Rapid Sequence Induction Neuromuscular Blocking Agents - Essay Example

? Rapid Sequence Induction Neuromuscular Blocking Agents of the Health sciences and medicine of the July 3, Discussion (both): A. Discuss the aims, indications for, and complications of Rapid Sequence Induction (RSI). Select appropriate drugs and dosage and include required treatment post B. Describe the action of depolarizing and non – depolarizing agents. Introduction Airway management is a core lifesaving skill for any health care worker, especially for those working in emergency situations. In emergency and certain special preoperative cases for general anaesthesia, rapid sequence induction (RSI) is performed for endotracheal intubation as a ‘standard of care’. Emergency care staff should be well versed with this technique of airway management. Neuromuscular blockers (NMBs) are a group of drugs which are used for intubation. They play an important role in endotracheal intubation. Depending upon their mechanism of action, these drugs can be classified into depolarizing and non-depolarising agents. This essay will discuss aims, indications, technique and dugs, and complications of RSI. Separately, this essay will also focus upon the actions of depolarizing and non-depolarizing neuromuscular blockers. Rapid Sequence Induction Aims The aims of rapid sequence induction are to secure the airway as soon as the airway reflexes are lost, optimise oxygenation and ventilation, prevent contamination of the airways and lungs by aspiration of regurgitated oesophageal or stomach contents, or blood and prevent the complications of aspiration such as aspiration pneumonitis, hypoxemia and/or death (Sinclair & Luxton, 2005). Indications Rapid sequence induction is indicated in situations and patients where airway protection is immediately required and there is a danger of aspiration of regurgitated gastrointestinal contents and blood in the airway. It is performed in the operation theatre under controlled conditions, whereas in pre hospital setup, it is performed with limited resources and expertise (Sinclair & Luxton, 2005). It is performed in patients requiring intubation who are assumed to be ‘full stomach’ (non-fasting) and have a high risk of aspiration such as patients with traumatic brain or bodily injury and loss of consciousness, pregnant patients, patients with raised intra-abdominal pressure (ascites, obesity, chronic renal failure), head and neck injury and bleeding into the oral cavity or airway (Perry, Lee, Silberg & Wells, 2008; Bernard et al, 2009). Complications RSI can be associated with the following complications: 1. Failure to secure the airway and resultant hypoxemia, and organ damage or death (Sinclair & Luxton, 2005) 2. Interruption of chest compressions during cardiopulmonary resuscitation. 3. Unrecognised oesophageal or maintsem bronchial intubation 4. Complications due to under-dosing or over-dosing of drugs such as awareness, hypotension, hyperkalaemia, arrhythmias and cardiac arrest 5. Injury to oral and laryngeal structures 6. Raised intracranial and intraocular pressure and stress responses associated with laryngoscopy and intubation such as tachycardia, hypertension and bronchospasm (Sinclair & Luxton, 2005). Technique, drugs and dosages The opinions regarding the drugs, their dosages and their method of administration in RSI are changing (El-Orbany & Connolly, 2010). Conventionally, RSI has involved the components of preoxygenation, rapid administration of induction agents and muscle relaxants, cricoid pressure application (Sellick’s manoeuvre), endotracheal intubation and cuff inflation, and non-application of bag-mask or positive pressure ventilation (Bernard, 2006). A pre-calculated dose of induction agent is given followed by fast acting muscle relaxant and as the patient starts to lose consciousness, cricoid pressure is applied. After 45 seconds to one minute, laryngoscopy is done, patient is intubated and the cuff of endotracheal tube (ET) is inflated. Only after confirmation of endotracheal placement of the tube with EtCO2 and inflation of the cuff, cricoid pressure is released. Drugs used for RSI are mainly induction agents and muscle relaxants (depolarizing or non-depolarizing neuromuscular blockers). Sodium thiopentone 4-5 mg/kg or propofol 1-2 mg/kg are used as intravenous induction agents to induce sleep (Reves et al, 2010). In case of haemodynamic instability, the doses can be reduced, or ketamine or etomidate can be used. Midazolam in combination with ketamine or fentanyl can also be used with very few side effects. Traditionally, suxamethonium (succinylcholine) had been the drug of choice for RSI because of rapid onset of muscle relaxation, satisfactory intubating conditions and rapid recovery of muscle activity. However, it is associated with many contraindications and side effects. Rocuronium in the dose of 0.8 to 1.2 mg/kg achieves relaxation in nearly 1 minute and can be used where suxamethonium is contraindicated. Cochrane review concluded that intubation conditions created with suxamethonium were clinically superior as compared to rocuronium (Perry, Lee, Silberg & Wells 2008). With the discovery and clinical use of sugammadex, even rocuronium induced muscle paralysis can be rapidly reversed. Thus, rocuronium may well be on its way to become the relaxant of choice for RSI (Caldwell & Miller, 2009). As the duration of action of IV induction agents is very less, patients are concomitantly administered opioids (fentanyl,alfentanyl, morphine) and sedatives (benzodiazepines, propofol infusion) to prevent pain and awareness respectively. Clinical Implications The above mentioned standard protocol of RSI is not usually followed in pre-hospital and emergency settings. In these situations, RSI is being done by paramedics without any drugs or neuromuscular blockers (Bernard, 2006). Conflicting results have been reported by the authors in studies dealing with outcomes after intubations by paramedics, with or without drugs. Logically, it appears that RSI without any drugs in a semiconscious and combative patient may have a lower success rate and bad outcome. To investigate this, Bernard et al (2009) conducted a randomised controlled study and demonstrated that in patients with traumatic brain injury, when intubations were performed by paramedics trained in RSI with drugs, an improved neurological outcome was reported. Certain issues in context of RSI by paramedics need more research and discussion. These include training programs for imparting RSI skills, maintenance of these skills, management of ‘can’t ventilate, can’t intubate’ scenario and comparison of RSI with supraglottic devices which also provide airway protection such as laryngeal tube airway (LTA) and combitube. Depolarizing agents Suxamethonium is the only clinically used depolarizing agent. Structurally, it is formed by 2 molecules of acetylcholine (ACh) and thus, acts on the same ACh receptors across the neuromuscular junction (Lee, 2001). They bind to 2 anionic centres on the pentameric nicotinic acetylcholine receptors (nAChR) and allow ions to flow through it leading to a wave of depolarisation (Martyn, Fagerlund & Erikkson, 2009). In contrast to physiological degradation of ACh by acetylcholinestrase at the synaptic cleft in milliseconds, succinylcholine is degraded in the plasma by pseudocholinestrase and is present at the cleft for a longer time. There is an initial contraction (fasciculations) followed by prolonged relaxation. Onset of muscle paralysis is within 45 seconds to one minute at a dose of 1.5 to 2.0 mg/kg and recovery also occurs within minutes. Non-depolarizing agents Non-depolarizing neuromuscular blockers act as competitive antagonists of the natural ligand ACh at the 2 binding sites of nAChRs (Fagerlund & Erikkson, 2009). By binding to these receptors, as well as due to bulk hindrance, depolarisation is blocked (Lee, 2010). The extent of the blockade depends on the relative concentration of NMBs and ACh. Commonly used non-depolarising muscle relaxants are atracurium, vecuronium, recuronium and pancuronium with varying durations of action. Summary RSI is performed in emergency airway management scenarios and currently most paramedics perform RSI without drugs or NMBs. More research is required to determine the best practice for RSI in out-of-hospital settings. Knowledge about NMBs is also essential for airway management and RSI. References Bernard, S. A. (2006). Paramedic intubation of patients with severe head injury: a review of current Australian practice and recommendations for change. Emergency Medicine Australasia, 18, 221–228. doi: 10.1111/j.1742-6723.2006.00850.x Bernard, S. A., Nguyen, V., Cameron, P., Masci, K. Fitzgerald, M., Cooper, D. J., et al. (2010). Prehospital rapid sequence intubation improves functional outcome for patients with severe traumatic brain injury: A randomized controlled trial. Annals of Surgery, 252(6), 959–965. doi: 10.1097/SLA.0b013e3181efc15f Caldwell, J. E., & Miller, R. D. (2009). Clinical implications of sugammadex. Anaesthesia, 64(S1), 66–72. doi: 10.1111/j.1365-2044.2008.05872.x El-Orbany, M., & Connolly, L. A. (2010). Rapid sequence induction and intubation: Current controversy. Anesthesia Analgesia, 110 (5), 1318–1325. doi:10.1213/ANE.0b013e3181d5ae47 Fagerlund, M. J. & Eriksson, L. I. (2009). Current concepts in neuromuscular transmission. British Journal of Anaesthesia, 103(1), 108–114. doi:10.1093/bja/aep150 Lee, C. (2001).Structure, conformation, and action of neuromuscular blocking drugs. British Journal of Anaesthesia, 87(5), 755-769. Martyn, J. A., Fagerlund, M. J., & Eriksson, L. I. (2009). Basic principles of neuromuscular transmission. Anaesthesia, 64(S1), 1-9. doi: 10.1111/j.1365-2044.2008.05865.x Perry J. J., Lee J. S., Sillberg, V. A. H., & Wells, G. A. (2008). Rocuronium versus succinylcholine for rapid sequence induction intubation (review). Cochrane Database of Systematic Reviews, 2, CD002788. doi: 10.1002/14651858.CD002788.pub2. Reves, J. G., Glass, P., Lubarsky, D. A., McEvoy, M. D., & Martinez-Ruiz, R. (2010). Intravenous anesthetics. In R. D. Miller, L. I. Eriksson, L. A. Fleisher, J. P. Wiener-Kronish & W. L. Young (Eds.), Miller’s Anesthesia (pp. 719-768). Philadelphia: Churchill Livingstone Elsevier. Sinclair, S. C. F., & Luxton, M. C. (2005). Rapid sequence induction. Continuing Education in Anaesthesia, Critical Care & Pain, 5(2), 45-48. doi 10.1093/bjaceaccp/mki016 Read More