an 18-year - old male presented with a complaint of chest discomfort , exertional dyspnea , and an intractable dry cough . chest radiography revealed a mass like lesion in left upper mediastinum and trachea deviated to the right - side . multi detector computed tomography ( mdct ) revealed a 12  9  15 cm sized heterogenously enhancing mass in anterior mediastinum extending ventrally into the left pectoralis major muscle , and dorsally into the aortic arch , pulmonary artery trunk , and descending aorta , and encroaching the left lung field ( fig . 1 and 2 ) however , the diameters of involved vessels were preserved ( not shown ) , and the trachea and both main bronchi were patent ( fig . 2 and 3 ) . transthoracic echocardiography demonstrated minimal pericardial effusion with moderate mitral regurgitation and a left ventricular ejection fraction of 52% . pulmonary function test ( pft ) findings were within normal limits , and including a peak expiratory flow rate ( pefr ) of 50% the predicted value . although the patient underwent a fluoroscopy - guided percutaneous needle lung biopsy twice , the type of tumor was not confirmed , and thus , a thoracotomic incisional biopsy was decided upon under general anesthesia . after intravenously injecting 1% propofol and succinylcholine in the supine position , a univent tube was successfully intubated by direct laryngoscopy . anesthetic maintenance was then carried out by the target - controlled infusion of propofol and remifentanil with o2 , air , and intermittent intravenous rocuronium . during the first 45 minutes after induction in the supine position , end - tidal carbon dioxide partial pressure ( petco2 ) , heart rate ( hr ) and systolic / diastolic blood pressures were 37 - 39 mmhg , 109 - 120 bpm , and 121 - 181/85 - 103 mmhg , respectively . even after closing the left main bronchus using a bronchial blocker , pulse oximetry o2 saturation ( spo2 ) was maintained at 97 - 99% , and central venous pressure ( cvp ) was maintained at 14 - 15 mmhg under controlled positive pressure ventilation . he was then placed in the right lateral decubitus for the left thoracotomy approach , and for the first 30 minutes after this positional change , his vital signs remained unchanged . however , spo2 then began to decline , and fiberoptic bronchoscopy demonstrated the left main bronchus was almost totally obstructed , and that the ballooned bronchial blocker had been dislodged into the carina . accordingly , we immediately turned patient supine to relieve the mass effect on the main bronchi . however , hypoxemia was further aggravated up to 65% even after two lung ventilation and increasing the inspiratory oxygen fraction ( fio2 ) to 1.0 . nevertheless , blood pressure ( 112 - 123/72 - 77 mmhg ) and petco2 ( 32 - 36 mmhg ) remained in their normal ranges . eventually , the patient was placed in the left lateral decubitus position to detach the mass from the site of obstruction by gravity , and thereafter , spo2 improved from 79% to 93 and then to 97 - 99% , and cvp simultaneously decreased from 65 to 18 - 20 mmhg . surgery was then undertaken under a partial ( femoro - femoral ) cardiopulmonary bypass ( cpb ) in the right lateral decubitus position . the total bypass time was 150 minutes , and blood pressures and heart rates perioperatively were 89 - 120/44 - 50 mmhg and 95 - 115 bpm , respectively . during bypass , core temperature was maintained at normothermia ( 36 ) and petco2 was 36 - 43 mmhg . a frozen biopsy later confirmed hodgkin 's lymphoma . after weaning the patient off cpb , his spo2 was 100% , petco2 42 - 46 mmhg , and cvp 12 - 16 mmhg under controlled positive pressure ventilation supplying fio2 1.0 . muscle relaxation was reversed using glycopyrrolate and pyridostigmine . after observing full recovery of spontaneous respiration and of extremity muscle power , we extubated the univent tube and transferred the patient to an intensive care unit ( icu ) with o2 5 l / min administered through a venturi mask . in the icu , no signs of hypoxemia were evident ( spo2 98% ) , and no cardiorespiratory or neurologic abnormalities were found . on postoperative day 2 , the patient was moved to a general hospital ward . loss of muscle tone , especially that induced by muscle relaxants , makes airways susceptible to collapse due to external compression by mediastinal masses , and furthermore , the supine position leads to cephalic displacement of the diaphragm and reduces thoracic anteroposterior diameter . in addition , controlled positive pressure ventilation reduces negative intrathroacic pressure , which tend to move the mediastinal mass away from the airway and cardiovascular system . furthermore , in combination , these influences can provoke severe airway obstruction in the supine position under general anesthesia , and thus , the use of muscle relaxants is not recommended under general anesthesia , and accordingly , surgery is best performed under local anesthesia . however , when surgery must be performed under general anesthesia , especially with muscle relaxants , resuscitating methods should be provided to manage cardiorespiratory complications . in addition , a number of resuscitating methods have been introduced , such as , positional changes , tracheobronchial stenting , and rigid bronchoscopy to relieve airway obstructions and cardiopulmonary bypass [ 6 - 10 ] . changing posture is more feasible than any other method , and we recommend before induction that the position which frees the patients from tumor - related cardiorespiratory complications be determined . if this comfortable position is not determined preoperatively , the sitting position is preferable for resuscitation in the presence of an airway obstruction . this position moves the diaphragm caudally and alleviates the pressure of the mediastinal mass on surrounding organs . however , as in our case , the sitting position does not always effectively relieve cardiorespiratory complications during general anesthesia , and as has been previously reported , the lateral decubitus or prone position should then be adopted to enable the nature of the complication to be determined . nevertheless , it is unclear which position is best for clearing an airway obstruction due to a mediastinal mass during general anesthesia . the right lateral decubitus position could either prevent compression of the cardiorespiratory system during induction or relieve hypoxemia and hypotension during general anesthesia , irrespective of whether a tumor in the anterior mediastinum primarily expands toward the left or right side of the chest . however , in another report , the right lateral decubitus position did not solve the hypoxemia or hypotension caused by an anterior mediastinal mass , which was misdiagnosed as a pericardial effusion by preoperative echocardiography . in addition to changing posture , emergency percutaneous cardiopulmonary bypass support   or extracorporeal membrane oxygenation ( ecmo ) support   can be applied to an unexpected airway collapse during general anesthesia caused by a mediastinal mass . furthermore , when a patient with a mediastinal mass complains of cardiorespiratory symptoms before induction , it may be advisable to have a prepared cardiopulmonary support system available in the operating room . our case showed a rise in cvp after being positioned in the right lateral decubitus that was sustained even in the sitting position . the right heart and pulmonary artery , which are at lower pressures than the left heart and aorta , are more vulnerable to compression by a mediastinal mass . although the pulmonary trunk was not compressed by preoperative mdct in our case , the positional change might have caused a mass effect on the right heart or pulmonary artery and the observed increase in cvp . however , the maintenance of normal blood pressures suggested a partial obstruction of the pulmonary circulation . furthermore , the airway below the right main bronchus was probably only partially collapsed because petco2 remained in the normal range . when the cross - sectional area of the trachea is compressed by more than 50% of predicted , or pericardial or pleural effusions are visualized by preoperative ct , the patient may be more vulnerable to perioperative complications . furthermore , a peak expiratory flow rate ( pefr ) by the pulmonary function test ( pft ) of less than 50% of the predicted value should raise concerns about complications due to a mediastinal mass . in our patient , the preoperative tracheal cross - sectional area was patent , but pefr by pft was 50% of predicted and minimal pericardial effusion was observed by echocardiography . our patient also complained of exertional dyspnea , and thus , we should have expected hypoxemia or hypotension during general anesthesia . in conclusion , positional changes can be used to relieve an unexpected airway obstruction caused by an anterior mediastinal mass . however , before applying this method , it should be considered whether the intended posture is likely to be hazardous or effective . we recommend that when a patient is positioned that the center of the mass should be located in the dependent site of the body .
an 18-year - old male with huge anterior mediastinum mass was scheduled for thoracotomic incisional biopsy under general anesthesia after failed fluoroscopy - guided percutaneous needle biopsy . under propofol and succinylcholine anesthesia , 
 intubation was successfully achieved using a univent tube . 
 however , when we changed the patient 's position from supine to right lateral decubitus , oxygen saturation declined . 
 he was then positioned supine , but hypoxemia did not improve . 
 because the tumor expanded toward the left thoracic field , we considered that the left lateral decubitus position might help relieve the mass effect on the main bronchus . 
 his position was changed accordingly and soon after , hypoxemia improved and surgery was undertaken under cardiopulmonary bypass ( cpb ) . 
 the biopsy was successfully performed under cpb without complication .