Chapter 14 - Cryosurgery

Question 1

1. What are the 3 fundamental features of good cryosurgical technique?

Answer 1

• Rapid freezing
• Slow thawing
• Repetition of the freeze-thaw cycle

Question 2

2. What is the ‘immediate mechanism’ of cryotherapy cell injury

Answer 2

• Direct injury to cells, caused by ice crystal formation

Question 3

3. When cells are cooled, primary injury begins with the formation of _____ in both the intracellular and extracellular environment

Answer 3

• ice crystals

Question 4

4. Describe the sequence of events involved in primary injury that occurs with cryosurgery

Answer 4

• Extracellular ice crystal formation results in a hyperosmotic environment (electrolyte concentrations and pH changes). Intracellular ice crystal formation disrupts organelles and cell membranes, causing immediate cell death. During thawing, ice crystals fuse to form large crystals (recrystallization). Large crystals are disruptive to cell membranes in tissues with closely packed cells

Question 5

5. What is the ‘delayed mechanism’ of cryotherapy cell injury

Answer 5

• Progressive microcirculation failure and vascular stasis. Endothelial damage causes increased permeability of the capillary wall, edema, and platelet aggregation, and microthrombus formation, resulting in progressive stagnation of the circulation.

Question 5

6. When is maximal tissue disruption obtained from cryosurgery?

Answer 5

• When the freeze-thaw cycle is repeated at least once or twice

Question 5

7. The first freeze cycle does what to the tissue that makes the repeated cycle more effective?

Answer 5

• Increases the thermal conductivity of the tissue as a result of cellular breakdown

Question 6

8. Mammalian cells are destroyed when cooled to a temperature of _____

Answer 6

• -30 - -40 C for 1 or more minutes

Question 7

9. Cells with what characteristics are more sensitive to cryonecrosis? (3)

Answer 7

• High water content
• High mitotic rate
• High oxygen consumption

Question 8

10. Which are more sensitive to cryonecrosis, epithelial cells and melanocytes or fibrocytes?

Answer 8

• epithelial cells and melanocytes

Question 9

11. What are 3 cryogenic agents which have been utilized in equine medicine?

Answer 9

• Liquid nitrogen
• Carbon dioxide
• Gaseous nitrous oxide (N2O)

Question 10

12. T/F: As permeability of vessels is increased after freezing, plasma loss causes local hemoconcentration

Answer 10

• True

Question 10

13. Damaged ____ in arterioles and venules induces thrombosis formation

Answer 10

• endothelium

Question 11

14. Infarction of vessels occurs within ____ of freezing (think timeframe)

Answer 11

• several hours

Question 12

15. T/F: Slow freezing results in the greatest intracellular concentration of ice

Answer 12

• F, fast freezing (slow freezing promotes extracellular ice)

Question 13

16. T/F: Slow thawing of tissue results in recrystallization, during which small crystals enlarge, which produces more cell damage

Answer 13

• True

Question 14

17. What should be done to ensure all target tissue receives a lethal dose of cold

Answer 14

• colder temp and multiple freeze thaw cycles

Question 15

18. T/F: Precooled tissue freezes slower than normal tissue

Answer 15

• F, faster

Question 16

19. T/F: Repeating a freeze thaw cycle results in more consistent necrosis of the target tissue

Answer 16

• T

Question 16

20. Tissues respond differently to cryotherapy depending on what 3 tissue characteristics.

Answer 16

• Water content (high)
• Mitotic rate (high)
• Oxygen consumption (high)

Question 16

21. T/F: Dry tissues do not readily form ice crystals

Answer 16

• True

Question 17

22. How can nanoparticles improve freezing efficiency

Answer 17

• Maximize the freezing heat-transfer process, to regulate the freezing scale, to modify ice ball formation, to enhance the ice ball margin US imaging, and thus prevent healthy tissues from being frozen

Question 18

23. What is the most common condition treated with cryotherapy in horses?

Answer 18

• Skin tumors (sarcoid and SCC)

Question 19

24. Name 3 cryogens that can be used in vet med

Answer 19

• liquid nitrogen
• carbon dioxide
• gaseous nitrous oxide (N2O)

Question 20

25. What is the most common cryogen used in vet med

Answer 20

- liquid nitrogen

Question 21

26. What types of probes are used to deliver cryotherapy

Answer 21

- solid probes - hollow probes

Question 22

27. How do hollow probes work

Answer 22

- cooled by liquid nitrogen circulating through them

Question 23

28. How do solid probes work

Answer 23

- chilled by immersion in liquid nitrogen then applied to the lesion

Question 24

29. What is a downside to using a solid probe for cryotherapy?

Answer 24

- They warm up quickly when in contact with living tissue and deep freezing is hard to achieve

Question 25

30. What types of lesions can be treated with cryotherapy?

Answer 25

- Smaller cutaneous and ocular tumors. - Distichiasis.

Question 26

31. What is the most effective method of cryogen delivery

Answer 26

- pouring or spraying (self pressurizing spray guns)

Question 27

32. What is the mechanism of action of self pressurizing spray guns

Answer 27

- deliver a combination of vapor and droplets of liquid nitrogen, controlled by the needle orifice diameter and the trigger in the spray gun.

Question 27

33. What is the major drawback to spraying liquid nitrogen?

Answer 27

- If too much liquid nitrogen is applied to tissue at one time, it can bead up and drip down, resulting in “frost lesions” - It is advisable to use “cups” to confine the cryogen to the lesion and prevent runoff

Question 27

34. T/F: Hollow probes are the easiest to control freezing and cools the target area at a fast rate

Answer 27

- F, cools slows

Question 28

35. Hollow probes can be used for ____ or _____ freezing techniques

Answer 28

- contact - penetration

Question 29

36. Contact freezing with ____ probe is very efficient

Answer 29

- solid

Question 30

37. What is the benefit of using an Esmarch bandage during cryosurgery on the distal limb?

Answer 30

- It reduces hemorrhage and achieves lower tissue temperatures

Question 31

38. T/F: The outer edge of the ice ball is around 0C (32 F) and is adequate temperature for tissue destruction

Answer 31

- F, temp is inadequate for tissue destruction

Question 32

39. What are the preferred margins of the palpable ice ball during cryosurgery?

Answer 32

- 5-10mm

Question 33

40. The depth of contact freezing is estimated to be ____

Answer 33

- slightly less than radius of ice ball

Question 34

41. _____% of the tissue within the ice ball is destroyed by freezing

Answer 34

- 75%

Question 35

42. Name 6 normal biological reactions to cryotherapy

Answer 35

- local edema - limited bleeding - coagulation necrosis - complete sloughing - depigmentation - odor

Question 36

43. Why does swelling occur after freezing

Answer 36

- increased vascular permeability

Question 37

44. Swelling usually resolves within ____

Answer 37

- 24-48h

Question 38

45. When does necrosis occur

Answer 38

- for several days after thawing (14-21d)

Question 39

46. When the eschar sloughs following cryosurgery, name 3 things that could be underneath the eschar

Answer 39

- yellowish exudate and malodorous smell (should disappear once necrotic tissue sloughed) - granulation bed - tumor recurrence

Question 40

47. Post cryosurgery, the necrotic eschar gradually detaches from the underlying granulation tissue starting at about ___-___days after surgery. Complete sloughing takes approximately ___-___weeks but can take as long as ___weeks

Answer 40

- 7-10 days - 2-4 weeks - May take up to 8 weeks

Question 41

48. Why is there depigmentation after freezing

Answer 41

- due to destruction of melanocytes and hair follicles

Question 42

49. What complications may occur with cryosurgery near a joint capsule

Answer 42

- Tissue sloughing resulting in joint penetration (subsequent septic arthritis) - Loss of periarticular tissue causing fibrous reactions and osseous perarticular-new bone developing, which may cause functional impairment or osteoarthritis

Question 43

50. What are the 3 most significant complications that can occur with cryotherapy?

Answer 43

- Dripping of the cryogen during the procedure - Insufficient freezing of tumors resulting in recurrence - Too aggressive freezing resulting in necrosis of tissues that should have been preserved

Question 44

51. Name 3 tissues that do not respond well to cryotherapy

Answer 44

- bone, - joint capsule - tendon sheath

Question 45

52. T/F: Cryo-treated tumors interfere with the efficacy of chemotherapy treatment

Answer 45

- F, they enhance