Berlis, Ansgar

Hildebrandt, G.

Kersjes, W.

König, R.

Schild, H.

Schunk, K.

English

OPUS Augsburg

                                          A New Technique for Oral EndotrachealAirway Access in Rabbits underFluoroscopic Control: An Easy Way for DrugAdministration in Chronic ExperimentsW. Kersjes G. Hildebrandt K. Schunk R. König A. BerlisH. SchildDepartment of Radiology, University of Bonn, Germany                                                 Wilhelm Kersjes, MDDepartment of Radiology, University of BonnSigmund-Freud-Strasse 25D–53105 Bonn (Germany)Tel. +49 228 9289670, Fax +49 228 9289671                                                                                                                                                                                                                                                               AbstractEndotracheal  drug  administration  plays  animportant role in rabbit models of pulmonaryinjury and lung disease. However, anatomi-cal features of the oral fissure and pharynx ofrabbits  make  orotracheal  intubation  a  diffi-cult  task with a high failure rate.  We devel-oped a  new technique for  airway access  inrabbits  under  fluoroscopic  control  using  aballoon catheter.  The procedure consists  offour  major  steps:  (1)  a  shortened  5-frenchvertebralis catheter is placed into the meso-pharynx  just  above  the  epiglottic  valve,  (2)through  the  catheter  lumen  a  guidewire  iscarefully moved across the epiglottis and in-serted  into  the  trachea,  (3)  the  vertebraliscatheter is replaced by a balloon catheter thatsubsequently is introduced into the trachealtree over the guidewire, and (4) with the bal-loon catheter in the right position the guide-wire is removed and the balloon is inflated sothat  finally  the  drug  can  be  delivered.  Thisprocedure was performed in 55 New ZealandWhite rabbits under general anesthesia withketamine/xylazine. In all 55 cases the proce-dure  was  performed  successfully  withoutany  major  complications  and  within  a  rea-sonably  short  time  period.  Removal  of  thecatheter and awakening of the animals wereuneventful. The described technique is a sim-ple and safe method for airway access in rab-bits and can be useful in chronic experimentsfor endotracheal drug administration.IntroductionEndotracheal drug administration plays animportant role in rabbit models of pulmonaryinjury and lung disease. However, because ofthe narrow mouth, the relatively thick tongue,Downloaded by:UB Augsburg137.250.131.3 - 1/27/2022 8:58:16 AM                                                                                 the upper incisors and because of the presenceof sagittal niches located along both sides ofthe vocal cords getting airway access is knownto be a difficult task. Various techniques forairway access have been described. The stan-dard technique of orotracheal intubation hasbeen  successfully  modified  by  differentgroups  [1–6].  In  acute  animal  experimentsairway access may also be gained by trache-ostomy.  However,  in  chronic  experimentalstudies tracheostomy can present difficulties.Although  these  difficulties  can  be  avoidedpartially by using retrograde orotracheal intu-bation  [7]  this  procedure  still  causes  directtrauma to the cervical soft tissue and to thetrachea.We introduce a new technique for airwayaccess and endotracheal drug administrationin rabbits. The technique we used is related tothe  well-known  Seldinger  technique  oftenused in interventional radiology.Material and Methods55 New Zealand White rabbits weighing between2.5 and 3.5 kg were studied. All procedures were per-formed after initial administration of 1–2 ml generalanesthesia [4 ml ketamine (50 mg/ml), 2.5 ml xylazine(0.02 mg/ml), 0.9% NaCl ad 50 ml] into an ear vein,followed by repeated injection of 0.2–0.5 ml to main-tain  anesthesia  as  needed.  Fluoroscopy was  used  formonitoring and documentation of each step during theprocedure.After  the  onset  of  general  anesthesia  the  animalswere placed in a lateral decubitus position their neckbeing overextended. Their  mouth was opened gentlyand a 5-french vertebralis catheter that had been short-ened to a length of 25 cm was placed into the mesopha-rynx just above the epiglottic valve. Through the cathe-ter lumen a Terumo® guidewire was introduced. Most-ly the guidewire first entered the proximal esophagus(fig. 1). In this case the catheter was also slid into theesophagus  and  the  whole  system  was  subsequentlydrawn back with the curved tip of the guidewire point-ing  to  the  front.  The  correct  position  of  the  systemimmediately proximal to the epiglottic valve was indi-cated by a sudden ventral movement of the tip of theguidewire (fig. 2). Careful movements of the guidewiretip made the animals swallow due to contact with thepharyngeal  mucosa.  While  swallowing  the  guidewirecould be carefully moved forward across the epiglottisand inserted into the trachea. After correct placementof the guidewire into the trachea the catheter was alsoadvanced  into  the  trachea  (fig.  3).  Subsequently  theanimals  were  rotated  into  a  prone  position  and  theTerumo guidewire was replaced by a thinner guidewirewith a very soft  distal  tip (Terumo guidewire with adiameter of 0.018 inch, 0.46 mm. This guidewire couldbe placed into the distal tracheal tree without any diffi-culties  and  without  causing  injuries  to  the  tracheo-bronchial  tree  or  lung  parenchyma.  Finally  the  5-french vertebralis catheter was exchanged for a ballooncatheter which was introduced into either the right orleft lower lobe bronchus over the guidewire. After cor-rect positioning of the balloon catheter the guidewirewas removed and the balloon was inflated with a smallamount of contrast  medium (Solutrast® 300) (fig. 4).Now the drug could be administered.In  our  study  either  bleomycin  sulfate  (10  mg/kgbody weight) diluted in 5 ml 0.9% NaCl solution (n =44), or 5 ml of pure 0.9% NaCl solution (n = 11) wereslowly delivered to the lung. After the application ani-mals were rotated carefully in order to get a homoge-neous  distribution  of  the  instilled  agent.  During  thewhole  procedure  the  balloon  was  kept  inflated  todelimit the area of the involved lung tissue from theremaining healthy uninvolved lung parenchyma. Dur-ing the removal of the balloon catheter and for the next5–10  min  the  animals  were  kept  in  a  left  or  rightrecumbent position depending on the side into whichthe agent was injected. After complete awakening fromanesthesia the animals were put back into their box.Finally, the animals were killed with 20 ml of keta-mine/xylazine [4 ml ketamine (50 mg/ml), 2.5 ml xyla-zine (0.02 mg/ml),  0.9% NaCl ad 50 ml]  plus 20 mlpotassium hydrochloride solution (1 mol/ml) at differ-ent time intervals (3 and 24 h, 8, 14, 30 and 80 days)after  intrabronchial  application  of  the  agents.  Thelungs were removed and a fixative solution of 10% for-malin was infused into the trachea under the pressureof 10 cm H2O. After being immersed in the fixativesolution for 4 weeks, the lungs were cut into 10-mmslices and certain areas were selected for histologicalstudies after hematoxylin-eosin and van Gieson/elas-tica staining.Downloaded by:UB Augsburg137.250.131.3 - 1/27/2022 8:58:16 AM                                                                             Fig. 1. Guidewire and catheter are positioned in theproximal esophagus.Fig. 2. Retraction of catheter and guidewire into thelarynx immediately above the epiglottic valve with thetip of the guidewire pointing to the front.Fig. 3. Introduction of guidewire and catheter into thetrachea.Fig.  4.  Inflated  balloon  catheter(with  contrast  me-dium) in the right main bronchus for selective and safeintrabronchial drug administration.Downloaded by:UB Augsburg137.250.131.3 - 1/27/2022 8:58:16 AM                                                                                 ResultsIn all 55 cases endotracheal or endobron-chial  placement  of  the  balloon  catheter  andadministration  of  the  drug  were  performedsuccessfully.  On  average,  the  procedureslasted between 10 and 15 min from the onsetof general anesthesia until the drug could bedelivered.  Removal  of  the  balloon  catheterand  awakening  were  uniformly  uneventful.All animals tolerated the procedures very wellwithout major complications or death.Examination  of  specimens  from  tracheaand lungs did not show any macroscopic inju-ry  due  to  the  technique  itself.  At  histologicevaluation lung tissue, which was altered sec-ondarily to drug effects, could clearly be de-limited  from  the  remaining  healthy  unin-volved lung parenchyma. Without exceptiondrug  effects  were  restricted  to  the  lung  areathat was demarcated by the inflated balloon.DiscussionAirway access in rabbits is known to be adifficult  task.  Davies et  al.  [3]  reported thatthe standard technique of orotracheal intuba-tion is enormously facilitated by placing theoperator behind the animal, viewing it fromthe dorsal surface of the head. Krüger et al. [5]recommended the use of a transparent tube inorder to see respiration moisture with the tubein  the  correct  location.  Since  the  tube  willobstruct  the  view  of  the  vocal  cords  whenintroduced  into  the  channel  of  the  laryngo-scope, Bechtold and Abrutyn [2] developed away  of  side  placement  of  the  endotrachealtube  into  the  rabbit  mouth  that  permittedvisualization of the laryngeal structures. Thesame problem was overcome by Macrae andGuerreiro [6] who inserted a tube which con-tained a catheter extending beyond the open-ing  and  into  the  trachea.  Blind  intubationwithout  the  use  of  a  laryngoscope  was  per-formed  by  Alexander  and  Clark  [1]  and  byFick  and  Schalm  [4].  Their  results  indicatethat the narrowness of the oropharynx lowersthe  chances  of  misplacing  the  tube  into  theesophagus. In acute animal experiments tra-cheostomy  provides  an  alternative  methodfor airway access. However, in chronic experi-mental studies the suturing of a tracheostomais difficult and can be hazardous. These diffi-culties can be avoided partially by using retro-grade orotracheal intubation. Corleta et al. [7]described  a  modification  of  the  retrogradeorotracheal  intubation  technique  with  theintroduction  of  an  orotracheal  tube  over  aguidewire.  The  guide  was  inserted  into  thetrachea  via  cervicotomy  and  deliveredthrough the mouth. However, this procedurestill causes direct trauma to the cervical softtissue and to the trachea.In comparison to the technique describedabove  our  method  of  getting  airway  accessand of endotracheal drug administration hasbeen  shown  to  be  very  reliable,  simple  andsafe.  The  placement  of  the  balloon  cathetercould be performed without any trauma to theoropharyngeal mucosa, the trachea or the dis-tal tracheal tree. However, the use of a guide-wire  with  a  very  soft  tip  is  strongly  recom-mended  for  the  prevention  of  injuries.  It  isalso important not to increase force if the for-ward  movement  of  guidewires  or  cathetersbecomes  more  difficult.  A  repeated  carefulmovement back and forward is often helpfulin  this  situation.  All  procedures  should  bedone under fluoroscopy. The use of contrastmedium for  balloon  inflation  allows  for  theearly detection of complications like incorrectcatheter  position,  for  example  complete  oc-clusion of airways due to an incorrect positionof the inflated balloon in the trachea. The bal-loon is an easy and very efficient tool to keepthe catheter in place, to control the regionaldistribution  of  the  injected  drug  and,  there-Downloaded by:UB Augsburg137.250.131.3 - 1/27/2022 8:58:16 AM                                                                             fore,  to  prevent  injury  to  the  adjacent  lungparenchyma. Whereas other techniques makeuse of readily available equipment and can beperformed in nearly any laboratory [1–5], theneed for specific catheters and guidewires aswell as the use of fluoroscopy are the disad-vantages of the technique used in this study.However,  the easy performance,  the reason-ably  short  time  period  needed,  the  lack  ofcomplications and the well-controlled distri-bution of the administered drug suggest thatthe described technique provides an excellentway  of  endotracheal  drug  administration  inrabbit models of pulmonary injury and lungdisease.References1 Alexander DJ, Clark GC: A simplemethod of oral endotracheal intuba-tion in rabbits. Lab Anim Sci 1980;30:871–873.2 Bechtold  SV,  Abrutyn  D:  An  im-proved method of  endotracheal  in-tubation  in  rabbits.  Lab  Anim  Sci1991;41:630–631.3 Davies A, Dallak M, Moores C: Oralendotracheal  intubation  of  rabbits(Oryctolagus cuniiculus). Lab Anim1996;30:182–183.4 Fick TE, Schalm SW: A simple tech-nique  for  endotracheal  intubationin rabbits. Lab Anim 1987;21:265–266.5 Krüger J, Zeller W, Schottmann E:A simplified procedure for endotra-cheal  intubation  in  rabbits.  LabAnim 1994;28:176–177.6 Macrae DJ, Guerreiro D: A simplelaryngoscopic technique for the en-dotracheal  intubation  of  rabbits.Lab Anim 1989;23:59–61.7 Corleta  O,  Habazettl  H,  KreimeierU, Vollmar B: Modified retrogradeorotracheal intubation technique forairway  access  in  rabbits.  Eur  SurgRes 1992;24:129–132.                                                                                                                                                                                                                                                                                        

A new technique for oral endotracheal airway access in rabbits under fluoroscopic control: an easy way for drug administration in chronic experiments

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A new technique for oral endotracheal airway access in rabbits under fluoroscopic control: an easy way for drug administration in chronic experiments

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