Use of angulated video-intubation laryngoscope in children undergoing manual in-line neck stabilization

Transcription

1 British Journal of Anaesthesia 87 (3): 453±8 (2001) Use of angulated video-intubation laryngoscope in children undergoing manual in-line neck stabilization M. Weiss 12 * ², K. Hartmann 1, J. E. Fischer 2 and A. C. Gerber 1 Departments of 1 Anaesthesia and 2 Intensive Care, University Children's Hospital, Steinwiesstrasse 75, CH-8032 Zurich, Switzerland *Corresponding author Laryngeal views obtained during direct laryngoscopy with and without manual in-line neck stabilization (MILNS) and during video-assisted intubation with MILNS using the angulated videointubation laryngoscope were assessed in 100 paediatric patients (aged 0.25±17.3 yr). Visualization of the larynx (Cormack and Lehane score) as well as time taken for video-assisted tracheal intubation by six nurses and four resident anaesthetists not experienced in the technique were recorded. Cormack and Lehane scores were signi cantly worse during direct laryngoscopy when MILNS was applied. Video-assisted visualization of the larynx during MILNS produced scores, which were as good or better than those observed during direct laryngoscopy alone. Intubation times ranged from 19±75 s (mean 35 (SD 13.4); median 32). Br J Anaesth 2001; 87: 453±8 Keywords: intubation tracheal, dif cult; complications, neurological; equipment, laryngoscopes; anaesthetic techniques, video-assisted endoscopy Accepted for publication: May 10, 2001 In children suffering from congenital syndromes associated with cervical spine instability, exible bre-optic-tracheal intubation, or proper care during direct laryngoscopy is mandatory to reduce the risk of neurological damage. 1±6 Direct laryngoscopy with minimal force and manual in-line neck stabilization (MILNS) is a commonly used technique for tracheal intubation in under these circumstances. 7 However, MILNS impedes direct laryngeal visualization, increasing the probability that external laryngeal manipulation and/or blind tracheal intubation may be required. 8±10 The angulated video-intubation laryngoscope (AVIL) is a new endoscopic intubation device designed to improve glottic visualization when direct laryngoscopy is dif cult or impossible (Fig. 1). 11 It consists of a cast plastic intubation laryngoscope with a blade angulated distally, similar to the activated McCoy laryngoscope. 12 The vertical ange of the blade is attened, which improves sagittal manoeuvring and allows its use in paediatric patients. A thin channel leads from the handle to the tip of the blade and permits insertion of a bre-optic endoscope (external diameter: 2.8 mm; length 1.8 m; manufacturer: Volpi AG, Schlieren, Switzerland). The endoscope carries optic bres for image transmission ( pixels) and light bres for airway illumination. The view nder of the endoscope is attached to a conventional video-endoscope camera system and the light-adaptor is connected to a standard light source by means of a light cable. Because of the angulated tip, the device provides an improved view of the vocal cords, which is transmitted to a bedside video monitor. The aim of this study was to assess the ability of inexperienced operators to obtain a good view of the larynx using the AVIL in the presence of MILNS in infants and children during tracheal intubation. Methods With approval of the hospital's Institutional Review Board, we enrolled 100 consecutive patients, who satis ed the following inclusion criteria: ASA I or II, age from birth to 18 yr, scheduled for elective surgery requiring orotracheal intubation, and no indication for rapid sequence induction. Pre-medication and induction of anaesthesia (inhalational or i.v.) depended upon the patient's medical condition and preference. Routine monitoring included praecordial stetho- ² Declaration of interest: Dr Weiss is the inventor of the angulated video-intubation laryngoscope, which has been realised with a local bre-optic manufacturer (Volpi AG, Schlieren, Switzerland). The manufacturer has provided the equipment for the study without charge. Dr Weiss does not hold any patent rights or agreements on the device nor does he receive any nancial support from the manufacturer for the study. Ó The Board of Management and Trustees of the British Journal of Anaesthesia 2001

2 Weiss et al. Fig 1 Angulated video-intubating laryngoscope consisting of a plastic cast, compact laryngoscope with an integrated ultrathin bre-optic endoscope. The proximal ocular and light adaptor is connected to a bedside video-endoscopy system. scope, pulse oximetry, electrocardiography and non-invasive blood pressure recording. After adequate mask ventilation was achieved, a non-depolarizing neuromuscular blocking agent was administered and anaesthesia was maintained with sevo urane in oxygen. Before starting intubation, the AVIL (Fig. 1) was connected to a videoendoscopy system. An anti-fog agent was applied to the lens tip and the device was checked for an adequate and clear view. In addition, a lubricated intubation stylet (Portex Tracheal Intubation Stylet, SIMS Portex Limited, Hythe, Kent, UK) was inserted into an age-appropriate standard or RAE tracheal tube (ETT) with or without a tracheal cuff. Care was taken to avoid protrusion of the stylet tip beyond the distal ori ce of the tracheal tube. After placing the patient's head in a stabilization ring, the best laryngoscopic views obtained by conventional direct laryngoscopy without MILNS (procedure A) and with MILNS (procedure B) were assessed by the intubator and the investigator using the classi cation of Cormack and Lehane. 13 An additional assistant, positioned opposite the intubator, performed the MILNS. Subsequently, the laryngoscope was removed and the patient ventilated again by mask. In a second step (procedure C), while maintaining MILNS, the intubator inserted the tip of the AVIL blade around the tongue into the oropharynx. Then the tongue was lifted by the AVIL tip until the video display revealed a full view of the vocal cords (Fig. 2). If this manoeuvre did not reveal an adequate glottic view on the monitor, the operator was allowed to gently lift the epiglottis with the AVIL tip. While maintaining an adequate monitor view of the cords, the styletted and distally angled (~45 ) ETT was guided from the right corner of the mouth to the distal blade tip. As soon as the tracheal tube tip became visible on the monitor, Fig 2 Video-assisted tracheal intubation in the presence of MILNS in an 11-yr-old child using the angulated video-intubation laryngoscope. The monitor gives a display of the vocal cords from the angulated blade tip for endoscopic guidance of the tracheal tube (with permission of a patient). it was guided into the larynx. After the ETT tip had passed through the vocal cords, the stylet was removed from the ETT and the ETT was advanced into the trachea. External laryngeal manipulation was not applied during any of the three intubation procedures. The nal position of the ETT in the trachea was adjusted according to the black depth marking on the ETT or the position of the ETT cuff as visualized on the video display. Correct tracheal ETT placement was further con rmed by chest auscultation and capnography. All intubations were performed by four residents or by six nurse anaesthetists with varying experience in anaesthesia. Every participant received brief instructions before the study but had no previous training on the use of the AVIL. Each participant performed tracheal intubation on six or more patients. The time from insertion of the AVIL into the oral cavity until achievement of an adequate monitor view of the vocal cords was recorded as T 1. Total intubation time to nal placement of the tracheal tube was de ned as T 2. Intubation was considered a failure if the ETT was placed in the oesophagus or if arterial oxygen saturation dropped to less than 94% during intubation. Dif culties attributed to use of 454

3 Video-assisted tracheal intubation Table 1 Number of laryngoscopic views obtained during direct laryngoscopy (procedure A), direct laryngoscopic views with MILNS (procedure B), and monitored laryngoscopic views (classi cation Cormack and Lehane) 13 provided by the angulated video-intubation laryngoscope during tracheal intubation with MILNS (procedure C) Patients All 0 to <4 yr 4 to <8 yr 8 to <12 yr 12 to 18 yr Procedure A B C A B C A B C A B C A B C Grade I Grade II Grade III Grade IV the angulated video-intubation laryngoscope during intubation, and problems regarding the insertion of the ETT into the trachea were recorded. After completing the procedure, participants had to estimate the subjective degree of dif culty (DOD) in establishing an adequate monitor view of the cords with the AVIL (DOD 1 ), and of the endoscopic insertion of the ETT into the trachea (DOD 2 ), on a 10 point Likert-scale ranging from 1 (very simple) to 10 (very dif cult). Statistical analysis We compared laryngeal visibility in the three procedures using Fishers' exact test. Logistic regression analysis was employed to identify variables that increased the risk of an impaired direct laryngoscopic view during MILNS or the improvement of laryngoscopic view obtained with the AVIL during MILNS. Possible variables included patient characteristics (age, sex, weight, and height), the blade used (Miller vs Macintosh) and experience of the operator (nurse vs resident, years of experience in anaesthesia, number of previous AVIL procedures during this study). Time until successful visualization of the cords (T 1 ) and until nal intubation (T 2 ) were compared across groups (e.g. nurses vs residents) by the unpaired Student's t-test. Multivariable regression analyses were used to identify variables associated with T 1 and T 2. These independent variables included: patient characteristics, experience of the intubator, subjectively perceived dif culty, number of intubation attempts (learning curve), and best direct laryngoscopic view with or without MILNS. In a separate regression analysis, we investigated possible associations between the aforementioned variables and subjective dif culty. All tests were two tailed. A type I error probability of <0.05 was considered to indicate statistical signi cance. Analyses were carried out using the SAS software package (Version 6.12, SAS Inc., Cary, NC, USA). Results We enrolled 100 paediatric patients (mean age 7.2 (SD 4.5) yr, interquartile range 3.2±10.3 yr). Direct and monitored laryngoscopic views obtained during the different procedures (A, B, C) are summarized in Table 1. The MILNS procedure was more likely to impair laryngoscopic visualization in older patients than in younger patients (Table 1). After controlling for the age of the patient (P=0.001), no other variable was signi cantly associated with the degree of impairment of visualization by the MILNS procedure (sex, weight and height, nurse vs resident, years of experience in anaesthesia, type and size of blade used; all P>0.15). Likewise the degree of improvement by optical visualization with the AVIL was positively associated with age (P=0.001), but no other variable (all P>0.2). MILNS signi cantly impaired visualization of the larynx (Fisher's exact test, two-tailed, P<0.001). Video-assisted visualization under MILNS provided better visualization than unrestricted direct laryngoscopy (Fisher's exact test, P=0.003). Two patients, in whom direct laryngoscopy under MILNS revealed a Grade III and Grade IV view, respectively, required direct elevation of the epiglottis with the AVIL tip to obtain an adequate monitor view of the vocal cords (Grade I and Grade II, respectively). Tracheal intubation with the AVIL was successfully performed in all patients. Intubation time (T 1 ) ranged from 8±45 s (mean 14 (SD 5.4); median 16.5) and total intubation time (T 2 ) ranged from 19±75 s (mean 35 (13.4); median 32). None of the patients suffered from arterial desaturation or oesophageal intubation during the intubation procedure. Visual positioning of the ETT in the trachea using the monitor was possible in 86 patients. In two patients visual ETT positioning was impaired by lens fogging and in 12 patients the RAE tubes used did not have a cuff or a black depth marking to adjust the nal tracheal tube position. No problems were reported with the endoscopic cable leading from the AVIL to the bedside monitor system. Fogging of the distal lens occurred in 12 patients, and soiling of the lens by secretions in three patients. In six patients, the AVIL had to be transiently removed for lens cleaning. In 21 patients, the angle of the styletted ETT had to be readjusted because of limited ETT manoeuvrability. Although the angulated video-intubation laryngoscope successfully provided an adequate view of the cords in all patients aged from 3 months to 18 yr, operators considered that the blade was too long. This led to too deep an initial insertion of the blade, particularly in infants and smaller children 455

4 Weiss et al. Crude analysis revealed that residents (40 intubations) needed more time to obtain visualization than nurses (60 intubations) (mean 16.3 (6.9) vs 12.9 (3.7) s; t-test P=0.007) and took longer to intubate (mean 38.0 (14.3) vs 32.2 (12.3) s; t-test P=0.039). In the multivariable model, additional factors that were signi cantly related to time to visualization (T 1 ) were: perceived dif culty of visualization, and years of experience in anaesthesia. Variables that were associated with intubation time (T 2 ) were time until visualization and the need to rebend the ETT tube. The direct laryngoscopic score with MILNS was not associated with time to intubation using the AVIL. Neither the required time to visualization (r=±0.1, P=0.32) nor intubation time (r=±0.13, P=0.13) was associated with prior experience with the video-assisted procedure. However, the more procedures operators had performed, the less dif culties they observed (r=±0.3, P=0.002). Failure to intubate the trachea within 30 s of beginning the procedure (n=53, 53%) was related to the need to adjust the angle of the ETT tip (odds ratio=6.8, 95% CI: 1.9±24.3). No other externally observable variable (resident or nurse, age of patient, weight, size of tube) showed a signi cant association. Mean estimated degree of dif culty for video-laryngoscopic visualization of the larynx (DOD 1 ) was 2.9 (1.2) (median 3) and 3.7 (2.1) (median 3) for video-assisted ETT insertion (DOD 2 ). As expected, the subjective perception of the dif culty to visualize or to intubate correlated strongly with time to visualization or time to intubate, respectively. Discussion Our main nding was that the AVIL signi cantly improved the laryngeal view in infants and children in whom cervical spine immobilization impaired direct visualization of the vocal cords. Intubations were successfully performed in all patients by intubators without prior experience of the technique. The AVIL combines the advantages of improved visualization from an angulated or curved `optical' laryngoscope blade (Siker, Huffmann, Belscope, Bullard) 14±18 with video-transmission of the view from the blade tip to a monitor. 19 In contrast to the Belscope or the Bullard laryngoscope, the AVIL is mainly used for gently lifting the tongue without the need to directly elevate the epiglottis by passing the blade tip beneath it. This reduces the risk of mechanical trauma to the epiglottis and of soiling of the lens, should blood and secretions be present between the epiglottis and the posterior pharyngeal wall. The use of a thin, lightweight endoscopic cable instead of a video camera head and additional light cable facilitates handling of the device. The video-assisted intubation technique, combining laryngoscopy with the use of a styletted tube is almost a conventional manoeuvre, which can be performed without additional skilled assistance or extensive patient preparation. The familiarity of the technique is demonstrated by the high intubation success rate, low estimated degree of dif culty, absence of an objective learning curve (as measured by time to visualization or time to intubation), and clinically acceptable intubation times. The fact that nurses and resident anaesthetists without any prior experience in paediatric bre-optic intubation were able successfully to intubate a child with a Grade III laryngoscopic view underscores the potential usefulness of the device in such circumstances. The better performance by nurses was not clinically relevant (mean difference in intubation time 5.8 s). It may be related to the longer experience of nurses in paediatric anaesthesia compared with resident anaesthetists, who are scheduled to paediatric anaesthesia during a 6-month period only. Although an adequate monitor view of the cords was obtained within a short time period (mean 15 s), insertion of the ETT into the trachea was signi cantly delayed in some patients by the limited manoeuvrability of the tracheal tube within the oropharynx, which made it necessary to re-adjust the angle of the ETT tip. This problem can be partly overcome by directing the ETT from the lateral corner of the mouth, which increases the sagittal manoeuvrability of the ETT tip. However, the lack of manoeuvrability limits the use of the video-assisted technique in patients with reduced mouth opening. It is possible that in such circumstances the ETT would be more easily guided into the trachea with the use of a directional intubation stylet, or by a non-malleable intubation stylet attached to the AVIL as used in the Bullard laryngoscope. 20 The observed intubation times were longer then those reported by Nolan and Wilson, who used the gum elastic bougie intubation technique in patients with potential cervical spine injuries (median 25 s; all within 45 s). 10 There is no doubt that tracheal intubation is more rapidly achieved with direct laryngoscopy and the gum elastic bougie, but the procedure is a blind technique in some cases, with the associated risk of oesophageal intubation, repeated intubation attempts or even failed intubation. It should be noted that, in contrast to the study by Nolan and Wilson, operators in this study had no prior experience with the AVIL. The intubation times achieved should not therefore be directly compared. A strategy that was not explored in this study is the combination of the AVIL with a gum elastic bougie. It is conceivable that this would further facilitate rapid intubation of the trachea with the additional advantage of not having to remove the gum elastic bougie until the ETT tip is placed in its nal position. As the presented technique closely resembles conventional laryngoscopy and did not jeopardize the patients' safety, the technique could be regularly used for training during routine anaesthesia. The AVIL, which does not include control wires and working channels, is much cheaper (estimated cost: 1200), less susceptible to damage during handling and is easier to clean than sophisticated bre-optic bronchoscopes. This allows more frequent use of the angulated video-intubation laryngoscope for training than exible bre-bronchoscopes. 456

5 Video-assisted tracheal intubation The AVIL is cleaned in the same way as exible brebronchoscopes, namely by washing or immersion as well by sterilization using ethylene oxide, except that cleaning the working channels and leak testing do not have be performed with the AVIL. Cleaning of airway devices has become an increasing problem and disposable laryngoscope blades have been proposed to prevent the transmission of infection. 21 The use of disposable AVIL blades, in which the optic channel is closed distally by a small membrane, would protect the inserted brescope from contamination by a patient, so that the bre-optic part could be immediately reused. Fogging of the lens and interference by secretions are problems inherent to bre-optic intubation devices and resulted in prolonged intubation times in six of our 100 patients in this study. Fogging of the lens may be prevented by the use of appropriate anti-fog agents applied by ne gauze. The incidence of lens soiling can be reduced by oropharyngeal suction before insertion of the laryngoscope blade. Carefully guiding the AVIL around the tongue instead of blindly placing the device into the oropharynx further helps to prevent lens contamination with secretions or blood. Oxygen ushing at the distal lens tip, as used in the Bullard laryngoscope, might help to prevent fogging and soiling of the lens by secretions, and also prolongs available time for intubation by apnoeic oxygenation Oxygen insuf ation through the bre-bronchoscope is not recommended during bre-bronchoscopic intubation because of the risk of gastric or pulmonary barotrauma when the scope enters the upper oesophagus or becomes sealed within the trachea. Although different sized AVIL-blades would be bene cial, the device was successfully used in patients aged from 3 months up to 17 yr, in whom at least two or three sizes of exible bre-bronchoscope would have been required. A further bene t of the device over blind railroading of the ETT over a gum elastic bougie or a exible brebronchoscope is the provision of a view of the ETT passing between the vocal cords. On the other hand, exible bronchoscopes provide unrestricted manoeuvrability and allow suctioning of secretions and blood from the airway ± an advantage over the AVIL technique. The dependence on a video-endoscopic monitor system limits the use of the AVIL and thus the technique is currently not suitable for use at an accident site. However, the availability of miniature video screens as reported by Popat and Lehane will broaden the application spectrum. 26 The angulated video-intubation laryngoscope will not replace exible bre-bronchoscopic intubation in all cases of dif cult direct laryngoscopy, but the AVIL provides rapid endoscopic assistance if unanticipated dif culties arise during direct laryngoscopy. In paediatric patients with cervical spine instability requiring immediate emergency tracheal intubation under MILNS, it provides a simple and effective tool for the anaesthetist who is not familiar and/or not equipped with paediatric bre-optic bronchoscopes. The usefulness of the device for children and adult patients with genuine dif cult tracheal intubation and comparison to other endoscopic intubation techniques requires further investigation. A caveat of our study design was to refrain from applying optimal external laryngeal manipulation. This might have improved visualization of the larynx during the MILNS procedure. However, the study design was chosen to provide an ethically acceptable simulation of patients with poor laryngeal visibility during conventional intubation. In conclusion, the angulated video-intubation laryngoscope effectively facilitated tracheal intubation in children, in whom immobilization of the head and neck impaired direct visualization of the larynx. The intubation technique is simple and closely resembles conventional intubation. Intubators therefore become familiar with it after only very brief training. The ef cacy of the AVIL for routine direct laryngoscopy and for genuinely dif cult intubation in children and adults needs to be elucidated and to be compared with other endoscopic intubation techniques. References 1 Berkowitz ID, Raja SN, Bender KS, Kopitis SE. Dwarfs: Physiology and anesthetic implications. Anesthesiology 1990; 73: 739±9 2 Lynn A, Sasaki S. Unusual conditions in paediatric anaesthesia ± syndromes affecting airway management. In: Sumner E, Hatch DJ, eds. Paediatric Anaesthesia. London: Arnold, 1999; 535±51 3 Lipson S. Dysplasia of the odontoid process in Morquio's syndrome causing quadriparesis. J Bone Joint Surgery 1977; 59: 340±4 4 Beighton P, Craig J. Atlanto-axial subluxation in the Morquio syndrome. Report of a case. J Bone Joint Surgery 1973; 55: 478±81 5 Redl G. Massive pyramidal tract signs after endotracheal intubation. A case report of spondyloepiphyseal dysplasia congenita. Anesthesiology 1998; 89: 1262±3 6 Auden SM. Cervical spine instability and dwar sm: breoptic intubation for all. Anesthesiology 1999; 91: 580 (letter) 7 McLeod ADM, Calder I. Spinal cord injury and direct laryngoscopy ± the legend lives on. Br J Anaesth 2000; 84: 705±9 8 Hastings RH, Wood PR. Head extension and laryngeal view during laryngoscopy with cervical spine stabilisation manoeuvres. Anesthesiology 1994; 80: 825±31 9 Heath KJ. The effect of laryngoscopy of different cervical spine immobilisation techniques. Anaesthesia 1994; 49: 843±5 10 Nolan JP, Wilson ME. Orotracheal intubation in patients with potential cervical spine injuries. An indication for the gum elastic bougie. Anaesthesia 1993; 48: 680±3 11 Weiss M, Biro P. Simulated tracheal intubation in cervical spine injury: comparison of the video-optical intubation stylet with the video-optical laryngoscope in a mannequin. Eur J Anaesthesiol 2000; 17 (Suppl 19): 36 (Abstract) 12 McCoy EP, Mirakhur RK. The levering laryngoscope. Anaesthesia 1993; 48: 516±9 13 Cormack RS, Lehane J. Dif cult tracheal intubation in obstetrics. Anaesthesia 1984; 39: 1005±11 457

6 Weiss et al. 14 Siker ES. A mirror laryngoscope. Anesthesiology 1956; 17: 38±42 15 Huffman J. The application of prisms to curved laryngoscopes: a preliminary study. J Am A Nurse Anesthetists 1986; 35: 138±9 16 Bellhouse CP. An angulated laryngoscope for routine and dif cult tracheal intubation. Anesthesiology 1988; 69: 126±9 17 Cooper MG, Donnelly J, Overton JH. Assessment of an angulated laryngoscope for dif cult paediatric intubation. Paediatr Anaesth 1993; 3: 33±6 18 Bjoraker DG. The Bullard laryngoscopes. Anesthesiology Rev 1990; 17: 64±70 19 Shorten GD, Roberts JT. Some applications of beroptics in anesthesia. Anesth Clin North Am 1991; 9: 187±93 20 Cooper SD, Benumof JL, Ozaki GT. Evaluation of the Bullard laryngoscope using the new intubating stylet: comparison with conventional laryngoscopy. Anesth Analg 1994; 79: 965±70 21 Asai I, Uchiyama Y, Yamamoto K, Johmira S, Shingu K. Evaluation of the disposable Vital ViewÔ laryngoscope. Anaesthesia 2001; 56: 342±5 22 Todres ID, Crone RK. Experience with a modi ed laryngoscope in sick infants. Crit Care Med 1981; 9: 544±5 23 Bucx MJL, Droogers W, Mallios C. A method to prevent clouding of the Belscope prism. Anaesth Intensive Care 1994; 22: Hershey MD, Hannenberg AA. Gastric distension and rupture from oxygen insuf ation during bre-optic intubation. Anesthesiology 1996; 85: 1479±80 25 Ovassapian A, Mesnick PS. Oxygen insuf ation through the brescope to assist intubation is not recommended. Anesthesiology 1997; 87: 183±4 26 Popat MT, Lehane J. Miniature screen for breoptic intubation using a camera. Anaesthesia 1997; 52: 802±3 458