Anesthesia Monitoring

Use in the Operating Room

The measurement of anesthetic concentrations in exhaled breath is not new to the community of anesthesia clinicians. Anesthesia providers routinely measure the inspiratory and expiratory concentrations of a number of gasses (e.g., oxygen, carbon dioxide) and volatile anesthetics (e.g., isoflurane, sevoflurane, desflurane, nitrous oxide) in exhaled breath using off-the-shelf technology or sensors that are factory mounted into the anesthesia machine. The breath propofol monitor represents an evolution of this practice made possible by technological innovations enabling rapid, point-of-care measurement of other anesthetics with vapor pressures much lower than traditional volatile anesthetics (for example, isoflurane’s vapor pressure is 238 mm Hg @ 20° C). For patients under anesthesia during surgery, anesthesia providers may intravenously administer a bolus of propofol (2-3 ml/kg) for induction and then provide balanced anesthesia with a propofol infusion (75-200 μg/kg/min) co-administered with another agent (e.g., nitrous oxide). The addition of exhaled breath propofol concentrations would allow anesthesia providers to more finely titrate the anesthesia for an individual patient when integrated into a data set of other signs of anesthetic depth.  Moreover, the propofol monitor could give accurate, precise, real-time information about significant medical errors such as possible overdose (e.g., malfunction or mis-programming of a syringe pump) or underdose (e.g., exhausted propofol syringe, infiltrated intravenous catheter) of propofol. In the intraoperative context, a breath propofol monitor would allow anesthesia personnel to provide patients the same level of care whether the patients receive propofol or a typical volatile anesthetic and would enable safer intravenous infusion of propofol.