Anesthesiology
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The authors report on the appearance of misleading square wave "phantom" capnograph tracings for approximately 3 min after disconnection from the Siemens Servo 900c ventilator. A series of experiments are described to examine the mechanism of this phenomenon. ⋯ After accidental disconnection of the patient from the breathing system, or after accidental extubation of the trachea, the "phantom" capnograph is likely to confuse even an experienced anesthesiologist into the mistaken belief that his rapidly deteriorating patient is being ventilated adequately. Several potential mechanisms to eliminate this phenomenon are outlined, including the avoidance of zero positive end-expiratory pressure. "Phantom" capnography provides an illustration of the dangers of using monitoring techniques, however reliable, as a substitute for vigilant clinical observation.
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The influence of anesthetic agents on the infarction process in the ischemic myocardium is unclear. This study evaluated the effects of three intravenous and three inhalational anesthetic agents on myocardial infarction within a quantified ischemic risk zone in rabbit hearts subjected to a standardized regional ischemia-reperfusion insult. ⋯ The volatile anesthetics tested protected the ischemic rabbit heart from infarction, in contrast to the three intravenous agents tested. Protection was independent of the hypotensive effect of the inhalational agents because halothane also protected isolated hearts, in which changing vascular tone is not an issue and coronary perfusion pressure is constant. Cardioprotection by volatile anesthetics depended on both adenosine receptors and protein kinase C, and thus is similar to the mechanism of protection seen with ischemic preconditioning.