A small dog that was mask induced with sevoflurane for removal of retained deciduous canine teeth is exhibiting hyperventilation, rapid heart rate, and head movement whenever the extraction is attempted, but there is no response to a toe pinch. Premedication consisted of acepromazine, and the sevoflurane is being delivered at 5% with an oxygen flow rate of 1 liter per minute using a rebreathing circuit. The most appropriate response is:.