Anesthésie halogénée utilisant un respirateur muni d''un circuit-filtre

Thirty-six patients were anaesthetized for a maxillofacial surgical procedure. Ventilation was controlled by a ventilator (Kontron ABT 4100) with a semi-closed circle system. The flow of fresh gases was 1,200 ml.min-1. The vaporizer for the halogenated anaesthetic agent was placed out of the circle before the ventilator. Halothane was used for maintenance of anaesthesia and isoflurane for induced hypotension in orthognathic surgery. The inspired concentration of the halogenated agent was monitored by an analyser. A linear correlation between the delivered and the inhaled concentration of halogenated agent was established, the latter never reaching the delivered concentration. Monitoring the inspired oxygen concentration was required, so as to maintain a constant value. Carbon dioxide absorption by soda lime was also studied. The known advantages were: substantial economies in nitrous oxide and halogenated agents, prevention of contamination of the operating theatre, humidification and warning of the inspired gases. The use of such a system with the vaporizer out of the circle was safe, all the more so as the concentration of inhaled halogenated agents could be predicted.     

Low-flow anaesthesia

An 8-week survey was conducted to determine whether the introduction of low-flow anaesthesia (a fresh gas flow of 4 litres/minute or less) into routine use would be acceptable to members of a representative anaesthetic department and if the consequent reduction in use of volatile anaesthetics would result in financial savings. The hourly consumption of the volatile agents was measured during anaesthesia conducted using either conventional or low fresh gas flows. Anaesthetists' acceptance of low-flow anaesthesia was assessed using a questionnaire. Data were gathered on 286 patients undergoing inhalational anaesthesia for routine operative procedures. A 54.7% reduction in the consumption of isoflurane and a 55.9% reduction in that of enflurane was found. Of the 28 anaesthetists at the hospital, 21 would use low-flow anaesthesia routinely. The routine use of low-flow anaesthesia would therefore be acceptable and could result in annual savings of 26,870 pounds at Northwick Park Hospital.     

Cost minimisation and cost effectiveness in anaesthesia for total hip replacement surgery, in Belgium? A study comparing three general anaesthesia techniques

The aim of the prospective randomised study is to compare the cost effectiveness of three general anaesthesia techniques for total hip replacement surgery and the cost minimisation by use of anaesthetics. For induction propofol was used in the three techniques. For maintenance, we used desflurane, or sevoflurane, or propofol. There was no significant difference in consumption of drugs for pain treatment, treatment of nausea and vomiting or cost of hospital stay or total cost for pharmacy. In terms of cost-effectiveness we can consider that the three techniques are similar. The cost of an i.v. technique was always higher than inhaled anaesthetics. The major cost in anaesthesia is the fee for the anaesthesiologist. But all in, the cost of anaesthesia was only 15.1% of the total cost of the procedure. Cost of inhaled or i.v. anaesthetics was 0.55% to 1.0% of the total cost. There was a discrepancy between the measured consumption of inhaled anaesthetics and the consumption (and cost) on the invoice. Cost minimisation based on anaesthetic medication is ridiculously by small considering the total cost of the procedure.     

Inhalational anaesthesia

The use of inhalational agents for the induction and maintenance of anaesthesia in clinical practice has undergone significant advances in safety and effectiveness since its introduction in the 1800s. In the United Kingdom, desflurane, sevoflurane and isoflurane are the most commonly used agents. The ideal inhalational anaesthetic would have a low blood:gas solubility coefficient and a high oil:gas coefficient, which would generate a fast onset and high potency, respectively. Inhaled agents are delivered by vaporizers that are specific to each agent, and concentrations are closely measured to deliver safe anaesthesia. Expired concentrations of the volatile are used to monitor alveolar concentrations, which are used as a surrogate for the partial pressure in the brain, governing the effect of the agent. Unfortunately, inhaled anaesthesia is a cause of global warming, with inhalational agents representing 5% of the carbon footprint of the whole NHS. Consequently, their use needs to be tightly regulated.     

Repeat anaesthesia: hepatic injury

Hepatic injury following repeat anaesthesia is a very rare but potentially fatal complication. The halogenated anaesthetic agents have been implicated in hepatic injury. Predisposing factors include repeat exposure to halogenated anaesthetics, genetic factors, middle age, female gender and liver enzyme induction. Halothane is a well-known cause of halothane hepatitis, but isoflurane, enflurane and desflurane have also been implicated with this clinical syndrome. A cross-sensitivity has been shown that is potentiated by the use of nitrous oxide. Although sevoflurane is metabolized differently, cases of hepatic injury following sevoflurane anaesthesia have been reported. The diagnosis of halothane hepatitis can be made only once other causes have been eliminated. Halogenated anaesthetics should be avoided for patients who have survived halothane hepatitis. Total intravenous anaesthetics and or regional techniques may be used instead.     

Ökonomische Aspekte beim Einsatz moderner Inhalationsanästhetika am Beispiel des Sevofluran

The economic impact of the new German health care laws requires an awareness of cost-effectiveness when using newer drugs. The main goal in patient care, i.e., effective treatment, must be achieved by the rational use of restricted resources at a maximum degree of effectiveness. Economic aspects of the new inhalational anaesthetics such as sevoflurane are discussed in this article. The cost of inhalational anaesthetic agents accounts for up to 5% of all the running expenses of an anaesthesia department. The consumption and cost of an inhalational agent depend on fresh gas flow, vapour setting, and duration of anaesthesia. Comparing the cost for 1 MAC-h of anaesthesia, desflurane is more expensive at current market prices than sevoflurane and isoflurane. However, at low or minimal fresh-gas flows, the price for one MAC-h is almost the same for these volatile anaesthetics. Total intravenous anaesthesia using propofol is even more expensive, partly due to wastage, i.e., opened ampoules with a remainder of propofol that has to be discarded after each case. When choosing an anaesthetic agent, the price of 1?ml liquid anaesthetic is an important factor. However, the overall cost-effectiveness analysis must balance the cost of the agent with its pharmacodynamic advantages such as more rapid recovery from anaesthesia. Furthermore, the indirect costs of side effects have to be taken into account. For example, nausea and vomiting lead to a prolonged stay in the recovery room after anaesthesia for outpatient surgery, which in turn incurs additional costs for antiemetic drugs and the extra time for nursing care. Therefore, a lower incidence of nausea and vomiting and a more rapid recovery from anaesthesia leading to earlier discharge from the recovery room may compensate for the higher price. Volatile agents account for up to 1% of the total intraoperative costs. In analysing the costs of 1?h of anaesthesia, other products such as plasma substitutes and blood products account for a much higher proportion than anaesthetic agents, and reductions or increases in costs pertaining to these products have a bigger impact on overall costs than do volatile anaesthetics. We conclude that volatile anaesthetics account for only a minor portion of the anaesthesia department budget and the cost of anaesthesia delivery. The higher market price of the new agents may be compensated for by the economic impact of fewer side effects and a shorter post-anaesthesia stay in the hospital. In analysing data for sevoflurane, this agent may be cost-effective, for example, for outpatient anaesthesia.     

Sevoflurane: an ideal agent for adult day‐case anesthesia?

Sevoflurane has several properties which make it potentially useful as a day case anaesthetic. Following induction of anaesthesia with propofol, awakening from sevoflurane is faster compared to isoflurane, faster or similar compared to propofol and comparable (in the majority of studies) to desflurane. Subsequent recovery and discharge is generally similar following all agents. Sevoflurane may also be used to induce anaesthesia, which is generally well-received and causes less hypotension and apnoea compared to propofol. When used as a maintenance anaesthetic, the incidence of postoperative nausea and vomiting after sevoflurane is comparable to other inhaled anaesthetics, but this complication appears more common after inhaled inductions. The tolerability and low solubility of sevoflurane facilitate titration of anaesthesia and may reduce the need for opioid analgesia, which in turn may limit the occurrence of nausea and vomiting.     

Low-flow isoflurane-nitrous oxide anaesthesia offers substantial economic advantages over high-and medium-flow isoflurane-nitrous oxide anaesthesia

Isoflurane consumption was studied for three different fresh gas flows in patients scheduled for major elective abdominal, urological or gynaecological surgery under general anaesthesia with an expected duration of 2 h or more. Thirty patients were randomly assigned to either high-flow anaesthesia using a partial rebreathing system without carbon dioxide absorption (Mapleson D) or medium- or low-flow anaesthesia using a circle system with carbon dioxide absorption. Patients were anaesthetised with isoflurane in 40% oxygen and 60% nitrous oxide. The amount of isoflurane consumed was measured with a precision scale. The total consumption of liquid isoflurane (mean ± s.d.) during the first 2 h was 40.8± 12.2 ml in the high-flow group, 18.5 ± 5.4 ml in the medium-flow group and 7.9 ± 2.2 ml in the low-flow group. The corresponding cost of isoflurane for the three groups was 214 Danish kroner (DKK) (±19.5), 97 DKK (±8.8) and 42 DKK (±3.8), respectively. The calculated total cost of anaesthetics was 286 DKK(±26), 155 DKK (±14.1) and 91 DKK (±8.3), respectively. In conclusion, low-flow isoflurane-nitrous oxide anaesthesia offers substantial economic advantages over high- and medium-flow isoflurane-nitrous oxide anaesthesia.     

From d-tubocurarine to sugammadex: the contributions of T. Cecil Gray to modern anaesthetic practice

One hundred years after Morton's demonstration of the anaesthetic effects of ether, T. Cecil Gray revolutionized anaesthesia with his introduction of balanced general anaesthesia. Gray's technique involved i.v. induction, administration of a neuromuscular blocking agent (curare), tracheal intubation, controlled ventilation, maintenance of unconsciousness with a light inhaled anaesthetic (supplemented with opioids if necessary), and reversal of neuromuscular blocking agent at the conclusion of the anaesthetic. In the 65 yr since his seminal papers, our drugs have changed, and i.v. anaesthetics suitable for maintenance of anaesthesia have been introduced, but the basic principles of general anaesthesia today are those set forward by Gray 65 yr ago.     

Anaesthesia defined (gentlemen, this is no humbug)

Our charge was to define anaesthesia as produced by inhaled anaesthetics. A definition may be useful to an understanding of the anaesthetic state, and it may guide studies of the mechanisms by which anaesthesia is produced. All inhaled anaesthetics act on the central nervous system to produce two reversible conditions, immobility and amnesia, that define the anaesthetic state. No other reversible, clinically useful, conditions are essential to the definition. Some conditions are unmeasurable (unconsciousness), not present for all inhaled anaesthetics (relaxation), or are not present at anaesthetizing concentrations (suppression of autonomic reflexes.) One (analgesia) is unmeasurable (the anaesthetized patient cannot tell an investigator that he/she hurts or does not hurt), and surrogate measures (increases in breathing, blood pressure, and heart rate with surgery) suggest that some pain is perceived. These and myriad other changes produced by inhaled anaesthetics are side effects; they do not define anaesthesia; only immobility and amnesia supply such a definition.     

(Part 2) Economic aspects of concentration-oriented anaesthesia: halogenated agents

Wastage of halogenated agents is correlated to the rate of fresh-gas flow (FGF) into the anaesthetic circuit. An overall reduction in FGF allows a decrease in the cost of inhalation anaesthesia. Low-flow anaesthesia is economically advantageous but it prevents the rapid establishment of a useful alveolar concentration and intra-operative adjustment of depth of anaesthesia. Both calculations and modelling have shown that FGF has to be transiently increased either to establish alveolar concentrations or to allow adaptation to surgical stimulations, even with maximum vaporizer settings. Closed circuit anaesthesia requires the injection of halogenated agents into the circuit, as occurs in the Physioflex^TMmachine. The Physioflex^TMmachine uses a closed circuit that is washed out by a blower. A computer regulates the gas flows and the agent injection in order to maintain end-tidal concentrations at a predetermined level. A charcoal filter allows circuit agent concentration to be decreased without changing the FGF. This system allows a reduction of costs and a precise and rapid control of anaesthesia.     

Desflurane: a clinical update of a third-generation inhaled anaesthetic

Available volatile anaesthetics are safe and efficacious; however, their varying pharmacology provides small but potentially clinically important differences. Desflurane is one of the third-generation inhaled anaesthetics. It is the halogenated inhaled anaesthetic with the lowest blood and tissue solubilities, which promotes its rapid equilibration and its rapid elimination following cessation of administration at the end of anaesthesia. The low fat solubility of desflurane provides pharmacological benefits, especially in overweight patients and in longer procedures by reducing slow compartment accumulation. A decade of clinical use has provided evidence for desflurane's safe and efficacious use as a general anaesthetic. Its benefits include rapid and predictable emergence, and early recovery. In addition, the use of desflurane promotes early and predictable extubation, and the ability to rapidly transfer patients from the operating theatre to the recovery area, which has a positive impact on patient turnover. Desflurane also increases the likelihood of patients, including obese patients, recovering their protective airway reflexes and awakening to a degree sufficient to minimise the stay in the high dependency recovery area. The potential impact of the rapid early recovery from desflurane anaesthesia on intermediate and late recovery and resumption of activities of daily living requires further study.     

The Manhattan legacy

The Manhattan Project was the highly secret American atomic research study which led to the making of the atom bomb. What is not so well known is that before the Project, fluorine was a difficult and dangerous element, while afterwards it became a key ingredient in all the new inhalational anaesthetics. Prior to this, the only practical inhalational agents available apart from nitrous oxide, ethylene and cyclopropane, (and a few others of short-lived popularity like acetylene) were non-halogenated ethers and some chlorinated compounds such as chloroform and ethyl chloride. When chemists learnt how to handle fluorine, a whole new world opened up, first with the 'Freons' as used in refrigeration and then the halogenated anaesthetics. Along the way, many halogenated compounds other than ethers were tried but abandoned, and now we are left effectively with two halogenated ethers. Is this the end of the line for inhalational anaesthesia?     

Induction and recovery characteristics of desflurane in day case patients: A comparison with propofol

Desflurane is an ether halogenated exclusively with fluorine. It has a blood/gas partition coefficient of 0.42 (cf. isoflurane 1.40 and nitrous oxide 0.46). This characteristic suggests that it should provide both a fast induction of anaesthesia and a rapid recovery from anaesthesia. To assess this, 60 patients were entered into a study and allocated at random to one of four groups receiving either desflurane or propofol for induction and maintenance of anaesthesia. Desflurane caused loss of consciousness in approximately 2 minutes during gaseous inductions. The psychomotor scores in the patients who received propofol for induction and maintenance of anaesthesia were significantly worse compared with those who were given desflurane for either induction and maintenance or for maintenance only. There was also a tendency for other recovery parameters to be faster in the patients receiving desflurane although this did not reach statistical significance. This suggests that desflurane would be a suitable agent for day case anaesthesia providing for a rapid recovery.     

Animal dependence of inhaled anaesthetic requirements in cats

Background. The minimum alveolar concentration (MAC) of an inhaledanaesthetic describes its potency as a general anaesthetic.Individuals vary in their sensitivity to anaesthetics and wesought to determine whether an individual animal’s sensitivityto inhaled anaesthetics would be maintained across differentagents. Methods. Six female mongrel cats, age 2 yr (range 1.8–2.3)and mean weight 3.5 (SD 0.3) kg, were studied on three separateoccasions over a 12-month period to determine the MAC of isoflurane,sevoflurane and desflurane. Induction of anaesthesia in a chamberwas followed by orotracheal intubation and maintenance of anaesthesiawith the inhaled agent in oxygen delivered via a non-rebreathingcircuit. MAC was determined in triplicate using standard tail-clamptechnique. Results. Mean MAC values for isoflurane, sevoflurane and desfluranewere 1.90 (SD 0.18), 3.41 (0.65) and 10.27 (1.06)%, respectively.Body temperature, systolic pressure and Sp_O2 recorded at thetime of MAC determinations for isoflurane, sevoflurane and desfluranewere 38.3 (0.3), 38.6 (0.1) and 38.3 (0.3)°C; 71.2 (8.3),74.6 (15.9) and 88.0 (12.0) mmHg; 99.2 (1.1), 99.1 (1.3) and99.4 (0.8)%, respectively. Both the anaesthetic agent and theindividual cat had significant effects on MAC. Correlation coefficientsfor comparisons between desflurane and isoflurane, desfluraneand sevoflurane, and sevoflurane and isoflurane were 0.90, 0.89and 0.97, respectively. Conclusions. These findings show that an individual has a consistentdegree of sensitivity to a variety of inhaled anaesthetics,suggesting a genetic basis for sensitivity to inhaled anaestheticeffects. Br J Anaesth 2004; 92: 275–7     

Cost-effectiveness and high patient satisfaction in the elderly: sevoflurane versus propofol anaesthesia

BACKGROUND AND OBJECTIVE: The use of propofol compared with isoflurane is associated with improved patient comfort and decreased costs. However, as the cost saving, the quicker recovery time and patient comfort may not be evident if sevoflurane is substituted for isoflurane; these two anaesthetic agents were analysed in elderly patients. METHODS: In a prospective randomized study, 96 patients undergoing elective ophthalmic surgery received either total intravenous anaesthesia with propofol (Group P), propofol for induction and sevoflurane for maintenance (Group P/S) or sevoflurane for inhalation induction and maintenance (Group S). Analyses focussed on haemodynamics, the quality of recovery, and the costs for the anaesthetic and the entire procedure. RESULTS: Bradycardia or hypotension, mainly registered in Groups P and P/S, did not influence patients' recovery. In Group S, postoperative nausea and vomiting occurred frequently, and 50% of patients complained of discomfort during induction. In Group P/S, the costs for anaesthetics and total costs were lower than those in Groups P and S. CONCLUSIONS: Propofol- and sevoflurane-based maintenance of anaesthesia were similar with regard to patient comfort and recovery in the elderly. Cost analysis revealed that it was less expensive to use propofol for induction and sevoflurane for maintenance than to use either propofol or sevoflurane as sole agents for anaesthesia.     

Enflurane (Ēthrane*) and isoflurane (forane*): A comparison with nine general anaesthetics administered with passive hyperventilation

Studies were carried out on 22 large, male, mongrel dogs at two-week intervals, in a crossover design, to determine the metabolic, blood-gas and cardiovascular effects, and the rate of recovery to steady ambulation from a surgical depth of general anaesthesia administered with passive hyperventilation. To prepare the animal, induction of anaesthesia was accomplished with 20 mg/kg body weight of 2 per cent thiopentone, trachéal intubation and inhalation of 50 per cent nitrous oxide and oxygen. After attachment of recording equipment and drawing of control blood samples, a respirator was attached to the anaesthetic circuit to provide passive hyperventilation by providing pulmonary ventilation of 15 ml/kg body weight at the rate of approximately 25 cycles per minute for 90 minutes, adding an anaesthetic concentration of methoxyflurane, chloroform, trichlorethylene, halothane, halothane-ether, azeotrope, isoflurane, cnflurane, diethyl ether, or fluorexcne from an out-of-circuit calibrated vapourizer. Thiopentone and Innovar were also tested and were given by an intravenous drip infusion. Nitrous oxide 50 per cent was given with 50 per cent oxygen with all the maintenance agents. No muscle relaxants were used and no stimulants were administered at the end of the test period. The data support the advantages of passive hyperventilation which have been reported. Full oxygénation is maintained; mild respiratory alkalosis is generally safe with particular respect to the incidence of ventricular arrhythmias and effecton myocardiac contractility (as judged by the lack of appreciable hypotension); metabolic acidosis does not occur except with diethyl ether; excess lactate accumulation is no greater than with isocarbic pulmonary ventilation and is negligible except with diethyl ether. Myocardial oxygen consumption is probably not increased with halogenated anaesthetics except with fluroxene, chloroform and trichlorethylene. The hypotension that occurred with some of the anaesthetics (~30 per cent) is an inherent effect of a surgical depth of general anaesthesia on the peripheral vascular resistance and occurs also with the non-depolarizing skeletal muscle relaxants. Full recovery after anaesthesia with passive hyperventilation is not delayed significantly, since deep general anaesthesia was not greatly prolonged. Recovery of spontaneous respiration was rapid after diethyl ether (<10 minutes) but took approximately 30 minutes (means of 18 to 35 minutes) with the other agents. Steady ambulation usually took approximately 45 minutes longer (means of 25 to 71 minutes) due to muscle weakness after isoflurane, enflurane and methoxyflurane and a prolonged hypnotic effect of the other agents. Neuromuscular disturbances did not occur with enflurane or isoflurane in any of the tests in spite of fairly deep anaesthesia and induction of hypocarbia. On the basis of these animal experiments, there appear to be no obvious disadvantages to the employment of moderate passive hyperventilation for surgical anaesthesia with inhalational or parenteral anaesthetics.     

Anaesthesia and pyruvate dehydrogenase deficiency

A ten-month-old infat with pyruvate dehydrogenase deficiency received anaesthesia on two occasions, once for a laparotomy and once for a trachecstomy. During both anaesthetics (different techniques) she developed an increase in arterial lactate levels and a metabolic acidosis. Pyruvate dehydrogenase deficiency results in the inability to metabolize pyruvate with resultant accumulation of pyruvate and lactate. Inhibition of gluconeogenesis, which may be produced by halothane and thiopentone, will also increase lactate levels. Other causes of increased lactate levels are hypocarbia and high carbohydrate intake. In this patient hypocarbia may have produced increased lactate levels and increased the metabolic acidosis. Recommendations include avoidance of halogenated anaesthetics, avoidance of lactate containing solutions, maintenance of normocarbia, and stress-free anaesthesia.     

Propofol en perfusion ou isoflurane en circuit fermé. Etude du coût

The choice of an anaesthetic agent is influenced by its cost. The use of a circle absorber system decreases the cost of the maintenance of anaesthesia with halogenated agents. Fast recovery and low incidence of postoperative nausea and vomiting are the main advantages of propofol. The cost of propofol can limit its use for the maintenance of anaesthesia except for short procedures. This prospective study compared in 50 ASA 1 and 2 patients the cost of anaesthesia with either propofol (group P, n = 25) or the association thiopentone-isoflurane administered with a rebreathing circuit (group I, n = 25). Patients were premedicated the evening before surgery with 2.5 mg lorazepam. Anaesthesia was induced with either propofol (2–3 mg · kg⁻¹) or thiopentone (4–6 mg · kg⁻¹) and maintained with either propofol (6–10 mg · kg⁻¹ · h⁻¹) in group P or isoflurane continuously injected as liquid in the expiratory limb of the circuit in group I. The side effects of anaesthesia and the delay of recovery and discharge from the recovery room were assessed. Peroperative cost of anaesthesia included nitrous oxide, isoflurane and i.v. agents, fluids volumes and disposable devices. The total cost of anaesthesia included also the recovery room stay. The mean duration of anaesthesia was not significantly different between the two groups (109.4 ± 7.1 min vs 107.3 ± 7.3 min group P vs group I). The delay of recovery (eyes opening) was shorter in the propofol group (14.4 ± 1.3 min vs 19.4 ± 1.4 min) as well as the delay of discharge from the recovery room (70 ± 4 min, vs 82.4 ± 4.6 min). Nausea or vomiting occurred in 2 group P patients and 6 group I patients. The cost of propofol anaesthesia was 1.7 times that of thiopentone-isoflurane (305.7 ± 13.3 FF vs 179.6 ± 8.9 FF, p < 0.001). This additionnal cost of propofol is not excessive in comparison with the cost of surgery and is out-weighted by the advantages of this drug. When the use of propofol for maintenance of anaesthesia is considered, the cost should not be a contraindication to this technique.     

Propofol in paediatric anaesthesia

Propofol has been used in paediatric anaesthesia since 1985 and an increasing body of evidence has shown that it is a safe, effective induction agent which has dose-related side-effects comparable with other agents. Pain on injection can be ameliorated by the use of antecubital veins or by pre-mixing an adequate amount of lignocaine with propofol immediately prior to administration. The pharmacokinetics of propofol are different in children with their larger central compartment volume and clearance reflected in higher dose requirements for induction and maintenance of anaesthesia. This has important implications when propofol is given for sedation or anaesthesia by continuous infusion.