Peripheral Nerve Blocks MCQs

When the patient fails to regain consciousness within an expected period of time after general anesthesia, the most frequent cause is residual drug effect. Delayed emergence may occur as a result of absolute or relative drug overdose. The effects of preoperative sleep deprivation or drug ingestion (alcohol, sedatives) can be additive to those of anesthetic agents in producing prolonged emergence. Intravenous naloxone and flumazenil will readily reverse the effects of an opioid and benzodiazepine, respectively. Intravenous physostigmine may partially reverse the effect of other agents. Reference : Morgan and Mikhail's clinical anesthesiology, page 1289

Although all agents could be used, sevoflurane would be the preferred choice. Sevoflurane could be used in combination with nitrous oxide Wrong Answers: Option A : Isoflurane could also be used, but because of its high blood: gas solubility it may delay emergence, which is undesirable in outpatients Option B : Desflurane has a lower blood: gas solubility that would provide rapid awakening , but desflurane is irritating to inhale and can cause bronchoconstriction in smokers Reference : Drugs in Anesthesia and Intensive Care, Edward Scarth, Susan Smith 5th edition

Since local anesthetics are weak bases, they exist largely in the ionic form, making it difficult for them to cross the cell membrane, thus delaying their local anesthetic action. Further they become ionized when the local tissue is infected and the local pH is acidic. Their action becomes unreliable. Addition of sodium bicarbonate promotes nonionized fraction of local anesthetic, promoting more rapid onset of its action. Reference: Stoeltings pharmacology and physiology in anesthetic practice 5th edition pg. 291

Lidocaine has been the drug used most frequently for intravenous regional anesthesia Prilocaine, mepivacaine, chloroprocaine, procaine and etidocaine have also been used successfully Intravenous regional anaesthesia or Bier’s block involves the intravenous administration of a local anesthetic into a tourniquet- occluded limb It is used to provide anesthesia for short surgical procedures ( ) on the limbs Note: Bupivacaine is not used for Biers block. It is the most cardiotoxic local anesthetic. Accidental early inflation of the tourniquet →can lead to massive systemic doses of bupivacaine resulting in → cardiac arrhythmias and cardiovascular collapse Reference : Stoelting's pharmacology and physiology in anaesthetic practice 5th edition

These signs described above are specific to Horner Syndrome. Horner syndrome (miosis, ptosis, and anhydrosis) frequently results from proximal tracking of local anesthetic and blockade of sympathetic fibers to the cervicothoracic ganglion. Other site-specific risks include vertebral artery injection (suspect if immediate seizure activity is observed), spinal or epidural injection, and pneumothorax. In patients where a CVA may also be within the differential diagnosis, a thorough history and neural exam should always be included. Reference: Morgan and Mikhail's clinical anesthesiology 6th edition pg 1007.

Although some anatomical variation can be found with the brachial plexus at the level of the axilla, the musculocutaneous nerve is most commonly positioned within the coracobrachialis muscle or between the bellies of the biceps and coracobrachialis muscles. Reference: Morgan and Mikhail's clinical anesthesiology 6th edition pg 1019.

Immediate access to a functioning anesthesia ventilator is not always necessary while administering regional anaesthesia. Regional anesthesia should be administered in a monitored location where standard ASA monitors. Supplemental oxygen along with resuscitative medications and equipment should be readily accessible and immediately available. Reference: Morgan and Mikhail's clinical anesthesiology 6th edition pg 999.

The intercostal block has one of the highest complication rates of any peripheral nerve block due to the close proximity of the intercostal artery and vein (intravascular local anesthetic injection), as well as underlying pleura (pneumothorax). Intercostal blocks result in the highest blood levels of local anesthetic per local anesthetic dose injected of any nerve block procedure, and if multiple blocks will be performed care must be taken to avoid toxic levels of local anesthetic. Reference: Morgan and Mikhail's clinical anesthesiology 6th edition pg 1040.