infection or disease (10).

Among the various gas sterilization techniques, EO gas is considered the best due to its ability to penetrate a wide variety of materials. However, its potential toxicity raises health concerns for personnel, and as a result, it is not commonly used in veterinary medicine (10). A previous study in human medicine looked at the effect of repeated sterilization of ET tubes with EO gas on the physical integrity of the cuffs (12). In that study, as the number of EO treatments increased, the compliance and tensile strengths of the ET tube cuffs increased and decreased, respectively. This demonstrated that increasing numbers of sterilizations using EO gas caused the cuffs to become softer and more likely to stretch and break, especially after > 3 sterilizations (12). Although it was unclear exactly how many times the ET tubes used in these cases were sterilized, it is likely that the number was > 3, thereby increasing the risk of cuff softening and rupture.

The second contributing factor for cuff rupture considered was overinflation of the cuff, possibly due to the use of ET tubes that were too small. The ET tube size should be selected such that orotracheal intubation does not damage the larynx or trachea while also providing an effective seal when the cuff is inflated (4). Endotracheal tube sizes that have been recommended based on BW are 5 to 6 mm and 7 to 8 mm ID for Cases 1 and 2, respectively (13). Considering these suggested sizes, it is possible that the ET tubes selected for the dogs in the present report were too small, thus requiring overinflation of the cuff to obtain an adequate seal — especially in Case 2. After orotracheal intubation, ET tube cuffs should be inflated such that an adequate seal is achieved for positive pressure ventilation, preventing anesthetic gas leakage, and reducing the risk of aspirating fluids into the lungs (4). Considering the tracheal mucosal blood flow, the recommended pressure range for ET tube cuffs is between 18 and 25 mmHg (14).

In veterinary medicine, 2 techniques are commonly used to inflate ET tube cuffs. The first technique is to inflate the cuff and digitally palpate the pilot balloon to estimate cuff pressure. A previous study demonstrated that this technique resulted in overinflation of the cuff, with 91% of dogs having mean cuff pressures > 25 mmHg (2). The second technique is the minimum occlusive volume technique, in which air is injected into the pilot balloon until there is no audible air leakage while a pressure of 20 to 25 cmH₂O is applied to the breathing system (2). Two studies concluded this technique also resulted in overinflation of ET tube cuffs in 37 and 80% of cases, respectively (2,15). Overinflation of ET tube cuffs can impede tracheal blood flow, thus increasing the risk of tracheal mucosal damage that can ultimately lead to inflammation, stenosis, ischemia/necrosis, or, in extreme cases, tracheal rupture (3,4,16,17). Another study demonstrated that using a specialized syringe device containing a pressure sensor (AG Cuffill syringe; Medline/Hospitech) effectively reduced the incidence of both over- and underinflation of ET tube cuffs when compared to a regular injectable syringe (15). In the present cases, the cuffs were inflated with a conventional syringe using the digital palpation method. Therefore, it is highly likely that both cuffs were overinflated — especially in Case 2, in which additional air had to be insufflated into the cuff because the initial leak test had failed.

The final contributing factor for cuff rupture considered was the application of positive pressure ventilation. In both cases, ET tube cuff rupture was noted not during insufflation of air into the cuff, but during IPPV and during an air-leak test in Cases 1 and 2, respectively. When high-volume, low-pressure cuffs are inflated, they easily adapt and conform to the borders of the tracheal wall, ultimately assuming a cylindrical shape (18). As airway pressures increase during positive pressure ventilation, the trachea expands and gas within the cuff moves away from the end that is exposed to the increased pressure (19). As a result, the distal end of the cuff collapses while the proximal end moves proximally and laterally, changing the cuff shape from cylindrical to conical (19). Perhaps movement of air within the cuff from one side to the other during positive pressure ventilation also contributed to cuff rupture in both cases.

The authors strongly suspect that the 3 factors discussed above worked together to produce ET tube cuff rupture. Overinflation of the cuff likely resulted in a greater stretch, thus exposing any weakened area of the cuff caused by repeated sterilizations with EO gas. Subsequently, application of positive pressure to the airway would cause the air within the cuff to shift to one side to such an extent that the cuff could no longer withstand the stretch, ultimately leading to rupture.

In conclusion, repeated sterilization of ET tubes with EO gas can negatively affect the tensile strength and compliance of cuffs. Although no complications related to cuff rupture were observed in the cases reported here, there is always the risk of damage to the tracheal mucosa, which may lead to life-threatening post-anesthetic complications, as demonstrated in human medicine. Therefore, care should be taken not to overinflate ET tube cuffs, especially when they have been sterilized > 3 times. The use of a manometer or a specialized syringe device is recommended to reduce the incidence of cuff overinflation. Further, in practices where discarding ET tubes after a single use is not economically feasible, a tagging system indicating the number of sterilizations is recommended. CVJ

Funding Statement

This work was supported by a National Research Foundation of Korea (NRF) grant funded by the Korean government (Ministry of Science and ICT) (No. 2021R1G1A1013034).