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USMLE - Pharm
Kaplan Section 4 Chapter 1 CNS Pharm - Anesthetics
| Question | Answer |
|---|---|
| What is the MAC value? | Minimal alveolar anesthetic concentration (% of inspired air) at which 50% of pts do not respond to a surgical stimulus. Measures potency of an anesthetic. The lower the MAC value, the stronger the anesthetic. |
| Name 6 inhaled anesthetics in MAC order | In order of decreasing MAC value (increasing potency): NO, Des Sevo, En, Iso, Halo. Nitrous oxide, desflurane, Sevoflurane, Enflurane, Isoflurane, Haloflurane. ISOdora has SEVeral HALOs, so has NO DESire to ENhale that cigarette. |
| Name 6 inhaled anesthetics in blood-gas solubility order | In order of decreasing rate of onset/recovery: Des, NO, Sevo, Iso, En, Halo. Desire NOthing and SEVer all ties with IsoEnHalo. |
| What does the blood-gas ratio tell you about the anesthetic? | Rate of onset and recovery of inhaled anesthetics. The more soluble a gasin the blood, the longer that drug takes to exert its effects on the CNS or other body tissues (it wants to stay in ght |
| Which inhaled anesthetic has the lowest potency? | NO - but relatively fast, so often used in combo with other anesthetics |
| What are the cardiovascular effects of NO? | Minimal |
| Which inhaled anesthetic has the most rapid onset and recovery? Adverse effects? | Desflurane, but causes airway irritation and coughing |
| What are the cardiovascular effects of Desflurane? | Vasodilation and increased HR (reflex?) |
| Which inhaled anesthetics cause vasodilation and increased heart rate? | Desflurane and Haloflurane |
| Which inhaled anesthetics cause decreased heart rate? | Sevoflurane, Enflurane, Haloflurane |
| Which inhaled anesthetic sensitizes the heart to catecholamines? | Haloflurane |
| Which inhaled anesthetic causes tonic/clonic muscle spasms? | Enflurane |
| Which inhaled anesthetic causes bronchiolar secretions and spasms? | Isoflurane |
| Which inhaled anesthetic causes hepatitis? | Haloflurane |
| Which inhaled anesthetic causes malignant hyperthermia? | Haloflurane |
| Which inhaled anesthetic causes cardiac arrhythmias? | Haloflurane |
| What are the three actions of inhaled anesthetics? | 1. lowers response to increased PCO2, 2. increase cerebral blood flow, 3. relax uterine smooth muscle |
| Name the 5 IV anesthetics | Thiopental, Midazolam, Propofol, Fentanyl, Ketamine. Rich-as-MIDAs THIO PROPOsed to FEN-yen while on IV special K (ketamine). |
| Which IV anesthetic should be used for induction? Why? | Thiopental (barbiturate). Highly lipid soluble, but RAPID onset and SHORT-acting. RAPID recovery (redistribution from CNS to peripheral tissues). |
| Which IV anesthetic should be used for preoperative sedation? Why? | Midazolam (BZ). Allows conscious sedation and anterograde amnesia. |
| Which IV anesthetic should be used for outpatient surgery? Why? | Propofol. Very rapid onset and recovery. Can be used both for induction and maintenance. Has antiemetic effects. |
| Which IV anesthetic is a potent analgesic? | Fentanyl. An opioid analgesic, but shorter duration of action than most opioids. |
| Which is the only anesthetic to cause CV stimulation? | Ketamine (NMDS receptor antagonist) |
| How is thiopental eliminated from the body? | Liver metabolism |
| What is the effect of thiopental? | Depresses respiratory and cardiac function, but does not increase cerebral blood flow. |
| What is the effect of midazolam? | Depresses respiratory function. |
| How do you reverse the effects of midazolam? | Flumazenil. (BZ receptor antagonist) |
| Which anesthetic causes dissociative amnesia? | Ketamine (NMDA receptor antagonist). Dissociative: drug which reduces (or blocks) signals to the conscious mind from other parts of the brain. State of sensory deprivation and dissociation can facilitate hallucinations & dreamlike states. |
| Adverse effects of fentanyl | Can cause chest wall rigidity with IV use (can also be used orally or delivered through a patch) |
| What is neurolept anesthesia? | Intravenous sedation - partially conscious. Uses combination of fentanyl, droperidol, and NO. |
| What are the properties of ketamine? | rapid onset and short-duration, causes amensia, catatonia, and analgesia. |
| What are emergence reactions? | Occurs with ketmine use - vivid dreams and hallucinations. Can be offset by BZ's. |
| Esters and amides are what kind of anesthetic? How can you tell the difference? | Local anesthetics. Esters have one i (procaine, cocaine, benzocaine), amides have >1 i's (lidocaine, bupivacaine, mepivacaine). |
| How are esters metabolized? | by plasma and tissue esterases |
| How are amides metabolized? | liver amidases |
| What is the mechanism of local anesthetics (LA)? | LA must first be in nonionized form to cross lipid bilayer of axon --> gets into cell --> becomes ionized --> binds to component of Na channel on inner side of membrane --> binds in INACTIVATED state (M open h closed) --> block reactivation |
| Increases in extracellular acidity does what to the effectiveness of local anesthetics? | Increased acidity would protonate the LA's (which are usually weak bases), so they can't cross the lipid bilayer to bind to the inactivated Na channel --> decrease LA activity |
| Which nerve fibers are most sensitive to the actions of local anesthetics? List in order of sensitivity. | Nerve fibers of smaller diameter and higher firing rates are the most sensitive to blockade. Order of sensitivity: type B and C > A delta > A beta and gamma > A alpha |
| What happens when local anesthetics are coadministered with a adrenoceptor agonists (such as epinephrine)? | LA absorption into systemic circulation decreases --> prolong LA effects, decreases toxicity. |
| Adverse effects of local anesthetics | Neuro: dizzines, nystagmus, sensory impairment, seizures. CV: CV depression, except for cocaine, which increases HR and BP. Allergies: esters --> PABA --> people are allergic to PABA |
| What is tetrodotoxin? | toxin from puffer fish. Binds externally to READY state (M closed, h open) of Na channels in both cardiac and nerve cell membranes --> block Na influx --> no depolarization --> no conduction |
| What is saxitoxin? | toxin from dinoflagellates in "red tide". Binds externally to READY state (M closed, h open) of Na channels in both cardiac and nerve cell membranes --> block Na influx --> no depolarization --> no conduction |
| What is ciguatoxin? | toxin from exotic fish and Moray eels. Binds in the Na channel in the OPEN state (both M and h are open) --> persistent depolarization --> channel inactivation |
| What is batrachotoxin? | toxin from south American frogs. Binds in the Na channel in the OPEN state (both M and h are open) --> persistent depolarization --> channel inactivation |
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christinapham
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