Journal of clinical monitoring
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Multicenter Study Comparative Study Clinical Trial
Transcutaneous PCO2 and PO2: a multicenter study of accuracy.
A multicenter study used 756 samples from 251 patients in 12 institutions to compare arterial (PaO2, PaCO2) with transcutaneous (PsO2, PsCO2) oxygen and carbon dioxide tensions, measured usually at 44 degrees C. Of these samples, 336 were obtained from 116 neonates, 27 from 25 children with cystic fibrosis, and 140 from 40 patients under general anesthesia. Ninety-one patients were between 4 weeks and 18 years of age, 32 were between 18 and 60 years, and 12 were over 60. ⋯ Bias was + 0.2 +/- 2.7 mm Hg when PaCO2 was less than 30 mm Hg (N = 175, NS), 1.0 +/- 3.4 with 30 less than PaCO2 less than 40 (n = 329, p less than 0.001), and + 2.04 +/- 4.00 mm Hg with 40 less than PaCO2 less than 70 (n = 229, p less than 0.001). These data suggest that, using transcutaneous PCO2 monitors with inbuilt temperature correction of 4.5%/degrees C, the skin metabolic offset should be set to 6 mm Hg. The linear regression was PsCO2 = 1.052(PaCO2) - 0.56, Sy.x = 3.92, R = 0.929 (n = 756); and PsCO2 = 1.09(PaCO2) - 1.57, Sy.x = 4.17, R = 0.928 in neonates (n = 336).(ABSTRACT TRUNCATED AT 250 WORDS)
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Comparative Study
Self-tuning adaptive control of induced hypotension in humans: a comparison of isoflurane and sodium nitroprusside.
Induced hypotension is commonly used during surgery to decrease arterial pressure. Sodium nitroprusside and isoflurane are well-known hypotensive agents. The use of self-tuning adaptive control of induced hypotension was assessed with the use of sodium nitroprusside and isoflurane as hypotensive agents. ⋯ This group of patients was compared with 10 similar patients in whom infusions of sodium nitroprusside were controlled manually by an anesthesiologist. Although the results of the two studies varied, no conclusion could be drawn regarding the superiority of either manual or closed-loop control. When manual versus automatic control of isoflurane-induced hypotension was assessed in a similar fashion, the two methods of induction were found to be comparable.
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Numerous medical applications of closed-loop control have been developed over the past 40 years. For the patient breathing system, appropriate sensors are available. ⋯ With the sensors, controllers, and delivery devices developed and tested, it seems likely that closed-loop control will be an integral part of future anesthesia workstations. The convenience and improved stability and response time will be important advantages in future anesthesia delivery systems.
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Infrared analysis can determine exhaled concentrations of the three volatile anesthetics in common use because each absorbs infrared light. Many infrared analyzers use a single source of infrared light at a wavelength of 3.3 microns for measurements of all three agents but cannot identify which agent is in use. Organic gases such as ethanol also absorb infrared light. ⋯ Conversely, with the monitor set for isoflurane, 1 vol% halothane mixed with isoflurane resulted in readings 0.2 vol% too high. In a model simulating alveolar gas, ethanol vapor corresponding to blood alcohol levels of 0.10, 0.30, and 0.50% had a slight but not clinically significant effect on readings for enflurane and isoflurane but increased readings with the halothane setting 3.5 times the corresponding level of blood alcohol. Clinicians can test for an interfering gas such as ethanol before induction by checking the reading in the halothane setting during preoxygenation.
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Anesthesia ventilators with bellows that rise on expiration (standing bellows) are favored over ventilators with bellows that descend during expiration (hanging bellows). Standing bellows will not rise if there is a disconnection, and thus they facilitate detection of disconnections. ⋯ Thus, spirometers that measure tidal volume (VT) in the expiratory limb of the breathing system may falsely indicate an expiratory VT after a disconnection of the breathing system at the Y-piece or the endotracheal tube. Existing low-pressure alarms and capnography alarms provide redundant warning of disconnection, however, should the ventilator continue to deliver small VTs after a disconnection.