Title: Attenuation of haemodynamic responses to tracheal intubation by the StyletScope
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. 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. 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.1Kitamura T Yamada Y Du HL Hanaoka K Efficiency of a new fiberoptic stylet scope in the tracheal intubation.Anesthesiology. 1999; 91: 1628-1632Crossref PubMed Scopus (45) Google Scholar It allows successful tracheal intubation in a short time.2Kitamura T Yamada Y Du HL Hanaoka K An efficient technique for tracheal intubation using the StyletScope alone.Anesthesiology. 2000; 92: 1210-1211Crossref PubMed Scopus (75) Google Scholar Direct larynoscopy for tracheal intubation frequently causes haemodynamic responses.3Shribman AJ Smith G Achola KJ Cardiovascular and catecholamine responses to laryngoscopy with and without tracheal intubation.Br J Anaesth. 1987; 59: 295-299Crossref PubMed Scopus (366) Google Scholar 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. 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.4Samsoon GLT Young JRB Difficult tracheal intubation: a retrospective study.Anaesthesia. 1987; 42: 487-490Crossref PubMed Scopus (1118) Google Scholar All patients were pre-medicated with atropine 0.01 mg kg−1 and hydroxyzine 0.5 mg kg−1 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 kg−1, propofol 1 mg kg−1 followed by continuous infusion at 10 mg kg−1 h−1, and vecuronium 0.15 mg kg−1. 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.2Kitamura T Yamada Y Du HL Hanaoka K An efficient technique for tracheal intubation using the StyletScope alone.Anesthesiology. 2000; 92: 1210-1211Crossref PubMed Scopus (75) Google Scholar Intubation was started 5 min after starting the infusion of propofol, with the patient's 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,3Shribman AJ Smith G Achola KJ Cardiovascular and catecholamine responses to laryngoscopy with and without tracheal intubation.Br J Anaesth. 1987; 59: 295-299Crossref PubMed Scopus (366) Google Scholar 5Helfman SM Gold MI DeLisser EA Herrington CA Which drug prevents tachycardia and hypertension associated with tracheal intubation: Lidocaine, fentanyl, or esmolol?.Anesth Analg. 1991; 72: 482-486Crossref PubMed Google Scholar, 6McCoy EP Mirakhur RK McCloskey BV A comparison of the stress response to laryngoscopy: the Macintosh versus the McCoy blade.Anaesthesia. 1995; 50: 943-946Crossref PubMed Scopus (71) Google Scholar, 7Thompson JP Hall AP Russell J Cagney B Rowbotham DJ Effect of remifentanil on the haemodynamic response to orotracheal intubation.Br J Anaesth. 1998; 80: 467-469Crossref PubMed Scopus (136) Google Scholar 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,8Cormack RS Lehane J Difficult tracheal intubation in obstetrics.Anaesthesia. 1984; 39: 1105-1111Crossref PubMed Scopus (1945) Google Scholar 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).Table 1Characteristics of patients and changes in haemodynamics. Data are shown as means (sem). *P<0.05, paired t-test, compared with pre-induction value of the same group. †P<0.05, unpaired t-test, compared with the per cent increase in the same haemodynamic parameter of group L. ASA-PS, American Society of Anesthesiologists physical status. SBP, systolic arterial pressure; DBP, diastolic arterial pressure. HR, heart rate. Per cent increase, per cent increase in each haemodynamic parameter from pre-intubation period to post-intubationPatient characteristicsGroupSex (M/F)Age (yr)Height (cm)Weight (kg)ASA-PS (I/II/III)Patients with hypertensionClass of Mallampati (I/II/III/IV)L (n=11)4/754 (4)159 (2)55 (3)7/2/24/118/3/0/0S (n=13)5/855 (4)160 (2)57 (4)7/5/13/138/4/1/0Changes in haemodynamicsGroupPre-inductionPre-intubationPost-intubationPer cent increase (%)HR (beat min−1)L74 (4)68 (4)*91 (5)*34 (5)S74 (3)66 (3)*73 (3)11 (4)†SBP (mm Hg)L139 (10)101 (8)*135 (13)34 (7)S129 (6)100 (3)*121 (6)21 (5)DBP (mm Hg)L80 (4)58 (5)*78 (9)35 (7)S74 (4)58 (3)*69 (6)20 (7) Open table in a new tab No ECG abnormalities were observed. SpO2 remained above 99% in all patients. Success rates of tracheal intubation at the first attempt were 11/11 and 12/13 in group L and group S, respectively. The failed case in group S was because of mucus on the distal tip of the StyletScope, and was intubated successfully at the second attempt. Mean times (sem) required for tracheal intubation were 21 (2) and 20 (3) s in group L and group S, respectively. There were no significant differences between the two groups (unpaired t-test). No adverse effects were associated with tracheal intubation were observed, but on the first postoperative day, slight sore throat was observed in 6/11 and 2/13 patients of group L and group S, respectively. The incidence of sore throat was significantly lower in group S than group L (chi-squared test). We found that the StyletScope reduced the increase of HR during tracheal intubation. Direct laryngoscopy causes haemodynamic responses to tracheal intubation.3Shribman AJ Smith G Achola KJ Cardiovascular and catecholamine responses to laryngoscopy with and without tracheal intubation.Br J Anaesth. 1987; 59: 295-299Crossref PubMed Scopus (366) Google Scholar Placement of the tracheal tube through the vocal cords and inflation of a cuff causes little greater stimulus.3Shribman AJ Smith G Achola KJ Cardiovascular and catecholamine responses to laryngoscopy with and without tracheal intubation.Br J Anaesth. 1987; 59: 295-299Crossref PubMed Scopus (366) Google Scholar 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.9Estafanous FG Tarazi RC Systemic arterial hypertension associated with cardiac surgery.Am J Cardiol. 1980; 46: 684-694Abstract Full Text PDF Scopus (92) Google Scholar HR is a major determinant of myocardial oxygen balance.10Sill JC Prevention and treatment of myocardial ischemia and dysfunction.in: Tarhan S Anesthesia and Coronary Artery Surgery. Year Book Medical Publishers, Chicago1986: 218-268Google Scholar 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.1Kitamura T Yamada Y Du HL Hanaoka K Efficiency of a new fiberoptic stylet scope in the tracheal intubation.Anesthesiology. 1999; 91: 1628-1632Crossref PubMed Scopus (45) Google Scholar 2Kitamura T Yamada Y Du HL Hanaoka K An efficient technique for tracheal intubation using the StyletScope alone.Anesthesiology. 2000; 92: 1210-1211Crossref PubMed Scopus (75) Google Scholar 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.