Hydrofluoric acid burn treatment

This is the eighth in a series of blog posts on new research in emergency toxicology. The last post was about nitazenes and can be found here. We deal with all sorts of poisons here in Virchester, so be prepared for anything.

Hydrofluoric acid (HFA) is a corrosive substance used widely in industry and occasionally in hobbyist products. Accidental exposures are rare in the UK, but when they do occur, the skin is the most common site of injury. Exposure risks can be greatly reduced by use of chemical-resistant personal protective equipment.

If untreated, HFA burns have the potential to get very, very nasty. As with most acids, some corrosion is caused by hydrogen ions, but the real menace here is fluoride ions, which are highly electronegative and pass easily through the skin. Within minutes, HFA can induce severe liquefactive injury in the nerves, vessels, and bone underlying the exposed site. This process may be painless with some dilute preparations.

The antidote for HFA burns is calcium. The UK National Poisoning Service (NPIS) recommends topical treatment with calcium gluconate gel (2.5%) in the first instance, with alternative routes to be considered in severe cases. For example, calcium gluconate (10%) can be infiltrated subcutaneously around the burn, or injected into a proximal artery.

Calcium gluconate gel is a Category A antidote and should, in principle, be available in all UK emergency departments. We certainly have it in our cupboards at St Emlyn’s. Unfortunately, nationwide compliance with RCEM guidelines for antidote stocking appears to be mixed, and it is unclear whether even well-prepared departments would have enough supplies in the event of a mass exposure.

For this reason, many toxicology resources describe a “home brew” calcium mixture be used in HFA burns when the licensed antidote is not available. This typically consists of a water-based gel and an injectable calcium solution.

As much as I love a bit of jury-rigging in emergency medicine, I would be uneasy about using one of these “home brew” calcium gels without evidence to back me up. Fortunately, a study was recently published in Clinical Toxicology on this topic.

Abstract

Background & Objectives: Hydrofluoric acid is a weak acid with the potential for local and systemic fluoride toxicity. Standard care for dermal exposures includes the application of a topical calcium gel. If a commercially produced 2.5% calcium gel is not available, bedside mixing of one is recommended. We sought to determine whether bedside mixing of a calcium gel can reliably produce a suitable product for the treatment of this exposure.
Methods: A survey was sent to the medical directors of America’s Poison Centers® to collect information on current treatment recommendations for dermal hydrofluoric acid exposures. Following this, bedside mixing of a 2.5% calcium gel was attempted with seven brands of water-based gels and one brand of petroleum-based gel. Each brand of gel was mixed in a 3:1 mL ratio with 10% calcium salt solutions (calcium gluconate or calcium chloride) in an attempt to create a 2.5% calcium gel solution. Mixtures were photographed and assessed visually for viscosity and precipitations and were analyzed for final calcium concentration.
Results: Five of seven water-based gels exhibited a rapid loss of gel-like viscosity and immediate development of gross precipitates upon mixing with calcium-containing salts. The mean calcium concentrations in these non-viscous, precipitate-containing mixtures were lower than the expected 2.5% for both calcium gluconate and calcium chloride mixtures. The petroleum-based gel failed to produce a usable mixture when combined with water-based calcium salt solutions.
Conclusions: The standard recommendation of mixing a calcium gel at the bedside may result in the production of a non-viscous mixture with a calcium concentration lower than the expected 2.5%.
Cowdery CP, Kazmierczak SC, Thompson JA. Bedside mixing of calcium gels for dermal hydrofluoric acid treatment leads to precipitate formation and loss of dissolved calcium.
Journal of Clinical Toxicology. 2025 Jun.

Where and when was this research done?

This study was conducted in 2023 by emergency physicians and toxicologists affiliated with the Oregon Health & Science University in Portland, USA.

What kind of study was this?

This was a basic science study. Except for a few papers involving animal models, we rarely cover these on St Emlyn’s. There were no patients involved, and the design does not fit into the categories we usually apply to journal articles.

So what was the methodology?

The researchers sent a survey to fifty-five American poison centres to ask if they recommended bedside calcium gel mixtures for HFA exposures, and if so, what precisely they instructed referring clinicians. The response rate was low (40%) but nearly all replying centres (n=21) stated that they had recommended one or more of these mixtures, and most provided examples.

After this initial stage, seven different brands of water-based gels (and one petroleum jelly) were purchased based on responses to the survey. Among them was Aquasonic® gel, which is commonly used here in Virchester for ultrasound probes.

The researchers combined these different agents with 10% calcium gluconate or chloride in a 3:1 mL ratio to create mixtures emulating the 2.5% gel. They then examined these mixtures for viscosity and ran them through a chemistry analyser (Beckman AU700) to measure the calcium concentration.

What were the key findings?

When combined, most (n=5) mixtures — including the one containing Aquasonic® — immediately lost their viscosity and generated large, clumpy precipitates. The contents of these precipitates were not analysed, but they were associated with a significantly reduced calcium concentration in the left-over solution.

Two of the remaining brands (KY Classic® and Surgilube®) retained viscosity when combined with calcium and did not precipitate. These mixtures achieved a final calcium concentration comparable with 2.5% calcium gluconate gel.

The petroleum jelly failed to form an emulsion and so was not analysed.

What were the authors’ conclusions?

The authors concluded that most bedside calcium mixtures recommended by poison centres do not have sufficient viscosity and calcium concentration to be safely used as an antidote for HFA burns.

How much should I read into these results?

I like this study. The researchers used scientific methods to scrutinise a “trick of the trade” commonly employed by emergency clinicians. Studies like this are few and far between, although a few fantastic examples have been published in the EMJ this year.

Obviously, there are limitations. There were no actual patients in this study, and therefore no burns. It may be that some of the “failed” mixtures would work perfectly well on real HFA injuries, despite being less viscous and containing less calcium. The evidence for 2.5% calcium gel is fairly thin on the ground so it is perhaps begging the question to use its chemical properties as a reference standard.

Also: the authors purchased a wide variety of water-based gels, but this was an American study, and the brands reflect this. Some of the products widely used here in the UK (e.g. OptiLube®) were not included. Perhaps they perform better?

Should this study change my practice?

Yes. If your emergency department does not currently stock the correct antidote for HFA burns, order some in. This study shows that even under laboratory conditions, most “home-brew” mixtures fail to achieve the properties of 2.5% calcium gel. Giving a sub-optimal treatment is risky business for these patients, as it can give the impression that “something has been done” and steer care away from recommended alternatives, such as calcium injections.

A study was published in Burns around the same time as this paper assessing the use of calcium gluconate soaks as an alternative to gel. I imagine this will enter the NPIS guidance soon.

Greg Yates