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Paper text:
a 69-year - old female patient ( 59.3 kg , 154.6 cm , body mass index 24.8 ) was scheduled for total knee replacement ( tkr ) . past medical history
revealed that the patient underwent general anesthesia for prior tkr of the other knee three years at another hospital , and the patient failed to recall any specific events associated with anesthesia other than a sore throat , which is fairly common after intubation .
the patient complained of occasional mild dyspnea during exercise , but chest radiographic readings by radiology were non - specific and we pursued further testing .
spirometry ( fev 2.27 liters ( l ) , fev1 1.84 l , fvc / fev1 81% ) and arterial blood gas analysis showed normal results .
both lung sounds were clear and no chest abnormalities were observed . upon entering the operating room , the patient was monitored with electrocardiograph electrodes , pulse oximeter , bispectral monitoring , and noninvasive blood pressure .
after 3 minutes of pre - oxygenation with 100% oxygen , she was anesthetically induced with propofol ( 60 mg ) and rocuronium ( 30 mg ) .
after ventilating the lungs with a facial mask for two minutes without any difficulties , initial intubation was attempted with a conventional laryngoscope with the aim of inserting a 7.0 mm internal diameter endotracheal tube ( ett ) , which failed to pass the larynx .
after a second attempt failed with a 6.5 mm internal diameter ett due to continuous resistance when passing the vocal cords , we used a glidescope ( verathon inc . , burnaby , canada ) to visualize and identify the source of the resistance .
the glidescope view indicated that the subglottic area was divided into two sections with a septum ( fig .
1 ) . a laryngeal mask airway ( lma , i - gel , 4.0 , intersurgical ltd . ,
wokingham , uk ) was inserted for temporary ventilation with a tidal volume of 7 ml / kg and 12 breaths / min , but peak airway pressures of 30 mmhg did not improve even after injection of additional neuromuscular blockade . predicting inadequate ventilation over several hours of anesthesia with
i - gel inevitably resulted in the attending anesthesiologist awakening the patient and postponing surgery until further evaluation . after reversing the neuromuscular blockade with sugammadex ( bridion , msd , kenilworth , nj , usa ) 200 mg , the patient regained consciousness without any respiratory symptoms and the i - gel was removed .
3 ) performed consecutively after surgery revealed fibrous tissue at the glottic level dividing the anterior and posterior portion into 5.8 mm and 1.7 mm lengths , respectively .
an initial chest radiograph revealed evident narrowing at the level of the glottis ( fig .
re - questioning the patient regarding any discomfort or complications from the previous surgery revealed that the patient suffered from severe dyspnea and dysphagia after surgery 3 years ago , which lasted several weeks .
afterwards , she complained of continuous mild dyspnea on exertion , but did not consider these symptoms to be anesthetic sequelae .
an otorhinolaryngologist consulted for treatment diagnosed post - intubation tracheal stenosis , but did not recommend aggressive or invasive treatment . after constructing a plan including the use of a supraglottic airway ( sga ) or smaller diameter ett in case of failed regional anesthesia , the patient underwent successful surgery with continuous epidural block .
the main concern with difficult intubation or in cases where intubation fails is how to improvise methods for preventing such cases from becoming catastrophic before or during induction .
thus , providing safe anesthetic care and preventing intubation - related injuries remains a critical issue .
we first explored why preoperative tests such as chest radiographs , spirometry , and abga were unable to diagnose the tracheal stenosis . because most patients remain asymptomatic until 30% of the original diameter becomes obstructed , medical history alone is insufficient in predicting difficult airways .
post - intubation tracheal stenosis may go unrecognized or even misdiagnosed as asthma   in patients whose symptoms are atypical .
thus , preoperative evaluations are essential in predicting difficult tracheal intubation , but with highly predicable tests currently lacking , only 50% of patients are actually found to have a difficult airway .
in addition , screening via methods such as mallampati scores or measurement of thyromental distance lack reliability . a cohort study on the diagnostic accuracy of anesthesiologists in predicting difficult
airways   claimed that 93% ( 3154 out of 3391 anticipated difficult intubations ) were actually not difficult , calling into question the accuracy of the anesthesiologists ' predictions and emphasizing the challenges that are constantly encountered during anesthetic preparation .
guidelines such as the difficult airway algorithm by the american society of anesthesiologists   provide strategies that ensure patient safety .
in addition , brichet et al .   have proposed a stepwise therapeutic algorithm for optimal management according to the severity of post - intubation tracheal stenosis . in this case
, we did not evaluate the airway tree upon the initial chest x - ray and relied solely on radiology interpretations .
it may be challenging to differentiate true stenosis from vocal cord closure due to tracheal narrowing , or even c7 and t1 spinous process and lamina density without significant clinical symptoms or impressions .
therefore , more specific information regarding the patient 's history may be useful for additional testing .
when encountering a patient with airway stenosis , an anesthesiologist would in general instinctively reattempt intubation with a narrower diameter ett , but manipulation may compromise ventilation by increasing the risks of airway resistance , intubation failure , trauma , edema , bleeding , or perforation .
however , the use of smaller ett remains controversial due to the possibility of inadequate oxygen delivery and maintenance of ventilation from increased airway resistance and the work of breathing , and would not have been attempted .
even if this attempt had succeeded , potential airway edema and obstruction would have delayed extubation after observation in the intensive care unit .
positioning of the tube above or below the stenosis is also discouraged due to difficulties of proper fixation . despite known difficulties ,
donaldson and michalek   inserted an i - gel in a patient with no specific medical history other than having been informed to warn future anesthesiologists of her " small breathing pipe " as observed during her previous anesthesia .
furthermore , lee et al .   ventilated a patient with a previous history of pulmonary tuberculosis and suspicious chest radiography findings in the beach - chair position with an i - gel. subglottic stenosis was visualized with a fiberscope through the i - gel in both cases .
asai and shingu   used a sga and a tube - exchange catheter and inserted a reinforced 6.0 mm ett in a patient undergoing surgery in the prone position .
we believe that in our case , multiple attempts at intubation may have caused laryngeal edema , elevating peak inspiratory pressures which hindered ventilation with the use of i - gel. in our backup scenario , if continuous epidural anesthesia failed , intubation may have been attempted with a 5.5 mm ett via a flexible fiberoptic bronchoscope ( because the largest diameter between the septum measured 5.8 mm ) and possibly fixed past the stenosis to avoid accidental extubation or tracheal damage .
finally , preventable measures should be taken in daily practice to avoid factors causing lts , such as high endotracheal cuff pressures exceeding 30 mmhg , which induce tracheal damage .
perhaps choosing an ett resistible to bending and collapse , with soft , thin - walled cuffs that are compliant , may be beneficial .
practitioners should also consider improvements in high - volume low - pressure cuffs by switching from standard polyvinylchloride cuffs to polyurethane cuffs   or the use of taperguard tubes to decrease the length of cuff contact with the trachea and internal pressure , thereby reducing the incidence of compromised capillary perfusion resulting in tissue ischemia and proliferation . at this time , because no clear recommendations or definite data indicate that one method is superior to the other , it may be best to adhere to the recommended internal cuff pressures and continuously check for over - inflation during surgery .
however , with detailed history taking and comprehensive reevaluation , its cause can be determined .
anesthesiologists must always be prepared with anesthetic management plans that ensure patient safety in case of failure .
encountering a patient with unanticipated laryngotracheal stenosis ( lts ) during anesthetic induction is challenging for an anesthesiologist . because routine history taking and pre - anesthetic evaluation can not rule out the possibility of lts , other measures should be taken . 
 perioperative airway maintenance is considered crucial for avoiding complications such as airway edema , bleeding , obstruction , collapse , and ultimately respiratory failure and arrest . 
 we report an unanticipated tracheal stenosis discovered during anesthetic induction that hindered endotracheal intubation . 
 because airway maintenance was difficult , we postponed surgery until determining the cause of the difficult entry , considered possible therapeutic approaches ( both anesthetic and surgical ) , and provided successful surgery with a continuous epidural block .