Oxygen fluctuations in the brain and periphery induced by intravenous fentanyl: effects of dose and drug experience

By using electrochemical oxygen sensors in freely moving rats, we show that intravenous fentanyl induces opposite changes in brain oxygen at varying doses, increasing at lower doses (<10 µg/kg) and inducing a biphasic response, decrease followed by increase, at higher doses (>10–90 µg/kg). In contrast, fentanyl-induced dose-dependent oxygen decreases in the subcutaneous space. We consider the mechanisms underlying distinct oxygen responses in the brain and periphery and discuss naloxone’s role in alleviating fentanyl-induced brain hypoxia.