Neuromuscular Blockers (NMBAs) Complete Review

Vocabulary-style practice flashcards covering classifications, pharmacology, monitoring, and reversal agents for Neuromuscular Blockers (NMBAs) based on lecture notes.

Neuromuscular Blockers (NMBAs)

Drugs that produce skeletal muscle paralysis by acting at the neuromuscular junction; they provide paralysis only and do not provide sedation, analgesia, or amnesia.

Succinylcholine (Suxamethonium)

A depolarizing neuromuscular blocker that acts as an agonist at the $Nm$ receptor, causing persistent depolarization, initial fasciculations, and flaccid paralysis.

Non-depolarizing NMBAs

Competitive antagonists at the $Nm$ receptor that prevent Acetylcholine ($ACh$) binding, do not depolarize the muscle membrane, and cause Train-of-Four (TOF) fade.

Phase I block

A characteristic of depolarizing NMBAs like Succinylcholine where initial fasciculations lead to flaccid paralysis with no Train-of-Four (TOF) fade and no post-tetanic facilitation.

Phase II block

A block state caused by prolonged exposure or high doses of Succinylcholine where desensitization occurs and Train-of-Four (TOF) fade may appear, resembling a non-depolarizing block.

Hofmann elimination

An organ-independent elimination process that is $pH$ and temperature dependent, used for the metabolism of Atracurium and Cisatracurium.

Plasma butyrylcholinesterase (pseudocholinesterase)

The enzyme responsible for the metabolism of Succinylcholine and Mivacurium.

Train-of-Four (TOF)

A monitoring method involving four stimuli at $2\,Hz$ (every $0.5\,sec$); a $T_4/T_1$ ratio of $\geq 0.9$ is required before extubation to ensure recovery.

Post-tetanic facilitation

The phenomenon where muscle response is temporarily enhanced following tetanic stimulation, present in non-depolarizing blocks and Phase II depolarizing blocks but absent in Phase I depolarizing blocks.

Rocuronium

An aminosteroid non-depolarizing NMBA with a rapid onset ($60-90\,sec$) and duration of $30-60\,min$, commonly used as a Rapid Sequence Induction ($RSI$) alternative and reversible by Sugammadex.

Vecuronium

A hemodynamically stable aminosteroid non-depolarizing NMBA with an intubating dose of $0.08-0.1\,mg/kg$ and a duration of $30-60\,min$.

Pancuronium

A long-acting ($60-100\,min$) aminosteroid non-depolarizing NMBA that is vagolytic, causing increased heart rate ($\uparrow HR$) and blood pressure ($\uparrow BP$).

Atracurium

A benzylisoquinolinium non-depolarizing NMBA metabolized by Hofmann elimination and ester hydrolysis; it causes moderate histamine release and the production of a laudanosine metabolite.

Cisatracurium

A stereoisomer of Atracurium with minimal histamine release and excellent cardiovascular stability, preferred in severe renal or hepatic failure due to Hofmann elimination.

Mivacurium

A short-acting non-depolarizing NMBA ($10-20\,min$) metabolized by plasma butyrylcholinesterase that may cause hypotension through moderate histamine release.

Sugammadex (\gamma-cyclodextrin)

A direct reversal agent that encapsulates aminosteroid NMBAs (Rocuronium/Vecuronium) into an inactive complex to be eliminated by the kidneys.

Neostigmine

An indirect reversal agent that acts as an Acetylcholinesterase ($AChE$) inhibitor to increase $ACh$ in the synapse, always administered with an antimuscarinic to prevent side effects like bradycardia.

Post-tetanic Count (PTC)

A monitoring technique used when the TOF count is zero; it involves a $50\,Hz$ tetanus for $5\,sec$ followed by a single twitch every $1\,sec$ to assess deep neuromuscular block.

Malignant Hyperthermia (MH)

A life-threatening condition for which Succinylcholine is a known trigger.

Hyperkalemia

A life-threatening adverse effect of Succinylcholine, particularly in patients with major burns ($> 24-48\,h$), denervation, or spinal cord injury.