Respiratory depression by analgesics at 41 bar

The effects of morphine and fentanyl on respiration and tissue CO2 measured transcutaneously were studied at surface and at 41 bar ambient pressure in conscious, trained rats. Morphine and fentanyl were given in equianalgesic doses i.v., 7 and 0.025 mg/kg, respectively. Fentanyl caused a rapid but brief respiratory depression which was the same at 1 and 41 bar, and essentially the same results were found in the morphine groups, although there was a longer latency and duration of action. No statistical differences in the degree of respiratory depression were found at 41 bar compared to 1 bar for either analgesic.