Grant CRNA Local Anesthetics Quiz Review

Locals are weak bases prepared as hydrochloride salts.

Another benefit of adding NaHCO3 = less pain on injection.

Bupivicaine may precipitate with NaHCO3 addition
Use lower amounts of bicarb
0.1mEq/20 mL of bup vs. 1 mEq/10 mL of lido – not on test but for regionals

Direct correlation

Different concentrations of local anesthetics can produce different types of blocks. In this case, a concentration of 0.125% Bupivicaine only blocks sensory function, while a concentration of 0.5% blocks both sensory and motor function.

The statement is true because CNS depression associated with CNS toxicity occurs when inhibitory cortical neurons are selectively depressed, which means they are not functioning properly. This leads to excitatory pathways being unopposed, meaning they are not balanced or regulated by the inhibitory neurons. As a result, there is an increase in excitatory activity in the CNS, leading to symptoms of CNS toxicity.

Increased lipid solubility allows a drug to easily cross cell membranes and distribute throughout the body, leading to increased protein binding. This binding can enhance the drug's potency and prolong its duration of action. However, it also increases the drug's potential for toxicity, particularly in organs such as the heart. Therefore, drugs with high lipid solubility are more likely to cause severe toxicity, especially cardiac toxicity.

Voltage gated Na+ channels are found only in the nerve's axon. This is because the axon is responsible for transmitting electrical signals, known as action potentials, from one neuron to another. Voltage gated Na+ channels play a crucial role in generating and propagating these action potentials. They open in response to a change in voltage, allowing Na+ ions to flow into the axon and depolarize the membrane. This depolarization triggers the opening of voltage gated K+ channels, leading to repolarization and the propagation of the action potential along the axon. Therefore, voltage gated Na+ channels are specifically located in the axon to facilitate efficient and rapid transmission of electrical signals.

This describes amides.

Patients w/liver disease or reduced liver blood flow may have prolonged effects.
P450 is INHIBITED by anesthesia gases, propanolol, and cimetidine.

The addition of a vasoconstrictor to a local anesthetic allows for higher maximum doses to be used. Vasoconstrictors, such as epinephrine, constrict blood vessels at the site of administration, reducing blood flow and delaying the systemic absorption of the local anesthetic. This reduces the risk of toxicity and allows for higher doses to be used safely.

This type of linkage is important clinically because it has implications for metabolism and allergic potential

Administering a local anesthetic (LA) into a neuraxial compartment, such as the epidural or intrathecal space, is contraindicated if it contains a preservative. Preservatives can cause neurotoxicity and other adverse effects when injected into these compartments. Therefore, it is important to ensure that the LA being administered is preservative-free to avoid potential harm to the patient.

The word "potentiate" means to increase the effect or strength of something. In the context of the given question, the blank is asking for a word that completes the sentence and relates to the non-depolarizing muscle relaxant blockade. By choosing "potentiate" as the correct answer, it suggests that the action being described is the enhancement or strengthening of the blockade caused by the non-depolarizing muscle relaxant.

The explanation for the given correct answer is that the non-ionized form of a substance is able to easily pass through the cell membrane and diffuse into the nerve axon. On the other hand, the ionized form of the substance binds to specific receptors on sodium channels, but only when the channel is in the inactivated state. This means that both forms of the substance have different mechanisms of action, but they are both involved in the transmission of signals within the nerve axon. Therefore, the statement is true.

Cocaine is also metabolized by liver esterases

Avoid the use of ester LA's with pseudocholinesterase deficiency.

The other three are factors that can produce LA toxicity but most likely due to an accidental IV injection.

Hyperventilation helps to decrease the chance of ion trapping the LA in the brain.

Chloroprocaine has NO (0%) protein binding – very short DOA – half life is 6 minutes

Esters are a type of local anesthetics that are broken down into para-aminobenzoic acid (PABA), which is a known allergen. This can potentially cause localized edema, urticaria, bronchospasm, and anaphylaxis. Therefore, the correct answer is Esters.

Toxicity is based on peak plasma levels.

The addition of vasoconstrictors facilitates neuronal uptake, enhancing the quality of analgesia, and limits toxic side effects.

**Always assume you could accidentally inject into the blood stream.

Local anesthetics need to bind with a minimum of three successive nodes of Ranvier in order to be effective. The nodes of Ranvier are small gaps in the myelin sheath that surrounds nerve fibers. By binding to these nodes, local anesthetics can block the transmission of nerve signals, effectively numbing the area. Binding to fewer than three nodes may not provide enough coverage to fully block the nerve signals, resulting in incomplete anesthesia.

Benzocaine is ideally suited for topical anesthesia because it has a pKa of 3.5, which means it is completely ionized in a pH of 7.4. This allows it to easily penetrate the skin and provide effective anesthesia. Additionally, it comes in a 20% solution, delivering 200-300 mg per brief spray, which is a suitable dosage for topical anesthesia. However, it is important to note that doses over 300 mg can lead to methemoglobinemia, a condition where the blood is unable to carry oxygen effectively.

Cocaine has vasoconstrictive properties because it blocks the reuptake of norepinephrine. Norepinephrine is a neurotransmitter that plays a role in regulating blood vessel constriction. When cocaine inhibits its reuptake, norepinephrine remains in the synaptic cleft for a longer period, leading to increased stimulation of alpha-adrenergic receptors and causing vasoconstriction. This narrowing of blood vessels can result in increased blood pressure and reduced blood flow to certain areas of the body.

Protein binding, however, is more important than lipid solubility when it comes to duration of action

When a drug is bound to protein it is not available to be metabolized by the liver or plasmaesterases.

Nerve conduction is determined mainly by two factors: nerve fiber diameter and the degree of myelination. Myelination refers to the presence of a myelin sheath, which is a fatty substance that surrounds and insulates nerve fibers. This insulation allows for faster and more efficient conduction of electrical impulses along the nerve fibers. Therefore, the degree of myelination directly affects the conduction velocity of the nerve.

The drugs mentioned in the question, echthiophate, neostigmine, pyridostigmine, and edrophonium, are known to prolong ester LA (local anesthetic) activity. This means that these drugs increase the duration of the effects of local anesthetics, making them last longer.

This is an issue when your dermatome level is ~T4 because your sympathetic/autonomic blockade would be affecting your cardiac accelerators.

Tetracaine is the most toxic ester because it undergoes hydrolysis at a slower rate compared to other esters. Hydrolysis is a chemical reaction in which a compound is broken down by water. In the case of esters, hydrolysis leads to the release of toxic byproducts. Since tetracaine is hydrolyzed more slowly, it remains in the body for a longer time, increasing its toxicity.

Prilocaine>lidocaine>mepivacaine>ropivacaine>bupivacaine

Mnemonic:
Please lease my rusty bus.

Via decreasing plasma cholinesterase activity.

Respiratory alkalosis does not increase the risk of LA (local anesthetic) toxicity. Local anesthetics are weak bases, and they exist predominantly in the ionized form in an alkaline environment. In respiratory alkalosis, there is a decrease in carbon dioxide levels, resulting in increased blood pH. This alkalotic state decreases the ionization of local anesthetics, reducing their toxicity. On the other hand, pregnancy, hypoxemia, and respiratory acidosis increase the risk of LA toxicity as they all lead to an acidic environment, promoting the ionization of local anesthetics and increasing their toxicity.

The minimum blocking concentration (Cm) for motor fibers is approximately twice that of sensory fibers. This means that it takes a higher concentration of a blocking agent to inhibit the function of motor fibers compared to sensory fibers.

When a local anesthetic is injected into the venous system, it bypasses the liver, which is responsible for metabolizing drugs before they enter systemic circulation. Instead, the drug travels directly to the lungs, where it undergoes first-pass uptake. This means that a significant amount of the drug is taken up by the lungs before it can enter systemic circulation, resulting in less drug reaching the rest of the body.

Ropivacaine, lidocaine, and cocaine are all drugs that have vasoconstrictor properties. Vasoconstrictors are substances that cause the narrowing of blood vessels, leading to a decrease in blood flow. This can be beneficial in certain medical procedures, such as local anesthesia, as it helps to reduce bleeding and prolong the effects of the anesthetic. Therefore, the statement that ropivacaine, lidocaine, and cocaine are vasoconstrictors is true.

Causes tachycardia.

Patients w/severe anemia or heart failure cannot tolerate the reduced O2 carrying capacity.

Tx w/1-2 mg/kg of 1% methylene blue.

Alpha 1-acid glycoprotein (remember – weak base)


Therefore, less metabolism of the drug since it is staying at the site of action (less likely cleared by blood flow)

Ester local anesthetics usually have a shorter duration of action than amides

Increased lipid solubility = greater plasma protein binding and greater tissue uptake

The correct order of nerve fiber blockade is autonomic, sensory, then motor. This means that the autonomic nerves, which control involuntary bodily functions, are blocked first. Then, the sensory nerves, responsible for transmitting sensations such as pain, are blocked. Finally, the motor nerves, which control movement, are blocked. This order ensures that the patient does not feel pain or discomfort during a procedure, while still allowing them to maintain some motor function.

Epi is effective for increasing DOA of short acting and intermediate acting drugs, clinically does not really effect DOA of long acting drugs because they are already long

Typically will cause v-fib/v-tach

Propofol is a medication commonly used for anesthesia induction and maintenance, as well as for terminating seizure activity. It is administered intravenously in a dose range of 0.5-2mg/kg. This dosage is effective in stopping seizures and restoring normal brain activity. Propofol works by enhancing the inhibitory effects of gamma-aminobutyric acid (GABA), a neurotransmitter that reduces neuronal excitability. By increasing GABA's activity, propofol helps to control and terminate seizure activity.

Local anesthetics work by binding to sodium channels in nerves, blocking the conduction of nerve impulses and producing a reversible loss of sensation. They primarily bind to the open and inactivated states of the sodium channels, preventing the influx of sodium ions and inhibiting nerve cell depolarization. However, they do not bind to the closed/resting state of the sodium channels, as this is the state in which the channels are not actively conducting impulses. Therefore, local anesthetics do not have an effect on the closed/resting state of sodium channels.

Peripheral nerve blocks are a less likely source of systemic absorption unless accidentally injecting IV - always aspirate prior to injection.

Benzocaine can also cause methemoglobinemia.

LA stands for local anesthetics. Local anesthetics produce a differential blockade, meaning that they interrupt different modes of nerve transmission in an equal fashion. In this case, the correct order of nerve transmission interruption by LA is temperature sensation, sharp pain, and light touch.

Use the 1:200,000 concentration (5 mcg/mL)

The addition of epi to local anesthesia should be avoided in patients with unstable angina, cardiac dysrhythmias, uncontrolled hypertension, uteroplacental insufficiency, and areas that lack collateral blood flow such as the fingers/toes. These conditions can increase the risk of adverse cardiovascular events or compromise blood flow to vital organs or extremities, making the use of epi in local anesthesia contraindicated.