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Query: UMLS:C0020672 (hypothermia)
 17,327 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We evaluated cerebral metabolism during retrograde cerebral perfusion (RCP) and circulatory arrest during profound hypothermia, and also investigated the effects of perfusion pressure on RCP. Twenty-four adult mongrel dogs were placed on cardiopulmonary bypass and cooled to a nasopharyngeal temperature of 20 degrees C. At this temperature, hypothermic circulatory arrest (HCA; n = 6), and RCP with a perfusion pressure of 10 mmHg (RCP10; n = 6), 20 mmHg (RCP20; n = 6), and 30 mmHg (RCP30; n = 6) were carried out for 60 minutes. RCP was performed with oxygenated blood via the bilateral maxillary veins, and the retrograde flow rate was regulated to maintain a mean perfusion pressure of 10, 20, or 30 mmHg in the external jugular vein. At 60 minutes of RCP, we measured nasopharyngeal temperature; regional cerebral blood flow (rCBF); cerebral oxygen consumption, carbon dioxide excretion, and excess lactate; cerebral tissue adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine monophosphate (AMP) and energy charge; and cerebral tissue water content. In the RCP10 group, there was excess cerebral lactate, and ATP and energy charge were low. In the RCP30 group, the water content of cerebral tissue was significantly higher than in other groups. In the RCP20 group, temperature was maintained in a narrow range, oxygen consumption and carbon dioxide excretion could be observed, there was no excess lactate, and ATP and energy charge were significantly higher than in the HCA group. In conclusion, RCP can provide adequate metabolic support for the brain during circulatory arrest, and a perfusion pressure of 20 mmHg is most appropriate for RCP.
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PMID:Optimal perfusion pressure for experimental retrograde cerebral perfusion. 799 97

In a prospective study, we analyzed the intraoperative electroencephalographic (EEG) changes during open heart surgery with deep hypothermia in 66 infants aged 6 months or younger, 70% of whom were neonates. Suppression of amplitude and continuity at the nadir of temperature reduction and following rewarming, and the appearance of periodic paroxysmal activity, was compared with neurologic abnormalities before and following operation, patient characteristics, and operation variables. EEG changes disclosed no relationship to abnormal neurologic findings, age at operation, type of anesthetic, duration of cardiopulmonary bypass (CPB), duration of low-flow CPB or cooling, temperature at circulatory arrest (HCA) or low flow, or nasopharyngeal-venous return temperature differences. EEG suppression following rewarming was associated with the use of thiopentone and duration of HCA. Use of thiopentone was also related to decreased levels of alertness at the end of the first postoperative week. We could not demonstrate any association between operation variables, including duration of HCA, and postoperative neurologic findings which include abnormalities of tone, alertness, seizures, generalized pyramidal signs, choreoathetosis, and hemiparesis. Severe hypotonia before operation was associated with continuing severe hypotonia during the postoperative period. EEG changes during cooling for open heart surgery on infants appear to be physiologic, and these plus EEG suppression following HCA or low-flow CPB are not useful predictors of early neurologic morbidity.
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PMID:EEG changes during open heart surgery on infants aged 6 months or less: relationship to early neurologic morbidity. 802 60

We evaluated cerebral metabolism during retrograde cerebral perfusion (RCP) and circulatory arrest under profound hypothermia, and also investigated the effect of pulsatile flow on RCP. Eighteen adult mongrel dogs were placed on cardiopulmonary bypass and were cooled to a nasopharyngeal temperature of 20 degrees C. At this temperature, hypothermic circulatory arrest (HCA; n = 6), non-pulsatile RCP (NP-RCP; n = 6), and pulsatile RCP (P-RCP; n = 6) were performed for 60 minutes. Retrograde cerebral perfusion was performed via the bilateral internal maxillary veins, and retrograde flow rate was regulated to maintain a mean perfusion pressure of 20 mmHg in the external jugular vein. During RCP, the temperature was maintained in a narrow range, oxygen consumption and carbon dioxide excretion could be observed, the excess lactate was maintained at a negative value, and cerebral tissue ATP concentration was significantly higher than in the HCA group. The cerebral tissue water content was significantly lower in the P-RCP group than in the NP-RCP group. These findings suggest that hypothermia of the central nervous system, the supply of oxygen, the excretion of metabolites, aerobic metabolism, and the cerebral ATP level were maintained by RCP. In conclusion, RCP may possibly provide adequate metabolic support for the brain during total circulatory arrest, and pulsatile flow appears to reduce cerebral edema when compared with non-pulsatile flow in dogs.
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PMID:Cerebral metabolism and effects of pulsatile flow during retrograde cerebral perfusion. 830 Jul 12

Optimal use of hypothermic circulatory arrest during aortic surgery requires understanding of its physiology. Research in laboratory animals and clinical observations have now documented that considerable residual cerebral metabolism remains with cooling to levels of 15-18 degrees C, especially if cooling intervals are short, reflected by persistent jugular venous desaturation. Cooling should be continued to below 15 degrees C if the duration of HCA is expected to exceed 20 minutes, and continued until jugular venous saturations exceed 95%. There is considerable laboratory evidence that even short durations of HCA are followed by a prolonged interval of increased cerebral vascular resistance during which cerebral metabolism is maintained at normal levels by markedly increased oxygen extraction. Clinical observations have now confirmed that considerable jugular venous desaturation is present in patients following HCA: it is more pronounced with prolonged HCA, and is still present as late as six hours after the start of rewarming. This reinforces the concept of a prolonged postoperative vulnerable interval following HCA, during which any compromise in oxygen delivery has the potential for producing cerebral injury. Several adjunctive measures have been shown to improve outcome following HCA. The simplest and most important is topical hypothermia: packing the head in ice during the interval of HCA. Retrograde cerebral perfusion (RCP) has also been shown to improve EEG recovery as well as histological and behavioral outcome in laboratory animals following prolonged HCA, but some of its effect may be secondary to its efficacy in keeping the brain cold, since RCP provides very low rates of flow and supports metabolism at a much lower level than antegrade perfusion at the same temperature. But despite the clear superiority of antegrade perfusion, and the documentation of some benefits of RCP in laboratory measures of cerebral protection, clinical results using RCP and ACP have not yet demonstrated the superiority of these methods over use of HCA alone, perhaps because these modalities are usually employed in patients with unusually high risk of neurological injury: those with dissection or with clot or atheroma in the aorta. Nevertheless, recent years have seen considerable reduction in mortality following aortic surgery, especially in older patients, and a trend toward a lower incidence of permanent neurologic dysfunction. The presence of preoperative rupture or hemodynamic compromise, and of clot or atheroma in the aorta, remain the most significant risk factors both for death and occurrence of stroke.
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PMID:Use of hypothermic circulatory arrest for cerebral protection during aortic surgery. 927 61

With the current available information, the use of RCP for cerebral protection during HCA in the clinical setting will continue to be debated. Laboratory evaluation in a variety of animal models has thus far produced conflicting results and a variety of mixed information. Accumulating clinical evidence has confirmed that RCP is safe, provided flow rates and central venous (intracerebral) pressures are maintained at relatively low levels. The use of RCP is clinically safe and does not incur additional expense. In the event that the only clinical benefits of RCP are the maintenance of cerebral hypothermia and the flushing of air and particulate debris from the arterial circulation, consequently reducing the risk of embolism, then the continued use and investigation of RCP techniques is justified.
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PMID:Retrograde cerebral perfusion is an effective means of neural support during deep hypothermic circulatory arrest. 930 19

Renal preservation at for 24 hours at hypothermia was studied in a rabbit model after flush cooling with sucrose-based solution (SBS), compared with a standard preservation solution (in this case, Marshall's Hypertonic Citrate solution - HCA). Polyethylene glycol supplementation to SBS (SBS-PEG) was also investigated. Renal function was measured by plasma creatinine assays during 1 months post transplantation, and pathology of the explanted kidneys was undertaken. Results showed that survival at 28 days was similar in all groups, (HCA - 3 out of 6; SBS - 2 out of 5; SBS-PEG - 3 out of 5), and there were no differences in recovery of plasma creatinine values. Histopathological evaluation of the grafts indicated that SBS preservation resulted in more severe damage after transplantation (P less than 0.05 in both corticomedullary region and medulla compared to HCA), whilst addition of PEG reduced the damage score to that seen with HCA. SBS can be used as a simple, inexpensive preservation solution for kidney cold storage provided that PEG is used as an additional colloid.
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PMID:Hypothermic renal preservation with a sucrose/ polyethylene glycol solution in a rabbit renal transplant model. 1679 44

Cerebral protection strategies in aortic surgery have undergone significant evolution over the years, but its tenets remain rooted in maintenance of hypothermia and cerebral perfusion to limit adverse neurologic outcomes. While deep hypothermic circulatory arrest alone remains a viable approach in many instances, the need for prolonged duration of circulatory arrest and increasing case complexity have driven the utilization of adjunctive cerebral perfusion strategies. In this review, we present the most recent studies published on this topic over the last few years investigating the efficacy of deep hypothermic circulatory arrest, retrograde cerebral perfusion, and unilateral and bilateral antegrade cerebral perfusion, as well as the emerging trend toward mild and moderate HCA temperatures. We highlight the ongoing controversies in the field that underscore the need for large-scale randomized trials using well-defined neurologic endpoints to optimize evidence-based practice in cerebral protection.
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PMID:Optimal Cerebral Protection Strategies in Aortic Surgery. 3063 77