Induction Drugs - Barbiturates Exam 2

Question 1

What is the definition of procedural sedation/conscious sedation/MAC?

Answer 1

Combination of sedatives and analgesics to induce a depressed level of consciousness
Promotes safety in invasive procedures

Question 2

What group of organs utilize the most blood supply?
What organs utilize the least?
What organs are in between these two groups?

Answer 2

• Vessel-rich group = 75% CO (brain, heart, lungs, liver, kidneys)
• Skeletal muscles & skin = 18% CO
• Fat = 5% CO
• Bone, tendons, & cartilage = 2% CO

Question 3

What organs are part of the vessel-rich group? How much CO goes to them?

Answer 3

brain, heart, lungs, liver, kidneys
75% of CO

Question 4

What are the stages of anesthesia?

Answer 4

Analgesia
Delirium
Surgical Anesthesia
Medullary paralysis

Question 5

What are the COMPONENTS of general anesthesia?

Answer 5

Hypnosis
Analgesia
Muscle Relaxation
Sympatholysis
Anterograde Amnesia

Question 6

When does stage 1: analgesia of anesthsia begin and end?

Answer 6

begins with the initiation of an anesthetic agent
ends with the loss of consciousness

Question 7

What stage offers the lightest level of anesthesia?

Answer 7

Stage 1
-Able to open eyes on command
-normal respiration
-reflexes are maintained
-tolerate mild stimuli

Question 8

When does stage 2: delirium of anesthesia begin and end?

Answer 8

Starts with the loss of consciousness
Ends with onset of automatic rhythmicity of vital signs

Question 9

During induction, when would one most likely see laryngospasm?

Answer 9

Stage 2

Question 10

How long does stage 2 typically last? what symptoms might we see?

Answer 10

5-30 seconds (this stage is passed rather rapidly)
CV excitation
dysconjugate ocular movements
laryngospasm
emesis

Question 11

During emergence, when would one most likely need to be re-intubated?

Answer 11

Stage 2
response to stimulation is exaggerated and violent!

Question 12

What is stage 3 of anesthesia? How do you know you are in stage 3?

Answer 12

Absence of response to surgical incision. Depression in all elements of nervous system function
-hypnosis
-analgesia
-muscle relaxation
-sympatholysis
-amnesia
Patient is now ready to be intubated!

Question 13

What is stage 4 of anesthesia? Is it a good stage?

Answer 13

Associated with cessation of spontaneous respiration and medullary cardiac reflexes.
Undesired stage suggests oversedation and can lead to death.
-all reflexes absent
-flaccid paralysis
-marked hypotension, irregular pulse

Question 14

What is the MOA of barbiturates?

Answer 14

Potentiate GABA-A receptor activity, mimics GABA, causing Cl⁻ influx & cellular hyperpolarization.

Question 15

Barbiturates also act on which receptors?

Answer 15

Glutamates, adenosine, nACH-R

Question 16

What effects do barbiturates have on CBF and CMRO2?

Answer 16

Decreases CBF and CMRO2 by 55%

Question 17

Do barbiturates offer any analgesia?

Answer 17

No analgesic component

Question 18

What do barbiturates do to CBF & CMRO₂? How is this accomplished?

Answer 18

↓ CBF & ↓ CMRO₂ (by 55%) via cerebral vasoconstriction

Question 19

What drug class is represented by the figure below? How do you know this?

Answer 19

Barbiturates
Rapid redistribution & lengthy context-sensitive half-time (noted by fat build-up over time)

Question 20

Where is the site of initial redistribution for barbiturates?
When is equilibrium between plasma concentrations & muscle concentrations reached?

Answer 20

Skeletal muscles
15 min

Question 21

Where is the main reservoir for barbiturates?
What does this mean clinically?

Answer 21

Adipose tissue
Dose on lean body weight and note cumulative effects of barbiturates.

Question 22

What is the metabolism and excretion of barbiturates?

Answer 22

Hepatic metabolism; Renal excretion

Question 23

How protein bound (in a percentage) are barbiturates?

Answer 23

70 - 85% protein bound

Question 24

What are the characteristics of a non-ionized barbiturate?

Answer 24

Lipophillic;
Acidotic environment is favored.

Question 25

What are the characteristics of an ionized barbiturate?

Answer 25

Lipophobic;
Alkalotic-favored

Question 26

Why might barbiturates be considered cerebro-protective?

Answer 26

Barbs = ↓CBF & ↓CMRO₂

Question 27

Regarding barbiturates, are S-isomers or R-isomers more potent?
Which is used clinically?

Answer 27

S-isomer barbiturates are more potent
Trick question. Racemic mixtures are only ones used.

Question 28

How would one differentiate thiobarbiturates vs oxybarbiturates?

Answer 28

Thiobarbiturates: thiopental, thiamylal.
Oxybarbiturates: methohexital, phenobarbital, pentobarbital.

Question 29

What is the dose for Thiopental?
How much is in the brain 30 minutes post-administration? Why?

Answer 29

4 mg/kg/IV
10% in the brain after admin. Rapid redistribution to skeletal muscles occurs.

Question 30

What is the fat/blood partition coefficient of thiopental?
What does this mean?

Answer 30

• 11
• Dosing needs to be calculated on Ideal Body Weight.

Question 31

What does a partition coefficient describe?

Answer 31

Distribution of a drug between two substances that have the same temp, pressure, and volume.

Question 32

What is the blood-gas coefficient?

Answer 32

Number that describes the distribution of an anesthetic between blood and gas at the same partial pressure.

Question 33

What would a high blood-gas coefficient indicate?

Answer 33

Slower Induction time
Essentially, drug is taken up into the blood and wants to stay in the blood rather than going to tissues like the brain.

Question 34

Which is more lipid soluble, thiopental or methohexital?

Answer 34

Thiopental (Sodium Pentothal)

Question 35

At a normal pH _____% of methohexital is non-ionized.
At a normal pH ____% of sodium pentothal is non-ionized.
What does this mean in regards to induction for comparing these drugs?

Answer 35

• 76%
• 61%
• Methohexital for induction has a faster metabolism and recovery due to its increased lipid-solubility.

Question 36

Which barbiturate causes excitatory symptoms like myoclonus and hiccups?

Answer 36

Methohexital

Question 37

How would methohexital infusions differ from induction?

Answer 37

Very lipid-soluble so:
* Drug persists from infusion but clears quickly from induction.

Question 38

What is the IV methohexital dose?
What if it needs to be given rectally?

Answer 38

1.5 mg/kg IV
20 - 30 mg/kg PR

Question 39

What is the seizure profile of methohexital?

Answer 39

Can induce seizures but is better than etomidate or when used with ECT.
1. Continuous infusions induce post-op seizures in ⅓ of patients.
1. Seizures are induced in patients undergoing temporal lobe resection.
1. Seizure duration reduced 35-45% in ECT patients vs etomidate.

Question 40

What cardiovascular side effects would occur with thiopental administration in a normovolemic patient?

Answer 40

Transient sBP decrease of 10-20mmHg;
Transient HR increase of 15-20 bpm

Question 41

What patient conditions could result in poor baroreceptor response after barbiturate administration?

Answer 41

Hypovolemia, CHF, & β-blockade

Question 42

Thiopental can have a __________ type response due to __________ release coupled with previous exposure to the drug.

Answer 42

anaphylactic ; histamine

Question 43

What are the respiratory effects of barbiturates?

Answer 43

Dose-dependent medullary & pontine respiratory depression.
(Less sensitivity to CO₂ levels).

Question 44

What would occur with accidental arterial administration of a barbiturate?
What is the treatment?

Answer 44

Immediate vasoconstriction, excruciating pain
Injecting vasodilators: Lidocaine or Papaverine

Question 45

When would CYP450 enzyme induction be seen with a barbiturate infusion?
How long could it last?

Answer 45

2-7 days post-infusion
CYP450 induction could last up to 30 days.

Question 46

What renal effects would one expect to see after barbiturate administration?

Answer 46

Transient ↓RBF and ↓GFR