airway management perioperative

EDUCATION Anesthesiology 2010; 112:9708Copyright 2010, the American Society of Anesthesiologists, Inc. Lippincott Williams & Wilkins

Bruno Riou, M.D., Ph.D., Editor

Case Scenario: Perioperative Airway Management of aPatient with Tracheal StenosisShiroh Isono, M.D.,* Yuji Kitamura, M.D., Takashi Asai, M.D., Ph.D., Tim M. Cook, F.R.C.A.

TRACHEAL stenosis is a rare but a life-threatening con-dition and is caused by congenital problems, postintu-bation injury, trauma, tracheal tumor, and compression ofthe trachea by tumor. Although accurate prevalence of thiscondition is unknown, an incidence of 4.9 cases per millionper year is estimated for postintubation tracheal stenosis.1 Astenosis commonly occurs at the cuff of the tube (intratho-racic trachea) or at the level of the tracheostomy stoma (ex-trathoracic trachea).

Anesthesia of a patient with tracheal stenosis is challeng-ing for anesthesiologists. Depending on the severity and lo-cation of the stenosis and the type of surgical procedure,there may be a variety of choices for perioperative airwaymanagement such as a facemask, laryngeal mask airway,2 antracheal intubation tube,3,4 cardiopulmonary bypass,5 andextracorporeal membrane oxygenation.6 The American So-ciety of Anesthesiologists practice guidelines for manage-ment of the difficult airway primarily focus airway problemscaused at the extrathoracic airway and may not be helpful,particularly formanaging patients with intrathoracic trachealstenosis.7 In this case scenario, we present a patient with

severe intrathoracic tracheal stenosis, who required surgeryfor a lumbar fracture in the prone position. Various airwaymanagement strategies and the actual management used arediscussed.

Preoperative Information of the Case

A 38-yr-old obese man (height, 172 cm; weight, 95 kg; bodymass index, 32 kg/m2) was scheduled to have a thoracolum-bar laminectomy and fixation for a burst fracture of the firstlumbar vertebra. Surgery was to be performed in the proneposition. The operation duration and blood loss were preop-eratively estimated to be 4 h and 500 ml. He had a history ofprolonged intubation when he suffered a traumatic braininjury at 8 yr of age. He had epilepsy treated with phenobar-bital but had no impairment of neurologic development andwas cooperative. Despite undergoing tracheal resection andplasty for severe postintubation tracheal stenosis at 17 yr ofage, he had relatively loud inspiratory and expiratory stridorwhile awake. Spirometry in the sitting position revealed re-duced forced expiratory volume in the first second (FEV11.95 l, 53%-predicted) and peak expiratory flow rates(PEF 180 l/min, 30% predicted). Arterial blood gas anal-ysis indicated mild impairment of oxygenation but normalventilation (FIO2 0.2, pH 7.43, PaO2 71 mmHg,PaCO2 33 mmHg). A flow-volume loop showed a typicalupper airway obstruction pattern (fig. 1). Three-dimensionalcomputed tomography (CT) of the trachea revealed severeintrathoracic tracheal stenosis more than 3 cm in length. Incross-section, the stenotic lesion was elliptical with a minoraxis of 0.5 cm and a major axis of 1.5 cm (fig. 2). Despite thetracheal stenosis, he had no dyspnea during daily activitiesand was otherwise healthy. Nurses in the ward witnessedloud snoring and occasional apnea during sleep. Preoperativeairway examination revealedMallampati class 3, normal thy-romental distance, and no limitation of neck or mandiblemovements. The orthopedic surgeons considered that nei-ther conservative therapy nor surgery with regional anesthe-sia was appropriate because of his neurologic symptoms andthe estimated operational duration and invasiveness of thesurgery.

* Associate Professor, Department of Anesthesiology, GraduateSchool of Medicine, Chiba University, Chiba, Japan. Staff Anesthe-siologist, Department of Anesthesiology, Chiba Emergency MedicalCenter, Chiba, Japan. Assistant Professor, Department of Anesthe-siology, Kansai Medical University Takii Hospital, Osaka, Japan. Consultant in Anaesthesia and Intensive Care Medicine, Departmentof Anaesthesia, Royal United Hospital, Bath, United Kingdom.

Received from the Department of Anesthesiology, GraduateSchool of Medicine, Chiba University, Chiba, Japan; Department ofAnesthesiology, Chiba Emergency Medical Center, Chiba, Japan;Department of Anesthesiology, Kansai Medical University TakiiHospital, Osaka, Japan; and Department of Anaesthesia, RoyalUnited Hospital, Bath, United Kingdom. Submitted for publicationNovember 22, 2009. Accepted for publication December 18, 2009.Support was provided solely from institutional and/or departmentalsources.

Address correspondence to Dr. Isono: Department of Anesthesiol-ogy, Chiba University, Graduate School of Medicine, 1-8-1 Inohana-cho, Chuo-ku, Chiba 260-8670, Japan. [email protected];[email protected]. Information on purchasing reprints may befound at www.anesthesiology.org or on the masthead page at thebeginning of this issue. ANESTHESIOLOGYs articles are made freely ac-cessible to all readers, for personal use only, 6 months from the coverdate of the issue.

Anesthesiology, V 112 No 4 970 April 2010

Airway Management Plans by AirwayExperts

Only the preoperative information with the figures describedabove was initially sent to both Drs. Asai and Cook. Theywere selected because of their previous reports of similarcases.3,4 The following are their airway management plansfor this patient.

Dr T. AsaiI follow an algorithm for anesthetic management of patientswith tracheal stenosis based on its pathophysiology (fig. 3).Although the patient had relatively loud inspiratory and ex-piratory stridor and apnea during sleep, he had no dyspneaduring daily activities. Therefore, I consider that spontane-ous breathing or mechanical ventilation is likely to be possi-ble through the stenosis with general anesthesia. Neverthe-less, severe airway obstructionmay occur during induction ofgeneral anesthesia, and thus the appropriate backup methodwill be required to prevent disaster.

There are three possible methods for airway management ofthis case: (1) the use of a supraglottic airway alone, (2) the use ofa supraglottic airway and a tube-exchange catheter, and (3) theuse of a supraglottic airway, an endotracheal tube, and a tube-exchange catheter such as Cook Airway Exchange Catheter(Cook Medical, Bloomington, IN; 2.7 mm internal diameter[ID]). The choice ofmethodwould depend on both the risks ofairway obstruction or dislodgement of the selected airwaydeviceand accessibility of the airway for reinsertion of the device.

In this case, the airwaymight bemanagedwith a supraglotticairway alone, but there are two major potential problems withthis method: airway obstruction after induction of anesthesiaand dislodgement of the supraglottic airway (particularly whenthe patient is turned to prone position from the supine posi-tion). One possible solution is to place the patient in the proneposition and insert a supraglottic airway while the patient is stillawake, and then induce anesthesia with increasing concentra-tions of sevoflurane while maintaining spontaneous breathing.Although the presence of the supraglottic airway would preventairway obstruction above the vocal cords, worsening of the tra-cheal stenosis and hence severe airway obstruction may developduring inhalational induction with sevoflurane. In such a case,administration of sevoflurane should be terminated and the pa-tient should be woken up. If inadvertent dislodgement of theairway device in the prone position is a risk, safety would beincreased by prior insertion of a tube-exchange catheter, becausethis would enable both the maintenance of oxygenation untilreinsertionof the supraglottic airway and the tracheal intubationthrough it.4,8

Alternatively, a more conservative but a safer approach,which I consider the most appropriate in this case, is trachealintubation with the two backup methods of the use of both asupraglottic airway and a tube-exchange catheter. In thiscase, the narrowest caliber of the trachea is 5 mm, and thusthe largest size of an endotracheal tube, which can be passedthrough the stenosis, would be 4.0 mm ID, and ventilation

Fig. 1. A flow-volume loopduring forcedexpiration and inspiration in thiscase. Note marked reduction in both PEF and PIF. insp inspiration;exp expiration; PEF peak expiratory flow rate; PIF peak inspira-tory flow rate; FEV1 forced expiratory volume in the first second.

Fig. 2. Tracheal three-dimensional computed tomography of thiscase revealed severe intrathoracic tracheal stenosis over 3 cm inlength (arrows) and elliptical airway shape with a minor axis of 0.5 cmand a major axis of 1.5 cm.

Fig. 3. An algorithm for anesthetic management of patients withtracheal stenosis. #1: Airway imaging and pulmonary function testare helpful for this decision making. #2: Collapsibility or expandabilityof the trachea needs to be assessed for this decision making. GAgeneral anesthesia; ET endotracheal tube; PCPS percutaneouscardiopulmonary support.

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may not be sufficient. Therefore, it would be necessary toinsert a larger endotracheal tube with its tip proximal to thestenosis. Three-dimensional CT indicates that the stenosis isin the mid to lower trachea, and thus it would only be pos-sible to insert the distal 34 cm of the endotracheal tube intothe trachea, necessitating backup plans, in case of tube dis-lodgement. In such an event, either the supraglottic airway orthe exchange catheter could then be used for maintainingoxygenation and reinserting the endotracheal tube. I wouldprepare for jet ventilation through the exchange catheter.

After preoxygenation of the patient in the supine position, Iwould allow the patient to breathe increasing concentrations ofsevoflurane in oxygen, and then assist ventilationmanually via afacemask. After injection of a neuromuscular blocking agent, Iwould insert a Cook airway exchange catheter into the tracheaunder direct laryngoscopy, and then insert either the ProSealLaryngeal Mask Airway (PLMA; Laryngeal Mask Com-pany,Henley-on-Thames, United Kingdom) #5 or i-gel (Inter-sugical Ltd., Wokingham, Berkshire, United Kingdom), an-other supraglottic airway, while the exchange catheter is placedoutside the supraglottic airway. With the aid of a fiberopticbronchoscope, I would pass a reinforced endotracheal tubethrough the supraglottic airway into the trachea so that the tip ofthe endotracheal tube is approximately 12 cm proximal to thestenosis. I would not inflate the endotracheal tube cuff, becauseit would be positioned at the glottis. Wrapping adhesive tapearound the endotracheal tube at the connecter of the supraglot-tic airwaywould prevent both dislodgement of the endotrachealtube and gas leakage through the supraglottic airway. I wouldthen adjust the position of the exchange catheter so that its tip isbeyond the tracheal stenosis. After the patient is turned to theprone position, I would confirm (using a fiberscope) the appro-priate positions of both endotracheal tube and exchange cathe-ter. I would maintain the tidal volume as low as possible allow-ing hypercapnia to prevent excessive peak airway pressure.Whenpossible, spontaneous breathingwouldbe resumed.Aftersurgery, Iwould remove the supraglottic airway once the patienthas recovered fromgeneral anesthesia and is responsive to verbalcommands, butwould leave the tube exchange catheter in place,until it becomes certain that the patient can maintain a clearairway.

Dr. T. M. CookThis is a truly difficult patient. I would first reiterate to thesurgeons that perioperative airway complications are a potentialrisk to the patients life. The options of conservative treatmentor transfer to a center with facility for combined tracheal recon-structive and trauma surgery must be explicitly considered.

Assuming neither is possible I would premedicate the pa-tient with a proton pump inhibitor 12 h before anesthesia.Two experienced anesthetists and an experienced anestheticassistant would be required and briefed. I would start byplacing a narrow gauge cricothyroid cannula specifically a13-gauge Ravussin cannula (VBM Medizintechnik, Sulz,Germany) with local anesthesia and confirm its position byfeeling expired gas, seeing gas exit through a bubble of saline

and with capnography. If there was concern about the posi-tion of the Ravussin cannula, I would perform awake fiber-optic inspection to confirm its position before proceeding.Next, I would place a PLMA. If the patient was coopera-tive, I would do this during topical anesthesia. If he was notI would place it during general anesthesia. I would preoxy-genate the patient fully with continuous positive airway pres-sure performed with at least 25 degrees head up position toincrease lung volumes and maximize the apnea period beforehypoxemia develops. I would administer a modest dose ofopioid (e.g., fentanyl 100 g titrated in 23 min) andpropofol by target-controlled infusion. I would start with alow propofol effect site target (11.5g/ml) and increase thisin steps of 0.5 g/ml for every 13 min while maintainingspontaneous ventilation. At the point of eye closure, butbefore full anesthesia, I would assess ease of assisted ventila-tion. If ventilation was difficult or impossible, I would aban-don this attempt and allow the patient to wake up. Afterconfirmation of adequate mask ventilation, I would thenparalyze with rocuronium, increase the depth of anesthesia,and insert a PLMA, using a bougie-guided technique.9,10

After placement of the PLMA, I would then intubate thetrachea through it. If the PLMA was placed awake, Iwould induce anesthesia after PLMA placement. For in-tubation, I would use a 4.2-mm fiberscope on which anAintree Intubating Catheter (AIC; Cook Medical, Bloom-ington, IN) was mounted. After passage of the AIC, I wouldrailroad a 6.5-mm ID intubating Laryngeal Mask Airway(LMA) endotracheal tube over it. If the AIC passed easily,I anticipate that the intubating LMA endotracheal tubewould also pass. If the AIC was tight/snug, I would pass aCook airway exchange catheter through the AIC and railroada 5.0-mm ID microlaryngoscopy tube over the airway ex-change catheter. I would then confirm position of the endo-tracheal tube beyond the stenosis. If the AIC could not passwithout undue force, I would ventilate until paralysis wasreversed (sugammadexmay be useful here due to its ability toproduce rapid and complete reversal of rocuronium paraly-sis) and then wake up the patient. During surgery, I wouldadminister 8.0 mg of intravenous dexamethasone to mini-mize edema of the stenotic region. At the end of surgery, Iwould exchange the endotracheal tube for a Cook airwayexchange catheter and a PLMA. I would then assess ease ofventilation (and spirometry) with the patient still anesthe-tized. I would then allow the patient to wake and remove thePLMA, but not the exchange catheter. If there was anysuggestion of trauma during the intubation or concern aboutedema at the time of extubation, I would admit the patient tointensive care unit for 2448 h of sedation, ventilation, andsteroid to allow airway edema to settle.

Actual Airway Management in This Patient

The history of tracheal surgery and persistent stridor suggested arigid tracheal wall at the stenotic region allowing insertion of anendotracheal tube with 57 mm outer diameter, that is, only

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Anesthesiology, V 112 No 4 April 2010 Isono et al.

4.05.5mm IDwithout injuring the tracheal wall.We consid-ered that positive pressure ventilationwith such a small diametertube might be difficult in this obese patient during surgery inprone position. Furthermore, traumatic insertion and pro-longed placement of a larger diameter tube were considered tobe disadvantageous because of the potential for development ofmucosal edema and further narrowing of the trachea after tra-cheal extubation. Therefore, we decided not to intubate thetrachea, but to use the PLMA for positive pressure ventila-tion. The patient agreed with this strategy after we explained itspotential benefits and risks to him.

Because of clinical symptoms and body habitus suggest-ing potential obstructive sleep apnea, we performed noctur-nal oximetry preoperatively. We calculated 4% oxygen de-saturation index (i.e., the average number of oxygendesaturations by 4% or more below the baseline level perhour). Although an oxygen desaturation index greater than 5h1 is suggestive of sleep-disordered breathing, the index was3 h1 in this patient.11 Despite the negative result of thesleep study, nasal continuous positive airway pressure wasprescribed because this could help maintain tracheal patencyboth for treatment of his snoring and in case of mucosaledema at the tracheal stenosis developed after surgery. Thepatient tolerated this treatment well.

General anesthesia was induced with intravenous admin-istration of remifentanil, propofol, and vecuronium, and aPLMA (#5) was inserted, guided by a gum elastic bougie.Anesthesia was maintained with inhaled sevoflurane and aninfusion of intravenous remifentanil. With pressure-con-trolled ventilation during surgery (peak inspiratory pressure22 cm H2O, positive end-expiratory pressure 7 cm H2O,respiratory rate 8 breaths/min, inspiratory expiratory ratio1:3) through the PLMA, we saw no signs of high airwayresistance or airflow limitation such as low tidal volume orlack of formation of an alveolar plateau on capnography(tidal volume 730 ml, end-tidal CO2 31 mmHg). The sur-gery was uneventfully accomplished. The PLMA was re-moved when the patient was fully aroused. Optimal postop-erative analgesia was achieved by intravenous injection ofnonsteroidal antiinflammatory drug and a continuous intra-venous infusion of fentanyl. After the patient arrived on theward, nasal continuous positive airway pressure with oxygenwas applied immediately and was continued for three post-operative nights. This was effective in eliminating both snor-ing and stridor during sleep.12 He did not complain of dys-pnea after surgery and was discharged fully mobile.

Comments by the Airway Experts onPerioperative Airway Management

Dr. T. AsaiI believe that preoperative assessment and anesthesia man-agement of the case described are generally reasonable andaccord with my assessments and plans.

The preoperative respiratory state during wakefulness andsleep was sufficiently assessed, and the visual assessments of

the stenotic region with three-dimensional CT imaging ofthe trachea in addition to chest radiographs were informa-tive. These meticulous assessments may certainly be useful toplan a safer anesthesia management (providing that the timeand cost can be spent). Nevertheless, caution may be re-quired, because the absence of significant airway obstructionduring sleep does not guarantee that there will be no airwayobstruction during anesthesia. There have been several re-ports of complete airway obstruction in patients with medi-astinal masses, without any preoperative signs of airway ob-struction.13 In this case, the three-dimensional CT andpreoperative assessments suggest that complete airway ob-struction is unlikely, but it might have been safer to induceanesthesia by inhalation of increasing concentrations of avolatile anesthetic (such as sevoflurane) and then to give aneuromuscular blocking agent after confirming that no air-way obstruction has occurred.

There may be two major possible problems with the an-esthesia management performed by Drs. Isono and Kita-mura. First, air trapping may occur beyond the stenosis,when the ventilation is controlled. This can be reduced bydecreasing the inspiratory/expiratory ratio (that is increasingthe expiratory time). In this case, because the stenosis had aminimally acceptable caliber, the pressure-controlled venti-lation worked well, and sufficient ventilation volume wasobtained. Spontaneous breathing might have been a betterchoice if ventilation had been insufficient during controlledventilation.

Another possible problem is that the use of the PLMAalonemight have become difficult if (although not likely in thiscase) the device had been inadvertently dislodged or airway ob-struction at the stenotic region had occurred. If there are con-cerns about access to the patients face, or about a prolongedoperation time, I would use a backupmethod of leaving a tube-exchange catheter beyond the stenosis and possibly an endotra-cheal tube with its tip proximal to the stenosis.

Postoperatively, nasal continuous positive airway pres-sure, known to minimize airway obstruction, was appliedfor three postoperative nights. Because tracheal intuba-tion seemed not difficult, the choice of applying nasalcontinuous positive airway pressure postoperatively seemsbetter than my plan of leaving a tube exchanger to thetrachea after operation.

Dr. T. M. CookFor each possible solution that is explored, several potentialcomplications arise. I will limit myself to answering the fol-lowing specific questions. I do not know whether my planswould work: Drs. Isono and Kitamura have the massive ad-vantage of knowing their plans did! In many respects whatmatters most in this case is not what plan A is, but how theanesthetist plans to respond if plan A fails immediately ormid-surgery. It is essential for the anesthetist to have a plan B,as a minimum, before induction of anesthesia.How Do I Assess the Problem? My first consideration isthat all aspects of this patients care potentially put him at

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risk. His features offer the possibility of supraglottic andsubglottic problems leading to both difficult mask ventila-tion and difficult intubation.14 Hypoxemia will be rapid andsevere if the airway is lost in this obese patient who will havea limited functional residual capacity. Passage of a tube be-yond his tracheal narrowing may be the most problematic.

However, there are two patient features that I find reas-suring. First, the fact that the tracheal narrowing (althoughonly 5 mm in its minor diameter) is 15 mm in its majordiameter suggests strongly to me that it will admit a largerendotracheal tube than one with an external diameter of 5mm. The trachea is a dynamic and nonrigid structure, andanyone who has observed tracheal dilation will confirm thatit will often accept a larger diameter tube than its restingdimensions. Second, the fact that the patient suffers no lim-itation to his daily activities indicates that gas flow is consid-erably better than some of the patients features suggest.Why Do I Believe This Patient Needs Intubation? I didconsider use of the PLMAas the primary airway through-out anesthesia. The PLMAismy go to airway and I haveextensive experience with it for both routine15 and difficultairwaymanagement.16 Such ismy confidence in it that I haveabandoned use of the LMA-Classic (Laryngeal MaskCompany), because I believe that its performance and safetyprofile is inferior to that of the PLMA. Despite this, Irejected its use for this case because I was concerned that if itfailed with the patient in the prone position, rescue would behazardous and might fail with fatal consequences.

I did not consider the option of use of PLMA with anairway exchange catheter in place through the vocal cords incase rescue was required. This is ingenious and adds a level ofsafety. Despite this, if I was required to anesthetize this pa-tient I would still advocate tracheal intubation before com-mencing a 4-h procedure in the prone position. I have usedthe PLMA myself in approximately 10 patients in theprone position and I am aware that it has been used in severalseries of patients in the prone position.17,18 However, thepatients enrolled in these studies were at low risk and thelargest series is 245 patients17: airway obstruction occurred inthree patients (1%). In contrast, the patient in this case hasan increased risk of problems with both ventilation and ox-ygenation. Minor degrees of misplacement and airway swell-ing during surgery in the prone position would likely lead toairway obstruction. If airway obstruction occurred in thispatient, hypoxia would likely be rapid and profound. Hisairway is likely difficult to manage in the supine position inideal circumstances. Despite my experience, I would be con-cerned that problems occurring in the prone position, mid-surgery would be so difficult to manage that the patients lifewould be at risk. Despite the difficulties posed by intubation(and extubation), I would chose tracheal intubation in thiscase.Why Do I Induce with Incremental Target-controlled Infu-sion Propofol? Most anesthesiologists, performing sponta-neous breathing induction of anesthesia, reach for a volatileagent.With the experience of both, I have a strong preference

for use of a slowly increasing, incremental dose of tar-get-controlled propofol, while maintaining spontaneousventilation. There are only limited descriptions of this tech-nique.19,20 The main advantage of incremental target-con-trolled infusion of propofol over rapid intravenous inductionis that spontaneous ventilation is maintained. The techniquealso has advantages over gaseous induction. First, low-dosepropofol provides excellent anxiolysis that notably assists theprogress of anesthesia. Second, increasing depth of anesthesiais independent of the patients ventilation. This allows rate ofincrease of the depth of anesthesia to be titrated carefully, bythe anesthetist (rather than dictated by the patient). It alsomeans that if difficulty is encountered stopping the infusionimmediately enables anesthesia to lighten, without requiringthe patient to blow off anesthesia via an airway that waspartly obstructed and has now worsened. Finally, airway re-flexes are rapidly obtunded, so coughing increased secretionsand the complications these lead to during gaseous inductionare rare. In many cases, patients will tolerate gentle manualventilation even when still responsive to verbal stimulus.This enables confirmation of ability to ventilate, or of in-creasing difficulty, and airway adjuncts (e.g., Guedel airway)are tolerated considerably earlier and better than during gas-eous induction. Importantly, the technique does demandscrupulous attention to technique to detect problems withthe airway early.Why Introduce the PLMA over a Bougie? The PLMAis a device with a pedigree in management of the difficultairway.16,21 If there is one weakness in PLMA perfor-mance, it is that insertion can bemore difficult than for othersupraglottic airway devices: conventional insertion tech-niques enable a first-time insertion rate with the PLMAof87%, (5% lower than that for the LMA-Classic).21

There is ample evidence that the use of a bougie aids first passsuccess with the PLMA, increasing success close to 100%without any increase in morbidity.9,10 Therefore, in circum-stances where I consider first time success to be stronglydesirable, I insert the PLMAover a reusable Smith Portexgum elastic bougie: the type of bougie is important to mini-mize the risk of esophageal trauma.15,21

Why the Aintree Intubation Catheter? The AIC is perhapsthe ideal tube to use to (a) intubate via a supraglottic airwayand (b) intubate narrow airways.22 It has the smallest externaldiameter (a little less than 7.0mm) of any endotracheal tubethat will fit over a standard size fiberscope and its ID (4.6mm) means that it does not rattle around during use,making impingement on the glottis unusual. Its use viathe LMA-Classic and PLMA in difficult airway man-agement is reported in two series.3,23 Once placed it en-ables oxygenation and then, depending on circumstances,placement of a larger endotracheal tube (railroaded overit), or a smaller one (by passing an airway exchange cath-eter through it, followed by the smaller tube).What Are My Rescue Plans and Plans for Management ofProblems at Extubation? The small minor diameter of thetrachea raises the significant possibility of difficulties with



ventilation or intubation. If ventilation becomes impossibleat any stage after induction or intubation with an AIC is notpossible, my plan is graceful withdrawal before consideringanother plan. Both are designed before any bridges havebeen burnt. Certainly I would avoid aggressive attempts atpassing an endotracheal tube, risking tracheal edema.

In the event of loss of the airway, presumably with hyp-oxia, my emergency rescue technique will be high-pressuresource ventilation using a Manujet (VBM Medizintechnik,Sulz, Germany): unlike other injectors the Manujet incor-porates a pressure-reducing mechanism so that the anesthe-siologist may deliver only the minimum driving pressure toventilate the lungs (so reducing the risk, and extent, of anybarotraumas).24 Ventilation would be via the Ravussin can-nula, placed before induction of anesthesia. Profound hyp-oxia and a peri-arrest situation is not an ideal time to place acricothyroid cannula. Peterson examined almost 200 cases ofdifficult airway management which led to medicolegalclaims25: 42% of cases ended with Cannot Intubate CannotVentilate situation and in two-thirds of these cases a surgicalairway was obtained but was placed too late to avoid pooroutcome. Needle cricothyroidotomy and high-pressuresource ventilation performed in these circumstances wereeach associated with a high incidence of barotrauma. Al-though these cases are undoubtedly affected by outcome bias,the message is clear: waiting for Cannot Intubate CannotVentilate situation and a peri-arrest patient before interven-tion is a poor plan. The technique of insertion of a prophy-lactic cricothyroid cannula for difficult airway managementhas been previously described26 and is a frequent componentof my management of patients with airway obstruction. It iseasily performed in the awake patient, is almost painless, andis well tolerated. Ideally, the catheter would be placed underfiberscopic control as this improves position and reducescomplications27 but in this case that may not be practical. Itis remarkable how much more confident one feels when therescue route is established before undertaking other difficulttechniques that may fail. Should I need to use the cricothy-roid cannula I would not anticipate great difficulty with in-spiration but great care would be needed to ensure that fullexhalation had occurred (perhaps over 510 s or longer)before commencing the next breath: placing a hand on thepatients chest and palpating complete chest fall is a usefultechnique. Failure to confirm complete expiration wouldrapidly lead to severe barotraumas.28

Knowledge Gap

For some questions in clinical anesthesia, there may be nocorrect answer or alternatively several appropriate answers.The airway experts chose different airway management strat-egies for this patient. Importantly, this does not supportthoughtless airway management: through this case scenario,one of the notable findings is that we all fundamentallyagreed that ventilation would be possible during anesthesiainduction. Despite this, why did we each choose different

airway management strategies and include in these plansbackups in case of failure? Probably, this is either becausepreoperative assessments of airway size and collapsibility maybe imperfect in predicting ease of ventilation during generalanesthesia or because the airwaymanagement techniques anddevices currently available for managing tracheal stenosis isalso imperfect.

Critical Stenosis for Breathing and MechanicalVentilation during General AnesthesiaEven in patients with severe tracheal stenosis, normal gasexchange is maintained by respiratory compensatory mech-anisms. Therefore, the presence of hypercapnia in preopera-tive patients without other respiratory diseases strongly indi-cates the potential for failure of both spontaneous andmechanical ventilation during general anesthesia. In con-trast, the ability to compensate breathing through a narrowairway is well marked during general anesthesia and some-times better than that during wakefulness, because behav-ioral influences such as panic and anxiety are eliminated andoxygen consumption is reduced.29 Nunn and Ezi-Ashi29

found breathing through a tubular resistor of 4.5mm ID and2.5 cm in length or 3.0 mm ID and 2.5 cm in length reducedthe mean minute ventilation by 7 and 21%, respectively,during general anesthesia, although responses were variableand unpredictable. The subsequent studies by Moote et al.(inspiratory resistive loads), Kochi and Nishino (inspiratoryresistive loads), and Isono et al. (expiratory resistive loads)confirm that the critical fixed narrowing through whichanesthetized patients can spontaneously breathe without anincrease in PaCO2 is 4.04.5 mm ID.

3032 Respiratory com-pensation for breathing through a tubular resistor is achievedby decreasing the respiratory rate, with prolongation of bothinspiratory and expiratory times and the increase in respira-tory drive. Although the patients respiratory drive decreasesor ceases during assisted and controlled ventilation, tolerablesize of the stenosis for breathing may not be greatly affectedby the ventilatory modes.2 However, I found that no studyhas systematically examined the critical stenosis for mechan-ical ventilation in anesthetized and paralyzed patients and thespeculation needs to be tested in the future.

Imaging Techniques for Assessment of Severity ofTracheal StenosisHow can we assess structural and functional severity of tra-cheal stenosis? Patients with mild to moderate tracheal ste-nosis rarely have clinical symptoms such as dyspnea. Evenpatients with severe tracheal stenosis may present withoutstridor and dyspnea during quiet breathing and, therefore,clinical symptoms may not be good indices for severity oftracheal stenosis.33 Various imaging techniques possibly as-sess the structural severity of the stenosis. Chest radiographshave limited clinical utility for determining the presence andthe severity of an airway stenosis. Saggital CT images alongthe airway provide significant information regarding the se-verity, location, and shape of the airway narrowing and the

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structures surrounding the airway.34 Recently developedthree-dimensional imaging techniques such as CT and mag-netic resonance imaging can more accurately delineate com-plicated airway shapes and determine the minimal airwaysize.35 Using a fiberoptic bronchoscope for measuring thecross-sectional area and the length, the mean cross-sectionalarea and the length of stenotic region of the trachea in pa-tients who underwent trachea reconstruction surgery werereported to be 48.3 31.9 mm2 (8 mm in diameter) and9.3 3.3 mm, respectively, suggesting large structural vari-ability among them.36 Because of the structural variabilityand complexity of the stenotic airway determined by theimaging techniques, functional impact of the tracheal steno-sis on breathing during general anesthesia is often difficult topredict even by the sophisticated imaging techniques.

Potential Usefulness of Spirometry for Predicting theObstruction Site and Airway CollapsibilityAirway size is determined by the transluminal pressure acrossthe airway wall and its stiffness. A collapsible extrathoracicairway narrows during inspiration and dilates during expira-tion because the transluminal pressure decreases during in-spiration and increases during expiration. In contrast, therelationship between airway caliber and respiratory phase isopposite in the collapsible intrathoracic airway. Therefore,airflow limitation predominantly (but not exclusively) oc-curs in the extrathoracic airway during inspirations and inthe intrathoracic airway during expiration.37,38 This dy-namic airway behavior is exaggerated during forced expira-tory and inspiratorymaneuvers particularly when collapsibil-ity of the airway caliber is increased. In this context,old-fashioned pulmonary function tests may be clinically

useful for predicting the site of airway occlusion and airwaycollapsibility.39,40 Harrison39 found that the mean PEF/PIFvalues during a cycle of forced expiratory and inspiratorymaneuvers were greater in 12 patients with extrathoracic air-way obstructions than those of normal subjects (2.26 0.84vs. 1.32 0.26). Two patients with collapsible intrathoracictracheas had PEF/PIF values less than 0.7, which increased tomore than 1.0 after removal of the mediastinal tumor andinsertion of tracheal stent. In two patients with posttrache-ostomy tracheal stenosis, both PEF and PIF were signifi-cantly decreased but PEF/PIF value did not differ from nor-mal subjects. According to the flow-volume loop in figure 1,our patient had significant reduction in both PEF and PIFand a normal PEF/PIF ratio (1.33), suggesting significantcentral airway stenosis and arguably adding evidence for ri-gidity of the airway wall. Nevertheless, caution is required forinterpretation of the results, because PIF can be influencedgreatly by patient effort.

Shamberger et al.40 demonstrated a direct association be-tween the tracheal cross-sectional area measured by the CTscan and PEF values in children with anterior mediastinaltumors. Interestingly, they found significant but variablePEF reduction (242% reduction) in the supine positioncompared with the sitting position and significant PEF im-provement in all children after therapeutic mass reduction.Azizkhan et al.41 reported complete airway obstruction afterinduction of anesthesia in children with greater than 50%tracheal narrowing. As these authors suggested, the patientwith a highly collapsible trachea (suggested by lower PEF andnarrower tracheal cross-sectional area) should not have gen-eral anesthesia induced before securing the airway. In sum-mary, spirometric variables may be useful for functionally

Fig. 4. (A) Forced expiratory volume in the first second/peak expiratory flow (FEV1/PEF) in normal subjects with and without resistances addedat mouthpieces. Diameter of orifice is shown in each case. (B) FEV1/PEF in patients with lower airways obstruction, interstitial lung disease, andupper airways obstruction. Black circles indicate cases requiring tracheostomy. PEFR peak expiratory flow rate. Reproduced and modifiedfrom the BMJ, Empey DW, volume 3, pages 5035, 1972, with permission from BMJ Publishing Group Ltd.33



characterizing tracheal collapsibility and for detecting therisk of critical airway collapse after induction of anesthesia,but further investigations are necessary.

Spirometry for Predicting Functional Airway Size forBreathing during General AnesthesiaWhen the airway is rigid, the severity of airflow limitation isdetermined by airway size. Among the spirometric variables,Empey33 clearly demonstrated a significant association be-tween FEV1/PEF and the cross-sectional area of the centralairway stenosis, and therefore FEV1/PEF might be used as aclinically useful parameter for predicting functional airwaysize without sophisticated imaging analysis. Because of thecomplexity of the contribution of stenotic length and airwayshape to total airway resistance, FEV1/PEF may have advan-tages over imaging information as an index for totalupper airway resistance. Empey found that FEV1/PEF([ml s1] [l min1]1) was greater than 10 in all patientswith upper airway obstruction: equivalent to a normal sub-ject breathing through an external resistance of less than 6mm diameter (fig. 4). Breathing through a 4-mm orifice,possibly resulting in impossible mechanical ventilation dur-ing general anesthesia, increased the FEV1/PEF tomore than15. In our patient with 3 cm tracheal stenosis with minimalcross-sectional area of 59 mm2, FEV1/PEF is calculated as1950/180 10.8. The FEV1/PEF is much higher than thatin normal subjects and corresponds to breathing through a,at least, 6 to 8mmorifice. Therefore, this assessment suggestspossible breathing or mechanical ventilation during generalanesthesia, assuming noncollapsible airway characteristics.This functional assessment of the tracheal stenosis can giveanesthesiologists significant information for determiningperioperative airway management strategies (fig. 1). AnFEV1/PEF of more than 15 (equivalent to 4 mm orificebreathing) may indicate a potential inability of mechanicalventilation after induction of general anesthesia, althoughthis needs to be validated and other approaches should beconsidered in future studies.

In conclusion, we discussed anesthetic management of apatient with tracheal stenosis and found significantly differ-ent airway management strategies among us. Lack of reliableand accurate prediction of airway patency and breathing dur-ing general anesthesia in the patient with tracheal stenosisseems to be the fundamental reason for the variable airwaymanagement strategies. For patients with difficult airways,our progress in preoperative airway assessment as a predictivetool is rather limited, when compared with the outstandingdevelopments in airway management techniques anddevices.

Dr. Cook acknowledges Dominic Hurford, M.B.Ch.B., F.R.C.A., Spe-cial Registrar, Royal United Hospital, Combe Park, Bath, UnitedKingdom, and Andy Giorgiou, B.Sc., M.B.Ch.B., F.R.C.A., SpecialRegistrar, Royal United Hospital, with whom informal discussion ofthe case assisted in clarification of concepts and details. Dr. Isonothanks Toshihito Sai, M.D., Head of the Department of Anesthesi-ology, Naruto General Hospital, Sanmu, Japan, for his assistancewith preparation of this manuscript.

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