Now, we're gonna talk about anaphylaxis.
So the exact incidence of anaphylaxis is not known
but it’s a pretty common problem
and actually there's evidence
that the incidence of allergic disease across the board
and anaphylaxis in particular are increasing.
There's about 1.500 fatal cases per year in the US
but it’s not known how many additional cases beyond that
present to Emergency Departments around the country
because it's only a tiny minority of patients
who will die from anaphylaxis.
Anaphylaxis is often misdiagnosed
and its often undertreated even when it is correctly diagnosed
and we're gonna talk about the correct way to treat it
so that doesn't happen to any of our patients.
Its most common in patients
who have some kind of history of allergic disease.
So they're atopic, they have asthma, they have eczema,
seasonal allergies, any of those kind of things,
you wanna think about a higher risk of anaphylaxis.
There are a lot of triggers
that are commonly described for anaphylaxis.
Foods represent about a third of total cases of anaphylaxis,
and nuts in particular both peanuts and tree nuts
are very common triggers for anaphylaxis.
Insect stings are also a common cause.
Most common are the bees and wasps
but there are other classes of insects
that can produce anaphylaxis as well.
Drugs are a common cause.
and non-steroidal anti-inflammatory drugs
are the most common ones
but any drug can potentially reduce an allergic reaction.
Latex is a common cause.
We've largely gotten that out of our hospitals in the US,
there are settings in which patients
who are sensitized might be exposed.
And then radiocontrast agents,
especially CT contrast dye
can produce anaphylactic responses in some cases.
The really alarming thing though
is more than half of patients
have no identifiable trigger for their anaphylaxis.
So they come in,
and you don't actually know what they are reacting to,
which is obviously alarming for the patient
because you can't tell them what to avoid
to prevent it from happening again.
There are specific diagnostic criteria for anaphylaxis.
Its considered to be highly likely
that anaphylaxis is occurring
if the patient meets any one of these three criteria.
they have an acute onset of illness involving the skin
plus either respiratory symptoms
or cardiovascular symptoms.
So skin plus lungs or heart,
The second criterion is likely allergen exposure
plus two of the following symptoms:
involvement of skin, respiratory compromise,
cardiovascular compromise or GI symptoms.
So you think it’s an allergen
and they have two or more organ systems involved,
think about anaphylaxis.
The third criterion is hypotension.
If your patient is hypotensive
following exposure to a known allergen,
not just something that
you think they might potentially be allergic to,
but something they've definitely either reacted to
or tested positive for in the past,
then that's also a manifestation of anaphylaxis.
Now, these are national expert guidelines
for diagnosing anaphylaxis.
They're very useful and reliable
but they're a little bit complicated.
An easy way to remember anaphylaxis is basically,
if you have allergic symptoms plus compromise of airway,
breathing or circulation,
you should be thinking pretty hard
that your patient is in anaphylaxis.
So what's the pathophysiology?
Well very simply,
initial exposure to some sort of antigen
causes the body to form IgE antibodies.
once those antibodies have been formed,
cause immediate release of inflammatory mediators from mast cells,
And those inflammatory mediators
are what produce the anaphylactic reaction.
So mediators again,
histamine is the number one,
but mast cells are involved,
basophils, prostaglandins, leukotrienes, cytokines,
there's — it’s a very complex cascade
that ultimately produces the clinical anaphylactic reaction.
initial sensitization occurs when you're exposed to an allergen.
The B-cells in particular are exposed to the allergen
and they produce IgE antibodies.
Those IgE antibodies
bind to the surface of mast cells or basophils.
Now, any subsequent exposure to the same antigen
is gonna cause these preformed antibodies
to bind on to the relevant cell types and degranulate,
releasing all of those inflammatory mediators,
which increase the permeability of capillaries
and causes all of the clinical symptoms that you see
at the bedside with the patient.
So there are a lot of different organ systems involved.
Skin is by far the most common.
So up to 90% of people with anaphylaxis
will have some degree of skin involvement
and urticaria and hives is the most common manifestation,
though patients might simply be itchy,
they might have flushing,
or they might have angioedema or swelling,
particularly in the highly vascularize parts of the body
like the face.
On the pulmonary side,
70% of patients have some degree of pulmonary involvement
which most commonly affects either the airway or the lungs.
So from an airway standpoint,
you can have stridor,
that's that high-pitched inspiratory sound that occurs
when you pull air past an obstructed airway.
You can also have voice changes,
a sensation of subjective throat tightness.
And then, for lower airway involvement,
you can have coughing, wheezing, dyspnea, etcetera.
Gastrointestinal symptoms are also pretty common.
Nearly half of patients will have those
and those include nausea, vomiting, diarrhea,
abdominal cramping, etcetera,
obviously that's a relatively non-specific finding.
And then the cardiovascular collapse
that we all associate with anaphylaxis
is actually relatively rare.
Some studies have estimated it up to 45% of patients
but most placed in the 10 or 20% range
and manifestations include hypotension, tachycardia,
cardiac arrhythmias, or syncope.
So this is the overall picture of anaphylaxis
and patients can have any combination of these symptoms
when they're presenting with anaphylaxis.