Investigation of endotracheal tube complications in anaesthetised cats and dogs

Lloyd, Ffion Sian (2024) Investigation of endotracheal tube complications in anaesthetised cats and dogs. MVM(R) thesis, University of Glasgow.

Abstract

1. Abstract:
Endotracheal tubes (ETT) are commonly used in the anaesthesia of cats and dogs. They perform a variety of essential functions that may facilitate safe general anaesthesia in these animals. However, their use is not without risk, and complications can arise. This work presents the findings of a retrospective and an experimental study, both investigating complications related to ETT use in cats and dogs.

1.1 Retrospective study:
The retrospective study aimed to discover the prevalence of ETT constriction and rostral and caudal mispositioning in anaesthetised cats and dogs, and to identify associated risk factors.

Computed tomography (CT) images of the head/neck/thorax from orotracheally intubated cats and dogs were visually assessed for constriction or mispositioning of the ETT. If constriction was present, measurements of the cross-sectional area (CSA) of the ETT lumen at constricted and un-constricted locations were compared. Location and cause of constriction was noted and expected increase in resistance to gas flow was calculated. Patient information was collected from clinical records. Normality of continuous variables was assessed via the Shapiro-Wilk test. Chi square tests examined associations between variables. Kendall’s tau-b test was performed between measured ETT size and degree of constriction.

The ETT extended rostrally beyond incisors in 52% of cases. The ETT connector was within the oral cavity in 19% of cases. The ETT extended beyond the first rib in 25.5% of cases. The prevalence of ETT constriction was 22.7%. Median reduction in CSA was 7.68% (0.14 – 64.19%). Median increase in resistance assuming laminar and turbulent flow was 16.5% (0.3 – 680%) and 21% (0.3 – 1200%), respectively. The most common cause of constriction was the presence of a radiotherapy mouth gag. Significant associations existed between presence of constriction and rostral mispositioning, and caudal mispositioning and extreme brachycephaly. Increased severity of constriction was more likely in smaller ETT.

Constriction and mispositioning of ETT occurred very commonly in the population studied. Checking the ETT within the oral cavity for constriction and mispositioning is consequently recommended. Radiotherapy mouth gags increased the risk of ETT compression. Smaller ETT were at greater risk of severe constriction. Brachycephalic dogs were at particular risk of caudal mispositioning.

1.2 Experimental study:
The influence of three variables on the force required to cause constriction of the ETT lumen by application of a securing tie was evaluated. The variables assessed were ETT material (polyvinyl chloride (PVC) and silicone), ETT size (4.0, 7.0 and 11.0 mm, internal diameter) and securing tie material (knitted stretch, non-stretch woven and plastic).

Each combination of ETT material, size and tie material was tested. The tie material was secured to a fixed structure with a loop tied 30 cm away. A knot was created around the body of the ETT. A luggage scale was hooked into the loop and pulled, tightening the knot until constriction of the ETT lumen occurred. The maximum force applied was recorded. Constriction was evaluated via CT imaging. The process was repeated, with the force applied decreasing by 1 kg (~ 9.81 N ) each time, or halved if the preceding force was ≤1 kg, until no constriction of the ETT was detected.

The median minimum force required for constriction of silicone and PVC ETT was 9.8 and 28.4 N, respectively. The median minimum force required for constriction of the small, medium and large ETT was 6.9, 18.6 and 37.3 N, respectively. The median minimum force required for constriction by the stretch and woven materials was 14.7 and 22.6 N, respectively. The plastic securing tie loosened spontaneously in all combinations prior to CT. Silicone ETT were more likely to be constricted by a tie than PVC ETT. Smaller ETT were more vulnerable to constriction by the tie. Stretch fabric was most likely to cause constriction of the ETT. Plastic securing ties may fail to adequately secure the ETT.

• Item Type: Thesis (MVM(R))
• Qualification Level: Doctoral
• Subjects: S Agriculture > SF Animal culture > SF600 Veterinary Medicine
• Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Biodiversity, One Health & Veterinary Medicine
• Supervisor's Name: Murison, Professor Pamela and Robertson, Mrs Josephine
• Date of Award: 2024
• Depositing User: Theses Team
• Unique ID: glathesis:2024-84050
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 24 Jan 2024 16:00
• Last Modified: 04 Mar 2026 11:50
• Thesis DOI: 10.5525/gla.thesis.84050
• URI: https://theses.gla.ac.uk/id/eprint/84050

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