Drugs Acting on the Central Nervous System: General Anesthetic Drugs

Flashcards about general anesthetic drugs acting on the central nervous system.

What is the aim of general anesthesia (GA)?

Suppression of CNS functions while maintaining the function of other vital body organs.

What are the requirements for general anesthesia?

Loss of consciousness, analgesia, skeletal muscle relaxation, and suppression of visceral reflexes with maintenance of physiological stability.

List characteristic features of an ideal general anesthetic.

Wide safety margin, devoid of side effects, rapid smooth induction with rapid recovery.

What is balanced anesthesia?

Combination therapy to fulfill the requirements for GA and minimize the side effects of each individual drug.

What does balanced anesthesia include?

Pre-operative administration of sedatives and analgesics, the use of neuromuscular blockers during the operation, and the use of both intravenous and inhalation anesthetics.

What are the stages of general anesthesia?

Stage of Analgesia (Induction), Stage of Excitation (Delirium), Stage of Surgical Anaesthesia, and Stage of Medullary Paralysis.

How do you resuscitate a patient in the 4th stage of General Anaesthesia?

Stop administration of the anaesthetic, mechanical control of ventilation, and I.V administration of Doxapram to support respiration and circulation.

What are the two main classifications of general anesthetics?

Inhalation anesthetics and Intravenous anesthetics.

Give examples of Gas Anaesthetics.

Nitrous Oxide

Give examples of Volatile liquid anaesthetics.

Halothane, Enflurane, Methoxyflurane, Isoflurane, Desflurane and Sevoflurane, Diethyl ether and Vinyl ether

Give examples of Ultra-short acting barbiturates.

Thiopental sodium

Give examples of Non-barbiturate intravenous anaesthetics.

Ketamine, Propofol, Benzodiazepines e.g. Midazolam, Diazepam, Opiate analgesics e.g. Morphine, Fentanyl

How do Inhalation Anaesthetics act?

produce hyperpolarization via activation of potassium current decreasing the ability of neurons to initiate action potentials

How do Barbiturates and Benzodiazepines act?

facilitate the action of GABA at the GABA-A receptors resulting in Chloride ion channel opening resulting in hyperpolarization that leads to decreased neuronal excitation

How does Propofol act?

facilitate the inhibitory effects of GABA

How does Ketamine act?

Blocks the membrane effects of the excitatory neurotransmitter Glutamine at the N-methyl-D-Aspartate receptor subtype

What is MAC (Minimum Alveolar Concentration)?

Concentration of the inhaled anesthetic required to eliminate movements in 50% of patients challenged by a standardized skin incision.

Name factors which reduce MAC value.

Presynaptic Alpha-2 agonists e.g. Clonidine, Anaesthetic adjuvants e.g. Opioids and Sedative-Hypnotics, Elderly patients

Name factors affecting the rate of induction and recovery of inhalation anaesthetics.

Uptake and distribution of the anaesthetic (Affect induction), Elimination of the anaesthetic (Affect recovery)

List some pharmacological actions of inhalation anesthetics on the CNS.

Decreased oxygen consumption of the brain and Cerebral vasodilatation leading to increased intracranial pressure (ICP).

List some pharmacological actions of inhalation anesthetics on the Respiratory System.

Dose-related depression of respiratory centre (RC), Bronchoconstriction (except with Halothane and Enflurane), Hypoxia with prolonged use of Nitrous Oxide, Suppression of the mucociliary function, therefore premedication with anti-muscarinic agents is essential to prevent atelectasis

List some pharmacological actions of inhalation anesthetics on the Cardiovascular System (CVS).

Dose-related hypotension due to decreased cardiac output and/or vasodilatation, Dose-related myocardial depression (especially with Halothane and Enflurane), Bradycardia with Halothane and tachycardia with Isoflurane and Desflurane, Decreased myocardial oxygen consumption

List some pharmacological actions of inhalation anesthetics on the Kidney.

Decreased renal blood flow and glomerular filtration rate (GFR) and Renal tubular damage with Methoxyflurane

List some pharmacological actions of inhalation anesthetics on the Liver.

Transient liver dysfunction, Reduced hepatic blood flow and Halothane-induced hepatitis with hepatic necrosis (in adults)

List some pharmacological actions of inhalation anesthetics on the Muscles.

Potent uterine relaxant effect (Nitrous Oxide has minimum effect), Skeletal muscle relaxation (Halothane has minimum effect), All can trigger malignant hyperthermia

List some adverse effects of inhalation anesthetics on the Respiratory tract.

Dose-related respiratory depression, Brochoconstriction (except with Halothane and Enflurane), Hypoxia with prolonged use of Nitrous Oxide, Suppression of muco-ciliary function leading to Lung atelectasis

List some adverse effects of inhalation anesthetics on the CVS.

Hypotension, Bradycardia, Disarrhythmias (especially with Halothane)

Name a Nephrotoxic Inhalation Anaesthetic.

Methoxyflurane (Renal tubular damage due liberation of an inorganic Fluoride ion)

How is malignant hyperthermia treated?

By the muscle relaxant, Dantrolen

List some adverse effects of Nitrous Oxide.

Postoperative bowel distension, Postoperative nausea and vomiting, Hypoxia with prolonged use

List some chronic adverse effects of Inhalation Anaesthetics.

Abortion, Teratogenicity, Carcinogenicity, Leucopenia and Megaloblastic anaemia

What is Neurolept analgesia?

Produced when a neuroleptic drug e.g. Druperidol is combined with a narcotic analgesic e.g. Fentanyl. The patient is sedated, detached from the environment with muscle relaxation, analgesia and amnesia

What is Neurolept Anaesthesia?

Neurolept analgesia can be converted to Neurolept Anaesthesia by concurrent administration of 65% Nitrous Oxide in Oxygen.

Why does Ultra-short acting barbiturates have short duration of action?

Due to rapid distribution from the brain to other tissues (e.g. Muscles). Slowly metabolized and tend to accumulate in body fat, so it can cause prolonged effect if given repeatedly

List some pharmacological actions of Ultra-short acting Barbiturate on the CNS.

Decrease Oxygen consumption of the brain, Decrease cerebral blood flow leading decreased ICP
So they are suitable as anaesthetics in cases of head injuries and brain tumors

List some pharmacological actions of Ultra-short acting Barbiturate on the RS.

Depression of the respiratory center, Brochoconstriction, Suppression of muco-ciliary function

List some pharmacological actions of Ultra-short acting Barbiturate on the CVS.

Hypotension - Negative inotropic and chronotropic actions

List some pharmacological actions of Ultra-short acting Barbiturate on the Liver and Kidney.

Decreased hepatic and renal blood flow

Give some side effects of Ultra-short acting barbiturate.

Narrow safety margin, Respiratory depression, Cardiovascular depression, Hypotension, Severe vasospasm in injected accidentally intra-arterial, Hypersensitivity reactions

What are the advantages of Propofol over Ultra-short acting barbiturates?

Rapid onset, Anti-emetic action, Prolonged sedation, Decreases ICP

Give some side effects of Propofol.

Pain at the site of injection, Supplementation with narcotic-analgesic is required, Hypotension, Acidosis in dehydrated children, Anaphylactic shock and convulsions (Rare)

What type of anaesthesia does Ketamine produce?

dissociative anaesthesia, the patient is dissociated from the environment with analgesia and amnesia

What are the advantages of Ketamine?

Potent analgesic, No respiratory changes, Increased sympathetic outflow so it can be used in case of shock

What are the side effects of Ketamine?

Increased ICP, Hallucination and Disorientation

Give some example of Benzodiazepines.

Midazolam

How is respiratory depression from Benzodiazepines antagonized?

Flumazenil

Give some example of Opiates.

Morphine, Fentanyl

What are the aims of Pre-anaesthetic Medication?

Reduce anxiety and produce sedation to facilitate endotracheal intubation, Produce amnesia, Suppress autonomic reflexes, Decrease salivary and bronchial secretions, Potentiate weak anaesthetics

Give some examples of Drugs Used for Pre-anaesthetic medication.

Opiates eg Morphine, Antimuscarinic drugs e.g Atropine sulphate, Sedatives eg Diazepam, Phenothiazines eg Metoclopramide