[Low flow anesthesia at a fresh gas flow of 10 ml.kg-1.min-1 for hours using time-cycled ventilator].
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Low flow anesthesia (LFA) at a fresh gas flow (FGF) level of 10 ml.kg-1.min-1 with oxygen flow set at 0.5 ml.kg-1.min-1: 0.5 ml.kg-1.min-1 nitrous oxide and 3% isoflurane was performed using time-cycled ventilator on 10 patients of ASA class I or II, with age of 55 +/- 13 (mean +/- SD) years and body weight of 55 +/- 10 kg for 5 h. Excessive anesthetic gases from the anesthesia gas monitor were led to an expiratory breathing tube. After rapid induction and tracheal intubation, denitrogenation was performed for about 5 min using a 100% oxygen flow of 6 l.min-1 before LFA. The inspired/expired oxygen concentration decreased gradually from 96 +/- 2%/90 +/- 2% at beginning of LFA to 42 +/- 3%/37 +/- 4% at 5 h. The operation was started after 29 +/- 10 min of beginning of LFA. The nitrous oxide concentration reached 37 +/- 4%/35 +/- 4% at the beginning of operation and further increased to 55 +/- 3%/53 +/- 3% at 5 h. The isoflurane concentration reached 1.0 +/- 0.1%/0.8 +/- 0.1% at the beginning of operation and further increased to 1.2 +/- 0.1%/1.0 +/- 0.1% at 5 h. The anesthetic potency was 1.2 +/- 0.1 MAC/1.0 +/- 0.2 MAC at the beginning of operation. The isoflurane vaporizer setting was changed only once in two cases from 3% to 2% exceeding 1.5% in inspired concentration. There was no need to change the flow of oxygen and nitrous oxide for 5 hrs. No SpO2 lower than 95% was observed during this study. This method is a clinically safe, easily applicable anesthesia method and used the smallest FGF reported in LFA without occurrence of low FIO2.Keywords:
Fresh gas flow
Vaporizer
Nitrous oxide
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Background: We reported a 1-1-12 wash-in scheme for desflurane-nitrous oxide (N 2 O) low flow anesthesia that is simple, rapid, and predictable. There remain some situations where N 2 O should be avoided, which limits the generalizability of this wash-in scheme. The objective of our study was to determine the performance of this scheme in contexts where N 2 O is not used. Methods: We recruited 106 patients scheduled for elective surgery under general anesthesia. After induction and intubation, wash-in was started with a fresh gas flow of air:O 2 1:1 L/min and a vaporizer concentration of desflurane of 12%. Controlled ventilation was then adjusted to maintain P A CO 2 at 30–35 mmHg. Results: The alveolar concentration of desflurane (F A D) rose rapidly from 0% to 6% in 4 minutes in the same pattern as observed in our previous study in which N 2 O was used. An F A D of 7% was achieved in 6 minutes. An F A D of 1% to 7% occurred at 0.6, 1, 1.5, 2, 3, 4, and 6 minutes. The rise in heart rate during wash-in was statistically significant, although not clinically so. There was a slight but statistically significant decrease in blood pressure, but this had no clinical significance. Conclusion: Performance of the 1-1-12 wash-in scheme is independent of the use of N 2 O. Respective F A Ds of 1%, 2%, 3%, 4%, 5%, 6%, and 7% can be expected at 0.6, 1, 1.5, 2, 3, 4, and 6 minutes. Keywords: low flow anesthesia, wash-in, desflurane, air
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A computer program that models anesthetic uptake and distribution has been in use in our department for 20 yr as a teaching tool. New anesthesia machines that electronically measure fresh gas flow rates and vaporizer settings allowed us to assess the performance of this model during clinical anesthesia. Gas flow, vaporizer settings, and end-tidal concentrations were collected from the anesthesia machine (Datex S/5 ADU) at 10-s intervals during 30 elective anesthetics. These were entered into the uptake model. Expired anesthetic vapor concentrations were calculated and compared with actual values as measured by the patient monitor (Datex AS/3). Sevoflurane was used in 16 patients and isoflurane in 14 patients. For all patients, the median performance error was -0.24%, the median absolute performance error was 13.7%, divergence was 2.3%/h, and wobble was 3.1%. There was no significant difference between sevoflurane and isoflurane. This model predicted expired concentrations well in these patients. These results are similar to those seen when comparing calculated and actual propofol concentrations in propofol infusion systems and meet published guidelines for the accuracy of models used in target-controlled anesthesia systems. This model may be useful for predicting responses to changes in fresh gas and vapor settings.We compared measured inhaled anesthetic concentrations with those predicted by a model. The method used for comparison has been used to study models of propofol administration. Our model predicts expired isoflurane and sevoflurane concentrations at least as well as common propofol models predict arterial propofol concentrations.
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Summary: An in-circuit vaporizer for delivery of isoflurane was evaluated. The isoflurane concentration within an isolated circle breathing circuit was determined for 1 hour in 6 in-the-circuit vaporizers with the wicks removed. A mechanical ventilator and artificial lung were connected to the circuit. Isoflurane concentration increased as vaporizer setting increased, and delivered concentration (%) at 60 minutes ( ± sem ) ranged from 0.46 ± 0.10 at tap setting 1 to 3.67 ± 0.30 at setting 5. Temperature of the isoflurane did not change. Cardiovascular and respiratory function were maintained within a clinically acceptable range in 6 dogs anesthetized with thiamylal and maintained with 1.87% end-tidal isoflurane delivered from the in-circuit vaporizer during spontaneous ventilation, controlled ventilation, and closed-circuit anesthesia. The range of vaporizer tap settings ( ± sem ) was lower during closed-system anesthesia (2.5 ± 0.1 to 3.5 ± 0.6) and during controlled ventilation (2.6 ± 0.2 to 3.3 ± 0.2) than during semi-closed system anesthesia (5.4 ± 0.3 to 6.8 ± 0.4). The in-circuit vaporizer was used to deliver isoflurane to 36 dogs anesthetized for a variety of surgical and medical procedures. Ventilation was spontaneous, assisted, and in 1 instance, controlled. Cardiovascular function, respiratory function, and recovery times were within clinically acceptable ranges. The initial vaporizer tap setting ( ± sem ) was 8.2 ± 0.4, and this corresponded to an end-tidal isoflurane concentration of 3.5 ± 0.6. The range of vaporizer settings during the maintenance phase ( ± sem ) was 2.8 ± 0.5 to 4.6 ± 1.9. This corresponded to an end-tidal isoflurane concentration of 1.2 ± 0.1 to 1.8 ± 0.1%. This study documents that when appropriate guidelines are followed and limitations understood, the in-circle vaporizer is suitable for delivery of isoflurane to dogs undergoing a variety of surgical and medical procedures. Guidelines include removal of the wick, attention to the relatively rapid increase of anesthetic depth during the first 5 minutes of anesthesia, and the need to decrease the setting of the vaporizer control lever if assisted or controlled ventilation is used, or if closed system flow rates are used. Limitations include unpredictability of output with changing ambient temperature and difficulty adapting its use with semi-open breathing systems such as the t -piece or Bain coaxial circuit.
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More than 80% of delivered anesthetic gases get wasted at high fresh gas flows as they are vented out unused. Use of minimal flow anesthesia is associated with less waste anesthetic gas emission and environmental pollution. There is no approved or validated technique to initiate minimal flow anesthesia and simultaneously achieve denitrogenation of the breathing circuit. We studied the wash-in characteristics of desflurane, when delivered with 50% nitrous oxide, to reach a target end-tidal concentration at two different gas flow rates.Patients were allocated randomly to two groups of 25 adults each. In Group A, with the vaporizer dial fixed at 4 vol %, after an initial fresh gas flow of 4 L/min was administered to wash-in of desflurane using the closed-circuit, with 50% N2O in O2, and in group B, 6 L/min was used. Minimal flow anesthesia, with 0.5 L/min, was initiated in both groups on attaining a target end-tidal desflurane concentration of 3.5 vol %. After initiation of desflurane delivery, the inspired/expired gas concentrations were noted every minute for 15 min.In Group A, the target desflurane end-tidal concentration was reached in 499.2 ± 68.6 s±, and in the Group B (P < 0.001), it was reached significantly faster in 314.4 ± 69.89 s. Denitrogenation of the circuit was adequate in both groups.Minimal flow anesthesia can be initiated, without any gas-volume deficit, in about 5 min with an initial fresh gas flow rate of 6 L/min and the vaporizer set at 4 vol%.
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Forty-four healthy dogs undergoing elective ovariohysterectomy were anesthetized with halothane or isoflurane delivered with an in-circuit vaporizer with closed system flow rates or an out-of-circuit vaporizer with semi-closed system flow rates. When dogs were anesthetized with halothane, there were no differences in heart rate, blood pressure, body temperature, respiratory rate, or lingual venous pH, PCO2, or PO2 during induction and maintenance. Lingual venous PO2 was significantly less but still within a clinically acceptable range when isoflurane was used in an in-circuit vaporizer. Recovery times tended to be longer with in-circuit vaporizers. The amount of anesthetic used was not affected by vaporizer location. In-circuit vaporizers were suitable for delivery of halothane or isoflurane to healthy dogs.
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Low flow anesthesia (LFA) at a fresh gas flow (FGF) level of 10 ml.kg-1.min-1 with oxygen flow set at 0.5 ml.kg-1.min-1: 0.5 ml.kg-1.min-1 nitrous oxide and 3% isoflurane was performed using time-cycled ventilator on 10 patients of ASA class I or II, with age of 55 +/- 13 (mean +/- SD) years and body weight of 55 +/- 10 kg for 5 h. Excessive anesthetic gases from the anesthesia gas monitor were led to an expiratory breathing tube. After rapid induction and tracheal intubation, denitrogenation was performed for about 5 min using a 100% oxygen flow of 6 l.min-1 before LFA. The inspired/expired oxygen concentration decreased gradually from 96 +/- 2%/90 +/- 2% at beginning of LFA to 42 +/- 3%/37 +/- 4% at 5 h. The operation was started after 29 +/- 10 min of beginning of LFA. The nitrous oxide concentration reached 37 +/- 4%/35 +/- 4% at the beginning of operation and further increased to 55 +/- 3%/53 +/- 3% at 5 h. The isoflurane concentration reached 1.0 +/- 0.1%/0.8 +/- 0.1% at the beginning of operation and further increased to 1.2 +/- 0.1%/1.0 +/- 0.1% at 5 h. The anesthetic potency was 1.2 +/- 0.1 MAC/1.0 +/- 0.2 MAC at the beginning of operation. The isoflurane vaporizer setting was changed only once in two cases from 3% to 2% exceeding 1.5% in inspired concentration. There was no need to change the flow of oxygen and nitrous oxide for 5 hrs. No SpO2 lower than 95% was observed during this study. This method is a clinically safe, easily applicable anesthesia method and used the smallest FGF reported in LFA without occurrence of low FIO2.
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Objective: The purpose of this study was to observe the safety and the advantage of the low-flow anesthesia (LFA). Methods: One hundred and ten patients undergoing general anesthesia were randomly divided into two groups: LFA group(n=88) and high-flow Anesthesia(HFA) group(n=22).The patients of LFA group were undergone semi-closed circuit LFA with N 2O-O 2-Isoflurane and compared with HFA group. The end expiratory nitrous oxide and Isoflurane cencentration, FiO 2, SpO 2, EtCO 2, HR and MAP were monitored continuously during the whole procedure Results: The safety of the two groups was much the same. 74%～90% of volatile anesthetic and carrier gas can be saved in LFA group, and it can decrease pollution in operation room. Conclusion: In view of the reliable function of the anesthesia machine, the advantages of the LFA are as follows the anesthesia is safe, reliabe and stable; patients regain consciousness quickly; large amount of anesthetic can be saved and the condition of the inhalating gas can be improved.
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After institutional approval, we studied the effect of animal size, anesthetic concentration, and fresh gas flow (FGF) rate on inspired carbon monoxide (CO) and carboxyhemoglobin (COHb) during anesthesia in swine, using soda lime previously dried to 1 ± 0.1% water content. To ascertain the effect of anesthesia, eight adult pigs were anesthetized with either 1 minimum alveolar anesthetic concentration (MAC) desflurane or isoflurane and, to characterize the effect of the FGF rate, it was doubled in four pigs. To determine the effect of animal size, four small and four large pigs received 1 MAC desflurane or isoflurane, and to determine the effect of the anesthetic concentration, a group of four swine was exposed to 0.5 MAC. CO and COHb concentrations were larger with desflurane (5500 ± 980 ppm and 57.90% ± 0.50%, respectively) than with isoflurane (800 ppm and 17.8% ± 2.14%, respectively), especially in the small animals. Increasing the FGF rate significantly reduced peak CO and COHb concentrations resulting from both anesthetics; however, when each anesthetic was reduced to 0.5 MAC, the concentrations obtained were similar. We conclude that CO intoxication is more severe with desflurane than with isoflurane, that small animals are at higher risk for CO poisoning, and that low FGF can increase COHb concentrations. Implications The present study shows that the use of desflurane with desiccated carbon dioxide absorbents in pediatric anesthesia can produce a dangerous carbon dioxide intoxication, especially with low-flow anesthesia.
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