Comparison of mainstream (Capnostat 5) and two low-flow sidestream capnometers (VM-2500-S and Capnostream) in spontaneously breathing rabbits anesthetized with a Bain coaxial breathing system

Sedation and Anesthesia in Exotic Animal Critical Care

Sedation and anesthesia of exotic animals in inherently challenging, but often facilitates the best care for patients. Critical illness or injury adds on another layer of complexity to their management for obtaining diagnostics and providing treatments. This article serves to review some of the more recent literature of sedation and anesthesia within exotics practice, bringing to light some nuances and considerations for when those patients are critically ill or injured.

Comparison between mainstream (Capnostat 5) and a low-flow sidestream capnometer (Capnostream) in mechanically ventilated, sevoflurane-anesthetized rabbits using a Bain coaxial delivery system

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.

Ferret Sedation and Anesthesia

Providing safe anesthetic events in ferrets can be achieved if fundamental principles in anesthesia are followed. Each phase of the anesthetic, event including preanesthetic, maintenance, and postanesthetic phase, have certain considerations. The anesthetic supervisor or veterinarian providing management should have a firm understanding of the species-specific anatomy, physiology, and common indications of general anesthesia along with perspective of their own experience with ferrets. Ensuring these guidelines are followed will facilitate safe administration of general anesthesia in this species.