Neuromuscular blocking and reversal agents? Flashcards
when is neuromuscular blockade/ paralysis required?
- To facilitate surgery e.g. intra-abdominal surgery
- surgeries where patient movement is strictly prohibited, e.g. neurosurgery, robotic surgery
- surgery where muscles have to be relaxed, e.g. intra-thoracic, major intra-abdominal surgery with good exposure and complete retraction to increase size of working field, laparoscopy (pumping 15 L/min of CO2 to lift up abdominal wall to improve view and working field) - For intubation and controlled mechanical ventilation
what are the depolarising neuromuscular blocking agents (NMBAs)?
Succinylcholine
what are the non depolarising neuromuscular blocking agents (NMBAs)?
- Atracurium
- Rocuronium
- Pancuronium
What are the MOA of succinyl choline?
Structurally very similar to acetylcholine, and is an agonist at the nicotinic receptor
Leads to rapid depolarisation across muscles
Continued occupation at nicotinic receptor leads to desensitisation: closure of sodium channels, opening of potassium channels, membrane hyper-polarisation and decreased membrane excitability
Subsequent flaccid paralysis
What are the clinical uses of succinyl choline?
- To achieve rapid intubating conditions e.g. Rapid Sequence Induction, emergency settings
- Rapid onset – paralysis within 30-45 seconds
- Short duration – 5-10 mins, metabolised by plasma pseudocholinesterase - Difficult airway situations
- Treatment of laryngospasm : at ¼ to ½ usual intubating doses
What are the side effects of succinyl choline?
- Sinus bradycardia : especially with repeated doses
- Muscle pains: worse in patients with large muscle mass (rhabdomyolysis with hyperkalaemia)
- Hyperkaelemia: serum K+ can increase by 0.5 mmol/l after bolus
- Increased intragastric, intraocular and intracranial pressures 🡪 may ppt vomiting, C/I in penetrating globe trauma
- Can precipitate malignant hyperthermia
- Can lead to prolonged apnea in patients with abnormal plasma cholinesterase activity
- Potential for allergic reactions and anaphylaxis
what are the contraindications of succinyl choline?
- Pre-existing hyperkaelemia
- Patients with muscular dystrophies, neuromuscular diseases and neuropathies
- Patients with recent burns, spinal cord injuries or denervation
- Known history of malignant hyperthermia
what are the side effects of NMBAs?
- Histamine release: can lead to vasodilatation, hypotension and bronchospasm
- Hypersensitivity/allergic reactions
- Blockade of Cardiac M2 receptors, leading to tachycardia: seen with pancuronium
When should NMBAs not be administered?
NMBAs should not be administered in situations where there is potential difficulty in providing positive pressure ventilation to the paralysed patient
E.g. known or anticipated difficult airway, large mediastinal masses
what is the MOA of NMBAs?
Competitive antagonist at nicotinic receptors: leads to flaccid paralysis
What is the MOA of neostigmine?
Under normal circumstances , Acetylcholinesterase enzyme (AChE) is naturally present at NMJ, and hydrolyses Acetylcholine to limit duration of neuromuscular transmission
- Inhibition of AChE will increase the amount of ACh molecules present in the NMJ, and overcome the competitive inhibition rendered by NMBAs
what needs to be given concurrently with neostigmine?
anti-muscarinic agent (atropine or glycopyrrolate) has to be given concurrently.
Neostigmine: this overall flood of ACh molecules also lead to action on the muscarinic Acetylcholine receptors, producing side effects such as bradycardia, bronchoconstriction, increased oral secretions, nausea and gastrointestinal hypermotility
What is the CVS effects on atropine?
- Onset time more rapid than neostigmine
- Can lead to increased tachycardia seen clinically
What is the CNS effects on atropine?
- Tertiary ammonium compound which can cross blood brain barrier
- Can lead to confusion especially in the elderly
What is the CVS effects of glycopyrrolate?
- Onset time matches that of neostigmine better
- Less tachycardia seen clinically
