End-tidal control vs. manually controlled minimal-flow anesthesia: a prospective comparative trial

End-Tidal Control Versus Manual Control of Inhalational Anesthesia Delivery: A Randomized Controlled Noninferiority Trial

BACKGROUND

Precise anesthesia delivery helps ensure amnesia, analgesia, and immobility. Conventionally, the end-tidal anesthetic concentration is maintained through manual adjustment of the fresh gas flow and anesthetic vaporizer output. Some anesthesia delivery systems can deliver and maintain clinician-selected end-tidal anesthetic agent (EtAA) concentration using a modified closed-loop system. We evaluated the performance of an End-tidal Control (EtC) system on the Aisys CS 2 anesthesia machine (GE HealthCare). We hypothesized EtC anesthetic delivery would be noninferior to manually controlled anesthetic delivery.

METHODS

The Multi-site Anesthesia randomized controlled STudy of End-tidal control compared to conventional Results (MASTER) Trial evaluated anesthetic delivery in 210 adult patients receiving inhaled anesthesia. Patients were randomized to either EtC or manual control (MC) anesthetic delivery. The primary objective was to determine whether, compared to conventional anesthesia practice, EtC achieves and maintains clinician-specified EtAA and end-tidal oxygen (Et o2 ) concentrations within defined noninferiority limits. Noninferiority was concluded if the lower limit of the 95% confidence interval (CI) of the difference between the percent duration within the acceptable range (5% of steady state or a margin of ~10% of each agent's minimum alveolar concentration) for EtC and MC was ≥ -5% for both EtAA and Et o2 . Secondary objectives included performance measures: response time: time required to attain 90% of the first desired EtAA, overshoot: amount the controller (or vaporizer delivery) exceeded the desired EtAA, and accuracy: average deviation from the desired EtAA.

RESULTS

EtC achieved and sustained targeted EtAA and Et o2 concentrations within the noninferiority threshold. The EtAA was within 5% of the desired value 98% ± 2.05% of the time with EtC compared to 45.7% ± 31.7% of the time with MC (difference 52.3% [95% CI, 45.9%-58.6%], P < .0001). For Et o2 , EtC was within the noninferiority limit 86.3% ± 22.8% of the time compared with MC at 41% ± 33.3% ( P < .0001, difference 45.3% [95% CI, 36.1%-54.5%]). The median response time for achieving 90% of the initial EtAA desired value was 75 seconds with EtC and 158 seconds with MC ( P = .0013). EtC exhibited a median overshoot of 6.64% of the selected EtAA concentration, whereas MC often failed to reach the clinician's desired value. The difference in median percent deviation from desired EtAA value was 15.7% ([95% CI, 13.5%-19.0%], P < 0001).

CONCLUSIONS

EtC achieves and maintains the EtAA and Et o2 concentration in a manner that is noninferior to manually controlled anesthesia delivery.

A novel, cassette-based nitric oxide delivery system with an advanced feedback control algorithm accurately delivers nitric oxide via the anesthesia machine independent of fresh gas flow rate and volatile anesthetic agent

Nitric oxide (NO), a selective pulmonary vasodilator, can be delivered via conventional ICU and anesthesia machine ventilators. Anesthesia machines are designed for rebreathing of circulating gases, reducing volatile anesthetic agent quantity used. Current cylinder- and ionizing-based NO delivery technologies use breathing circuit flow to determine NO delivery and do not account for recirculated gases; therefore, they cannot accurately dose NO at FGF below patient minute ventilation (MV). A novel, cassette-based NO delivery system (GENOSYL® DS, Vero Biotech Inc.) uses measured NO concentration in the breathing circuit as an input to an advanced feedback control algorithm, providing accurate NO delivery regardless of FGF and recirculation of gases. This study evaluated GENOSYL® DS accuracy with different anesthesia machines, ventilation parameters, FGFs, and volatile anesthetics. GENOSYL® DS was tested with GE Aisys and Dräger Fabius anesthesia machines to determine NO dose accuracy with FGF < patient MV, and with a Getinge Flow-i anesthesia machine to determine NO dose accuracy when delivering various volatile anesthetic agents. Neonatal and adult mechanical ventilation parameters and circuits were used. GENOSYL® DS maintained accurate NO delivery with all three anesthesia machines, at low FGF with recirculation of gases, and with all volatile anesthetic agents at different concentrations. Measured NO2 levels remained acceptable at ≤ 1 ppm with set NO dose ≤ 40 ppm. GENOSYL® DS, with its advanced feedback control algorithm, is the only NO delivery system capable of accurately dosing NO with anesthesia machines with rebreathing ventilation parameters (FGF < MV) regardless of anesthetic agent.

Comparison of automated and manual control methods in minimal flow anesthesia

PURPOSE

New-generation anesthesia machines administer inhalation anesthetics and automatically control the fresh gas flow (FGF) rate. This study compared the administration of minimal flow anesthesia (MFA) using the automatically controlled anesthesia (ACA) module of the Mindray A9 (Shenzhen, China) anesthesia machine versus manual control by an anesthesiologist.

METHODS

We randomly divided 76 patients undergoing gynecological surgery into an ACA group (Group ACA) and a manually controlled anesthesia group (Group MCA). In Group MCA, induction was performed with a mixture of 40-60% O2 and air with a 4 L/min FGF until the minimum alveolar concentration (MAC) reached 1. Next, MFA was initiated with 0.5 L/min FGF. The target fraction of inspired oxygen (FiO2) value was 35-40%. In Group ACA, the MAC was defined as 1, and the FiO2 was adjusted to 35%. Depth of anesthesia, anesthetic agent (AA) consumption, time to achieve target end-tidal AA concentration, awakening times, and number of ventilator adjustments were analyzed.

RESULTS

The two groups showed no statistically significant differences in depth of anesthesia or AA consumption (Group ACA: 19.1 ± 4.9 ml; Group MCA: 17.2 ± 4.5; p-value = 0.076). The ACA mode achieved the MAC target of 1 significantly faster (Group ACA: 218 ± 51 s; Group MCA: 314 ± 169 s). The number of vaporizer adjustments was 15 in the ACA group and 217 in the MCA group.

CONCLUSION

The ACA mode was more advantageous than the MCA mode, reaching target AA concentrations faster and requiring fewer adjustments to achieve a constant depth of anesthesia.

Effect of a non-reactive absorbent with or without environmentally oriented electronic feedback on anesthesia provider's fresh gas flow rates: A greening initiative

STUDY OBJECTIVE

To examine the effects of a non-reactive carbon dioxide absorbent (AMSORB® Plus) versus a traditional carbon dioxide absorbent (Medisorb™) on the FGF used by anesthesia providers and an electronic educational feedback intervention using Carestation™ Insights (GE HealthCare) on provider-specific change in FGF.

DESIGN

Prospective, single-center cohort study set in a greening initiative.

SETTING

Operating room.

PARTICIPANTS

157 anesthesia providers (i.e., anesthesiology trainees, certified registered nurse anesthetists, and solo anesthesiologists).

INTERVENTIONS

Intervention #1 was the introduction of AMSORB® Plus into 8 Aisys CS2, Carestation™ Insights-enabled anesthesia machines (GE HealthCare) at the study site. At the end of week 6, anesthesia providers were educated and given an environmentally oriented electronic feedback strategy for the next 12 weeks of the study (Intervention #2) using Carestation™ Insights data.

MEASUREMENTS

The dual primary outcomes were the difference in average daily FGF during maintenance anesthesia between machines assigned to AMSORB® Plus versus Medisorb™ and the provider-specific change in average fresh gas flows after 12 weeks of feedback and education compared to the historical data.

MAIN RESULTS

Over the 18-week period, there were 1577 inhaled anesthetics performed in the 8 operating rooms (528 for intervention 1, 1049 for intervention 2). There were 1001 provider days using Aisys CS2 machines and 7452 provider days of historical data from the preceding year. Overall, AMSORB® Plus was not associated with significantly less FGF (mean - 80 ml/min, 97.5% confidence interval - 206 to 46, P = .15). The environmentally oriented electronic feedback intervention was not associated with a significant decrease in provider-specific mean FGF (-112 ml/min, 97.5% confidence interval - 244 to 21, P = .059).

CONCLUSIONS

This study showed that introducing a non-reactive absorbent did not significantly alter FGF. Using environmentally oriented electronic feedback relying on data analytics did not result in significantly reduced provider-specific FGF.

Target-controlled inhalational anesthesia-isoflurane consumption with adequacy of anesthesia monitoring in conventional and multimodal analgesia – A comparative study

Background:

In a time of increased concern over the environmental impact of chlorofluorocarbons, there is an impetus to minimize inhalational anesthetic consumption. It is possible with multimodal analgesia (MMA) and the use of end-tidal controlled anesthesia (EtCA) which is a low-flow anesthesia technique with adequacy of anesthesia (AoA) monitoring. In MMA, all four elements of pain processing namely transduction, transmission, modulation, and perception are targeted with drugs having a different mechanism of action. In EtCA, anesthetic gases are automatically adjusted for the set minimal alveolar concentration by newer anesthesia work station (GE Healthcare Aisys CS2). AoA is a derived parameter of entropy and surgical pleth index which measures the depth of anesthesia and analgesia, respectively.

Aim:

The aim is to assess the difference in isoflurane consumption between MMA and conventional groups for a given period of time with EtCA and AoA monitoring.

Setting and Design:

This was a prospective randomized controlled trial involving 60 patients undergoing laparoscopic cholecystectomy. They were divided into MMA group and conventional group.

Materials and Methods:

Both the groups received preemptive intravenous diclofenac sodium 75 g and 2% xyloadrenaline infiltration at entry ports. MMA group in addition received paracetamol 1 g and clonidine 0.75 μg.kg^{− 1}. Intraoperatively, patients were on EtCA with AoA monitoring.

Statistical Analysis:

Mean differences in isoflurane consumption between the two groups were compared using an independent t-test. Postextubation adverse effects of analgesic drugs and awareness under general anesthesia were compared using the Chi-square test and presented as numbers and percentages. P < 0.05 was considered a statistically significant.

Results:

Mean isoflurane consumption in the conventional group was 12.7 ± 5.3 mL which was significantly higher than the MMA group which was 8.9 ± 4.1 mL (P = 0.002). The duration of anesthesia between the groups was not significant clinically (P = 0.931).

Conclusion:

EtCA with MMA significantly reduces isoflurane consumption compared to the conventional group of anesthesia.

Environmental sustainability in veterinary anaesthesia

OBJECTIVE

Attention is drawn to the potential of global warming to influence the health and wellbeing of the human race. There is increasing public and governmental pressure on healthcare organisations to mitigate and adapt to the climate changes that are occurring. The science of anaesthetic agents such as nitrous oxide and the halogenated anaesthetic agents such as greenhouse gases and ozone-depleting agents is discussed and quantified. Additional environmental impacts of healthcare systems are explored. The role of noninhalational anaesthetic pharmaceuticals is discussed, including the environmental life-cycle analyses of their manufacture, transport, disposal and use. The significant role of anaesthetists in recycling and waste management, resource use (particularly plastics, water and energy) and engagement in sustainability are discussed. Finally, future directions for sustainability in veterinary anaesthesia are proposed.

CONCLUSIONS

Veterinary anaesthetists have a considerable opportunity to drive sustainability within their organisations through modification of their practice, research and education. The principles of sustainability may help veterinary anaesthetists to mitigate and adapt to our environmental crisis. Due to their particular impact as greenhouse gases, anaesthetic agents should be used conservatively with the lowest safe fresh gas flow possible. Technologies for reprocessing anaesthetic agents are described.