Special Article Laryngoscope design and the difficult adult tracheal intubation

Transcription

1 94 J.W.R. Melntyre MRCS LRCP FRCPC Speial Artile Laryngosope design and the diffiult adult traheal intubation Clinial examination of a patient is very likely to reveal the fators making traheal intubation diffiult and thus inreasing the likelihood of a traumatized temporo-mandibular joint or mouth. Although laryngosopes and bronhosopes inorporatingfiberoptie visual devies are invaluable they are usually only employed for extremely diffiult patients. Other laryngosopes exist in a variety of designs and an be ategorised aording to the partiular problem they address: (i) prominent sternal region, (io narrow spae between the inisors, (iii) redued intraoral spae and, (iv) the anteriorly positioned larynx. An atraumati traheal intubation will be assisted if the laryngosope blade to be used is seleted on the basis of the anatomi diffiulties presribed by the patient, The Miller, Jakson- Wisonsin, Maintosh, Soper, izarri-guffrida. and ainton blades together with appropriate handles and fittings omprise a group from whih seletion an be made. Many laryngosopes have been designed sine William MaEwan in 1878 passed a tube from the mouth into the Irahea using his fmgees as a guide. J The purpose has been to provide appropriate and rapid aess to the trahea and minimize damage to teeth, tempero mandibular joints, and other vulnerable strutures. A laryngosope onsists of a handle joined by a folding fitting to a blade that inorporates arrangements for lighting. The blade omprises a fitting, spatula, beak and flange. The flange projets from the edge of the spatula and serves to deflet interfering tissues. In some models the flange is uniformly urved, in others it lies at right-angles to the spatula at first and then hanges diretion. This initial vertial piee and even the ross- Key words COMPLICATIONS: intubation, traheal; EQUIPMENT: laryngosopes; INTUAT[ON: tehnique. From the Department of Anaesthesia, University of Alberta, Street, Edmonton, Alberta T6G 27. setional height of a parabola-shaped piee is sometimes referred to as a step. Currently popular laryngosope blades in the United States market are the Miller 2 (Figure 1), the Jakson-Wisonsin (Figure 2), and the Maintosh 3 (Figure 3). In Canada the Maintosh blade is the most popular. All were designed approximately fifty years ago and during the subsequent period numerous new designs have been proposed. These address speifi problems presented by patients that ould be diffiult to intubate 4 and indeed some of the design hanges might have rendered the blade more appropriate for routine use in the operating room as well. However, suh attempts have been largely unsuessful and the popularity of early blades remains. Morbidity assoiated with traheal intubation ontinues to our a and inreasingly stringent standards of pratie are demanded. The purpose of this presentation is to lassify laryngosopes aording to the linial problem that they partiularly address and enourage the problem-oriented approah to laryngosope seletion, assuming that a laryngosope or bronhosope inorporating a fiberopti visual devie will not be used. The Miller laryngosope was desribed in and referene is not made here to medial literature before that date. Only subsequent designs have been inluded. Additional blades that apparently have not been doumented by their designers in the medial literature and not readily available ommerially although desribed by Dorsh and Dorsh 6 are not inluded. Problems presented by patients, with referene to laryngosope design Protruding sternal region The handle of many straight-bladed laryngosopes lies approximately 90 degrees to the blade. In the ase of the blade urved throughout its length, suh as that designed by Maintosh, 3 the important feature is the 58 degree angle between the part of the blade initially inserted into the mouth and the handle.7 In either instane if the patient is obese, has a prominent sternum, or is in a body ast, use CAN J ANAESTH 1989! 36: I / pp94-s

2 Mlntyre: LARYNGOSCOPE DESIGN 95 A A FIGURE l The Miller blade: A, side view;, top view; C, fitting view. FIGURE 2 The Jakson -Wisonsin blade: A, side view;, top view; General Caption for Figures I to 6. A laryngosope blade onsists of fitting to the handle, spatula, beak and flange. The top is that part that appropriates the roof of the mouth. The bottom ontats the tongue. In side view the flange is seen nearest to the viewer. The fitting is viewed end-on as it would be seen by the anaesthetist after the blade had been positioned in the moulh. of a onventional laryngosope may be impossible and the appliation of rioid pressure may be hindered. Suh diffiulties have been addressed by inreasing the angle between the blade and the handle 7- t2 and by offsetting the blade from the handle Setting the handle more in line with the blade sarifies the mehanial advantage of the 90 degrees angle and alters a pattern of use to whih the anaesthetist is likely to have beome austomed. Ideally the ability to apply fore.should not play a role in modem traheal intubation. However, if this is onsidered important, a simple and attrative solution has been to allow the angle to remain the same and halve the length of the laryngosope handle, t4 Narrow spae between fully parted inisor teeth In the late 1930's ommonly employed laryngosopes inorporated a blade that was a straight tube opened longitudinally at the right side and whih might have a beak extending beyond the distal end. To failitate insertion of the blade and its subsequent upward angulation Miller 2 flattened the flange thus reduing the height of the step (Figure l). Subsequently other anaesthetists redued the area of the flange even more or abolished it altogether, and redued the height of the step.is- ~9 Other blades, straight and designed for diret lifting of the / -- L FIGURE 3 The Maintosh blade: A, side view;, top view; epiglottis, have a redued step and a flange whih is reversed 2~ (Figure 4). The reversed flange, redued step, and some urvature throughout the length of the blade were believed to be attrative design features by many anaesthetists, partiularly if the beak was designed for indiret lifting of the epiglottis.s,21,22 A omparison of the Maintosh 3 (Figure 3) with the izarri-guffrida blade 22 (Figure 5) illustrates modifiation of the urved blade by redution of the step. Although redution of the step is helpful, partiularly as an aid to angulation of the blade in patients with

3 96 CANADIAN JOURNAL OF ANAESTHESIA / I FIGURE 4 The Soper blade: A, side view;, top view; C, fitting view. mirognathia or maxillary overgrowth, the traheal tube itself often must pass between the teeth as well. Suh blades may not neessarily provide easier onditions for intuhation unlesg missing molar or premolar teeth provide a spae through whih it an be passed. The surgery proposed may permit a nasal route for the tube but attempts risk the life-threatening event of profuse nasal bleeding in art anaesthetised, perhaps paralysed, patient who annot be intubated. In addition, abolition of the step sarifies its role in maintaining separation of the upper and lower teeth one the blade has been positioned appropriately. However, if the larynx is to be visualised it does make it almost impossible to use the blade as a lever using the upper teeth as a fulrum - a ause of dental damage. Redued infra oral avity The available spae for the laryngosope blade and manipulation of the traheal tube is redued if the oral avity is small and funnel-shaped. A large tongue has a similar effet whih will be ompounded by a narrow submental angle or sarring in the front of the nek hindering ompression of the tongue. Under these kumstanes vision and tube diretion may be assisted by a blade with a substantial flange and step. The Wisonsin laryngosope is suh an instrument ~'~ (Figure 2) as are the Flagg 24 and Guede124 laryngosopes. Modifiation of these straight blades to improve their versatility has also involved some redution of the step, flange, or beak. t6.19,25 Another proposal to help ope with the large tongue has been to widen the reversed flange of the Maintosh blade and to add an additional flange on the other side to keep the right-hand heek of the patient out of the way. z6 Another possibility is to use the left-handed versions of FIGURE 5 The izarri-guffrida blade: A, side view;, top view; Maintosh and Miller instruments that were produed originally to aommodate left-handed anaesthetists. 27-z9 Traumatised tissues, malformations, and tumours on the right side of the month an ause serious interferene. Straight blades that are wholly or partially tubular possess a lumen that will aommodate the endotraheal tube and through whih other manipulations are possible. There is renewed interest in modifying 3~ (Figure 6) laryngosope blades designed many years ago and still popular with ENT surgeons. The "anterior" larynx A ommon triad that makes intubation partiularly diffiult ours when the voal ords are anterior to the anaesthetist's line of vision, the tip of the tube approahes the voal ords at an angle approahing 90 degrees, and the oropharynx is partiularly small. "Straight" blades designed to elevate the epiglottis diretly often have a distal urve or beak diretet] anteriorly. Theoretially 19"32 this is helpful and explains the widespread use of suh blades. Sine 1941 many new blades have been designed with that triad in mind whih suggests that neither the Miller blade nor the original design of the Maintosh blade is ideal under these irumstanes. 3a In 1944 Maintosh had modified his original straight blade with its epiglottis retrator and introdued a urve blade to elevate the epiglottis indiretly by strething the hypo epiglotti ligament, a4 The instrument provided more room in the oropharynx, but he did not believe that for routine use there was a differene between three urves tested. 34 The priniples of the

4 Mlntyre: LARYNGOSCOPE DESIGN 97 FIGURE 6 The ainton blade: A, side view;, top view; C, fitting view; D, ross setion of bak. Maintosh blade were reognised as sound for routine patients and modifiations were direted to improve performane in patients who presented the triad of diffiulties and perhaps others as well.'* Fink applied information aquired during an oropharyngeal airway study 35 to the design of the Fink blade. The wider blade with an inreasingly anteriorly urved tip would enable the hyoid bone to be pushed forward from behind in the valleula dragging the epiglottis with it. This inreased exposure of the voal ords and the room in whih to manoeuvre the traheal tube. Gabuya and Orkin 36 raised the level of the middle third of suh a blade and diminished the radius of the urved tip of the blade as well as extending it. They emphasised that to produe optimum results after insertion into the valleula the blade must be withdrawn slightly while simultaneously elevating the root of the tongue in an anteroephalad diretion. This manoeuvre an be valuable when other laryngosope blades are in use. Mirrors and prisms have had a plae in medial optis for a long time and Siker's and Hoftman's mirrors 37'3s improved visualisation of the voal ords. However, under these diffiult irumstanes it has been the inorporation of fiberopti visual devies in bronhosopes and laryngosopes 39'4~ that has simplified intubation of the anteriorly plaed larynx. Disussion and onlusion In North Ameria three laryngosope blades, urved (Maintosh), straight (Wisonsin) and straight with urved tip (Miller) fulfil anaesthetists' requirements for most patients. However, as every experiened liniian knows, going through every "trik of the trade" using one's favourite blade, taking the neessary time, and exerting the neessary fore may not be in the patient's best interests even though the tube is eventually passed into the trahea. Under ideal irumstanes preanaestheti examination 4 will identify the patient for whom intubation employing a bronhosope 39'4~ or laryngosope inorporating a fiberopti visual devie is highly desirable. If this is not deemed neessary, a laryngosope blade suitable for the oasion must be seleted. Sykes 41 stated that: "Aessories for endotraheal anaesthesia are without end. There is no living anaesthetist who holds the distintion of not having designed one or more." Aessories must inlude laryngosope blades and testifies to the ontinuing diffiulty of intubating some patients. The basis for the design of new laryngosopes seems to have been x-ray and anatomial studies as well as mental imagery derived from linial experienes. As there are many individual fators influening the proess of intubation, it is not surprising that detailed evaluations of the performane of any partiular laryngosope blade are extremely rare and ritial analysis virtually nonexistent. Eah anaesthetist has a preferene based on his linial experiene. Any one of a wide variety of blades an be suitable for the routine patient one the anaesthetist has learned how to use it. However, ertain blades have been designed to help ope with problems that present only oasionally. These an be lassified aording to the intubation problems that seem to have been addressed by the design. A representative seletion omprises the Maintosh, izzari-guffrida, Wisonsin, and ainton blades with appropriate handles and fittings. On the basis of linial examination the anaesthetist an selet the laryngosope most likely to be helpful. That group of instruments should also be readily available for use when a patient is unexpetedly diffiult to intubate. Aknowledgement The generous assistane of Mr. A.C. Salerno, Anesthesia Medial Speialities, East Park Avenue, Santa Fe Springs, California U.S.A., who supplied some of the laryngosope blades, is gratefully aknowledged. Referenes 1 MaEwan W. Clinial observations on the introdution of traheal tubes by the mouth instead of performing traheotomy or laryngosopy. r Med J 1880; 2:122-4, Miller RA. A new laryngosope. Anesthesiology 1941 ; 2: Maintosh RR. A new laryngosope. Lanet 1943; 1: Mlntyre JWR. The diffiult traheal intubation. Can Anaesth So J 1987; 34: Cooper J, Newbower RS, Kitz RJ. An analysis of major errors and equipment failures in anesthesia manage-

5 98 ment: onsiderations for prevention and dettion. Anesthesiology 1984; 60: , 6 Dorsh JA, Dorsh SE. Understanding anesthesia equipment. Williams and Wilkins, altimore. 2nd ed Jellioe JA, Harris NR. A modifiation of a standard laryngosope for diffiult traheal intubation in obstetri ases. Anaesthesia 1984; 39: Maeth RG, annister F. A new laryngosope, Lanet 1944; 247: owen RA, Jakson/. A new laryngosope. Anaesthesia 1952; 7: eaver RA, Speial laryngosopes. Anaesthesia 1955; 10: KesseUJ. A laryngosope for obstetrial use, an obstetrial laryngosope. Anaesth Intensive Care 1977; 5: Lagade MRG, Poppers PJ. Revival of the polio laryngosope blade. Anethesiology 1982; 57: Yentis SM. Alaryngosopeadaptorfordiffiuhintubation. Anesthesia 1987; 42: Datta S, riwa J. Modified laryngosope for endotraheal intubation of obese patients. Anesth Analg 1981; 60: 120-1, 15 Wiggin SC. A new modifiation of the onventional laryngosope and tehni for laryngosopy. Anesthesiology 1944; 5: Portzer M, Wasmuth CE. Endotraheal anesthesia using a modified Wis-Foregger laryngosope blade. Cleve Clin Q 1959; 26: Gubya R, Orkin LR. Design and utility of a new urved laryngosope blade. Anesth Ana]g 1959; 38: Shapira M. A modified straight laryngosope blade designed to failitate endotraheal intubation. Anesth Analg 1973; 52: Phillips OC, Duerksen RL. Endotraheal intubation: a new blade for diret laryngosopy. Aneslh Analg 1973; 52: Soper RJ. A new laryngosope for anaesthetists. r Med J 1947; 1: GouldR. Modified laryngosope blade. Anaesthesia 1954; 9: izarri DV, GuffrMa JG. Improved laryngosope blade designed for ease of manipulation and redution of trauma. Anesth Analg 1958; 37: Onkst HR. Modified laryngosope blade. Anesthesiology 1961; 22: Gillespie N. Endotrahaeal anaesthesia. University of Wisonsin Press, 1st ed. 194]. 25 SnowJC. Modifiationoflaryngosope blade. Anesthesiology 1962; 23: 394, 26 DeCiutiis VL. Modifiation of Maintosh laryngosope. Anesthesiology 1959; 20: Cartwright FF. Devies for anaesthesia in throat surgery. Anaesthesia 1953; 8: CANADIAN JOURNAL OF ANAESTHESIA 28 Pope ES. Left-handed laryngosope. Anaesthesia 1960; 15: Lagade MRG, Poppers P J, Use of the left-entry laryngosope blade in patients with right-sided oro-faeial lesions. Anesthesiology 1983; 58: Homan, Hild J, Georgi W. Das modifizierte kleinsasserrohr: ideal fur dieshwierige intubation. Anaesthetist 1985; 34: ainton CR. A new laryngosope blade to overome pharyngeal obstrution. Anesthesiology 1987; 67: Cassels WA. Advantages of a urved laryngosope. Anesthesiology 1942; 3: Maintosh RR. An improved laryngosope. r Med J 1941; 27: Maintosh RR. Laryngosope blades. Lanet 1944; 246: Fink R. Roentgen ray studies of airway problems. 1. The oropharyngeal airway. Anesthesiology 1957; 18: Gabuya R, Orkin LR. Design and utility of a new laryngosope blade. Anesth Analg 1959; 38: 364-9, 37 Siker ES. A mirror laryngosope. Anesthesiology 1956; 17: Huffman J, Elam JO. Prisms and fiber optis for laryngosopy. Anesth Analg 1971; 50: Patil VU, Stehling LC, Zanier HC. Fiberoptie endosopy in anaesthesia. Year ook Medial Publishers In. Chiago; 1983, 40 Donlon Jg. Anesthesia for Eye, Ear, Nose, and Throat. In: Miller, RD (Ed). Anesthesia. 2nd ed. Vol 3. Churhill Livingstone, New York 1986; Sykes WS. Essay on the first hundred years of anesthesia. Vol 2. E & S Livingstone, Edinburgh 1961; Ch 7. R6sum6 Lors de l'examen physique d'un patient, on peut habituellepnent pr~dire si l'intubation trahdule risque d'dtre diff~ile et suseptible d'endommager bouhe et artiulation temporomandibulaire. Pourtant, on a tendane ~ rdserver I'usage des laryngosopes et bronhosopes ti fibres optiques flexibles au.r as les plus omplexes. On peut lassifier les autres types de laryngosope en fontion des partiularitds anatomiques qu' ils permettent de ontourner: sternum prodminent, espae resleh~t entre les inisives, petit volume de la avitd orale, laryrv dit antdrieur. En hoisissant parmi les Miller, Jakson-Wisonsin, Maintosh, Soper, izarri-guffrida et ainton, les lames et manhes de larygosope appropri~s ~ la morphologie dn patient, on pourra plus failement intuber la trahde en doueur.