Current opinion in critical care
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Curr Opin Crit Care · Jun 2001
ReviewAssessment of the microcirculatory flow in patients in the intensive care unit.
Various techniques have been used at bedside to assess the microcirculation of critically ill patients, including nailfold videomicroscopy, laser doppler techniques, and orthogonal polarization spectral imaging. Nailfold videomicroscopy was introduced first, but its value may be limited by the extreme sensitivity of nailfold microcirculation to external temperature or vasoconstrictive agents. Laser Doppler techniques can measure gastric or jejunal mucosal blood flow as well as skin and muscle blood flow, but do not take into account blood flow heterogeneity, a major parameter of microcirculation. The recent introduction of orthogonal polarization spectral imaging techniques allows direct visualization of microcirculation in critically ill patients, opening a new area for the investigation of the pathophysiologic processes involved in the hemodynamic alterations of shock states.
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Neuroemergencies are life-threatening situations in which, whatever the cause, common pathologic phenomena result in secondary brain lesions. The goal of critical care management is to stop these self-aggravating processes as soon as possible. Initial resuscitation is devoted to control of the airway and hemodynamic and hydroelectrolytic stabilization. ⋯ Normoventilation, deep sedation, osmotherapy with mannitol or hypertonic saline solutions, and optimization of mean arterial pressure are the basis of management. A purely pressure-driven approach aimed at controlling cerebral perfusion pressure could be potentially harmful, and associated measurement of blood flow velocity with transcranial Doppler and jugular bulb oxygen saturation monitoring allows an approach to cerebral blood flow and metabolism. Outcome can be improved in dangerous situations such as severe brain injuries, cerebral arteriovenous malformation rupture, status epilepticus, and acute hydrocephalus, provided that emergency management could be applied efficiently.
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The brain is sensitive to changes in substrate delivery. In neurologically critically ill patients (e.g., those with head injury, subarachnoid hemorrhage, or stroke), interruption of this supply causes ischemic brain damage and thus impairs the outcome. To prevent, detect, and treat these ischemic events as soon as possible, the cerebral blood flow is continuously monitored, its coupling or not with the consumption of oxygen and so forth, and the detected derangements of normal physiology. ⋯ Transcranial Doppler ultrasonography is a noninvasive technique with the same purpose but with less clinical relevance. The new neuromonitoring technique, microdialysis, is useful for understanding the mechanisms involved in brain ischemia. However, it is clear that the physician who interprets the measurements given by devices and the clinical data (e.g., temperature, glycemia) is still the cornerstone in the management of neurologically critically ill patients.
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Neurologic complications in intensive care occur as the result of critical illness, intensive care therapies and procedures, or medical or surgical conditions; perioperatively; or because of underlying primary neurologic disease. These complications occur at greater frequency and are often unrecognized because critically ill patients are often intubated, sedated, and/or receiving neuromuscular blocking agents. ⋯ Neurologic complications are associated with increased disability, longer hospital stay, and increased mortality. This review focuses on neurologic complications that are the result of critical illnesses and intensive care management.
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Cumulative evidence of potential benefits of electroencephalography (EEG) and evoked potentials in the management of patients with acute cerebral damage has been confirmed. Continuous EEG monitoring is the best method for detecting nonconvulsive seizures and is strongly recommended for the treatment of status epilepticus. Continuously displayed, validated quantitative EEG may facilitate early detection of secondary cerebral insults and may play a decision-making role in the management of patients with head injury, stroke, or subarachnoid hemorrhage. ⋯ Motor evoked potentials may become clinically important both in acutely injured and elective postoperative patients. In the neurointensive care units adequate techniques can be selected to answer targeted clinical questions. The efficacy can be improved by implementing educational projects based on ad hoc training of nurses and neurointensive care specialists.