Cardiovascular effects of nitrous oxide during enflurane anesthesia were studied in 12 healthy, young volunteer subjects ventilated to maintain normal PaC0]. Twelve circulatory variables were measured and 13 more calculated. When nitrogen, 70 per cent, was added to enflurane, 1.86 per cent (1 MAC), or enflurane, 2.93 per cent end-tidal, no change was observed. When nitrous oxide, 70 per cent, was added, only minimal changes were observed. In a second part of the study, enflurane was compared with enflurane-nitrous oxide, 70 per cent, at equipotent levels. The following three variables (in percentages) decreased less in relation to awake control values at 1 MAC enflurane-nitrous oxide-oxygen than at 1 MAC enflurane-oxygen: left ventricular stroke work, -47.2 vs. -55.9; aortic dP/dt, -44.0 vs. -57.1; pressure- pulse product, -26.6 ns. -39.4. Forearm venous compliance decreased more: -26.0 vs. 2.9. The difference between the anesthetic mixtures was much more noticeable at 1.5 MAC, where eight variables (in percentages) decreased less with enfluranenitrous oxide-oxygen than with enflurane-oxygen: cardiac output, -6.9 vs. -22.1; stroke volume, -31.4 ns. -46.0; left ventricular minute work, -32.6 vs. —49.6; left ventricular stroke work, -50.8 vs. -65.8; left ventricular stroke power, -48.2 us. -63.1; ballistocardiogram, -34.5ns. -49.1; aortic dP/dt, -49.7ns. -65.8; pressure-pulse product, -32.3 vs. -42.3. Heart rate increased less when nitrous oxide was included in the mixture: 34.5 ns. 43.6. The lack of response during the addition of nitrous oxide to enflurane-oxygen is contrary to the significant sympathomimetic response seen when nitrous oxide is added to halothane, fluroxene, or diethyl ether. The apparent protection afforded by nitrous oxide at equipotent anesthetic levels is small enough that the main consideration in choosing between the two mixtures should be the concentration of oxygen needed by the patient.
Joseph Thomas Clover (1825–1882) was the leading anaesthetist of Victorian England for more than two decades following the death of John Snow in 1858. His reputation as a clinician, inventor and author is remembered in the United Kingdom through the Clover lectures of the Royal College of Surgeons of England. Anaesthetists of other countries, however, have little knowledge of his remarkable career beyond identifying a celebrated photographic study of Clover anaesthetizing a seated man while palpating his patient's pulse. His life is important to us, however, for his history carries anaesthetic practice from its beginnings in 1846 until 1882, when his achievements were the latest advance exactly a century before our meeting.
The effects of prolonged enflurane and halothane administration on urine-concentrating ability were determined in volunteers by examining their responses to vasopressin before anesthesia and on days 1 and 5 after anesthesia. A significant decrease in maximum urinary osmolality of 264 +/- 34 mOsm/kg (26 per cent of the preanesthetic value) was present on day 1 after enflurane anesthesia, whereas subjects anesthetized with halothane had a significant increase in maximum urinary osmolality of 120 +/- 44 mOsm/kg. Serum inorganic fluoride level peaked at 33.6 muM and remained above 20 muM for approximately 18 hours. Thus, the threshold level for inorganic fluoride nephrotoxicity is lower than previously suspected.
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