|Year : 2017 | Volume
| Issue : 3 | Page : 155-161
A study of intubating conditions: Sevoflurane versus propofol-suxamethonium in children
Morayo M Salawu1, Elizabeth O Ogboli-Nwasor2, Shola S Jamgbadi1, Fidelia N Akpa1
1 Department of Anaesthesia and Intensive Care, National Hospital, Abuja, Nigeria
2 Department of Anaesthesia, Ahmadu Bello University Teaching Hospital, Zaria, Kaduna State, Nigeria
|Date of Web Publication||30-Oct-2017|
Elizabeth O Ogboli-Nwasor
Department of Anaesthesia, Ahmadu Bello University Teaching Hospital Shika, Zaria, Kaduna State
Source of Support: None, Conflict of Interest: None
Background: Endotracheal intubation is an integral part of general anaesthesia in children, and the choice of induction agents and technique may affect the ease of intubation and thus the outcome of paediatric patients. We compared the ease of endotracheal intubation following sevoflurane and propofol-suxamethonium induction using Helbo–Hansen score. Patients and Methods: A prospective, randomized double-blinded comparative study conducted on sixty-six children (two groups of 33 each) between the ages of 3–10 years undergoing different elective surgeries. Group I received intravenous propofol and intravenous suxamethonium while Group II had inhalational induction with sevoflurane in 60% nitrous oxide and oxygen. Data including intubating conditions, time to tracheal intubation and haemodynamic changes were analysed using SPSS version 18, with statistical significance set at P < 0.05. Results: Using the Helbo–Hansen intubation score, the study reveals that 28 patients (85%) scored 4, 5 (15.2%) scored 5 and no patient scored 6 in Group I whereas 15 (45.5%) scored 4, 16 (48.5%) scored 5 and 2 (6.1%) scored 6 in Group II with P = 0.002. The mean time taken from induction to laryngoscopy was 91.27 ± 29.96 s in Group I and 219.09 ± 63.88 s in Group II (with P < 0.0001); mean time taken from laryngoscopy to completion of intubation was 29.03 ± 10.61 s and 28.09 ± 9.48 s which was not statistically significant with P = 0.71. Conclusion: Sevoflurane provides clinically acceptable intubating conditions and can be a suitable alternative to propofol-suxamethonium for endotracheal intubation in children. We recommend the use of sevoflurane to facilitate intubation in elective procedures in children.
Keywords: Children, propofol, sevoflurane, suxamethonium, tracheal intubation
|How to cite this article:|
Salawu MM, Ogboli-Nwasor EO, Jamgbadi SS, Akpa FN. A study of intubating conditions: Sevoflurane versus propofol-suxamethonium in children. Niger Postgrad Med J 2017;24:155-61
|How to cite this URL:|
Salawu MM, Ogboli-Nwasor EO, Jamgbadi SS, Akpa FN. A study of intubating conditions: Sevoflurane versus propofol-suxamethonium in children. Niger Postgrad Med J [serial online] 2017 [cited 2018 Mar 21];24:155-61. Available from: http://www.npmj.org/text.asp?2017/24/3/155/217403
| Introduction|| |
Tracheal intubation is one of the critical steps during administration of general anaesthesia, a major responsibility of the anaesthetist being provision of adequate airway for the patient. This is more so in paediatric anaesthesia because of the peculiar anatomical, physiological and pharmacological characteristics of the child. The method of inhalational induction using agents like ether or halothane for the intubation of the trachea has been practiced but recently, sevoflurane has been used especially in paediatric anaesthesia. Over the last decade, the use of halothane has declined in favour of sevoflurane because halothane is a potent depressant of myocardial contractility and it causes hypotension and bradycardia. Halothane is also associated with arrhythmias such as atrioventricular dissociation, ventricular tachycardia, ventricular extrasystoles, nodal rhythm and asystoles when compared with other volatile agents., Sevoflurane causes less bradycardia and myocardial depression when compared to halothane. This could also have led to reduction in the proportion of cases of inhalation agent-related cardiovascular depression resulting in cardiac arrest in the United States.
The introduction of sevoflurane into clinical anaesthetic practice started in Japan in May 1990, and by 1993, one million patients had received it. Since then, its use has superseded the use of halothane for inhalational induction and intubation in paediatric anaesthesia. Several studies have compared intubation in children without the use of muscle relaxants. These studies employed sevoflurane with or without nitrous oxide in oxygen. Others employed use of sevoflurane with opioids and also in combination with propofol and benzodiazepines such as midazolam.,,, All these combinations showed comparable conditions with the traditional use of suxamethonium which is thought to provide the optimal condition for tracheal intubation.,,, To the best of our knowledge, study such as this has not been reported in Nigeria, or in West African subregion or in sub-Saharan Africa. Therefore, the quest to ascertain if sevoflurane can take the place of propofol suxamethonium for tracheal intubation in children. The aim of the study is to compare the effectiveness of sevoflurane and propofol/suxamethonium for endotracheal intubation in children.
| Patients and Methods|| |
This was a prospective, randomized, double-blinded study carried out at National Hospital Abuja, Nigeria. Institutional Research and Ethics approval with protocol number NHA/EC/188/2012 was obtained on 17 August, 2012. A total of 66 children aged 3–10 years were recruited. This study was conducted between September 2012 and August 2013. Patients scheduled for surgeries such as herniotomy, adenotonsillectomy and cleft lip repair requiring general anaesthesia had pre-operative anaesthetic assessment and investigations (full blood count, serum urea and electrolytes and urinalysis) after obtaining written informed consent from the parents/guardians.
Inclusion criteria included ASA I or II and elective procedures lasting <90 min. The exclusion criteria were ASA III or IV, anticipated difficult airway, known allergy to study drugs and those patients who could not be intubated after two attempts at laryngoscopy. Regarding sample size calculation, Blair et al. reported that the excellent intubating conditions which occurred in 45% of patients were achieved with a combination of 8% sevoflurane and 60% nitrous oxide . An acceptable intubation success rate of 80% was considered clinically significant in this study. We assumed that sevoflurane will provide clinically acceptable conditions for endotracheal intubation comparable to propofol-suxamethonium in children.
The sample size was determined using the formula for the comparison of two proportions: Sample size, 2N = 4 (2α +2β) 2 × P (1 − P)/(PC− P1) 2
2N = Total sample size,
2α = A constant conditional value that corresponds to the significance level of 5% = 1.960,
2 β = A constant, the value of the standard normal value not exceeded with probability β, it corresponds to the power of 80% = 0.84.
P = Pc+ Pi; Pc= event control group;
Pi= event rate on the intervention group.
Total sample size = 60, with attrition of 10% making a total of 66.
Patients were randomized into two groups; randomization was done by computer-generated random numbers using WINPEPI. Group I received intravenous propofol 2.5 mg/kg and intravenous suxamethonium 1.5 mg/kg while Group II had inhalational induction with sevoflurane in 60% nitrous oxide and oxygen. All the patients were fasted for 6 h and allowed oral intake of clear fluids (water or Sprite ® 1 ml/kg) 2 h before surgery. All the children were cannulated with 22G cannula on the dorsum of the hand after local anaesthesia was achieved with EMLA cream that was applied 45 min earlier.
In the operating room, pre-anaesthetic checks were done and resuscitation drugs drawn, diluted and labeled (atropine and adrenaline). Non-invasive blood pressures, heart rate, electrocardiogram, oxygen saturation multiparameter monitor and precordial stethoscope were attached, and baseline vital signs were obtained. Intravenous fluid 4.3% dextrose in 0.18% saline was commenced using a burette with fluid calculated according to the patient's weight using 4 ml/kg for the first 10 kg, 2 ml/kg from 10 to 20 kg and subsequently, 1 ml/kg from 20 kg upwards. Pre-oxygenation was done using Ayre's T-piece with Jackson Ree's modification or Bain's circuit for the children weighing more than 25 kg. All the patients were given premedication using atropine 0.01 mg/kg and intravenous fentanyl 2 μg/kg at induction; the fentanyl was administered before giving the induction agent. Induction of anaesthesia was performed by anaesthetists conversant with the methodology of the study. Patients in Group I received intravenous propofol 2.5 mg/kg with addition of lidocaine 0.2 mg/kg to prevent pain on injection. The anaesthetist observed the patients for wincing and withdrawal of hand to pain. Suxamethonium 1.5 mg/kg was administered by intravenous route for laryngoscopy and tracheal intubation. The intravenous line was flushed with intravenous fluid to prevent identification of the drug. Tracheal intubation was done by the investigator anaesthetist who was called into the theatre to intubate the trachea when the jaw was relaxed. The vaporiser was concealed by covering with a drape so that the investigator anaesthetist was blinded to the induction agents used for both groups. The application of face mask was discontinued by the investigator anaesthetist who carried out laryngoscopy and intubation.
Using a Macintosh laryngoscope an appropriate sized endotracheal tube was inserted through the larynx with the aid of a stylet. The endotracheal tube size was calculated using the formula n/4 + 4, where n is the age of the patient in years. External pressure on the cricoid cartilage by an assistant was used to aid visualisation of the larynx in some cases. After confirmation of correct placement, conditions for endotracheal intubation were assessed by the investigator who performed the intubation using the four-point scoring system of Helbo–Hansen.
Helbo–Hansen scoring system [Appendix 1] [Additional file 1] involves the assessment of four criteria, which are ease of laryngoscopy, vocal cord position, and coughing and limb movements. Laryngoscopic view was assessed using the Cormack and Lehane grading at laryngoscopy. Grade I (vocal cord visible) was regarded as easy, II (arytenoid and posterior part of cords visible) as fair. Grade III (epiglottis visible was regarded as difficult) and IV (epiglottis not visible) as impossible. The overall conditions for intubation would be clinically acceptable if the Helbo–Hansen score was 2 or less in each category which will add up to a total score of 8 or less. An excellent intubation condition is described as a score of 1 in each criterion. Non-invasive blood pressure, heart rate and arterial oxygen saturation were measured at 0, 1, 3 and 5 min post-intubation. Complications of laryngoscopy such as trauma to the upper airway, hypertensive response, tachycardia, desaturation, laryngospasm and bronchospasm were assessed and noted by an independent anaesthetist.
Maintenance of anaesthesia was achieved with isoflurane 1%–1.5% in 60% nitrous oxide in oxygen in both groups. Intravenous atracurium 0.5 mg/kg was given when patient resumed spontaneous respiration and intravenous diclofenac 1 mg/kg was administered. At the end of procedure, residual neuromuscular block was reversed with intravenous neostigmine 0.04 mg/kg and atropine 0.02 mg/kg. The patient's oropharynx was suctioned and patient's trachea was extubated when fully awake and transferred to the recovery room in the recovery position. The patients were given supplemental oxygen in the recovery room and monitoring continued for 1 h before the patients were certified fit for discharge to the wards.
Group II patients received incremental concentrations of sevoflurane to 8% in 60% nitrous oxide and oxygen using Datex-Ohmeda Aespire TEC7 (manufactured by Datex-Ohmeda Inc, Madison, WI 53707-7550, USA) anaesthesia machine. It was increased by 1.5% after every three breaths, and when there was loss of eyelash reflex, patients were manually ventilated. Both pupils were checked with a pen torch and when the pupils were fixed and central, and jaw was relaxed, the investigator was called inside the operating room to intubate the trachea. Time taken from induction to completion of intubation was noted by an independent anaesthetist who also recorded vital signs at 0, 1, 3 and 5 min post-intubation. The time taken for the investigator to walk in after induction was also considered and was standardised by the investigator staying at the same location outside the anaesthetic induction room in the theatre suite and being invited in straight to the patient's operation table. Each time, the measurement was taken using a stopwatch and the time taken was within 30–60 s range, and this was also recorded. Complications of laryngoscopy were assessed and noted. Sevoflurane was discontinued after successful tracheal intubation by an independent anaesthetist that performed the induction of anaesthesia. Maintenance of anaesthesia was achieved with isoflurane and recovery from anaesthesia was conducted as previously described.
The primary outcome measures include the proportion of participants with excellent intubation conditions (4) and good intubation conditions (8) using the Helbo–Hansen scoring system for assessment of the conditions for intubation. The time taken (≤60 s) for the investigator to walk in after induction was also considered and was standardised by the investigator staying at the same location outside the anaesthetic induction room in the theatre suite and being invited in straight to the patient's operation table. And each time, measurement was taken using a stopwatch and it was within 30–60 s. Thus, the time taken from commencement of induction to when patient is ready for laryngoscopy was also determined. The secondary outcome measures were the incidence of side effects such as laryngospasm and pain on injection.
Data analysis was done using Statistical Product and service solutions (SPSS) Statistics for Windows, IBM SPSS Statistics. Version 18.0. (IBM SPSS Inc, Chicago, Ill), with statistical significance set at P < 0.05. Demographic, haemodynamic and other intraoperative variables were presented in tables expressed as means and counts as appropriate. Chi-square was used for categorical data while Student's t-tests and Mann–Whitney U-tests were used for numerical data.
| Results|| |
There was no statistically significant difference in the sociodemographic characteristics between the two groups. The baseline and intraoperative vital signs were also comparable [Table 1]. The mean duration of surgery was 59.94 (±19.43 min) for Group I and 53.91 (±21.09 min) for Group II with P = 0.23 which was not statistically significant. The time taken from induction to laryngoscopy was 91.27 ± 29.96 s in Group I and 219.09 ± 63.85 s in Group II and mean time taken from induction to completion of intubation was 120.30 ± 34.13 s and 247.18 ± 64.66 s, respectively, in both groups with P < 0.0001 which was highly significant, as shown in [Table 2]. Mean oxygen saturation was 99% in both groups with P = 0.956 which is not statistically significant.
[Table 3] shows intubation patterns in the two groups. The intubation scores using Helbo–Hansen scoring system revealed that 28 (84.8%) patients scored 4(excellent intubation conditions), five patients (15.2%) scored 5 and no patient scored 6 in Group I whereas 15 patients (45.5%) scored 4(excellent intubation conditions), sixteen patients (48.5%) scored 5 and two patients (6.1%) scored 6 in Group II with P = 0.00 which was statistically significant. Thus, though patients in Group II had higher scores than Group I patients, their scores were within clinically acceptable intubation conditions. The number of laryngoscopic attempt at intubation was one in 31 (93.9%) patients and 30 (90.9%) patients in Groups I and II, respectively; while two laryngoscopic attempts were required in 2 (6.1%) patients and 3 (9.1%) patients in Groups I and II, respectively, with P = 1.00 which was not statistically significant. Cormack-Lehane grading was grade I in 30 (90.9%) patients and 29 (87.9%) patients in Groups I and II, respectively, grade 2 was seen in 3 (9.1%) patients and 4 (12.1%) patients in propofol-suxamethonium and sevoflurane groups, respectively, with P = 1.00.
[Figure 1], [Figure 2], [Figure 3] show the immediate post-intubation vital signs which include heart rate, mean arterial blood pressure and arterial oxygen saturation had no significant difference in both groups. However, there is statistically significant difference between the diastolic blood pressure in the sevoflurane group (Group II), compared to the propofol/suxamethonium group (Group I).
Analysis of immediate post induction and post intubation side effects revealed that laryngospasm was not seen in the patients in Group I whereas in Group II, 2 (6.1%) patients had laryngospasm (P = 0.47). Pain on injection was observed from patient's expression during administration of propofol in the propofol-suxamethonium group (Group 1) in 7 patients (21.2%) with P = 0.016 which was statistically significant [Table 4].
| Discussion|| |
This study demonstrates that successful tracheal intubation in children is achievable, using sevoflurane when compared with propofol-suxamethonium. The implication is that endotracheal intubation is possible without muscle relaxant using sevoflurane although propofol suxamethonium had better conditions for intubation. The finding by Sarner et al. in which induction time was longer revealed that total time to completion of intubation was 6.7 min (402 s) compared to this study which was 4.1 min (247.18 ± 64.66 s). This longer time might be due to non-use of opioid analgesic and the use of TEC3 vaporiser (maximum sevoflurane that can be delivered was 7%) compared to TEC 7 used in this study which can deliver a maximum of 8%.
In Blair et al.'s study and Sabapathy et al.'s study,, the success rate of acceptable clinical conditions for intubation using 8% sevoflurane in 60% nitrous oxide and oxygen was 87.5%. This study demonstrated a higher success rate where all the patients had acceptable clinical conditions for intubation. These studies used a fixed induction time for intubation (150 and 180 s, respectively); their high success rate despite short induction time could be attributed to overpressure technique in which the circuit was primed with sevoflurane. In this index study, conventional incremental dosing was used so that the children could tolerate the agent and prevent excitement associated with overpressure technique.
The quality of tracheal intubation as determined by Helbo–Hansen score which is a score of 1–4 in each criterion and included laryngoscopy, vocal cords position, coughing and limb movements [See Appendix 1]. Excellent intubating conditions is a score of 3–4, good intubating conditions is a score of 5–6, while 9–12 is considered poor and 13–16 is bad. Excellent and good scores are considered as clinically acceptable, fair and poor scores are considered as clinically unacceptable. Blair et al. demonstrated that excellent intubating conditions- which was a score of 1 in each criterion -were achieved in 70% of the propofol suxamethonium group in 45% of the sevoflurane group. In this present study, excellent intubating condition score was seen in 84.8% of patients in propofol-suxamethonium group and 45.5% in sevoflurane group. The excellent intubating conditions were similar in sevoflurane groups of both studies, but lower value of 70% obtained in their propofol-suxamethonium group could be attributed to the lack of analgesics used in their study whereas our patients were given intravenous fentanyl 2 μg/kg before intubation in this study. Analgesics, especially opioids, have been shown to deepen anaesthesia and attenuate laryngopressor response.
Excellent intubating conditions were seen in 100% of patients in a study by Kumar et al., sevoflurane was used for induction and intubation following apnoea at 4.5 min, and then, intravenous propofol 1 mg/kg was administered. Thereafter, laryngoscopy and intubation were done at 5.5 min. This high success rate could be attributed to the use of sevoflurane till the patients were apnoeic at 4.5 min and use of propofol which causes apnoea in all their patients. Propofol also causes suppression of pharyngeal and laryngeal reflexes.
Excellent conditions are less frequently associated with laryngeal morbidity according to studies done by Mencke et al. From their study, they concluded that the quality of tracheal intubation contributes to laryngeal morbidity, and excellent conditions are less frequently associated with post-operative hoarseness and vocal cord sequelae. Adding atracurium to a propofol-fentanyl induction regimen significantly improved the quality of tracheal intubation and decreased post-operative hoarseness and vocal cord sequelae.
The difference in immediate post-intubation heart rate was not statistically significant between the two groups. The reduction in heart rate at 1 and 3 min was more in the propofol/suxamethonium group as a result of their pharmacological effect on heart rate. The use of fentanyl and lignocaine could also have contributed to attenuation of laryngopressor response. The immediate post-induction and post-intubation side effects were minimal in this study. However, there was statistically significant difference between the diastolic blood pressure in the sevoflurane group (Group II) and the propofol/suxamethonium group (Group I) with lower post-intubation diastolic blood pressures in Group I. This could be due to the fact that diastolic pressure is a measure of systemic vascular resistance and propofol causes a greater decrease in systemic vascular resistance.
None of the patients experienced desaturation (SpO2 <90%), bronchospasm and trauma to the airway, implying that both propofol-suxamethonium and sevoflurane groups had good conditions for intubation. Only 6.1% had laryngospasm in the sevoflurane group which was similar to studies done by Rhedu et al. and Thwaites et al., This suggests that using sevoflurane may not completely provide a ready airway for intubation. In this index study, Helbo–Hansen score was <2 in each criterion which was considered clinically acceptable, and tracheal intubation was successful in all children. This was similar to results obtained by Thwaites et al. who also demonstrated high success rates.
In the study by Thwaites et al., fixed induction time was 150s in both propofol suxamethonium and the sevoflurane group. They had acceptable clinical conditions despite this fixed induction time of 150 s because the patients in the propofol suxamethonium group were also maintained on isoflurane after the drugs were given. This might be responsible for their success rate in their study. In their study, the dose of propofol was 3–4 mg/kg and suxamethonium was 2 mg/kg which was higher than the dose used in this study. They were able to achieve clinically acceptable intubating conditions in their sevoflurane group despite attempting intubation at 150 s because sevoflurane was started at a high concentration (8% in nitrous oxide and oxygen) and the patients were manually ventilated.
| Conclusion|| |
Sevoflurane provides clinically acceptable intubating conditions and can be a suitable alternative to propofol-suxamethonium for endotracheal intubation in children. Although sevoflurane is not as effective as propofol-suxamethonium for endotracheal intubation in children, it could be used as an alternative in elective procedures. We recommend the use of sevoflurane to facilitate intubation in elective procedures in children.
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Conflicts of interest
There are no conflicts of interest.
| References|| |
Martin J, Njoku DB. Metabolism and toxicity of modern inhaled anaesthetics. In: Miller RD, Heisher LA, Johns RA, Savarese JJ, Wiener Kronish J, Young WL, editors. Miller's Anaesthesia. 6th
ed. London: Churchill Livingstone; 2005. p. 231-72.
Rhedu S, Jalwal GK, Saxema M, Shrivastava OP. Comparative study of characteristics of sevoflurane and halothane in anaesthesia in paediatric patients (6 months to 6 years). J Anaesthesiol Clin Pharmacol 2010;26:484-7.
Rivenes SM, Lewin MB, Stayer SA. Cardiovascular effects of sevoflurane, halothane and fentanyl-midazolam in children with congenital heart disease: An echocardiographic study. Anesthesiology 2001;94:223-9.
Sanjay M, Chanda Ramamothy B, Geiduschek JM. Anaesthesia-related cardiac arrest in children: Update from the pediatric preoperative cardiac arrest registry. Anesth Analg 2007;105:344-50.
Blair JM, Hill DA, Bali IM, Fee JP. Tracheal intubating conditions after induction with sevoflurane 8% in children. A comparison with two intravenous techniques. Anaesthesia 2000;55:774-8.
Rajan S, Gotluru P, Andrews S, Paul J. Evaluation of endotracheal intubating conditions without the use of muscle relaxants following induction with propofol and sevoflurane in paediatric cleft lip and palate surgeries. J Anaesthesiol Clin Pharmacol 2014;30:360-5.
] [Full text]
Raghavendra TR, Yoganarasimha N, Radha MK, Mahdu R. A clinical study to compare the ease of intubation with combination of sevoflurane and propofol alone. Innov J Med Health Sci 2013;3:143-8.
Shaikh SI, Bellagali VP. Tracheal intubation without neuromuscular block in children. Indian J Anaesth 2010;54:29-34.
] [Full text]
Gupta A, Kaur R, Malhotra R, Kale S. Comparative evaluation of different doses of propofol preceded by fentanyl on intubating conditions and pressor response during tracheal intubation without muscle relaxants. Paediatr Anaesth 2006;16:399-405.
Batra YK, Al Qatten AR, Ali SS, Qureshi MI, Kuriakose D, Migahed A. Assessment of tracheal intubating conditions in children using remifentanil and propofol without muscle relaxants. Paediatr Anaesth 2006;14:452-6.
Agrawal S, Kumar A, Srivastava U. Intubation without muscle relaxant: Comparison of propofol-fentanyl or propofol-halothane anaesthesia in children. Afr J Anaesth Intensive Care 2011;11:7-11.
Erhan E, Ugur G, Gunusen I, Alper I, Ozyar B. Propofol-not thiopental or etomidate with remifentanyl provides adequate intubating condition in the absence of neuromuscular blockage. Can J Anaesth 2003;50:108-15.
Kadam P, Bhalero S. Sample size calculation. Int J Ayurveda Res 2010;1:50.
] [Full text]
Helbo-Hanson S, Ravlo O, Trap-Anderson S. The influence of alfentanil on intubating conditions after priming with vecuronium. Acta Anaesth Scand 1988;32:41-4.
Cormack RS, Lehane J. Difficult tracheal intubation in obstetrics. Anaesthesia 1984;39:1105-11.
Sarner JB, Levine M, Davis PJ, Lerman J, Cook DR, Motoyama EK, et al.
Clinical characteristics of sevoflurane in children. A comparison with halothane. Anesthesiology 1995;82:38-46.
Sabapathy VA, Prabhu T, Srinivasa SM, Srinivasta P. Endotracheal intubation without muscle relaxants in children undergoing cleft lip, palate and alveolar surgery. A comparative study of sevoflourane and propofol. J Clin Diagn Res 2011;5:1421-5.
Kumar N, Galante D, Shetty KB. Tracheal intubation in children using sevoflurane without muscle relaxant. A novel approach using apnea as clinical indicator. Paediatr Anaesth Crit Care J 2015;3:53-60.
Mencke T, Ecthtermach N, Kleinschmidt S, Lux P, Barth V, Plinkert PK. Laryngeal morbidity and quality of tracheal of tracheal intubation. Anesthesiology 2003;98:1049-62.
Aakash A, Derwitz M. Intravenous induction agents. In: Sikika PK, Usman RD, Dershwitz M, Segal BS, editors. Essential Clinical Anaesthesia. New York: Cambridge University Press; 2011. p. 227-32.
Thwaites AJ, Edmends S, Tomlinson AA, Kendall JB, Smith I. Double-blind comparison of sevofluran vs. propofol and succinylcholine for tracheal intubation in children. Br J Anaesth 1999;83:410-4.
[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3], [Table 4]