Published Online
on October 26, 2006

A more recent version of this article appeared on December 1, 2006

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Submitted on March 14, 2006
Revised on May 11, 2006
Accepted on June 6, 2006

Oximetry-Guided Reoxygenation Improves Neurological Outcome After Experimental Cardiac Arrest

Irina S. Balan PhD; Gary Fiskum PhD; Julie Hazelton MS; Cynthia Cotto-Cumba MD; and Robert E. Rosenthal MD^*

From the Departments of Anesthesiology (I.S.B., G.F., J.H., R.E.R.) and Surgery (C.C.-C., R.E.R.), Program in Trauma, University of Maryland School of Medicine, Baltimore, Md.

^* To whom correspondence should be addressed. E-mail: rrosenthal{at}umm.edu.

Background and Purpose--Current guidelines suggest that cardiac arrest (CA) survivors should be ventilated with 100% O₂ after resuscitation. Breathing 100% O₂ may worsen neurological outcome after experimental CA. This study tested the hypothesis that graded reoxygenation, with oximetry guidance, can safely reduce FiO₂ after resuscitation, avoiding hypoxia while promoting neurological recovery.

Methods--Mature dogs underwent 10 minutes of CA and restoration of spontaneous circulation with100% O_2. Animals were randomized to 1-hour additional ventilation on 100% FiO₂ or to rapid lowering of arterial O₂ saturation to <96% but >94% with pulse oximeter guidance. Animals were awakened at hour 23, and the neurological deficit score (0=normal; 100=brain-dead) was measured. Reanesthetized animals were perfusion-fixed and the brains removed for histopathology.

Results--The neurological deficit score was significantly better in oximetry (O) dogs. O dogs appeared aware of their surroundings, whereas most hyperoxic (H) animals were stuporous (neurological deficit score=43.0±5.9 [O] versus 61.0±4.2 [H]; n=8, P<0.05). Stereological analysis revealed fewer injured CA1 neurons in O animals (cresyl violet: 35.5±4.3% [O] versus 60.5±3.3% [H]; P<0.05). There were also fewer fluoro-Jade B-stained degenerating CA1 neurons in O animals (3320±267 [O] versus 6633±356 [H] per 0.1 mm³; P<0.001).

Conclusions--A clinically applicable protocol designed to reduce postresuscitative hyperoxia after CA results in significant neuroprotection. Clinical trials of controlled normoxia after CA/restoration of spontaneous circulation should strongly be considered.

Key words: canine model • cerebral ischemia • neurological deficit • oxygen utilization

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