The use of viscoelastic materials in surgery is based on a general concept of solving problems that occur during cataract surgery (6). In this case, viscoelastic
materials protect the endothelial layer of the cornea from damage during phacoemulsification and aspiration and maintain operative space. Two types of HA are used in cataract surgery: higher molecular weight HA (1900-3900 kDa) and lower molecular weight HA (600-1200 kDa). The former has high viscoelasticity and is mainly used to maintain operative space. The latter has higher dispersity and is mainly used to protect the endothelial layer. HA has now become indispensable in cataract surgery (7).
Endoscopic mucosal resection (EMR) is a useful method for excision of non-polyploid and flat early neoplastic lesions in mucous membranes, and is an effective and minimally invasive method of treatment. Although an early tumor that has not reached the muscle properly can be excised endoscopically, it is difficult to excise flat lesions with a snare. To make excision safer and easier, physiological or hypertonic saline is commonly injected submucosally underneath the target region to create and maintain tissue elevation.
Yamamoto (8,9) reported EMR using submucosal injection of HA in the expectation of an advantage to reduce the risk of perforation and to accomplish complete en bloc resection. Mucosal elevations created by submucosal injection of HA remained for a longer time with a clearer margin compared with those made by saline injection (9). Use of HA instead of saline for EMR could make the procedure easier and more reliable. Onaya et al. (personal communication) evaluated various concentrations of HA as a novel submucosal injectant for EMR. In their study, the pressure of the fluid through the catheter, which was measured by a rheometer, increased with increasing concentrations of injected HA in the submucosal layer of resected porcine stomach at concentrations of 0.1-0.8%. However, it was difficult to measure HA solutions of 0.5% or higher since their resistance force was very high. Therefore, three concentrations of HA (0.2, 0.3 and 0.4%) were selected for injection into the submucosal layer of live rabbit stomachs. During 1 h of observation, the mucosal elevation produced by 0.4% HA solution was more prominent than that with the other two concentrations. In addition, 0.4% HA injection created a significantly higher protrusion at 30 min. Then they compared the height of the protrusion after injection of 0.4% HA, physiological saline, 50% dextrose, hypertonic saline and glycerol, which are used in Japanese clinical practice. Among them, 0.4% HA showed the highest value. Moreover, histological analyses showed no tissue injury after injection of a 0.4% HA solution or physiological saline, while other materials induced tissue injury, apparently caused by their hypertonicity.
These results suggest that an appropriate concentration of HA may be more useful in EMR than saline and other kinds of viscous materials such as dextrose and glycerol.
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