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In animals that maintain body temperature within a tight range (homeotherms), thermoregulation represents the balance between heat production (thermogenesis) and heat loss. Thermogenesis occurs as a result of metabolic activity, particularly in skeletal muscle, the kidneys, the brain, the liver and (in infants) adipose tissue. Body heat is lost by conduction, convection, radiation and evaporation (Table 24.1). Cold-induced hypothalamic stimulation activates autonomic, extra-pyramidal, endocrine and behavioural mechanisms to maintain the core temperature.
Most patients with critical cardiac or thoracic conditions will at some stage pass through the cardiothoracic critical care unit. Critical care presents more complex clinical data than any other area of medicine. The new edition of Core Topics in Cardiothoracic Critical Care focuses on the latest practise in the management of patients in cardiothoracic intensive care. The practice of cardiothoracic critical care medicine is constantly evolving, and this new edition reflects the modernized learning styles for trainees. Each chapter includes key learning points as well as sample multiple choice questions and answers to assist in exam preparation. This edition also features updated chapters on ECMO, perioperative management of patients undergoing emergency cardiothoracic surgery, and advanced modes of organ support for patients. This text provides key knowledge in a concise and accessible manner for trainees, clinicians and consultants from specialities and disciplines such as cardiology and anaesthesia, and nursing and physiotherapy.
Cerebrovascular reactivity monitoring has been used to identify the lower limit of pressure autoregulation in adult patients with brain injury. We hypothesise that impaired cerebrovascular reactivity and time spent below the lower limit of autoregulation during cardiopulmonary bypass will result in hypoperfusion injuries to the brain detectable by elevation in serum glial fibrillary acidic protein level.
Methods
We designed a multicentre observational pilot study combining concurrent cerebrovascular reactivity and biomarker monitoring during cardiopulmonary bypass. All children undergoing bypass for CHD were eligible. Autoregulation was monitored with the haemoglobin volume index, a moving correlation coefficient between the mean arterial blood pressure and the near-infrared spectroscopy-based trend of cerebral blood volume. Both haemoglobin volume index and glial fibrillary acidic protein data were analysed by phases of bypass. Each patient’s autoregulation curve was analysed to identify the lower limit of autoregulation and optimal arterial blood pressure.
Results
A total of 57 children had autoregulation and biomarker data for all phases of bypass. The mean baseline haemoglobin volume index was 0.084. Haemoglobin volume index increased with lowering of pressure with 82% demonstrating a lower limit of autoregulation (41±9 mmHg), whereas 100% demonstrated optimal blood pressure (48±11 mmHg). There was a significant association between an individual’s peak autoregulation and biomarker values (p=0.01).
Conclusions
Individual, dynamic non-invasive cerebrovascular reactivity monitoring demonstrated transient periods of impairment related to possible silent brain injury. The association between an impaired autoregulation burden and elevation in the serum brain biomarker may identify brain perfusion risk that could result in injury.