Tracheal necrosis as a fatal complication of endotracheal intubation

Lower airway ultrasonographic, endoscopic, and cytological changes in horses undergoing inhalation anesthesia with controlled ventilation for minor elective surgeries

Effects of general anesthesia with controlled ventilation on the respiratory system have had limited evaluation in horses. A prospective observational study was performed with eleven client-owned horses undergoing elective surgery. Physical examination, auscultation with a rebreathing bag, complete blood cell count, lung ultrasound imaging, tracheal endoscopy imaging and transendoscopic tracheal wash were conducted before and 24 hours after anesthesia. Lung ultrasound imaging was also repeated just after recovery. A significant increase in blood neutrophil count between pre- and post-anesthesia (P=0.004) was observed. There was an increase in ultrasonographic score of the lungs at recovery (left P=0.007, right P=0.017). The score of the dependent lung was higher than the independent lung at recovery time (P=0.026) but no difference was observed 24 hours after anesthesia. The tracheal mucus score was higher after anesthesia (P=0.001); severe local inflammation was present in several horses at the site of endotracheal tube cuff. Neutrophil count was significantly higher on tracheal wash fluid cytology after anesthesia (P=0.016), without any significant changes on bacterial load. Increased tracheal mucus score and neutrophil count in tracheal wash samples were observed after general anesthesia in healthy horses without clinical evidence of pneumonia (fever, cough). Tracheal inflammation secondary to endotracheal intubation and cuff inflation was, therefore, suspected. Elective surgery without complications can induce inflammation of the trachea and changes in ultrasound images of the lungs in healthy horses and should be considered when evaluating respiratory system after a general anesthesia.

Methods Used for Endotracheal Tube Cuff Inflation and Pressure Verification in Veterinary Medicine: A Questionnaire on Current Practice

Endotracheal intubation is a routine procedure in veterinary anaesthesia, yet no consensus guidelines exist for endotracheal tube (ETT) cuff inflation and pressure measurement. The aim of this study was to assess current practice of ETT cuff inflation and seal verification in veterinary medicine. An online questionnaire was distributed among veterinary professionals who administer anaesthesia, comprising six demographic and twelve ETT cuff-related questions per species. N = 348 questionnaires were completed. Cuff pressure was measured by 30% of respondents in cats, 32% in dogs and 9% in both farm animals and horses. Anaesthesia diplomates were not more likely to measure cuff pressure than others, except in cats (OR: 1.8; 95% CI: 1.1−2.9). The most frequently selected recommended range of cuff pressure was 20−30 cm H2O, regardless of species, although >30 cm H2O was selected significantly more often in horses compared to dogs, cats and farm animals. The preferred technique to verify cuff seal was minimal occlusive volume in dogs, cats and farm animals, whereas in horses, the preferred method was verification of normal capnogram waveform. ETT cuff pressure measurement remains uncommon in veterinary anaesthesia. The development of consensus recommendations for cuff inflation, including evidence-based target cuff pressure ranges for various species and different ETT models or materials, can help to improve practice.

Impact of endotracheal tube size and cuff pressure on tracheal and laryngeal mucosa of adult horses

OBJECTIVE

To assess the effects of two sizes of silicone endotracheal tubes with internal diameter 26 mm (ETT₂₆) and 30 mm (ETT₃₀) inflated to minimum occlusive volume on tracheal and laryngeal mucosa of adult horses anesthetized for 2 hours with isoflurane.

STUDY DESIGN

Prospective, randomized, blinded, crossover experimental study.

ANIMALS

A total of eight healthy adult mares.

METHODS

Upper airway endoscopy and ultrasound measurements of internal tracheal diameter were performed the day before anesthesia. Horses were anesthetized and orotracheally intubated with ETT₂₆ or ETT₃₀. Ease of intubation was scored. The cuff was inflated in 10 mL increments to produce a seal. Final volume of air used and intracuff (IC) pressure (measured by pressure transducer) were recorded. At the end of anesthesia, a manometer was used to measure IC pressure and these measurements compared against measurements from the pressure transducer. Laryngeal and tracheal mucosa were assessed via endoscopy and assigned a score 0-3 before anesthesia, and at 2 and 24 hours following extubation.

RESULTS

Data are from seven horses because one horse with laryngeal hemiplegia was excluded. Mean tracheal ultrasound measurement was 3.5 ± 0.4 cm. No significant differences were noted between endotracheal tube sizes for intubation score, IC pressures, inflation volumes or tracheal or laryngeal injury scores at any time point. IC pressure measured by manometer was slightly higher than that by transducer (+1.0 ± 2.8 mmHg).

CONCLUSIONS AND CLINICAL RELEVANCE

Results identified no clear advantage of one endotracheal tube size over the other in the population of horses studied, when endotracheal intubation is properly applied and IC pressure is carefully monitored. However, given that ETT₂₆ was associated with the highest observed IC pressures and the only observed incidents of tracheal circumferential erythema, the larger ETT₃₀ may be the better choice in most cases where tracheal size is sufficient.

Evaluation of Endotracheal Tube Cuff Pressure and the Use of Three Cuff Inflation Syringe Devices in Dogs

Over-inflation of an endotracheal tube (ETT) cuff may lead to tracheal mucosal irritation, tracheal wall ischemia or necrosis, whereas under-inflation increases the risk of pulmonary aspiration as well as leaking anesthetic gas and polluting the environment. The objectives of this two-phase study were to (1) identify the incidence of improper ETT cuff inflation (both over- and under-inflation) using the minimum occlusive volume (MOV) technique coupled with a regular injectable syringe in the anesthetized dogs, and (2) evaluate the performance of two commercially available inflation syringe devices (Tru-Cuff and AG Cuffill®) with the regular injectable syringe in inflating the ETT cuff to a recommended safe cuff pressure range (20–30 cmH₂O). Dogs undergoing general anesthesia at Purdue Veterinary Medicine Teaching Hospital were included. The ETT cuff pressure was assessed with an aneroid manometer after the syringe inflation. The results of the first objective showed that a total of 80 dogs enrolled and that 50 of these 80 dogs required ETT cuff inflation. Among the 50 dogs, only 14% had proper ETT cuff inflation; 76% of the ETT cuffs were over-inflated and 10% were under-inflated. Ninety dogs were enrolled for the second objective study and they were randomly and equally assigned to the three syringe device treatment groups. The results showed that 80% of the ETT cuffs were over-inflated in the regular injectable syringe treatment group, whereas only 6.7% and 3.3% ETT cuffs were over-inflated in the Tru-Cuff and AG Cuffill® syringe treatment groups, respectively. The AG Cuffill® syringe treatment group had a significantly (p < 0.05) higher percentage of properly inflated ETT cuffs (86.7%) compared to the other two groups (regular injectable syringe [3.3%]; Tru-Cuff syringe [50%]. We concluded that there was a high incidence of improper ETT cuff inflation when using MOV technique coupled with a regular injectable syringe. The use of an AG Cuffill® syringe significantly reduced improper ETT cuff inflation.

Selection of appropriate endotracheal tube size using thoracic radiography in Beagle dogs

OBJECTIVE

To determine the optimal endotracheal tube size in Beagle dogs using thoracic radiography.

STUDY DESIGN

Prospective, randomized, crossover experimental study.

ANIMALS

A total of eight healthy adult Beagle dogs.

METHODS

Lateral thoracic radiographs were used to measure the internal tracheal diameter at the thoracic inlet. This measurement was multiplied by 60, 70 and 80% to determine the outer diameter of the endotracheal tube for each dog. In each treatment, medetomidine (5 μg kg^-1) was administered intravenously (IV) for premedication. Anesthesia was induced with alfaxalone (2 mg kg^-1) IV and maintained with isoflurane. After induction of anesthesia, the resistance to passage of the endotracheal tube through the trachea was scored by a single anesthesiologist. Air leak pressures (P_leak) were measured at intracuff pressures (P_cuff) of 20 and 25 mmHg (27 and 34 cmH₂O). The results were analyzed using Friedman tests and repeated measures anova.

RESULTS

There were statistically significant increases in resistance as the endotracheal tube size increased (p = 0.003). When P_cuff was 20 mmHg, mean P_leak for the 60, 70 and 80% treatments were 9.7 ± 6.7, 16.2 ± 4.2 and 17.4 ± 3.9 cmH₂O, respectively, but no significant differences were found. When P_cuff was 25 mmHg, mean P_leak for the 60, 70 and 80% treatments were 10.6 ± 8.5, 19.7 ± 4.9 and 20.8 ± 3.6 cmH₂O, respectively, and statistically significant increases were found between treatments 60 and 70% (p = 0.011) and between treatments 60 and 80% (p = 0.020). Three dogs in the 80% treatment had bloody mucus on the endotracheal tube cuff after extubation.

CONCLUSIONS AND CLINICAL RELEVANCE

Results based on resistance to insertion of the endotracheal tube and the ability to achieve an air-tight seal suggest that an appropriately sized endotracheal tube for Beagle dogs is 70% of the internal tracheal diameter measured on thoracic radiography.