The Annals of thoracic surgery
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Profound hypothermic circulatory arrest and profound hypothermia with continuous low-flow cardiopulmonary bypass are used to facilitate repair of complex congenital heart lesions. Extended periods of profound hypothermic arrest may impair cerebral function and metabolism and produce ischemic brain injury. Low-flow bypass has been advocated as preferable to profound hypothermic arrest with respect to neurologic outcome as it maintains continuous cerebral circulation during repair of heart defects. ⋯ Transcranial Doppler sonography has enabled the noninvasive study of cerebral perfusion during operations using either circulatory arrest or low-flow bypass. Although these studies have demonstrated the presence of cerebral perfusion at low perfusion pressures, evidence exists to suggest that cerebral perfusion abruptly ceases at cerebral perfusion pressures of 7 to 9 mm Hg and is unrelated to pump flow rate. Transcranial Doppler sonography is a useful tool for monitoring cerebral perfusion during low-flow bypass, and future studies with this modality may help to develop improved modes of cerebral protection during repair of complex congenital heart lesions.
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We describe a new noninvasive method using near-infrared spectroscopy for monitoring cerebral hemodynamics during cardiopulmonary bypass in children. All patients were undergoing open heart operations for repair of congenital heart defects. Standardized anesthesia, an alpha-stat method of blood gas management, and nonpulsatile flow were used in all cases. ⋯ During hypothermic bypass (25 degrees C), CBVR was significantly reduced to 0.05 +/- 0.02 mL x 100 g-1 x kPa-1. In addition, there were three values at mean arterial pressure of lower than 40 mm Hg in which CBVR was negative (-0.04 +/- 0.01 mL x 100 g-1 x kPa-1). We conclude that near-infrared spectroscopy is useful for the noninvasive investigation of cerebral hemodynamics during cardiopulmonary bypass.
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Comparative Study
Cerebral lactate release after circulatory arrest but not after low flow in pediatric heart operations.
Arteriovenous (jugular bulb) differences in blood lactate were followed throughout the procedure and until 18 hours postoperatively in 17 children undergoing congenital heart operations during profound hypothermia. Transcranial Doppler sonography was used to monitor changes in blood flow velocity in the middle cerebral artery. Ten children had a period of total circulatory arrest (39 +/- 6 minutes) during profound hypothermia (arrest group). ⋯ Differences in blood lactate level were significantly less than zero (p < 0.05) from the start of rewarming until 3 hours after the end of cardiopulmonary bypass in the arrest group, whereas differences in blood lactate level remained close to zero in the low-flow group. We conclude that circulatory arrest during profound hypothermia is followed by a period with release of lactate from the brain, indicating anaerobic cerebral metabolism and possibly disturbed cerebral aerobic metabolism. This study argues for the avoidance of circulatory arrest whenever possible.
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Practice Guideline Guideline
Practice guidelines in cardiothoracic surgery. Council of the Society of Thoracic Surgeons.
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We investigated the effects of pulsatile flow for retrograde cerebral perfusion under profound hypothermia. Total cardiopulmonary bypass was carried out in adult mongrel dogs to induce hypothermia. One hour of total circulatory arrest was then performed at 20 degrees C in the control group of 6 dogs. ⋯ As for cerebral flow and adenosine triphosphate content, no significant differences could be found between the groups perfused retrogradely with pulsatile or with non-pulsatile flow. Values were always higher, nonetheless, in the groups perfused with pulsatile flow. We conclude that retrograde cerebral perfusion with pulsatile flow, when used under conditions of profound hypothermia, possesses more cerebroprotective effects than does non-pulsatile perfusion or circulatory arrest.