Barbiturates Flashcards
Do Barbiturates cause areflexia?
No! Little to no effects on any muscles
Name the uses of barbiturates (6)
Seizure treatment, short painless procedures, induction, increased ICP, cardio version, ECT
What determines the effects of the barbiturates?
The molecule substitutions
Do oxybarbiturates have a long or short duration of action?
Long
Comment on thiobarbiturates lipophilicity, onset, duration of action
Lipophilic, rapid onset, shorter DOA
Methohexital has a longer or shorter DOA?
shorter
Phenobarbital has what key use?
Anticonvulsant
Which 4 receptors can barbiturates act on? What is the primary receptor?
GABA (primary), adenosine, nicotinic Ach, glutamate
Are barbiturates appropriate in patients with increased ICP?
Yes - decrease CBV, CBF, CMRO2, and ICP. Neuroprotective due to reverse steal (ischemic areas still get BF), free radical scavenging, liposomal membrane stabilizing, excitatory amino acid blockade
Dose required may cause significant hypotension
Contraindication of barbiturates? Why?
Acute intermittent porphyria
due to accelerated heme production
What happens and what do you do if a barbiturate is accidentally administered into an artery?
Area vasoconstricts -> blanching -> cyanosis -> gangrene -> necrosis -> permanent nerve damage
Dilute with lidocaine, give heparin, give papaverine, peripheral nerve block
Are barbiturates lipophilic?
Yes - rapid distribution, rapid termination after re-distribution
Do barbiturates undergo phase I or phase II metabolism?
Phase I - liver oxidation
Why is thiopental’s half life ten fold of that of propofol?
Thiopental has an active metabolite - pentobarbital (oxybarbiturate) - that is very long-acting
In what patients would half-time of barbiturates be affected?
Pediatrics - shorter half-time due to rapid hepatic clearance
Pregnancy - longer-half time due to protein binding
Do barbiturates cause pain on injection?
No - no additives
Do barbiturates cause an isoelectric EEG?
Yes - burst suppression
What are the CV effects of barbiturates?
Decreased SVR, MAP, CO, direct myocardial depression
What are the respiratory effects of barbiturates?
Cause central apnea (1 min) with return to baseline in 6 minutes which is shorter than with prop
some anti-bronchospastic effects with thiopental, but not as much as with prop
not as much bronchodilaton (airway reflexes maintained)
large doses can depress laryngeal/cough reflexes
Dose dependent depression of medullary and pontine ventilatory centers
Enzyme induction from which barbiturate causes accelerated metabolism of which other drugs?
Phenobarbital.
Causes accelerated metabolism of tricyclics, anticoagulants, phenytoin, endogenous substances (vitamin K, bile salts, corticosteroids)
What are the 4 stages of anesthesia that are produced with the induction of IV anesthetics?
There are no 4 stages with induction of IV anesthetics
Is thiopental used for long-term sedation?
Not commonly - accumulation, prolonged half time, slow recovery
How are the effects of thiopental terminated?
Very lipophilic - fast onset - quick re-distribution*
What is thiopental’s hepatocyte? Does it cross the BBB?
hydroxythiopental - no, it is water soluble so it can be really excreted quickly
What phase of metabolism does thiopental undergo?
Phase I (oxidation in the liver)
Will liver injury impact the metabolism of thiopental?
No - you must have severe liver dysfunction to affect metabolism due to large reserve capacity of the liver to oxidize barbiturates
Is half life longer or shorter than propofol?
Longer due to pentobarbital metabolite
Is apnea likely with Thiopental?
Yes! Decreased sensitivity of ventilatory center to stimulation of CO2
In terms of onset, effect time, half-life, and side effects, why would thiopental be less desirable than propofol?
Onset and effect time are similar (lipophilic = fast onset, rapid re-distribution = short effect time), but half-life is longer in thiopental due to pentobarbital and thiopental results in more N&V
Induction dose of Thiopental for adults, pediatrics, and infants
Adults: 2.5-5.0 mg/kg IV
Peds: 5-6 mg/kg IV
Infants: 6-8 mg/kg IV
In what 3 patients would you lower your induction dose of thiopental?
Elderly, early pregnancy, obesity
If you pre-medicate with a benzo or opioid, what will you need to do with your dose of thiopental?
Decrease it
Which 3 co-morbid states would you have to decrease your thiopental dose?
HF, shock, anemia
Which is more potent, methohexital or thiopental?
Methohexital (2.7x)
Methohexital is the induction agent of choice for which procedure?
ECT
Therapeutic effect is related to duration of the seizure
Principle disadvantage of Methohexital?
Myoclonus
How can you decrease the excitatory effects of Methohexital (hiccups and myoclonus)
Administer opioid
Does methohexital have metabolites?
Inactive hydroxy derivatives
What is clearance dependent upon for Methohexital? is it higher or lower than in thiopental?
liver blood flow
higher
results in shorter elimination half life
What are the CV effects of Methohexital?
Less CV effects than with this due to tachycardia reflex response offsetting CV changes
Induction dose of methohexital?
Rectal dose?
Infusion dose?
1-2mg/kg IV
25 mg/kg rectal
50-100 mcg/kg/min infusion
Is methohexital appropriate for a patient on an anti epileptic?
No - lowers seizure threshold
