Heart & lung : the journal of critical care
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As an acute episode of respiratory failure resolves for the patient who is receiving mechanical ventilation, the sometimes difficult task of resuming spontaneous ventilation begins. The resumption of spontaneous ventilation, commonly referred to as weaning, is often difficult for the patient with preexisting lung disease. ⋯ Weaning is conceptualized as a process of three phases: preweaning, weaning, and extubation. Important considerations during each phase are examined.
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A major responsibility of the critical care practitioner is to assure adequate ventilation of the critically ill patient. The traditionally used methods for evaluating ventilation, such as physical examination and measurement of vital signs, are indirect. The most commonly used direct method, measurement of arterial carbon dioxide tension, is invasive and intermittent. ⋯ We review relevant respiratory physiology as a basis for understanding the value of capnography. The technology on which capnography is based is described with emphasis on methods of gas sampling, limitations of capnography, and features available on currently marketed instruments. Representative capnograms are presented and the data interpreted to enable the practitioner to determine when capnography is an appropriate monitor for the critically ill adult.
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Comparative Study
Comparison of thermodilution and transthoracic electrical bioimpedance cardiac outputs.
Current methods of measuring cardiac output require the invasive insertion of a thermodilution catheter with its concomitant risks and complications. We examined the noninvasive method of transthoracic electrical bioimpedance (TEB) in comparison with thermodilution cardiac outputs in a sample of 44 critically ill patients with poor left ventricular function (left ventricular ejection fraction less than 30%) and with either ischemic or idiopathic dilated cardiomyopathy. Dyspnea, mitral regurgitation, tricuspid regurgitation, and difference between real and ideal weight had the most marked effects on the correlation between the two methods, with lesser influence by left ventricular ejection fraction, height, weight, hemoglobin, hematocrit, and aortic regurgitation. TEB and thermodilution cardiac outputs were correlated, at r = 0.51 (p less than 0.00009), but the low reliability and low percentage of TEB readings within 0.5 L/min of thermodilution cardiac outputs (31%) renders TEB inadequate for clinical measurement of cardiac outputs in this patient population.