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Chemistry and Phys
SIUE CHEM & PHYS Neuro-muscular blockade
| Question | Answer |
|---|---|
| The nervous system consists of what two systems? | Peripheral and Central |
| What components make up the the peripheral nervous system? | The autonomic-controls self regulated action of internal organs & glands and the somatic-which controls voluntary movements of skeletal muscles. |
| The autonomic nervous system consists of what other two nervous systems? | Sympathetic and parasympathetic |
| Where do motor neurons originate in the spinal cord? | Originate in the anterior (ventral) horn of the spinal cord. |
| Motor nerves are what type of neurons? | Efferent neurons |
| Sensory neurons from skeletal muscle carry action potentials to the spinal cord via? | Dorsal horn |
| Afferent neurons | Sensory neurons |
| Somatic nerves | motor and sensory nerves |
| A neuromuscular junction is? | Region between a motor neuron and a muscle cell. |
| 3 components of the neuromuscular junction | 1)Motor nerve terminal 2)Synaptic Cleft 3)Motor end plate |
| This narrow space separates the cell membranes of the neuron and the muscle fiber | Synaptic cleft |
| What causes the skips between myelin sheath to gets the impulse through quicker? | Sultation |
| Once the motor nerve action potential arrives at the nerve terminal what happens? | It depolarizes it |
| What channel opens when the nerve terminal is depolarized? | Voltage gated calcium channels |
| How does Ca++ diffuse down into the nerve terminal? | Through a concentration gradient |
| Once the Ca++ is inside the nerve terminal the influx causes what? | Causes the vesicles containing ACh to fuse with the nerve cell membrane and open to the exterior. |
| ACh spills out into the synaptic cleft via? | Exocytosis |
| Once ACh is in the synaptic cleft what type of receptors does it bind to on the presynaptic membrane? | Nicotinic receptors |
| Once ACh bind with the nicotinic receptors on the presynaptic membrane what happens as a positive feedback? | Once ACh bind with nicotinic receptors on presynaptic membranes the nicotinic receptors respond by increasing the synthesis and release of ACh. |
| Once ACh diffuses down a concentration gradient from the presynaptic membrane to the motor end plate of what type of the ___ membrane? | Postsynaptic membrane |
| What type of receptors does the ACh bind to at the postsynaptic membrane? | nicotinic receptors of the protein channel at the postsynaptic membrane |
| What is required to open each nicotinic ACh receptor? | Both of the alpha subunits of the nicotinic receptor have to be occupied by 2 ACh molecules. |
| Once 2 ACh molecules are bonded with a nicotinic ACh receptor what ions duffuse into the cell and what ions diffuse out of the cell through the channel? | Sodium and calcium ions diffuse into the cell through the channel while potassium diffuses out to the extracellular space |
| What causes the threshold to be reached to illicit an action potential? | The ion diffusion of Na+ & Ca++ into the cell and the diffusion of K+ out of the cell. |
| The action potential sweeps across the skeletal muscle cell and triggers __? | A contraction |
| What breaks down ACh? | Acetylcholinesterase (AChE). Products are 1)Choline 2)Acetate |
| What causes the motor end plate to repolarize? | ACh being metabolized by acetylcholinesterase |
| What product from the break down of ACh is transported back into the nerve terminal and re-synthesized back into ACh | Choline |
| Skeletal muscle relaxation can be produce by what three mechanisms? | 1)Deep inhalation anesthesia 2)Regional nerve block 3)Neuromuscular blocking agents |
| 2 types of neuromuscular blocks? | Depolarizing blocks and nondepolarizing blocks |
| Succinylcholine | Only depolarizing muscle relaxant |
| Nondepolarizing blocks | 1)Short-acting, mivacurium 2)intermediate-acting, atracurium, cisatracurium, Vecuronium, Rocuronium 3)long-acting, Doxacurium, Pancuronium, pipecuronium |
| About how long would succinylcholine last after administering to your patient? | About 8 min |
| If you were to give Rocuronium how long would it be before your patient would start attempting to breath on their own? | 40-50 min |
| Composed of two ACh molecules linked together | Succinylcholine |
| Succinylcholine works by? | Binds to nicotinic receptors and opens channels in the same way that ACh does. |
| What allows succinylcholine to keep the channels open and maintain depolarization? | It is not metabolized by acetylcholinesterase, which allows for the channels to remain open |
| After sux is administered IV it diffuses into? | The tissues, and the molecules of sux that reach motor nerve terminal of skeletal muscle bind to nicotinic receptors and cause the channels of motor end plate to open |
| After sux causes depolarization of skeletal muscle, what channels span into the inactivated state? | Voltage-gated Na+ channels adjacent to the motor end plate snap into the inactivated state and remain in this state until sux diffuses away. A single contraction occurs |
| When do you only see ONE single contraction occur? | After the administration of sux, and depolarization occurs and the voltage gated Na channels snap into the inactivated state. |
| How many seconds after the administration of sux would you see your patient twitch or vesiculate? What does this indicate? | About 45 sec. It indicates that the drug is working and they are paralyzed. |
| A higher C.O. would would increase or decrease the onset of action of sux? | It would increase the onset of action and vise versa |
| When the skeletal muscle is depolarized after the administration of sux, can an another action potential be initiated? | NO WAY HOSE! |
| Channels stay open until sux diffuses back into the circulation and is metabolized by what enzyme? | Plasmacholinesterase a.k.a. pseudocholinesterase & butyrocholinesrerase |
| Where does the metabolism of sux occur? Is is slow or fast? | Metabolism of sux occurs in the plasma and is rapid |
| As circulating sux is metabolized what else is occurring? | More sux is diffusing from skeletal muscle motor end plate into the blood and then the action is terminated. |
| What type of agent are competitive inhibitors? | Nondepolarizing agents |
| What happens when a nondepolarizing agent binds to a nicotinic receptor? | ACh cannot bind to that receptor and the channel cannot open! |
| What type of agent does not allow depolarization to take place and inhibits the channels from opening? | A non depolarizing agent- S.A.->Mivacurium, I.A.->Atracurium, Cisatracurium, Vecuronium, Rocuronium, L.A.->Doxacurium, Pancuronium, Pipecuronium |
| Once a non depolarizing neuromuscular blocker (NDNB) is given IV, and it diffuses from the vascular space into the synaptic cleft of the neuromuscular junction what does the drug bind too? | The drug binds with the nicotinic receptors of the channels of the motor end plate. |
| Once the NDNB competitively blocks acetylcholine from attaching to it's receptors what does this cause? | The channel can't open and therefore stays closed, the postsynaptic membrane remains polarized. The drug has no direct effect on the channel. |
| When is a non depolarizing neuromuscular blockade established? | When it blocks ACh from attaching to its receptors and keeps the channel closed and the postsynaptic membrane remains polarized. |
| Monitoring a patient who is under a neuromuscular blockade is important why? | Because they are in a vulnerable state. We need to know the degree of neuromuscular blockade in the diaphram, larynx, or surgical field, and is accomplished using a nerve stimulator. |
| What is the most common monitoring method of neuromuscular blockade? | Peripheral nerve stimulator (PNS). Indirectly determines the relaxation of musculature |
| PNS works in what way? | Electrical device that delivers a series of shocks to the patient, and on activation of PNS, muscle contraction is visible in the absence of neuromuscular blockers. |
| What are the four settings on a PNS? | Double burst stimulation, single twitch, tetnus, train of four |
| Where are the monitoring sites while using a PNS? | Ulnar nerve most common-stimulates contraction of the adductor pollicis, muscle of the thumb. Facial nerve cranial nerve 7, stimulates the orbicular muscle around the eye or the orbicular muscle that contacts the lip. |
| While stimulating the ulnar nerve what are you going to see if you get a response? | The adductor pollicis is a muscle in the hand that will adduct the thumb because it is innervated by the ulnar nerve. |
| Why do we use the facial nerve, cranial nerve (7) to give us a response to the PNS? | B/c C.N (7) has SENSORY(functions for conveyance of taste sensations from the anterior 2/3 of the tongue) & MOTOR (controls the muscles of facial expression) components. Also supplies preganglionic parasympathetic fibers to several head & neck ganglia. |
| What happens when the facial nerve is stimulated using a PNS and a response is noted? | Stimulates the orbicular muscle around the eye or the orbicular muscle that contracts the lip. Orbicularis oculi |
| Where does the facial nerve emerge from in regards to the anatomy of the patient? | Emerges from the brainstem between the pons and medulla. |
| If the obicularis oculi contracts where should we note it's contractions? | Above the eyebrow is where you will see the contractions |
| What are other monitoring sites besides the ulnar nerve and the facial nerve? | First dorsal interosseous muscle in the hand, abductor muscle of the little finger, and nerves of the foot. |
| How does the PNS illicit a contraction? | PNS elicits the same activity as the depolarization and contraction of a muscle by an action potential. |
| Where are the disposable electrodes placed over the ulnar nerve? | Distal electrode over the proximal flexor crease of the wrist, the other electrode is plaved over and parallel to the carpi ulnaris tendon. Upon stimulation, addiction of the thumb is visible. |
| Where are the disposable electrodes placed over the facial nerve to contract the orbicularis oculi muscle? | Electrodes are placed over the stylomastoid foramen where the facial nerve surfaces. Upon stimulation, contraction of the muscles areound the eye and the face are visible. |
| Why is is best to use the orbicularis oculi to determine degree of neuromuscular block still on board as opposed to the adductor pollicis? | Because it along with the diaphram, the rectus abdominus, and the larygneal adductors recover from neuromuscular blockade before the adductor pollicis giving a better indicator if the patient will be able to breath on their own. More reliable |
| What should you NOT use the PNS for? | To wake up the patient! |
| What are the monitoring settings that can be used on the PNS, including ones w/o specific buttons. | Single twitch, train of four, tetanus, post tetanic count, double burst stimulation. |
| Single twitch | Delivered at 0.1 to 1 Hz over 0.1-0.2 milliseconds. Delivered automatically every 10 seconds, automatically every second, or manually. Requires baseline for comparison. Qualitative assessment. 75-80% of receptors may still be occupied w a normal response. |
| Is the single twitch very reliable? | NOPE! |
| Train of four | Most common. Four separate stimuli are delivered. Each has a duration of less than 0.5 milliseconds. Each stimuli is delivered at a frequency of 2 Hz. |
| What happens when the twitches in the TOF pattern progressively fade? | Relaxation of the patient is increasing meaning the paralytic is working and still on board |
| When the fourth twitch disappears what is this called and it represents how much of a block? | Called fade, and represents a block of 75% |
| The third twitch disappears and represents how much of a block? | 80% block |
| 90% block using a TOF | When the second twitch disappears |
| Disappearance of the first twitch indicates a __ % block? | 99-100% of a block |
| Do you need to use a baseline with a TOF? | NO! |
| Does not require a control height, good measure of surgical relaxation level and is useful in following recovery of blockade? | Train of Four BABY! |
| How many twitches have to be visible while using a TOF in order for a reversal of the paralytic? | 1-2 twitches. If you give to early they can have a reverse effect |
| Tetanus | Consists on continuous electrical stimulation for 5 sec. at 50-100 Hz. Observe for tetanic fade. Should be used sparingly for DEEP BLOCK ASSESSMENT!-->PAINFUL |
| What percent of receptors may be occupied with a normal reading (NO FADE) while using tetanus? | 70% of the receptors may be occupied with a normal reading. |
| What does tetanus cause? | ACh being continuously flooded to continue muscle stimulation. Don't do tetanus first because if we use all of the ACh then the patient will take longer to wake up. |
| Post tetanic count | Give 5 seconds of tetany at 50 Hz. Allow for a 3 second pause, deliver multiple single twitches at 1 Hz 8 different times. |
| When do you use a post tetanic count? | Used only when train of four or double burst stimulation response is absent. |
| What does a count of less than eight indicate on a post tetanic count? | Indicates a deep block and prolonged recovery is likely. |
| On a post tetanic count the number of twitches inversely correlates with what? | The time necessary for return of the first twitch of a TOF stimulation. |
| Double burst stimulation | Consists of 3 short 300 microsecond high frequency 50 Hz bursts separated by 20 millisecond intervals. No activity for 0.75 seconds. 3 more short 200 microsecond high freq 50 Hz bursts separated by 20 millisecond intervals. Clinically see 2 twitches. |
| When is the double burst stimulation useful? | During onset, maintenance, and emergence of blockade. More accurate and sensitive means of assessing nondepolarizing blockade. |
| May be easier to detect fade than w TOF, only compare 2 twitches instead of 4, and tactile evaluation. | Double-burst stimulation |
| What is the most sensitive monitor setting that allows a reading showing 60-70% of receptors being blocked? | Double burst stimulation. |
| 99-100% of the receptors occupied | Complete paralysis (no twitches in TOF) |
| How much of the receptors are still blocked while the diaphram can now move but still not twitches in TOF? | 95%-look at capnogram and see cuaree cleft |
| 90% of the receptors occupied | Abdominal relaxation adequate (1 twitch present in TOF) |
| 75-80% of the receptors occupied | Tidal volume returns to normal or greater than 5ml/kg (single twitch is as strong as baseline) |
| No palpable fade in TOF, useful as a gauge of recovery. | 70-75% receptors still blocked |
| No palpable fade in double burst stimulation, more sensitive than TOF indicator | 60-70% ocuupied |
| 50% of receptors occupied | True Test- Passes inspiratory pressure test, at least -40 cmH2O; head lift for 5 sec., sustained strong handgrip; sustained bite (very reliable indicator) |
| When does a phase I block occur? | With depolarizing agents such as sux. |
| What precedes the onset of a phase I block? | Muscle fasciculations |
| In a phase I block what does a decreased amplitude of a single twitch indicate? | Is proportional to the degree of the block. Sustained response of a decreased amplitude to tetany. Lack of fade to TOF or DBS-decreased amplitude does occur. |
| This type of block has absence of posttetanic potentiation and is potentiated by anticholinesterase drugs. | Phase I block |
| Anticholinesterase drugs in which potentiate a phase I block | Edrophonium, Neostigmine, and Pyridostigmine |
| A phase I block is antagonized by what? | Nondepolarizing muscle relaxants. |
| Phase II blocks occurs with what type of agents? | Nondepolarizing agents |
| Phase II blocks | Absence of muscle fasiculations. amplitude of single twitch contractions decreases with increasing intensity of block, appearance of tetanic fade and posttetanic potentiation, fade w TOF & DBS |
| What type of block is reversed with anticholinesterase drugs (Edrophonium, Neostigmine, Pyridostigmine)? | Phase II block |
| What can occur if sux is given at doses >6mg/kg? Pretty much, you give way to much sux. | A phase II block may be produced |
| Can a Phase I block be reversed? | Most of the time no, but if sux is given in high enough amounts to produced a phase II block the paralytic may be reversed. |
| Can you reverse a phase II block? | Yes siree! |
| What occurs when a phase I block is transformed to a phase II block? | Phase I the motor end plate is depolarized, the ion channels open and remain open. Tx w higher doses of sux cause the ion channels of the motor end plate to close, and the motor end plate repolarizes-Phase II block is now on board. |
| Phase II block or desensitization block has the characteristics of what type of agent? | A nondepolarizing block. |
| What is the order of the progression of paralysis w neuromuscular blocking drugs | 1)Eye muscles 2)Extremities 3)Trunk (from the neck muscles downward through the intercostals) 4)Abdominal muscles 5)Diaphram |
| Even though this may be the last to become paralyzed it is the first to recover? | The diaphram! |
| Why is it important to make sure that the patient is awake B4 you extubate them if they have a history of reflux disease? | Because the protective reflex muscles of the pharynx and upper esophagus recover later than the diaphram, larynx, hands, or face. |
| Monitoring of what is important and preferable for determination of onset and readiness for intubation? | The facial nerve |
| Monitoring of the offset and recovery form neuromuscular blockade is better at where? The facial or ulnar? | The ulnar nerve |
| Tactile evaluation of DBS may be better to differentiate fade than TOF, why? | Because we are only needing to compare 2 stimuli than 4 stimuli |
| With only one response to TOF, successful reversal may take how long? | Up to 30 minutes |
| At a TOF count of two to three responses, recovery may take up to _-_ min. after long acting relaxants and _-_ min. after intermediate-acting drugs | 10-12 minutes; 4-5 minutes |
| How many twitches is best to have prior for reversal of a nondepolarizing block? | Two twitches are best to have |
| When a fourth twitch is visible adequate recovery can be achieved within how many minutes of reversal? | Within 5 minutes |
| What can twitch tension be reduced by? | Hypothermia- they may not have any twitches but are ready for reversal. |
| PLEASE BE AWARE! | MUSCLE RELAXATION DOES NOT UNSURE UNCONSCIOUSNESS, AMNESIA, OR ANALGESIA!!!!!!!! |
Created by:
ngawlik
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