Use of the respiratory stimulant doxapram in southern elephant seals (Mirounga leonina)

The use of doxapram to stimulate breathing was examined in southern elephant seals chemically restrained with ketamine and xylazine. Animals which were breathing spontaneously received doxapram (approximately 0.5, 1, 2, or 4 mg/kg) or saline into the extradural intravertebral vein. Doxapram caused a dose-dependent increase in the depth and rate of respiration which began within one minute, peaked after two minutes and lasted for up to five minutes. A dose of 2 mg/kg appeared to be safe and effective for the stimulation of respiration, while 4 mg/kg caused arousal and shaking. Doxapram (2 mg/kg) was tested on 14 occasions in animals which had developed apnoea during chemical restraint. Doxapram had no effect when administered into the extradural intravertebral vein and appeared to be of more benefit when administered directly into the lungs via an endotracheal tube, but it was not effective in all cases. There was evidence to suggest that the endotracheal tube prevented some of the animals from breathing. The effect of intubation and endotracheal doxapram administration was therefore examined in 19 apnoeic and 31 spontaneously breathing seals. Intubation induced apnoea in animals at low levels of chemical restraint and endotracheal doxapram was unreliable for the stimulation of breathing.