NMBA Quiz Questions

Question 1

Why use NMBAs in vet med?

Answer 1

• Prior to intubation: administered to gain rapid control of animal’s airway without coughing, gagging, or laryngospasm
• Intraoperatively: mechanical ventilation, relaxation during fracture or luxation repairs, thoracotomies, ensure motionless/central eye during ophthalmic procedures

Question 2

Do NMBAs provide sedation or analgesia?

Answer 2

NO!

Should never be given alone for immobilization for any reason

Question 3

How are NMBAs classified?

Answer 3

1. Depolarizing

2. Non-depolarizing

Question 4

Describe MOA for depolarizing NMBAs

Answer 4

-Bind to postsynaptic ACh R at NMJ –> transient muscle fasciculations followed by persistent depolarization of the muscle fiber

Question 5

Describe MOA for non depolarizing NMBAs

Answer 5

-Interfere with postsynaptic action of ACh by binding to ACh R –> preventing depolarization and muscle ctx of the m fiber

Question 6

What depolarizing NMBAs used in vet med?

Answer 6

Succinylcholine

Question 7

Describe features of succinylcholine

Answer 7

• Rapid onset, short duration of action
• Termination of effects = hydrolysis by plasma cholinesterase
• Anything that decreases plasma cholinesterase level (organophosphates, malnutrition, liver dz) will prolong succinylcholine’s duration of action

Question 8

What non depolarizing NMBAs used in vet med?

Answer 8

Atracurium
Vecuronium
Pancuronium
Mivacurium 
Cisatracurium

Question 9

Describe features of mivacurium

Answer 9

• Duration of action: 15-20’
• Rapid onset of action
• Histamine release can occur
• Metabolism via plasma cholinesterase

Question 10

Describe features of cisatracurium

Answer 10

• Stereoisomer of atracurium - approx 10x potency
• At equipotent doses: similar onset, duration of action as atracurium
• Lack of histamine release
• Undergoes Hoffman elimination

Question 11

Describe features of atracurium

Answer 11

• Intermediate duration of action (20-35’)
• Termination of effects primarily from Hoffman elimination
• Histamine release can occur following administration of high doses
• Laudanosine, a metabolite of atracurium can cause central nervous system stimulation or CV depression
• Dose: 0.2mgkg (0.1-0.4mgkg)

Question 12

Describe features of vecuronium

Answer 12

• Intermediate duration of action
• Lack of histamine-releasing or CV side effects
• Hepatic metabolism
• Dose: 0.1mgkg IV

Question 13

Describe features of pancuronium

Answer 13

• Long duration of effect (30-45’)
• Possible sympathetic, vagolytic effects including tachycardia, increased ABP
• Primary route of elimination = kidneys
• Dose: 0.044-0.11mgkg

Question 14

How is the degree of NM blockade monitored?

Answer 14

• Observation of evoked responses following supra maximal nerve stimulation using a peripheral nerve stimulator
• Most commonly: ulnar, peroneal/tibial nerves q

Question 15

Why should an anticholinergic drug be given immediately prior to or concurrently with the reversal agent?

Answer 15

• Anticholinesterase drugs have both nicotinic and cholinergic effects - can cause significant bradycardia
• Prevented/attenuated with administration of an anticholinergic drug

Question 16

Can the effects of NMBAs be antagonized?

Answer 16

• Residual blockade following administration of a non depolarizing NMBA can be reversed with use of anticholinesterase drugs ie neostigmine, pyridostigmine, edrophonium
• These drugs act by inhibiting AchE –> allows for build up of ACh at NMJ and restoration of NM transmission

Question 17

What are possible complications during anesthesia recovery period in patients given NMBAs?

Answer 17

• Resp depression, muscle weakness due to residual paralysis even in patients given an AChE drug
• Very important to observe these patients closely to ensure adequate ventilation and muscle strength during recovery

Question 18

Describe the train of four pattern of stimulation

Answer 18

• TOF delivers four supra maximal impulses at a frequency of 2 per second (2Hz)
• Degree of muscle relaxation can then be evaluated by comparing the fourth to the first twitch response in the TOF
• Prerelaxant ratio approx 1.0 –> 1st, 4th twitches equal in strength
• As degree of relaxation deepens, the ratio decreases followed by loss of one or more twitches in the TOF
• Fourth, third, second, and first twitches disappear as block becomes more profound
• During recovery, first twitch returns first followed by 2nd, 3rd, 4th
• Twitches gradually return to prerelaxant strength during recovery period
• Must have at least 2 twitches to reverse
• 4th to 1st ratio >0.7 correlates with clinical signs of recovery