a 9-month - old boy ( weight : 9 kg , height : 70.5 cm ) was brought into our emergency department with a complaint of vomiting . his past medical history included a repair of a congenital diaphragmatic hernia 8 months prior . chest radiography showed left lung haziness with pleural effusion and gaseous distended bowel loops in the upper abdomen . computerized tomography of the chest revealed herniated bowel loops in the left lower lung field and consequent passive atelectasis , suggesting recurrent diaphragmatic hernia and bowel strangulation . he was given 1 l / min oxygen by nasal prong , and peripheral oxygen saturation was maintained at 100% . general anesthesia was induced with intravenous propofol 3 mg / kg , and rapid sequence intubation with a cuffed endotracheal tube ( inner diameter 4.0 mm ) was performed after intravenous infusion of atropine 0.02 mg / kg and succinylcholine 2 mg / kg . breath sounds were bilaterally audible on chest auscultation , but with decreased sound at the left middle and lower lung field . anesthesia was maintained with sevoflurane in 50% oxygen / air , and an arterial catheter was placed at the left radial artery . after successful ultrasound - guided central venous catheterization in the left internal jugular vein , chest radiography was performed to determine the positions of the central venous catheter and the endotracheal tube . a specific surgical plan had not yet been fully confirmed , and the need for isolating the operative - side lung was considered . to determine whether endobronchial intubation with a single - lumen tube was enough to provide one - lung ventilation , or whether other techniques such as bronchial blockers were required for lung isolation , we introduced the endotracheal tube into the right main bronchus as a trial . although the breath sound at the left upper lung field was likely to decrease after inserting the tube 2 cm deeper , we could not ensure right endobronchial intubation . to confirm the placement of the tube , portable chest radiography was considered . fiberoptic bronchoscopy was equipped in the operating room , but it was not favorable due to the lack of a skilled anesthesiologist and the risk of hypoxia . therefore , we decided to identify the endobronchial intubation using ultrasonography ( z.one ultra sp , zonare medical system , mountain view , ca , usa ) . the patient was positioned supine , and a 4 cm sized pediatric 5 - 14 mhz linear ultrasound probe was placed sagittally into both midclavicular lines . an initial exam revealed rhythmical movement of the pleural line synchronized with respiratory movement ( lung sliding sign ) at both upper lung fields . using motion mode ( m - mode ) imaging 1a ) , known as a ' seashore sign ' , below the echogenic pleural line . when we gently inserted the endotracheal tube , we observed pleural movement of the left upper lung field using real - time ultrasonography . after insertion of the endotracheal tube ( at a depth of 15 cm ) , the lung sliding sign disappeared and a ' lung pulse ' , the recording of vibrations synchronized with heart activity , was detected ( fig . in contrast to the left side , the lung sliding sign of the right upper lung field could still be detected , suggesting that the right endobronchial intubation was performed successfully . after confirming the disappearance of left lung sliding sign , the endotracheal tube was pulled back to a 13 cm depth and the left lung sliding sign reappeared . finally , thoracoscopic surgery began without lung isolation , and an acceptable surgical field was obtained . the operation was completed with no adverse events , and the patient was delivered to the pediatric intensive care unit without extubation . immediate postoperative chest radiography showed improved haziness in the left lung , and the patient was extubated 1 hour later . one - lung ventilation technique during thoracoscopic surgery requires advanced skills especially when performed in infants . because of the small tracheal and bronchial diameter of infants , lung isolation is usually achieved by endobronchial intubation with single - lumen endotracheal tube . it is imperative to confirm appropriate tube placement in order to provide an adequate surgical field . in our present case , traditionally , lung auscultation , chest wall observation , fiberoptic bronchoscopy , chest radiography , and fluoroscopy   have been used to confirm proper lung isolation . auscultation and chest wall observation are simple techniques and require no special equipment , but are not reliable methods . although chest radiography and fluoroscopy are accurate enough to determine the appropriate tube position , they are time consuming   and may not be suitable in emergency situations . however , in small infants , it is difficult to define the tracheobronchial anatomy   and there is a potential risk of desaturation during bronchoscopy due to their low oxygen reserve . recently , the applicability of ultrasonography has been expanded to airway management , and several authors have described ultrasonographic identification of endobronchial intubation . two characteristic signs , the lung sliding sign and the lung pulse , can be used to verify endotracheal or endobronchial tube position . the lung sliding sign is the sliding movement of hyperechoic pleural layers against each other , synchronized with respiration . the application of m - mode facilitates to identify lung sliding by detecting superficial multiple horizontal lines and fuzzy imaging under the pleura , referred to as the see - shore sign . the presence of the lung sliding sign suggests normal lung movement with intact interpleural space during respiration . the lung pulse is the recording of vibrations synchronized with heart activity at the pleural line and can be explained by transmission of the heartbeat through a motionless lung . in a well - ventilated lung , the lung sliding sign is dominant , overriding the heart signal . on non - ventilated lung segments , the absence of the lung sliding sign and the presence of the lung pulse indicate the existence of non - ventilated lung segments produced by endobronchial intubation . lung ultrasonography is less time - consuming than chest radiography   and lessens the risk of multiple radiation exposure . moreover , it is a relatively simple technique that even the beginners can perform with least training . ultrasonographic lung isolation has some limitations . in the presence of pneumothorax , pleural adhesion , or subcutaneous emphysema hence , careful evaluation of preoperative chest radiography and an initial ultrasonography exam before intubation are necessary . in addition , the reliability and accuracy of lung ultrasonography to confirm the endotracheal tube position in pediatric patients have not been fully evaluated compared to adult patients . moreover , when the patient 's position changes or desaturation develops during one - lung ventilation , appropriate endotracheal tube position must be reconfirmed . however , the usefulness of lung ultrasonography to detect dislodgement of the tube has not been clearly elucidated . hence , lung ultrasonography can not be utilized as a standard technique instead of fiberoptic bronchoscopy . despite these limitations , lung ultrasonography may be an attractive technique to confirm lung isolation in pediatric patients . it can be utilized as a good adjuvant method to fiberoptic bronchoscopy and as a fast and easy alternative method particularly in emergency situations .