[Low-flow anesthesia with desflurane]

Desflurane consumption with automated vapour control systems in two different anaesthesia machines. A randomized controlled study

BACKGROUND

In general anaesthesia practice a fresh gas flow (FGF) of ≥0.5 L/min is usually applied. Automated gas delivery devices are developed to reduce volatile anaesthetic consumption by limiting gas flow. This study aimed to compare desflurane consumption between automated gas control devices compared to conventional low flow anaesthesia in the Flow-I and Aisys anaesthesia machines, and to compare desflurane consumption between the two automated gas delivery devices. We hypothesised that desflurane consumption would be lower with automated gas delivery compared to conventional low flow anaesthesia, and that desflurane consumption could differ between the different gas delivery devices.

METHODS

We allocated 160 patients undergoing robot-assisted laparoscopic surgery into four groups, Flow-I with automated gas control, Flow-i with conventional low-flow (1 L/min), Aisys with end tidal gas control and Aisys with conventional low flow. Patients were maintained at minimum alveolar concentration (MAC) 0.7-0.8. Desflurane consumption was recorded after 9, 30 and 60 minutes of anaesthesia.

RESULTS

After 60 minutes, compared to conventional low flow anaesthesia, automated gas delivery systems reduced desflurane consumption from 25.8 to 15.2 mL for the Aisys machine (P < .001) and from 22.1 to 16.8 mL for the Flow-I (P < .001). Time to MAC 0.7 and stable FGF was shorter with Aisys endtidal control compared to Flow-I automated gas control.

CONCLUSION

Under clinical conditions, we found a reduction in desflurane consumption when using automated gas delivery devices compared to conventional low flow anaesthesia. Both devices were reliable in use.

Effects of Minimal Flow Sevoflurane or Desflurane Anaesthesia on Hemodynamic Parameters, Body Temperature and Anaesthetic Consumption

Objective

We aimed to compare minimal flow sevoflurane and desflurane anaesthesia in terms of hemodynamic parameters, body temperature, anaesthetic gas consumption and cost.

Methods

120 patients with ASA I–II (>18yo) who underwent elective surgery for longer than 60 min after general anaesthesia were randomized into two groups. The Dräger Perseus^® A500 workstation was used. Pre-oxygenation was performed for 3 min with 6 L min⁻¹ to 100% oxygen. Fractional inspirium oxygen concentration (FiO₂) was reduced to 40%, fresh gas flow was 4 L min⁻¹ after intubation. Sevoflurane or desflurane was started at 1.5 minimal alveolar concentration (MAC). When the MAC value reached 0.9, fresh gas flow was reduced to 0.5 L min⁻¹, FiO₂ was increased to 68%. At the end of the surgery, the vaporizer was switched off, the fresh gas flow was increased (4 L min⁻¹, FiO₂ 100%). When the train-of-four (TOF) ratio was 100%, extubation was carried out.

Results

There were no differences in patient characteristics and initial hemodynamic parameters of the groups. There were statistically significant differences between the times to reach 0.9 MAC, extubation and eye opening; anaesthetic, O₂ and air consumption in both groups.

Conclusion

With minimal flow, the time to reach target MAC, time to extubation and eye opening were significantly faster for desflurane and anaesthetic, oxygen and air consumption in desflurane anaesthesia were less than sevoflurane. Thus, we can say that desflurane has faster anaesthetic induction and recovery time with lower anaesthetic consumption than sevoflurane.

Effect of entropy-guided low-flow desflurane anaesthesia on laryngeal mask airway removal time in children undergoing elective ophthalmic surgery - A prospective, randomised, comparative study

Background and Aims:

In children, entropy-guided titration of isoflurane and sevoflurane leads to faster recovery after anaesthesia. However, role of entropy in recovery following desflurane anaesthesia is not known. Hence, we compared laryngeal mask airway (LMA) removal time and desflurane consumption with entropy and minimal alveolar concentration–guided titration in children given low-flow desflurane anaesthesia.

Methods:

After ethics committee approval and parental consent, 80 American Society of Anesthesiologists grade I–II children, age 2–14 years, undergoing elective ophthalmic surgery were randomised into entropy and minimal alveolar concentration–guided groups. After LMA insertion, anaesthesia was maintained using oxygen, air (FiO₂ 0.5) and desflurane using low fresh gas flow of 0.75 L/min. In the entropy-guided group, desflurane was titrated to maintain state entropy between 40 and 60. In the minimal alveolar concentration–guided group, desflurane was titrated to maintain a minimal alveolar concentration between 1 and 1.3. We recorded LMA removal time (from switching off desflurane at the end of surgery till removal of LMA), haemodynamic parameters, uptake and consumption of desflurane between the groups.

Results:

LMA removal time was significantly decreased in the entropy-guided group in comparison to the minimal alveolar concentration–guided group (4.34 ± 2.03 vs 8.8 ± 2.33 min) (P < 0.0001). Consumption of desflurane was significantly less in the entropy-guided group compared with the minimal alveolar concentration–guided group (18.7 ± 5.07 vs 25.3 ± 8.11 mL) (P < 0.0001).

Conclusion:

Entropy-guided low-flow desflurane anaesthesia is associated with faster LMA removal and reduced consumption of desflurane in children undergoing ophthalmic surgery.

Advantages of 1-1-12 Wash in Scheme during Induction with Low Flow Anesthesia with and without Nitrous Oxide

Introduction

In the past, many wash-in schemes have been used with initially high fresh gas flow (FGF) to achieve the necessary alveolar concentration of inhalational agent in 10-15 min. This study was designed to show whether 1-1-12 wash-in scheme proposes an earlier achievement of induction or is there any requirement of high FGF phase to know the time taken for induction with and without nitrous oxide (N₂O).

Aims

The aim of the study was to find out the time required for the alveolar concentration of desflurane to be from 1% to 6% with and without N₂O.

Design

It was a potential randomized study which was conducted on sixty patients admitted for elective surgery.

Materials and Methods

Two groups of thirty patients each were made and randomly assigned. Group N received desflurane with N₂O plus oxygen and Group A received desflurane with air plus oxygen.

Statistical Analysis

The observations were noted and evaluated accordingly. Analysis was done using unpaired t-test.

Results

Hemodynamic parameters were almost similar in both the groups. In Group N, gradual F_AD (Alveolar Desflurane concentration, i.e., end-tidal desflurane) from 1% to 6% was achieved at 0.5, 1, 1.5, 2, 3, and 4 min. In Group A, the same was achieved at 0.6, 1, 1.5, 2, 3, and 4 min (P > 0.05). No significant difference was found between the recuperation time and score in both the groups. Rather complications were more in Group N and statistically significant for nausea and vomiting.

Conclusion

Time taken to attain F_AD from 1% to 6% was 4 min in both the groups. It is concluded that the recitation of 1-1-12 wash-in scheme is autonomous on the use of N₂O and high FGF phase.

Low-flow anaesthesia - underused mode towards "sustainable anaesthesia"

Any technique that employs a fresh gas flow that is less than the alveolar ventilation can be classified as low-flow anaesthesia. The complexities involved in the calculation of uptake of anaesthetic agents during the closed-circuit anaesthesia made this technique less popular. However, the awareness of the dangers of theatre pollution with trace amounts of the anaesthetic agents and the prohibitively high cost of the new inhalational agents, have helped in the rediscovery of low-flow anaesthesia. Moreover, the time has arrived for each of us, the practicing anaesthesiologists, to move towards the practice of low-flow anaesthesia, to achieve lesser theatre and environmental pollution and also to make anaesthesia more economical. The article also reviews low-flow anaesthesia (LFA) in paediatrics, recent advances such as automated LFA and updates on currently undergoing research to retrieve and reuse anaesthetic agents.

1-1-12 one-step wash-in scheme for desflurane low flow anesthesia: performance without nitrous oxide

Background

We reported a 1-1-12 wash-in scheme for desflurane-nitrous oxide (N₂O) low flow anesthesia that is simple, rapid, and predictable. There remain some situations where N₂O 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 N₂O 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:O₂ 1:1 L/min and a vaporizer concentration of desflurane of 12%. Controlled ventilation was then adjusted to maintain P_ACO₂ at 30–35 mmHg.

Results

The alveolar concentration of desflurane (F_AD) rose rapidly from 0% to 6% in 4 minutes in the same pattern as observed in our previous study in which N₂O was used. An F_AD of 7% was achieved in 6 minutes. An F_AD 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 N₂O. Respective F_ADs of 1%, 2%, 3%, 4%, 5%, 6%, and 7% can be expected at 0.6, 1, 1.5, 2, 3, 4, and 6 minutes.

1-1-12 one-step wash-in scheme for desflurane-nitrous oxide low-flow anesthesia: rapid and predictable induction

Background. We propose a 1-1-12 wash-in scheme for desflurane-nitrous oxide (N₂O) low-flow anesthesia. The objective of our study was to determine the time to achieve alveolar concentration of desflurane (F_AD) at 1, 2, 3, 4, 5, and 6%. Methods. We enrolled 106 patients scheduled for elective surgery under general anesthesia. After induction and intubation, wash-in was started with a fresh gas flow (FGF) of N₂O : O₂ 1 : 1 L min⁻¹ and vaporizer concentration of desflurane (FD) of 12%. Ventilation was controlled to maintain P_ACO₂ at 30–35 mmHg. Results. The F_AD rose rapidly from 0 to 4% in 2 min in a linear manner in 0.5 min increments. An F_AD of 6% was achieved in 4 min in a linear fashion from F_AD of 4% but in 1 min increments. An F_AD of 1 to 6% occurred at 0.6, 1, 1.5, 2, 3, and 4 min. Heart rate during wash-in showed a statistically, albeit not clinically, significant pattern of increase. By contrast, blood pressure slightly decreased during this period. Conclusions. We developed a 1-1-12 wash-in scheme using a FGF of N₂O : O₂ 1 : 1 L min⁻¹ and FD of 12% for desflurane-nitrous oxide low-flow anesthesia. A respective F_AD of 1, 2, 3, 4, 5, and 6% can be expected at 0.6, 1, 1.5, 2, 3, and 4 min.

Comparison of effects of low-flow sevoflurane and desflurane anesthesia on neutrophil and T-cell populations

BACKGROUND

Numerous transient effects of anesthesia on postoperative immune status have been documented in the literature.

OBJECTIVE

This study was performed to test the hypothesis that the effects on neutrophil and T-cell populations differ with use of low-flow sevoflurane- and desflurane-induced anesthesia during abdominal surgery.

METHODS

Fifty adult patients (American Society of Anesthesiologists physical status I or II) aged 20 to 60 years were recruited for the study. Patients were randomly assigned to one of two study groups. Anesthesia was induced using fentanyl, propofol, and vecuronium. After intubation, patients in group 1 received sevoflurane, oxygen, and nitrous oxide at a flow rate of 6 L/min, and those in group 2 received desflurane, oxygen, and nitrous oxide at a flow rate of 6 L/min. Ten minutes after induction of anesthesia, the flow rate was decreased to 1 L/min in both groups. Total leukocyte, lymphocyte, and neutrophil counts, percentage of T helper lymphocytes (CD4), cytotoxic T lymphocytes (CD8), natural killer lymphocytes, and active T lymphocyte, CD4/CD8 ratio, and plasma cortisol values were assessed before and at 2 and 24 hours after induction of anesthesia.

RESULTS

In the desflurane group, at 2 hours after induction of anesthesia, a significant decrease was observed in the lymphocyte count, percentage of CD4 cells, and CD4/CD8 ratio, and a significant increase was noted in the neutrophil count and percentage of CD8 cells (P < 0.05). At 24 hours after induction of anesthesia, a significant increase was observed in the leukocyte and neutrophil counts, percentage of CD4 cells, and CD4/CD8 ratio (P < 0.05). There was no change in the other parameters studied. In the sevoflurane group, a significant decrease was observed in the lymphocyte count and percentage of natural killer cells. In addition, a significant increase was noted in the leukocyte and neutrophil counts at 24 hours after induction of anesthesia (P < 0.01). The increase in the neutrophil count in the desflurane group compared with that in the sevoflurane group was statistically significant (P < 0.05).

CONCLUSIONS

With use of the low-flow anesthesia technique, compared with desflurane, sevoflurane exerts minimal effects on neutrophil and T-cell populations, which supports our hypothesis.

Brief review: theory and practice of minimal fresh gas flow anesthesia

PURPOSE

The aim of this brief review is to provide an update on the theory regarding minimal fresh gas flow techniques for inhaled general anesthesia. The article also includes an update and discussion of the practical aspects associated with minimal-flow anesthesia, including the advantages, potential limitations, and safety considerations of this important anesthetic technique.

PRINCIPAL FINDINGS

Reducing the fresh gas flow to < 1 L·min(-1) during maintenance of anesthesia is associated with several benefits. Enhanced preservation of temperature and humidity, cost savings through more efficient utilization of inhaled anesthetics, and environmental considerations are three key reasons to implement minimal-flow and closed-circuit anesthesia, although potential risks are hypoxic gas mixtures and inadequate depth of anesthesia. The basic elements of the related pharmacology need to be considered, especially pharmacokinetics of the inhaled anesthetics. The third-generation inhaled anesthetics, sevoflurane and desflurane, have low blood and low tissue solubility, which facilitates rapid equilibration between the alveolar and effect site (brain) concentrations and makes them ideally suited for low-flow techniques. The use of modern anesthetic machines designed for minimal-flow techniques, leak-free circle systems, highly efficient CO(2) absorbers, and the common practice of utilizing on-line real-time multi-gas monitor, including essential alarm systems, allow for safe and cost-effective minimal-flow techniques during maintenance of anesthesia. The introduction of new anesthetic machines with built-in closed-loop algorithms for the automatic control of inspired oxygen and end-tidal anesthetic concentration will further enhance the feasibility of minimal-flow techniques.

CONCLUSIONS

With our modern anesthesia machines, reducing the fresh gas flow of oxygen to 0.3-0.5 L·min(-1) and using third-generation inhaled anesthetics provide a reassuringly safe anesthetic technique. This environmentally friendly practice can easily be implemented for elective anesthesia; furthermore, it will facilitate cost savings and improve temperature homeostasis.

Desfluran und Isofluran bei Niedrigflussnarkosen

BACKGROUND

In the present investigation we compared the consumption of desflurane (DES) and isoflurane (ISO) using a standardized minimal-flow protocol with a forced reduction of the fresh gas flow (FGF).

METHODS

54 adult women were examined. After induction of anaesthesia a forced reduction of the FGF was started: 5 min 0.5 l/min O(2) + 1 l/min N(2)O, 10 min 0.5 l/min O(2) + 0.5 l/min N(2)O; finally 0.3 l/min O(2) + 0.2 l/min N(2)O up to the end of surgery. The consumption of DES/ISO was determined with a precision balance.

RESULTS

In the DES group the uptake was around 0.3 vol-%, i.e. less than 8% of the target 2/3 MAC value was taken up. For ISO the uptake was around 0.25 vol-%, i.e. the uptake was approximately 30% of the target 2/3-MAC value. The DES consumption was after 60 min 17.0+/-1.1 g, 120 min--27.3+/-1.8 g and 180 min--36.5+/-1.7 g. ISO consumption was significantly lower: 7.6+/-0.8 g, 12.4+/-1.7 g and 15.5+/-1.6 g. The use of DES yielded higher costs, i.e. 2.28 EUR for 60 min, 3.63 EUR for 120 min and 4.97 EUR for 180 min. The consumption of the inhaled anaesthetics can be calculated as: DES (g)=4.84+0.184 x duration (min) (R(2)=0.981), ISO (g)=2.049+0.0826 x duration (R(2)=0.979). The costs are: DES (EUR)=0.85+0.0323 x duration (min); ISO (EUR)=0.19+0.0077 x duration (min).

CONCLUSION

With a forced reduction of the FGF the DES consumption is still higher.

Minimal-flow anaesthesia with controlled ventilation: comparison between laryngeal mask airway and endotracheal tube

BACKGROUND AND OBJECTIVE

Minimal- and low-flow anaesthesia (fresh gas flow below 1 L min(-1)) provide many advantages, including reduced cost, conservation of body heat and airway humidity. An airtight seal is essential between the airway device and the airway of the patient. Therefore, we investigated whether the airtight seal created by a laryngeal mask airway allows controlled ventilation of the lungs when the fresh gas flow is reduced to 0.5 L min(-1) and compared this with an endotracheal tube.

METHODS

In a prospective clinical study, 207 patients were managed using a laryngeal mask or an endotracheal tube. After intravenous induction of anaesthesia and 15 min of high fresh gas flow, the flow was reduced to 0.5 L min(-1). The breathing system was monitored for airway leaks, and the patients were assessed for complications after airway removal and postoperative discomfort.

RESULTS

Both the laryngeal mask and endotracheal tube allowed fresh gas flow reduction to 0.5 L min(-1) in 84.7% and 98.3% of cases respectively (small leaks: 12% laryngeal mask, 1.7% endotracheal tube). Three patients with the laryngeal mask (3.3%) had airway leaks that were too large to permit any reduction in the fresh gas flow.

CONCLUSIONS

The use of the laryngeal mask airway was more likely to be associated with a gas leak than use of an endotracheal tube; however, if modern anaesthesia machines and monitors are used, in 96.7% of the patients managed with a laryngeal mask a reduction in the fresh gas flow to 0.5 L min(-1) was possible. The incidence of coughing and postoperative complaints (sore throat, swallowing problems) was higher after use of an endotracheal tube.

Clinical and economic factors important to anaesthetic choice for day-case surgery

Clinical and economic factors that are important to consider when selecting anaesthesia for day-case surgery can differ from those for inpatient anaesthesia. Patients undergoing day-case surgery tend to be healthier and have shorter durations of surgery. They expect less anxiety before surgery, amnesia for the surgical experience, a rapid return to normal (normal mentation with minimal pain and nausea) after surgery, and lower expenses. However, the latter 2 expectations can conflict; older generic drugs have lower acquisition costs but often impose longer recovery times. Longer recovery periods can increase costs by prolonging the time to discharge from labour-intensive areas such as the operating suite or the post-anaesthesia recovery unit. The challenge for today's anaesthetist is to use newer drugs judiciously to minimise their expense without compromising the rate or quality of recovery. Several approaches can secure these aims. Most apply the least anaesthetic needed. 'Least anaesthetic' may mean the particular form of anaesthetic (e.g. local infiltration with monitored anaesthesia care versus a general anaesthetic), or may mean the delivery of the smallest effective dose, perhaps guided by anaesthetic monitors such as end-tidal analysers or the bispectral index. For patients requiring general anaesthesia, a combination of several drugs usually secures the closest approach to the ideal. Drug combinations used usually include a short-acting properative anxiolytic (e.g. midazolam), intravenous propofol (a short-acting potent anxiolytic and amnestic agent) for induction of anaesthesia (and sometimes for maintenance) and primary maintenance of anaesthesia with inhaled nitrous oxide combined with a poorly soluble (low solubility produces rapid recovery; the least soluble is desflurane) potent inhaled anaesthetic delivered at a low inflow rate (to minimise cost). Although old, nitrous oxide is inexpensive and has favourable pharmacokinetic and cardiovascular advantages; however, it is limited in its anaesthetic/amnestic potency, and has the capacity to increase nausea. In children, induction of anaesthesia is often accomplished with sevoflurane rather than desflurane; although sevoflurane is modestly more soluble than desflurane, it is non-pungent whereas desflurane is pungent. Moderate- or short-acting opioids (fentanyl is popular) or nonsteroidal anti-inflammatory agents (especially ketorolac), or local anaesthetics are added to secure analgesia during and after surgery. Similarly, when needed, moderate- or short-acting muscle relaxants are selected. Before the end of anaesthesia, an intravenous antiemetic may be given. With this drug combination, patients usually awaken within minutes after anaesthesia and can often move themselves to the vehicle for transport to the recovery unit. These combinations of anaesthetics and techniques minimise use of expensive drugs while expediting recovery (again minimising cost) with minimal or no compromise in the quality of recovery.

[Adsorption of carbon dioxide gas]

OBJECTIVES

To analyse the various methods for carbon dioxide absorption in anaesthesia, the available absorbents and their modes of use.

DATA SOURCES

We searched the Medline and Internet databases for papers using the key words: carbon dioxide absorption, soda-lime, zeolite. We also had correspondence and contacts with soda lime manufacturers.

STUDY SELECTION

All types of articles containing data on CO2 absorption.

DATA EXTRACTION

The articles were analysed for the benefits and adverse effects of the various absorbents.

DATA SYNTHESIS

Carbon dioxide absorption enables the use of low flow anaesthesia, and a decreased consumption of medical gases and halogenated anaesthetics, as well as reduced pollution. Chemical absorbents (soda-lime and barium hydroxide lime (Baralyme) may produce toxic compounds: carbon monoxide with all halogenated anaesthetics and compound A with sevoflurane. Simple measures against desiccation of the lime prevent carbon monoxide production. The toxicity of compound A, shown in the rat, has not been proven in clinical anaesthesia. Recent improvements in manufacture processes have decreased the powdering of lime. Moreover, filters inserted between the anaesthesia circuit and the patient abolish the risk for powder inhalation.