Succinylcholine

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Succinylcholine = Suxamethonium chloride 

Succinylcholine acts as a Depolarizing neuromuscular blocker (=DMR - Depolarising muscle relaxant)

Mnemonic : SSSS

• FasSiculations
• FaSt dissociation at receptors (Therefore Short acting )

Mnemonic : DND

• Not reversed by Neostigmine
• No fade or Post tetanic stimulation. 

Potentiated by

1. Isoflurane
2. Respiratory Alkalosis
3. Hypothermia
4. Mg

Antagonised by : Acidosis and NDMR

Repeated use  - causes Phase II block (similar to NDMR) -- (MCQ)

Other points about Sch :

• Onset within 30 sec --- lasts 10-12 mins.
• Bradycardia in children (especially after 2nd dose) (MCQ)
• All presures are increased ( BP , ICP , IOP , Intra gastric )
• Enzyme metabolism - by PseudoCholinestrase (= plasma = Butyrylcholinesterase) (read below in short about Cholinestrases )

Dibucaine Number :

• The Dibucaine Number is a measure of the qualitative activity of Pseudocholinesterase and is the percentage of inhibition of the enzyme by the local anesthetic Dibucaine.
Normally 75 - 85 % inhibition , But if homozygous defficiency - then 30%

• It is used to differentiate individuals who have substitution mutations of the Butrylcholinesterase enzyme.

Side effects :

• Increase K+ (especially after Burns , spinal cord injury , stroke , cerebral palsy )

Therefore Sch is Avoided 48hrs - 9months after acute injury. 

• Post Op muscular pain which can be decreased by :

                                  1. Self Taming (Pretreatment with small (10 mg) doses of succinylcholine)

                                  2. Precurarization (NDMR + Sch)

                                  3. Lignocaine

• Malignant Hyperthermia

Note: 

1. Sch is the MC drug which causes Malignant Hyperthermia.
2. All Fluranated inhalational anaesthetics & Lignocaine are other drugs which can cause Malignant Hyperthermia.

• Allergy - releases histamine.

• Contraindicated in Myotonic Dystrophy : as it causes severe muscle rigidity , preventing respiration and intubation.

• Can cause Masseter spasm in children.

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NeuroMuscular monitoring (Adductor Pollicis , Ulnar Nerve)  (No use in Sch block)

1. TOF (Train of 4)
2. PTC ( Post tetanic count )
3. DBS ( Dual burst stimulation )
4. Tetanus

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Cholinesterases :

1. True :  RBC and Grey Matter.
2. Pseudo/False :  Liver and Plasma.

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