Appropriate amounts proportions of lidocaine gel, indigo carmine and lipiodol mixture for preoperative marking in video-assisted thoracic surgery

Preoperative marking is necessary in thoracoscopic wedge resections of lung nodules expected to be invisible or nonpalpable during surgery. Recently, lidocaine gel was added to a dye solution containing indigo carmine and lipiodol to promote micelle formation, but the optimal mixing ratio was not determined. Thus, an in vitro experiment was performed to identify the optimal mixing ratio of lidocaine gel, indigo carmine and lipiodol. To fixed volumes of indigo carmine and lipiodol of 0.5 ml each, 0.1, 0.2, 0.3, 0.4 and 0.5 ml of lidocaine gel was added. Changes were examined every 2 h. No changes were seen in the mixtures containing 0.1 and 0.2 ml of lidocaine gel, whereas those with 0.3, 0.4 and 0.5 ml had clearly separated after 2 h. Our findings suggest that the ideal proportion of indigo carmine, lipiodol and lidocaine gel for use in preoperative marking is 5:5:2.