Evaluating the clinical use of different breathing systems and assessing their effects on respiratory function in small dogs under anaesthesia

Murray, Andrew Gordon (2025) Evaluating the clinical use of different breathing systems and assessing their effects on respiratory function in small dogs under anaesthesia. MVM(R) thesis, University of Glasgow.

Abstract

There is little consensus on the selection and use of breathing systems in small dogs. There is a wide array of systems available and several factors which govern breathing system selection. The current guidance for the use of breathing systems in 5–10 kg dogs is unclear. There is a trend to advise the use of more economical systems, however, the use of these has not been evaluated.

Survey study

This study aimed to investigate which breathing systems are available and why they are selected in 5–10 kg dogs. This was an anonymous online voluntary open survey. Research was approved by the University of Glasgow College of Medical, Veterinary & Life Sciences Ethics committee (Ref. 200220025).

An online survey, designed following CHERRIES guidelines (Eysenbach, 2004), was advertised through the American College of Veterinary Anesthesiologists - List (ACVA-List), Association of Veterinary Anaesthesia (AVA) and European College of Veterinary Anaesthesia and Analgesia (ECVAA) (February-March 2022). A convenience sample was taken.

Of the 256 responses received, 138 were completed. This included (n responses received) veterinarians (107) and veterinary nurses or technicians (29) actively involved in the anaesthesia of dogs.

The most prevalent breathing systems available to respondents were circle (99%), coaxial Bain (79%) and modified Ayre’s T-piece (with adjustable pressure limiting valve) (72%). When recommending a dog weight range suitable for the use with these systems, respondents advised a median (interquartile range) of 5 (3–10) to 100 (100–100), 3 (0–8) to 20 (10–33) and 0 (0–0) to 10 (7–10) kg, respectively. Respondents agreed or strongly agreed that important factors in selecting a breathing system were the fresh gas flow requirement (92%), dog weight (91%), resistance (83%) and environmental pollution (79%). In clinical scenarios based on 5–10 kg dogs, the circle system was chosen by 58% for a thin and 77% for a keel chested versus 44% for an obese and 66% for a barrel-chested dog, respectively.

The circle system is the most commonly available breathing system. The minimum weight limit used for the circle system is less than previous surveys have reported (Nicholson and Watson, 2001). Several factors influence the choice of breathing system other than dog weight.

Clinical study

This study aimed to compare different breathing systems during spontaneous ventilation in anaesthetised 5–10 kg dogs. This was a randomised, non-blinded, crossover clinical trial. Ethical approval was obtained from the University of Glasgow School of Biodiversity One Health and Veterinary Medicine Ethics Committee (Ref EA34/21).

Thirty 5–10 kg dogs were anaesthetised for a range of procedures.

A Mapleson D T-piece system was used as a control in all dogs. The dogs were equally randomised to the test breathing systems: circle or Bain. All dogs received a standard anaesthetic protocol. Respiratory rate (fR), end expired carbon dioxide (PE′CO2), tidal (VT) and minute (V̇E) volume were compared using a paired student’s t test or Wilcoxon rank test.

The circle PE’CO2 (6.04 ± 0.64 kPa), VT (12.1 ± 3.9 ml kg-1) and V̇E (116.7 (97.5–166.0) ml kg-1) were significantly higher (p = <0.001, 0.035 and 0.002 respectively) than the T-piece PE’CO2 (5.31 ± 0.78 kPa), VT (10.6 (7.7–13.3) ml kg-1) and V̇E (107.8 (77.3–131.9) ml kg-1). The Bain PE’CO2 (5.22 ± 0.98 kPa) was significantly lower (p = 0.032) and the VT (7.1 ± 2.7 ml kg-1) significantly higher (p = 0.041) than the T-piece PE’CO2 (5.61 ±0.90 kPa) and VT (6.6 (4.8–7.0) ml kg-1). Between the Bain and T-piece there was no significant difference in V̇E. Neither test system had a significant difference in fR compared with the control.

Whilst differences were found between both test systems and the control, the clinical consequences appear minimal. Both circle and Bain appear suitable for use in healthy 5–10 kg dogs as overall ventilatory function was adequate.

• Item Type: Thesis (MVM(R))
• Qualification Level: Masters
• 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 > Veterinary Biosciences
• Supervisor's Name: Murison, Professor Pamela J. and Woodhouse, Dr. Kerry
• Date of Award: 2025
• Depositing User: Theses Team
• Unique ID: glathesis:2025-85512
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 09 Oct 2025 13:39
• Last Modified: 09 Oct 2025 13:50
• Thesis DOI: 10.5525/gla.thesis.85512
• URI: https://theses.gla.ac.uk/id/eprint/85512

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