Anesthesia – is a reversible condition of comfort, quiescence and physiological stability in a patient before, during and after performance of a procedure
General anesthesia – for surgical procedure to render the patient unaware / unresponsive to the painful stimuli. Drugs producing General Anaesthesia – are called General Anaesthetics
Local anesthesia – reversible inhibition of impulse generation and propagation in nerves. In sensory nerves, such an effect is desired when painful procedures must be performed, e.g., surgical or dental operations. Drugs producing Local Anaesthesia – are called Local Anaesthetics
General anesthetics (Inhalation and Intravenous). Are drugs which produce reversible loss of all sensation and consciousness, or simply, a drug that brings about a reversible loss of consciousness
These drugs are generally administered by an anesthesiologist/anesthetist in order to induce or maintain general anesthesia to facilitate surgery.
Inhalation anesthetics: They serve to induce and maintain anesthesia. Examples are Gas: Nitrous Oxide;
• Enflurane, Isoflurane, Desflurane, sevoflurane
Intravenous anesthetics are frequently employed for induction. Examples are
• thiopental (Thiopentone),
Indications of General Anesthetics
• Halothane is occasionally used for inhalation induction of anaesthesia with careful monitoring for cardiorespiratory depression and arrhythmias.
• Ketamine is useful in induction and maintenance of anaesthesia it is used during surgery and intubation.
• Isoflurane is a volatile liquid anaesthetic. It is used in induction and maintenance of anaesthesia. It is useful during surgery and intubation
• Thiopental is used in induction of general anaesthesia, anaesthesia of short duration reduction during surgery and intubation
Contraindication of General Anesthetics
• Halothane is contraindicated if the anesthetist is not confident of being able to maintain the airway (e.g. in the presence of a tumour in the pharynx or larynx). Extreme care is required in surgery of the mouth, pharynx, or larynx and in patients with acute circulatory failure.
• Ketamine is contraindicated if the anesthetist is not confident of being able to maintain the airway (e.g. in the presence of a tumour in the pharynx or larynx). Extreme care is required in surgery of the mouth, pharynx, or larynx and in patients with acute circulatory failure. Also in hypertension, pre-eclampsia or eclampsia, severe cardiac disease, raised intracranial pressure, head trauma, and porphyria.
• Isoflurane is contraindicated to women who are breast feeding.
• Thiopental is contraindicated if the anesthetist is not confident of being able to maintain the airway (e.g. in the presence of a tumour in the pharynx or larynx). Extreme care is required in surgery of the mouth, pharynx, or larynx and in patients with acute circulatory failure. Also in acute porphyria, myotonic dystrophy and breast-feeding.
Side Effects and Adverse Effects of General Anaesthetics
• Halothane; Side effects include severe hepatotoxic which can be fatal in repeated uses.
• Ketamine; Side effects include incidence of hallucinations, nightmares, and other transient psychotic effects. Other side effects are tachycardia, hypertension, arrhythmias, hypotension, bradycardia, increased salivation, laryngospasm, anxiety, insomnia, diplopia, nystagmus, raised intra-ocular pressure and rashes at injection-site.
• Isoflurane; Side effects include irritation of mucous membranes causing cough, breath holding and laryngospasm.
• Thiopental; Side effects include hypotension, arrhythmias, myocardial depression, laryngeal spasm, cough, sneezing, hypersensitivity reactions, rash at injection-site reactions. Excessive dose is associated with hypothermia and profound cerebral impairment
• Esters: Cocaine, Procaine, Tetracaine, benzocaine
• Amides: Lidocaine/lignocaine, Mepivacaine, bupivacaine
Indication of Local Anaesthetics include
Bupivacaine: –labour, surgery and local infiltration
Contraindication of Local Anaesthetics
Bupivacaine and Lignocaine are contraindicated in hypovolaemia, complete heart block and should not be used in solutions containing adrenaline for anaesthesia in appendages
Side Effects and Adverse Effects of Local Anaesthetics
Bupivacaine and Lignocaine Side effects include
• initially a feeling of inebriation and lightheadedness followed by sedation, circumoral paraesthesia and twitching.
• Convulsions can occur in severe reactions.
• Also CNS effects which include confusion, respiratory depression and convulsions, hypotension and bradycardia (may lead to cardiac arrest)
Group: local anaesthetic agent Injection (hydrochloride): 2.5 mg/ml (0.25%) or 5 mg/ml (0.5%) in 10-ml ampoule; 5 mg/ml (0.5%) in 1.8-ml cartridge for dental anaesthesia; 7.5 mg/ml (0.75%) with glucose 82.5 mg/ml (8.25%) in 4-ml ampoule
Bupivacaine is a long-acting local anaesthetic. Addition of epinephrine is thus rarely required. It blocks initiation and transmission of nerve impulses at the site of application by stabilizing the neuronal membrane. The compound is ultimately metabolized in the liver. Depending upon the site of injection and the concentration used, anaesthesia usually lasts 2-4 hours.
Nitrous oxide, commonly known as laughing gas or nitrous, is a chemical compound, an oxide of nitrogen with the formula N2O. At room temperature, it is a colourless non-flammable gas, with a slight metallic scent and taste. At elevated temperatures, nitrous oxide is a powerful oxidizer similar to molecular oxygen. It is soluble in water.
Nitrous oxide has significant medical uses, especially in surgery and dentistry, for its anaesthetic and pain reducing effects. Its name “laughing gas”, coined by Humphry Davy, is due to the euphoric effects upon inhaling it, a property that has led to its recreational use as a dissociative anaesthetic. It is on the World Health Organization’s List of Essential Medicines, the most effective and safe medicines needed in a health system. It also is used as an oxidizer in rocket propellants, and in motor racing to increase the power output of engines.
Group: local anaesthetic agent
Injection (hydrochloride): 5 mg/ml (0.5%), 10 mg/ml (1%) in 20-ml ampoule; 10 mg/ml (1%) + epinephrine 5 micrograms/ml (1:200 000) in 20-ml ampoule; 20 mg/ml (2%) + epinephrine 12.5 micrograms/ml (1:80 000) in 2.2-ml cartridge for dental anaesthesia; 50 mg/ml (5%) in 2-ml ampoule to be mixed with 75 mg/ml (7.5%) glucose solution
Topical forms: 20-40 mg (hydrochloride)/ml (2-4%) as gel or solution
Lidocaine is a moderately long-acting local anaesthetic. It blocks initiation and transmission of nerve impulses at the site of application by stabilizing the neuronal membrane. The compound is ultimately metabolized in the liver.
Anaesthesia, which persists for 1-3 hours, is induced within 1-5 minutes following mucosal application, infiltration and spinal or dental nerve block, and within 10-15 minutes following other methods of administration.
Isoflurane, sold under the trade name Forane among others, is a general anesthetic. It can be used to start or maintain anesthesia. Often another medication is used to start anesthesia due to airway irritation with isoflurane. It is used by inhalation.
Isoflurane (isoflurane, USP) is a nonflammable, nonexplosive general inhalation anesthetic agent. Its chemical name is 1-chloro-2,2,2-trifluoroethyl difluoromethyl ether.
Isoflurane has a lower solubility coefficient than that of halothane, so induction and recovery with isoflurane is faster than with halothane. However, isoflurane causes moderate to severe airway irritability if used as an induction agent.
Halothane, sold under the brand name Fluothane among others, is a general anesthetic. It can be used to start or maintain anaesthesia. One of its benefits is that it does not increase the production of saliva which can be particularly useful in those who are difficult to intubate.
It is used by inhalation. It is a potent anesthetic with a MAC of 0.74%. Its blood/gas partition coefficient of 2.4 makes it an agent with moderate induction and recovery time. It is not a good analgesic and its muscle relaxation effect is moderate.