Adjuvant agents in regional anaesthesia

The addition of adjuvant agents to intrathecal and epidural anaesthetic techniques is well established, in particular opioids and clonidine. These adjuvants are utilized to improve the quality of anaesthesia and analgesia. Several other adjuvants have been studied but ongoing concerns surrounding safety and efficacy may limit their use in clinical practice. Epinephrine has for many years been administered in combination with local anaesthetic, although more recently a diverse range of adjuvants have been added to peripheral nerve block solutions, again with the aim of prolonging surgical anaesthesia. The evidence to support or refute the benefit of these agents is increasing, as is our understanding of which agents have demonstrable efficacy and safety at clinically appropriate doses. Clinicians must be aware that many adjuvants are not licensed for central neuraxial or perineural use and should be aware of the risks, in particular of neurotoxicity and unwanted side effects.     

New insights into paediatric regional anaesthesia: new drugs

Over the years paediatric regional anaesthesia has gained a worldwide consensus, and it can now be considered a significant part of perioperative pain control in children. As in many fields, with the use of drugs administered epidurally there is a fundamental need for safety and efficacy. Two new local anaesthetic agents have recently entered the market, ropivacaine and levobupivacaine, which seem to offer a wider safety margin in comparison with the old drugs as well as valid pain control. To prolong their analgesic duration, many adjuvants can be used, and clonidine and ketamine are probably the best solution. This review summarizes the most recent data on these drugs and their use in children.     

Anxiolytics,sedatives and hypnotics

Anxiolytics and sedatives are used in current anaesthetic practice for two main reasons: for anxiolysis before surgery and as adjuvants during anaesthesia. A wide choice of agents are available. Their safety profile is dependent on their pharmacokinetic and pharmacodynamic profiles, patient co-morbidity and the experience of the clinician using them. All sedative drugs have the potential to cause severe respiratory depression, and hence they should only be used with standard physiological cardiorespiratory monitoring. This is especially true of procedural sedation administered by non-anaesthetists in remote locations. Drugs used for anaesthesia vary in their pharmacology, but have broadly similar clinical effects. The choice of drug is usually a matter of individual preference, although pharmacokinetic and pharmacodynamic parameters do influence the selection of anaesthetic agents, especially in day case surgery. Most intravenous agents are thought to alter consciousness by an effect at the GABA_A or N-methyl-d-aspartate receptors or both. Our understanding of the mechanisms of action of anaesthetic drugs is incomplete, not least because of a lack of understanding of consciousness. Several theories have been proposed over the last century, but none of them have managed to comprehensively elucidate the processes involved. There is now a sense of expectation that with the use of modern imaging techniques, anaesthetic drug action can be better understood, and that this may help in our understanding of consciousness and cognitive functions.     

Anxiolytics,sedatives and hypnotics

Anxiolytics and sedatives are used in current anaesthetic practice for anxiolysis before surgery and as adjuvants during anaesthesia. The safety profile of these agents depends on their pharmacokinetic and pharmacodynamic profiles, patient comorbidity and the experience of the clinician. Sedative drugs have the potential to cause severe respiratory depression, and hence they should be used only with standard physiological cardiorespiratory monitoring. The potential for respiratory depression is especially high for procedural sedation administered by non-anaesthetists in remote locations. Drugs used for anaesthesia vary in their pharmacology, but have broadly similar clinical effects. The choice of drug is usually a matter of individual preference, although pharmacokinetic and pharmacodynamic parameters influence the choice of anaesthetic agents, especially in day surgery. Most intravenous agents are thought to alter consciousness by an effect at the γ-aminobutyric acid (GABA_A) or N-methyl-d-aspartic acid (NMDA) receptors or both. Our understanding of the mechanisms of action of anaesthetic drugs is incomplete, not least because of a lack of understanding of consciousness. Several theories have been proposed during the past century, but none has elucidated the processes involved. With the use of modern imaging techniques, anaesthetic-drug action may be better understood, leading to a better understanding of consciousness and cognitive functions.     

Anxiolytics,sedatives and hypnotics

Anxiolytics and sedatives are used in current anaesthetic practice for two main reasons: for anxiolysis before surgery and as adjuvants during anaesthesia. A wide choice of agents are available. Their safety profile is dependent on their pharmacokinetic and pharmacodynamic profiles, patient comorbidity and the experience of the clinician using them. All sedative drugs have the potential to cause severe respiratory depression, and hence they should only be used with standard physiological cardiorespiratory monitoring. This is especially true of procedural sedation administered by non-anaesthetists in remote locations. Drugs used for anaesthesia vary in their pharmacology, but have broadly similar clinical effects. The choice of drug is usually a matter of individual preference, although pharmacokinetic and pharmacodynamic parameters do influence the selection of anaesthetic agents, especially in day case surgery. Most intravenous agents are thought to alter consciousness by an effect at the γ-aminobutyric acid type A (GABA_A) or N-methyl-D-aspartate (NMDA) receptors or both. Our understanding of the mechanisms of action of anaesthetic drugs is incomplete, not least because of a lack of understanding of consciousness. Several theories have been proposed over the last century, but none of them has managed to comprehensively elucidate the processes involved. There is now a sense of expectation that with the use of modern imaging techniques, anaesthetic drug action can be better understood, and that this may help in our understanding of consciousness and cognitive functions.     

Awareness during anaesthesia: a review.

Following the introduction of muscle relaxants into anaesthesia there became recognised a state in which patients may be aware of their surroundings but unable to communicate their plight. This state of awareness is more likely to occur during light inhalational or total intravenous anaesthesia. Detection of awareness is difficult and several methods have been described. Measurement of the depth of anaesthesia is also difficult as clinical signs are unreliable and even sophisticated monitoring equipment is unhelpful. Awareness can occur without patient recall and may be due to equipment failure or anaesthetic failure. The former is avoidable and the latter ought to be. Recommendations have been made regarding the use of premedicant drugs and volatile anaesthetic agents to reduce the incidence of awareness.     

Awareness and general anaesthesia

A state exists after the induction of anaesthesia in which patients may be aware of their surroundings yet unable to communicate. This problem of awareness and recall during general anaesthesia is a recent one in the relatively short history of anaesthesia. Prior to the introduction of muscle relaxants in 1942 by Griffith and Johnson, it was felt that "light anaesthesia" would be signified by violent movements. Today, the concepts of anaesthetic depth, awareness, and recall have become more complicated with the addition of numerous newer, shorter-acting, intravenous anaesthetic agents with varying effects on the conscious state. Several methods have been described to detect awareness. None has yet been found to be totally reliable and numerous reports of awareness can be found in the literature. Light inhalation and total intravenous anaesthesia have been blamed for the majority of these case reports. However, awareness during total intravenous anaesthesia is avoidable with the proper use of a combination of a hypnotic and an analgesic such as midazolam and alfentanil for general anaesthesia.     

Anaesthesia for procedures in the intensive care unit

Taking in charge severely ill patients in the intensive care environment to manage complex procedures is a performance requiring highly specific knowledge. Close collaboration between anaesthetists and intensive care specialists is likely to improve the safety and quality of medical care. Three forms of anaesthetic care should be considered in clinical practice: sedation and analgesia; monitored anaesthetic care; and general anaesthesia or conduction block anaesthesia. Even in the field of sedation and analgesia, the anaesthesiologist can offer expertise on new anaesthetic techniques like: the most recent concepts of balanced anaesthesia in terms of pharmacokinetics and dynamics, favouring the use of short-acting agents and of sedative-opioid combinations. New modes of administration and monitoring intravenous anaesthesia have been developed, with potential application in the intensive care unit. These include the use of target-controlled administration of intravenous drugs, and of electroencephalographic signals to monitor the level of sedation.     

Balanced anaesthesia today

An 'ideal' anaesthetic can be approached by using a combination of different compounds. A variety of anaesthetic techniques has been described to ensure safe administration and an early recovery with high patient satisfaction. In particular, the inhalational anaesthetics desflurane and sevoflurane, with their rapid pharmacokinetics, re-established the notion of balanced anaesthesia as an equivalent, well-controllable technique. With the choice of anaesthetics and anaesthetic adjuvants clinically available today, especially the combination of a volatile anaesthetic with a short-acting opioid, balanced anaesthesia represents a big step towards an ideal anaesthetic.     

Total intravenous anaesthesia

Total intravenous anaesthesia (TIVA) is the induction and maintenance of general anaesthesia exclusively via intravenous anaesthetic agents. TIVA provides an anaesthetic alternative when inhalational agents are relatively or absolutely contraindicated and is also used in a number of practical situations where delivery of inhalational anaesthetic is not feasible, such as during patient transfers. It is essential that all anaesthetists understand the pharmacokinetic principles involved with TIVA and are confident in their ability to deliver TIVA safely. This article describes the key pharmacokinetic principles and models used for TIVA with additional focus on practical and safety aspects during its use.     

Intravenous regional anaesthesia

Intravenous regional anaesthesia (IVRA) was first described almost a century ago by August Bier and has been used for the past 50 years. It is a safe anaesthetic technique for upper or lower distal limb surgery. It utilizes a tourniquet, ideally a double tourniquet, followed by exsanguination of the appropriate limb after insertion of a cannula, through which local anaesthetic is injected. Anaesthesia and analgesia follow rapidly, the tourniquets preventing systemic local anaesthetic toxicity as well as fixing the local anaesthetic to where it is required. The safest local anaesthetic is prilocaine 0.5%. Lidocaine 0.5% can also be used. Several adjuvants have been described to prolong anaesthesia time and reduce tourniquet pain.     

The role of nonmedical staff in the delivery of anaesthesia service

PURPOSE OF REVIEW: There are many different ways of organizing anaesthetic teams, in particular because the role of nonmedical staff as assistants and anaesthesia providers varies between countries. Nevertheless, in many countries the nature and organization of anaesthesia teams is under review. A discussion of the ideas being expressed is timely. RECENT FINDINGS: Debate, comment and even developments are often based more on opinion than evidence. Anaesthesia teams are being extended both by the increased use of nonmedical staff to administer anaesthesia and by the use of specialized assistants to undertake anaesthetic and peri-anaesthetic tasks. These developments have not been shown to be unsafe and may alleviate potential shortages of anaesthesia providers. SUMMARY: Many factors influence the organization of anaesthesia teams. This review focuses on issues of manpower, standards, inter-professional working and the extending of the anaesthesia team. There are many ways of constructing viable anaesthesia teams. They must be fit for purpose within the context of their work and must satisfy criteria for outcome and audit of their processes.     

Anaesthesia and the 'inert' gases with special reference to xenon.

Xenon has many of the properties of the ideal anaesthetic agent and has been proposed as a suitable replacement for nitrous oxide in routine clinical anaesthesia. Xenon, krypton and argon are chemically inert under most circumstances, yet all have anaesthetic properties. Xenon is of particular interest because it is the only 'inert' gas which is an anaesthetic under normobaric conditions. Because of this property, xenon has an important place in the history of the development of theories of anaesthetic action and of concepts such as MAC. Cost is likely to be a major impediment to the regular use of xenon.     

Local infiltration anaesthesia with ropivacaine 0.5% for excision of benign naevi

Ropivacaine is a new type of long-acting local anaesthetic of less systemic toxicity than bupivacaine. The objective of this double-blind study was to compare the efficacy and safety of ropivacaine 0.5% and mepivacaine 1% for infiltration anaesthesia in dermatologic surgery. Sixty out-patients aged 18–65 years, scheduled for excision of a benign naevus on the back, were randomly assigned to infiltration anaesthesia with either ropivacaine or mepivacaine. Both agents had a fast onset, and provided reliable anaesthesia and painfree surgery which could be carried out without the use of vasoconstrictive adjuncts or diathermy. Ropivacaine resulted in a longer duration of analgesia than mepivacaine, and both treatments were well tolerated.     

Muscle relaxants and histamine release

Many anaesthetic drugs and adjuvants can cause the release of histamine by chemical (anaphylactoid) or immunologic (anaphylactic) mechanisms. While both types of reactions can be clinically indistinguishable, they are mechanistically different. In anaphylactoid reactions, only preformed mediators are released, of which histamine may be the most clinically important. In true immunologic reactions, mast cell degranulation occurs, and many vasoactive substances (including histamine) are released. Clinical signs and symptoms of both classes of reactions include hypotension (most common), tachycardia, bronchospasm, or cutaneous manifestations. Anaphylactoid reactions may occur commonly under anaesthesia in response to many drugs, including induction agents, some opiates, plasma expanders, and curariform relaxants. Anaphylactic reactions are far less common than anaphylactoid reactions, but they nevertheless represent more than half of the life-threatening reactions that occur in anaesthetic practice. Muscle relaxants are the most frequently implicated class of drugs; suxamethonium is the most common agent implicated in anaphylactic reactions during anaesthesia, but even drugs without apparent chemical histamine release (i. e., vecuronium) are frequently implicated in anaphylactic reactions.     

Inhalational anaesthetic agents

The continued development of anaesthetic agents since the late 18th century has paved the way for the progression of surgical techniques. Inhalational agents are used worldwide for the delivery of safe, effective anaesthesia. These include the volatile agents halothane, isoflurane, sevoflurane and desflurane, in addition to the anaesthetic gases nitrous oxide and xenon. Although the newer volatiles have an improved safety profile in comparison to older agents, the ideal anaesthetic agent remains elusive. It is vital for anaesthetists to understand the physical properties, pharmacodynamics and pharmacokinetics of the individual inhalational anaesthetic agents so that the most appropriate agent for a patient or procedure is selected and administered correctly.     

Anaesthesia for coronary artery surgery — a plea for a goal-directed approach

The purpose of the current literature review was to examine whether changes in current anaesthetic techniques are warranted for patients undergoing coronary artery surgery in light of recent information presented in the literature. The objectives of a cardiac anaesthetic technique are to maintain haemodynamic stability and myocardial oxygen balance, minimize the incidence and severity of ischaemic episodes, be aware of cardiopulmonary bypass-induced pharmacokinetic changes, and facilitate early tracheal extubation if appropriate. Many techniques have been utilized. Provided attention is paid to the details of managing myocardial oxygen supply and demand, none has emerged as superior in preventing intraoperative myocardial ischaemia. Silent myocardial ischaemia (i.e., ischaemia occurring in the absence of haemodynamic aberrations) is common throughout the perioperative period and may occur even in the presence of an appropriately used anaesthetic technique. The incidence and severity appear to be greatest in the postoperative period when the effects of anaesthesia are dissipating. The use of high-dose opioid anaesthesia may no longer be the most appropriate technique to facilitate the anaesthetic objectives. The role of pain management in altering the incidence of ischaemia requires further study. Increased waiting lists for cardiac surgery and ever-diminishing resources should prompt a re-evaluation of early extubation (i.e., within eight hours) as a method of improving utilization of scarce ICU resources. It is suggested that this should be possible with currently available agents to achieve the anaesthetic objectives. Future suggestions for research in this area are made.     

Laboratory animal anaesthesia: influence of anaesthetic protocols on experimental models

The use of experimental animals requires anaesthesia to provide immobility and analgesia. Animals require anaesthesia not only for ethical reasons but also because pain and stress can alter the quality of research results. Recognition of pain, and its treatment is important throughout the procedure. Before anaesthesia, animals are acclimated and rehydrated. Except in small rodents and in ruminants, in order to avoid vomiting, a fast of 8 to 12 hours before anaesthesia is recommended. In order to protect animals against suffering and distress during transfer, restraint and management, a premedication is administered. Most human anaesthetic products can be used in animals. There are some specific veterinary anaesthetics. Moreover, the anaesthetic effects could be different from specie to an other. In most big animals, induction is realized by intravenous administration. In small rodents, venous puncture and contention could be difficult, and anaesthetic agents may be injected via intraperitoneal or intramuscular way. The principal inconvenient of these administration routes is the impossibility to adjust dose to animal response. In large animals, human anaesthesia material can be used. Some technical adaptations could be necessary in smaller animals. In rodents or in neonatology, specific devices are recommended. ECG, arterial pressure, tidal volume, expired CO(2) and oxygen saturation monitoring assess quality of, and tolerance to anaesthesia. If animals are awaked after anaesthesia, postoperative management is closed to human clinical problems. During animal experimentations, anaesthesia may interact with results. All anaesthetic drugs alter normal physiology in some way and may confound physiologic results. In the literature, most publications do not mention this possible interaction. Investigators need to understand how animals are affected by anaesthetic drugs in order to formulate anaesthetic protocols with minimal effects on data. Extrapolation between different animal species and human and animals about the effects of anaesthetic agents are very hazardous. Great differences exist between the effects observed in vitro and in whole animals. The effects of the anaesthetics could be totally different if they are used alone or in association. The same anaesthetic could have opposite effects from an organ to another. For results validation, the anaesthesia side effects (hypoventilation, hypotension, cooling em leader ) have to be minimized. All new experimental models should require discussing the possible interferences between anaesthesia and results and to compare results obtained with different anaesthetic protocols.     

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.