Kittens were delivered via caesarean section. The umbilical cord remained intact and was covered with diclofenac diethylammonium (Voltaren Emugel, GlaxoSmithKline Consumer Health B.V, UK). A custom-made esophageal tube was inserted, with the tip located in the mid thoracic region. This tube exited through a custom-made, soft rubber facemask that was placed over the kitten's head and sealed with tissue glue to prevent leak if necessary (small kittens). The umbilical cord was then clamped, and the kitten weighed before it received naloxone (0.2 mg/kg), anexate (10 μg/kg) and caffeine (20 mg/kg) injected intraperitoneally to reverse maternally administered sedatives/analgesics and to stimulate spontaneous breathing. Kittens were then transferred to the imaging hutch, placed on their right side on a heated platform and connected to a temperature probe, oximeter and ECG leads. The facemask was connected to a custom-build ventilator in CPAP mode 33 , whereas the esophageal tube was connected to a pressure transducer to detect breathing (BP Transducer/Cable kit, ADInstruments, New South Wales Australia). All devices were connected to a PowerLab and LabChart data acquisition system (ADInstruments, NSW, Australia) for continuous physiological recording.
All kittens were included, except if they were still born or were too small for instrumentation (<15 grams).
All kittens were included, except if they were still born or were too small for instrumentation (<15 grams).