New horizons (Baltimore, Md.)
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The aim of the present study was to explore methods, concepts, and techniques that provide recognition of circulatory deficiencies at the earliest possible time in the patient's illness. We used both the standard invasive pulmonary artery thermodilution catheter and noninvasive hemodynamic monitoring systems consisting of a new bioimpedance cardiac output device, pulse oximetry, transcutaneous oxygen (PtCO2) and carbon dioxide tensions as well as the transcutaneous oxygen tension/fraction of inspired oxygen ratio (PtCO2/FIO2). These three noninvasive systems were used to evaluate cardiac function, pulmonary function, and tissue perfusion, respectively. ⋯ We found that hypotensive shock usually was preceded by episodes of high flow followed by low flow and inadequate tissue perfusion indicated by reduced PtCO2; this frequent pattern was modified by associated co-morbid conditions, especially hypovolemia, limited cardiac reserve capacity, age, hypertensive states, and increased body metabolism from infection, trauma, stress, exercise, temperature, and endocrine disorders. Reduced pulmonary function occurred in 18% of emergency patients; these were usually patients with thoracic trauma, severe hypovolemia, head injuries, chronic obstructive pulmonary disease, asthma, drug overdose, and central nervous system failure (massive stroke and coma). We concluded that noninvasive measurements identify early circulatory problems reliably and provide objective criteria for physiologic analysis as well as for definition of therapeutic goals and titration of therapy.
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Multicenter Study
Application of total body bioimpedance to the critically ill patient. Brazilian Group for Bioimpedance Study.
In the past several years, considerable interest has developed in the study of total body bioimpedance analysis (TBBIA) and body composition in healthy subjects. This simple and noninvasive technique uses derived and regression equations to validate data comparative to the gold standards of total body water determination and body composition. However, this approach has not proved to be of value in the critically ill patient with distorted body composition under the effects of multiple drugs and interventions. ⋯ Some authors have demonstrated that this relation Xc/R is highly correlated with mortality and could be used for the staging of critically ill patients throughout their stay in the ICU. The role of TBBIA as a simple and noninvasive technique, and its implications for the management of critically ill patients are presented and discussed. Areas for future investigations, with single and multiple frequency, have the potential to clarify many aspects of this emergent technology at the bedside.
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Patients undergoing prolonged, complex oncological surgery are at increased risk of developing the adult respiratory distress syndrome (ARDS) and other organ failures. Our hypothesis is that maintaining adequate tissue perfusion and oxygenation may prevent tissue hypoxia and acidosis in pulmonary, peripheral, and splanchnic microcirculations. Experimental evidence suggests that the hypoxic, acidotic endothelium stimulates the release of cytokines, kinins, and other mediators. ⋯ Nitroglycerin and fluids were used to maintain tissue perfusion and prevent tissue hypoxia as reflected by transcutaneous oxygen tension values. In 155 high-risk patients, none developed ARDS. We conclude that maintenance of tissue perfusion and oxygenation in high-risk surgical patients decreases the incidence of ARDS.
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Near-infrared spectroscopy (NIRS) is a relatively new tool that allows continuous noninvasive monitoring of in vivo oxygenation in selected tissues such as muscle and brain. Since hemoglobin, myoglobin, and cytochrome c oxidase are the only biological compounds to exhibit variable absorption of near-infrared (NIR) light in response to changes in oxygen availability, NIRS can determine changes in tissue oxygenation. ⋯ As a comprehensive monitor of regional oxygen metabolism, NIRS has been applied in certain clinical and research settings. Despite technical limitations and the lack of definite "gold standards" to allow validation of results, NIRS remains a promising technology with applications in both the critical care environment and the research laboratory studying mechanisms of oxygen metabolism.
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Burn resuscitation has been performed predominantly by means of the Parkland formula for the past 25 years. Normalization of heart rate, blood pressure, and production of 1 mL/kg/hr of urine were proposed as suitable guides to resuscitation. Recently, it has become apparent that the standard circulatory criteria of fluid replacement adequacy are too inaccurate to produce optimal hemodynamic end points. ⋯ Elderly burn patients were resuscitated at lower end points than younger individuals because of volume intolerance. Inability to be aggressively resuscitated results in twice the mortality in burn-injured elderly patients. These experiences indicate that burn resuscitation as currently practiced with existing formulas produces inadequate circulatory responses, and both survival and organ function can be improved by maximizing circulatory end points.