Comment Regarding “Vapocoolant Analgesia for Breast Lymphoscintigraphy: A Prospective Clinical Trial”

TO THE EDITOR: I am writing to you regarding the article “Vapocoolant Analgesia for Breast Lymphoscintigraphy: A Prospective Clinical Trial” (1). Although the trial highlights the benefits of vapocoolants for the control of pain with needle procedures, I have several issues with the trial to address.

First, the trial design is limited by its 29-patient sample size, which weakens its overall clinical significance. Second, the trial does not contain a control group to compare the self-reported pain scale value, which further weakens its overall clinical significance. Third, the trial used a vapocoolant product that was irradiated to obtain sterility, creating toxic hydrofluoric acid in the product far in excess of permissible Occupational Safety and Health Administration (OSHA) limits.

The article states “that the Food and Drug Administration cleared a vapocoolant for sterile procedures, which instigated this clinical trial, the specific product being Nüm topical anesthetic spray, created by 623 Medical and distribution by Gilero.” According to Nüm’s Food and Drug Administration 510(k) summary (2), this hydrofluorocarbon-based product uses radiation to achieve sterility. No other Food and Drug Administration–cleared vapocoolants have used radiation. Previous literature (3) and recent independent third-party testing has shown that radiating a hydrofluorocarbon creates toxic hydrofluoric acid far greater than U.S. OSHA immediate danger to life and health levels. Nüm’s Food and Drug Administration 510(k) summary failed to address the presence of hydrofluoric acid created by the radiation.

In independent third-party testing, 5 Nüm lots were tested for hydrofluoric acid (HF) by 2 independent testing laboratories. We had 4 Nüm lots analyzed at Kent State University’s Department of Chemistry using ion chromatography (IC) and nuclear magnetic resonance (NMR) spectroscopy. The Kent State IC methodology was performed by bubbling Nüm sample contents into IC buffer, analyzed by IC, and calculated by a hydrogen fluoride (HF) standard curve. Similarly, Kent State’s NMR methodology was performed by bubbling Nüm contents into buffer, analyzed by NMR, and calculated with an HF standard curve. The 4 Nüm lots tested by Kent State revealed between 27 and 64 ppm of HF, 68 and 91 ppm of HF, 71 and 101 ppm of HF, and 56 and 107 ppm of HF (5).

Honeywell had 2 Nüm lots analyzed by IC at Honeywell Performance Materials and Technologies Buffalo Research Lab. Honeywell Lab bubbled Nüm into IC buffer, analyzed by IC, and calculated with an HF standard curve. The 2 Nüm lots tested by Honeywell IC demonstrated 49 ppm of HF and 69 ppm of HF (6).

OSHA Immediate Danger to Life and Health for hydrofluoric acid is 30 ppm (4). The test results for the Nüm product indicated a substantially greater HF level than the permissible OSHA level. Notably, the elevated HF readings reveal a significant safety risk to patients sprayed with the Nüm product.

In summary, whereas this study highlights the benefits of vapocoolants to control pain for needle procedures for radiologic purposes, irradiated products, such as Nüm, pose a new risk for hydrofluoric acid contamination and, therefore, patient safety. For this reason, no manufacturers, other than the manufacturer of Nüm, have chosen to irradiate their vapocoolant products due to the safety risk of hydrofluoric acid contamination. Therefore, for these reasons, the results of the recent Nüm clinical trial should be disregarded.

• Received for publication January 22, 2024.
• Accepted for publication January 24, 2024.