Effects of Diazoxide on the Cardiovascular Response to Tracheal Intubation
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The efficacy of 2 or 3 mg/kg diazoxide given 2.5 min before laryngoscopy in attenuating the cardiovascular responses to laryngoscopy and intubation was studied in 30 patients undergoing elective surgery. Data were compared with those from 10 control patients receiving saline. Anaesthesia was induced using 5 mg/kg thiopentone given intravenously and tracheal intubation was facilitated with 0.2 mg/kg vecuronium bromide. Patients receiving saline showed a significant increase in mean arterial pressure and rate – pressure product associated with tracheal intubation. The increases following tracheal intubation were significantly reduced ( P <0.05) in diazoxide-treated patients compared with those in the control group, but there were no significant differences in heart rate following tracheal intubation among the three groups. Data suggest that diazoxide can be used as a supplement during induction of anaesthesia to attenuate the hypertensive response associated with laryngoscopy and tracheal intubation.Keywords:
Diazoxide
Tracheal tube
Rate pressure product
Mean arterial pressure
Tracheal tube
Laryngoscopes
Laryngeal Masks
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The relationship between the forces applied during laryngoscopy and cardiovascular changes were studied in patients undergoing laryngoscopy with or without intubation. This enabled us to differentiate between the cardiovascular effects of laryngoscopy and the effects of tracheal intubation. The forces applied during laryngoscopy were only weakly related to the cardiovascular changes, whereas tracheal intubation had a major influence. The many difficulties encountered in interpreting results from these studies are discussed. It is concluded that tracheal intubation causes more cardiovascular changes than laryngoscopy in routine uncomplicated procedures.
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Summary We investigated the diagnostic accuracy of a documented previous difficult tracheal intubation as a stand‐alone test for predicting a subsequent difficult intubation. Our assessment included patients from the Danish Anaesthesia Database who were scheduled for tracheal intubation by direct laryngoscopy. We used a four‐point scale to grade the tracheal intubation. A previous difficult intubation was defined according to the presence of a record documenting a difficult penultimate tracheal intubation‐score for the 15 499 patients anaesthetised more than once. Our assessment demonstrates that a documented history of previous difficult or failed intubation using direct laryngoscopy are strong predictors of a subsequent difficult or failed intubation and may identify 30% of these patients. Although previous investigators have reported predictive values that exceed our findings markedly, a documented previous difficult or failed tracheal intubation appears in everyday anaesthetic practice to be a strong predictor of a subsequent difficult tracheal intubation.
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The haemodynamic response to the insertion of the laryngeal mask airway (LMA) was assessed and compared to that of laryngoscopy and tracheal intubation in a study of forty patients (ASA 1) randomly allocated into two groups and anaesthetised using a standard balanced anaesthetic technique. The results show that the changes in all cardiovascular parameters measured following LMA insertion were significantly less (P<0.05) when compared with those following laryngoscopy and tracheal intubation. We conclude that airway management with the LMA may be used to avoid the haemodynamic response to tracheal intubation where such a response is undersirable.
Laryngeal Masks
Haemodynamic response
Mascara
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Tracheal tube passage can be difficult when the Miller laryngoscope is used with the paraglossal straight laryngoscopy technique (PGSLT) [1, 2]. In a survey of use of the PGSLT in the Western Infirmary, Glasgow, in the summer of 1998, consultant anaesthetists were asked ‘If you use the Miller laryngoscope, how often do you find it difficult to pass the tracheal tube, when you have achieved a good view of the larynx’. Figure 1 illustrates the responses of 11 out of 27 consultants. These show a bimodal distribution, with four (36%) reporting difficulty in over 40% of patients. Frequency of difficult tracheal tube passage in patients in whom a good view of the larynx is achieved with the Miller laryngoscope. Limited space in which to pass the tracheal tube with the PGSLT is the price to be paid for its ability to facilitate visualisation of the larynx, when this proves impossible with the Macintosh laryngoscope. It is important to find solutions to the problem of difficult tracheal tube passage with the PGSLT, as tracheal intubation under vision is always preferable to attempted blind intubation. This problem can be addressed by: technique of laryngoscopy; technique of passage of the tracheal tube; and design of the laryngoscope. The technique of laryngoscopy can be modified to maximise the space available for passage of the tracheal tube to the right of the laryngoscope. When the view of the larynx has been optimised, the lifting force is adjusted to maximise the distance between the maxillary teeth and the laryngoscope. An assistant retracts the corner of the mouth. Dr Dhakshinomoorthi (Anaesthesia 1999; 54: 202–3) is to be congratulated on success with his novel technique of passing a styletted tracheal tube to the left of the laryngoscope (between the laryngoscope and the tongue) while passage of the tube through the larynx is observed from the right side of the laryngoscope. I would be surprised if this technique works well in difficult patients, in whom there is limited space in the mouth. An account of his further experience is awaited, with interest. Three standard methods of passing the tracheal tube via the space on the right side of the Miller laryngoscope comprise: (1) over a bougie (introducer) passed into the trachea under vision, (2) use of a stylet to optimise the shape of the tracheal tube or (3) neither of these. In the previously mentioned survey, consultants were asked how often they used each of these techniques with the Miller laryngoscope. Figure 2 illustrates their responses. The order of popularity was: neither, bougie and stylet. Use of three techniques of tracheal tube passage when the Miller laryngoscope is used with the paraglossal straight laryngoscopy technique. Median values are shown. I recommend the bougie for routine use by beginners. Dr Dhakshinomoorthi is correct in stating that vision of the larynx can be lost during passage of the tube over a bougie. However, the certain knowledge that the bougie has been positioned in the trachea under vision compensates for loss of vision while passing the tube. Incidentally, I would advise against removal of the laryngoscope while passing (‘railroading’) the tracheal tube over the bougie. It is advisable to keep the laryngoscope in place during ‘railroading’ with the Macintosh laryngoscope [3], and I believe that this is also true of the PGSLT. Finally, some of the difficulties experienced with tracheal tube passage may be a consequence of the cross-section of the Miller laryngoscope, in that the flange tends to divert the tube from the larynx. A semitubular straight laryngoscope (manufacturer Karl Storz; UK, European and US patents applied for) has been designed to facilitate passage of the tracheal tube with the PGSLT. The tip of the laryngoscope and the light are improved in relation to the Miller laryngoscope (Fig. 3), and the cross-section is designed to facilitate passage of an 8-mm ID tracheal tube down the lumen of the laryngoscope. Techniques of tracheal tube passage with this laryngoscope are: down the lumen (directly or over a bougie passed under vision) or lateral to the lumen of the laryngoscope. Visual confirmation of correct positioning of the tracheal tube is usually possible (Fig. 4). This laryngoscope is currently undergoing evaluation. View of the larynx through a prototype semitubular straight laryngoscope. The cross-section of the laryngoscope is seen. This photograph was taken with a straight laparoscopy telescope. Visual confirmation of tracheal intubation with the new laryngoscope. I hope that these comments are useful to those learning the paraglossal straight laryngoscopy technique. I am grateful to Keymed UK for the loan of the Olympus SC-35 camera and SM-ER2 adapter used for laryngeal photography.
Tracheal tube
Laryngoscopes
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Unanticipated difficulties during tracheal intubation and failure to intubate are among the leading causes of anaesthesia-related morbidity and mortality. Using the technique of video laryngoscopy, the alignment of the oral and pharyngeal axes to facilitate tracheal intubation is unnecessary. In this study we evaluated the McGrath Series 5 videolaryngoscope for tracheal intubation in 61 patients who exhibited Cormack and Lehane grade 3 or 4 laryngoscopies with a Macintosh laryngoscope. Using the McGrath resulted in an improved glottic view, compared to Macintosh laryngoscope. Laryngoscopy was improved by one grade in 10%, by two grades in 80% and by three grades in 10% of cases (p < 0.0001). The success rate for intubation was 95% with the McGrath. These results suggest that the McGrath videolaryngoscope can be used with a high success rate to facilitate tracheal intubation in difficult intubation situations.
Laryngoscopes
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BACKGROUND Gum elastic bougie (GEB) is one of the most useful devices for patients whose tracheas are difficult to intubate during anesthetic induction. But no previous study has evaluated the effects of the types of the tracheal tube. We hypothesized that wire-reinforced tracheal tubes were superior to standard tracheal tubes in the success rate of tracheal intubation when using GEB. We compared these two different types of tracheal tubes in using GEB. METHODS Forty patients were subjected and randomly allocated into two groups; patients intubated with standard tracheal tubes (Group , n = 20) and those with wire-reinforced tracheal tubes (Group S, n = 20). Measured variables were intubation time defined as elapsed time from mouth opening to removal of GEB from tracheal tube, heart rate (HR), and systolic blood pressure(SBP). We also compared trial times of intubation and pharyngeal or laryngeal bleeding as a minor side effect. RESULTS Trachea was successfully intubated in the frist attempt in 37 patients (92.5%), and the rest of the patients were all intubated at second trial. Intubation times of Group P and Group S were 41.5 +/- 13.9s and 41.3 +/- 11.1s, respectively. There were no significant differences in HR and SBP between the groups. CONCLUSIONS The type of tracheal tube would not affect the success rate and time of intubation when using gum elastic bougie.
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Summary Before completion of this study, there was insufficient evidence demonstrating the superiority of videolaryngoscopy compared with direct laryngoscopy for elective tracheal intubation. We hypothesised that using videolaryngoscopy for routine tracheal intubation would result in higher first‐pass tracheal intubation success compared with direct laryngoscopy. In this multicentre randomised trial, 2092 adult patients without predicted difficult airway requiring tracheal intubation for elective surgery were allocated randomly to either videolaryngoscopy with a Macintosh blade (McGrath™) or direct laryngoscopy. First‐pass tracheal intubation success was higher with the McGrath (987/1053, 94%), compared with direct laryngoscopy (848/1039, 82%); absolute risk reduction (95%CI) was 12.1% (10.9–13.6%). This resulted in a relative risk (95%CI) of unsuccessful tracheal intubation at first attempt of 0.34 (0.26–0.45; p < 0.001) for McGrath compared with direct laryngoscopy. Cormack and Lehane grade ≥ 3 was observed more frequently with direct laryngoscopy (84/1039, 8%) compared with McGrath (8/1053, 0.7%; p < 0.001) No significant difference in tracheal intubation‐associated adverse events was observed between groups. This study demonstrates that using McGrath videolaryngoscopy compared with direct laryngoscopy improves first‐pass tracheal intubation success in patients having elective surgery. Practitioners may consider using this device as first choice for tracheal intubation.
Elective surgery
Laryngoscopes
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We randomly allocated 60 patients with normal airways into three groups to compare the ease of fibrescope‐aided tracheal intubation using 8.0‐mm internal diameter (group F 8 ) and 6.0‐mm (group F 6 ) reinforced tracheal tubes and to evaluate the efficacy of the laryngeal mask as an aid for fibreoptic tracheal intubation (group L). In group F 8 tracheal intubation was optimal in 2 of 20 patients and in two patients in whom intubation over the fibrescope was difficult the attempts resulted in inadvertent oesophageal intubation. In group F 6 intubation was always successful and significantly easier than in group F 8 (p < 0.005; 95% confidence interval for the difference in the proportion of the optimal intubation grade: 20–70%). In group L tracheal intubation was optimal in 18 of 20 patients and easier than in group F 6 (p = 0.014; 95% confidence interval for difference: 10–60%). In both groups F 6 and L tracheal intubation was completed within less than about 1 min. We conclude that conventional fibrescope‐aided tracheal intubation with a 6.0‐mm tracheal tube is easier than with an 8.0‐mm tube and that the laryngeal mask facilitates fibrescope‐aided tracheal intubation.
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Mascara
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Confirmation of translaryngeal placement of the tracheal tube can be unexpectedly difficult. This study examined the usefulness of displacing the larynx posteriorly with the tracheal tube during laryngoscopy with a straight laryngoscope blade to confirm tracheal tube placement. One hundred ASA Classes I, II, or III patients presenting for elective surgery whose normal anesthetic care included placement of an orotracheal tube via direct laryngoscopy were enrolled in this institutionally approved study after giving their written, informed consent. The view of the larynx at laryngoscopy was graded, and the tracheal tube was then inserted. When the larynx was incompletely exposed, the tracheal tube was displaced posteriorly while the laryngoscope was maintained in the intubating position in an attempt to better visualize the larynx. The effect of the maneuver on Mallampati grade for laryngeal exposure was noted. During laryngoscopy with a Miller blade none of the glottis was initially visualized in 17 patients (Mallampati laryngeal Grades 3 and 4). Thus, the tracheal tube actually was not seen to pass between these patients' vocal cords. Use of the maneuver resulted in improved visualization of the intubated larynx in 12 of these patients, and confirmed tracheal intubation. This maneuver is recommended as an aid to the anesthesiologist in the confirmation of tracheal intubation.
Tracheal tube
Epiglottis
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