1Surgical Center, The Institute of Medical Science, The University of Tokyo, 4-6-1 Shirokane-dai, Minato-ku, Tokyo 108-8639, Japan. 2Surgical Center and 3Department of Anesthesiology, Faculty of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8655, Japan*Corresponding author: Department of Anesthesiology, The University of Tokyo Branch Hospital, 3-28-6 Mejiro-dai, Bunkyo-ku, Tokyo 112-8688, Japan
Accepted for publication: October 1, 2000
Abstract
Tracheal intubation often causes a haemodynamic response probably generated by direct laryngoscopy. The StyletScope is a new intubation device that does not require direct laryngoscopy. We prospectively measured haemodynamic changes after tracheal intubation using the StyletScope. The increase of heart rate was less during tracheal intubation with the StyletScope when compared with the Macintosh laryngoscope.
Br J Anaesth 2001; 86: 2757
Keywords: airway; equipment, layngoscopes fibreoptics; cardiovascular system, responses; complications, intubation tracheal
The StyletScope (NihonKohden Corp., Tokyo, Japan) is a new fiberoptic intubation device with a lightweight stylet, manoeuverability of the distal tip, a built-in light source and does not need time to set up or external video systems.1 It allows successful tracheal intubation in a short time.2 Direct larynoscopy for tracheal intubation frequently causes haemodynamic responses.3 As intubation with the StyletScope does not require direct laryngoscopy, haemodynamic responses to tracheal intubation may be less. We compared the haemodynamic responses to tracheal intubation using the StyletScope or the Macintosh laryngoscope.
Methods and results
After approval from the ethics committee of our institute and with informed consent from each patient, we studied 24 consecutive patients. Exclusion criteria were ages less than 20 or greater than 85 yr, American Society of Anesthesiologists physical status IV, and the known risks of regurgitation.
At the pre-operative visit the difficulty of the airway was graded by the Mallampati test modified by Samsoon and Young.4 All patients were pre-medicated with atropine 0.01 mg kg1 and hydroxyzine 0.5 mg kg1 i.m. Electrocardiography (ECG), capnography, pulse oximetry, and non-invasive arterial pressure monitoring were applied. After pre-oxygenation with 100% oxygen, general anaesthesia was induced with fentanyl 2 µg kg1, propofol 1 mg kg1 followed by continuous infusion at 10 mg kg1 h1, and vecuronium 0.15 mg kg1. Patients were then randomly allocated to one of two groups. Patients in group L (n=11) underwent tracheal intubation using the Macintosh laryngoscope (blade No. 3). Patients in group S (n=13) underwent tracheal intubation using the StyletScope alone. The intubation procedure using the StyletScope alone has been described previously.2 Intubation was started 5 min after starting the infusion of propofol, with the patients head and neck in the sniffing position. The infusion rate of propofol was not changed until 5 min after tracheal intubation. All intubation procedures were carried out by the same anaesthesiologist (T.K.) after familiarization with the StyletScope.
Ethical considerations did not allow the use of any invasive monitoring. Non-invasive arterial pressure and heart rate (HR) were recorded. As several studies have found that maximum haemodynamic responses occur about 1 min after tracheal intubation,3 57 we calculated the per cent changes in haemodynamic variables from before intubation to 1 min after the completion of intubation. We also recorded the time required for tracheal intubation, beginning at the moment of inserting the Macintosh laryngoscope (group L) or a tracheal tube with the StyletScope (group S) into the mouth until a standard stylet (group L) or the StyletScope (group S) was removed.
Data are shown as means (SEM). Paired and unpaired t-tests and chi-squared tests were used to compare data. Statistical analyses were performed using StatView for Windows version 5.0. A P value less than 0.05 was considered to be statistically significant.
The groups were similar in respect of all characteristics. The laryngeal structures of patients in group L were graded according to Cormack and Lehane,8 at direct laryngoscopy. All patients in group L were graded as grade I or II.
As shown in Table 1, after induction of general anaesthesia, all haemodynamic measurements decreased significantly from baseline values in both groups (paired t-test). After intubation, only the HR in group L was significantly greater than the baseline value (paired t-test), but other haemodynamic variables returned toward baseline values in both groups. The increase in HR was less in group S than group L (unpaired t-test). The increases in systolic and diastolic arterial pressure tended to be less in group S than group L, but there were no significant differences (unpaired t-test).
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Comment
We found that the StyletScope reduced the increase of HR during tracheal intubation. Direct laryngoscopy causes haemodynamic responses to tracheal intubation.3 Placement of the tracheal tube through the vocal cords and inflation of a cuff causes little greater stimulus.3 The StyletScope eliminates direct laryngoscopy. We consider that this reduces haemodynamic responses. Although these responses are usually transient and uneventful, they could be harmful in some patients with cardiovascular or cerebrovascular diseases. In patients with ischaemic heart disease, strict control of haemodynamics is required, as ischaemic events are associated with a greater rate of perioperative myocardial infarction.9 HR is a major determinant of myocardial oxygen balance.10 Although this study included no patients with ischaemic heart disease, our results suggest that the StyletScope is a good choice as an intubation device for such patients.
The reduced response to tracheal intubation using the StyletScope was accompanied by a significantly smaller incidence of sore throat. This is probably for the same reason that the stimuli from direct laryngoscopy are eliminated. Compared with the Macintosh laryngoscope, some fiberoptic devices need more time for intubation, but we found no significant difference in the time required for intubation between the two groups. The success rate for tracheal intubation using the StyletScope was high enough for practical use, confirming the efficiency of the StyletScope we have reported previously.1 2
In conclusion, the StyletScope causes less haemodynamic response to tracheal intubation. Because of this, the StyletScope may be a valuble intubation device especially for patients in whom haemodynamics disturbances should be limited.
References
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