Optimal Head Rotation and External Landmark for Internal Jugular Vein Cannulation After Placement of Proseal Laryngeal Mask Airway

• overlap index [ Time Frame: at 5 min after anesthesia induction ] [ Designated as safety issue: No ]
  The overlap index was derived from the ratio of the overlapping length of the IJV to the horizontal diameter of the CCA measured on the ultrasonographic image. The formula of calculation is as follows: overlap index = [overlap length (mm)/ CCA diameter (mm)] X 100(%), the measurements were repeated according to the degree of head rotation (neutral, 15 degree, 30 degree, 45 degree)
  
  

• The success of simulated internal jugular vein puncture (central landmark) [ Time Frame: at 5 min after anesthesia induction ] [ Designated as safety issue: No ]
  The success of internal jugular vein puncture guided by the central landmark simulated on the ultrasonographic images, the measurements were repeated according to the degree of head rotation (neutral, 15 degree, 30 degree, 45 degree)
  
  
• The success of simulated internal jugular vein puncture (external jugular vein landmark) [ Time Frame: at 5 min after anesthesia induction ] [ Designated as safety issue: No ]
  The success of internal jugular vein puncture as guided by 1.5 cm or 2.5 cm medial to the external jugular vein simulated on the ultrasonographic images, the measurements were repeated according to the degree of head rotation (neutral, 15 degrees, 30 degrees, 45 degrees)
  
  

Recently, laryngeal mask airway (LMA) placements are frequently performed for general anesthesia. The investigators occasionally encounter a clinical situation to perform internal jugular vein (IJV) cannulation after LMA insertion, especially for difficult airway in subjects undergoing major surgery. However, anatomic relations of IJV and common carotid artery (CCA) in patient with LMA placement have been reported to be different from those in patients with endotracheal tube. The degree of overlapping of the right IJV and CCA after LMA placement was greater than before LMA placement. Furthermore, there are many cases of complete overlapping right IJV and CCA after LMA placement. Therefore, the risk of puncturing CCA increases when the investigators try to cannulate IJV after LMA placement. Furthermore, the central landmark commonly used for IJV cannulation was proved to show low success rate after LMA placement in previous report. Previous study recommended the lower puncture point near that area where the clavicular head of the sternocleidomastoid muscle attaches to the clavicle, because CCA was not observed in the vicinity of the IJV after LMA insertion. Even though they performed test puncture at the lower puncture point in 20 patients and found no complications, the lower puncture point is not the usual site for IJV cannulation for most anesthesiologists. It is known that increased head rotation is associated with high probability of CCA contact. The investigators carefully examined the anatomic relations of IJV and CCA after LMA insertion with ultrasonography, and found that the degree of overlapping is different according to the degree of head rotation. The investigators postulated that if the degree of overlapping is different according to the degree of head rotation after LMA insertion, the investigators can find the angle of head rotation for least overlapping and reduce the risk of CCA puncture. Therefore, the investigators tried (1) to find the optimal head rotation angle appropriate for puncturing IJV after LMA placement, and (2) to find suitable landmark adequate for IJV cannulation after LMA placement.