To determine if learning occurs during general anaesthesia, 72 women undergoing surgery were given postoperative implicit memory tests in which performance could be influenced by auditory information presented during general anaesthesia. Two methods of anaesthesia were used: nitrous oxide and opioids (n = 24) or nitrous oxide and isoflurane (1, 1.3 and 1.5 MAC for n = 12, 24 and 12, respectively). Three tests showed some retention, apparently unconscious, of information presented during anaesthesia: in Behavioural Suggestions tests, patients who were instructed during anaesthesia to touch a particular body part (ear or nose) during later questioning touched the "correct" (suggested) body part longer than the "incorrect" (not suggested) body part during a postoperative interview on the day of surgery (means 2.5 vs 0.2 s); in World Completion tests, patients shown a page containing the first three letters of words and asked to give words beginning with those letters gave more words from a list that had been played during anaesthesia than from a list not played (means 0.48 vs 0.27 words); in Nonsense Word tests, patients who were played different nonsense words between two and 16 times during anaesthesia preferred and guessed more accurately those that had been played most often (16 times) relative to those played less often in subsequent preference and recognition tests (means 56% vs 46% for preference and 62% vs 48% for recognition), while showing no such patterns in additional control tests. Learning did not vary with the method of anaesthesia, as might have been expected if learning was a monotonic function of brain depression. Some information processing functions of the brain evidently continue to function during adequate general anaesthesia.

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To evaluate the reliability of capnography in identifying esophageal intubation in the presence of a carbonated beverage in the stomach, we first investigated the amount of CO2 released from different carbonated beverages and antacids in a simulated stomach; next we measured the end-expired CO2 level during esophageal ventilation with a carbonated beverage in the stomachs of six swine. CO2 levels of approximately 20% were consistently observed in all carbonated beverages. The CO2 levels obtained with sodium bicarbonate, Maalox, and sodium citrate were 19.3%, 2.0%, and 0%, respectively. CO2 waveforms were observed during esophageal ventilation in five of six animals after intragastric administration of a carbonated beverage. An end-expired CO2 level of 2.5% or more was observed in two swine. The highest end-expired CO2 level measured was 5.3%. We conclude that although capnography is convenient and effective, it lacks all the attributes of an ideal monitor for detecting esophageal intubation.