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Are Muscle Relaxants still necessary in Paediatric Anaesthesia? |
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George H Meakin MB ChB, MD, FRCA, DA Senior Lecturer in Paediatric Anaesthesia, Royal Manchester Children's Hospital, Pendlebury, Manchester M27 4HA, United Kingdom Vol. 4, N. 2, Maggio 2006 |
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Writing in 1955, Alan Stead summarised the main advantages of muscle relaxants in paediatric anaesthesia as follows: (3) 1 - They provide a means of effecting [tracheal intubation] and maintaining control of respiration throughout the operation 2 - The patient is completely relaxed and the work of the surgeon facilitated. 3 - The quantity of toxic anaesthetic agents is greatly reduced. In recent years, several changes have occurred that have reduced or obviated the need for muscle relaxants during paediatric anaesthesia. These include the introduction of newer less toxic, shorter acting anaesthetic drugs and adjuvants (such as propofol, sevoflurane and remifentanil) and the introduction of the laryngeal mask airway (LMA) which has replaced the tracheal tube as the method of controlling the airway in many paediatric operations. In addition, there have been concerns about the safety of succinylcholine (SCh) in children. This presentation reviews these developments and aims to determine the current place of muscle relaxant drugs in paediatric practice. LMA The LMA was introduced into adult practice in 1983. (4) An early trial of the paediatric LMA notes that the design was a scaled down version of the adult LMA and not anatomically designed for children. (5) Moreover it was clear that the range of available sizes was inadequate. Since then, improvements in the design and availability of suitable sizes together with favourable clinical experiences have led to an increasing use of the LMA in children. As the LMA can be inserted easily without the use of a muscle relaxant, its increasing popularity for airway control in children represents a decline in the use of muscle relaxants, which were previously widely used to facilitate tracheal intubation. Succinylcholine Until the early 1990s SCh was the unrivalled drug for facilitating tracheal intubation in children due to its rapid onset and ultra-short duration of action. This was despite numerous problems associated with its use including muscle pains, dysrhythmias, masseter spasm, hyperkalaemia, prolonged neuromuscular block and malignant hyperthermia. However, following a report of hyperkalaemic cardiac arrests in young children with undiagnosed Duchenne Muscular Dystrophy (6), the FDA placed a warning in the package insert indicating that “the use of SCh in children should be reserved for emergency intubation or instances where immediate securing of the airway was necessary, or for i.m. use when a suitable vein is inaccessible”. Since then, the routine use of SCh in paediatric anaesthesia has declined. While 84% of anaesthetists surveyed in the UK in 1996 routinely used SCh for intubation in children, (7) only 45% were using it in 1999 (8) and this trend seems to have continued. Intubation without muscle relaxants. Concerns about the dangers of SCh in children led to studies of intubation conditions without the use of a muscle relaxant. Use of intravenous agents Several studies have looked at intubation under propofol and a short-acting opioid drug. (9-13). In these studies, satisfactory intubating conditions were found in 35-90% of patients following administration of propofol and alfentanil or remifentanil. This compared with >95% satisfactory intubating conditions obtained with thiopental and SCh. (9,12). In one study, intubating conditions were improved by increasing the dose of remifentanil from 2 µg kg -1 to 3 µg kg -1 , (13) but this also produced a signifcant reduction in heart rate and blood pressure. As all the studies were performed in healthy children scheduled for elective surgery, it is probable that the adverse effects of such regimens would be greater in sick/emergency/dehydrated children or young infants. Furthermore, inadequate neuromuscular blockade at the time of intubation could put patients at increased risk of pulmonary aspiration of gastric contents. (14). In children anaesthetised with thiopental-N2O, satisfactory intubating conditions were observed in 98% and 100% of cases 90 and 70s following 2 x ED 95 doses of mivacurium or rocuronim respectively. (15,16) These and other studies suggest that a balanced approach to anaesthesia for intubation, combining moderate degrees of hypnosis and analgesia with the use of a non-depolarising muscle relaxant provides the best conditions for intubation with the minimal potential for adverse effects. Similar conclusions have been drawn from studies in anaesthetised adults. (17) Use of volatile agents Inhalation induction and intubation remains popular in children in whom intravenous induction may be difficult due to poor venous access or the fear of needles. Although halothane was used for tracheal intubation for many years it has largely been superseded by sevoflurane which has a less pungent odour and is less likely to cause cardiac depression (18) or arrhythmias. (19) In children aged 1-9 yr, the MAC for tracheal intubation ( MAC TI 50 ) has been shown to be 2.7%, 30% above the MAC 50 level of 2%. (20) In another study, 80 and 100% of 2-8 yr old children who were given 5% sevoflurane to breathe underwent smooth tracheal intubation at end-tidal concentrations of 4.0 and 4.5% respectively. (21) The time to reach 4.5% sevoflurane in this study was 3.5 min. The addition of nitrous oxide 33 and 66% has been shown to decrease the MAC 50 TI for sevoflurane alone from 2.7% to 2.2% and 1.6% respectively. (22) In a comparative study of sevoflurane 8% in 66% N 2 O (intubation at 3 min), propofol 3 mg kg -1 with alfentanil 10 µg kg -1 and propofol 3 mg kg -1 with succinycholine 1 mg kg -1 (both intubated at 1 min) in children aged 3-12 yr, acceptable intubation conditions were found in 87.5%, 52.5% and 97.5% of patients respectively. (23) The end-tidal sevoflurane at intubation in the sevoflurane group was 4.2%, which agrees with the previous study showing that an end-tidal sevoflurane concentration of about 4% is required for successful intubation in almost all children. From these studies it would appear that deep inhalational anaesthesia is superior to co-administration of intravenous hypnotics and short-acting opioids for tracheal intubation, but the end-tidal concentration required is high when these agents are used alone. Although none of the above studies reported significant dysrhythmia or hypotension in children exposed to high end-tidal concentrations of sevoflurane, a previous study in 90 healthy patients reported hypotension (decrease in systolic arterial pressure = 30%) in 27-66% of neonates and infants and 0-8% of children at ˜ 1 MAC sevoflurane. (24) This suggests that the use of > 4% sevoflurane (1.3-1.6 MAC) for intubation has the potential to produce hypotension, especially in very young patients. These problems can be avoided by adopting a balanced approach as advocated in the preceding section on intravenous agents. In a study on 60 children aged 2-7 yr, good to excellent intubating conditions were achieved in all patients at 1 MAC anaesthesia with sevoflurane, 2 min after injection of 0.3 mg kg -1 (˜ 1 x ED 95 ) of rocuronium. (25) Similar results have been achieved with low doses of atracurium and vecuronium administered to children during halothane (26) and isoflurane (27) anaesthesia. Alternatively, a dose of a short-acting opioid may be given to facilitate intubation. Pretreatment with 1 µg kg-1 of fentanyl (28) or 1 µg kg -1 remifentanil followed by an infusion of 0.25 1 µg kg -1 min -1 (29) has been shown to reduce the MAC TI 50 of sevoflurane by ˜ 40%. Muscle relaxation during surgery During maintenance of anaesthesia muscle relaxants are used to keep the patient immobile, facilitate controlled ventilation and produce the desired degree of muscle relaxation to allow surgical access. Moderate anaesthesia with sevoflurane (1.4 MAC) and a narcotic agent can keep healthy patients still without producing hypotension, and will often suppress spontaneous ventilation sufficiently to allow controlled ventilation (if desired) once the effects of an intubating dose of a muscle relaxant has worn off. This has the advantage that supplementary doses of non-depolarising relaxants may not be necessary and pharmacological reversal can be omitted at the end of surgery. However, experience suggests that neuromuscular blocking agents will still be needed if profound muscle relaxation is required or in young infants and sick children in whom deep anaesthesia is poorly tolerated. Conclusions Changes in practice and the development of new anaesthetic drugs have reduced the need for muscle relaxants in paediatric anaesthesia. However, a balanced approach to anaesthesia for intubation in children, combining a moderate depth of anaesthesia with the use of a non-depolarising muscle relaxant provides the best intubating conditions with the minimal potential for adverse effects. Muscle relaxants are still required for procedures requiring profound muscle relaxation and to minimise the doses of anaesthetic drugs in infants and sick children. References 1. Griffiths HR, Johnson GE. The use of curare in general anaesthesia. Anesthesiology 1942; 3 : 418-420. 2. Foldes F. The final steps leading to anaesthetic use of muscle relaxants. In: Fukushima K, Ochiai R, eds. Muscle Relaxants Tokyo: Springer, 1995:8-12. 3. Stead AL. The response of the newborn infant to muscle relaxants. Br J Anaesth 1955; 27 : 124-113. 4. Brain AIJ. The laryngeal mask - a new concept in airway management. Br J Anaesth 1983; 55 : 801-805. 5. Mason DG, Bingham RM. The laryngeal mask airway in children. Anaesthesia 1990; 45 : 760-763. 6. Rosenberg H, Gronert GA. Intractable cardiac arrest in children given succinylcholine. Anesthesiology 1992; 77 : 1054. 7. Robinson AL, Jerwood DC, Stokes MA. Routine suxamethonium in children. Anaesthesia 1996; 51 : 874-878. 8. Hatcher IS, Stack CG. Postal survey of the anaesthetic techniques used for paediatric tonsillectomy surgery. Paediatr Anaesth 1999; 9 : 311-315. 9. Rodney GE, Reichert CC, O'Regan DN et al. Propofol or propofol/alfentanil compared to thiopentone/succinlycholine for intubation of healthy children. Can J Anaesth 1992; 39 : A128. 10. Steyn MP, Quinn AM, Gillespie JA et al. Tracheal intubation without neuromuscular block in children. Br J Anaesth 1994; 72 : 403-406. 11. Robinson DN, O'Brien K, Kumar R et al. Tracheal intubation without neuromuscular blockade in children: a comparison of propofol combined either with alfentanil or remifentanil. Paediatr Anaesth 1998; 8 : 467-471. 12. Annila P, Vitanen H, Reinikainen P et al. Induction characteristics of thiopentone/suxamethoniium, propofol/alfentanil or halothane alone in children aged 1-3 years. Eur J Anaesthesiol 1999; 16 : 359-366. 13. Batra YK, Al Qattan AR, Ali SS et al. Assessment of tracheal intubation conditions in children using remifentanil and propofol without muscle relaxant. Paediatr Anaesth 2004; 14 : 452-456. 14. Warner MA, Warner ME, Weber JG. Clinical significance of pulmonary aspiration during the peroperative period. Anesthesiology 1993; 78 : 56-62. 15. McCluskey A, Meakin G. Dose-response and minimum time to satisfactory intubation conditions after mivacurium in children. Anaesthesia 1996; 51 : 438-441. 16. Hopkinson JM, Meakin G, McCluskey A et al. Dose-response relationship and effective time to satisfactory intubation conditions after rocuronium in children. Anaesthesia 1997; 52 : 428-432. 17. Donati F. Tracheal intubation: unconsciousness, analgesia and muscle relaxation. Can J Anaesth 2003; 50 : 99-103. 18. Holzman RS, van der Velde ME, Kaus SJ et al. Sevoflurane depresses myocardial contractility less than halothane during induction of anesthesia in children. Anesthesiology 1996; 85 : 1260-1267. 19. Johannesson GP, Floren M, Lindahl SG. Sevoflurane for ENT-surgery in children. A comparison with halothane. Acta Anaesthesiol Scand 1995; 39 : 546-550. 20. Inomata S, Watanabe S, Taguchi M et al. End tidal sevoflurane concentration for tracheal intubation and minimum alveolar concentration in pediatric patients. Anesthesiology 1994; 80 : 93-96. 21. Inomata S, Nishikawa T. Determination of end tidal sevoflurane concentration for tracheal intubation with the rapid method. Can J Anaesth 1996; 43 : 806-811. 22. Swan DH, Crawford MW, Pua HL et al. Additive contribution of nitrous oxide to sevofurane minimum alveolar concentration for tracheal intubation in children. Anesthesiology 1999; 91 : 667-671. 23. Blair JM, Hill DA, Bali IM et al. Tracheal intubation conditions after induction with sevoflurane 8% in children. Anaesthesia 2000; 55 : 774-778. 24. Lerman J, Sikich N, Kleinman S et al. The pharmacology of sevoflurane in infants and children. Anesthesiology 1994; 80 : 814-824. 25. Eikermann M, Peters J. Low dose rocuronium optimizes both intubating conditions and time-course of action during anesthesia with sevoflurane in children. Anesthesiology 1999; 91 : A1275. 26. Ved SA, Chen J, Reed M et al. Intubation with low-dose atracurium in children. Anesth Analg 1989; 68 : 609-613. 27. Frediani M, Capanna M, Casini L et al. The use of low doses of intermediate acting muscle relaxants in adenotonsillectomy. Minerva Anestesiol 1993; 59 : 109-114. 28. Katoh T, Nakajima Y, Moriwaki G et al. Sevoflurane requirements for tracheal intubation with and without fentanyl. Br J Anaesth 1999; 82 : 561-565. 29. Cros AM, Lopez C, Kandel T et al. Determination of sevoflurane alveolar concentration for tracheal intubation with remifentil, and no muscle relaxant. Anaesthesia 2000; 55 : 965-969.
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