Exam 4 - Local Anesthetics II Flashcards by Brandon Simpson

What is the average pKa of local anesthetics?

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What is the function of the alkalinization of LA Solutions?

What are the benefits of alkalinization?

Alkalinization increases the percentage of lipid-soluble or non-ionized forms.

Benefits:
* Faster onset of action by 3-5 mins
* Enhances the depth
* Increase the spread of epidural blocks

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If Drug V (weak base) has a pKa of 9.1, will the drug be more ionized or nonionized at physiological pH?

pKa - pH
9.1 - 7.4 = +1.7

Drug V will be more ionized at physiological pH.

Weak Bases, pKa before pH
Weak Acids, pKa afterpH

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If the pKa of LA (a weak base) is at 4.5, will the drug be more ionized or nonionized at physiological pH?

pKa - pH
4.5 - 7.4 = -2.9

LA will be more non-ionized at physiological pH.

Weak Bases, pKa before pH
Weak Acids, pKa afterpH

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LA1’s pKa is 9.2, and LA2’s pKa is 7.5. Which of the following are correct when placed in physiological pH? Select 2 answers.

A. LA2 has more non-ionized components
B. LA1 has more ionized components
C. LA2 has more ionized components
D. LA1 has more non-ionized components

A and B

LA1
9.2 - 7.4 = +1.8 (ionized)

LA2
7.5 - 7.4 = +0.1 (less ionized)

Weak Bases, pKa before pH
Weak Acids, pKa afterpH

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What adjuvant medications prolong the duration of local anesthetics?

Dexmedetomidine
Magnesium
Clonidine
Ketamine
Dexamethasone

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What will be the results of combining LA Chloroprocaine & Bupivacaine?

Produce a rapid onset
Tachyphylaxis
Additive effects

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What is added to 30 mL of choloroprocaine solution to improve the efficacy of a chlorprocaine-bupivicaine epidural?

1 mL of 8.4% Sodium Bicarbonate

This will increase the non-ionized form of LA.

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The toxic effects of combining LA are _______

Additive. (1+1 =2)

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Compare the onset of action between chloroprocaine and bupivacaine.

Chloroprocaine: Rapid
Bupivacaine: Slow

But they have the same potency

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What vasoconstrictors are available to use with LA?

Epinephrine
Phenylephrine

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Why is it important to use vasoconstrictors with LA?

The duration of action of a LA is proportional to the time the drug is in contact with nerve fibers. For this reason, epinephrine may be added to LA solutions to produce vasoconstriction, which limits systemic absorption and maintains the drug concentration in the vicinity of the nerve fibers to be anesthetized.

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Use of vasoconstrictors with LA:
* Increased ____ uptake of LA
* ____ effects may have some degree of analgesia
* ____ effect on the onset rate of LA
* Enhanced ____ with inhaled anesthetics
* Systemic absorption will cause ____ and ____

Increased neuronal uptake of LA
α-adrenergic effects may have some degree of analgesia
No effect on the onset rate of LA
Enhanced cardiac irritability with inhaled anesthetics
Systemic absorption will cause HTN and tachycardia

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How much epinephrine or phenylephrine is given with bupivacaine or lidocaine for a subarachnoid block (SAB)?

0.2 mg Epi
2 mg Phenylephrine

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Compute 1:500,000 Epi to mcg/mL

1,000,000/ 500,000=2

2 mcg/mL

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Compute 1:10,000 Epi to mcg/mL

1,000,000/ 10,000 = 100

100 mcg/mL

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Compute 1:1000 Epi to mcg/mL

1,000,000/ 1000 = 1000

1000 mcg/mL

This is the epinephrine that we find in our crash carts.

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0.25% concentration is how many mg/mL

2.5 mg/mL

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0.5% concentration is how many mg/mL

5 mg/mL

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1% concentration is how many mg/mL?

10 mg/mL

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2% concentration is how many mg/mL?

20 mg/mL

2% lidocaine is the most common concentration used in the OR

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4% concentration is how many mg/mL?

40 mg/mL

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Your surgeon injected 20 mLs of Bupivacaine 0.25% with 1:200,000 of Epi.

What are the total mgs for Bupivacaine and the total mcgs for Epinephrine?

Bupivacaine:
0.25% = 2.5 mgs/mL
2.5 mgs x 20 mLs = 50 mgs total

Epinephrine:
1:200,000 = 5 mcg/mL
5 mcg x 20 mLs = 100 mcg total

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Lidocaine Recommended Max Single Dose:

Lidocaine Recommended Max Single Dose with/Epi

Lidocaine Recommended Max Single Dose for Spinal

300 mg

500 mg w/ Epi

100 mg

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Bupivacaine Recommended Max Single Dose Bupivacaine Recommended Max Single Dose with/Epi Bupivacaine Recommended Max Single Dose for Spinal

175 mg 225 mg w/ Epi 20 mg

Clinical Scenario Question 112.5 mg of Bupivacaine with Epi and 250 mg of Lidocaine with Epi were given during surgery. What are the percentages of each LA based on the recommended max single dose in mg?

Max single dose of Bupivacaine with Epi: 225 mg 112.5/225 = 50% Max single dose of Lidocaine with Epi: 500 mg 250/500 = 50%

Rank these from greatest to least absorbed topically: tetracaine, lidocaine, cocaine

Cocaine > tetracaine > lidocaine

Which anesthetic has localized vasoconstriction that will decrease blood loss and improve surgical visualization?

Cocaine (4-10%)

Which anesthetic is great with surface anesthesia?

Lidocaine (2-4%)

Lidocaine inhalation does not alter airway resistance, but causes ______

vasodilation

What LA are not effective for topical anesthetic?

Procaine and Chloroprocaine *These drugs do not penetrate mucous membranes as effectively as cocaine or lidocaine.*

What is an LTA?

* Lidocaine tracheal anesthesia * Localized tracheal anesthesia

Eutectic Mixture of LA (EMLA) contains what LA? Dose: Onset:

Lidocaine 2.5% + Prilocaine 2.5% = 5% LA Dose: 1 to 2 gms/ 10 cm2 area Onset: 45 mins

EMLA has to be applied for ______ hours before skin graft.

2 hours

EMLA can be applied for 10 minutes before any of these procedures:

Cautery of genital warts Venipuncture, lumbar puncture Arterial cannulation (Nitroglycerine) Myringotomy

EMLA considerations

* Caution with methemoglobinemia (prilocaine) * Not recommended for skin wounds * contraindicated with amide allergies

How can you double the duration of LA for local infiltration?

add Epinephrine 1:200,000

What are the contraindications of using epinephrine in LA for local infiltrations?

* Not intracutaneously or into tissues at end arteries * Fingers, toes, ears, nose, penis *Can cause necrosis.*

Order of blockade during Peripheral Nerve Block?

The proximal area (site of LA administration) is affected first and then distal.

When the peripheral nerve block is wearing off, what comes back first? Proximal or Distal?

Proximal comes back first & then distal.

Peripheral Nerve Block onset of action is dependent on _________. Lidocaine OOA: Bupivacaine OOA:

LA pK Lidocaine OOA: 3 mins Bupivacaine OOA: 15 mins

Peripheral Nerve Block Duration depends on _____ of local anesthetic.

dose

What is a Region Bier Block?

Bier Block IV injection of LA into an extremity isolated from the rest of the systemic circulation with a tourniquet. Sensation and muscle tone dependent on tourniquet

What LA is commonly used in Bier Block?

Lidocaine

Bier Block Steps

* IV start * Exsanguination * Double cuff * LA injection * Surgeon will perform procedure * IV D/C

What is the sequence of blockades for a segmental block in Neuraxial Anesthesia? What nerves are involved?

1. SNS (Myelinated preganglionic B fibers) 2. Sensory (Myelinated A, B fibers, unmyelinated C fibers) 3. Motor (Myelinated A-δ and unmyelinated C fibers)

Clinical Scenario: Neuraxial blockade is the last reference with which assessment parameters A. NIBP B. Heart Rate C. Cold Alcohol Pad D. Leg Movement

D. Leg Movement

What is the principal site of action for SAB?

Preganglionic fiber

For SAB, the _______ effect is on the same level of denervation.

sensory

For SAB, the _______ effect is 2 spinal segments cephalad of the sensory block. For SAB, the _______ effect is 2 spinal segments below the sensory block.

SNS Motor

If the sensory block is at T5, where is the SNS block?

T3 *This SNS block will trigger an asystole event.*

What dermatomes correspond with our cardiac accelerator?

T1 to T4

Clinical Scenario Slide: If the assessed sensory level after SAB is T6 ( Top of Xiphoid Process), what are the blocked SNS and motor levels?

SNS Block: T4 Motor Block: T8

5 most common LAs used in SAB?

Most common: Tetracaine, Lidocaine, Bupivacaine, Ropivacaine, and Levobupivacaine

What factors affect SAB dosage?

* Height of patient (volume of subarachnoid space) * Segmental level of anesthesia desired * Duration of anesthesia desired

For SAB, ____ is more important than ____ of drug (%) or the volume (mLs) of the solution injection.

Dose; Concentration

SAB Dose: 5 ft = ____ mL of 0.75% Bupivacaine Add ____ mL for every inch above 5 ft

1 mL 0.1 mL *For someone who is 5'5", you will give 1.5 mL of bupivacaine for a SAB.*

For SAB, the _________ of LA is important in determining the spread of the drug.

specific gravity

What can be added to LA so that its specific gravity can increase? What can be added to LA so that its specific gravity can decrease?

Glucose added → hyperbaric solution. Distilled water added → hypobaric solution

Which side will you want to position a right-hip arthroplasty patient on if they receive a hyperbaric LA solution?

Right side lying, the hyperbaric solution will "sink."

Which side will you want to position a right-hip arthroplasty patient on if they receive a hypobaric LA solution?

Left side lying, the hypobaric solution will "float".

The most common LA used in Epidural Anesthesia.

Lidocaine *Good diffusion through tissue and safer*

What is the onset of epidural anesthesia?

Onset: 15 to 30 minutes

Epi 1:200,000 with ____ does not increase duration of action of epidural block.

bupivacaine

Can epidural anesthesia cross the placental barrier with OB and C-section patients?

Yes

What is the difference between SAB and epidural blocks?

No differential zone of SNS, sensory, and motor blockade.

What is considered an acceptable additive to both epidural and SAB to produce a synergistic effect?

Opioids

Will lidocaine or bupivicaine cross the transplacental barrier more?

Lidocaine (more lipid soluble, less protein bound)

What is Tumescent LA?

Subcutaneous infiltration of large volume of dilute local anesthetic (5L or more)

What makes up the tumescent solution?

* Diluted Lidocaine (0.05% to 0.1%) * Epinephrine 1:100,000

What is the tumescent effect during liposuction?

The taut stretching of overlying blanched skin d/t large volume *Fat can be aspirated without blood loss and provide prolonged post-op analgesia.*

Where is tumescent usually administered?

* Thigh * Abdomen * Hips * Buttocks

When is the plasma peak for tumescent?

12 to 14 hours s/p injection.

Regional Anesthesia Lidocaine with Epi Dose.

7 mg/kg

Highly diluted Lidocaine with Epi Tumescent dose (mg/kg).

35 to 55 mg/kg

What is the theory with the Tissue Buffering System?

1 gram of SQ tissue can absorb up to 1 mg of Lidocaine