, they may be misdiagnosed to have bronchial asthma as they present with inspiratory stridor and/or expiratory wheezing .
it is difficult to accurately predict the distensibility of the trachea even with an array of preoperative tests like flow  volume loop , computerized tomography ( ct ) , and bronchoscopy .
a 45 year old female , with body mass index ( bmi ) 24 kg / cm , presented to our hospital with shortness of breath on lying supine for the past 3 months , more so when lying on right side , hence she preferred to sleep on the left side .
she was treated elsewhere as bronchial asthma and referred to our center for evaluation of hemoptysis . on examination ,
she was found to have a swelling in the left lobe of the thyroid , compressing and pushing the trachea to the right .
ct of the neck and thorax revealed an enlarged left lobe of thyroid measuring 3.4  3.3  3.4 cm with dense nodular calcification , causing short segment external compression and tracheal luminal narrowing .
the stenosis extended from upper margins of c7 to t2 vertebrae , with a length of 3.1 cm and minimal diameter of 0.31 cm [ figure 1 ] .
fine needle aspiration cytology ( fnac ) of the swelling revealed colloid goiter and she was posted for a left hemithyroidectomy .
three - dimensional computerized tomography and corresponding virtual bronchoscopic images of our patient room air arterial blood gas analysis showed partial pressure of arterial oxygen ( pao2 ) of 80.5 mmhg , paco2 of 41 mmhg , ph of 7.41 .
preoperative fiberoptic bronchoscopy with a 4.8 mm bronchoscope revealed tracheal compression by extraluminal mass with a smooth margin 1.5 cm below the glottis .
preoperative fiberoptic bronchoscopy revealed tracheal luminal narrowing of about 80% , which was 1.5 cm below the glottis when the patient was explained about the risks and options , she was not willing for any major resection or procedure .
after written informed consent , patient was nebulized with 5 ml of 4% lignocaine and pre oxygenated with 100% o2 for 10 min through a nasopharyngeal airway .
intravenously ( iv ) , glycopyrrolate 0.2 mg , incremental doses of midazolam ( 2 mg ) and fentanyl ( 100 g ) were given .
a 4.5 mm fiberoptic bronchoscope ( fob ) threaded through a 5 mm internal diameter ( i d ) microlaryngeal tracheal tube ( mlt ) was passed nasally .
the fob was introduced close to the mass , and gently pushed past the obstruction .
a little resistance was noted but the tube could be passed below the mass without undue force .
the fob was withdrawn and trachea ventilated with a tidal volume of 450 ml , 8 breaths /min , and i : e = 1:3 .
the left lobe of the thyroid being stony hard and densely adherent to trachea could not be completely resected .
as the patient was not willing for tracheal resection and reconstruction , an isthumectomy and release of fibrotic tissue around the trachea was done . before closure
, the 5.0 mm ( i d ) mlt was replaced with a 6.0 mm i d mlt over an aintree intubating catheter .
as this could be passed without any resistance , it was followed by the passage of a 7.0 mm i d endotracheal tube with little resistance .
postoperatively , patient was electively ventilated , anticipating airway edema . under steroid cover , 24 h later , the patient was extubated over a tube exchanger , with standby tracheostomy .
as the patient did not want any major definitive surgery ; she was referred to a regional cancer institute for further management .
while anesthetizing patients with tracheal stenosis , despite having newer imaging modalities like multi - slice , three - dimensional -ct , virtual bronchoscopy to determine the size and anatomy of the airway , it is difficult to accurately predict the distensibility of the trachea with the available preoperative tests .
preoperative assessments of airway size and collapsibility may not be perfect in predicting patency of the airway and ease of ventilation during general anesthesia .
on one hand , it is important to maintain a patent airway till it is secured with an endotracheal tube . on the other ,
it is important not to over - estimate the airway narrowing as this will result in the patient being ventilated with an unnecessarily small endotracheal tube .
pulmonary function tests are useful in the functional assessment of obstruction , but were contraindicated in our patient because of hemoptysis . the ability to compensate breathing through a narrow airway may be better during general anesthesia than during wakefulness , because behavioral influences such as anxiety are eliminated and oxygen consumption reduced .
however , azizkhan et al . , reported total collapse of the airway by mediastinal masses causing > 50% narrowing of the trachea .
this helped , as we were able to pass the fob beyond the mass when it was not possible during the preoperative bronchoscopy .
the presence of hypercapnia preoperatively , in the absence of respiratory pathology , strongly suggests the potential for failure of both spontaneous and mechanical ventilation during general anesthesia .
critical fixed narrowing through which anesthetized patients can breathe spontaneously without increase in partial pressure of carbon dioxide in the blood ( paco2 ) is 4.0 - 4.5 mm i d .
as our patient was maintaining normocapnia , we assumed that her dynamic airway would be at least this wide .
as the tracheal diameter varies with respiration , it is inaccurate to rely on static ct images in cases of external compression .
toyoto et al . , used a 5.5 mm i d reinforced endotracheal tube with an external diameter of 7.5 mm in their patient whose ct image showed the narrowest portion as being 2.6 mm .
the serial passage of increasing sizes of endotracheal tubes was similar to dilatation of stenosis under direct vision .
the isthumectomy and release of fibrotic bands also decreased the external compression of the trachea and increased the airway caliber post surgery and we were able to provide symptom relief .
this also made the anterior surface of the trachea accessible for a low tracheostomy , which was not possible preoperatively . in conclusion ,
newer imaging modalities are just an adjunct in the assessment of the compromised airway in case of dynamic compression .
our experience is with a single case and probably , only randomized control trials can answer the question whether newer imaging modalities really help airway assessment in dynamic tracheal compression or not .
clinical assessment will , however , remain very important in deciding the plan of management .
 anesthetic management of a patient with tracheal stenosis is challenging . though we have newer imaging modalities like multislice , three - dimensional computerized tomography , virtual bronchoscopy to determine the size and anatomy of the airway , it is difficult to accurately predict the distensibility of the trachea with the available preoperative tests . with our experience in this case , we believe that newer imaging modalities are just an adjunct in the assessment of the compromised airway in case of dynamic compression . 
 clinical assessment is very important in deciding the plan of management . 
Introduction
Case Report
Discussion