• Respiratory system – apnoea following injection may require assisted ventilation. If opioids are also administered, as with other agents, the respiratory depression is more marked. • Pain on injection – this is common, and the incidence is reduced if a larger vein is used or lidocaine mixed with propofol. • Involuntary movements and convulsions (which can be delayed). KETAMINE Use and pharmacokinetics Ketamine is chemically related to phencyclidine (still used as an animal tranquillizer, but no longer for therapeutic use in humans because of its psychogenic effects and potential for abuse), and produces dissociative anaesthesia, amnesia and profound analgesia. It is a relatively safe anaesthetic from the viewpoint of acute cardiorespiratory effects since, unlike other intravenous anaesthetics, it is a respiratory and cardiac stimulant. A patent airway is maintained and it is a bronchodilator. Because of its ease of administration and safety, its use is widespread in countries where there are few skilled anaesthetists. It has been used for management of mass casualties or for anaesthesia of trapped patients to carry out amputations, etc. It is used in shocked patients, because unlike other intravenous anaesthetics it raises rather than lowers blood pressure. An intravenous dose produces anaesthesia within 30–60 seconds, which lasts for 10–15 minutes. An intramuscular dose is effective within three to four minutes, and has a duration of action of 15–25 minutes. There is a high incidence of hallucinations, nightmares and transient psychotic effects. Children cannot articulate such symptoms and it is disturbing that it is still used particularly in this age group. Adverse effects • Psychosis and hallucinations are common. • Intracranial pressure is increased by ketamine. • Blood pressure and heart rate are increased. • Salivation and muscle tone are increased. • Recovery is relatively slow. Key points • Intravenous anaesthetics may cause apnoea and hypotension. • Adequate resuscitation facilities must be available. OTHER AGENTS Etomidate has a rapid onset and duration of action and has been used for induction. Its use has declined because it causes pain on injection, nausea and vomiting, and excitatory phenomena including extraneous muscle movements. Etomidate can suppress synthesis of cortisol (see below) and it should not be used for maintenance of anaesthesia. Key points Intravenous induction agents SUPPLEMENTARY DRUGS BENZODIAZEPINES SUPPLEMENTARY DRUGS 149 All have a rapid onset of action, with propofol gradually replacing thiopental in the UK as the usual agent of choice. • Propofol – rapid recovery, pain on injection, bradycardia which may be avoided by use of an antimuscarinic agent, rarely anaphylaxic and causing convulsions. • Thiopental – smooth induction but narrow therapeutic index, cardiorespiratory depression, awakening usually rapid due to redistribution, but metabolism slow and sedative effects prolonged, very irritant injection. • Methohexitone – barbiturate similar to thiopental, less smooth induction, less irritant, may cause hiccup, tremor and involuntary movements. • Etomidate – rapid recovery and less hypotensive effect than propofol and thiopental, but painful on injection. Extraneous muscle movements and repeated doses cause adrenocortical suppression. • Ketamine – good analgesic, increases cardiac output and muscle tone. Due to unpleasant psychological effects (e.g. nightmares and hallucinations) it is restricted to high-risk patients. Useful in children (in whom central nervous system (CNS) effects are less problematic), particularly when repeated doses may be required, and in mass disasters (relatively wide therapeutic index, may be used intramuscularly, slow recovery, safer than other agents in less experienced hands). See Chapters 18 and Chapter 22. Midazolam is a water-soluble benzodiazepine and useful intravenous sedative. It has a more rapid onset of action than diazepam and a shorter duration of action, with a plasma half-life of 1.5–2.5 hours. Dose is titrated to effect. Midazolam causes amnesia, which is useful for procedures such as endoscopy or dentistry. The use of benzodiazepines for induction of anaesthesia is usually confined to slow induction of poor-risk patients. Prior administration of a small dose of midazolam decreases the dose of intravenous anaesthetic required for induction. Large doses can cause cardiovascular and respiratory depression. Repeated doses of midazolam accumulate and recovery is prolonged. Diazepam is used for premedication (oral), sedation (by slow intravenous injection) and as an anticonvulsant (intravenously). A preparation formulated as an emulsion in soyabean oil has reduced thrombophlebitis from intravenous diazepam. OPIOIDS High-dose opioids (see Chapter 25) are used to induce and maintain anaesthesia in poor-risk patients undergoing major surgery. Opioids such as fentanyl provide cardiac stability.
150 ANAESTHETICS AND MUSCLE RELAXANTS Onset is slow and the duration of action prolonged so that ventilatory support is required post-operatively. Addition of a small dose of volatile anaesthetic, benzodiazepine or propofol is required to avoid awareness during anaesthesia. High-dose opioids can cause chest wall rigidity interfering with mechanical ventilation. This can be prevented by muscle relaxants. FENTANYL Fentanyl is a synthetic opioid and is the most commonly employed analgesic supplement during anaesthesia. It is very lipid soluble and has an onset time of one to two minutes. It has approximately 100 times the analgesic activity of morphine. Fentanyl is rapidly and extensively metabolized, the t1/2 being two to four hours, the short duration of action (the peak effect lasts only 20–30 minutes) being explained by redistribution from brain to tissues. Particular care should be taken after multiple injections because of saturation of tissue stores. Depression of ventilation can occur for several minutes. Fentanyl and the other potent opioids must not be used in situations where ventilation cannot be controlled. Fentanyl has little cardiovascular effect, but bradycardia may occur. Neuroleptanalgesia is produced by a combination of a butyrophenone (droperidol) and an opioid (fentanyl). It is a state of inactivity and reduced response to external stimuli, sometimes used for complex diagnostic procedures. ALFENTANIL Alfentanil is a highly lipid-soluble derivative of fentanyl that acts in one arm–brain circulation time. It has a short duration of action of five to ten minutes, and is often used as an infusion, but causes marked respiratory depression for some minutes. REMIFENTANIL Remifentanil is a μ agonist with a rapid onset and short duration. It has an ester linkage, making it susceptible to rapid hydrolysis by a number of non-specific esterases in blood and tissues. It is administered as an infusion and does not accumulate even after a three-hour infusion. Its t1/2 is five to seven minutes. It is a useful adjunct to anaesthetics, particularly in patients with renal or hepatic impairment. α 2-ADRENOCEPTOR AGONISTS Clonidine has analgesic, anxiolytic and sedative properties. It potentiates inhalational and intravenous anaesthetics. The reduction of MAC of anaesthetics is more marked with the more specific α 2-adrenoceptor agonist dexmetomidine, but this is not currently available in the UK. Adverse effects include hypotension and bradycardia. SEDATION IN THE INTENSIVE CARE UNIT Patients in the intensive care unit frequently require sedative/ analgesic drugs to facilitate controlled ventilation, to provide sedation and analgesia during painful procedures, to allay anxiety and psychological stress and to manage confusional states. The choice of agent(s) used is tailored to meet the needs of the individual patient and must be frequently reviewed. Most sedative and analgesic drugs are given by continuous intravenous infusion both for convenience of administration and for control. Opioids are often used to provide analgesia. They also suppress the cough reflex and are respiratory depressants, which is useful in ventilated patients. Morphine and fentanyl have been used for long-term sedation. Alfentanil has a short half-life and is given by infusion. Opioids are often combined with benzodiazepines (e.g. midazolam). Monitoring the level of sedation is particularly important in cases where long-acting opioids or benzodiazepines are being used whose action may be prolonged due to accumulation of drug and active metabolites. Propofol is increasingly used where shortterm sedation or regular assessment is required, because its lack of accumulation results in rapid recovery. It is not recommended in children. Etomidate was used for intensive care sedation before it was shown to increase mortality by adrenocortical suppression. Inhalational agents, such as isoflurane, have also been successfully used to provide sedation. Occasionally, muscle relaxants are indicated in critically ill patients to facilitate ventilation. Atracurium is then the drug of choice and sedation must be adequate to avoid awareness. PREMEDICATION FOR ANAESTHESIA Premedication was originally introduced to facilitate induction of anaesthesia with agents, such as chloroform and ether, that are irritant and produce copious amounts of secretions. Modern induction methods are simple and not unpleasant, and the chief aim of premedication is now to allay anxiety in the patient awaiting surgery. Oral temazepam is often the only premedication used before routine surgery. Adequate premedication leads to the administration of smaller doses of anaesthetic than would otherwise have been required, thereby resulting in fewer side effects and improved recovery. Intravenous midazolam, which causes anxiolysis and amnesia, can be used. Opioids such as morphine, phenothiazines and muscarinic receptor antagonists (e.g. hyoscine) are also used. Gastric prokinetic agents, anti-emetics and H 2-receptor antagonists are used to enhance gastric emptying, decrease the incidence of nausea and vomiting, and reduce gastric acidity and volume in certain situations. MUSCLE RELAXANTS Muscle relaxants are neuromuscular blocking drugs which cause reversible muscle paralysis (Figure 24.3). They are grouped as follows: • non-depolarizing agents (competitive blockers), such as vecuronium and atracurium, which bind reversibly to the post-synaptic nicotinic acetylcholine receptors on the motor end-plate, competing with acetylcholine and thereby preventing end-plate depolarization and blocking neuromuscular transmission; • suxamethonium, a depolarizing agent which also binds acetylcholine receptors at the neuromuscular junction,
Soliman s Auricular Therapy Textbook: New Localizations and Evidence Based Therapeutic Approaches was created ( M.D. Nader Soliman )
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Soliman s Auricular Therapy Textbook This textbook is considered the finest ever written in the field of auricular therapy. The auricular acupuncture microsystem is one of the most widely used special acupuncture techniques. This textbook is dedicated to teaching the sound foundations of this unique approach as introduced by its founder Dr. Paul Nogier of France. The scientific bases of the acupuncture microsystem with its three dime... Full description
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