Neuromuscular Flashcards
Succinylcholine
onset the & duration?
SEs
Metabolism?
Onset ~ 1 min (Duration: ~ 10 min)
SEs (salivation, myalgia, MH, allergic rxn, hyperkalemia)
Metabolized by acetylcholinesterase aka psudeocholinesterase
Cis-atrachrium metabolism
By physiological pH via Hofmann elimination and ester hydrolysis in the plasma
Alkalosis promotes elimination where acidosis decreases elimination
Rocuronium metabolized by
Liver (RF has no effect on t1/2)
NMB Reversal agents
They inhibit acetylcholinesterase
1) Physostigmine
- crosses BBB -> cholinergic syndrome
- SE: N/V and diarrhea
- used for: MG, atropine/scopolamine overdose inducing CNS toxicity, Alzheimer’s, glaucoma
2) Neostigmine
- duration 2-4 hrs
- greatest effect on muscles
- SE: bradycardia, N/V, diarrhea
- Uses: MG, urinary retention 2/2 GA, ogilvie’s
3) Edrophonium
- Faster onset than neostigmine but not as much potent in reversing deep blockades
Competitive antagonists of muscarinic Ach receptors
Prevent bradycardia, salivation, diarrhea, bronchospasm
1) Atropine
- crosses BBB
- more tachycardia
- duration 60-90 min
2) glycopyrolate
- no BBB
- 2-4 hours duration
- slower action
Dibucaine test
Under standardized test conditions, dibucaine inhibits expression of the normal enzyme by about 80% and the abnormal enzyme by about 20%. The dibucaine number indicates the genetic makeup of an individual with respect to butyrylcholinesterase. It does not measure the concentration of the enzyme in plasma, nor does it indicate the efficiency of the enzyme in hydrolyzing substrates such as succinylcholine or mivacurium. Both of the latter factors are determined by measuring butyrylcholinesterase activity, which may be influenced by genotype.
Homozygous atypical pseudocholinesterase occurs in 1 in 3,200 individuals with a typical dibucaine number of 20 to 30. Response to succinylcholine or mivacurium can be prolonged 4 to 8 hours.
Can sugammadex be used in RF patients?
sugammadex is predominantly eliminated unchanged by the kidneys. In patients with renal impairment, clearances of sugammadex are decreased by a factor of 16 and that of rocuronium by 3.7. Additionally, it is unclear if sugammadex is consistently eliminated by dialysis. For these reasons, it is recommended to avoid sugammadex if creatinine clearance is less than 30 mL/minute.
A 48-year-old man is scheduled for a lung resection to remove a malignant tumor under general anesthesia. He has type I diabetes and is taking insulin. The patient has been NPO since 10 p.m. last night. Intravenous fluid therapy is initiated followed by the induction of anesthesia. Which of the following statements best explains body fluid compartments?
A. Total body water is divided into 55% extracellular fluid and 45% intracellular fluid
B. The intracellular fluid can be subdivided into interstitial fluid and intravascular fluid
C. Water in bone and connective tissue is a part of the functional extracellular fluid
D. Interstitial fluid compartment contains the highest percentage of extracellular fluid
The interstitial fluid compartment contains the highest percentage of extracellular fluid. Total body water can be divided into two main fluid compartments, i.e., the intracellular compartment, which comprises of 55% of the total body water, and the extracellular fluid compartment, which contains the remaining 45%.
The extracellular fluid compartment can be subdivided into interstitial fluid, intravascular fluid, transcellular fluid, and water in bone and dense connective tissue. The interstitial fluid compartment, also known as tissue space, surrounds tissue cells and is filled with lymphatic fluid and protein-poor fluid occupying cell spaces. The interstitial fluid provides the immediate microenvironment that allows the movement of ions, proteins, and nutrients across the cell barrier.
The interstitial fluid compartment contains the highest percentage (20%) of the extracellular fluid. Water in bone and dense connective tissue constitutes a substantial proportion of total body water, but is not a part of the functional extracellular fluid because it is not immediately available for equilibration with the other fluid compartments due to slow kinetics of water distribution
In which of the following will you find only nicotinic type of acetylcholine receptors?
A. Heart
B. Adrenal medulla
C. Sweat glands
D. Brain
Acetylcholine receptors are classified as nicotinic and muscarinic types. They differ in their structure, location, and functions. Nicotinic receptors are so named, as they respond to acetylcholine as well as nicotine. Muscarinic receptors are named so because they are more sensitive to muscarine than nicotine. Nicotinic receptors are ligand-gated ion channels, whereas muscarinic receptors are G-protein coupled receptors.
Nicotinic receptors are found in autonomic ganglia of both sympathetic and parasympathetic nervous system, neuromuscular junctions, brain, and adrenal medulla. In the adrenal medulla, acetylcholine is used as a neurotransmitter. In comparison, the muscarinic receptors are located in brain, stomach, autonomic ganglia, end organs of parasympathetic system (heart, smooth muscle, etc.) Muscarinic receptors are also found in the sweat glands.
A 55-year-old man who is a known case of myasthenia gravis is to undergo surgery for hernia repair. Myasthenia gravis was diagnosed eight years ago. He is doing fine on his medications and has no ptosis or diplopia. Speech and swallowing difficulties are absent. The lung function tests are normal. Which of the following may be a predictor of the need for postoperative ventilation in a patient with myasthenia gravis?
A. Disease duration of fewer than two years
B. Preoperative forced vital capacity of less than 2.9L
C. Daily pyridostigmine requirement of less than 750 mg
D. Absence of significant bulbar weakness
Post-operative ventilation may be required in patients with myasthenia gravis, who have a pre-operative forced vital capacity of less than 2.9 L. Myasthenia gravis is a chronic, autoimmune, neuromuscular disorder, characterized by progressive skeletal muscle weakness and fatigue. Skeletal muscles innervated by cranial nerves are most commonly affected, thus causing extraocular and facial muscle weakness.
Bulbar and oropharyngeal weakness may result in difficulties in talking, chewing, and swallowing, and an increased risk of pulmonary aspiration of gastric or oral contents. There are increased chances of post-operative myasthenic crisis and a requirement of post-operative ventilation in patients with myasthenia gravis of prolonged duration, i.e. longer than 6 years, a pre-operative forced vital capacity of less than 2.9 L, presence of coexisting lung disease e.g.
COPD, and a daily pyridostigmine requirement of 750 mg in association with significant bulbar weakness. However, adequate control of symptoms with medication, better pre-operative preparation, and increased use of minimally invasive surgery has made this requirement of post-operative ventilation infrequent nowadays.
