Critical care clinics
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Arterial blood gas (ABG) measurements are one of the most frequently requested laboratory examinations in critically ill patients. ABGs include measurement of pHa, PaCO2, PaO2, and oxyhemoglobin saturation. These measurements allow for assessment of the nature, progression, and severity of metabolic and respiratory disturbances.
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Pulmonary capillary pressure (Pcap) is the true edema-forming pressure within the pulmonary vascular bed. Pulmonary artery occlusion pressure has long been used to approximate Pcap. These two pressures may not always be well correlated, which has significant implications for fluid resuscitation and the evolution of pulmonary edema. This article reviews the technique for bedside measurement of Pcap.
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NIRS is an attractive monitoring technology because it is a noninvasive, real-time, repeatable method that allows for regional assessment of the adequacy of tissue oxygenation. It is able to evaluate the oxygenation state of hemoglobin in tissue and redox state of cyt a1,a3, which reflects the overall activity of oxidative metabolism in the cells. The primary technical limitation of current technology is the inability to measure accurately the optical pathlength online, limiting the ability to quantify precisely concentrations of oxygen-dependent chromophores. Even with this limitation, NIRS can provide unique and valuable in vivo metabolic information without invasive intervention.
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Critical care clinics · Oct 1996
ReviewPulmonary artery catheters in the critically ill. An overview using the methodology of evidence-based medicine.
Evidence-based approaches to assessing the clinical literature are used increasingly in issues relating to critical care medicine. As we discussed previously, this approach attempts to provide a logical and convenient framework from which the quality and relevance of clinical studies may be assessed in an unbiased manner. An evidence-based approach also allows the reader to differentiate between solid evidence and evidence that is based on a presumed mechanism, standard practice, or conventional wisdom. ⋯ However, what this exercise has taught us is that there is little objective evidence to support this conclusion. The challenge to critical care practitioners is not only to apply the evidence-based processes more frequently to our environment but also to use the information to separate out clearly what is fact versus opinion. Where there is little evidence to support a particular clinical practice, as we have demonstrated with the PAC review earlier, the challenge to the clinician should be the design and conduct of clinical trials clarifying debate between opinion and evidence.
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Critical care clinics · Oct 1996
ReviewDetermination of oxygen delivery and consumption versus cardiac index and oxygen extraction ratio.
Measuring cardiac output without knowledge of the oxygen extraction by the tissues is of limited value. Instead of calculating oxygen consumption and oxygen delivery, a diagram relating cardiac index to the oxygen extraction ratio is proposed to interpret hemodynamic data at the bedside. This diagram is particularly helpful in interpreting cardiac index in the presence of changes in hemoglobin or oxygen demands and in evaluating the effects of therapy.