Tick killing in situ before removal to prevent allergic and anaphylactic reactions in humans: a cross-sectional study

The Australasian Society of Clinical Immunology and Allergy (ASCIA) recommends killing ticks in situ with an ether-containing spray and allowing them to drop off. The rationale is that this helps prevent allergy or anaphylaxis, since removal by other means might squeeze intra-abdominal contents and introduce more allergens.

One would think such a recommendation is based on high-quality evidence. It turns out this paper is probably the best evidence we have to inform practice. Oh great! Let’s have a look.

Just a word of warning, this ride is about to get bumpy.

Let’s start with the paper’s conclusion. It states, “[Our] results support killing ticks in situ before careful removal by mouthparts to reduce allergic/anaphylactic reactions…”

This wording suggests the researchers prospectively compared freezing with other methods of removal. But they didn’t. I am not joking.

The authors report their experience essentially using one method of tick removal and conclude it worked well. Once again, they did not properly compare it with anything else.

They do mention that anaphylaxis still occurred in some patients after ticks were frozen. Is it possible that the brief act of freezing a tick causes it to regurgitate more allergenic contents compared with careful removal using fine tipped forceps? The honest answer is that we simply do not know. There is clear clinical equipoise here and a proper comparative trial would be entirely ethical.

Unfortunately, there has now been a considerable amount of confidently expressed advice from ASCIA and others telling people that ticks must be killed before removal and that you should “freeze it and don’t squeeze it.” The certainty of these recommendations is not justified based on the evidence available.

One might ask, what is the harm in freezing before removal? Well, putting aside the possibility that we do not actually know whether freezing could worsen allergic reactions, the sprays themselves come with some cost. I checked my local pharmacy and they were about $25. The recommendation may also encourage people to present to busy emergency departments and wait hours before removal. Even worse, some people may become reluctant to remove ticks at all, despite prolonged attachment being associated with tick paralysis and tick-borne infections.

Oh, and not to be pedantic, but the title of the paper describes it as a cross-sectional study. It isn’t. It’s a prospective case series, or at best a prospective cohort study without a comparator group.

This is not a rant. It is simply pointing out the obvious. There is currently no good quality evidence supporting the recommendation to kill ticks in situ before removal. For all we know, it may even make things worse.

The emperor has no clothes!

 

Covering:

Taylor BWP, Ratchford A, Nunen S, et al. Tick killing in situ before removal to prevent allergic and anaphylactic reactions in humans: a cross-sectional study (although it’s not). Asia Pac Allergy. 2019;9(2):e15. [Link to full text of paper]

 

Evolution of secondary findings in acute cholecystitis: A temporal analysis from POCUS to subsequent imaging

Sonographic signs of cholecystitis tend to progress from the primary findings of cholelithiasis and a positive sonographic Murphy’s sign to the secondary findings of gallbladder wall changes, namely wall thickening and pericholecystic oedema. The presence of these secondary signs increases the specificity for diagnosing cholecystitis and surgeons often rely on them to guide admission and treatment decisions.

How quickly these changes develop has not really been established… until now.

These authors from the USA performed a dual site retrospective cohort study with good methodology. They included adult patients who underwent POCUS in the ED and later had a formal radiology ultrasound after admission.

The gold standard for diagnosing cholecystitis was primarily positive histology following cholecystectomy.

A total of 352 patients were included, with a 50% prevalence of cholecystitis.

Among the 252 patients without initial gallbladder wall changes on ED POCUS, around 20% developed wall changes on subsequent imaging, with a median time of 4 hours. Gallstones and a positive sonographic Murphy’s sign predicted the later development of wall changes.

The authors conclude that the evolution of cholecystitis is a dynamic process. This makes intuitive sense, as inflammatory conditions evolve over time, so there are no major surprises here.

There was another important finding. Acute cholecystitis can occur without gallbladder wall changes. In this study, most patients with cholecystitis did not have wall changes in the ED and never developed them prior to cholecystectomy. Importantly, these patients had positive histology following surgery, so this was unlikely to represent false positive diagnoses.

Interestingly, there was no mention of stones impacted in the gallbladder neck. This is the most common cause of cholecystitis. In my experience, it is also a fairly specific finding that strongly suggests developing cholecystitis.

So what is the take home message?

Yes, cholecystitis is a dynamic process. It takes time, with a median of 4 hours in this study, for gallbladder wall changes to appear on ultrasound if they are going to develop at all. This raises the possibility of repeat imaging in early presenters or in patients observed in a short stay unit when there is reasonable clinical suspicion for cholecystitis. 

Covering:

D. Ivanov, D. Cannata, K. A. Chin et al. Evolution of Secondary Findings in Acute Cholecystitis: A Temporal Analysis from Point of Care to Subsequent Imaging. J Emerg Med 2025;78:266-274. [link to article]

Duration of resuscitation interruption using point-of-care ultrasound versus traditional manual pulse check: A systematic review and meta-analysis

We know manual pulse checks during CPR are unreliable and often slow. “Do you feel a pulse…? I’m not sure… is that my pulse?”

So, is a POCUS pulse check faster and more accurate? Hmmm…

But first: what is a POCUS pulse check?

No, it’s not just looking at the heart during a rhythm check. It means using a linear probe to assess the carotid artery for compressibility and pulsatility, or using pulse-wave Doppler at the femoral artery to assess flow velocity.

So, is this actually better than our old-school manual checks?

The authors reviewed seven studies involving 496 participants. Overall, ultrasound was associated with a shorter pulse-check duration—by about 1.39 seconds.

Yes, that is not exactly a clinically earth-shattering difference.

(For what it’s worth, I’m a little skeptical of the overall data. Pulse checks in both groups were remarkably quick—around 3 to 10 seconds. This is quite different from earlier studies reporting much longer interruptions.)

But the more interesting difference is accuracy. Who cares how fast it is if it gets the answer wrong?

Three studies reported accuracy data. Manual pulse checks had a pooled sensitivity of 62% and specificity of 91%. POCUS pulse checks performed much better, at 99% and 96%, respectively.

Thoughts? Should we abandon manual pulse checks?

To be fair, major guideline groups (ILCOR, ACC/AHA, etc.) have recognised this problem and have been moving away from manual pulse checks for years. For lay rescuers, they now recommend looking for signs of life instead. Even so, health professionals are still checking pulses.

The authors do add some caution: the overall certainty of evidence is low. They also highlight the need for standard protocols, operator training, and high-quality prospective studies before practice changes too much.

For what it’s worth, I usually have a quick peek at the heart during rhythm and pulse checks. If it’s not moving, there's no point hunting for a pulse. (If you want to see this in action, check out Vijay’s paper in Emergency Medicine Australasia.)

Oh, and a strong word of caution: do not waste time checking for a pulse when a shockable rhythm is present!

If you want the best paper using a femoral artery catheter as the gold standard, look at Cohen’s study below. They used femoral pulse-wave Doppler to calculate peak systolic velocity and correlated it with blood pressure. It sounds complicated, but it's not. To me, this looks like the most promising technique.

What’s the takeaway?

POCUS pulse checks may catch on. Keep your eyes peeled and your finger on the pulse… or maybe not.

Covering:

Neto ES, Scapin M, Lazaro-Paulina F, et al. Duration of resuscitation interruption using point-of-care ultrasound versus traditional manual pulse check: A systematic review and meta-analysis. Amer J Emerg Med. 2025;98:145-152. [Link to article]

Cohen AL, Li T, Becker LB, et al. Femoral artery Doppler ultrasound is more accurate than manual palpation for pulse detection in cardiac arrest. Resuscitation. 2022;173:156-65. [Link to article]