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(Circulation. 1995;91:431-444.)
© 1995 American Heart Association, Inc.
Articles |
From the Cryobiology and Hypothermic Medicine Program (M.J.T., A.M.E), Neurosciences Research Center, Allegheny-Singer Research Institute, Departments of Neurosurgery (M.J.T., J.E.B., A.M.E., S.-R.S., M.L.L., J.C.M.) and Anesthesiology (E.T.), Allegheny General Hospital, and Medical College of Pennsylvania (Allegheny Campus), Pittsburgh, Pa; and Cryomedical Sciences Inc (J.G.B.), Rockville, Md.
Correspondence to Dr M.J. Taylor, Department of Neurosurgery Research, Allegheny-Singer Research Institute, 320 East North Ave, Pittsburgh, PA 15212.
Background The benefits of hypothermia for preventing ischemic injury are well known, but its application in surgery to protect the whole body during procedures requiring circulatory arrest is currently limited to <1 hour at 15°C using 50% hemodilution. In a significant departure from previous methods, we have developed a technique of asanguineous blood substitution with low-flow perfusion and cardiac arrest at <10°C in a canine model. Our approach has been to design a hypothermic blood substitute that would protect the brain and visceral organs during several hours of bloodless perfusion. Two different solutions have been designed to fulfill separate requirements in the procedure.
Methods and Results With the use of extracorporeal cardiac
bypass, 14 adult dogs were exsanguinated during cooling; 11 dogs were
blood substituted using in combination the "purge" and
"maintenance" solutions (group 1), and 3 dogs were perfused
throughout with the "purge" solution alone as controls (group 2).
After cardiac arrest, the solutions were continuously circulated for
3
hours by the extracorporeal pump (flow rate, 40
to 85
mL · kg-1 · min-1; mean
arterial
blood pressure, 25 to 40 mm Hg). The temperature was maintained at
<10°C (nadir, 6.6±0.1°C) for 3 hours, and the hematocrit was
kept
at <1% before controlled rewarming and autotransfusion. In the
experimental group, the heart always started spontaneously in the
temperature range of 11°C to 27°C, and 8 animals have survived
long-term (current range, 14 to 110 weeks) without any detectable
neurological deficit. In contrast, two control animals survived after
extensive and aggressive cardiac resuscitation efforts; after surgery
they exhibited transient motor and sensory deficits for approximately 1
week. Evaluation of biochemical and hematological parameters showed
only a transient and inconsequential elevation in enzymes (eg, brain,
liver, cardiac) in group 1 compared with the markedly greater
elevations in group 2. For example, immediate postoperative values
(mean±SEM) for lactate dehydrogenase were 114±10 for group 1
versus
490±210 for group 2 (P<.03); for SGOT, values were
93±18
for group 1 versus 734±540 for group 2 (P<.05). On day 1
for creatine kinase (CK), the group 1 value was 7841±2307 versus
71 550±2658 for group 2 (P=.03), and for CK-BB, the
group
1 value was 108±22 versus 617±154 for group 2
(P=.03).
Neurological evaluation using deficit scores (NDS) was based on a
modification of the Glasgow Coma Scale score: 0, normal; 1, minimal
abnormality; 2, weakness; 3, paralysis; 4, coma; and 5, death. At days
1 and 2 after surgery, NDS (mean±SEM) were 0±0 for the
experimental
group versus 1.5±0.5 for the control group. At days 3 and 7 after
surgery, NDS were 0±0 for group 1 versus 1.0±1.0 for group
2.
Conclusions The faster neurological recovery of dogs treated with the "intracellular-type" maintenance solution supports the biochemical data showing the benefits of this type of blood substitute for extending the safe limits of hypothermic cardiac arrest procedures to >3 hours.
Key Words: hypothermia blood substitutes heart arrest ischemia
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