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OJVRTM
Online Journal of
Veterinary Research©
Volume 19(1): 15-25, 2015. Redacted 2018.
Profiles of resistance
to breathing in spontaneously ventilating anaesthetised
dogs attached to an Ayre’s T-piece.
Saul Chemonges1,2 BVetMed, PGDipVetClinSt, MVSt.
1School
of Veterinary Science, The University of Queensland, Gatton, Australia, 2Central
Analytical Research Facility, Institute for Future Environments, Queensland
University of Technology, Gardens Point, George Street, Brisbane QLD, Australia.
ABSTRACT
Chemonges S., Profiles of
resistance to breathing in spontaneously ventilating anaesthetised
dogs attached to an Ayre’s T-piece, Onl J Vet Res., 19(1): 15-25, 2015. Resistance to breathing is a primary
consideration when determining the choice of patient anaesthesia
breathing apparatus. To date however, there are limited studies that have
categorically quantified resistance to breathing due to specific breathing
apparatus in veterinary patients. The aim of this study was to assess the
relationship between resistance to breathing, body weight (BW) and fresh gas
flow in dogs attached to an Ayre’s T-piece as
proof-of-principle. Eight healthy dogs of mixed breeds and age ranging from
6.8-17 kg were anaesthetised by intravenous injection
of 2.5% sodium thiopentone at a bolus dose of 12
mg/kg and then endotracheally intubated. The dogs
were initially attached to a circle absorber before switching to an Ayre’s T-piece for maintenance of general anaesthesia with 2.5% halothane vapour
in oxygen. Resistance to breathing was measured within the endotracheal tube
connector using a pressure transducer connected to a pressure-calibrated
module. Resistance to breathing was a function of the patient’s
body weight. Interestingly, the increase in resistance to breathing
corresponded to fresh gas flow to a point of critical fresh gas flow of 0.6
L/min, and then it began to decrease despite increasing fresh gas flow. It has
been demonstrated that at very low fresh gas flow, the resistance to breathing
is elevated which later eases considerably with increasing fresh gas flow until
a continuum is reached. The Ayres’ T-Piece functions best at 2.0 L/min
for small to medium sized dogs and there is no benefit to the patient or
the clinician in exceeding this fresh gas flow. It is suggested that future
studies should compare the various types and sizes of T-piece systems and
determine if size influences the magnitude of Resistance to breathing. Future
studies on resistance to breathing could also consider enrolling candidates
with respiratory pathology.
Keywords: Resistance to breathing;
Ayres T-Piece; Fresh gas flow; Dogs; Anaesthesia.
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