INTRODUCTIONRecently, the laryngeal mask airway (LMA) is frequently used for patients under general anaesthesia.(1-7) Occasionally, a clinical situation that requires internal jugular vein (IJV) cannulation after LMA insertion is encountered, especially for difficult airways in patients undergoing major surgery. (8,9) However, the anatomic relationship of the IJV and the common carotid artery (CCA) has been reported to change significantly in patients after LMA insertion.(10) The degree of overlap between the right IJV and the right CCA was found to be greater after LMA insertion.(10) In our experience, there are many cases of complete overlap between the right IJV and the right CCA after LMA insertion. This means that there is a higher risk of puncturing the CCA and a lower rate of successful IJV cannulation, when IJV cannulation is performed after LMA insertion. Lieberman et al reported that an increase in head rotation was associated with a higher probability of CCA contact; (11) we postulated that the effect of head rotation would be similar in patients with LMA insertion. If the degree of overlap between the right IJV and the right CCA varies according to the degree of head rotation after LMA insertion, the degree of head rotation with the least amount of overlap can be determined and the risk of CCA puncture can therefore be reduced.The central landmark approach, which is commonly used for IJV cannulation, was shown to have a low success rate in patients with LMA insertion.(12) Takeyama et al recommended the use of a lower puncture point -near the area where the clavicular head of the sternocleidomastoid muscle (SCM) attaches to the clavicle; the CCA was not observed to be in the vicinity of the IJV when the patient was in that position even after LMA insertion.(10) Although the authors performed test punctures at the supraclavicular lower puncture point in 20 patients without any complications, Kim et al (13) opined that the supraclavicular puncture could still be associated with pneumothorax, hydrothorax or cardiac tamponade. Takeyama et al evaluated the puncture point using only a 30° head rotation, (10) without evaluating the effect of different degrees of head rotation. Another commonly used landmark approach for IJV cannulation is the skin point 1.5 cm or 2.5 cm medial to the external jugular vein (EJV). (14) The use of this landmark has not been evaluated in patients with LMA insertion.In the present study, we compared the degrees of overlap between the right IJV and the right CCA as well as the success rates of simulated right IJV cannulation between patients with LMA insertion and patients with endotracheal intubation (E-tube) using ultrasonography. We aimed to find: (a) the optimal degree of head rotation for right IJV cannulation; and (b) a suitable skin landmark for right IJV cannulation after LMA insertion. To achieve these goals, we compared the success rates of simulated right IJV cannulation at different degrees of head rotation and used different skin landmarks for right IJV cannulation.