Untersuchungen zur Neurologie und zerebralen Inflammation nach tief hypothermem Kreislaufstillstand der Ratte: Einfluss der Wiedererwärmungsgeschwindigkeit

„Investigation of neurologic outcome and cerebral inflammation
after deep hypothermic circulatory arrest in the rat: The impact of
the rewarming rate” Despite considerable progress in medicine, and
the adapt use of CPB with DHCA, congenital heart defects are still
considered a challenge for surgery. Today`s scientific research
focuses on CPB with DHCA and the possible cerebral inflammatory
reaction, contributing to the often adverse neurologic and
neurocognitive outcome following CPB with DHCA. Aim o f this study
is to investigate the impact of the rate and duration of rewarming
have on postoperative neurologic function, histologic outcome and
cerebral inflammatory reaction in a clinically relevant animal
model of CPB with 45 min of DHCA in the rat. 20 male Sprague Dawley
rats (330 – 390 g) were anaesthetized, endotracheally intubated and
ventilated with 2 to 2.5 Vol % Isoflurane in 40 Vol % O2. For pain
management all animals received repititive 5µg boli of Fentanyl.
Animals were surgically cannulated as follows: the A. sacralis
mediana for arterial inflow during CPB, the taking of blood samples
and drug administration. The A. epigastrica superficialis for blood
pressure monitoring and the V. jugularis externa and V. cava
cranialis for venous drainage during CPB. During the cooling phase
anaesthesia was maintained with 0.8 to 1Vol % Isoflurane and
Cisartracurium was given additionally for muscle relaxation
(1,6mg/h). To cool rats down to a rectal temperature of 15 – 18 °C
within 30 min, cooling blankets, ice bags and a heat exchanger in
the oxygenator were used. At 15 – 18 °C, CPB and anaesthesia were
terminated for 45 minutes and the venous drainage was opened every
ten minutes to allow the animals to exsanguinate to prevent a right
heart dilatation. Rats were then randomly assigned to one of two
rewarming groups (n = 10): with reinstitution of CPB and
anaesthesia, one group was rewarmed slowly over 40 minutes and a
second group fast over 20 minutes back to a rectal temperature of
35.5 °C. When reaching 35.5 °C, animals were weaned from CPB, and
anaesthesia was maintained for one hour folllowing CPB. During that
time the blood left in the circuit was collected, centrifuged,
adjusted with HES and calcium to a hematocrit below 50% and
returned to raise the animal`s hematocrit above 30%. Anaesthesia
was terminated one hor following CPB. Animals were extubated when
showing sufficient spontaneous breathing and allowed to recover
under observation in an oxygen enriched environment. Rats were
neurologically tested one day prior to CPB with DHCA as well as on
the postoperative day. 24 hours following the end of CPB, animals
were sacrificed, their brains removed and deep frozen (-70 °C) for
further analysis. H&E staining was performed using slices taken
at bregma –0.3 and –3.3 to investigate the histological damage in
the Gyrus cinguli, Striatum, motor cortex, Hippocampus and Vermis.
NF-kB- positive neurons were labelled with an immunhistochemical
double staining and counted using light microscopy. Inflammatory
parameters TNF-α, COX-2 and I-kB were evalueted using Wetsern
Blotting. For the first time this study compares the neurologic
outcome following two different rewarming protocols after DHCa in a
clinically relevant animal model of CPB with DHCA. Unexpectedly, a
better neurologic outcome is seen after fast rewarming. Although
results for histology and immunehistochemistry show higher amounts
of eosinohilic and NF-kB- positive neurons in this group. Western
Blot also shows increased levels of inflammatory parameters COX-2
and I-kB in the fast rewarming group. These findings suggest that
the rewarming rate alone is not the chief cause for an adverse
neurological out-come after CPB with DHCA. Further studies
concerning the mechanisms leading to adverse neurologic outcome and
cerebral inflammatory reaction following CPB with DHCA are
required.