Cryosurgery Flashcards
Aim of cryo (WRT freeze/thaw times) to maximise benefit
rapid freezing, slow thawing and repetition of the freeze-thaw cycle
What are the 2 mechanisms of tissue injury by freezing
1. Immediate effect - direct injury to cells dt ice crystal formation, rx in a hyper-osmotic environment which dehydrates cells rx in cell death dt incr electrolyte concentrations and pH changes. Intracellular ice crystal formation maximised by lower temperatures and rapid cooling rates - crystals disrupt cellular organelles and membranes rx in immediate death
During thawing, (most pronounced between −25°C and −20°C), ice crystals fuse to form large crystals,(= recrystallisation). Large crystals are disruptive to cell membranes. With further thawing, the water enters the damaged cells and cell membranes rupture.
2. Delayed effect - happens after thawing dt progressive microcirculation failure and vascular stasis. Endothelial damage rx in incr. capillary permeability, oedema, platelet aggregation and and micro-thrombi and progressive circulatory loss
What temperature is required for tissue destruction
Initial thinking was to achieve −20°C for 1 or more minutes, more recent studies have shown that lower temperatures are often required to destroy tumour cells
Not all cells will be subjected to the same cooling and thawing temperatures and rates
Tissue close to the probe freezes very quickly to very low temps, while periphery cools slower and to a higher temp w less of a destructive effect
Human studies suggest temps -30- -40°C for 1 min+ using a double freeze protocol yields complete cell destruction.
Which cells are most sensitive to cryo
Give one tissue example where cryo not effective
Major advantage of cryo is selective cellular sensitivity; cells w high water content, mitotic rate & O2 consumption are more sensitive to cryonecrosis; and epithelial cells and melanocytes are more prone to cryonecrosis compared with fibrocytes
Cornea insensitive to cryo (low water content)
What is the boiling point for liquid nitrogen and nitrous oxide
Liquid notrogen = -196°C
Nitrous oxide = -89°C
