Muscle Relaxants

Objectives

  • Classify Neuromuscular Blocking Drugs by their mode of action and their chemical structure
  • Recall the pertinent chemical, pharmacokinetic and pharmacological properties of SuxamethoniumRocuroniumVecuronium and Atracurium
  • Compare and contrast the properties of these drugs and their clinical uses in anaesthetic practice
  • Use this knowledge and understanding to select an appropriate Neuromuscular Blocking Drug for use at induction and intra-operatively in various clinical scenarios

Depolarising Agents

Non Depolarising Agents

Non-depolarising neuromuscular blocking drugs are competitive antagonists at nicotinic acetylcholine receptors.

There are 2 classes of NMBDs:

  • Aminosteroids
  • Benzylisoquinoliniums

You’ll likely use Rocuronium most often in your practice, which is an Aminosteroid, so we’ll look at those first.

Aminosteroids

Benzylisoquinoliniums

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Created on By Anaestheasier

Muscle Relaxants

1 / 14

You are working with your consultant on an ENT list today and you have just anaesthetised your first patient. You have induced anaesthesia with Propofol and a paralysing agent. You are maintaining anaesthesia with a Target-Controlled Infusion of Propofol and Remifentanil (i.e. no inhalational agent) and monitoring depth of anaesthesia with BIS. Over the course of the next few minutes, while waiting for the surgeons to prep, you notice the patient becoming increasingly tachycardic and the etCO2 has risen from 5.3 to 10.2. The ODP also informs you the patient’s temperature is now 38.6oC. Your consultant tells the surgeons to stop, switches the FiO2 100% and asks for additional consultant help immediately. She also asks for the AAGBI Quick Reference Handbook. Which paralysing agent is most likely to have been used?

2 / 14

A 36-year-old lady of 60kg with severe Bipolar Affective Disorder is undergoing Electroconvuslive Therapy, which should take a maximum of 5 minutes. The anaesthetist plans to anaesthetise the patient with a bolus of methohexital (a barbiturate that does not lower the seizure threshold) and does not plan on inserting an advanced airway. The patient has no past medical history otherwise and her FBC, U&Es and LFTs tests yesterday were all entirely normal. What is the most appropriate agent to use to paralyse this patient to prevent violent seizure activity?

3 / 14

You are performing an RSI for a 23-year-old male for an appendicectomy at 00:45. He is an ASA1 and all observations are within normal limits. He has a BMI of 25 and weighs 90kg.

His blood tests reveal: Hb 154, WCC 23.3, Plts 453, Na 143, K 4.2, Cr 86, CRP 132.

You choose to use 200mg Propofol and 1000mg Alfentanil for induction. You want to achieve intubating conditions as fast as possible. Which drug would achieve this?

4 / 14

Which of the following agents undergoes Hoffman degradation?

5 / 14

Which of the following is not an effect of Suxamethonium?

6 / 14

You have just anaesthetised a 18-year-old male for a Scrotal Exploration using 240mg Propofol, 1000mcg Alfentanil and 100mg Rocuronium as an RSI. There were no concerning features in his airway assessment, but you are unable to gain any better than a grade 4 view on laryngoscopy. You call for help immediately and ask for a size 5 iGel. You are unable to ventilate the patient using a size 5 nor a size 4 iGel and so you insert a guedel and nasopharyngeal airway and succeed in ventilating the patient via a facemask. Your consultant arrives and is also unable to gain better than a grade 4 view and so you continue ventilating the patient with 100% oxygen + Sevoflurane. Your consultant decides to wake the patient up. What will you need administer in order to do this?

7 / 14

Which of the following agents can be fully reversed even if no twitches are present on nerve stimulation?

8 / 14

A 35-year-old male of 90kg has been booked on the CEPOD list for an emergency appendicectomy. He had a diving accident 2 months ago in which he suffered spinal cord transection at the level of T12 and so is now wheelchair-bound with spastic paralysis of his lower limbs. Your consultant carefully plans this anaesthetic and will be present throughout the case. What would be an appropriate choice of neuromuscular blockade to perform an RSI on this gentleman?

The agent you choose needs to have a fast onset and be safe given this patient’s renal condition and hyperkalaemia.

9 / 14

General Surgeons have listed a 56-year-old male for an emergency laparotomy for small bowel obstruction on CEPOD. He has a background of hypertension and end-stage kidney disease for which he is on 3-times-weekly haemodialysis.

His observations are as follows: HR 82, BP 125/82, RR 16, SpO2 97% on air, T 37.2.

You note the venous blood gas taken by the surgical team reveals: Hb 93, pH 7.31, Na 136, K 5.9, BE -7.5.

Your registrar performs an epidural anaesthetic while you prepare drugs for the RSI. You have drawn up Propofol & Alfentanil. Which neuromuscular blocking agent would be most appropriate in this 80kg patient?

10 / 14

Which agent is least dependant on hepatic/renal elimination?

11 / 14

You go to a 32-year-old male to pre-assess him for his ORIF of fractured tibia. He is adamant he does not want to be awake for the procedure but is worried because his older sister had a general anaesthetic a few years ago and had to be kept asleep on ICU over night for an unforeseen issue. After further questioning, you ascertain that she was given a paralysing agent and it unexpectedly took many hours to wear off. He heard his father has also had the same issue. Which agent is likely causative?

12 / 14

Laudanosine may precipitate seizures; it is an inactive metabolite of which neuromuscular-blocking drug?

All neuromuscular-blocking drugs are highly polar and so will not be absorbed into the bloodstream when injected subcutaneously.

Rocuronium cannot be administered via the IM route and would be a very large volume to inject into a muscle given its 1% presentation. Rocuronium cannot be given as a nebuliser.

13 / 14

A 5-year-old female is undergoing a gas induction with Sevoflurane and N2O for extraction of RU2 for dental abscess. Your consultant recognises laryngospasm during the process and applies CPAP to no effect and so she asks you to paralyse the patient. As you have not yet established IV access, how will you do this?

14 / 14

A 65-year-old lady is undergoing an Anterior Resection for bowel cancer. She has no known allergies but has a background of CKD and HTN. As she has severe reflux, you perform an RSI with your consultant using Propofol, Fentanyl, Suxamethonium and then maintain her anaeshesia with Sevoflurane and her paralysis with Atracurium. While the surgeons are prepping, you then notice she becomes increasingly tachycardic and hypotensive, unresponsive to metaraminol. The ventilator is also alarming due to high peak pressures. Your consultant calls for help from a colleague, applies 100% O2 and administers IV adrenaline. You have not yet given antibiotic prophylaxis. Which is the most likely causative agent of anaphylaxis?

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