# A Comparison of Two Different Methods for Inducing Apnoea During Thoracic Computed Tomography of Dogs

## TL;DR

This study compares two methods for inducing apnoea in dogs during chest CT scans, finding that using a ventilator provides better control and image quality than midazolam.

## Contribution

The study provides new insights into the efficacy and safety of ventilator-based apnoea induction compared to midazolam in dogs undergoing thoracic CT.

## Key findings

- Ventilator-induced apnoea resulted in improved image quality and fewer side effects compared to midazolam.
- Apnoea onset was quicker and longer-lasting with ventilator use.
- Midazolam caused greater changes in cardiorespiratory parameters and atelectasis.

## Abstract

To prevent movement blur, patients must remain still and not breathe for computed tomography (CT), an advanced medical imaging modality of the chest. Whilst people can be instructed to do this, animals must be anaesthetised and given a drug or their lungs ventilated to temporarily stop their breathing, so-called apnoea. This study’s main aim was to compare two methods used commonly in the authors’ institution to induce apnoea in dogs. One was the administration of midazolam, a drug that depresses breathing among multiple other applications. The other was using a ventilator to mechanically deliver breaths, overcoming the patient’s own drive to breathe, before pausing the machine for the chest CT scan. Both methods had a similar efficacy in over three quarters of the dogs investigated but the use of the ventilator resulted in improved image quality and a greater degree of control, with fewer side effects. The onset and duration of apnoea induced by each method was also described for the first time, being quicker and longer, respectively, when using the ventilator compared to midazolam. These findings will enhance the understanding of veterinary professionals on how to safely and effectively induce apnoea in dogs under general anaesthesia.

Apnoea may be induced by pharmacological or ventilatory measures in animals under general anaesthesia to prevent motion blur on thoracic computed tomography (CT) sequences. The effectiveness of such methods has previously been reported in terms of CT image quality but not in the success of apnoea induction. Therefore, the purpose of this study was to evaluate the efficacy of two different methods used to induce apnoea. A total of 61 client-owned dogs undergoing general anaesthesia for thoracic CT were randomised to group M (n = 30) and group V (n = 31). In group M, midazolam 0.2 mg kg−1 was administered by rapid intravenous injection. In group V, dogs were mechanically ventilated to maintain normocapnia, before pausing the ventilator for image acquisition. Apnoea was induced in 77% of dogs in group M and 94% in group V (p = 0.08). The onset of apnoea was quicker and of a longer duration in group V (p < 0.001). Changes in cardiorespiratory parameters and the degree of atelectasis were greater following midazolam administration. For these reasons, the authors recommend interruption of mechanical ventilation to induce apnoea in suitable dogs, as it enables the period of apnoea to be more controlled and repeated if required.