Intercostal Cryoneurolysis Following Traumatic Rib Fractures

Rib fractures represent a significant source of morbidity in trauma patients, with approximately 10% of trauma patients presenting with rib fractures.1 Pain from rib fractures is associated with decreased ability to cough and inspire deeply, predisposing patients to atelectasis and pulmonary complications. Neuraxial blocks, both thoracic epidurals and paravertebral blocks, have been associated not only with decreased pain, but also decreased pulmonary complications and overall mortality in patients with rib fractures.2 Furthermore, intercostal nerve blocks with local anesthetic have been shown to improve pain scores, peak expiratory flow rates, and arterial oxygen saturation on room air.3 However, intercostal nerve blocks are not without risk and incidence of pneumothorax has been reported as 1.4% for each individual intercostal nerve that is blocked.4 Although it is possible that the use of in-plane ultrasound guidance may decrease the risk of pneumothorax, this has not been evaluated. Additionally, intercostal blocks with bupivacaine have been reported to resolve in as little as six hours,5 likely due to the high vascularity and consequent uptake of local anesthetic from the intercostal space.

An alternative analgesic technique is cryoneurolysis, consisting of the application of exceptionally low temperatures to reversibly ablate peripheral nerves, resulting in temporary pain relief termed "cryoanalgesia".6 The intense cold temperature at the probe tip produces Wallerian degeneration-a reversible breakdown of the nerve axon-subsequently inhibiting transmission of afferent and efferent signals. Because the nerve endoneurium, perineurium, and epineurium remain intact, the axon regenerates along the exoskeleton at a rate of approximately 1-2 mm/day. While cryoneurolysis of peripheral nerves through surgical incisions has been commonly used to treat pain since 1961, the development of cryo probes that may be inserted percutaneously promise a revolution in the use of this modality. The combination of newly-designed narrow-gauge probes (upper right) and ultrasound now make percutaneous cryoanalgesia as simple as placing a peripheral nerve block: the probe tip is inserted adjacent to the target nerve under ultrasound guidance, and a series of 2-minute freezing cycles are administered followed by probe withdrawal. The procedure is essentially the same as placing an ultrasound-guided peripheral nerve block; however, instead of injecting local anesthetic, a gas circulates through the probe, inducing cold at the tip and freezing the target nerve. Nothing remains within the patient and there is no external equipment to prepare or manage. Importantly, cryoneurolysis and the probes are already approved by the United States Food and Drug Administration for the treatment of acute and chronic pain, so no additional regulatory approval is required for the proposed clinical trial.

Theoretical benefits of cryoneurolysis include an ultra-long duration of pain control without opioid involvement, no catheter management/removal (reducing infection risk), the lack of an infusion pump and anesthetic reservoir to carry, an extraordinarily-low risk of infection (approaching zero), and no risk of local anesthetic toxicity, catheter dislodgement or leakage. With a single 8-minute percutaneous cryoneurolysis procedure consisting of several freeze/defrost cycles, a truncation of sensory nerve conduction is induced for 6-8 weeks, with the complete restoration of nerve structure and function following remyelination. Cryoneurolysis offers the possibility of potent, side effect-free analgesia outlasting the surgical pain, and obviating the need for postoperative opioids.

All subjects would continue to receive standard and customary analgesics, so there is no risk of subjects receiving a lower degree of analgesia than if they otherwise did not enroll in the study. The cryoneurolysis procedure will be done in addition to the investigator's current UCSD standard practice.

Study Overview