Anesthetic Drugs 2023 PDF

1 What is anesthesia Anesthesia is a loss of feeling or sensation. An anesthesiologist is a physician with special training in administering anesthesia. Anesthesia may be induced by various drugs that are able to bring about partial or complete loss of sensation. There are two types of...

1 What is anesthesia Anesthesia is a loss of feeling or sensation. An anesthesiologist is a physician with special training in administering anesthesia. Anesthesia may be induced by various drugs that are able to bring about partial or complete loss of sensation. There are two types of anesthesia: local anesthesia and general anesthesia. 2 Local anesthesia As the term implies, is the provision of a pain-free state in a specific area (or region). With a local anesthetic, the patient is fully awake but does not feel pain in the area that has been anesthetized. Some procedures done under local anesthesia may require the patient to be sedated. Sedated patients, although not fully awake, may still hear what is going on around them. 3 General anesthesia General anesthesia is the provision of a pain-free state for the entire body. When a general anesthetic is given, the patient loses consciousness and feels no pain. Reflexes, such as the swallowing and gag reflexes, are lost during deep general anesthesia. General anesthesia is essential to surgical practice because it acts on the CNS or ANS to render the patient analgesic, amnesic, and unconscious while causing muscle relaxation and suppression of undesirable reflexes. 4  No single drug can achieve these effects rapidly and safely. Rather, several different categories of drugs are utilized to produce “balanced anesthesia”. The choice of anesthetic drug depends on many factors, including: The general physical condition of the patient The area, organ, or system being operated on The anticipated length of the surgical procedure Ideal general anesthetics induce anesthesia rapidly and smoothly and permit rapid recovery of the patient once administration of the agent ceases. 5  The administration of general anesthesia may require the use of one or more drugs. Used alone or in combination with other agents, an optimum depth of anesthesia may be obtained for a variety of surgical procedures. 6 Anesthetic management Contemporary anesthetic management requires: 1. rapid loss of consciousness, which eliminates awareness, memory of pain, anxiety, and stress throughout the surgical period; 2. a level of analgesia sufficient to abolish the reflex reactions to pain, such as muscular movement and cardiovascular stimulation; 3. minimal and reversible influence on vital physiological functions, such as those performed by the cardiovascular and respiratory systems; 7 4. relaxation of skeletal muscle to facilitate endotracheal intubation, provide the surgeon ready access to the operative field, and reduce the dose of anesthetic required to produce immobility; 5. prompt patient recovery to psychomotor competence, facilitating the clinician’s assessment of the patient and the patient’s ability to become physiologically self- supporting; and 6. lack of operating room safety hazards, such as flammability and explosiveness 8 Balanced anesthesia Balanced anesthesia is a term used to describe the multidrug approach to managing the patient’s anesthetic needs. Balanced anesthesia takes advantage of each drug’s beneficial effects while minimizing each agent’s adverse qualities. 9 Stages of anesthesia The depth of anesthesia can be divided into a series of four stages; Each stage is characterized by increased CNS depression that is caused by accumulation of the anesthetic drug in the brain. Stage I – analgesia, stage II – excitement (delirium), stage III – surgical anesthesia, stage IV – medullary paralysis. 10 Stage I anesthesia Induction is a part of stage I anesthesia. It begins with the administration of an anesthetic drug and lasts until consciousness is lost. With some induction drugs, such as the short-acting barbiturates, this stage may last only 5 to 10 seconds. 11 Stage II anesthesia STAGE II is the stage of delirium and excitement. This stage is also brief. During this stage, the patient may move about and mumble incoherently. The muscles are somewhat rigid, and the patient is unconscious and cannot feel pain. During this stage, noises are exaggerated, and even quiet sounds may seem extremely loud to the patient. 12 Stage II anesthesia If surgery were attempted at this stage, there would be a physical reaction to painful stimuli, yet the patient would not remember sensing pain. During these first two stages of anesthesia, the nurse and other health care professionals avoid any unnecessary noise or motion. 13 Stage III anesthesia STAGE III is the stage of surgical analgesia and is divided into four parts, planes, or substages. The anesthesiologist differentiates these planes by the character of the respirations, eye movements, certain reflexes, pupil size, and other factors. The levels of the planes range from plane 1 (light) to plane 4 (deep). At plane 2 or 3, the patient is usually ready for the surgical procedure. 14 Stage IV anesthesia STAGE IV is the stage of respiratory paralysis and is a rare and dangerous stage of anesthesia. At this stage, respiratory arrest and cessation of all vital signs may occur. 15 16  Intravenous (IV) anesthetics are generally employed to induce anesthesia, to provide supplemental anesthesia, or to permit anesthesia for short operative procedures. The inhalational anesthetics are most often used for longer term maintenance of the anesthetic state. Although (IV) agents produce anesthesia rapidly, most are metabolized slowly, so recovery may be prolonged when an IV anesthetic is used as the primary drug during a long surgical procedure. In contrast, while the anesthetic partial pressure of an inhalational agent is achieved slowly, the patient recovers at a clinically acceptable rate. 17 INTRAVENOUS ANESTHETIC AGENTS Ultra–Short-Acting Barbiturates Among the barbiturates, three compounds are useful as induction agents, as supplemental drugs only during short periods when surgery requires increased depth of anesthesia, or as maintenance hypnotics for short surgical procedures. The three agents are thiopental sodium (Pentothal Sodium), thiamylal sodium (Surital), and methohexital sodium (Brevital Sodium), 18 Benzodiazepines Midazolam (Dormicum, Versed), diazepam (Valium), and lorazepam (Ativan) are benzodiazepine derivatives that are useful in anesthesia. Midazolam is the most popular of these agents for the induction of anesthesia. Its popularity is related to its aqueous solubility and to its short duration of action, which permits a prompt return of psychomotor competence. 19 Etomidate The pharmacological properties of etomidate (Amidate) are similar to those of the barbiturates, although its use may provide a greater margin of safety because of its limited effects on the cardiovascular and respiratory systems. Due to its relatively short elimination half-life of 2.9 hours, etomidate has been used as a supplement to maintain anesthesia in some critically ill patients, in addition to its use as an induction agent,. Etomidate is rapidly hydrolyzed in the liver. 20 Adverse Effects Etomidate may cause pain on injection and may produce myoclonic muscle movements in approximately 40% of patients during its use as an induction anesthetic therefore, caution should be exercised with induction in patients with seizure activity. In addition, etomidate can suppress the adrenocortical response to stress, an effect that may last up to 10 hour 21 Propofol Propofol (Diprivan) is primarily a hypnotic drug with substantial cardiorespiratory depressant actions and with no ability to produce neuromuscular blockade. Propofol is rapidly acting, has a short recovery time, and possesses antiemetic properties. A rapid onset of anesthesia (50 seconds) is achieved, and if no other drug is administered, recovery will take place in 4 to 8 minutes. The recovery is attributed to redistribution of the drug and rapid metabolism. 22 Propofol Rapid recovery and its antiemetic properties make propofol anesthesia very popular as an induction agent for outpatient anesthesia. Propofol can also be used to supplement inhalational anesthesia in longer procedures. Both continuous infusion of propofol for conscious sedation and with opioids for the maintenance of anesthesia for cardiac surgery are acceptable techniques While propofol lacks analgesic properties, its use permits lower doses of opioids. 23  Likewise, less propofol is required for adequate hypnosis when it is administered with opioids. Thus, it is said that propofol and opioids interact synergistically. The dose of propofol should be reduced in older patients. Anesthesia induction with propofol causes a significant reduction in blood pressure. 24 Ketamine Ketamine pharmacological actions are quite different from those of the other IV anesthetics. The state of unconsciousness it produces is trance- like (i.e., eyes may remain open until deep anesthesia is obtained) and cataleptic; it has frequently been characterized as dissociative (i.e., the patient may appear awake and reactive but does not respond to sensory stimuli). The term dissociative anesthesia is used to describe these qualities of profound analgesia, amnesia, and superficial level of sleep 25 Advantages of ketamine A most important advantage of ketamine over other anesthetic agents is its potential for administration by the IM route. This is particularly useful in anesthetizing children, since anesthesia can be induced relatively quickly in a child who resists an inhalation induction or the insertion of an IV line. 26 Disadvantages of ketamine The most serious disadvantage to the use of ketamine is its propensity to evoke excitatory and hallucinatory phenomena as the patient emerges from anesthesia. Patients in the recovery period may be agitated, scream and cry, hallucinate, or experience vivid dreams. Other reported side effects include vomiting, salivation, lacrimation, shivering, skin rash, and an interaction with thyroid preparations that may lead to hypertension and tachycardia. 27 Neuroleptansthesia When neuroleptic agent is combined with a powerful narcotic, neuroleptanalgesia is produced. The addition of nitrous oxide and oxygen to this combination produces neuroleptanesthesia. A combination of fentanyl and droperidol available as product called Innovar. When Innovar is given (IM) 45 minutes preoperatively: It provides excellent operative sedation, analgesia, and patient cooperation. Postoperative complications are minimized, and the quantity of postoperative analgesics and antiemetics is drastically reduced when Innovar is used as a preoperative medication. 28 Inhalational anesthetics Inhalational anesthetics can be divided into two classes based on their physical properties. 1. Nitrous oxide (N2O) and cyclopropane are gases at room temperature and are supplied in gas tanks that are regulated by the anesthesia machine. 2. The others are liquids that are volatile following the application of low heat, which is supplied by a vaporizer attached to the anesthesia machine. The halogenated hydrocarbons are among the most potent volatile anesthetics. 29  Since the anesthesiologist has control over the partial pressure of anesthetic delivered to the lung, it can be manipulated to control the anesthetic gas concentration in the brain, hence the level of unconsciousness. For this reason, anesthetic dose is usually expressed in terms of the alveolar tension required at equilibrium to produce a defined depth of anesthesia. The tension required is defined as the minimum alveolar concentration (MAC) and is usually expressed as the percentage of inhaled gases that is represented by anesthetic gas at 1 atm. 30  Various anesthetic agents require widely different partial pressures to produce the same depth of anesthesia The anesthetic dose is determined experimentally as the partial pressure needed to eliminate movement in 50% of patients challenged with a standardized skin incision. 31 Halogenated Hydrocarbon Anesthetics Sevoflurane, desflurane, enflurane, isoflurane, halothane, and methoxyflurane are quite potent halogenated hydrocarbon anesthetics, since they produce surgical levels of anesthesia at low inspired partial pressures. None of the halogenated hydrocarbons, however, possess all the pharmacological properties that are considered desirable for an anesthetic agent, so they are often given with other anesthetics and adjunctive drugs to provide effective and safe anesthetic management. 32  Halothane Halothane is a highly potent (with a MAC of 0.75%), non- flammable general anesthetic with a relatively high blood: gas partition coefficient; thus, induction of and recovery from anesthesia with halothane may be prolonged. Halothane is a safe anesthetic for children. Side effects: arrhythmias, shivering during recovery is common, vomiting, liver damage. Enflurane It is less potent than halothane, but it produces rapid induction and recovery. Enflurane causes a lower incidence of arrhythmias and better skeletal muscle relaxant than halothane but unlike halothane, it can cause seizure activity. 33  Isoflurane Isoflurane is the anesthetic of choice among the dialkyl- haloethers, Unlike enflurane, isoflurane does not cause seizure activity, Unlike halothane. It does not induce arrhythmias. Methoxyflurane Methoxyflurane is the most potent inhalation anesthetic because of its high solubility in lipid. Sevoflurane Sevoflurane is used for induction and maintenance of general anesthesia, It has low pungency, allowing rapid uptake without irritating the airway during induction making it suitable for children. 34  Diethyl ether Is a highly flammable and explosive anesthetic agent that causes increased salivary secretions, vomiting and laryngospasm. It has been replaced by halogenated anesthetics; Nitrous Oxide (N2O) (laughing gas) It is an important and powerful analgesic that is well- tolerated weak general anesthetic thus; it is frequently combined with other more potent agents. Its onset of action is rapid, as is recovery from its effect. Because of this, it is frequently used for outpatient dental procedures. Adverse effect: expansion or rupture of pulmonary cyst, hypoxia, leukopenia, postoperative nausea and vomiting. Nitrous oxide is contraindicated in pregnant women, immunosuppressed patients and patient with anemia. 35 Preanesthetic medication A preanesthetic drug is one given before the administration of anesthesia. The preanesthetic may consist of one drug or a combination of drugs. The general purpose of the preanesthetic drug is to prepare the patient for anesthesia. 36  The more specific purposes of these drugs include the following: 1. Narcotic or antianxiety drugs: to decrease anxiety and apprehension immediately before surgery. The patient who is calm and relaxed can be anesthetized more quickly, usually requires a smaller dose of an induction drug, may require less anesthesia during surgery, and may have a smoother anesthesia recovery period. 2. Antiemetic drugs: to lessen the incidence of nausea and vomiting during the immediate postoperative recovery period. 37  3. Anticholinergic drugs: to decrease secretions of the upper respiratory tract. Some anesthetic gases and volatile liquids are irritating to the lining of the respiratory tract and thereby increase mucous secretions. The cough and swallowing reflexes are lost during general anesthesia, and excessive secretions can pool in the lungs, resulting in pneumonia or atelectasis ( the collapse of part or all of a lung) during the postoperative period. The administration of anticholinergic drugs, such as glycopyrrolate (Robinul) dries up secretions of the upper respiratory tract and lessens the possibility of excessive mucous production. Glycopyrrolate has lower incidence of undesirable side effects Glycopyrrolate, Atropine, and Scopolamine are used to decrease the flow of saliva. 38  4. Barbiturates (Secobarbital, Pentobarbital) are used as preoperative sedatives 5. Opioids (Morphine, Fentanyl) used for analgesia 6. Phenothiazines and Antihistamines Promethazine and hydroxyzine are used with opioids to potentiate the analgesic effect without increasing side effects. 7. Tranquilizers Diazepam is used for preoperative sedation 39 Local Anesthetics Local anesthetic agents block both sensory and motor nerve conduction to produce a temporary loss of sensation without a loss of consciousness. Mechanism of action Local anesthetics suppress action potentials in excitable tissues by blocking voltage-gated Na+ channels. In doing so, they inhibit action potentials in nociceptive fibres and so block the transmission of pain impulses. 40 Local Anesthetics Unlike general anesthetics, they normally do not cause CNS depression. Most local anesthetics are structurally similar to the alkaloid cocaine. The various methods of administering a local anesthetic include: 1. topical application, 2. local infiltration, or 3. regional anesthesia 41 Topical Anesthesia Topical anesthesia involves the application of the anesthetic to the surface of the skin, open area, or mucous membrane. The anesthetic may be applied with a cotton swab or sprayed on the area. This type of anesthesia may be used to desensitize the skin or mucous membrane to the injection of a deeper local anesthetic. In some instances, topical anesthetics may be applied by anesthesia technician or nurse. 42 Local infiltration Anesthesia Local infiltration anesthesia is the injection of a local anesthetic drug into tissues. This type of anesthesia may be used for: dental procedures, the suturing of small wounds, or making an incision into a small area, such as that required for removing a superficial piece of tissue for biopsy. 43 Regional Anesthesia Regional anesthesia is the injection of a local anesthetic around nerves so that the area supplied by these nerves will not send pain signals to the brain. The anesthetized area is usually larger than the area affected by local infiltration anesthesia. Two types of regional anesthesia are 1. Spinal anesthesia and 2. Conduction blocks. 44 Spinal Anesthesia Spinal anesthesia is a type of regional anesthesia that involves the injection of a local anesthetic drug into the subarachnoid space of the spinal cord, usually at the level of the second lumbar vertebra. There is a loss of feeling and movement in the lower extremities, lower abdomen, and perineum. 45 Conduction blocks A conduction block is a type of regional anesthesia produced by injection of a local anesthetic drug into or near a nerve trunk. Examples of a conduction block include: 1. Epidural block (injection of a local anesthetic into the space surrounding the dura of the spinal cord); Often used in obstetrics 46  2. Transsacral (caudal) block (injection of a local anesthetic into the epidural space at the level of the sacrococcygeal notch); Often used in obstetrics 3. Brachial plexus block (injection of a local anesthetic into the brachial plexus). Used for arm or hand surgery 47  Cocaine: used in 4%-10% concentrations and as crystals for topical anesthesia of the nose, pharynx and tracheobronchial tree. Procaine: is available with and without epinephrine. Epinephrine decreases the rate of anesthetic absorption in the bloodstream and so approximately doubles the duration of anesthesia produced by a given dose. A 1%-2% solution is used for nerve block and infiltrative anesthesia, a 5%-20% solution is used for spinal anesthesia Tetracaine: a 2% solution is used topically on mucous membranes 48  Lidocaine: have rapid onsets of anesthesia, minimal local irritation a greater potency and longer duration of action than procaine, a 0.5% solution is used for infiltrative anesthesia, 1%-2% solution is used for topical mucosal and nerve block anesthesia, 5% for spinal anesthesia, used intravenously as an antiarrhythmic agent. Lidocaine is available for topical anesthesia as an ointment, jelly, cream and solution. 49  Dibucaine, Pramoxine (only used as topical anesthesia), Prilocaine, Etidocaine, Mepivacaine and Bupivacaine Adverse systemic effects of local anesthetics: Seizures, CNS depression respiratory failure, hypotension, allergic reactions. 50