Barbiturates

Question 1

Barbiturate mechanism of action

Answer 1

• GABA receptor agonist (increases the receptors affinity for GABA)
• depression of the reticular activating system (suppress excitatory neurotransmitters [acetylcholine] and enhance inhibitory neurotransmitters [GABA])

(when GABA receptors are activated, transmembrane chloride conductance increases, resulting in hyperpolarization)

Question 2

The duration of action of highly lipid-soluble barbiturates is determined by what?

Answer 2

redistribution

Question 3

The duration of action of barbiturates is determined by what, after repeated administration?

Answer 3

elimination (redistribution cannot occur with repetitive doses)

Question 4

Induction doses of barbiturates can affect the cardiovascular system by a fall in what and an elevation in what?

Answer 4

a fall in blood pressure and an elevation in heart rate

Question 5

After barbiturate administration, cardiac output is often maintained by…

Answer 5

a rise in heart rate and increased myocardial contractility from compensatory baroreceptor reflexes

Question 6

Which patients would have an inadequate baroreceptor response?

Answer 6

hypovolemic, congestive heart failure, beta-adrenergic blockade

Question 7

What would happen if you gave a barbiturate and there was an inadequate baroreceptor response?

Answer 7

cardiac output and arterial blood pressure might fall dramatically due to uncompensated peripheral pooling and unmasked direct myocardial depression

Question 8

The cardiovascular effects of barbiturates depend on….

Answer 8

volume status, baseline autonomic tone, and preexisting cardiovascular disease

Question 9

Barbiturates increase or decrease ICP?

Answer 9

decrease

Question 10

Barbiturates increase or decrease cerebral oxygen consumption?

Answer 10

decrease (up to 50% of normal)

Question 11

Methohexital lowers what?

Answer 11

the seizure threshold

Question 12

What solution do you use to mix sodium thiopental?

Answer 12

sterile water

Question 13

Thiopental induction dose, onset, peak, duration?

Answer 13

dose: 3 - 6 mg/kg IV
onset: < 30 seconds
peak: 30 - 60 seconds
duration: 5 - 15 minutes

Question 14

Methohexital induction dose, onset, peak, duration?

Answer 14

dose: 1 - 2 mg/kg IV
onset: 30 seconds
peak: 30 seconds
duration: 5 - 10 minutes

Question 15

What will happen if you mix barbiturates with opioids, catecholamines, or muscle relaxants?

Answer 15

precipitation, due to the acids mixing with bases

Question 16

Barbiturates undergo maximal brain uptake within…

Answer 16

30 seconds

Question 17

Barbiturate equilibration with skeletal muscle is reached in….

Answer 17

about 15 minutes (decreased doses are needed when skeletal muscle perfusion is decreased [shock] or when skeletal muscle mass is decreased [elderly])

Question 18

Metabolism of thiopental takes place where?

Answer 18

in the liver (almost 99% metabolized).

(hepatic clearance is characterized by a low hepatic extraction ratio - influenced by hepatic enzyme activity, not hepatic blood flow)

Question 19

Thiopental decreases the sensitivity of the medullary ventilatory center to stimulation of what?

Answer 19

carbon dioxide

Question 20

Do barbiturates stimulate enzyme induction in the liver?

Answer 20

yes, after 2-7 days of sustained administration

Question 21

Intraarterial injection of thiopental usually results in what?

Answer 21

immediate, intense vasoconstriction and excruciating pain that radiates along the distribution of the artery

Question 22

What chemical are all barbiturates derived from?

Answer 22

barbituric acid (it is a cyclic compound formed from the condensation of urea and malonic acid)

Question 23

Substitution at the number 5 carbon (C5) determines what about a barbiturate?

Answer 23

hypnotic potency and anticonvulsant activity (longer side chains result in higher potency. adding a phenyl group, as in phenylbarbital, makes it an anticonvulsive)

Question 24

Replacing the oxygen on the number 2 carbon on barbituric acid with a sulfur atom increases what?

Answer 24

lipid solubility (thiobarbiturates are more lipid soluble than oxybarbiturates)

Question 25

Does an induction dose of thiopental adequately abtund laryngeal reflexes or produce analgesia?

Answer 25

no, thiopental does not produce analgesia. it is considered an antianalgesic.

Question 26

What types of patients should not receive barbiturate hypnotic agents?

Answer 26

• barbiturate allergy
• undergoing painful procedures
• patients with seizures
• patients with decreased ICP
• asthmatics

Question 27

Name three medications (or types) that can be affected by the induction of liver enzymes by barbiturates.

Answer 27

anticoagulants, phenytoin, and tricyclic antidepressants

Question 28

Is thiopental a weak acid or base?

Answer 28

weak acid

Question 29

Does thiopental cause a histamine release?

Answer 29

yes

Question 30

What is the standard thiopental dose for an RSI in an emergency cesarean section?

Answer 30

250mg