Cerebral perfusion in cardiac surgery : with special reference to circulatory arrest during profound hypothermia
Sammanfattning: Thirty-nine pediatric and 82 adult patients were studied during cardiac surgery with cardio pulmonary bypass (CPB) performed with moderate hypothermia or with deep hypothermia and circulatory arrest (DHCA) with or-without retrograde cerebral perfusion (RCP). Cerebral blood flow (CBF) was estimated from Doppler measurements of the blood velocity in the middle cerebral artery (MCAv). Arterio-venous (jugular bulb) differences of blood lactate and oxygen were used to study cerebral metabolism, while concentrations of S-IOOB were followed as an indicator of brain injury. In a cross-over designed study the gas-flow to the oxygenator and the pump-flow of the extra corporeal circuit were varied in a randomized order to achieve different perfusion pressures and different arterial carbon dioxide (PaCO2) levels. This was done to investigate the influence of PaCO2 on cerebral autoregulation during CPB at moderate hypothermia (27 °C). At a PaCO2 of 29.7+0.9 (mean+SEM) mm Hg (uncorrected for temperature) autoregulation was intact, while MCAv was pressure dependent (p=0.01) at a PaCO2 of 44.6+1.3 mm Hg. PaCO2 and MAP did not influence the calculated cerebral metabolic rate for oxygen (CMRO2), while CMRO2 was temperature dependent (p<0.01). 60 patients with a diagnosis of aortic aneurysm, aortic dissection or a combination of both sere operated during a 5-year period. RCP was used in 20 of the 60 patients during DHCA. Patiens with RCP during DHCA had a lower incidence of stroke postoperatively, 5% vs 28%, (p<0.05). The patterns of MCAv was compared in two groups of children operated with either circulatory arrest (n=12) or low-flow perfusion (n=10) during deep hypothemia. After CPB the diastolic blood flow was absent in 10 of 12 children in the arrest group, in contrast to 1 out of 10 patients in the low-flow group (p<0.05). Cerebral lactate metabolism was studied in two other groups of children undergoing surgery with either DHCA (n=10) or low-flow perfusion (n=7). CHCA resulted in a dignificant release (p<0.05) of lactate from the brain during rewarming and up to6 hours after CPB. Arterial levels of S-100B peaked after CPB (p<0.01) and remained elevated on the first postoperative day (p<0.01). The S-100B levels correlated with the duration of DHCA but not with duration of CPB. The highest correlation was between S-100B on the first postoperative day and the duration of DHCA minus RCP, i.e the period during DHCA with absent CBF (r=0.88, p<0.01). Conclusions: Autoregulation is preserved during hypothermic CPB with low PaCO2 and impaired with high PaCO2. CHCA is followed by impeded cerebral perfusion and a marked release of lactate from the brain, both indirect signs of a possible brain injury. Serum levels of the neurochemical marker S-100B correlated wit the duration of DHCA. RCP decreased the incidence of stroke after DHCA in adults. The use of maintained systemic circulation during deep hypothermic operations is recommended when possible. We advocate RCP when DHCA is needed.
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