Abstract
Objectives
To determine if the tidal volume (VT) delivered (VTDEL) to canine patients being mechanically ventilated by a volume-controlled ventilator
differed from the volume set on the ventilator (VTSET) at three fresh gas flow (FGF) rates. To determine if VTDEL could be accurately predicted by an FGF-based mathematical model.
Study design
Prospective proof-of-concept study.
Animals
A total of 23 adult client-owned dogs undergoing elective orthopedic surgery.
Methods
Dogs were anesthetized and ventilated with a volume-controlled mechanical ventilator
with constant respiratory rate (fR) of 10 breaths minute–1, inspiratory-to-expiratory ratio of 1:2 [fraction of inspiratory time (TI) in one respiratory cycle (Ttot) 1:3], and VTSET as body weight (kg) × 15 (mL kg–1). VTDEL was measured in 20 dogs at three FGF (500, 1000 and 4000 mL minute–1). A mathematical model was used to calculate predicted volume (VTPRED) for each animal at each FGF: VTSET + {FGF × [(TI/Ttot)/fR]}. Linear repeated measures models were fit comparing VTDEL to VTSET and to VTPRED by FGF.
Results
VTDEL was significantly higher than VTSET at every FGF (p < 0.05), and differences were larger at higher FGF (p < 0.001). There were no statistically significant differences between VTDEL and VTPRED at FGF rates of 500 and 4000 mL minute–1 and, although the mean VTDEL was statistically significantly higher than VTPRED at FGF 1000 mL minute–1 (p = 0.017), the mean difference of 9 mL was not clinically significant.
Conclusions and clinical relevance
Dogs on volume-controlled ventilators may be ventilated at a higher VTDEL than intended depending on the FGF settings. Ventilation of small animals at high
FGF could inadvertently induce pulmonary damage. A mathematical equation can be used
to achieve a desired VTDEL by adjusting VTSET values based on FGF, fR and TI/Ttot.
Keywords
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Article info
Publication history
Published online: November 03, 2022
Accepted:
October 28,
2022
Received in revised form:
October 27,
2022
Received:
May 27,
2022
Identification
Copyright
© 2022 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia. Published by Elsevier Ltd. All rights reserved.
