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Canadian Journal of Anesthesia 48:919-923 (2001)
© Canadian Anesthesiologists' Society, 2001
Cardiothoracic Anesthesia, Respiration and Airway

Use of the fibreoptic stylet scope (StyletscopeTM) reduces the hemodynamic response to intubation in normotensive and hypertensive patients

[L'utilisation d'un stylet fibroscopique (StyletscopeTM) réduit la réponse hémodynamique à l'intubation chez les patients normotendus et hypertendus]

Akira Kimura, MD, Michiaki Yamakage, MD, PhD, Xiangdong Chen, MD, Yasuhiro Kamada, MD and Akiyoshi Namiki, MD, PhD

From the Department of Anesthesiology, Sapporo Medical University School of Medicine, Sapporo, Hokkaido, Japan.

Address correspondence to: Dr. Michiaki Yamakage, Department of Anesthesiology Sapporo Medical University School of Medicine South 1, West 16, Chuo-ku, Sapporo, Hokkaido 060-8543, Japan. Phone: 81-11-611-2111, ext. 3568; Fax: 81-11-631-9683; E-mail: yamakage{at}sapmed.ac.jp


   Abstract
TOP
 Abstract
Introduction
 Methods
 Results
 Discussion
 References
 
Purpose: To compare hemodynamic changes after tracheal intubation when using a new fibreoptic stylet scope (StyletscopeTM) and a conventional laryngoscope in normotensive and hypertensive patients.

Methods: Normotensive (N; n=30) and hypertensive (H; n=30) patients undergoing general anesthesia participated in this study. Each group was divided into two groups. In one group, patients were intubated by using a stylet scope with a laryngoscope as an adjuvant (S; n=15 each), while patients in the other group were intubated using a laryngoscope by the usual technique (L; n=15 each). The time necessary for intubation, hemodynamic changes, and adverse effects were recorded.

Results: Patients in the normotensive groups (SN and LN groups) showed significant increases in both systolic and diastolic blood pressures from before induction to one minute after intubation; however, blood pressures in the SN group were significantly lower than those in the LN group. Both systolic and diastolic blood pressures increased after intubation in the LH group, but not in the SH group. Heart rates in all four groups showed significant increases, and there were no differences between heart rates in the stylet scope and laryngoscope groups or between the normotensive and hypertensive groups. The number of patients who complained of sore throat was greater in the laryngoscope groups.

Conclusions: Tracheal intubation with a stylet scope can attenuate hemodynamic changes and reduce the incidence of sore throat in comparison with the conventional laryngoscope technique in both normotensive and hypertensive patients.


   Introduction
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 Abstract
 Introduction
Methods
 Results
 Discussion
 References
 
CONVENTIONALLY, tracheal intubation is performed under direct vision by using a laryngoscope. Tracheal intubation using this technique is, however, often associated with an increase in blood pressure and heart rate,1,2 which may be severe in hypertensive patients.3 These changes greatly increase the risk of myocardial infarction or stroke, especially in elderly patients with hypertension.4–6 Kitamura et al.7,8 have recently described a new fibreoptic stylet scope (StyletscopeTM; Nihon Kohden, Tokyo, Japan, Figure 1AGo), for tracheal intubation. The stylet scope has the shape of a standard stylet, with the addition of a fibreoptic view and manoeuverability at its tip (Figure 1AGo). It was originally designed as an alternative to failed or difficult tracheal intubation. Since only elevation of the tongue is required for tracheal intubation when using the stylet scope with a laryngoscope as an adjuvant,7 it is expected that the use of this device can attenuate precipitous hemodynamic changes, especially in hypertensive patients. This study was undertaken to evaluate hemodynamic changes after tracheal intubation using the stylet scope and a Macintosh laryngoscope in normotensive and hypertensive patients.



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  		FIGURE 1 The new fibreoptic stylet scope, StyletscopeTM. A, By depressing the lever of the proximal handle, the distal tip of the stylet, together with the endotracheal tube, can be flexed 90. B, After lifting the tongue lightly using a standard laryngoscope blade, tracheal intubation is performed with the glottic opening viewed only via the stylet scope.

 

   Methods
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 Abstract
 Introduction
 Methods
Results
 Discussion
 References
 
After obtaining Institutional approval and informed consent from each patient, 30 normotensive patients (ASA physical status I) and 30 hypertensive patients (ASA physical status II) scheduled for elective surgery under general anesthesia were enrolled in this study. Patients with one of the following conditions were excluded: pulmonary disease, a history of previous difficult intubation, cervical spine fracture, and tumours or polyps of the upper airway. Hypertension was diagnosed if systolic blood pressure was >160 mmHg and/or diastolic blood pressure >95 mmHg (as defined by the World Health Organization). All hypertensive patients were already receiving oral medication consisting of a calcium antagonist (nifedipine, benidipine and/or amlodipine) and received their medication six hours before induction of anesthesia. Normotensive and hypertensive patients were randomly (by flipping a coin) assigned to one of the following groups: 1) patients with hypertension intubated by using a stylet scope with a laryngoscope as an adjuvant (SH group, n=15); 2) patients without hypertension intubated by using a stylet scope with a laryngoscope as an adjuvant (SN group, n=15); 3) patients with hypertension intubated by using a laryngoscope (LH group, n=15); and 4) patients without hypertension intubated by using a laryngoscope (LN group, n=15).

Patients were premedicated with 1.0 mg•kg–1 pentobarbitone po and 0.01 mg•kg–1 atropine im 30 min before the induction of anesthesia. Anesthesia was induced with 2.0 µg•kg–1 fentanyl iv, followed by 4 mg•kg–1 thiamylal iv one minute later. Vecuronium, 0.15 mg•kg–1 iv, was given after loss of consciousness, and the lungs were ventilated via a mask with 4 L•min–1 N2O, 2 L•min–1 O2, and 5% sevoflurane. The trachea was then intubated orally by using either a stylet scope with a laryngoscope as an adjuvant or a Macintosh laryngoscope (blade #2) three minutes after the administration of vecuronium. In the SN and SH groups, the tongue was lifted gently by the laryngoscope blade, and the epiglottis and vocal cords were viewed only through the stylet scope (Figure 1BGo).

All intubations were performed by a single investigator well experienced in using a stylet scope and laryngoscope. Only one attempt at intubation was allowed for both techniques, and it was decided to exclude cases in which initial tracheal intubation was not successful from the study. The duration of tracheal intubation, that is, the time from the introduction of the device into the oral cavity until its removal, was recorded. Blood pressure and heart rate were recorded at the following time points: 1) before the administration of fentanyl (control), 2) two minutes after the administration of vecuronium (before intubation), 3) immediately after tracheal intubation, and 4) one, two, three, four, and five minutes after tracheal intubation. All patients were asked about sore throat and hoarseness of voice on the following day.

Data are expressed as numbers, means or means ± SD. Hemodynamic changes during intubation were analyzed using one-way ANOVA for repeated measurements with Fisher's test or unpaired two-tailed t test. Postoperative complications were analyzed using the 2 test. In all comparisons, P <0.05 was considered significant.


   Results
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 Abstract
 Introduction
 Methods
 Results
Discussion
 References
 
All four groups were comparable with respect to gender, age, weight, height, and heart rate (Table IGo). Blood pressures in the hypertensive groups (SH and LH groups) were significantly higher than those in the normotensive groups (SN and LN groups) before the induction of anesthesia. There was no case in which more than one attempt was needed to intubate the trachea.


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  		TABLE I Demographic characteristics of the subjects
 
Hemodynamic changes after tracheal intubation in normotensive and hypertensive groups are shown in Figure 2Go. Patients in both the stylet scope and laryngoscope groups showed significant decreases in blood pressure after anesthetic induction and maximum increases in blood pressure one minute after tracheal intubation. The heart rate did not decrease following anesthetic induction, and it increased after tracheal intubation, peaking at one minute after tracheal intubation. When comparing hemodynamic changes from "before intubation" to "one minute after intubation," patients in the normotensive groups (both SN and LN groups) showed significant increases in both systolic and diastolic blood pressures. However, blood pressures in the SN group were significantly lower than those in the LN group. Similarly, patients in the LH group showed significant increases in both systolic and diastolic blood pressures, but these values did not change in the SH group. Heart rates in all four groups showed significant increases, and there were no significant differences between heart rates in the stylet scope and laryngoscope groups or between normotensive and hypertensive groups.



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  		FIGURE 2 Hemodynamic changes after tracheal intubation in normotensive (SN and LN groups, left panel) and hypertensive (SH and LH groups, right panel) patients. All values are expressed as means. B, baseline; BI, before induction; AI, immediately after intubation; one, two, three, four, and five, number of minutes after intubation. *P <0.05 compared with baseline values.

 
The number of patients who complained of sore throat was greater in the laryngoscope groups, although no differences were found in the incidence of hoarseness of voice (Table IIGo).


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  		TABLE II Duration of intubation and complications
 

   Discussion
TOP
 Abstract
 Introduction
 Methods
 Results
 Discussion
References
 
One of the main findings of this study is that there were smaller changes in blood pressure after tracheal intubation using a stylet scope than there were using conventional laryngoscopy in both normotensive and hypertensive patients. Orotracheal intubation with a laryngoscope requires elevation of the epiglottis and exposure of the glottis by lifting of the laryngoscope blade forward and upward. These procedures are associated with hemodynamic changes.1–3 One of the reasons for the smaller hemodynamic changes following tracheal intubation using a stylet scope was, probably, less stimulus to the perilaryngeal area. Similar investigations using a lightwand (TrachlightTM, Laerdal Medical, Armonk, NY, USA) technique have been conducted,9,10 since this method of intubation requires neither elevation of the epiglottis by the laryngoscope blade nor exposure of the glottic opening. However, both Hirabayashi et al.9 and Nishikawa et al.10 found that the circulatory responses to tracheal intubation were similar to those of direct-vision laryngoscopy. Hirabayashi et al.9 used a jaw-lifting technique for lightwand intubation, and they speculated that the magnitude of this stimulus was sufficient to cause a circulatory response.9 Nishikawa et al.10 required significantly more time for intubation and a greater number of attempts at intubation using the lightwand technique, compared to laryngoscopy. The technique employed in our study required only a short period of time and no jaw lifting for intubation. Heart rates in all four groups showed significant increases; however, there were no differences between groups. It is possible that premedication with atropine may have affected our results in this respect.

Another finding of this study is that the number of patients who complained of sore throat was greater in the laryngoscope group, although no differences were found in the incidence of hoarseness of voice. One of the reasons for the reduced frequency of sore throat in the stylet scope group might be the lack of direct stimuli to the mouth and the larynx. Nishikawa et al.10 reported that the number of patients who complained of hoarseness after tracheal intubation using the lightwand technique was greater than that after intubation using direct laryngoscopy. If the tip of the lightwand does not enter the trachea directly, an intense stimulus is applied to the upper airway,11 which may injure the vocal cords as well as the perilaryngeal tissue. It would therefore be an advantage to intubate the trachea under direct vision of the vocal cords through a stylet scope.

In conclusion, tracheal intubation using a stylet scope (with a laryngoscope as an adjuvant) can attenuate hemodynamic responses and reduce the incidence of sore throat in comparison with conventional laryngoscopy both in normotensive and hypertensive patients.


   Footnotes
 
Supported in part by an incentive grant (No. III-27, 2000) for research from the Uehara Memorial Foundation, Tokyo, Japan.

Revision received July 9, 2001. Accepted for publication May 16, 2001.


   References
TOP
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 
1 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]

2 Nishikawa T, Namiki A. Attenuation of the pressor response to laryngoscopy and tracheal intubation with intravenous verapamil. Acta Anaesthesiol Scand 1989; 33: 232–5.[Medline]

3 Prys-Roberts C, Greene LT, Meloche R, Foëx P. Studies of anaesthesia in relation to hypertension II: haemodynamic consequences of induction and endotracheal intubation. Br J Anaesth 1971; 43: 531–47.[Abstract/Free Full Text]

4 Omote K, Kirita A, Namiki A, Iwasaki H. Effects of nicardipine on the circulatory responses to tracheal intubation in normotensive and hypertensive patients. Anaesthesia 1992; 47: 24–7.[Medline]

5 Fujii Y, Tanaka H, Saitoh Y, Toyooka H. Effects of calcium channel blockers on circulatory response to tracheal intubation in hypertensive patients: nicardipine versus diltiazem. Can J Anaesth 1995; 42: 785–8.[Abstract/Free Full Text]

6 Goldman L, Caldera DL. Risks of general anesthesia and elective operation in the hypertensive patient. Anesthesiology 1979; 50: 285–92.[Medline]

7 Kitamura T, Yamada Y, Du H-L, Hanaoka K. Efficiency of a new fiberoptic stylet scope in tracheal intubation. Anesthesiology 1999; 91: 1628–32.[Medline]

8 Kitamura T, Yamada Y, Du LH, Hanaoka K. An efficient technique for tracheal intubation using the Styletscope alone (Letter). Anesthesiology 2000; 92: 1210–1.[Medline]

9 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]

10 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]

11 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.[Medline]




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This Article
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