Induction Drugs - Barbiturates Exam 2 Flashcards by Raymond Bas

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

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

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What are the 4 group of organs that utilize the blood supply?

Vessel-rich group = 75% CO
Skeletal muscles & skin = 18% CO
Fat = 5% CO
Bone, tendons, & cartilage = 2% CO

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

brain, heart, liver, kidneys
75% of CO

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What are the stages of anesthesia?

Analgesia
Delirium
Surgical Anesthesia
Medullary paralysis

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What are the COMPONENTS of general anesthesia?

Hypnosis
Analgesia
Muscle Relaxation
Sympatholysis
Anterograde Amnesia

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When does stage 1: analgesia begin and end?

initiation of an anesthetic agent
loss of consciousness

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What stage offers the lightest level of anesthesia?

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

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When does stage 2: delirium begin and end?

loss of consciousness
onset of automatic rhythmicity of vital signs

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During induction, when would one most likely see laryngospasm?

Stage 2

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

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

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

Stage 2
response to stimulation is exaggerated and violent!

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

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!

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

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

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What is the MOA of barbiturates?

Potentiate GABA-A receptor activity
mimics GABA
causes Cl⁻ influx & cellular hyperpolarization

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Barbiturates also act on which receptors? (3)

Glutamate
adenosine
neuronal nACH-R

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Do barbiturates offer any analgesia?

No analgesic component

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

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

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

Barbiturates
* Rapid onset 30 secs & awakening
* Rapid redistribution
* lengthy context-sensitive half-time (noted by fat build-up over time)

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

Skeletal muscles
15 min

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

Adipose tissue
* Dose on LEAN body weight and note cumulative effects of barbiturates

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What is the metabolism and excretion of barbiturates?

Hepatic metabolism 99%
Renal excretion

How protein bound (in a percentage) are barbiturates?

70 - 85% protein bound

What are the characteristics of a non-ionized barbiturate?

Lipid soluble
favors acidosis

What are the characteristics of an ionized barbiturate?

less lipid soluble
favors alkalosis

Why might barbiturates be considered **cerebro-protective**?

Barbs = **↓CBF & ↓CMRO₂**

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

* **S-isomer** barbiturates are more potent * Trick question. **marketed barbituarates are Racemic mixtures**

What are the 2 categories of barbiturates?

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

What is Theopental (Sodium Pentothal)?

* Introduced in **1934** * derived from **barbituric acid** * used for **capital punishment** * **GOLD standard** barbiturate

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

* **4-5 mg/kg/IV (IBW)** * **10%** in the brain after 30mins * **Rapid redistribution** to skeletal muscles occurs * elimination 1/2 time **> methohexital**

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

* **11** * Dosing needs to be calculated on **Ideal Body Weight** * High coefficient = **fat used as reservoir > blood**

What does a partition coefficient describe?

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

What is the blood-gas coefficient?

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

What would a high blood-gas coefficient indicate?

* **Slower Induction time** * High solubility in blood, thus slowing rate of induction (= Low Vd) * blood = **inactive reservoir**

Which is more **lipid soluble**, thiopental or methohexital?

Thiopental (Sodium Pentothal)

At normal pH, what percent of **methohexital** is **non-ionized**? At normal pH, what percent of **pentothal** is **non-ionized**? What does this mean in regards to induction for comparing these drugs?

* **methohexital: 76%** * **pentothal: 61%** * methohexital > pentothal (faster metabolism and recovery) * non-ionized = lipid soluble

Which class of barbituartes are **more lipid soluble** and why?

* **Thiobarbiturates > Oxybarbiturates** * **Oxygen** atom exchanged for **sulfur** * more lipid soluble and greater hypnotic potency

Why is there **less blood volume** if there is **more adipose tissue?**

Adipose tissue has **decreased** blood supply

What side effects are associated with methohexital?

* Myoclonus * Hiccoughs

How would methohexital infusions differ from induction?

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

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

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

What is the seizure profile of methohexital?

**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.

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

* Transient **sBP** **decrease** of **10-20mmHg** * Transient **HR** **increase** of **15-20 bpm** * (baroreceptor response)

What barbiturate side effects are seen in patients with **poor baroreceptor response**?

* Hypovolemia * CHF * β-blockade

What compensatory increase occurs after rapid administration of thiopental?

Incresease in HR (baroreceptor response)

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

* anaphylactic * histamine

What are the **respiratory** effects of barbiturates?

* Dose-dependent **medullary & pontine respiratory depression** * **Less sensitivity** to CO₂ levels * **slow RR and decreased Vt**

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

* Immediate **vasoconstriction, gangrene, and nerve damage** * **excruciating pain** * Injecting vasodilators: **Lidocaine** or **Papaverine**

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

* **2-7 days** post-infusion * CYP450 induction could last up to **30 days** * **accelerated metabolism** of drugs metabolized by liver

What does CYP450 induction result in?

**Accelerated metabolism** of: * anticoagulants * phenytoin * TCAs * digoxin * corticosteroids * bile salts and vit K

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

Transient **↓RBF and ↓GFR**