Articles: closed-circuit-anesthesia.
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Anesthesia and analgesia · Dec 1997
Dehydration of Baralyme increases compound A resulting from sevoflurane degradation in a standard anesthetic circuit used to anesthetize swine.
In a model anesthetic circuit, dehydration of Baralyme brand carbon dioxide absorbent increases degradation of sevoflurane to CF2=C(CF3)OCH2F, a nephrotoxic vinyl ether called Compound A. In the present study, we quantified this increase using "conditioned" Baralyme in a circle absorbent system to deliver sevoflurane anesthesia to swine. Mimicking continuing oxygen delivery for 2 days after completion of an anesthetic, we directed a conditioning fresh gas flow of 5 L/min retrograde through fresh absorbent in situ in a standard absorbent system for 40 h. The conditioned absorbent was subsequently used (without mixing of the granules) in a standard anesthetic circuit to deliver sevoflurane to swine weighing 78 +/- 2 kg. The initial inflow rate of fresh gas flow was set at 10 L/min with the vaporizer at 8% to achieve the target end-tidal concentration of 3.0%-3.2% sevoflurane in approximately 20 min. The flow was later decreased to 2 L/min, and the vaporizer concentration was decreased to sustain the 3.0%-3.2% value for a total of 2 h (three pigs) or 4 h (eight pigs). Inspired Compound A increased over the first 30 +/- 60 min to a peak concentration of 357 +/- 49 ppm (mean +/- SD), slowly decreasing thereafter to 74 +/- 6 ppm at 4 h. The average concentration over 2 h was 208 +/- 25 ppm, and the average concentration over 4 h was 153 +/- 19 ppm. Pigs were killed 1 or 4 days after anesthesia. The kidneys from pigs anesthetized for both 2 h and 4 h showed mild inflammation but little or no tubular necrosis. These results suggest that dehydration of Baralyme may produce concentrations of Compound A that would have nephrotoxic effects in humans in a shorter time than would be the case with normally hydrated Baralyme. ⋯ The vapor known as Compound A can injure the kidney. Dehydration of Baralyme, a standard absorbent of carbon dioxide in inhaled anesthetic delivery systems, can cause a 5- to 10-fold increase in Compound A concentrations produced from the inhaled anesthetic, sevoflurane, given at anesthetizing concentrations in a conventional anesthetic system.
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Low flow anesthesia (LFA) using a fresh gas flow (FGF) of 600 ml.min-1 with oxygen and nitrous oxide flow each set at 300 ml.min-1, and dial setting of sevoflurane 3% was administered to 30 patients for a duration of 5 hours. There were no problems such as unsuitable concentrations of nitrous oxide and sevoflurane in inspired and expired gases or low FIO2 below 0.3 during anesthesia in 15 patients of group A. Their body weight was 53 +/- 5 kg. ⋯ It was suggested that in group A the FGF per body weight was suitable; in group B though oxygen flow was larger than oxygen consumption, hypoxia occurred due to saturation of nitrous oxide in the body; and in group C the FGF was insufficient. The compound A was detected in the breathing circuit, and the concentration was around 20 ppm and it did not depend on the duration of LFA. It was concluded in this study that LFA using the FGF of 600 ml.min-1 with setting of 3% sevoflurane, 50% oxygen and nitrous oxide, could be performed safely without risks such as hypoxia and severe delay of induction for patients weighing 53 +/- 5 kg for a duration of 5 hours.
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Randomized Controlled Trial Comparative Study Clinical Trial
Laryngeal mask airway and uncuffed tracheal tubes are equally effective for low flow or closed system anaesthesia in children.
Low flow and closed system anaesthesia have considerable advantages in economy, limited atmospheric pollution, and maintenance of humidification and temperature. To benefit from these techniques leakage from the breathing system should be as low as possible. The sealing of the airway is crucial to ensure this. ⋯ Ventilation was adequate in all cases with both devices. Loss of gas from the breathing system was less than 100 ml min-1 in 13 (87%) patients in the LMA and in 12 (80%) patients in the TT group, with a maximum of approximately 700 ml min-1 in the TT and approximately 350 ml min-1 in the LMA group. We conclude that the airway sealing with both devices was tight enough to perform low flow or closed system anaesthesia in paediatric patients aged 2-6 yr.
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Anesthesia and analgesia · Sep 1997
Letter Case ReportsAn uncommon leak in the anesthesia breathing circuit.
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Randomized Controlled Trial Clinical Trial
Quantitative study of Lowe's square-root-of-time method of closed-system anaesthesia.
Intermittent injection of liquid anaesthetic into a closed breathing system is particularly suitable in countries with limited resources. A method of calculating appropriate times and magnitudes of the injected doses was described by Lowe but the method has never been assessed rigorously. Such an assessment was the purpose of this study. ⋯ However, end-tidal partial pressure (just before each dose) stabilized at a steady level of only 0.97, 0.42 and 0.77 MAC for halothane, enflurane and isoflurane, respectively. Recovery from enflurane was much more rapid than that from the other agents but no patient admitted to any dreams. We conclude that the rate of uptake of anaesthetic declines more slowly than predicted and that the patients receiving enflurane were less deeply anaesthetized because the greater hypotensive effect of enflurane led to the use of smaller doses.