IV ANESTHETICS- barbs

Question 1

What is the MOA of barbiturates?

Answer 1

Binds the GABA receptor and potentials the inhibitory effect through increasing the duration of opening the chloride channel

Depresses the RAS

Question 2

What determines the potency of a barb?

Answer 2

The length of the chain at C5

Longer = more potent = more lipid soluble

Question 3

What is the phenyl group for on phenobarbital?

Answer 3

Anticonvulsant

Question 4

Why are thiopental and thiamyal more potent?

Answer 4

Because their sulfur makes them more lipid soluble: more rapid onset and shorter duration of action

Question 5

Why do induction doses need to be lower in the elderly?

Answer 5

Slower redistribution

Question 6

How are barbiturates principally biotransformed?

Answer 6

By phase I metabolism in the liver

Question 7

What mechanism is responsible for the awakening from a single sleep doses of barbs?

Answer 7

Redistribution

Question 8

What decreases the GFR of barbs?

Answer 8

Increased protein binding

Question 9

What increases renal absorption about the barb?

Answer 9

Increased lipid solubility

Question 10

What are the properties of methohexital?

Answer 10

It is highly lipid soluble
Cleared by the liver more rapidly
Excreted in the feces

Question 11

Why are thiopental, thiamyal and methohexital fast onset?

Answer 11

They are highly lipid soluble

Thiopental is also highly protein bound

Question 12

What are the CV effects of barbiturates?

Answer 12

Decrease in BP due to vasodilation of the capacitance vessels (depresses the medullary vasomotor center)
Tachycardia
Maintenance of cardiac output
Increased myocardial contractility (compensatory responses)

Question 13

In what situations will the cardiac output and bp fall using barbs?

Answer 13

When someone has blunted barorerceptor response: CHF! Beta blockade, hypovolemia, HTN

Question 14

How do you avoid a drop in BP and HR when using barbs?

Answer 14

Adequate prep hydration

Slow induction

Question 15

What are the respiratory effects of barbs?

Answer 15

Depress the medullary vent center
Cause airway obstruction
Depress the airway reflexes –> laryngospasm (light anesthesia) or bronchospasm

Question 16

What are the cerebral effects of barbiturates?

Answer 16

Constrict the cerebral vessels:
Decrease CBF and ICP
INCREASE CPP (because arterial blood pressure does not decrease as much as ICP)

Question 17

What does CPP equal?

Answer 17

Cerebral artery pressure - greater of jugular venous pressure or ICP

Map - ICP
It represents the pressure gradient driving cerebral blood flow

Question 18

How much decline do barbs cause in cerebral oxygen consumption?

Answer 18

Up to 50% of normal

Question 19

What can you use to see the effects of barb-induced oxygen consumption pattern?

Answer 19

It is reflected in the EEG

Low voltage fast activity –> high voltage slow activity

Question 20

What might the patient taste when using thiopental?

Answer 20

Garlic, onions or pizza

Question 21

Are barbs analgesic?

Answer 21

No

Can actually decrease the pain threshold

Question 22

Do barbs cause muscle relaxation?

Answer 22

No

Some cause involuntary muscle contraction (methohexital)

Question 23

What are the renal effects of barbs?

Answer 23

Reduce RBF and GFR in proportion to the fall in blood pressure

Question 24

What are the hepatic effects of barbs?

Answer 24

Decreases hepatic blood flow
Reduces metabolism of TCAs and other drugs
Induces the production of aminolevulinic acid synthetase which stimulates the formation of porphyria

Question 25

How do barbs and BZDs decrease IOP?

Answer 25

By directly affecting control centers, decreasing aqueous production and increasing drainage