Barbiturates

Question 1

Barbiturate mechanism of action

Answer 1

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

pH of 2.5% thiopental

Answer 2

> 10

Question 3

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

Answer 3

redistribution

Question 4

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

Answer 4

elimination (redistribution cannot occur with repetitive doses)

Question 5

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

Answer 5

a fall in blood pressure and an elevation in heart rate

Question 6

After barbiturate administration, cardiac output is often maintained by…

Answer 6

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

Question 7

Which patients would have an inadequate baroreceptor response?

Answer 7

hypovolemic, congestive heart failure, beta-adrenergic blockade

Question 8

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

Answer 8

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

Question 9

The cardiovascular effects of barbiturates depend on….

Answer 9

volume status, baseline autonomic tone, and preexisting cardiovascular disease

Question 10

Barbiturates increase or decrease ICP?

Answer 10

decrease

Question 11

Barbiturates increase or decrease cerebral oxygen consumption?

Answer 11

decrease (up to 50% of normal)

Question 12

Methohexital lowers what?

Answer 12

the seizure threshold

Question 13

What solution do you use to mix sodium thiopental?

Answer 13

sterile water

Question 14

Thiopental dose - induction

Answer 14

3 - 6 mg/kg IV

Question 15

Methohexital dose - induction

Answer 15

1 - 2 mg/kg IV

Question 16

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

Answer 16

precipitation, due to the acids mixing with bases

Question 17

Barbiturates undergo maximal brain uptake within…

Answer 17

30 seconds

Question 18

Barbiturate equilibration with skeletal muscle is reached in….

Answer 18

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

Question 19

Metabolism of thiopental takes place where?

Answer 19

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 20

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

Answer 20

carbon dioxide

Question 21

Do barbiturates stimulate enzyme induction in the liver?

Answer 21

yes, after 2-7 days of sustained administration

Question 22

Intraarterial injection of thiopental usually results in what?

Answer 22

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

Question 23

What chemical are all barbiturates derived from?

Answer 23

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

Question 24

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

Answer 24

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

Question 25

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

Answer 25

lipid solubility (thiobarbiturates are more lipid soluble than oxybarbiturates)

Question 26

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

Answer 26

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

Question 27

What types of patients should not receive barbiturate hypnotic agents?

Answer 27

barbiturate allergy, undergoing painful procedures, patients with seizures, patients with decreased ICP

Question 28

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

Answer 28

anticoagulants, phenytoin, and tricyclic antidepressants

Question 29

Is thiopental a weak acid or base?

Answer 29

weak acid