Effect of time and velocity on selective parathyroid staining by intravenous infusion of methylene blue

Localization of the parathyroid gland (PTG) is often a challenge even to the experienced surgeons. While preoperative gland localization studies can improve the chance of success, their expense, limited availability and questionable reliability have generally relegated their use to instances where unilateral exploration alone is desired or, reexploration is required. Selective staining of the PTG by intraoperative methylene blue (MB) dye is rapidly available, simple, and effective adjunct to intraoperative gland identification. The purpose of this study was to evaluate the effect of variation in the rate of dye infusion.

Ten dogs underwent parathyroid gland exploration under general anesthesia (Halothane-Oxygen). Following the identification and exposure of at least one parathyroid gland in each animal intravenous infusion of MB was initiated at a dose of 5-7. 5 mg/kg mix with 200 cc D/W 5%. In Group A (5 dogs) a rapid infusion over a period of 3 to 5 minutes and in Group B (5 dogs) a slow infusion over a period of 20 to 30 minutes was done. The patterns of dye uptake (early, maximum, and diminution time) were recorded. Several digital photography was taken. After identification, the glands were removed and confirmed as parathyroid tissue histologically.

All animals tolerated infusion of dye without any obvious adverse effect intaoperatively. Twenty glands were identified with 3 intrathyroidal glands. Mean time for early uptake, maximum uptake, and diminution time in Group A was 8. 2,17. 2,and 32 minute respectively and in Group B was 10. 8, 17. 4, and 40. 6. This study showed the rate of infusion does not affect staining and the staining was seen much earlier as mentioned before. The time to initial dye uptake occurred between 6 and 15 minutes following dye infusion in both groups.

This investigation has demonstrated that the time of infusion is an important variable, with gland up taken occurring at a point much earlier than previously described. The uptake of dye shortly after infusion suggests reserving its use for those instances when standard PTG exploration fails to identify the glands.