Local Anaesthetics - General Properties MCQs

Aside from the issue of a high incidence of TNS with spinal administration, lidocaine has had an excellent record as an intermediate duration anaesthetic, and remains the reference standard against which most anaesthetics are compared. Reference: LANG’ Basic & clinical pharmacology by Bertram G. Katzung, Susen B. Masters and Anthony J. Trevor 12 th edition. Chapter 26- Local Anaesthetics by Dr. Kenneth Drasner,MD. Page no. 460

It is not clear what role these factors or others play in clinical injury. It is clear, however, that injury does not result from blockade of the voltage-gated sodium channel per se, and thus clinical effect and toxicity are not tightly linked. Reference LANG’ Basic & clinical pharmacology by Bertram G. Katzung, Susen B. Masters and Anthony J. Trevor 12 th edition. Chapter 26- Local Anaesthetics by Dr. Kenneth Drasner,MD. Page no. 459

Saxitoxin and Tetrodotoxin are two potent poisons whose mechanism of action is like that of local anaesthetics - blockade of Na channels. Saxitoxin is produced by certain dinoflagellates which are consumed by shellfish → When such shell fish are consumed by humans, fatal shell fish poisoning occurs with hypotension and respiratory paralysis → This is due to blockade of Na channels by the poison in excitable cells preventing action potential generation Treatment consists of Gastric lavage Vasopressors Mechanical ventilation if respiratory paralysis sets in Prognosis is good when the patient survives after 24 hours Tetrodotoxin is a poison found in some fish of the order Tetraodontiformes (puffer fish) and newts Mechanism of action and manifestations are like shellfish poisoning Reference: Morgan and mikhail's clinical anaesthesiology 6th edition

The rates of local anesthetic systemic absorption and rise of local anesthetic concentrations in blood are related to the vascularity of the site of injection and generally follow This rank order: intravenous (or intraarterial) > tracheal > intercostal > paracervical > epidural >brachial plexus > sciatic > subcutaneous. Reference: Morgan Anesthesia, edition 6, page no 267

Addition of epinephrine-or less commonly phenylephrine-causes Vaso- constriction at the site of administration. The consequent decreased absorption reduces the peak local anesthetic concentration in blood, facilitates neuronal uptake, enhances the quality of analgesia, prolongs the duration of analgesia, and limits toxic side effects. However, they cannot be used in parts having end arterial supply, as it will cause distal necrosis. Reference: Morgan anesthesia, edition 6, page no 267

Dentists usually add epinephrine to the local anesthetic to decrease the bleeding associated with the dental procedure. If any epinephrine gets access to the vascular system, it can cause transient tachycardia and hypertension that patient may describe as palpitations, flushing, and dizziness. If labeled as an allergic reaction, it may limit anesthetic options for the patient in the future. Reference: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5586559/

Vasoconstrictor should not be added for ring block of hand, finger, toes, penis, pinna as all these organs are supplied by end arteries and ischemic damage may occur Adrenaline is most commonly used vasoconstrictor. Felypressin is preferred in cardiovascular disease patient. Reference: Morgan, clinical Anesthesiology, 4 th ed. pg. 34

Esters of local anesthetics that produce metabolites related to para-aminobenzoic acid are more likely than amide local anesthetics, which are not metabolized to para-aminobenzoic acid, to evoke an allergic reaction. Of the given options, only procaine is the Ester LA, all others are amides. Reference: Stoelting's pharmacology and physiology in anaesthetic practice 5th edition pg 292