Cryoneurolysis Thermal Graphs: In Vivo Descriptive Data from Ultrasound-guided Percutaneous Thermocouples

Cryoneurolysis provides analgesia by reversibly ablating peripheral nerves using gas-induced exceptionally low temperature. The desired therapeutic temperature is between approximately -20°C and -100°C. Warmer temperatures can induce a neuropraxia that may itself induce pain; and colder temperatures can result in permanent nerve injury. Therefore, it is imperative that the target nerve reach but not exceed the therapeutic window.

A convenience sample of participants undergoing mastectomy (n = 3) received a high-thoracic paravertebral nerve block, while subjects being treated for traumatic rib fractures (n = 3) did not. All participants had ultrasound-guided cryoneurolysis of multiple intercostal nerves with a percutaneous thermocouple inserted approximately 3 mm adjacent to the cryoprobe shaft. The returning argon gas and tissue temperatures were correlated. Due to the limited sample size, the data are presented and not statistically analyzed.

Although in all cases (31 nerves) the returning gas was ultimately colder than -80°C, the tissue adjacent to the probe did not reach -20°C after 3 and 5 min in 71% (n = 5) and 42% (n = 10) of treatments, respectively. The coldest mean temperature in adjacent tissue was 60°C warmer than the returning gas with out a nerve block, and 95°C warmer with a concurrent nerve block. When treating adjacent intercostal nerves, the gas temperature remained unchanged, while the tissue became colder with each consecutive treatment.

During percutaneous cryoneurolysis, the temperature of tissue is frequently deceptively warm relative to the returning gas and tissue frequently does not reach an adequately cold temperature; prolonging gas treatment from 3 to 5 min improves the success of reaching therapeutic temperatures; the presence of a peripheral nerve block appears to lessen the chance of reaching therapeutic temperatures; and caution is warranted when treating consecutive intercostal nerves as tissue temperature may decrease with each level.