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Chapter 79

### INTRODUCTION

Cryoneuroablation is an interventional technique aimed at temporary destruction of the nerve providing relief of the pain. The origin of this technique lies in the ancient time but modern cryoanalgesia traces its roots to Cooper et al.1 In 1962, they developed a device that used liquid nitrogen circulating through a hollow tube, insulated except at the tip, to achieve a tip temperature of −196,°C. Amoils,2 an ophthalmic surgeon, developed a simpler handheld device in 1967, which used high-pressure carbon dioxide or nitrous oxide and could achieve temperatures of −70°C. Lloyd et al3 coined the term “cryoanalgesia” for its use in pain management. They proposed that this technique was superior to other methods of peripheral nerve destruction, for example, alcohol, phenol, or surgical lesions, because it is not followed by neuritis or neuralgia.

The cryoneuroablation unit:

• The cryoneuroablation relies on the ability of specially constructed probe to freeze tissue around it.

• The cryoprobe consists of a hollow tube with a smaller inner tube.

• Pressurized gas (usually N2O or CO2) at 600 to 800 psi travels down the inner tube and is released into the larger outer tube (which is at a low pressure of 10-15 psi) through a very fine aperture (0.002 mm), which allows the gas to rapidly expand into the distal tip (Figure 79-1).

• The heat is extracted from the tip of the probe, resulting in temperatures as cold as −89°C at the tip itself (Joule-Thompson effect), forming an ice ball with temperatures in the range of −70°C (Figure 79-2).

• The gas is then vented back to the machine itself through the outer tube and is scavenged through a ventilated outlet.

• The “closed system” construction of the probe and machine ensures that no gas escapes into the patient’s tissues.

• Precise gas flows are necessary for safe and effective cryoneuroablation; inadequate gas flows will not produce an ice ball, while excessive flows can cause freezing proximally up the probe, which may increase the risk of skin burns.

• The probe includes a built-in nerve stimulator with sensory and motor capabilities, which allows precise localization of the target nerve (Figure 79-3).

###### Figure 79-1.

Cryoneuroablation probe physics. (Reproduced with permission from Epimed, Farmers Branch, TX.)

###### Figure 79-2.

Cryoneuroablation ice ball. (Reproduced with permission from Epimed, Farmers Branch, TX.)

###### Figure 79-3.

Cryoneuroablation machine. (Used with permission from Andrea Trescot, MD.)

The mechanism of cryoneurolysis:

• Thermal injury interrupts the neuronal pathway and provides pain relief. More specifically, the application of cold to tissues creates a conduction block, similar to the effect of local anesthetics.

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