Brain Injury after Cerebral Arterial Air Embolism in the Rabbit as Determined by Triphenyltetrazolium Staining

Background: Microscopic cerebral arterial air embolism (CAAE) occurs commonly during cardiac surgery and causes acute and chronic nonfocal neurologic dysfunction. Nevertheless, most neuroimaging studies do not detect brain injury after cardiac surgery. Using a rabbit model, the authors hypothesized they could detect and quantitate severe brain injury and infarction 24 h after microscopic CAAE using the vital stain triphenyltetrazolium chloride.

Methods: Experiments were conducted in methohexital anesthetized New Zealand white rabbits. Surgical shams (n = 5) underwent surgery but had no neurologic insult. Positive controls (n = 3) received 200 [micro sign]l/kg of intracarotid air. Other animals were randomized to receive either 50 [micro sign]l/kg intracarotid air, which produces microscopic CAAE (n = 18), or 300 [micro sign]l intracarotid saline (control, n = 18). Outcomes included somatosensory evoked potential amplitude at 90 min, neurologic impairment score at 4 and 24 h (0 [normal] to 99 [coma]), and percentage of nonstaining brain at 24 h using color-discrimination image analysis. Severely injured or infarcted brain does not stain with triphenyltetrazolium chloride.

Results: Surgical shams had little neurologic impairment and a small amount of nonstaining brain at 24 h (5.2 +/- 2.4%; mean +/- SD). Positive controls had profound neurologic impairment and large amounts of nonstaining brain (40-97%). Ninety-minute somatosensory evoked potential amplitude was less in animals receiving 50 [micro sign]l/kg air versus saline: 38 +/- 28% versus 102 +/- 32%, respectively, P < 1 x 10-7. Neurologic impairment scores were greater in animals receiving 50 [micro sign]l/kg air versus saline: at 4 h, 43 +/- 16 versus 23 +/- 9, P < 1 x 10-7; at 24 h, 24 +/- 12 versus 15 +/- 8, P = 0.013. Nevertheless, there was no difference between 50 [micro sign]l/kg air and saline in nonstaining brain: 5.5 +/- 2.9% versus 6.8 +/- 5.4%, P = 0.83.