Tying Procalcitonin to Critical Care

It has been hard, over the years, to truly identify a role for procalcitonin.  Generally speaking, its best niche seems to be as a sort of C-reactive protein on steroids – a non-specific infectious or inflammatory marker with better sensitivity than WBC.  This has led to some usage in zero-miss contexts such as neonatal sepsis, as well as a potential role in antibiotic stewardship.

These authors, many of which are supported by the manufacturers of the procalcitonin assay, evaluate its predictive power in the setting of pneumonia hospitalization, attempting to risk-stratify patients for the combined endpoint of vasopressor support or invasive ventilation.  Their goal, they say, is to use procalcitonin levels to better inform level-of-care decisions – both escalated and de-escalated – at the time of hospital admission.

They analyzed 1,770 patients from a prior pneumonia study for whom banked serum samples were adequate for procalcitonin measurement, 115 of whom met their combined critical illness endpoint.  They report risk of critical illness increased approximately linearly with procalcitonin from 4% when procalcitonin was undetectable, to 22.4% when procalcitonin was 10ng/mL or above.  The AUC for procalcitonin alone was 0.69, as compared to WBC at 0.54.  Then, they further go on to add usage of procalcitonin in conjunction with other risk-stratification scores – ATS minor criteria, PSI, and SMART-COP – provided additional discriminatory information.

This could be a potentially useful and interesting application of procalcitonin – except they don’t really make any comparisons to other available tools, other than a straw man comparison with WBC.  Would the venerable CRP have a similar AUC?  Or, better yet, a lab we already use nearly ubiquitously to detect occult severe sepsis – a lactic acid level?  The authors do not present any specific discussion of alternative approaches – of which their friends at BioMerieux probably appreciate.

“Procalcitonin as an Early Marker of the Need for Invasive Respiratory or Vasopressor Support in Adults with Community-Acquired Pneumonia”
https://www.ncbi.nlm.nih.gov/pubmed/27107491

Prime Time for Dexamethasone in Asthma?

We adore dexamethasone here at EMLoN headquarters.  A pharmacy stocked solely with ketamine, droperidol, and dexamethasone could carry you far in life.  Unfortunately, because of our established bias, the challenge then arises to reconcile the actual results of a trial with what is so desperately wished to be true.

This is a randomized, double-blinded, non-inferiority trial comparing single-dose dexamethasone with five days of prednisone in the treatment of asthma with acute exacerbation.  Single-dose and double-dose dexamethasone protocols have been evaluated in pediatric trials of reasonable size, but data in adults has been lacking.  However, many clinicians – including myself – have assumed generalizability of the pediatric findings to adults, and have been using single-dose dexamethasone protocols for years.

If only one takeaway can be had from this trial, it is: never, ever, skimp on sample size. Far easier said than done, of course, but due to the complex structure and assumptions required for non-inferiority trials, this is a negative trial.  There were 465 subjects randomized – but 89 excluded from analysis as either subsequent admissions or as lost to follow-up.  Of the remaining 376 patients, 9.8% of the prednisone group demonstrated Emergency Department recidivism compared with 12.1% of dexamethasone.  This 2.3% difference between groups, however, suffers a 95% of -4.1 to 8.6%, and exceeds the pre-determined clinically-relevant non-inferiority margin of 8%.

So, unfortunately, we still do not have a precise estimate for the effectiveness difference between a prednisone-based strategy and dexamethasone.  Considering the healthcare burden of asthma in our Emergency Departments, it is somewhat surprising we still have such a paucity of data – as even a small difference in effectiveness may have profound effects on Emergency Department utilization.  In the end, it comes down to where you lay on the spectrum of pre-study odds for non-inferiority or equivalence.  For me, the guarantee of compliance with treatment derived from a single-dose of dexamethasone outweighs the continued uncertainty over its true effectiveness, and this study gives me no cause to change my practice.

“A Randomized Controlled Noninferiority Trial of Single Dose of Oral Dexamethasone Versus 5 Days of Oral Prednisone in Acute Adult Asthma”
https://www.ncbi.nlm.nih.gov/pubmed/27117874

Endovascular for Stroke – Even Better than the Evidence

What happens when you let Medtronic, et al, author an article on endovascular therapy in The Lancet:  exactly what you'd expect.

We are, in principle, fans of endovascular therapy for acute stroke as presented in the major trials: ESCAPE, EXTEND-IA, and SWIFT-PRIME.  These trials carefully selected eligible patients by use of advanced perfusion imaging and demonstrated high rates of revascularization.  Viable brain plus restored flow has face validity for improved outcomes.

However, these sponsored authors use the meta-analysis for its most nefarious purpose: to obfuscate the important subtleties and eligibility criteria of its included trials.  These authors pool the aforementioned trials, along with MR CLEAN and REVASCAT to provide the following conclusion:
“Endovascular thrombectomy is of benefit to most patients with acute ischaemic stroke caused by occlusion of the proximal anterior circulation, irrespective of patient characteristics or geographical location.”(emphasis mine)
The authors also provide a staggering number-needed-to-treat for endovascular therapy of 2.6.

But, of course, this was written to shock and awe the lay press and general medicine community, rather than edify the astute clinician.  Their NNT is not based on the typical dichotomous cut-off used in stroke trials of mRS 0-1 or 0-2 – but rather the hopelessly flawed ordinal shift analysis.  As the decades turn, apparently, we have forgotten why this approach was frowned upon from the start: it is not appropriate to equate the outcome value difference between mRS 5 and 4 with the difference between mRS 3 and 2, and the limitations in inter-rater reliability in the mRS introduce a vast additional amount of measurement error.  Then, by burying any mention of the strict imaging criteria responsible for the bulk of benefit seen in these trials, they mislead the reader into considering this therapy appropriate for all-comers.

Is there any value to these data as presented?  A little.  There is hypothesis generating evidence that tPA prior to endovascular therapy provides no additive benefit.  There is also evidence that increasingly distal sites of occlusion may not benefit from intervention.

Unfortunately, the flaws in this article outweigh the few potentially usable insights.  This is just yet another piece of direct-to-physician marketing masquerading as scientific evidence.

“Endovascular thrombectomy after large-vessel ischaemic stroke: a meta-analysis of individual patient data from five randomised trials”
https://www.ncbi.nlm.nih.gov/pubmed/26898852

How Many ED Visits are Truly Inappropriate?

I’ve seen quite a bit of feedback on social media regarding this research letter in JAMA Internal Medicine.

This study evaluated, using National Hospital Ambulatory Medical Care Survey data, the incidence of hospital admission stratified by triage Emergency Severity Index.  They analyzed 59,293 representative visits from the sample and found 7.5% of them, on a weighted basis, were categorized as “non-urgent” – an ESI level 5 or presumed equivalent.  The typical assumption regarding these non-urgent visits is they represent inappropriate Emergency Department utilization.  This study found, however:
“… a nontrivial proportion of ED visits that were deemed nonurgent arrived by ambulance, received diagnostic services, had procedures performed, and were admitted to the hospital, including to critical care units.”
There are always limitations regarding the NHAMCS data, particularly with missing and imputed data.  Based on this, I tend to feel these data lack face validity.  The weighted incidence of admission for non-urgent patients was 4.4% compared with 12.8% of urgent visits, while 0.7% of non-urgent visits were to critical care units compared with 1.3% of urgent visits.  I certainly do not see similar relative proportions of admission, and then to critical care, for level 5 patients in my multiple practice environments.

Regardless, the general implication made by these authors is probably reasonable, refuting usage of ESI triage level 5 to accurately represent inappropriate Emergency Department visits.  However, left equally unstated, is an acknowledgement that ESI also fails to accurately categorize urgent visits – which ties to the rhetoric of trying to conflate “non-urgent” as “inappropriate and “urgent” as “appropriate".

ESI, as currently implemented, will not be a reliable tool for directing patients to other sources of care – but, with some fuzziness, probably still gives a reasonable estimate of the overall burden of inappropriate ED visits for some policy applications.

“Urgent Care Needs Among Nonurgent Visits to the Emergency Department”
https://www.ncbi.nlm.nih.gov/pubmed/27089549

Try to Avoid tPA When Already Bleeding

Coming to us from the Department of Common Sense: don’t give tPA to stroke patients who already have intracranial hemorrhage.  There’s a little more subtlety here, of course, because in this instance, we’re dealing with cerebral microbleeds – tiny foci of angiographic damage visualized only on MRI.

These authors performed a pooled and individual-patient meta-analysis of those undergoing MRI prior to treatment with intravenous thrombolysis.  When stratified by CMB burden, arbitrarily divided into “none”, “1-10”, and “>10”, the obvious is … obvious: patients who are already bleeding are more likely to continue bleeding.  In the unadjusted raw numbers, patients with no CMB had a symptomatic intracranial hemorrhage rate of 4.3%, those with 1-10 CMB had 6.1%, and those with >10 had 40.0%.

There are many technical limitations inherent to the retrospective nature of their study, as well as likely other confounding variables – but, the basic gist: our current practice relying only on non-contrast CT likely misses an important safety indicator in the setting of tPA use.

“Risk of Symptomatic Intracerebral Hemorrhage After Intravenous Thrombolysis in Patients With Acute Ischemic Stroke and High Cerebral Microbleed Burden”
https://www.ncbi.nlm.nih.gov/pubmed/27088650