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In administering general anesthetics three important indicators communicate to the anesthesiologist the minute-to-minute changes that occur in the unconscious patient. Pulse, blood pressure, and respiration are the primary factors, although size of the pupils, position of the eyeball, color of the blood and nail beds, skin temperature, diaphoresis, and muscular relaxation are also important in this physiological appraisal. The character of the respiration, its rate and depth, and the patency of the air passage are probably the most important of the signals on which the anesthesiologist depends for his analysis of the progress of anesthesia. It was felt that an amplification of these important signals would be of considerable aid to anesthesiologists and to nurses and physicians caring for comatose or semicomatose patients, inasmuch as it would warn of vomiting before it occurred; it would obviate the intermittent compression of the corrugated breathing tubes against the ear to detect a
Shane SM, Ashman H, Gitt JS. AMPLIFICATION OF THE SOUNDS OF RESPIRATION OF ANESTHETIZED PATIENTS. JAMA. 1954;156(7):708–709. doi:10.1001/jama.1954.02950070036009a