General Anesthetics II Flashcards
Discuss the common aspects of all halogenated anesthetics. Give main examples
Examples - HALOTHANE, isoflurane, sevoflurane
CNS effects
- Decrease brain metabolic rate
- Increase cerebral blood flow
- Increase intracranial pressure
CV effects- IMPORTANT
- Decreased myocardial contractility and stroke volume causing lower blood pressure
- Sensitizes myocardium to catecholamines–>↑ automaticity
- Particularly in the presence of adrenergic agonists
Muscle relaxation at high doses
Malignant hyperthermia may occur with all inhaled anesthetics except N20 (worst is halothane)
Very general description of IV anesthetics vs inhalation anesthetics
Injectable anesthetics
- Act faster
- Best suited for induction of anesthesia
- Useful for short operative procedures
- Muscle relaxation after IV anesthetics is poor
- Unsuitable as a single drug anesthetic for many surgical procedures
Inhalation anesthetics
-Maintain anesthesia for longer procedures
Classes of injectable anesthetics
Barbiturates Benzodiazepines Propofol Ketamine Opioids
Describe the characteristics of an ideal inhalation anesthetic
Stable shelf life Compatibility with existing delivery equipment Inexpensive Non-explosive and nonflammable Easily vaporized under ambient conditions Low blood solubility Potent No cardiopulmonary depression Not irritating to airways No interaction with catecholamines Good muscle relaxation Minimal metabolism Not toxic to kidneys, liver or gut
Halothane–> Advantages and Disadvantages
Advantages
- Potent (good MAC)
- Rapid induction and recovery
- Among the least expensive volatile anesthetic
- no laryngospasm
Disadvantages
-Inadequate analgesia and muscle relaxation
-Depresses myocardium and baroreceptor reflexes:
↓ Cardiac output
↓ Blood pressure
-Sensitizes myocardium to catecholamines (epi)
-Respiratory depression
-hepatic toxicity “halothane hepatitis”
-Malignant hyperthermia (treat with dantrolene)
Isoflurane: Advantages and Disadvantages compared to halothane
Advantages
- Potent
- Induction in less than 10 minutes
- Doesn’t sensitize the myocardium to catecholamines
- Less hepatotoxicity and renal toxicity than halothane
Disadvantages
- Rarely arrhythmias
- Pungent odor (patient might rip off mask, not want it)
- Potential for malignant hyperthermia
methoxyflurane: Advantages and Disadvantages compared to Halothane
All he said is
-Metabolized faster than halothane
Desflurane: Advantages and Disadvantages compared to Halothane
All he said is
- less CV effects (BP and catecholamine interactions)
- increased respiratory depression
Justify or refute the statement that sevoflurane is an almost perfect inhalation anesthetic
-High potency (low % of inspired gas)
-Low blood solubility
-Rapid onset – 5-10 min
-Rapid recovery – same day surgery
BUT
-higher chance of respiratory depression than halothane
-smells worse than halothane
-slightly higher MAC than halothane
How does nitrous oxide compares to other inhalation anesthetics
-Only inhalation anesthetic that is a gas
Advantages
- Low blood solubility (rapid onset)
- Little effect on overall cardiovascular function
- Lowers MACs of other anesthetics
Disadvantages
- MAC = 104%! -can’t use as sole anesthetic agent
- No muscle relaxing effect
- Diffusion hypoxia if rapidly discontinued
Barbiturates: examples, mechanism, toxicity
-Thiopental (Pentothal) and methohexital (Brevital)
Mechanism of action
- Facilitates GABA induced Cl- entry into neurons, leading to CNS depression (hyper-polarizing)
- Rapid onset (sec) after iv administration
- short action (min) allows quick recovery
Toxicity at 50 to 75% of LD50
Benzodiazepines: Examples, mechanism, characteristics
-Midazolam (Versed) and diazepam (Valium)
-Mechanism of action
Facilitates GABA induced Cl- entry into neurons, leading to CNS depression (hyper-polarizing)
Characteristics
- Less cardiovascular and respiratory depression than barbiturates
- Most important characteristic is amnestic action
- Insufficient for anesthesia when given alone–>Used as induction agent prior to anesthesia
Barbiturates, Benzodiazepines and GABA: what is their relationship
Both barbiturates and benzodiazepines enhance GABA binding to GABA receptors
- GABA receptors allow Cl- to enter cell
- Barbiturates–> increase duration of channel opening
- Benzos–> increase frequency of channel opening
propofol: facts
- killed Michael Jackson
- Rapid induction (50 seconds)
- Rapid recovery (4-8 minutes) from anesthesia
- Used alone to maintain anesthesia or used for induction as part of balanced anesthesia technique
- Given with anesthetics as it has anti-emetic action
- significant respiratory effect is apnea
- May result in injection site pain
Ketamine (Ketalar): facts
-related to phencyclidine (PCP)
Dissociative anesthetic:
- Patient appears to be awake - eyes open
- Unaware of environment and doesn’t feel pain
-Rapid onset of action (1-2 min) when given intravenously or intramuscularly
-Relatively short duration of action (approximately 20 min)
Principal drawback: occurrence of emergence reactions (delirium and hallucinations)
Highly abused
