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Methods: The authors used high fresh oxygen flow (5 or 10 l/min) through a conventional circle breathing system of an anesthesia machine for 24 or 48 h to produce absorbent drying. Initial studies used 10 l/min oxygen flow with the reservoir bag removed or with the reservoir bag left in place during absorbent drying (this increases resistance to gas flow through the canister). A third investigation evaluated a lower flow rate (5 l/min) for absorbent drying. Water content of the absorbent and temperature were measured. Pigs received a 1.0 (human) minimum alveolar concentration desflurane anesthetic (7.5%) for 240 min using a 1 l/min oxygen flow rate with dried absorbent. Carbon monoxide concentrations in the circuit and carboxyhemoglobin concentrations in the pigs were measured.
Results: Pigs anesthetized with desflurane using Baralyme exposed to 48 h of 10 l/min oxygen flow (reservoir bag removed) had extremely high carboxyhemoglobin concentrations (more than 80%). Circuit carbon monoxide concentrations during desflurane anesthesia using absorbents exposed to 10 l/min oxygen flow (reservoir bag, 24 h) reached peak values of 8,800 to 13,600 ppm, depending on the absorbent used. Carboxyhemoglobin concentrations reached peak values of 73% (Baralyme) and 53% (soda lime). The water content of Baralyme decreased from 12.1 +/- 0.3% (mean +/- SEM) to as low as 1.9 +/- 0.4% at the bottom of the lower canister (oxygen flow direction during drying was from bottom to top). Absorbent temperatures in the bottom canister increased to temperatures as high as 50 [degree sign] Celsius. With the reservoir bag in place during drying (10 l/min oxygen flow), water removal from Baralyme was insufficient to produce carbon monoxide (lowest water content = 5.5%). Use of 5 l/min oxygen flow (reservoir bag removed) for 24 h did not reduce water content sufficiently to produce carbon dioxide with desflurane. 相似文献
Methods: Six healthy volunteers were anesthetized with desflurane and nitrous oxide. The cooling methods were 1) circulating water (5 [degree sign] Celsius, full-length mattress and cover), 2) forced air (10 [degree sign] Celsius, full-length cover), 3) gastric lavage (500 ml iced water every 10 min), 4) bladder lavage (300 ml iced Ringer's solution every 10 min), and 5) ice-water immersion. Each method was applied for 40 min or until the volunteers' core temperatures approached 34 [degree sign] Celsius. The volunteers were rewarmed to normothermia between treatments. Core cooling rates were evaluated using linear regression.
Results: The first volunteer developed abdominal cramping and diarrhea after gastric lavage. Consequently, the technique was not again attempted. Bladder lavage increased heat loss 10 [nearly =] 10 W and decreased core temperature 0.8 +/- 0.3 [degree sign] Celsius/h (r2 = 0.99 +/- 0.002; means +/- SD). Forced-air and circulating-water cooling comparably increased heat flux, [nearly =] 170 W. Consequently, core cooling rates were similar during the two treatments at 1.7 +/- 0.5 [degree sign] Celsius/h (r2 = 0.99 +/- 0.001) and 1.6 +/- 1.1 [degree sign] Celsius/h (r2 = 0.98 +/- 0.02), respectively. Immersion in an ice water slurry increased heat loss [nearly =] 600-800 W and decreased core temperature 9.7 +/- 4.4 [degree sign] Celsius/h (r sup 2 = 0.98 +/- 0.01). Immersion cooling was associated with an afterdrop of [nearly =] 2 [degree sign] Celsius. 相似文献
Methods: We investigated the actions of halothane on 50-200 micro Meter branches of the rat mesenteric artery that were cannulated and studied in vitro. The vessels were pressurized to 60 mmHg, and vascular dimensions were continuously monitored using a computer-based real-time image analysis system. The vessel bath was perfused with HCO3 -buffered saline (37 degrees Celsius) equilibrated with 95% Oxygen2 /5% CO2 (plus/minus halothane). The vascular endothelium was mechanically removed before cannulation in some vessels.
Results: In unstimulated vessels, halothane had a concentration-dependent vasoconstricting action (EC50 = 0.45 mM = 1.5 vol% at 37 degrees Celsius) that was largely transient and was similar to that produced by caffeine. Both halothane and caffeine constrictions were unaffected by bath [Calcium2+], nifedipine (1 micro Meter) or Cadmium2+ (100 micro Meter) and were abolished by ryanodine (10 micro Meter). In addition, caffeine responses were attenuated by halothane in a concentration-dependent manner (EC50 - 1.6 mM). In vessels preconstricted with KCl (40 mM) or phenylephrine (10 sup -6 M), halothane produced transient constriction followed by concentration-dependent vasodilation. Ryanodine, which abolished halothane constrictions, had little effect on the amplitude of KCl- or phenylephrine-induced constrictions or the vasodilating action of halothane. Removal of the endothelium likewise had little effect on the vasoconstricting or the vasodilating actions of halothane in unstimulated, KCl- or phenylephrine-constricted vessels. Halothane completely relaxed KCl and phenylephrine constrictions with EC50 values of 0.36 mM (1.2% at 37 degrees Celsius) and 0.75 mM (2.5%), respectively, in intact vessels before ryanodine; 0.25 mM (0.8%) and 0.59 mM (1.9%) in intact vessels after ryanodine; and 0.52 mM (1.7%) and 0.67 mM (2.2%) in endothelium-denuded vessels. 相似文献