![]() Graphic illustration of the changes that occurred in measured variables is shown in figure 2. All measured parameters were significantly altered by oxygen desaturation with remifentanil ( table 1). Subjects included four women and six men with a mean age of 29 ± 3 yr, mean weight of 71 ± 9 kg, and mean hemoglobin of 12.9 ± 1.1 g/dl. At 15-min after the discontinuing the infusion, a final arterial blood gas was obtained. If the subject’s TcCO 2 reached 80 mmHg before reaching an oxyhemoglobin saturation of 85%, a confirmatory arterial blood gas was obtained, and this time point was considered the endpoint of maximal desaturation. This time point was labeled time “zero” and pupillary measurements were repeated at 1, 2, 4, 6, 10, and 15 min after reaching this endpoint. As soon as this endpoint was reached, pupillary measurements were taken, arterial blood gases were obtained, the subjects were aroused by a verbal stimulus if they did not arouse spontaneously, and the remifentanil infusion was discontinued. Nasal cannula oxygen (3 l/min) was administered throughout the experiment to provide a more gradual rate of desaturation and potentially better mimic the hospitalized patient. Using the described remifentanil protocol, the oxyhemoglobin saturation fell gradually over time, typically taking 30 min to reach 85%. They were asked to remain quiet and only speak if they had a question or needed assistance. Pupil diameter, pupillary light reflex, and pupil area were measured with an infrared pupillometer (Neuroptics, Inc., Irvine, CA) before opioid administration, at the time of oxygen desaturation, and at 1, 2, 4, 6, 10, and 15-min after recovery.ĭuring the remifentanil infusion, the volunteers were not stimulated by voice, touch, or prompted to breathe. Samples were analyzed using an ABL800 FLEX (Radiometer Medical A/S, Copenhagen, Denmark). Arterial blood gases were sampled from the radial arterial line before opioid administration, at the time of oxygen desaturation, and 15-min after recovery. All continuous monitoring data were recorded using LabVIEW (National Instruments Corporation, Austin, TX). We measured the following parameters: continuous blood pressure and heart rate from the arterial catheter, additional measure of heart rate and rhythm from a 5-lead electrocardiogram (leads II and V5), fingertip oxyhemoglobin saturation (Masimo Corporation, Irvine, CA set on 2-s rapid response), respiratory rate from both an exhaled carbon dioxide tracing (Datex-Ohmeda, Inc., Madison, WI) and from a respiration transducer belt (Biopac Systems, Inc., Goleta, CA), and transcutaneous earlobe carbon dioxide (TcCO 2, TOSCA Linde Medical System, Linde Basel, Switzerland).
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