Abstract
Objective
To evaluate agreement between end-tidal carbon dioxide (Pe′CO2) and PaCO2 with sidestream and mainstream capnometers in mechanically ventilated anesthetized
rabbits, with two ventilatory strategies.
Study design
Prospective experimental study.
Animals
A total of 10 New Zealand White rabbits weighing 3.6 ± 0.3 kg (mean ± standard deviation).
Methods
Rabbits anesthetized with sevoflurane were intubated with an uncuffed endotracheal
tube (3.0 mm internal diameter) and adequate seal. For Pe′CO2, the sidestream capnometer sampling adapter or the mainstream capnometer was placed
between the endotracheal tube and Bain breathing system (1.5 L minute–1 oxygen). PaCO2 was obtained from arterial blood collected every 5 minutes. A time-cycled ventilator
delivered an inspiratory time of 1 second and 12 or 20 breaths minute–1. Peak inspiratory pressure was initially set to achieve Pe′CO2 normocapnia of 35–45 mmHg (4.6–6.0 kPa). A total of five paired Pe′CO2 and PaCO2 measurements were obtained with each ventilation mode for each capnometer. Anesthetic
episodes were separated by 7 days. Agreement was assessed using Bland-Altman analysis
and linear mixed models; p < 0.05.
Results
There were 90 and 83 pairs for the mainstream and sidestream capnometers, respectively.
The mainstream capnometer underestimated PaCO2 by 12.6 ± 2.9 mmHg (proportional bias 0.44 ± 0.06 mmHg per 1 mmHg PaCO2 increase). With the sidestream capnometer, ventilation mode had a significant effect
on Pe′CO2. At 12 breaths minute–1, Pe′CO2 underestimated PaCO2 by 23.9 ± 8.2 mmHg (proportional bias: 0.81 ± 0.18 mmHg per 1 mmHg PaCO2 increase). At 20 breaths minute–1, Pe′CO2 underestimated PaCO2 by 38.8 ± 5.0 mmHg (proportional bias 1.13 ± 0.10 mmHg per 1 mmHg PaCO2 increase).
Conclusions and clinical relevance
Both capnometers underestimated PaCO2. The sidestream capnometer underestimated PaCO2 more than the mainstream capnometer, and was affected by ventilation mode.
Keywords
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Article info
Publication history
Published online: November 17, 2022
Accepted:
November 12,
2022
Received in revised form:
November 11,
2022
Received:
July 7,
2022
Identification
Copyright
© 2022 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia. Published by Elsevier Ltd. All rights reserved.
