Anesthesiology clinics
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Pressure monitoring systems influence the contour of the displayed wave-forms and, on occasion, can introduce significant artifact in the pressure traces. It is important to understand the technical details of invasive pressure monitoring to interpret better the information presented. Careful observation of the arterial pressure waveform can provide information about ventricular function, the arterial system, and ventricular preload. ⋯ CVP monitoring is also used to assess intravascular volume, but this measurement is significantly influenced by ventricular compliance and intrathoracic pressure. Under most clinical circumstances, a trend in CVP values or its change with therapeutic maneuvers is more reliable than a single measurement. Like arterial pressure waveforms, CVP waveform morphology can provide important information about clinical pathophysiology.
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Depth-of-anesthesia monitoring with EEG or EEG combined with mLAER is becoming widely used in anesthesia practice. Evidence shows that this monitoring improves outcome by reducing the incidence of intra-operative awareness while reducing the average amount of anesthesia that is administered, resulting in faster wake-up and recovery, and perhaps reduced nausea and vomiting. As with any monitoring device, there are limitations in the use of the monitors and the anesthesiologist must be able to interpret the data accordingly. ⋯ Several monitoring devices are commercially available. The BIS monitor is the most thoroughly studied and most widely used, but the amount of information about other monitors is growing. In the future, depth-of-anesthesia monitoring will probably help in further refining and better understanding the process of administering anesthesia.
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As outlined in Table 1, the nonthermodilution techniques available to measure cardiac output are noninvasive and clinically applicable to a variable degree. The truly noninvasive monitors are bioimpedance and CO2 re-breathing. The latter, however, requires the patient to be intubated, and the former continues to be evaluated with regard to correlation with the thermodilution standard. ⋯ Pulse contour analysis requires an arterial catheter, and two of the three available monitors require external calibration, while the third has not been validated adequately. The reader can see that all four approaches continue to be refined, with new analysis algorithms and monitors continuing to appear on the market. In the absence of true tissue oxygenation monitors, it seems likely that some or all of these alternatives to thermodilution will play a greater role in the care of patients where measurement of cardiac output is desired.
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Exposures to toxins are prevalent, frequently complicate surgical emergencies, and impact critical care. A fundamental understanding of pathophysiologic principles and management strategies is essential for the anesthesiologist frequently responsible for the acute care of patients who have toxicologic exposures. Given their pervasiveness and ability to confound the clinical presentations in the perioperative or intensive care setting, substances of abuse and asphyxiants warrant particular attention and a high degree of vigilance.
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There is much more to study and learn about prevention of anesthesia complications and how technology may improve the safety and outcome of anesthesia. Large trials have never shown that a specific hemodynamic monitoring technique improves outcome. ⋯ Through all the controversy one thing remains constant: the response to information coming from monitors depends solely on the person administering the anesthesia. Aids to practitioner vigilance probably can never be proved to possess independent benefit, but their role in improving practitioner performance cannot be argued.