Automated gas control with the Maquet FLOW-i.

The FLOW-i anesthesia machine (Maquet, Solna, Sweden) can be equipped with automated gas control (AGC), an automated low flow tool with target control of the inspired oxygen concentration (FIO2) and end-expired concentration (FA) of a potent inhaled anesthetic. We examined the performance and quantitative aspects of the AGC. After IRB approval and individual informed consent, anesthesia in 24 ASA I-II patients undergoing abdominal or gynecological surgery was maintained with sevoflurane in O2/air with a target FIO2 of 40 % and a target sevoflurane FA (FAsevo) of 2.0 %. The AGC tool also allows the user to select 1 out of 9 different speeds with which the target FAsevo can be reached (with 9 being the fastest speed). Eight patients each were randomly assigned to speed 2, 4, and 6 (= group 2, group 4, and group 6, respectively); these three speeds were chosen arbitrarily. AGC was activated immediately after securing the airway, which defined the start of the study, and the study ended 60 min later. The following parameters were compared among the three groups: age, height, weight, FIO2, FAsevo, BIS values, heart rate, mean arterial blood pressure, fresh gas flow, and sevoflurane usage. Agent usage as reported by the FLOW-i was compared among the three groups. Patient demographics and maintenance FGF did not differ among groups. A very short-lived very high FGF (≈20 L min(-1) for 8-12 s) ensured that the target FIO2 was attained within 1-2 min in all patients. FAsevo was 1.8 % after 15, 10, and 6 min, and 1.9 % after 30, 20 and 15 min in groups 2, 4, and 6, respectively. Blood pressure, heart rate, and BIS values did not differ among the three groups. BIS values remained acceptable in all patients, even with the slowest speed. Cumulative agent usage differed among all three groups between 2 and 30 min (lower with the lower speed), and between group 2 and 6 between 35 and 60 min. AGC combines an exponentially decreasing FGF pattern with a choice of ramp functions for the end-expired target concentration of the inhaled anesthetic. Consequently, both FGF and the choice of speed become factors that influence agent usage. After 15 min, a 300 mL min(-1) maintenance FGF reduces agent usage to near closed-circuit conditions. This new addition to our automated low flow armamentarium helps to reduce anesthetic waste, cost, and pollution, while minimizing the ergonomic burden of low flow anesthesia.

Increase in the use of rebreathing gas flow systems and in the utilization of low fresh gas flows in Finnish anaesthetic practice from 1995 to 2002.

BACKGROUND: The use of rebreathing systems together with low fresh gas flows saves anaesthetic gases, reduces the costs of anaesthesia, causes less environmental and ergonomic adverse effects, i.e. less air contamination in the operating room, and has favourable physiological effects. We assessed whether the use of non-rebreathing vs. rebreathing gas flow systems and high vs. lower fresh gas flows has changed during recent years. METHODS: The use of rebreathing and non-rebreathing systems and the utilization of fresh gas flows were evaluated by sending a questionnaire to the heads of anaesthesia departments at all public health care hospitals in Finland in 1996 and 2003. The data was gathered from the previous years 1995 and 2002, respectively. RESULTS: The use of rebreathing systems increased from 62% to 83% of all instances of general anaesthesia (P < 0.001). In rebreathing gas flow systems, there was a significant shift from high fresh gas flows (3 l min(-1) and more) towards lower fresh gas flows (between 1 to 2 l min(-1) and even below 1 l min(-1)) (P < 0.001). CONCLUSIONS: The benefits of low fresh gas flows have now been achieved in most instances of rebreathing system anaesthesia, which was not the case in 1995.

Rebreathing improves accuracy of ventilatory monitoring.

OBJECTIVE: Our objective was to determine if rebreathing would reduce the gradient between arterial and end-tidal CO2 tension during positive-pressure ventilation. DESIGN: Experimental investigation. SETTING: Anesthesiology laboratory. SUBJECTS: A total of 10 dogs of either sex. INTERVENTIONS: Anesthesia (sodium pentobarbital) and muscle relaxation (pancuronium) were induced and animals were tracheally intubated and ventilated with a standard anesthesia ventilator and breathing circuit with CO2 absorber and then with a Mapleson D circuit with a fresh gas flow rate (VF) equal to alveolar ventilation plus the sampling flow rate of two capnometers. Rebreathing was varied by adjusting the respiratory rate (RR) so that minute ventilation (VE) to VF ratio was 1:1, 2:1, 3:1, and 4:1. RESULTS: CO2 production (ATPD) was determined as the product of expired concentration of CO2 and VE (BTPS). Alveolar ventilation (VA) was calculated by dividing the product of CO2 production and barometric pressure corrected for ambient temperature and water vapor pressure at body temperature by PaCO2. Tidal volume, RR, airway gas temperature, concentration of CO2 in gas at the tracheal tube and inlet/outlet of the mechanical ventilator, body temperature, arterial gas tensions and pH, heart rate, arterial blood pressure, and cardiac output were measured. Minute ventilation, mean arterial blood pressure and end-expiratory CO2 tension (PECO2) (BTPS) were calculated. During positive-pressure ventilation, concentration of inspired CO2 was zero with standard circuitry, and significantly increased with Mapleson D when VE:VF ratio was 1:1 (0.56 +/- 0.19%), 2:1 (1.97 +/- 1.30%), 3:1 (2.56 +/- 1.05%), and 4:1 (3.01 +/- 1.45%) (p < 0.05). PECO2 was 34.8 +/- 3.2 mm Hg during ventilation with the standard circuit, and significantly increased during ventilation with Mapleson D when VE:VF ratio was increased from 1:1 (35.4 +/- 2.5 mm Hg) to 2:1 (40.2 +/- 3.6 mm Hg) and was not further increased at a VE:VF ratio of 3:1 (41.8 +/- 2.7 mm Hg) or 4:1 (41.3 +/- 2.4 mm Hg). The selected fresh gas flow rate was appropriate, because PaCO2 remained unchanged regardless of VE:VF ratio, indicating PaCO2 was dependent on VF, not on VE. The gradient between PaCO2 and PECO2 during ventilation with the standard circuit was 6.6 +/- 3.0 mm Hg; during ventilation with Mapleson D, it decreased significantly when VE:VF ratio was increased from 1:1 (6.5 +/- 3.6 mm Hg) to 2:1 (2.9 +/- 1.5 mm Hg), but was not significantly reduced further at 3:1 (1.7 +/- 1.1 mm Hg) or 4:1 (1.8 +/- 0.5 mm Hg) (p < 0.05). CONCLUSIONS: Rebreathing with a Mapleson D circuit and a VF equal to VA permitted normal CO2 elimination. Arterial PCO2 to PECO2 gradient decreased significantly during rebreathing, thus improving the reliability of capnography for estimating arterial PCO2. Consideration should be given to using the Mapleson D as a rebreathing circuit.

[Closed circuit inhalation anesthesia. Consumption and cost]. / Anestesia inalatoria in circuito chiuso. Consumi e costi.

Closed circuit anaesthesia (CCA) and minimal flow anaesthesia diminish inhalatory anaesthetic consumption. Consumption of inhalatory anaesthesia was calculated using two different techniques: CCA and "non rebreathing" system. Costs were compared on the basis of the official list price. The CCA allowed for reduced consumption at lower costs. The resulting annual savings are equal to one third of the total price of the whole apparatus with its complementary monitoring and control systems.