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

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.