Over the course of human history,
more people have died from peritonitis than from any
other disease, save possibly pneumonia. It remains a
grave threat to surgical patients today, accounting
for about 60% of mortality in surgical intensive care
units.
Of course, it's not the peritonitis
that actually gets you, but the spread of infection
to the vitals, leading to multiple organ failure, or
septic multiorgan dysfunction syndrome (MODS).
While our ancestors were baffled
by the very nature of spreading systemic infection,
we are merely stymied by our inability to detect sepsis
in a timely manner. But a new tool might help us spot
these cases before it's too late, according to German
research published in Archives of Surgery.
The best methods currently at our
disposal are the CAT scan and fine-needle aspiration.
But the former is expensive and often unavailable, while
the latter can increase infection risk. One biomarker,
C-reactive protein, is in limited use as a predictor
of septic MODS. Unfortunately, C-reactive protein levels
rise sharply in the presence of surgical trauma, whether
there's infection or not, so it's of limited use in
surgical patients. "There is major interest in the search
for an optimum diagnostic tool for an early, noninvasive
and reliable diagnosis of abdominal infections and sepsis,"
the study authors wrote, adding that a biochemical marker
for identifying patients at risk would go a long way
in reducing mortality.
QUICK
OFF THE MARK
They set out to test C-reactive protein against another
potential blood sepsis marker: procalcitonin, an inactive
precursor to the hormone calcitonin. Unlike C-reactive
protein, procalcitonin levels aren't affected by surgical
trauma, but it has been shown to be more prevalent in
the presence of both bacterial and fungal infection.
There's even a rapid automated assay for procalcitonin,
the Kryptor PCT assay, which can be completed in about
20 minutes, even in emergency conditions.
It's a good thing too — emergency
conditions are the norm when peritonitis manifests in
surgical patients. Of 82 patients recruited in this
study, 42 developed lung failure, 25 developed kidney
failure, 35 had multiorgan dysfunction syndrome and
nine died.
While secondary peritonitis often
appears due to the surgical trauma itself, all of these
patients had it from pre-existing underlying conditions
that had caused perforations of some sort. Small- and
large-bowel perforation and appendicitis were the leading
causes. Escherichia coli was the most frequent
organism isolated, present in more than half of the
patients in whom the bacteria were identified. Nine
had fungal infections.
POSITIVE
PREDICTOR
Predicting which patients would go on to develop septic
MODS was the job of the procalcitonin assay. Sure enough,
levels of procalcitonin were markedly higher in patients
who later went on to suffer MODS, with peak levels occurring
on the third or fourth day after symptoms appeared.
All patients in this study were tested within 96 hours
of symptom onset. C-reactive protein had no useful predictive
value.
Using a cutoff of 10 ng/mL of blood,
procalcitonin had a positive predictive value for septic
MODS of 83%, a negative predictive value of 82%, sensitivity
of 65% and specificity of 92%. As the authors note,
this makes it better at identifying patients who won't
develop septic MODS than identifying patients who will.
"Although the sensitivity was only moderate, the high
specificity and negative predictive values of procalcitonin
for septic MODS could serve as helpful means to select
patients in whom further cost-intensive diagnostic and
therapeutic procedures are not necessary," they wrote.
The procalcitonin response didn't
vary according to the nature of the underlying disease,
nor the type of infectious organism. In fact the researchers
doubt that procalcitonin is really a sepsis marker at
all. "It could be hypothesised," they argue, "that the
degree and persistence of systemic procalcitonin concentrations
reflect an impaired immunologic response, rendering
the host susceptible to severe infections or unable
to overcome the initial infectious or noninfectious
local insult."
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