Neuromuscular blocking drugs Flashcards
1
Q
Neuromuscular blocking drugs
What do they do?
What does they result in?
Potentially what issue?
A
- NMBDs interrupt transmission of nerve impulses at the neuromuscular junction
- Results in complete paralysis of striated muscles while consciousness is retained, there is no analgesia, and spontaneous respiration ceases
- Potentially an animal welfare issue
2
Q
4 indications for NMBDs?
A
-
Position the eyeball centrally without traction
- Aids for intraocular or corneal surgeries
- Most common indication in vet med
- Relax resp. muscles to allow mechanical ventilation (rare indication)
- Sometimes in small animal ICU
- Relax the muscles for neurological or orthopedic surgeries (rare indication)
- Aid intubation (humans)
3
Q
What are the 3 minimum requirements for NMBD’s regarding ventilation and monitoring?
A
- Use mechanical ventilation (cuffed tube, etc.)
-
Monitor cardiovascular, resiratory systems, and oxygenation
- Eye position, pupillary reflex, etc. will not be available
- Tachycardia and high blood pressure is the only sign they can show in response to noxious stimuli
- Monitoring end tidal agent (e.g. ISO) is useful but not mandatory
- If not available, use high fresh gas flow and keep ISO vaporizer around 1%
4
Q
Contraindications for NMBDs?
A
- If there is no possibility to ventilate and monitor the patient
- If animal remains conscious
- Conscious experience of complete muscle paralysis is EXTREMELY DISTRESSING even without pain
- If there is insufficient analgesia during surgery
- NMBDs should not be used to “cover” the lack of analgesia
- If the personnel in charge does not have a complete understanding of the use of NMBDs
- It cannot be overemphasized that NMBDs MUST NOT be used as a sole agent for any kind of procedure (painful or nonpainful)
- Nevertheless, they MUST NOT be used as a sole agent for euthanasia
5
Q
Neuromuscular junction
Consists of?
Function (5 steps)?
A
- NMJ consists of a prejunctional motor nerve ending a highly folded postjunctional membrane of the skeletal muscle and a synaptic cleft between them
- Function
- An impulse arrives at the motor terminal (Ca2+ influx)
- Release of acetylcholine neurotransmitter
- ACh binds to nicotinic cholinergic receptors on the postjunctional membranes (opening K+ and Na+ channels)
- The resulting ion influx triggers an action potential that leads to muscle contraction
- ACh is rapidly metabolized by the enzyme acetylcholinesterase in the synaptic cleft
6
Q
Mechanism of action: depolarizing and non-depolarizing NMBDs
A
- Depolarizing NMBDs act as an agonist on the nicotinic ACh receptors, thus causing muscle membrane depolarization
- Non-depolarizing NMBDs act as a competitive antagonist on the nicotinic ACh receptors, thus stabilizing muscle membranes
7
Q
Order of muscle relaxation
A
- Ocular muscles are the most sensitive and will be paralyzed first even at low doses
- Diaphragm is the most resistant–last to complete blockade and first to recover
- All other muscles are between
- Typical order of onset:
- Eyes > larynx > diaphragm
8
Q
Drugs that potentiate NMBD effect?
A
- Inhalational anesthetics
- Aminoglycoside antibiotics
- Local anesthetics
- Cardiac antiarrhythmic drugs
- Diuretics
- Magnesium
9
Q
What are some other factors that influence the depth of NMBD effect?
A
- Hypothermia
- Electrolyte abnormalities
- Acid-base disorders
- Age
- Thermal burn
10
Q
NMBD chemical properties
A
- Water-soluble drugs
- Do not cross lipid barriers easily
- Therefore less likely to:
- Cross BBB or placental barrier
- Adsorb from GI tract
11
Q
Histamine release:
Occurs when?
Which NMBDs are more likely to cause it?
May cause what?
Treatment?
A
- Rare complication; mostly at high doses
- More likely to cause it:
- Atracurium
- Succinylcholine
- Histamine may cause
- Bronchoconstriction
- CV: vasodilation, (-) inotropy, tachycardia
- Treatment: e.g. low dose epinephrine
12
Q
What are the side effects of NMBDs at the ANS?
A
- Nicotinic ACh receptors are also found in the ANS
- Interactions with older NMBDs (e.b. pancuronium) are possible; those may have side effects related to ANS function
- Unlikely with modern NMBDs
13
Q
Classification/examples of NMBDs
A
- Depolarizing
- Succinylcholine
- Non-depolarizing
- Long-acting (>30 min): pancuronium
- Imtermediate acting (10-30 min): atracurium, cisatracurium, rocuronium, vecuronium
- Short-acting: rapacuronium
14
Q
Succinylcholine (SCh): general
A
- Cause sustained membrane depolarization on the end plate
- This will initially lead to muscle fasciculation, then the postjunctional Na channels close and remain closed until SCh is present
- This mechanism prevents neuromuscular transmission
- Called the phase-1 block
- After prolonged or high dose SCh administration another type of block (phase-2) may develop which is similar to the non-depolarizing blockade
15
Q
Adverse effects of Succinylcholase?
A
- Cardiac arrhythmias (bradycardia, sinus arrest)
- Hyperkalemia
- Fasciculation, myalgia, myoglobinuria
- Elevated intra-ocular and intra-gastric pressures
- May trigger malignant hyperthermia
- Not a preferred NMBD in vet med
