Mast cells in laser and surgical wounds

Precooling of tissues was investigated as a possible means of reducing thermal damage during CO2 laser surgery of the oral mucosa. The changes in mast cells in scalpel, and in non-cooled and precooled (tissue temperature lowered to approximately 10 degrees C) CO2 laser wounds were studied. Standard wounds five mm in length were created with the CO2 laser or scalpel on the dorsum of the tongues of 32 Sprague-Dawley rats under general anesthesia with fentanyl/fluanisone and midazolam. Animals were killed with excess anesthetic immediately or six hours after surgery, their tongues were removed, trimmed, fixed in neutral formalin and processed to paraffin wax. Acid (pH 1.4) toluidine blue stained sections were used to count normal and degranulated mast cells in five fields (0.1 mm2) located at defined positions immediately adjacent to the wound site. At both 0 and 6 hours normal mast cell numbers were significantly different between treatment groups (P<0.045; ANOVA) with mean numbers highest in scalpel wounds and lowest in uncooled laser wounds. Similarly, at 0 time, there were significant differences in degranulated mast cells between treatment groups (P=0.004; ANOVA) but highest numbers were detected in uncooled laser wounds and lowest in scalpel wounds. There were no significant differences in degranulated mast cell counts at six hours although there was a similar distribution in numbers between groups. Total numbers of mast cells (normal + degranulated) did not differ between treatment groups. These results demonstrated that i) laser wounds are associated with greater levels of mast cell degranulation than scalpel wounds and ii) precooling of tissues prior to laser treatment decreases the level of mast cell degranulation. It is concluded that tissue damage in CO2 laser surgery may be reduced by precooling of tissue.