Doxycycline reduces early neurologic impairment after cerebral arterial air embolism in the rabbit

Background: Previous studies indicate leukocytes play a role in the pathogenesis of cerebral arterial air embolism. Because doxycycline inhibits numerous leukocyte activities, the authors hypothesized doxycycline would decrease neurologic impairment after cerebral arterial air embolism. Methods: New Zealand White rabbits anaesthetized with methohexital received either intravenous saline (n = 7) or 10 mg/kg doxycycline (n = 7) 1 h before administration of 100 mu l/kg of air into the internal carotid artery. Somatosensory-evoked potentials (SSEPs) were recorded at 30-min intervals for the next 2 h. After the final recording, the anesthetic was discontinued, and animals recovered. Animals were neurologically evaluated 4 h after air embolism on a scale of 0 (normal) to 99 (coma) points. Results: At 4 h, doxycycline animals had lesser neurologic impairment (46 +/- 23; median, 41) than animals that received saline (77 +/- 20; median, 81); P = 0.007. SSEP amplitude was greater in the doxycycline group at 60, 90, and 120 min after air embolism; P = 0.001, 0.006, 0.026, respectively. SSEP amplitudes at 30, 60, 90, and 120 min inversely correlated with 4 h neurologic impairment; pi = -0.43, -0.75, -0.85, -0.79, respectively. Conclusions: Doxycycline decreased electrophysiologic and neurologic abnormalities after cerebral air embolism. Because groups could be distinguished electrophysiologically as soon as 1 h after air embolism and because SSEP amplitude inversely correlated with neurologic impairment, doxycycline appears to inhibit a key early (similar to 1 h) process in the pathophysiology of cerebral air embolism.