Clinical chemistry
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Medical diagnosis and therapeutic monitoring for critical illness require adaptation of laboratory analyses to the bedside. These are greatly helped by the modification of physiological and biochemical data-acquisition techniques to increase the number and accuracy of noninvasive variables that can be obtained from the patient. ⋯ I describe a noninvasive sensor system linked to a computer work-station that functions in a pattern recognition mode to permit classification of patients as to the type and severity of their physiological adaptation. This system can serve as a sophisticated bedside monitor of the severity of the patient's condition, as a guide to therapy.
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Cardiopulmonary monitoring remains the mainstay of intensive-care unit utilization of clinical chemistry resources. Its focus has been on the restoration and maintenance of oxygen transport. ⋯ Some of the clinical chemistry technologies used include analyses for amino acids and polyunsaturated fatty acids, measurement of cytokine concentration and activity, nutritional assessment and monitoring, more sensitive monitors of liver function, and assessment of altered immunity in critically ill patients. Use of these technologies, along with specific support measures, offers new avenues for decreasing infectious complications and reducing mortality and morbidity of patients in intensive-care units.
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Approximately 2 million people die in the United States each year, 80% of them in acute- or chronic-care institutions. Physicians now have at their disposal interventions that can postpone death in almost every instance. ⋯ On the other hand, the fact that medical resources are becoming increasingly expensive and scarce will inevitably lead to rationing. The critical-care physician will be caught in the middle--orchestrating clinical care to balance the interests of individual patients and families against those of the larger community.
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The primary defect that characterizes circulatory shock is acute perfusion failure, in which oxygen metabolism is critically impaired by decreased delivery of oxygen to tissues. Four categories of hemodynamic deficits are described as the basic mechanisms of circulatory shock: hypovolemia, cardiac failure, distributive deficits, and vascular obstruction. Perfusion failure can be identified by the development of lactic acidosis, because anaerobic metabolism is the consequence of the oxygen deficit during circulatory failure. Lactic acidosis at present represents the best single objective measure of the severity of shock.
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The status of conventional monitoring by vital signs and present concepts of invasive monitoring with the balloon-tipped pulmonary artery (Swan-Ganz) catheter are reviewed. Survivors of high-risk general surgery were observed to have cardiac index (CI) values averaging 4.5 L/min.m2, oxygen delivery (DO2) greater than 600 mL/min.m2, and oxygen consumption (VO2) greater than 170 mL/min.m2. By contrast, those who subsequently died during their hospitalization maintained relatively normal CI, DO2, and VO2 values. ⋯ Two-thirds recovered with increased cardiac function, more than one-half had improved perfusion, and paO2 increased in fewer than one-fifth of monitored events. These data provide an information base for criteria needed to develop therapeutic decision rules for noninvasive monitoring systems. When noninvasive data are continuously displayed early in the course of critical illness and high-risk conditions, therapy may be instituted early, while physiological deficits are still minimal and easily reversible.