AIRWAY PATENCY IN THE UNCONSCIOUS PATIENT

Transcription

1 Br.J. Anaesh. (1985), 57, AIRWAY PATENCY IN THE UNCONSCIOUS PATIENT M. P. BOIDIN Uncociousness may lead o asphyxia from obsrucion of he upper airway. To overcome such airway obsrucion, forward displacemen of he mandible was recommended firs over a cenury ago Heiberg (1874). In 1956 Finck described passive closure of he glois, which occurred in relaively deep anaeshesia and was iniiaed by he ipiraory gasflow when he Bernoulli effec was unopposed by abducion of he vocal cords. However, Shelon and Bosma (1962) showed ha a pharyngeal airway was mainained, jn cocious babies, despie changes in posure or movemens of he pharyngeal srucures. Even when he ongue was pushed backwards forcibly, an airway could be mainained in all babies. They concluded ha he relaive posiion of he mandible, hyoid and sernum, and heir relaion o he 6h cervical verebra, were mainained because of racion on he hyoid bone by he submandibular muscles only. The purpose of his sudy was o deermine wheher obsrucion of he upper airway was primarily a resul of he ongue falling back, or if anoher mechanism was respoible for airway closure in he uncocious paien. PATIENTS, MATERIALS AND METHODS Anaomical preparaio The relaiohips of he pharynx, larynx, hyoid bone and he ongue were sudied in six fresh cadaver preparaio, which were fixed laer in formaldehyde and preserved in alcohol. Paiens Tweny paiens (11 male) (ASA 1) scheduled for M. P. BoiDIN, Sae Universiy of Groningen. Presen address: Universiy hospial Dijkzig Roerdam, and S Ignaius Ziekenhuis, WUhelminasingel 33, P.O. Box 90158, 4800 RK Breda, The Neherlands. SUMMARY Airway paency was explored in paiens breahing sponaneously under deep halohane anaeshesia. Opening and closing of he airway was observed wih a flexible bronchoscope looking proximally from he nasopharynx a he epiglois and he ongue. Wih he occipu elevaed a various angles he smalles angle of reroflexion of he neck necessary o open he airway was measured. The influence of arificial airways on his angle of reroflexion was measured. Cadaveric preparaio of he upper airway were sudied o assess he mechanisms involved in airway paency. The resuls indicae ha he epiglois and no he ongue is he main cause of obsrucion of he upper airway. When mehods are applied o displace he hyoid aneriorly, he airway will be cleared on mos occasio. minor operaio on he exremiies were seleced for sudy. Mos were young (mean age 33 yr, range yr), of average coiuion and free from any disease of he air passages or lungs. Three paiens had a denal proshesis which was removed during he sudy. Each paien gave informed coen before enering he sudy. Anaeshesia was induced wih hiopenone 4 mg kg" 1 i.v., followed by sponaneous breahing of a mixure of oxygen, nirous oxide and halohane from a well-fiing face mask via a circle sysem. A fresh gas flow of 1.5 imes he paien's esimaed minue volume was used. The deph of anaeshesia was mainained a Guedel sage 3-2 wihou addiional opioids. The paiens were in a supine posiion on a fla operaing able. Neuromuscular blocking drugs were no given. A flexible bronchoscope (Olympus, ype BF- B3R) wih an operaive lengh of 60 cm and a diame-

2 AIRWAY PATENCY 307 er of almos 6 mm, was passed hrough a hole in he face mask via he nose and ino he naso-pharynx. No leak of gas was allowed and he expired volume was measured breah-by-breah (Drager Volumeer). The angle of reroflexion was recorded as he angle beween he horizonal plane of he operaing able and he line connecing he laeral corner of he eye and he ragus of he ear. The angle subended by he head in he neural posiion wihou manipulaion was recorded iniially, hen he head was exended slowly wih he mouh closed unil a free airway was esablished (fig. 1). A clear airway was indicaed by he expired idal volume becoming maximal. This manipulaion was repeaed wih an oral (mouh open) and a nasal pharyngeal airway (mouh closed) in place. The firs measuremens were underaken wihou elevaion of he occipu. All measuremens were hen repeaed wih pillows o produce a 4- and 8-cm elevaion of he occipu above he operaing able. During he measuremens he flexible bronchoscope remained in posiion behind he uvula, looking proximally a he srucures in he mouh, he vocal cords and he epiglois. The bronchoscope could be advanced in he direcion of he lower pharynx when necessary. Saisical analysis of he angles of reroflexion was performed using Suden's es for paired values. Measuremens wih and wihou he arificial circle sysem wih face mask airways were compared, and measuremens a vari-' ous heighs of he occipu (above he able) were compared wih elevaion of he occipu o 4 cm. RESULTS Anaomical preparaio In he cadaveric preparaio i was obseved ha he ongue did no usually reach o he poserior pharyngeal wall, because i was aached mainly o he poserior aspec of he mandible a he chin. When he ongue of he cadaver was pushed forcibly ino he mouh, obsrucion occurred mainly a he level of he sof palae by closure of he naural oral airway. When more pressure was exered, he naural nasal airway was occluded also, he sof palae being pushed agai he poserior pharyngeal wall. In he lower pharynx, wo mechanisms of obsrucion occurred which were independen of manipulaion of he ongue. The base of he epiglois closed over he rachea and he rims of he epiglois came ino conac wih he poserior pharyngeal wall and could close he respiraory rac. The visible par of he epiglois, he pars gloica, could exend ino he oesophagus and so proec he ineraryenoid fold from conaminaion wih foreign maerial. In one cadaveric preparaion he ongue was removed from he hyoid bone and i was angle of reroflexion (see ex) FIG. 1. The breahing circui,flexiblebronchoscope, pillows and landmarks ( ) used in his sudy o measure he posiion of he paien's head and o observe he mechanism of airway closure.

3 308 BRITISH JOURNAL OF ANAESTHESIA TABLE I. Angles of reroflexion of he head (mean (SD)) in 20 paiens. Significance calculaed wih he es for paired values: condiio compared wih he "no-adjunc' group fp < 0.001; elevaio ofo and 8 cm compared wih he values measured a 4 cm **P < 0.01; P < Upper airway closed Neural posiion Upper airway clear Elevaion of occipu 0 cm No adjunc 114(7.1) Oral airway 114(5.5) ** 110(5.5) 101(9.3) ** Nasal airway 4 cm 8 cm 105(9.1) 96(6.5) 91(2.3) * * 109(5.5) 102(8.2) 112(6.8) 106(7.1) 97(10.8) observed ha i was possible o obain an airigh seal in he upper airway wih he epiglois alone. The hyoid bone is horse-shoe shaped and can be moved in all direcio by he acion of he exriic pharyngeal muscles, alhough here is some resricion o movemen in a caudal direcion. The hyroid carilage is suspended from he hyoid bone and i is fixed dorsally o he dorsal conjoined endon of he pharyngeal muscles, which is in urn conneced o he preverebral fascia. The epiglois hangs, like he lid of a bin, from he poserior aspec of he hyoid wih he hyro-epigloic ligamen acing as he hinge and he hyo-epigloic ligamen acing as he lever for he lid. In he cadaveric preparaio i was demoraed ha he posiion of he epiglois in he hypopharynx depended principally on he relaive posiion of he hyoid in relaion o he hyroid carilage. Paiens The angle of reroflexion (able I) necessary o open he airway was no alered subsanially by he use of arificial airways in he hypopharynx. However, in eigh of he 20 paiens, wih a nasopharyngeal airway a 8 cm elevaion, and in one paien a 4 cm elevaion, here was a small difference in he required angle of reroflexion compared wih he angle in he neural posiion. In hese paiens he nasal airway suppored he epiglois clear of he reropharyngeal wall. In he oher paiens he angle of reroflexion required o open he airway was significanly greaer han ha presen in he neural posiion. The angle of reroflexion, required o achieve a clear airway became smaller as he occipu was elevaed, and once he airway began o open, only a lile more il was required o open i fully (fig. 2). epiglois hyoid bone hyroid carilage FIG. 2. Cross-secion of he larynx, showing obsrucion of he upper airway by he epiglois (A). Anerior displacemen of he hyoid bone by he exra pharyngeal muscles clears he airway (B).

4 AIRWAY PATENCY 309 The mechanism of airway closure was visualized using heflexiblebronchoscope. Wih his mehod i could be demoraed ha he epiglois was sucked over he enrance o he rachea by he ipiraory pressure and his occurred well before he ongue even approached he poserior pharyngeal wall. The airway was closed as he rims of he epiglois reached he pharyngeal wall. When aemps were made o venilae a paien wih he epiglois in his posiion, he pars gloica could be seen being forced ino he oesophagus. The gas mixure migh hen ener he oesophagus and be passed ino he somach. As he head was exended he epiglois was wihdrawn from he racheal enrance. When parial obsrucion occurred and he op of he epiglois vibraed in he lower pharynx, he characerisic snoring sound could be heard. DISCUSSION These observaio indicae ha he ongue is no he only facor concerned wih upper airway obsrucion. The mechanism is more complicaed and i seems necessary o recoider he facs. The daa presened by Safar and colleagues (1959) were accurae, bu heir conclusion, ha he ongue is he sole source of upper airway obsrucion, is no wholly jusified, as i has been shown ha he airway may close even when he ongue is bypassed. The hyoid bone can be coidered as forming he boundary of he wide end of wo funnels, he larynx and he pharynx, boh of which are suspended from he base of he skull and exend ino he horax. Which funnel is opened/closed is deermined by he posiion of he epiglois which, in urn, depends on he anero-poserior posiion of he hyoid bone in relaion o he hyroid carilage. This posiion may be alered volunarily by he exrapharyngeal musculaure of he hyoid bone, whereas he hyroid carilage remai raher immobile. I seems ha he omohyoid muscle, and he anerior belly of he digasric muscle, are essenial o manoeuvre he hyoid bone owards is venral posiion. I is obvious ha his does no occur in uncocious paiens. For he same reason, i is probable ha he riple airway manoeuvre (Morikawa, Safar and DeCarlo, 1961) remai he mos successful mehod of opening he airway because his manoeuvre moves he hyoid venrally. On he oher hand, he inroducion of a somach ube and an oesophageal oburaor airway should be assised byflexionof he neck, o push he hyoid bone backwards. This invesigaion showed ha he airway is hyoid bone epiglois hyroid carilage oesophagus rachea FIG. 3. The posiion of he hyoid bone deermines which of wo funnels is opened/closed. Noe ha he ongue is pushed away by he pressure of he epiglois in posiion (B).

5 310 BRITISH JOURNAL OF ANAESTHESIA almos invariably closed when he head is in is neural posiion, and ha he use of arificial airways did no always guaranee a clear airway. The airway was clear when he nose or he mouh, or boh were open, and he epiglois did no reach o he poserior pharyngeal wall. The ongue may obsruc he upper airway in wo Ways. I may push he sof palae agai he poserior pharyngeal wall, obsrucing boh he nasal and oral caviies. The ongue may close he oral caviy when he nose is obsruced, hen acing as a one-way valve obsrucing expiraion. In boh cases of obsrucion by he ongue here is an indicaion for Mayo or Guedel ype airways. Obsrucio of his ype were no seen during his sudy, bu are occasionally noiced in paiens wih a denal proshesis. The effec of opening he mouh wih a Mayo airway does no decrease significanly he angle of reroflexion, nor does he inroducion of arificial airways. Only he elevaion of he head decreases he head il necessary o clear he airway. When he head is elevaed, a nasal pharyngeal airway of sufficien lengh o suppor he epiglois will ofen provide a clear airway and decrease he angle of reroflexion significanly. However, in hese paiens i was possible o obsruc he upper airway byflexionof he neck. This concep of airway closure may conribue o he raining of medical and paramedical personnel and explain he managemen of he airway and he use of arificial airways, somach ubes and racheal ubes. However, a presen i does no seem pruden o give such complicaed deailed informaion during he raining of he lay public, alhough i may be possible o use a simplified version of his concep. REFERENCES Finck, B. R. (1956). The eiology and reamen of laryngeal spasm. Aneshesiology, 5, 569. Heiberg, J. (1874). A new expedien in adminisering chloroform. Med. Times Gaz., Jan. 10. Morikawa, S., Safar, P., and DeCarlo, J. (1961). Influence of he head jaw posiion upon airway paency. Aneshesiology, 22, 265. Safar, P., Lourdes, A., Escarraga, L. A., and Chang, F. (1959). Upper airway obsrucion in uncocious paiens. J. Appl. Physiol., 14, 760. Shelon, R. L., and Bosma, J. F. (1962). Mainenance of he pharyngeal airway. J. Appl. Physiol., 17,209.