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Anesth Analg 2002;95:480-484 © 2002 International Anesthesia Research Society
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Abstract |
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Lightwand devices are effective and safe as an aid to tracheal intubation. Theoretically, avoiding direct-vision laryngoscopy could allow for less stimulation by intubation than the conventional laryngoscopic procedure. We designed this prospective randomized study to assess the cardiovascular changes after either lightwand or direct laryngoscopic tracheal intubation in adult patients anesthetized with sevoflurane. Sixty healthy adult patients with normal airways were randomly assigned to one of three groups according to intubating procedure under sevoflurane/nitrous oxide anesthesia (fraction of inspired oxygen = 0.33) (n = 20 each). The lightwand group received tracheal intubation with Trachlight®, the laryngoscope-intubation group received tracheal intubation with a direct-vision laryngoscope (Macintosh blade), and the laryngoscopy-alone group received the laryngoscope alone. Heart rate and systolic blood pressure were recorded continuously for 5 min after tracheal intubation or laryngoscopy with enough time to intubate. All procedures were successful on the first attempt. The maximum heart rate and systolic blood pressure values obtained after intubation with Trachlight (114 ± 20 bpm and 143 ± 30 mm Hg, respectively) did not differ from those with the Macintosh laryngoscope (114 ± 20 bpm and 138 ± 23 mm Hg), but they were significantly larger than those in the laryngoscopy-alone group (94 ± 19 bpm and 112 ± 21 mm Hg) (P < 0.05). Direct stimulation of the trachea appears to be a major cause of the hemodynamic changes associated with tracheal intubation.
IMPLICATIONS: The magnitude of hemodynamic changes associated with tracheal intubation with the Trachlight® is almost the same as that which occurs with the direct laryngoscope. Hemodynamic changes are likely to occur because of direct tracheal irritation rather than direct stimulation of the larynx.
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Introduction |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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The lightwand intubating device is effective and safe as an aid to tracheal intubation (1–3). Use of the lightwand to intubate the tracheal tube may cause less adrenergic stimulation because elevation of the epiglottis by the laryngoscope blade is not required. However, whether the hemodynamic responses to intubation with the lightwand differ from those with direct laryngoscope is controversial (4–7). This study was designed to determine the differences in hemodynamic responses to intubation between the lightwand technique and direct laryngoscopy in sevoflurane-anesthetized adults with normal airways. The effects of direct tracheal stimulation on changes in hemodynamic variables such as heart rate (HR) and blood pressure (BP) were our special interests. To differentiate the hemodynamic effects between direct laryngoscopy and lightwand intubation, a group in which patients underwent direct laryngoscopy alone, without tracheal intubation, was included in this study.
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Methods |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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After obtaining approval from our institutional research committee and informed consent from each patient, we studied 60 nonpregnant ASA physical status I adult patients scheduled to undergo general anesthesia for elective surgeries. Patients with hypertension, cardiovascular disease, or arteriosclerosis were excluded from the study. Also excluded were those who had a history of gastroesophageal reflux, those <16 yr or >70 yr old, and those with a known history of a previous difficult tracheal intubation.
After fasting for 8–10 h, all patients received ranitidine 150 mg orally 90 min before the induction of general anesthesia. Patients were randomly assigned according to computer-generated random numbers into one of the following three groups: lightwand (Trachlight®; Laerdal Medical, Armonk, NY) (8) intubation group (LWI group; n = 20), direct laryngoscope (Macintosh blade) intubation group (LSI group; n = 20), and direct laryngoscopy (Macintosh blade)-alone group (LSA group; n = 20). The anesthetic technique was standardized as follows: on arrival in the operating room, patients received standard anesthetic monitors, including electrocardiogram (lead II), noninvasive BP cuff, and pulse oximeter (AS3; Datex Instrumentarium, Helsinki, Finland). Then an arterial cannula was placed into a radial artery under adequate local anesthesia for subsequent BP measurement. Lactated Ringer’s solution was administered and maintained at a constant rate of approximately 15 mL · kg-1 · h-1 throughout the study period. General anesthesia was induced with thiopental 5 mg/kg IV, followed by vecuronium 0.2 mg/kg IV. The patients’ lungs were ventilated for approximately 5 min via face mask with 5% sevoflurane and 67% nitrous oxide in oxygen.
After the optimal end-tidal sevoflurane concentration (approximately 3.5%) was obtained, the trachea was intubated orally with either the Trachlight (LWI group) or the Macintosh laryngoscope (LSI group). The patients in the LSA group underwent direct laryngoscopy for a period adequate to intubate, without intubation, under direct visualization of the vocal cords. The laryngoscopes used were the No. 3 or 4 Macintosh blade (Igarashi, Tokyo, Japan) for female patients and the No. 4 or 5 Macintosh blade for male patients. Tracheal tubes (SIMS Portex, Inc., Keene, NH) with an internal diameter of 7 mm were used for female patients and 8 mm for male patients. The cuff of the tracheal tube was inflated immediately with air after intubation so it would not leak at a peak airway pressure of 20 cm H2O. The duration of each attempt was recorded as the interval from the time the device was inserted (Trachlight or laryngoscope) into the oropharynx to the time when the device was removed from the oral cavity. Failure to intubate was defined as the inability to place the tracheal tube into the trachea or to visualize the vocal cords in the LSA group on the first attempt. Patients in whom there was failure to intubate and those requiring more than 30 s to achieve tracheal intubation were excluded from this study. Anesthesia was maintained with 3% sevoflurane and 66% nitrous oxide in oxygen for 5 min. The patients’ lungs were ventilated with a tidal volume of 10 mL/kg and a respiratory rate of 10–12 breaths/min to maintain end-tidal carbon dioxide tension (PETCO2) at 35–40 mm Hg in all the groups. Systolic BP (SBP) and HR were recorded at the time immediately before either device insertion, at the time when the trachea was just intubated, and every 20 s after intubation or laryngoscopy in the LSA group for 5 min. Maximum SBP and HR values and the times when these values were obtained were determined. All intubating procedures were performed by a single investigator (ST) experienced in using the Trachlight and laryngoscope.
As a power analysis based on a previous article (6) revealed, a sample size of 20 patients per group was required to achieve a power of 80% and an 
of 0.05 for detection of 20-bpm or 20 mm Hg differences in paired hemodynamic data. All data are expressed as mean ± SD. Statistical analysis consisted of analysis of variance with Bonferroni’s correction to detect differences in patients’ demographic data and hemodynamic data among the three groups. Pairwise hemodynamic data in each group were analyzed by using repeated-measures analysis of variance, followed by paired Student’s t-tests with Bonferroni’s correction. A P value of <0.05 was considered the minimal level of statistical significance.
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Results |
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There were no significant differences among the three groups in terms of age, weight, or height (Table 1). No significant differences in HR or BP values before anesthetic induction and insertion of the device were seen among the groups. Baseline BP values immediately before the insertion of the device were significantly lower than the preinduction values in every group (P < 0.01). The time necessary to place a tracheal tube or to perform laryngoscopy did not differ among the groups (Table 2). No patient was excluded from analysis according to the exclusion criteria mentioned previously. All the groups responded to both laryngoscopy and lightwand insertion with significant increases in HR and SBP from baseline values. The maximum increases in HR and SBP in the LWI and LSI groups were larger than those obtained in the LSA group. There were no significant differences in maximum increases in HR and SBP between the LWI group and the LSI group (Table 2).
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The HR changes were monophasic, and significant increases from the baseline value were observed within 0–180 s, 0–220 s, and 0–100 s in the LWI, LSI, and LSA groups, respectively (Fig. 1). Moreover, HR values significantly decreased from the baseline value at 300 s and 240–300 s after insertion of the devices in the LWI and LSA groups. There were significant differences in the HR changes after insertion of the devices between the intubated groups (LWI and LSI) and the LSA group (Table 2).
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), and laryngoscopy alone (LSA) group (
) (n = 20 each). Preinduction values were obtained before thiopental injection. Preinsertion values were obtained just before the device insertion. Time (s) = seconds after intubation or laryngoscopy. Data are mean ± SD. *P < 0.05 versus the preinsertion value.The SBP changes were monophasic, and significant increases from baseline value were observed within 0–300 s, 0–280 s, and 0–260 s in the LWI, LSI, and LSA groups, respectively (Fig. 2). There were significant differences in the HR changes after insertion of the devices between the intubated groups (LWI and LSI) and the LSA group (Table 2).
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Arterial oxygen saturation measured by pulse oximeter was
98% in all patients during the entire course of the study. PETCO2 values immediately before the insertion of a device were 31 ± 3 mm Hg, 32 ± 3 mm Hg, and 33 ± 3 mm Hg in the LWI, LSI, and LSA groups, respectively. End-tidal sevoflurane concentrations immediately before the insertion of a device were 3.3% ± 0.3%, 3.3% ± 0.3%, and 3.4% ± 0.2% in the LWI, LSI, and LSA groups, respectively. The numbers of the patients who developed decreases in HR from the baseline values in response to insertion of the devices were 0, 1, and 2 in the LWI, LSI, and LSA groups, respectively. None of the patients developed severe bradycardia (HR 
45 bpm) or severe hypotension (SBP 60 mm Hg) during the observation period. |
Discussion |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Our study clearly showed that cardiovascular responses to intubation with a lightwand did not differ from those with a laryngoscope. This is the first report comparing the differences in hemodynamic responses between lightwand intubation and direct laryngoscopy alone. The results of this study demonstrate that direct stimulation by a tracheal tube induces greater cardiovascular responses than stimulation by laryngoscopy. It is likely that the circulatory response to tracheal intubation with a direct laryngoscope is mainly due to stimulation of the trachea, rather than stimulation of the glottis by the laryngoscope.
The use of a lightwand, in comparison with the use of a rigid laryngoscope, has resulted in a less frequent incidence and severity of sore throat, hoarseness, and dysphasia after surgery (1,2,5). Therefore, we assumed that use of the Trachlight, which does not require a laryngoscope to elevate the epiglottis, would attenuate the cardiovascular responses to tracheal intubation. Hirabayashi et al. (6) studied the effects of the lightwand technique on circulatory responses to tracheal intubation in adult patients. Preanesthetic medication consisted of atropine (0.5 mg) and hydroxyzine (50 mg) IM. Forty patients (22–77 yr old, ASA status I–II) received propofol, lidocaine, and vecuronium, and their lungs were ventilated for three minutes via a face mask with 5% sevoflurane in oxygen. BPs were continuously measured by a catheter in a radial artery. Neither maximum mean arterial BP changes nor HR changes after tracheal intubation differed between the Trachlight group and the laryngoscope group (46 mm Hg and 18 bpm vs 44 mm Hg and 23 bpm, respectively). These results are in accordance with our study. However, their study did not demonstrate the difference in the duration of significant increases in HR in response to tracheal intubation between the Trachlight and laryngoscope. Also, the hemodynamic response to bronchoscopy alone was not examined.
However, Nishikawa et al. (4) showed that the lightwand technique attenuated hemodynamic changes after intubation in comparison with the laryngoscopic technique. The authors studied 40 normotensive patients (52.3 yr old in mean age, ASA status I) premedicated with atropine (0.01 mg/kg) and midazolam (0.05 mg/kg). Anesthesia was induced with 2 µg/kg of fentanyl, followed by 2 mg/kg of propofol three minutes later. The lungs were ventilated via face mask with 100% oxygen until the insertion of the devices two minutes after the administration of 0.15 mg/kg of vecuronium. The HR and BP were measured at one-minute intervals. Although the lightwand technique needed significantly more frequent attempts and a longer duration for intubation than the laryngoscopic technique, the lightwand technique was accompanied by smaller increases in SBP after tracheal intubation than the laryngoscopic technique. In their study, 2 µg/kg of fentanyl was administered before tracheal intubation. Previous studies (9–11) showed that fentanyl could attenuate the hemodynamic responses associated with tracheal intubation. Accordingly, the differences in anesthetic technique might affect the hemodynamic responses to tracheal intubation. In addition, the method of recording hemodynamic variables, i.e., intermittent measurement, in the study by Nishikawa et al. (4) could miss the maximum changes.
In this study, there were significant differences between cardiovascular responses to laryngoscopy with intubation and those without intubation. In contrast, Shribman et al. (12) reported that in 24 adult patients anesthetized with fentanyl 0.1 mg, thiopental 3–4 mg/kg, and 67% nitrous oxide, there were significant and similar increases in arterial BP and circulating catecholamine concentrations after laryngoscopy with and without intubation. However, intubation was associated with significant increases in HR; this did not occur in the laryngoscopy-alone group in their study. Also, SBP and diastolic BP were increased in the intubation groups at one and two minutes after laryngoscopy, although the increases were statistically insignificant. Possibly, therefore, a relatively small number in sample size might cause a ß error statistically. In addition, intermittent BP measurement might miss the maximum changes.
Maximum increases in the SBP values and the duration of significant increases from the baseline value after insertion of the devices did not differ between the LWI and LSI groups, although there were significant differences in maximum increases in SBP values compared with the LSA group. However, although the maximum HR increases after the insertion of the devices did not differ between the LWI and LSI groups, the duration of significant increases in HR from baseline values in the LSI group was longer than that in the LWI group. This result indicates that combined stimulation of the larynx and the trachea in the LSI group was more intense than stimulation of the trachea alone in the LWI group, although there was no difference in the maximum HR increase between the groups in this study.
The anesthetic methods using thiopental and sevoflurane in this study were selected according to our usual procedure. Approximately five minutes after inhalation of sevoflurane, the concentration of end-tidal sevoflurane was 3.5%, which is the sevoflurane requirement for achieving a 50% probability of no movement in response to laryngoscopy and tracheal intubation (13). Prolonged intubation time induces hypercarbia and decreasing anesthetic gas concentration, resulting in hypertension and tachycardia (14). There were no significant differences in the time necessary to intubate or to perform laryngoscopy among the groups in this study. Therefore, we believe that the data regarding hemodynamic variables were comparable.
Possible limitations of this study deserve mention. First, we conducted our study on patients with normal airways and no cardiac disease. A longer duration of intubation in difficult airways may produce different responses between the Trachlight and direct laryngoscope. Perhaps hemodynamic responses to intubation with these devices may be different in hypertensive patients. Second, we used the patients who were successfully intubated on the first attempt to clarify the effects of devices. Therefore, we could not observe the differences in hemodynamic changes in case of repeated trials. Third, although patients were randomly assigned into the groups, double-blinding to observe hemodynamic changes could not be used in this study. Fourth, we did not assess the postanesthetic complications associated with the lightwand and laryngoscope. Therefore, the severity of stimulation of the laryngeal tissue was not correctly compared with that of other studies.
We conclude that hemodynamic responses to tracheal intubation with the Trachlight do not differ from those with a direct laryngoscope under sevoflurane anesthesia. It is likely that direct stimulation of the trachea by a tracheal tube has a major role in causing the cardiovascular responses to tracheal intubation in sevoflurane-anesthetized patients.
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References |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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- Hung OR, Pytka S, Morris I, et al. Clinical trial of a new lightwand device (Trachlight) to intubate the trachea. Anesthesiology 1995; 83: 509–14.[Web of Science][Medline]
- Hung OR, Pytka S, Morris I, et al. Lightwand intubation. II. Clinical trial of a new lightwand for tracheal intubation in patients with difficult airway. Can J Anaesth 1995; 42: 826–30.[Web of Science][Medline]
- Ellis DG, Stewart RD, Kaplan RM, et al. Success rates of blind orotracheal intubation using a transillumination technique with a light stylet. Ann Emerg Med 1986; 15: 138–42.[Web of Science][Medline]
- Nishikawa K, Omote K, Kawana S, Namiki A. A comparison of hemodynamic changes after endotracheal intubation by using the lightwand device and the laryngoscope in normotensive and hypertensive patients. Anesth Analg 2000; 90: 1203–7.
[Abstract/Free Full Text] - Friedman PG, Rosenberg MK, Lebenbom-Mansour M. A comparison of lightwand and suspension laryngoscopic intubation techniques in outpatients. Anesth Analg 1997; 85: 578–82.[Abstract]
- Hirabayashi Y, Hiruta M, Kawakami T, et al. Effects of lightwand (Trachlight) compared with direct laryngoscopy on circulatory responses to tracheal intubation. Br J Anaesth 1998; 81: 253–5.
[Abstract/Free Full Text] - Knight RG, Castro T, Rastrelli AJ, et al. Arterial blood pressure and heart rate response to light stylet or direct laryngoscopy for endotracheal intubation. Anesthesiology 1988; 69: 269–72.[Web of Science][Medline]
- Agro F, Hung OR, Cataldo R, et al. Lightwand intubation using the Trachlight: a brief review of current knowledge. Can J Anaesth 2001; 48: 592–9.[Web of Science][Medline]
- Dahlgren N, Messeter K. Treatment of stress response to laryngoscopy and intubation with fentanyl. Anaesthesia 1981; 36: 1022–6.[Web of Science][Medline]
- Martin DE, Rosenberg H, Aukburg SJ, et al. Low-dose fentanyl blunts circulatory responses to tracheal intubation. Anesth Analg 1982; 61: 680–4.
[Abstract/Free Full Text] - Ko SH, Kim DC, Han YJ, Song HS. Small-dose fentanyl: optimal time of injection for blunting the circulatory responses to tracheal intubation. Anesth Analg 1998; 86: 658–61.[Abstract]
- Shribman AJ, Smith G, Achola KJ. Cardiovascular and catecholamine responses to laryngoscopy with and without tracheal intubation. Br J Anaesth 1987; 59: 295–9.
[Abstract/Free Full Text] - Kato T, Nakajima Y, Moriwaki G, et al. Sevoflurane requirements for tracheal intubation with and without fentanyl. Br J Anaesth 1999; 82: 561–5.
[Abstract/Free Full Text] - Stoelting RK. Circulatory changes during direct laryngoscopy and tracheal intubation: influence of duration of laryngoscopy with or without prior lidocaine. Anesthesiology 1977; 47: 381–3.[Web of Science][Medline]
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