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ANESTHESIA PHARM 1 > Barbiturates > Flashcards

Barbiturates Flashcards

1
Q

2 barbiturates:

1.

2.

A
  1. THIOPENTAL
  2. methohexital (brevital)
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2
Q

pH: thiopental

A

10.5

this is the reason that thiopental burns on injection; not because of an additive, but because it is so basic

also the reason that thiopental is bacteriostatic; to basic to support bacterial life

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3
Q

why did Europe stop selling US thiopental

A

we were using it for lethal injections

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4
Q

problem with injecting thiopental after fentanyl

A

fentanyl pH: 4

thiopental pH: 10.5

precipitate would form in veins as a result of two drugs mixing

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5
Q

stability of thiopental:

supplied in what form?

A

anhydrous

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6
Q

stability of thiopental after reconstitution:

  1. anhydrous
  2. refrigerated
  3. room temp
A
  1. indefinitely
  2. 7d
  3. 24hr
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7
Q

mechanism of action: thiopental

GABA

1.

2.

A
  1. decreased dissociation of GABA from receptors; increased inhibitory side of CNS, decrease excitatory side
  2. direct action/opening of chloride channel
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8
Q

mechanism of action: thiopental

sympathetic nervous system

A

decreased transmission: pseudosympathectomy

decreased BP

increased HR

(just like propofol)

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9
Q

pharmacology of barbiturates

1.

2.

3.

4.

A
  1. highly lipid soluble; onset of 30sec
  2. highly protein bound
  3. quick uptake because of high lipid solubility
  4. high redistribution: absorbed into fat as soon as it left brain -> hangover
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10
Q

thiopental: IV induction dose

A

3-5mg/kg

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11
Q

thiopental onset/duration

A

onset: 30-40sec
peak: 1min
duration: 5-8min

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12
Q

thiopental: protein binding

A

80%

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13
Q

thiopental: metabolism

  1. where
  2. length of time
  3. active metabolites
  4. thiopental v. methohexital
A
  1. metabolized in liver; liver dysfunction can further increase duration of action (decreased blood flow, hepatic function)
  2. slow metabolism
  3. no active metabolites
  4. Thiopental for inpatient procedures; methohexital for outpatient procedures
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14
Q

thiopental: elimination

A

renal elimination. no metabolites, so not a concern for pts with kidney diseases

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15
Q

thiopental: clinical uses

1.

2.

3.

A
  1. induction of anesthesia once-upon-a-time (Europe will no longer sell to US)
  2. treatment for increased ICP
  3. cerebral protection
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16
Q

thiopental was used as an induction agent from ________ to ________

A

1934 to 1989 (introduction of propofol)

55yrs

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17
Q

two types of ischemia

A

focal ischemia (only ischemia to one part of the brain, collateral flow perfuses brain everywhere else)

global ischemia (heart stopped, no flow anywhere)

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18
Q

value: normal cerebral perfusion pressure

A

80-100mmHg

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19
Q

value: normal intracranial pressure (supine)

20
Q

metabolic rate of the brain

A

brain has high metabolic rate, receives approximately 15% of cardiac output

21
Q

values: normal cerebral blood flow

A

50mL/100g/min

22
Q

percentage of CBF in brain

  1. gray matter
  2. white matter
A
  1. gray matter: 80% of CBF
  2. white matter: 20% of CBF
23
Q

percentage of brain’s energy used to support electophysiologic function

24
Q

relationship: cerebral blood flow to cerebral activity/cerebral metabolism

A

cerebral blood flow is directly proportional to cerebral activity.

suppression of cerebral metabolism leads to a reduction in blood flow.

increased cerebral activity in a particular region of the brain leads to an increase in blood flow to that region.

25
autoregulation of CBF: mean arterial pressure range of CBF given normal venous pressures
65-150mmHg
26
chemical regulation of CBF: PaCO2 range of CBF
25-70mmHg
27
normal brain oxygen requirements for neuronal electrical activity
60%
28
normal brain oxygen requirement for cellular integrity
40%
29
describe the concept of cerebral protection
decreasing the energy consumption/ electrophysiologic function of the brain so that less cerebral blood flow is necessary. SUPPRESSION OF OXYGEN REQUIREMENT/CEREBRAL METABOLISM LEADS TO REDUCTION IN BLOOD FLOW
30
effect of temperature on CBF
decreasing temperature decreases cerebral metabolism, thus decreasing CBF
31
cerebral protection: how many minutes of ischemia will you have bought your patient when you cool their brain to 18 degrees Celcius?
you buy yourself about 40min absolute bare-minimum blood flow
32
PaCO2 and cerebral blood flow are _____________ proportional
PaCO2 and CBF are DIRECTLY proportional decreased PaCO2 = vasoconstriction = decrease CBF increased PaCO2 = vasodilation = increased CBF
33
PaO2 and cerebral blood flow are _______________ proportional
PaO2 and CBF are INVERSELY proportional decreased PaO2 = vasodilation = increased CBF increased PaO2 = vasoconstriction = decreased CBF
34
ICP therapy 1. 2. 3.
decrease metabolic O2 requirements decrease cerebral blood flow potential for decrease in cerebral perfusion pressure (CPP)
35
calculate cerebral perfusion pressure
CPP = MAP - ICP (if no ICP, CVP can be used as substitute)
36
effects of anesthetic drugs on cerebral blood flow/ cerebral metaoblic O2 requirements
all anesthetic drugs decrease CBF and CMRO2 EXCEPT ketamine ketamine actually increases the CMRO2
37
cerebral protection and ischemia 1. 2.
1. not good for global ischemia (cooling the brain is only way to protect the brain) 2. great for focal ischemia CEA - carotid endarterectomy thoracic aneurysm resection cerebral aneurysm clipping
38
side effects: barbiturates 1. 2. 3. 4. 5. 6.
1. CARDIOVASCULAR (decrease SBP, increase HR) 2. HISTAMINE RELEASE (not significantly) 3. HEAT LOSS (vasodilation) 4. dose dependent VENTILATION SUPPRESSION 5. maintain LARYNGEAL RESPONSE (laryngospasm) 6. EEG (CMRO2 decreased up to 55%)
39
reasons not to use barbiturates 1. 2.
1. Hangover 2. Acute Intermittent porphyria
40
absolute contraindication of thiopental
history of acute intermittent porphyria
41
describe acute intermittent porphyria
porphobilogen deaminase deficiency that affects heme production often accompanied by seizures, which can be triggered by barbiturates
42
methohexital (brevital) lipid solubility
more lipid soluble than pentothal, therefore stays in central compartment longer
43
methohexital IV induction dose
1-1.5mg/kg
44
methohexital: rectal dose
20-30mg/kg (for uncooperative kids)
45
side effect: methohexital
hiccups
46

ANESTHESIA PHARM 1 (4 decks)

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