British Journal of Anaesthesia 1992; 69: 224-229
CORRESPONDENCE
I. CALDER
London 1. Brechner VL. Unusual problems in the management of airways. 1. Flexion/extension mobility of the cervical vertebrae. Anesthesia and Analgesia 1968; 47: 362-363. 2. Block C, Brechner VL. Unusual problems in airway management. 2. The influence of the tcmporomandibular joint, the mandible and associated structures in endotracheal intubation. Anesthesia and Analgesia 1971; 50: 114-123. 3. Cobley M, Vaughan RS. Recognition and management of difficult airway problems. British Journal of Anaesthesia 1992; 68: 90-97. 4. Cormack RS, Lehane J. Difficult tracheal intubation in obstetrics. Anaesthesia 1984; 39: 1105-1111. 5. Wilson ME, John R. Problems with the Mallampati sign. Anaesthesia 1990; 45: 486-^87.
6. Oates JDL, MacLeod AD, Oates PD, Pearsall FJ, Howie JC, Murray GD. Comparison of two methods of predicting difficult intubation. British Journal of Anaesthesia 1991; 66: 305-310. 7. Sansoom GLT, Young JRB. Difficult tracheal intubation: a retrospective study. Anaesthesia 1987; 42: 487^490. 8. Calder I, Calder J, Crockard HA. Radiological prediction of difficult intubation—the posterior C0-1 and Cl-2 "gaps". Antsthesiology 1991; 10: A190. 9. Londy F, Norton ML. Radiologic techniques for evaluation and management of the difficult airway. In: Norton ML, Brown ACD, eds. Atlas of the Difficult Airway. St Louis: Mosby Year Book Inc., 1991; 55-66. 10. Murphy P. A fiberoptic endoscope used for tracheal intubation. Anaesthesia 1967; 22: 489-491. 11. Ovassapian A. Topical anesthesia of the airway. In: Ovassapian A, ed. Fiberoptic Airway Endoscopy in Anesthesia and Critical Care. New York: Raven Press, 1990; 45-56. 12. Schaefer HG, Marsch SCU. Comparison of orthodox with fibreoptic orotracheal intubation under total i.v. anaesthesia. British Journal of Anaesthesia 1991; 66: 608-610. 13. Ovassapian A, Yelich SJ, Dykes MHM, Brunner EE. Blood pressure and heart rate changes during awake fiberoptic nasotracheal intubation. Anesthesia and Analgesia 1983; 62: 951-954. 14. Hawkyard S, Morrison A, Doyle L, Croton R, Wake P. Fibreoptic intubation: Attenuating the hypertensive response to laryngoscopy and intubation. British Journal of Anaesthesia 1989; 63: 624P. 15. Anderson KH, Hald A. Assessing the position of the tracheal tube. The reliability of different methods. Anaesthesia 1989; 44: 984-989.
Sir,—In their review article on the recognition and management of difficult airway problems [1], Drs Cobley and Vaughan refer to intubation through the laryngeal mask airway (LMA) as a possibility. I wish to draw readers' attention to the work carried out in this department [2, 3] which demonstrated the ease and practicality of this manouevre. A 6-mm cuffed tube passes easily through a correctly placed LMA into the trachea if the tube is rotated initially anticlockwise through 90° to avoid catching on the laryngeal aperture bars, and the patient is placed in a normal optimal intubating position. The pilot study [2] was undertaken in an unselected series of 50 adult patients and showed a 90% success rate. The study was extended to include the effects of cricoid pressure [3] which reduced the success rate (to 56 %), although momentary release of cricoid pressure allowed most of the failures to be resolved (final success rate 86 %). No difficulty was encountered in placing the LMA whilst cricoid pressure was maintained, and I am therefore at a loss to understand the report of failure to achieve this in a majority of cases from Drs Anserming, Blogg and Carrie [4]. The technique of intubation through the LMA is not only easy, it is usually extremely quick. The mean time in patients whose tracheas were intubated at the first attempt in the first series was 13 s (range 7-27 s). I would urge anaesthetists to familiarize themselves with the technique in a few elective cases. The equipment needed should be immediately to hand in all anaesthetizing locations: an advantage over some other options. M. L. HEATH
Lewisham 1. Cobley M, Vaughan RS. Recognition and management of difficult airway problems. British Journal of Anaesthesia 1992; 68: 90-97. 2. Heath ML, Allagain J. The Brain laryngeal mask airway as an aid to intubation. British Journal of Anaesthesia 1990; 64: 382P-383P. 3. Heath ML, Allagain J. Intubation through the laryngeal mask, a technique for unexpected difficult intubation. Anaesthesia 1991; 46: 545-548.
Downloaded from http://bja.oxfordjournals.org/ at Karolinska Institutet on May 27, 2015
RECOGNITION AND MANAGEMENT OF DIFFICULT AIRWAY PROBLEMS Sir,—I was sorry not to sec any mention of the work of Drs Block and Brechner [1,2] in Drs Cobley and Vaughan's review [3]. Block and Brechner delineated two of the three crucial areas of concern when attempting to predict difficult intubation. Their classic papers dealt with the function of the temporomandibular joint, and flexion/extension mobility of the cervical spine. The third main group of causes of difficulties in intubation, conditions that narrow the airway, surprisingly was not covered. Cormack and Lehane's classification [4] is incorrectly written in the review: grade III should be "epiglottis only" and grade IV "no glottic structure visible". The Mallampati test is acknowledged to be liable to serious observer error [5, 6], therefore it is surely inappropriate to continue to complicate the test with the fourth class added by Sansoom and Young [7]. The contribution of radiology to prediction is minimal, as Drs Cobley and Vaughan say, but it can be considerable in cervical disease, because lateral radiographs should be available. An absent adanto-axial gap is a more powerful predictor of difficult laryngoscopy than an absent atlanto-occipital gap. The positive predictive value (the proportion of patients predicted to be difficult, who actually were difficult) of an absent atlanto—axial gap is 83%, compared with 52% for an absent atlanto-occipital gap [8]. Some units in the U.S.A. hold pre-intubation clinics and use a C arm to screen their patients' cervical spine [9]. Drs Cobley and Vaughan appear to suggest the use of a fibreoptic bronchoscope. Purpose-built laryngoscopes, such as the Olympus LF-1, have been available for many years and are generally more suitable. Murphy pointed out, in the first report [10], that it is always worth giving an antisialagogue as premedication. We have been unable to obtain amethocaine lozenges for some years. Our Principal Pharmacist tells us that they are no longer available in the U.K. Lignocaine 1 % is ineffective: we have found that up to 10 ml of 4% lignocaine is required in a "spray as you go" technique, and have abandoned transtracheal injection because of the problems of coughing and bleeding [11]. Many practitioners regard cocainization as unnecessary [11], as lignocaine and non-toxic vasoconstrictors, such as xylometazoline (Otrivine), arc satisfactory. The cardiovascular responses to intubation under general anaesthesia are similar, whether fibreoptic or direct, but the changes can be attenuated [12]. Drs Cobley and Vaughan omitted to mention that awake fibreoptic intubation under topical anaesthesia and sedation is associated with stable cardiovascular variables [13, 14]; this also has been our experience, and it could be argued that patients at risk from hypertensive reactions should undergo intubation whilst awake! It is important to realise that Anderson and Hald found that auscultation over the chest wall was reliable as a means of confirming tracheal intubation only when the epigastrium also was auscultated [16]. They also found Wee's test to be reliable. Does anyone really use a fibrebronchoscope for routine confirmation of tracheal intubation ?
CORRESPONDENCE
225
4. Anserming JM, Blogg CE, Carrie LE. Failed tracheal intubation at Caesarean section and the laryngeal mask. British Journal of Anaesthesia 1992; 68: 118.
P. J. BUTLER
Melbourne 1. Cobley M, Vaughan RS. Recognition and management of difficult airway problems. British Journal of Anaesthesia 1992; 66: 90-97. 2. Oates JDL, Oates PD, Pearsall RJ, Howie JC, Murray GD. Comparison of two methods for predicting difficult intubation. British Journal of Anaesthesia 1991; 66: 305-309. 3. Mathew M, Hanna LS, Aldrete JA. Preoperative indices to anticipate difficult tracheal intubation. Anesthesia and Analgesia 1989; 68: S187. 4. Butler PJ, Dhara SS. Prediction of difficult laryngoscopy. An assessment of the thyromental distance and Mallampati predictive tests. Anaesthesia and Intensive Care 1992; (in press). Sir,—We thank you for the opportunity to respond to the letters received following our recent review article. Dr Calder's points are, as always, well made. He regrets that we did not quote the work of Block and Brcchner. However, we did mention the importance of temporomandibular joint movement, the degree of forward protrusion of the mandible and the mobility of the cervical spine. In everyday practice, radiology continues to be used more after encountering a difficult intubation and not during the prediction. We are grateful to Dr Calder for the helpful additional information in respect of patients with known cervical disease. The use of a fibreoptic bronchoscope is a personal choice, as we believe it is easier to use than a fibreoptic laryngoscope. Additionally, it enables the operator to see the Carina clearly and, as thefibrescopeis withdrawn, the end of the tracheal tube in the trachea. Although this may not be regarded as a routine method of confirmation of tracheal tube placement, under the circumstances of a difficult intubation it seems very appropriate. To each bis own! Dr Calder is correct that amethocaine lozenges are no longer manufactured. We are perhaps lucky that our pharmacy still has a store! Moreover, when that is depleted we intend to use benzocaine compound lozenges (Penn Pharmaceutical). We disagree that 1 % lignocaine is ineffective, but accept Dr Calder's contention that 4% lignocaine may be a better choice for "spray as you go", producing faster and perhaps better local anaesthesia. Although a dose of 400 mg is unlikely to produce a plasma concentration greater than the reported toxic plasma concentration of 5 ug ml"1 in the majority of patients, we would suggest that greater vigilance is required to avoid producing toxic plasma concentrations. We would most certainly take issue with the claim that fibreoptic intubation is associated with "stable cardiovascular variables". There are many papers in the world literature devoted to methods which reduce the tachycardia and hypertensive responses associated with intubation. While we accept that awake fibreoptic intubation need not necessarily result in hypertension and
M. COBLEY R. S. VAUGHAN Cardiff
VERAPAMIL AND CARDIOVASCULAR RESPONSES TO TRACHEAL INTUBATION Sir,—I read with interest the article by Yaku and colleagues [1] and wish to make some comments regarding the clinical implications. Their article demonstrated that verapamil 0.05— O.Imgkg"1 attenuated the increases in arterial pressure and rate-pressure product associated with laryngoscopy and tracheal intubation in normotensive patients, although they observed no significant effect on heart rate responses. These results are consistent with previous investigations [2, 3] showing little effect of either verapamil or sodium nitroprusside on heart rate increases after tracheal intubation. My previous study [2] in hypertensive patients showed that mean arterial pressure increased from baseline after tracheal intubation by 18 (9)% (mean (SD)) when verapamil 0.1 mg kg"1 was given i.v. 1 min before laryngoscopy and tracheal intubation, and by 53 (14)% after normal saline (P < 0.001). This result supports their assumption that pretreatment with i.v. verapamil may be useful in hypertensive patients undergoing txacheal intubation. Furthermore, I agree that failure of verapamil to attenuate tachycardia associated with tracheal intubation limits its usefulness in patients with ischaemic heart disease, as it is generally supposed that such patients tolerate hypertension better, and tolerate hypotension and tachycardia poorly; Lieberman and colleagues [4] have noted that myocardial ischaemia accompanied significant increases in heart rate and decreases in arterial and coronary perfusion pressure in patients undergoing coronary artery revascularizarion with halothane anaesthesia. T. NISHIKAWA
Tsukuba, Japan 1. Yaku H, Mikawa K, Maekawa N, Obara H. Effect of verapamil on the cardiovascular responses to tracheal intubation. British Journal of Anaesthesia 1992; 68: 85-89. 2. Nishikawa T, Namiki A. Attenuation of the pressor response to laryngoscopy and tracheal intubation with intravenous verapamil. Acta Anaesthesiologica Scandinavica
1989; 33:
232-235. 3. Stoelting RK. Attenuation of blood pressure response to laryngoscopy and tracheal intubation with sodium nitroprusside. Anesthesia and Analgesia 1979; 58: 116-119. 4. Lieberman RW, Orkin FK, Jobes DR, Schwartz AJ. Hemodynamic predictors of myocardial ischemia during halothane anesthesia for coronary-artery revascularizarion. Anesthesiology 1983; 59: 36-41. Sir,—Thank you for the opportunity to reply to Dr Nishikawa's letter. No data in patients with hypertension were presented, but we speculated that mean arterial pressure (MAP) increased markedly and that maximal values after intubation were more than 165 mm Hg in some of the hypertensive patients receiving normal saline. Bedford and Feinstein [1] have reported that peak MAP after intubation was mean 152 (SEM 4) mm Hg and observed
Downloaded from http://bja.oxfordjournals.org/ at Karolinska Institutet on May 27, 2015
Sir,—The review article by Cobley and Vaughan [1] discusses several of the preoperative screening tests for the prediction of difficult intubation. Whilst recent papers such as that by Oates and colleagues [2] have shown the unreliability of the Mallampati and Wilson tests, the thyromental distance is quoted still as a predictor of difficult or impossible laryngoscopy. The paper by Mathew, Hanna and Aldrete [3] was a retrospective study of 22 easy and 22 difficult intubations in 44 patients and showed correlation between thyromental distance less than 6 cm, Mallampati class III or IV and difficulty in intubation. A prospective study of 250 patients in Singapore [4] has shown a spread of thyromental distance from 3.5 to 9 cm, with patients either side of the 6-cm distance in easy and difficult laryngoscopy groups. It was found that a thyromental distance of less than 6 cm correctly predicted 61 % of difficult laryngoscopies, but just 25 % of easy laryngoscopies. Only 10% of predicted difficult laryngoscopies actually proved to be difficult. Even a measure of 6.5 cm or more could not be taken to signify an easy laryngoscopy, which further devalues the test.
tachycardia, especially when practised by experienced operators, nevertheless, we still contend that cardiovascular instability is a possible sequela which should be given close consideration. It is pleasing that we are both of the same opinion that sedation plus local anaesthesia produces the best conditions for awake intubation. We agree with Dr Heath. Intubation through an LMA is a recognized technique in normal patients. However, until such time as sufficient patients whose tracheas are known to be difficult to intubate are investigated, we should remain circumspect in its use for these patients'. After all, the design of the LMA was based on the anatomy of normal patients, which is probably quite different from that in patients in whom intubation is difficult. Notwithstanding, this technique may represent a welcome addition to the array of methods available for accomplishing intubation in a difficult patient. Finally, we are grateful for the letter from Dr Butler. It confirms that, where the prediction of airway problems is concerned, nothing is sacrosanct!
CORRESPONDENCE
I. CALDER
London 1. Brechner VL. Unusual problems in the management of airways. 1. Flexion/extension mobility of the cervical vertebrae. Anesthesia and Analgesia 1968; 47: 362-363. 2. Block C, Brechner VL. Unusual problems in airway management. 2. The influence of the tcmporomandibular joint, the mandible and associated structures in endotracheal intubation. Anesthesia and Analgesia 1971; 50: 114-123. 3. Cobley M, Vaughan RS. Recognition and management of difficult airway problems. British Journal of Anaesthesia 1992; 68: 90-97. 4. Cormack RS, Lehane J. Difficult tracheal intubation in obstetrics. Anaesthesia 1984; 39: 1105-1111. 5. Wilson ME, John R. Problems with the Mallampati sign. Anaesthesia 1990; 45: 486-^87.
6. Oates JDL, MacLeod AD, Oates PD, Pearsall FJ, Howie JC, Murray GD. Comparison of two methods of predicting difficult intubation. British Journal of Anaesthesia 1991; 66: 305-310. 7. Sansoom GLT, Young JRB. Difficult tracheal intubation: a retrospective study. Anaesthesia 1987; 42: 487^490. 8. Calder I, Calder J, Crockard HA. Radiological prediction of difficult intubation—the posterior C0-1 and Cl-2 "gaps". Antsthesiology 1991; 10: A190. 9. Londy F, Norton ML. Radiologic techniques for evaluation and management of the difficult airway. In: Norton ML, Brown ACD, eds. Atlas of the Difficult Airway. St Louis: Mosby Year Book Inc., 1991; 55-66. 10. Murphy P. A fiberoptic endoscope used for tracheal intubation. Anaesthesia 1967; 22: 489-491. 11. Ovassapian A. Topical anesthesia of the airway. In: Ovassapian A, ed. Fiberoptic Airway Endoscopy in Anesthesia and Critical Care. New York: Raven Press, 1990; 45-56. 12. Schaefer HG, Marsch SCU. Comparison of orthodox with fibreoptic orotracheal intubation under total i.v. anaesthesia. British Journal of Anaesthesia 1991; 66: 608-610. 13. Ovassapian A, Yelich SJ, Dykes MHM, Brunner EE. Blood pressure and heart rate changes during awake fiberoptic nasotracheal intubation. Anesthesia and Analgesia 1983; 62: 951-954. 14. Hawkyard S, Morrison A, Doyle L, Croton R, Wake P. Fibreoptic intubation: Attenuating the hypertensive response to laryngoscopy and intubation. British Journal of Anaesthesia 1989; 63: 624P. 15. Anderson KH, Hald A. Assessing the position of the tracheal tube. The reliability of different methods. Anaesthesia 1989; 44: 984-989.
Sir,—In their review article on the recognition and management of difficult airway problems [1], Drs Cobley and Vaughan refer to intubation through the laryngeal mask airway (LMA) as a possibility. I wish to draw readers' attention to the work carried out in this department [2, 3] which demonstrated the ease and practicality of this manouevre. A 6-mm cuffed tube passes easily through a correctly placed LMA into the trachea if the tube is rotated initially anticlockwise through 90° to avoid catching on the laryngeal aperture bars, and the patient is placed in a normal optimal intubating position. The pilot study [2] was undertaken in an unselected series of 50 adult patients and showed a 90% success rate. The study was extended to include the effects of cricoid pressure [3] which reduced the success rate (to 56 %), although momentary release of cricoid pressure allowed most of the failures to be resolved (final success rate 86 %). No difficulty was encountered in placing the LMA whilst cricoid pressure was maintained, and I am therefore at a loss to understand the report of failure to achieve this in a majority of cases from Drs Anserming, Blogg and Carrie [4]. The technique of intubation through the LMA is not only easy, it is usually extremely quick. The mean time in patients whose tracheas were intubated at the first attempt in the first series was 13 s (range 7-27 s). I would urge anaesthetists to familiarize themselves with the technique in a few elective cases. The equipment needed should be immediately to hand in all anaesthetizing locations: an advantage over some other options. M. L. HEATH
Lewisham 1. Cobley M, Vaughan RS. Recognition and management of difficult airway problems. British Journal of Anaesthesia 1992; 68: 90-97. 2. Heath ML, Allagain J. The Brain laryngeal mask airway as an aid to intubation. British Journal of Anaesthesia 1990; 64: 382P-383P. 3. Heath ML, Allagain J. Intubation through the laryngeal mask, a technique for unexpected difficult intubation. Anaesthesia 1991; 46: 545-548.
Downloaded from http://bja.oxfordjournals.org/ at Karolinska Institutet on May 27, 2015
RECOGNITION AND MANAGEMENT OF DIFFICULT AIRWAY PROBLEMS Sir,—I was sorry not to sec any mention of the work of Drs Block and Brechner [1,2] in Drs Cobley and Vaughan's review [3]. Block and Brechner delineated two of the three crucial areas of concern when attempting to predict difficult intubation. Their classic papers dealt with the function of the temporomandibular joint, and flexion/extension mobility of the cervical spine. The third main group of causes of difficulties in intubation, conditions that narrow the airway, surprisingly was not covered. Cormack and Lehane's classification [4] is incorrectly written in the review: grade III should be "epiglottis only" and grade IV "no glottic structure visible". The Mallampati test is acknowledged to be liable to serious observer error [5, 6], therefore it is surely inappropriate to continue to complicate the test with the fourth class added by Sansoom and Young [7]. The contribution of radiology to prediction is minimal, as Drs Cobley and Vaughan say, but it can be considerable in cervical disease, because lateral radiographs should be available. An absent adanto-axial gap is a more powerful predictor of difficult laryngoscopy than an absent atlanto-occipital gap. The positive predictive value (the proportion of patients predicted to be difficult, who actually were difficult) of an absent atlanto—axial gap is 83%, compared with 52% for an absent atlanto-occipital gap [8]. Some units in the U.S.A. hold pre-intubation clinics and use a C arm to screen their patients' cervical spine [9]. Drs Cobley and Vaughan appear to suggest the use of a fibreoptic bronchoscope. Purpose-built laryngoscopes, such as the Olympus LF-1, have been available for many years and are generally more suitable. Murphy pointed out, in the first report [10], that it is always worth giving an antisialagogue as premedication. We have been unable to obtain amethocaine lozenges for some years. Our Principal Pharmacist tells us that they are no longer available in the U.K. Lignocaine 1 % is ineffective: we have found that up to 10 ml of 4% lignocaine is required in a "spray as you go" technique, and have abandoned transtracheal injection because of the problems of coughing and bleeding [11]. Many practitioners regard cocainization as unnecessary [11], as lignocaine and non-toxic vasoconstrictors, such as xylometazoline (Otrivine), arc satisfactory. The cardiovascular responses to intubation under general anaesthesia are similar, whether fibreoptic or direct, but the changes can be attenuated [12]. Drs Cobley and Vaughan omitted to mention that awake fibreoptic intubation under topical anaesthesia and sedation is associated with stable cardiovascular variables [13, 14]; this also has been our experience, and it could be argued that patients at risk from hypertensive reactions should undergo intubation whilst awake! It is important to realise that Anderson and Hald found that auscultation over the chest wall was reliable as a means of confirming tracheal intubation only when the epigastrium also was auscultated [16]. They also found Wee's test to be reliable. Does anyone really use a fibrebronchoscope for routine confirmation of tracheal intubation ?
CORRESPONDENCE
225
4. Anserming JM, Blogg CE, Carrie LE. Failed tracheal intubation at Caesarean section and the laryngeal mask. British Journal of Anaesthesia 1992; 68: 118.
P. J. BUTLER
Melbourne 1. Cobley M, Vaughan RS. Recognition and management of difficult airway problems. British Journal of Anaesthesia 1992; 66: 90-97. 2. Oates JDL, Oates PD, Pearsall RJ, Howie JC, Murray GD. Comparison of two methods for predicting difficult intubation. British Journal of Anaesthesia 1991; 66: 305-309. 3. Mathew M, Hanna LS, Aldrete JA. Preoperative indices to anticipate difficult tracheal intubation. Anesthesia and Analgesia 1989; 68: S187. 4. Butler PJ, Dhara SS. Prediction of difficult laryngoscopy. An assessment of the thyromental distance and Mallampati predictive tests. Anaesthesia and Intensive Care 1992; (in press). Sir,—We thank you for the opportunity to respond to the letters received following our recent review article. Dr Calder's points are, as always, well made. He regrets that we did not quote the work of Block and Brcchner. However, we did mention the importance of temporomandibular joint movement, the degree of forward protrusion of the mandible and the mobility of the cervical spine. In everyday practice, radiology continues to be used more after encountering a difficult intubation and not during the prediction. We are grateful to Dr Calder for the helpful additional information in respect of patients with known cervical disease. The use of a fibreoptic bronchoscope is a personal choice, as we believe it is easier to use than a fibreoptic laryngoscope. Additionally, it enables the operator to see the Carina clearly and, as thefibrescopeis withdrawn, the end of the tracheal tube in the trachea. Although this may not be regarded as a routine method of confirmation of tracheal tube placement, under the circumstances of a difficult intubation it seems very appropriate. To each bis own! Dr Calder is correct that amethocaine lozenges are no longer manufactured. We are perhaps lucky that our pharmacy still has a store! Moreover, when that is depleted we intend to use benzocaine compound lozenges (Penn Pharmaceutical). We disagree that 1 % lignocaine is ineffective, but accept Dr Calder's contention that 4% lignocaine may be a better choice for "spray as you go", producing faster and perhaps better local anaesthesia. Although a dose of 400 mg is unlikely to produce a plasma concentration greater than the reported toxic plasma concentration of 5 ug ml"1 in the majority of patients, we would suggest that greater vigilance is required to avoid producing toxic plasma concentrations. We would most certainly take issue with the claim that fibreoptic intubation is associated with "stable cardiovascular variables". There are many papers in the world literature devoted to methods which reduce the tachycardia and hypertensive responses associated with intubation. While we accept that awake fibreoptic intubation need not necessarily result in hypertension and
M. COBLEY R. S. VAUGHAN Cardiff
VERAPAMIL AND CARDIOVASCULAR RESPONSES TO TRACHEAL INTUBATION Sir,—I read with interest the article by Yaku and colleagues [1] and wish to make some comments regarding the clinical implications. Their article demonstrated that verapamil 0.05— O.Imgkg"1 attenuated the increases in arterial pressure and rate-pressure product associated with laryngoscopy and tracheal intubation in normotensive patients, although they observed no significant effect on heart rate responses. These results are consistent with previous investigations [2, 3] showing little effect of either verapamil or sodium nitroprusside on heart rate increases after tracheal intubation. My previous study [2] in hypertensive patients showed that mean arterial pressure increased from baseline after tracheal intubation by 18 (9)% (mean (SD)) when verapamil 0.1 mg kg"1 was given i.v. 1 min before laryngoscopy and tracheal intubation, and by 53 (14)% after normal saline (P < 0.001). This result supports their assumption that pretreatment with i.v. verapamil may be useful in hypertensive patients undergoing txacheal intubation. Furthermore, I agree that failure of verapamil to attenuate tachycardia associated with tracheal intubation limits its usefulness in patients with ischaemic heart disease, as it is generally supposed that such patients tolerate hypertension better, and tolerate hypotension and tachycardia poorly; Lieberman and colleagues [4] have noted that myocardial ischaemia accompanied significant increases in heart rate and decreases in arterial and coronary perfusion pressure in patients undergoing coronary artery revascularizarion with halothane anaesthesia. T. NISHIKAWA
Tsukuba, Japan 1. Yaku H, Mikawa K, Maekawa N, Obara H. Effect of verapamil on the cardiovascular responses to tracheal intubation. British Journal of Anaesthesia 1992; 68: 85-89. 2. Nishikawa T, Namiki A. Attenuation of the pressor response to laryngoscopy and tracheal intubation with intravenous verapamil. Acta Anaesthesiologica Scandinavica
1989; 33:
232-235. 3. Stoelting RK. Attenuation of blood pressure response to laryngoscopy and tracheal intubation with sodium nitroprusside. Anesthesia and Analgesia 1979; 58: 116-119. 4. Lieberman RW, Orkin FK, Jobes DR, Schwartz AJ. Hemodynamic predictors of myocardial ischemia during halothane anesthesia for coronary-artery revascularizarion. Anesthesiology 1983; 59: 36-41. Sir,—Thank you for the opportunity to reply to Dr Nishikawa's letter. No data in patients with hypertension were presented, but we speculated that mean arterial pressure (MAP) increased markedly and that maximal values after intubation were more than 165 mm Hg in some of the hypertensive patients receiving normal saline. Bedford and Feinstein [1] have reported that peak MAP after intubation was mean 152 (SEM 4) mm Hg and observed
Downloaded from http://bja.oxfordjournals.org/ at Karolinska Institutet on May 27, 2015
Sir,—The review article by Cobley and Vaughan [1] discusses several of the preoperative screening tests for the prediction of difficult intubation. Whilst recent papers such as that by Oates and colleagues [2] have shown the unreliability of the Mallampati and Wilson tests, the thyromental distance is quoted still as a predictor of difficult or impossible laryngoscopy. The paper by Mathew, Hanna and Aldrete [3] was a retrospective study of 22 easy and 22 difficult intubations in 44 patients and showed correlation between thyromental distance less than 6 cm, Mallampati class III or IV and difficulty in intubation. A prospective study of 250 patients in Singapore [4] has shown a spread of thyromental distance from 3.5 to 9 cm, with patients either side of the 6-cm distance in easy and difficult laryngoscopy groups. It was found that a thyromental distance of less than 6 cm correctly predicted 61 % of difficult laryngoscopies, but just 25 % of easy laryngoscopies. Only 10% of predicted difficult laryngoscopies actually proved to be difficult. Even a measure of 6.5 cm or more could not be taken to signify an easy laryngoscopy, which further devalues the test.
tachycardia, especially when practised by experienced operators, nevertheless, we still contend that cardiovascular instability is a possible sequela which should be given close consideration. It is pleasing that we are both of the same opinion that sedation plus local anaesthesia produces the best conditions for awake intubation. We agree with Dr Heath. Intubation through an LMA is a recognized technique in normal patients. However, until such time as sufficient patients whose tracheas are known to be difficult to intubate are investigated, we should remain circumspect in its use for these patients'. After all, the design of the LMA was based on the anatomy of normal patients, which is probably quite different from that in patients in whom intubation is difficult. Notwithstanding, this technique may represent a welcome addition to the array of methods available for accomplishing intubation in a difficult patient. Finally, we are grateful for the letter from Dr Butler. It confirms that, where the prediction of airway problems is concerned, nothing is sacrosanct!
