general anaesthesia is associated with lower oxygen tension due to increased alveolar - arterial oxygen gradient and occasionally oxygen desaturation leading to hypoxaemia . the other mechanical causes of hypoxaemia are equipment failure , endotracheal tube blockade , endobronchial or oesophageal intubation and clinical causes are aspiration , hypoventilation , or pulmonary embolism especially in patients with trauma . intraoperative atelectasis of a bronchopulmonary segment , entire lobe , or lung due to mucus plug as a cause of hypoxaemia is uncommon and may be potentially fatal . we report a case of intraoperative right lung collapse due to mucus plug in a patient undergoing left laparoscopic nephrectomy . a 46-year - old male , chronic smoker , weighing 55 kg was diagnosed to have bilateral obstructive uropathy due to renal stone disease . he was posted for left laparoscopic nephrectomy for left - sided non - functioning kidney . stenting and cystolitholapaxy under spinal anaesthesia and right - sided percutaneous nephrolithotomy ( pcnl ) and ureterorenoscopy ( urs ) before 2 months . preoperative blood investigations were within normal limits with serum creatinine of 1.12 mg / dl . x - ray of the chest was also reported as normal [ figure 1 ] . trachea was intubated with an 8.5 mm cuffed endotracheal tube ( et ) after intubation , secretory sounds were felt in the bag with 100% oxygen saturation . when the patient was put in the right lateral kidney bridge position , on auscultation , breath sounds were reduced in the right supraclavicular , mammary , and scapular areas . since there was no improvement in the oxygen saturation , he was put in the supine position . on examination respiratory movement on auscultation , breath sounds were absent in right supraclavicular , mammary areas and bronchial breathing was present with crepitations in the right inframammary and infra - axillary regions . portable chest radiograph was suggestive of right upper lobe lung collapse [ figure 2 ] . preparation for fibreoptic bronchoscopy was done . in the mean time , postural drainage for the right upper lobe in the reverse trendelenberg position with head end of the operation table elevated by 18 inches was attempted and yielded a thick yellowish green mucus plug . a sudden improvement was seen in the respiratory movement in the supraclavicular and mammary area with normal vesicular breathing and 100% oxygen saturation . the repeat chest radiograph taken after 10 min showed complete expansion of the right upper lobe [ figure 3 ] . surgery was postponed and the patient was extubated and shifted to the postanaesthetic care unit . retrospective examination of the preoperative chest radiograph which was reported normal , showed multiple retrocardiac cystic shadows . high resolution computed tomography ( hrct ) thorax was advised and it showed cystic bronchiectasis in the left lower lobe [ figure 4 ] . a successful operation was done after 15 days with preoperative chest physiotherapy , incentive spirometry , antibiotic coverage , and intraoperative use of humidification and avoidance of anti - sialogogues . acute pulmonary collapse is common in the postoperative and intensive care unit ( icu ) setting but is a rare event after induction of anaesthesia and repositioning . the most common cause is endobronchial intubation or blockage of tube by secretions , blood , or herniated cuff . our report highlights the precipitous onset of hypoxaemia associated with considerable pulmonary collapse due to mucus plug . normally , general anaesthesia is associated with lower oxygen tensions , and occasionally oxygen desaturation leading to hypoxaemia can occur . mechanisms for hypoxaemia include ventilation perfusion ( v / q ) mismatch , hypoventilation , diffusion impairment , and physiologic or anatomic shunt . during anaesthesia and neuromuscular relaxation , ventilation is redistributed to the nondependent regions of the lungs due to atelectasis and airway closure in the dependent lung regions , resulting in increased alveolar - arterial oxygen gradients and hypoxaemia . in the lateral position , gravity - related preferential perfusion to the dependent lung worsens this v / q mismatch and hypoxaemia . in our patient , this was not the cause as hypoxaemia developed acutely with physical findings . in our patient , the initial clinical presentation included sudden onset of hypoxaemia on assuming a lateral position so initial diagnosis was blockage of et tube / endobronchial intubation as there was reduction or absence of breath sounds on right lung . et blockage was ruled out by passing of the suction catheter which aspirated few secretions and endobronchial intubation was ruled out by auscultation . due to persistent hypoxaemia , the patient was turned to the supine position which revealed diminished movement on right upper chest . immediate x - ray confirmed right upper lobe collapse . to find out the cause of collapse , fiberoptic bronchoscopy was planned but before that with postural drainage mucus plug was aspirated and the patient improved clinically and radiologically . to know the cause of mucus plug , we reviewed the chest x - ray taken on table and compared it with previous preoperative x - ray which was reported normal , which actually showed cystic cavity with air - fluid level in the left lower lobe which was concealed behind cardiac shadow . on giving right lateral position , secretions from this cavity must have shifted to right upper lobe bronchus causing right upper lobe collapse . significant lung collapse is usually associated with haemodynamic instability due to mediastinal shift and decreased venous return . however , our patient remained haemodynamically stable . the probable reason could be that in the setting of proximal airway obstruction the elevated airway pressure is not transmitted to the extraparenchymal intrathoracic structures like great vessels , so venous return and cardiac output remain preserved as it has been shown previously . while lung collapse and intraoperative hypoxaemia have been reported previously , few involve mucous plugging and atelectasis . in reviewing the literature , we found five reports describing mucous plugging , all associated with orthopaedic surgery following trauma and all diagnosed with chest radiographs . in these patients , the combination of recent trauma and surgery was the contributing factor to intraoperative atelectasis and lung collapse from mucous obstruction . four other cases of mucous plugging have been reported in quadriplegic patients initially diagnosed with pulmonary embolism . however , the chest radiograph was inconclusive , and diagnosis was made in these cases only by the use of ventilation scintiscans . this report highlights a rare but important cause of intraoperative hypoxaemia . though written normal , chest x - ray showed signs of bronchiectasis , but on reviewing the chest x - ray we understood there was missed diagnosis . if this was identified earlier thorough toileting before positioning could have prevented this complication . although intraoperative fibreoptic bronchoscopy is a gold standard to aid diagnosis and management , a trial of postural drainage may be life - saving .
desaturation after induction of anaesthesia and repositioning due to mucus plug causing atelectasis ( lung collapse ) is a rare event . 
 we present a case of intraoperative right lung collapse due to mucus plug in a patient undergoing left laparoscopic nephrectomy . 
 hypoxaemia occurred after the induction of anaesthesia and repositioning . 
 x - ray chest revealed right lung collapse and surgery was subsequently postponed . 
 lung re - expanded after postural drainage and suction . 
 postoperatively patient was diagnosed to have retrocardiac bronchiectasis . 
 after preoperative preparation with postural drainage , chest physiotherapy , and antibiotics , the patient underwent surgery uneventfully .