General and Local Anesthetics: Mechanisms, Effects, and Uses
General Anesthetics
Effects
Insensitivity to pain, loss of reflexes, amnesia, relaxation, loss of consciousness.
Drugs Used
- Opioids: analgesia (Fentanyl)
- Anxiolytics: anxiolysis, sedation, muscular relaxation (BDZ)
- Antiemetics: Avoid vomiting, aspiration (Metoclopramide)
General Anesthetics
Loss of consciousness, amnesia.
Administration
- Inhalation:
- Liquid Volatile: halothane, enflurane, isoflurane, desflurane, sevoflurane
- Gases: nitrous oxide, xenon
- Intravenous: propofol, thiopental, ketamine, etomidate, BDZ
Adverse Reactions (Inhalation)
Hypotension, respiratory depression, hepatotoxicity, nephrotoxicity, seizures.
Propofol
Mechanism of Action
Unknown.
Pharmacokinetics
Home-rapid elimination.
Central Effects
More powerful than thiopental.
Cardiovascular Effects
Bradycardia, hypotension.
Respiratory Effects
Sleep.
Adverse Reactions
Injection pain, cardiovascular depression in the elderly.
Thiopental & Etomidate
Mechanism of Action
GABA-mimetic.
Pharmacokinetics
Top 40 Recovery 30.
Central Effects
Depression, sedation, hypnosis.
Cardiovascular Effects
Hypotension.
Respiratory Effects
Sleep.
Adverse Reactions
Bronchospasm, respiratory depression, anaphylaxis, vomiting. No analgesia.
Opioids
Receptors
μ (μ1, μ2, μ3) Principal receptor being joined by the most powerful analgesics (opens potassium channels). Responsible for the analgesic activity and many secondary reactions. δ (δ1, δ2) in cerebral cortex (open potassium channels). (κ1, κ2, κ3) Closed Ca++ channels. Responsible for spinal analgesia.
Types
- Pure Agonists:
- Mild/Moderate: Codeine, Dextropropoxyphene, Tramadol
- Moderate/Severe: Morphine, Fentanyl, Methadone
- Partial Agonists Mixed: Pentazocine, Buprenorphine, Nalorphine, Nalbuphine
- Pure Antagonists: Naloxone, Naltrexone
Histamine Receptors
- H1: smooth muscle, endothelium, and brain
- H2: gastric mucosa, cardiac muscle, mast cells, and brain
- H3: Presynaptic: brain, myenteric plexus, and other neurons
Antihistamines (H1)
Types
- Central and Peripheral Actions: Diphenhydramine, promethazine, chlorpheniramine, cyproheptadine, orphenadrine, clemizol
- Without Central Actions: astemizole, terfenadine, ebastine, loratadine, Cetirizina
Uses
Rhinitis, urticaria, atopic dermatitis, anaphylactic reactions, asthma.
Side Effects
Sleepiness, loss of appetite, nausea, vomiting, dry mouth, tachycardia, hypotension, urinary retention, described fatal or serious poisoning.
H2-Blockers (Cimetidine)
Cimetidine, Ranitidine, Famotidine, Nizatidine.
Uses
Gastro-duodenal ulcer, erosive gastritis, reflux esophagitis, gastric hemorrhage, preanesthesia.
Side Effects
Hyperprolactinemia, dizziness, temporal and spatial disorientation, confusion, hallucinations, impotence, decreased libido, gynecomastia.
Local Anesthetics
Differentiate: latent period, duration of action, toxicity, potency, selectivity of blockade.
Types
- Ester Bond: cocaine, procaine, chloroprocaine, benzocaine, tetracaine
- Amide Bond: lidocaine, bupivacaine, prilocaine, mepivacaine, etidocaine, ropivacaine, levobupivacaine
Duration and Potency
- Short and Low Power Action: Procaine and Chloroprocaine
- Medium Action and Power: Lidocaine, mepivacaine, and prilocaine
- Long Action and High Power: Tetracaine, Bupivacaine, etidocaine, ropivacaine, and levobupivacaine
Mechanism of Action
Low permeability to sodium ions in the cell membrane leading to depolarization. Depends on these factors:
- Location of administration
- Dose and concentration used
- Anesthetic characteristics
- Adding a vasoconstrictor
- Contact time
Chronology of Blocking
Increased cutaneous temperature, vasodilation, loss of sense of temperature and relief of pain, loss of proprioception, loss of sensation of touch and pressure, loss of motor skills.
Pharmacological Actions
Speakers at the function of all organs in which there are nerve impulse transmission (CNS, ganglia, neuromuscular junction).
Central Nervous System
All cross the blood-brain barrier.
- Lidocaine:
- Low Dose: sedative and anticonvulsant
- Medium Dose: Action on the CNS stimulant, anxiety, and tremor which can lead to clonic seizures
- High Dose: Cortical and subcortical depression that can lead to death from respiratory failure
Cardiovascular System
On high dose myocardium: depressed contractility, decrease the volume. Minute and antiarrhythmic action. On vessel, hypotension, bradycardia, and cardiovascular collapse.
Local Reactions
Produced by anesthetic, Cocaine and drills vasoconstriction mucosa. Or ignorance of the anatomy: inadvertent IV injection.
Systemic Reactions
Anesthetic blood reaches and reaches high dose:
- Cardiovascular System: Hypotension, bradycardia, and arrhythmias
- Central Nervous System: Euphoria, sensation of well-being, excitation phase, seizures followed by respiratory depression, coma, and death
Intoxication Treatment
Respiratory assistance, diazepam for seizures.
Types of Local Anesthesia
- Topical: on broken skin or mucous membranes
- Infiltration: small quantities in the area where you wish to speak. Subcutaneously
- Regional: injected near a nerve trunk blocking the sensitivity in the area supplied by it
- Epidural: injected into the epidural space, passes slowly and blocks the nerve roots. Lidocaine and bupivacaine are injected into the lumbar region
- Spinal: injected into the subarachnoid space
Antiserotonergics
- Cyproheptadine
- Indications: Carcinoid syndrome, rapid emptying syndrome, postgastrectomy cold urticaria, skin allergies, migraine prophylaxis
- Side Effects: sedation, gastrointestinal discomfort, weight gain
- Ketanserin
- Indications: hypertension, vasospasm
- Side Effects: Asthenia, weight gain, hypotension
- Ondansetron
- Indications: Nausea and vomiting in postoperative and chemotherapy
- Side Effects: Headaches, constipation, flushing
Serotonin Agonists. Prostaglandins.