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Tracheal intubation without the use of neuromuscular blocking agents

2004; Elsevier BV; Volume: 94; Issue: 2 Linguagem: Inglês

10.1093/bja/aei006

1471-6771

A. W. Woods, Shalini D. Allam,

Medical History and Innovations

Before the early 20th century, intubation of the trachea had been described for conditions such as perioral tumours and laryngeal obstruction, and had been performed rather crudely, often using fingers as a makeshift laryngoscope and without any pharmacological agents.55MacEwen W Clinical observations on the introduction of tracheal tubes by the mouth instead of performing tracheotomy or laryngotomy.Br Med J. 1880; 2: 122Crossref PubMed Scopus (102) Google Scholar, 74Rushman GB Davies NJH Atkinson RS A Short History of Anaesthesia: Intubation of the Trachea. Butterworth-Heinneman, Oxford1996: 92-97Google Scholar Insufflation of the trachea for the purpose of ether anaesthesia was introduced in 1909 in the USA, and in 1912 in the UK.20Elsberg CA Clinical experiences with intratracheal insufflation with remarks upon the value of the method for thoracic surgery.Ann Surg. 1910; 52: 23-29Crossref PubMed Google Scholar, 46Kelly RE Anaesthesia by the intratracheal insufflation of ether.Br Med J. 1912; 3: 112Crossref Scopus (4) Google Scholar Rowbotham refined the technique and described a series of cases in 1913.72Rowbotham S Intratracheal anaesthesia.Lancet. 1920; 2: 583-584Google Scholar, 73Rowbotham S Intratracheal anaesthesia by the nasal route for operations on the mouth and lips.Br Med J. 1920; 3: 590-591Crossref Scopus (15) Google Scholar These early tracheal tubes were wide-bore catheters and were guided into the trachea using forceps. Neuromuscular blocking drugs to aid tracheal intubation were first introduced into clinical practice in 1942 in the USA,28Griffith HR Johnson GE The use of curare in general anesthesia.Anesthesiology. 1942; 3: 418-420Crossref Google Scholar and within several years gained widespread acceptance in this country.9Bourne JG Thiopentone–nitrous oxide–oxygen anaesthesia with curare for head and neck surgery.Br Med J. 1947; 2: 654-655Crossref PubMed Scopus (2) Google Scholar, 27Gray TC Halton J A milestone in anaesthesia (d-tubocurarine chloride).Proc R Soc Med. 1946; 39: 400-408Google Scholar Before this, tracheal intubation was usually performed under deep inhalational anaesthesia with ether. The continuing use of this technique to facilitate tracheal intubation with halothane and subsequently sevoflurane is still established, especially in paediatric practice. Since the advent of shorter-acting opioid drugs, intubating the trachea has been particularly successful when these drugs are used in combination with propofol. The technique has gained a small but popular niche in the armoury of the anaesthetist, when use of a neuromuscular blocking drug is undesirable. It may be used when there is a contraindication to a neuromuscular blocking drug, or in cases where tracheal intubation is necessary but prolonged muscle relaxation is not, such as in short ENT or gynaecological procedures. The technique may be the one of choice for the anaesthetist, using it as part of total intravenous anaesthesia without the use of a neuromuscular blocking drug. One avoids the potential serious and unwanted side-effects of succinylcholine, as well as the less common ones of non-depolarizing drugs, such as anaphylaxis. This review concentrates on the many studies that detail different techniques to intubate the trachea without muscle relaxation. Although no two studies are the same, and criteria for optimal intubating conditions vary, this review provides insight into how to approach this technique. The literature on this subject was retrieved using Medline (Pubmed, Medline Plus). The following search terms were used alone and in combination: tracheal intubation, inhalational anaesthetics, lidocaine, fentanyl, alfentanil, remifentanil, haemodynamic response, pressor response, complications. Although tracheal intubation under deep halothane anaesthesia was a well-established technique in paediatric patients, Yakaitis and colleagues were the first to evaluate the optimum end-tidal concentration for intubation.94Yakaitis RW Blitt CD Anguilo JP End tidal halothane concentration for endotracheal intubation.Anesthesiology. 1977; 47: 386-388Crossref PubMed Scopus (60) Google Scholar The concept of MACEI (EI=endotracheal intubation) was described—the minimum alveolar concentration of halothane needed by 50% of the population to prevent all movement both during and immediately after tracheal intubation. They studied 37 children, aged 2–6 yr, and found the MACEI value to be 1.4%, and found by extrapolation that the MACEI value for 95% of this population was 1.9%. The study was performed at altitude, and after appropriate barometric calculations the MACEI of halothane was recalculated as 1.3%. The same group then applied these study techniques to enflurane in a similar age group of patients and found the corrected MACEI value to be 2.9%.95Yakaitis RW Blitt CD Anguilo JP End tidal enflurane concentration for endotracheal intubation.Anesthesiology. 1979; 50: 59-61Crossref PubMed Scopus (36) Google Scholar For both halothane and enflurane, the MACEI appears to be about 30% greater than the MAC value. However, enflurane is known to produce central nervous system excitation at an alveolar concentration of 2.5%, and in 15 out of 17 patients studied, tonic–clonic twitching of the hands and feet was observed, making it an unsuitable agent for this purpose.52Lebowitz MH Blitt CD Dillon JG Enflurane-induced central nervous system excitation and its relation to carbon dioxide tension.Anesth Analg. 1972; 51: 355-363Crossref PubMed Scopus (39) Google Scholar Other complications of this technique with enflurane included a decrease in chest wall compliance and difficulty with ventilation. No similar studies have been published using isoflurane or desflurane, which is hardly surprising considering their potential for airway irritation.86TerRiet MF De Souza GJ Jacobs JS et al.Which is the most pungent: isoflurane, sevoflurane or desflurane.Br J Anaesth. 2000; 85: 305-307Crossref PubMed Scopus (90) Google Scholar Although halothane has been used for many years for smooth inhalational induction and good intubating conditions, it has been largely superseded by sevoflurane in the UK since the mid to late 1990s. The vast majority of publications in this subject have involved the inhalation of sevoflurane, using various approaches and combinations of other agents. A group of Japanese workers produced a series of studies, mostly in children, designed similar to those of Yakaitis, before sevoflurane became available in the UK. In the first of these, 36 children aged 1–9 yr were studied.40Inomata S Watanabe S Taguchi M Okada M End tidal sevoflurane concentration for tracheal intubation and minimum alveolar concentration in pediatric patients.Anesthesiology. 1994; 80: 93-96Crossref PubMed Scopus (122) Google Scholar If the patient coughed or made purposeful movement, they were given a bolus of thiopental or succinylcholine and excluded from the study, leaving 22 suitable patients. Each concentration at which laryngoscopy and tracheal intubation were attempted was predetermined with an up-and-down method, using 0.5% as a step size and a single measurement was obtained per patient. Laryngoscopy and intubation were attempted only after the ratio of alveolar to predetermined inspiratory concentration had been maintained at greater than 0.95 for 15 min. The calculated MACEI for sevoflurane was 2.7%, 30% above the MAC50 level of 2% for this age group, agreeing with the results from the halothane and enflurane studies by Yakaitis.94Yakaitis RW Blitt CD Anguilo JP End tidal halothane concentration for endotracheal intubation.Anesthesiology. 1977; 47: 386-388Crossref PubMed Scopus (60) Google Scholar, 95Yakaitis RW Blitt CD Anguilo JP End tidal enflurane concentration for endotracheal intubation.Anesthesiology. 1979; 50: 59-61Crossref PubMed Scopus (36) Google Scholar The same group of investigators then compared the MACEI with the MAC to prevent movement in 50% of patients undergoing laryngeal mask insertion. Forty-two children aged 1–9 yr were studied,85Taguchi M Watanabe S Asakura N Inomata S End tidal sevoflurane concentration for laryngeal mask airway insertion and for tracheal intubation in children.Anesthesiology. 1994; 81: 628-631Crossref PubMed Scopus (81) Google Scholar and the MACEI was similar to before, at 2.8%. Using this information, a study was designed to see how quickly, and at what optimal end-tidal concentration, the trachea could be intubated.39Inomata S Nishikawa T Determination of end tidal sevoflurane concentration for tracheal intubation with the rapid method.Can J Anesth. 1996; 43: 806-811Crossref PubMed Scopus (39) Google Scholar Twenty-nine children were studied, aged 2–8 yr. The breathing circuit was saturated with sevoflurane 5% and the children were allocated to seven predetermined end-tidal concentrations before induction, ranging from 1.5 to 4.5%, in 0.5% increments. The results showed that 80 and 100% of patients underwent smooth tracheal intubation at end-tidal concentrations of 4 and 4.5% respectively, and that the effective dose for 50% of the population (ED50, equivalent to the MACEI) was 3.1%. This is 0.3–0.4% higher than previously reported in a similar group of patients, presumably because of the difference in brain concentrations as a result of a shorter intubation time. The time taken to reach an end-tidal concentration of 4.5% and intubate averaged 210 s. However, numbers were small, ranging between two and eight patients in each group. The addition of nitrous oxide 33 and 66% has been shown to decrease the MACEI value in children aged 1–7 yr by 18 and 40%, from 2.7% with sevoflurane alone, to 2.2% and 1.6% respectively.84Swan DH Crawford MW Pua HL Stephens D Lerman J Additive contribution of nitrous oxide to sevoflurane minimum alveolar concentration for tracheal intubation in children.Anesthesiology. 1999; 91: 667-671Crossref PubMed Scopus (56) Google Scholar This is entirely predictable, considering the additive effect on MAC of nitrous oxide. Different inhalational agents have also been compared. In one study, O'Brien and colleagues67O'Brien K Kumar R Morton NS Sevoflurane compared with halothane for tracheal intubation in children.Br J Anaesth. 1998; 80: 452-455Crossref PubMed Scopus (36) Google Scholar studied 40 fit, healthy children, aged 3–10 yr in a double-blind randomized controlled trial. Patients were induced with either halothane and nitrous oxide 60%, or sevoflurane and nitrous oxide 60%. The concentrations of each potent inhalational agent were increased gradually to 5 and 8% respectively and the trachea was intubated when the pupils were small and central. The mean time to reach the clinical end-point for intubation was 200 s for the halothane group and 243 s for the sevoflurane group (P=0.015). Satisfactory intubating conditions, based on the Helbo-Hansen scoring system,35Helbo-Hansen S Ravlo O Trap-Anderson S The influence of alfentanil on the intubating conditions after priming with vecuronium.Acta Anaesthesiol Scand. 1988; 32: 41-44Crossref PubMed Scopus (59) Google Scholar were achieved in 19/20 patients in each group. In the sevoflurane group, however, only seven out of 20 patients had an ideal score, compared with 12 out of 20 patients in the halothane group. The time to tracheal intubation (TimeEI) using equipotent concentrations of sevoflurane (5%) and halothane (2.5%) has also been compared in 40 children aged 1–7 yr.41Inomata S Yamashita S Toyooka H Yaguchi Y Taguchi M Sato S Anaesthetic induction time for tracheal intubation using sevoflurane or halothane in children.Anaesthesia. 1998; 53: 440-445Crossref PubMed Scopus (21) Google Scholar Using the up and down method starting at 240 s, the TimeEI 50 and TimeEI 95 for the sevoflurane/halothane groups were 147 s/214 s and 194 s/255 s respectively, consistent with their relevant blood gas solubility. The success of these previous studies led researchers to determine if sevoflurane alone could achieve as rapid and effective intubating conditions as thiopental and succinylcholine. This would make it a potentially attractive technique to intubate the trachea for short procedures. Thwaites and colleagues studied 64 healthy children aged 3–10 yr,88Thwaites AJ Edmends S Tomlinson AA Kendall JB Smith I Double-blind comparison of sevoflurane vs propofol and succinylcholine for tracheal intubation in children.Br J Anaesth. 1999; 83: 410-414Crossref PubMed Scopus (21) Google Scholar undergoing tonsillectomy, receiving either sevoflurane 8% and nitrous oxide 66% in oxygen, or propofol 3–4 mg kg−1 and succinylcholine 2 mg kg−1. Both groups were intubated at 150 s by a blinded investigator. Although intubation was successful in all cases, excellent conditions were scored in only 55% of cases in the sevoflurane group, compared with 82% cases in the propofol/succinylcholine group. Using a technique from a previous study, sevoflurane 8% in nitrous oxide 60% was compared with propofol/succinylcholine (3 mg kg−1 and 1 mg kg−1) and propofol/alfentanil (3 mg kg−1 and 10 μg kg−1) in 120 children aged 3–12 yr.6Blair JM Hill DA Bali IM Fee JPH Tracheal intubating conditions after induction with sevoflurane 8% in children.Anaesthesia. 2000; 55: 774-778Crossref PubMed Scopus (35) Google Scholar Patients in the sevoflurane group were intubated after 3 min, whilst the other groups were intubated after 60 s. Acceptable conditions were found in 97.5, 87.5 and 52.5% respectively, prompting the authors to state that the sevoflurane technique is a satisfactory alternative to the gold standard of succinylcholine and propofol when intubating children in a non-urgent situation. The mean end-tidal concentration just before intubation was 4.2%. This agrees with the previously quoted studies that an end-tidal concentration of 2×MAC is required for successful intubation in almost all children. This would take approximately 3 min under normal circumstances when breathing these high concentrations of sevoflurane. Similar methods were used to determine the MACEI in adults, who seem to require much higher concentrations of volatile agent than children for the same effect.47Kimuru T Watanabe S Asakura N Inomata S Okada M Taguchi M Determination of end tidal sevoflurane concentration for tracheal intubation and minimum alveolar concentration in adults.Anesth Analg. 1994; 79: 378-381PubMed Google Scholar In 86 ASA I or II adult patients, the MACEI sevoflurane for 50% of the population was 4.5%. The authors account for this difference by the irritation and subsequent coughing caused by the cuff of adult tracheal tubes, and the fact that children have a relatively greater brain perfusion and quicker uptake. In another study, 20 healthy adult volunteers were anaesthetized on three separate occasions, using three different techniques:66Muzi M Robinson BJ Ebert TJ O'Brien TJ Induction of anesthesia and tracheal intubation with sevoflurane in adults.Anesthesiology. 1996; 85: 536-543Crossref PubMed Scopus (134) Google Scholar technique 1 was tracheal intubation after induction with sevoflurane 6–7% and nitrous oxide 66%; technique 2 was tracheal intubation after induction with sevoflurane 6–7% and oxygen 100%; and technique 3 was laryngeal mask insertion after induction with sevoflurane 6–7% and nitrous oxide 66%. The time to successful intubation was used as the end-point. The mean time in the sevoflurane/oxygen 100% group was 6.4 min, longer than that of the sevoflurane/nitrous oxide 66% group at 4.7 min. It can therefore be seen that even when breathing sevoflurane 8%, a significantly longer period of inhalation is required for adults. Sevoflurane 8% can be as satisfactory as neuromuscular blocking drugs for producing the necessary conditions for intubating the trachea, but cannot achieve the speed of onset of effect for rapid sequence intubation. Iamaroon studied 120 adult patients,38Iamaroon A Pitimana-aree S Prechawi C Anusit J Somcharoen K Caiyarroj O Endotracheal intubation with thiopental/succinylcholine or sevoflurane/nitrous oxide in adults: a comparative study.Anesth Analg. 2001; 92: 523-528Crossref PubMed Scopus (19) Google Scholar randomized into receiving thiopental 5 mg kg−1 and succinylcholine 1 mg kg−1, or sevoflurane 8% in nitrous oxide 66%. The succinylcholine group were intubated by a blinded investigator at 1 min and achieved almost 100% success rate with good or excellent conditions, whereas the sevoflurane group breathed 3 vital capacity breaths in a primed circuit followed by 4 min normal breathing to achieve almost the same results. To achieve a similar time profile to children, adults need to be premedicated. In one study, 24 healthy adult volunteers were anaesthetized on three separate occasions,65Muzi M Colinco MD Robinson BJ Ebert TJ The effects of premedication on inhaled induction of anesthesia with sevoflurane.Anesth Analg. 1997; 85: 1143-1148Crossref PubMed Google Scholar and premedicated with fentanyl (2.4 μg kg−1), midazolam (36 μg kg−1) or both drugs (B) using a quarter of the doses because of a previously described synergistic effect.4Ben Shlomo I abd-el-Kalim H Ezry J Midazolam acts synergistically with fentanyl for induction of anaesthesia.Br J Anaesth. 1990; 64: 45-47Crossref PubMed Scopus (121) Google Scholar Patients breathed sevoflurane 8% and nitrous oxide 66% in oxygen at time intervals varying between 2.5 and 6.5 min. Logistic regression analyses showed that good-quality intubating conditions could be achieved after 3.1 min and 2.5 min in the midazolam and combined groups respectively, several minutes shorter than in the fentanyl group. This is surprising, as it has been reported previously that midazolam and fentanyl have similar MAC sparing properties, but it may be that the synergistic effect mentioned previously was not evident here.4Ben Shlomo I abd-el-Kalim H Ezry J Midazolam acts synergistically with fentanyl for induction of anaesthesia.Br J Anaesth. 1990; 64: 45-47Crossref PubMed Scopus (121) Google Scholar The authors speculate that this inconsistency arises from the increased chest wall rigidity seen in the patients receiving fentanyl, leading to a reduced minute volume, and hence less delivery of anaesthetic to the alveoli. Katoh and colleagues44Katoh T Nakajima Y Moriwaki G et al.Sevoflurane requirements for tracheal intubation with and without fentanyl.Br J Anaesth. 1999; 82: 561-565Crossref PubMed Scopus (64) Google Scholar pretreated a group of 80 ASA I–II adults with fentanyl 1, 2 and 4 μg kg−1, given 4 min before intubation. This resulted in a markedly decreased MACEI of sevoflurane of 2.07, 1.45 and 1.37% respectively, compared with 3.55% without fentanyl. Similarly, the addition of remifentanil 1 μg kg−1 followed by an infusion of 0.25 μg kg−1 min−1 reduced the MACEI to 2%, the MACEI of 95% of the population being 3.2%.15Cros AM Lopez C Kandel T Sztark F Determination of sevoflurane alveolar concentration for tracheal intubation with remifentanil, and no muscle relaxant.Anaesthesia. 2000; 55: 965-969Crossref PubMed Scopus (43) Google Scholar Sevoflurane has a lower blood gas solubility and is less likely to cause cardiac depression or arrhythmias than halothane. This has made it an attractive alternative for use in the difficult airway. Several reports now exist of its successful use in predicted difficult intubations, including acute epiglottitis.30Gupta S Wilson JU Sevoflurane for inhalational induction in patients with anticipated difficult intubation.Acta Anaesthesiol Scand. 1998; 42: 1232Crossref PubMed Scopus (7) Google Scholar43Kandasamy R Sivalingam P Use of sevoflurane in difficult airways.Acta Anaesthiol Scand. 2000; 44: 627-629Crossref PubMed Scopus (46) Google Scholar56MacIntyre PA Ansari KA Sevoflurane for predicted difficult tracheal intubation.Eur J Anaesth. 1998; 15: 462-466Crossref PubMed Scopus (29) Google Scholar78Spalding M Ala-Koko TI The use of inhaled sevoflurane for endotracheal intubation in epiglottitis.Anesthesiology. 1998; 89: 1026Crossref Scopus (11) Google Scholar These patients have been managed in one of two ways: either by increasing the inspired concentration of sevoflurane in a stepwise way, or a high-concentration induction. There is disagreement among authors as to which technique actually produces the least amount of clinically significant side-effects, such as excitement, laryngospasm and coughing.89Thwaites AJ Smith I Sevoflurane for difficult tracheal intubation.Br J Anaesth. 1998; 81: 103-104Crossref PubMed Google Scholar Consensus appears to favour a stepwise approach either by increasing inspired concentrations by 1–2% quickly or by preoxygenation and starting at sevoflurane 8%, without priming the circuit first. Because of the relatively fast onset of sevoflurane, some authors advise caution with its use in difficult airways, noting that speed of induction may not be desirable in some circumstances because of increased risk of respiratory depression.8Board P Sevoflurane for difficult tracheal intubation.Br J Anaesth. 1998; 81: 14Crossref Scopus (5) Google Scholar18Davies MW Sevoflurane; a note of caution.Anaesthesia. 1996; 51: 1082Crossref Google Scholar32Hamill JF Bedford RF Weaver DC Colohan AR Lidocaine before endotracheal intubation: Intravenous or laryngotracheal.Anesthesiology. 1981; 55: 578-581Crossref PubMed Scopus (168) Google Scholar42Ip-Yam P.C Sevoflurane for difficult tracheal intubation.Br J Anaesth. 1998; 81: 104Crossref PubMed Scopus (3) Google Scholar Lidocaine has been reported to be a useful intravenous and topical adjunct to facilitate tracheal intubation, both on its own and with different short-acting opioids, in doses of 1–2 mg kg−1.10Bulow K Nielsen TG Lund J The effect of topical lignocaine on intubating conditions after propofol-alfentanil induction.Acta Anaesthesiol Scand. 1996; 40: 752-756Crossref PubMed Scopus (23) Google Scholar17Davidson JAH Gillespie JA Tracheal intubation after induction of anaesthesia with propofol, alfentanil and i.v. lignocaine.Br J Anaesth. 1993; 70: 163-166Crossref PubMed Scopus (78) Google Scholar25Grange CS Suresh D Meikle R Carter JA Goldhill DR Intubation with propofol: evaluation of pre-treatment with alfentanil or lignocaine.Eur J Anaesth. 1993; 10: 9-12PubMed Google Scholar37Hovorka J Honkavaara P Kortilla K Tracheal intubation after induction of anaesthesia with thiopentone or propofol without muscle relaxants.Acta Anaesthesiol Scand. 1991; 35: 326-328Crossref PubMed Scopus (47) Google Scholar64Mulholland D Carlisle RJT Intubation with propofol augmented with intravenous lignocaine.Anaesthesia. 1991; 46: 312-313Crossref PubMed Scopus (33) Google Scholar92Woods A Grant S Harten J Noble JS Davidson JAH Tracheal intubating conditions after induction with propofol, remifentanil and lignocaine.Eur J Anaesth. 1998; 16: 714-718Crossref Scopus (45) Google Scholar Mulholland and colleagues64Mulholland D Carlisle RJT Intubation with propofol augmented with intravenous lignocaine.Anaesthesia. 1991; 46: 312-313Crossref PubMed Scopus (33) Google Scholar found no statistically significant difference in intubating conditions when they compared two groups receiving propofol 2.5 mg kg−1 and either saline or lidocaine 1.5 mg kg−1, administered 1 min before attempted intubation. Thirty-three per cent of patients in the lidocaine group were deemed to have unsatisfactory or impossible intubating conditions compared with 52% in the saline group. This agrees with Grange,25Grange CS Suresh D Meikle R Carter JA Goldhill DR Intubation with propofol: evaluation of pre-treatment with alfentanil or lignocaine.Eur J Anaesth. 1993; 10: 9-12PubMed Google Scholar who also found pretreatment with lidocaine no better than saline. However, in doses of 1 mg kg−1, intravenous lidocaine has been shown to halve the dose of alfentanil or remifentanil needed to produce comparable intubating conditions.17Davidson JAH Gillespie JA Tracheal intubation after induction of anaesthesia with propofol, alfentanil and i.v. lignocaine.Br J Anaesth. 1993; 70: 163-166Crossref PubMed Scopus (78) Google Scholar, 92Woods A Grant S Harten J Noble JS Davidson JAH Tracheal intubating conditions after induction with propofol, remifentanil and lignocaine.Eur J Anaesth. 1998; 16: 714-718Crossref Scopus (45) Google Scholar Several papers have also examined the effectiveness of intravenous lidocaine to suppress the cough reflex.69Poulton TJ James FM Cough suppression by lidocaine.Anesthesiology. 1979; 50: 470-472Crossref PubMed Scopus (82) Google Scholar, 79Stenhause JE Gaskin L A study of intravenous lidocaine as a suppressant of cough reflex.Anesthesiology. 1963; 24: 285-290Crossref PubMed Scopus (85) Google Scholar Yukioka and colleagues96Yukioka H Yoshimoto N Nishimura K Fujimuri M Intravenous lidocaine as a suppressant of coughing during tracheal intubation.Anesth Analg. 1985; 64: 1189-1192Crossref PubMed Scopus (124) Google Scholar showed that the optimum dose to suppress the cough reflex completely was 2 mg kg−1 administered intravenously at 1 min before intubation. However, even though the authors did not report any patient with significant side-effects, they conclude that this dose may be associated with systemic toxicity, some patients having blood concentrations as high as 8 μg kg−1, as measured by gas chromatography from regular arterial sampling. Tracheal intubation causes a marked pressor response, raising the mean arterial pressure and mean heart rate significantly.77Shribman AJ Smith G Achola KJ Cardiovascular and catecholamine response to laryngoscopy with and without endotracheal intubation.Br J Anaesth. 1987; 59: 295-299Crossref PubMed Scopus (366) Google Scholar This may be potentially harmful in patients with cardiac disease or raised intracranial pressure, and may be exaggerated in both treated and untreated hypertensive patients.70Prys-Roberts C Greene LT Melloche R Foëx P Studies of anaesthesia in relation to hypertension. II: Haemodynamic consequences of induction and endotracheal intubation.Br J Anaesth. 1971; 43: 531-547Crossref PubMed Scopus (303) Google Scholar Lidocaine does not appear to alter this response. Miller and colleagues63Miller CD Warren SJ I.V. lignocaine fails to attenuate the cardiovascular response to laryngoscopy and tracheal intubation.Br J Anaesth. 1990; 65: 216-219Crossref PubMed Scopus (50) Google Scholar found no protective effect when 1.5 mg kg−1 was administered 3 min before laryngoscopy. Similar findings were seen in a study by Chraemmer-Jorgensen,11Chraemmer-Jorgenson B Hoilund-Carlsen PF Marving J Christensen V Lack of effect of intravenous lidocaine on haemodynamic responses to rapid sequence induction of general anesthesia.Anesth Analg. 1986; 65: 1037-1041PubMed Google Scholar using the same dose given 2 min before laryngoscopy. The addition of laryngotracheal lidocaine seems to be more successful in facilitating tracheal intubation. Bulow and colleagues10Bulow K Nielsen TG Lund J The effect of topical lignocaine on intubating conditions after propofol-alfentanil induction.Acta Anaesthesiol Scand. 1996; 40: 752-756Crossref PubMed Scopus (23) Google Scholar used propofol 2.5 mg kg−1 and alfentanil 30 μg kg−1, and then sprayed the vocal cords with lidocaine 160 mg 90 s before intubation. Satisfactory conditions were obtained in all 27 patients in this group compared with 73% in the saline group. But laryngotracheal administered lidocaine does not alter this pressor response to laryngoscopy and tracheal intubation.32Hamill JF Bedford RF Weaver DC Colohan AR Lidocaine before endotracheal intubation: Intravenous or laryngotracheal.Anesthesiology. 1981; 55: 578-581Crossref PubMed Scopus (168) Google Scholar, 51Laurito CE Bangham VL Becker GL Polek WV Reigler FX Vadenboncouer TR Effects of aerosolised and/or intravenous lidocaine on haemodynamic responses to laryngoscopy and intubation in out-patients.Anesth Analg. 1988; 67: 389-392Crossref PubMed Scopus (42) Google Scholar Thiopental has been used as the sole agent to facilitate tracheal intubation.54Lewis CB Endotracheal intubation under thiopentone.Anaesthesia. 1948; 3: 113Crossref PubMed Scopus (15) Google Scholar In 1948, Lewis described a series of 200 patients who received either a blind nasal, or direct oral intubation after thiopental 500–750 mg.54Lewis CB Endotracheal intubation under thiopentone.Anaesthesia. 1948; 3: 113Crossref PubMed Scopus (15) Google Scholar There were two failures in the blind nasal group and six in the direct laryngoscopy group. Lewis encountered severe problems with coughing, although the quality of overall intubating conditions was not specified as no scoring systems were used. This study merely highlights that any hypnotic, if given in significant doses, will provide enough obtundation to facilitate tracheal intubation. Propofol provides better jaw relaxation and attenuation of laryngeal reflexes than thiopental.61McKeating K Bali IM Dundee JW The effects of thiopentone and propofol on upper airway integrity.Anaesthesia. 1988; 43: 638-640Crossref PubMed Scopus (213) Google Scholar When used alone for tracheal intubation, propofol 2.5 mg kg−1 provided satisfactory conditions in 19/20 (96%) patients and ideal intubating conditions in 14/20 (60%) patients.45Keaveny JP Knell PJ Intubation under induction doses of propofol.Anaesthesia. 1988; 43: 80-81Crossref PubMed Scopus (76) Google Scholar These patients were premedicated with diazepam 10 mg and droperidol 5 mg, and therefore the results may be better than expected. This contrasts with Mulholland and Carlisle,64Mulholland D Carlisle RJT Intubation with propofol augmented with intravenous lignocaine.Anaesthesia. 1991; 46: 312-313Crossref PubMed Scopus (33) Google Scholar who found that 56% of patients had unsatisfactory conditions with the same dose of propofol. However, the method and standard end-points for quality of tracheal intubation vary in these two studies. Three opioid drugs h