Journal of clinical anesthesia
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Apneic, anesthetized patients frequently develop airway obstruction or may be disconnected from ventilatory support. The rate of PaCO2 rise is usually assumed to be equal to that of anesthetized humans who are receiving apneic oxygenation. Apneic oxygenation may eliminate CO2 because it requires a continuous O2 flow. ⋯ Piecewise linear approximation yielded a PaCO2 increase of 12 mmHg during the first minute of apnea, and 3.4 mmHg/minute thereafter. These values should be employed when estimating the duration of apnea from PaCO2 change for anesthetized patients who lack ventilatory support. In addition, it appears that the flows of O2 that most earlier investigators used when delivering apneic oxygenation probably did not eliminate significant CO2 quantities.
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The influence of increasing doses of propofol (from 6 to 12 mg/kg/h by continuous infusion) on hypoxic pulmonary vasoconstriction was studied in 10 patients prior to thoracic surgery. All patients were intubated with a left-sided double-lumen endobronchial tube. Initial anesthesia and muscle relaxation were accomplished by administering fentanyl, droperidol, and pancuronium. ⋯ There was no change in any respiratory or circulatory variables except systemic vascular resistance, which decreased significantly immediately after the propofol infusion commenced but returned to control values 15 min later for the rest of the observation period. After reestablishing two-lung ventilation, all variables did not differ from control values. In all patients, the hypoxic pulmonary vasoconstriction reflex was present after institution of one-lung ventilation and was not abolished after administration of propofol in doses from 6 to 12 mg/kg/h.
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During cataract surgery, both the surgeon and the anesthesiologist need access to the patient's face. At our institution we achieved a working compromise by using an oxygen insufflating hoop, which allowed the surgeon access to the eye and a sterile field. The patient's airway was kept free by the hoop, and the patient breathed a high inspired oxygen fraction. ⋯ Reducing the oxygen flow below 10 L/min led to increased retention of CO2 under the drapes. Paper drapes are permeable to CO2, but plastic drapes are impermeable. We did not measure the arterial partial pressure of CO2, and so we do not know whether CO2 accumulation was accompanied by respiratory acidosis.