General Anesthetics

General Anesthetics

Terminology:

* anesthetic in blood/anesthetic in lungs at equilibrium =

the Ostwald coefficient ()

* the greater the , the more lipid soluble the anesthetic

* the more lipid soluble the anesthetic, the slower the rate

of induction and elimination

* anesthetic potency is expressed as the minimum alveolar

concentration or MAC (where there is no response to a

skin incision in 50% of the patients

*the higher the , the lower the MAC!

Inhalation agents:

Nitrous oxide – not considered volatie; the others are

Enflurane

Halothane – sensitizes the heart to catecholamines

Isoflurane – most preferred GA; less hepatotoxicity

Methoxyflurane

Fixed, or IV agents:

*commonly given with inhalation agents to speed rate of

induction and attainment of stage III anesthesia; also

reduces the amount of inhalation agent necessary to

maintain the desired level of CNS depression

Innovar

Ketamine – blocks glutamate receptors

Thiopental – not an analgesic

Propofol – not an analgesic

Midazolam – not an analgesic

Droperidol – blocks dopamine receptors

Fentanyl – stimulates opiate receptors

Other preanesthetic medications:

Diazepam

Morphine

Cyclizine

Hydroxyzine

Scopolamine – often used to counteract the adverse

affects of inhalational agents

Glycopyrrolate -- often used to counteract the adverse

affects of inhalational agents

Skeletal Muscle Relaxants

Competitive:

Atracurium

Doxacurium (Nuromax)

Gallamine

Metocurine

Mivacurium

Pancuronium (Pavulon)

Pipercuronium (Arduvan)

Tubocurarine

Rocuronium

Vecuronium

Depolarizing:

Succinylcholine

Decamethonium
Local Anesthetics

* locals work by depressing neuronal soduim and potassium

conductance

* esters are hydrolyzed more readily, thus they are shorter

acting then the amides

* esters have a greater stimulatory effect on the CNS; esters

are more likely to cause convulsions than the amides

* all locals decrease HR and decrease vascular tone; so

hypotension is a common side effect

Esters:

Cocaine

Procaine (Novocaine) – only used for infiltration anesthesia

or spinal block

Chloroprocaine

Tetracaine (Pontocaine)

Benzocaine

* destroyed by esterases in the serum and the liver

Amides:

Lidocaine (Xylocaine)

Mepivacaine (Carbocaine)

Bupivacaine (Marcaine, Sensorcaine)

* destroyed by amidases in the liver only

Others: (I’m not sure where they fit yet)

Butamben picrate

Dibucaine

Dyclonine (Dyclone)

Etidocaine (Duranest)

Pramoxine (Prax, Tronothane)

Prilocaine (Citanest)

Closest to ideal:

Lidocaine

Procaine

Tetracaine

Opioid Antagonists

Naloxone – duration of only 1-4 hours, must be given

parentally because of poor oral absorption

Naltrexone – given orally, has a half-life of about 10 hours

Symptoms of Opioid Withdrawal

Apprehension

Tremor

Headache

increased HR

Muscle spasm

Ketosis

Vomiting

Anorexia
Opioid Analgesics

* Mu receptor stimulation causes: respiratory depression,

physical dependency, and the associated euphoria

* Kappa receptor stimulation causes: miosis and sedation

* Sigam receptor stimulation causes: dysphoria, cardiac

stimulation, and hallucinations

* easily pass the placental barrier and gain access to the

fetal brain; can lead to respiratory depression in the

newborn

* opioids prolong labor, due to direct relaxation of smooth

muscle

* opioids stimulate the release of: prolactin, somatotropin,

and ADH. They inhibit the release of LH.

Alfentanyl

Butorphanol (Stadol)

Codeine

Dezocine

Fentanyl (Sublimaze) – highly lipophilic; accumulates in fat

Hydromorphone (Dilaudid)

Levorphanol

Meperidine (Demerol)

Methadone (Dolophine)

Morphine

Nalbuphine (Nubain)

Hydrocodone

Oxycodone

Oxymorphone

Pentazocine

Propoxyphene (Davron)

Sufentanil

Combinations:

Codeine/acetaminophen (Tylenol-2, 3, etc..)

Codeine/aspirin (Empirin)

Hydrocodone/acetaminophen (Norcet, Vicodin, Lortab)

Oxycodone/acetaminophen (Percocet, Tylox)

Oxycodone/aspirin (Percodan)

Propoxyphene/aspirin (Darvon compound-65)

*never administer opioids in conjunction with MAO

inhibitors; this combination can precipitate hyperpyrexic

coma and hypertensive crisis!

*although there are many adverse effects, the most

important to watch out for is respiratory depression