ANAPHYLAXIS - INTRODUCTION

What is anaphylaxis?

Anaphylaxis is defined as a serious allergic or hypersensitivity reaction that is rapid in onset and may cause death.

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What is incidence of anaphylaxis?

In industrialized country, the estimated lifetime prevalence of anaphylaxis from all causes is between 0.05 and 2 percent in the general population.

How do we diagnose anaphylaxis?

Diagnosis of anaphylaxis is based upon signs and symptoms, history of allergen exposure.

A set of diagnostic criteria has been formulated by a multidisciplinary group of experts in 2005/06.

What are the diagnostic criteria?

There are three diagnostic criteria for anaphylaxis, each reflecting a different clinical presentation.

Anaphylaxis is highly likely when any one of the following three criteria is fulfilled:

Criterion 1 — Acute onset of an illness (minutes to several hours) involving the skin, mucosal tissue, or both (e.g., generalized hives, pruritus or flushing, swollen lips-tongue-uvula) and at least one of the following:

Respiratory compromise (e.g., dyspnea, wheeze/bronchospasm, stridor, reduced peak expiratory flow, hypoxemia)

OR

Reduced blood pressure (BP) or associated symptoms and signs of end-organ malperfusion (e.g., hypotonia [collapse], syncope, incontinence)

Note that skin symptoms and signs are present in up to 90 percent of anaphylactic episodes. This criterion will therefore frequently be helpful in making the diagnosis.

 

Criterion 2 — Two or more of the following that occur rapidly after exposure to a likely allergen for that patient (minutes to several hours):

Involvement of the skin-mucosal tissue (e.g. generalized hives, itch-flush, swollen lips-tongue-uvula).

Respiratory compromise (e.g., dyspnea, wheeze/bronchospasm, stridor, reduced peak expiratory flow, hypoxemia).

Reduced BP or associated symptoms and signs of end-organ malperfusion (e.g., hypotonia [collapse], syncope, incontinence).

Persistent gastrointestinal symptoms and signs (e.g. crampy abdominal pain, vomiting).

 

Criterion 2 incorporates gastrointestinal symptoms in addition to skin symptoms, respiratory symptoms, and reduced BP. It is applied to patients with exposure to a substance that is a likely allergen for them.

Criterion 3 — Reduced BP after exposure to a known allergen for that patient (minutes to several hours):

Reduced BP in adults is defined as a systolic BP of less than 90 mmHg or greater than 30 percent decrease from that person's baseline.

In infants and children, reduced BP is defined as low systolic BP (age-specific) or greater than 30 percent decrease in systolic BP.

* Low systolic BP for children is defined as:

Less than 70 mmHg from 1 month up to 1 year

Less than (70 mmHg + [2 x age]) from 1 to 10 years

Less than 90 mmHg from 11 to 17 years

Note that criterion 3 is intended to detect anaphylactic episodes in which only one organ system is involved and is applied to patients who have been exposed to a substance to which they are known to be allergic (for example, hypotension or shock after an insect sting).

 

There will be patients who do not fulfill any of these criteria but for whom the administration of epinephrine is appropriate. As an example, it would be appropriate to administer epinephrine to a patient with a history of severe anaphylaxis to peanut who presents with urticaria and flushing that developed within minutes of a known or suspected ingestion of peanut.

 

What is the most common clinical feature of anaphylaxis?

Cutaneous manifestations – 90% of episodes

Respiratory manifestations – 85% of episodes

GIT manifestations- 45% of episodes

CVS manifestations – 45% of episodes

What is the common cause of death?

Death from anaphylaxis usually results from asphyxiation due to upper or lower airway obstruction or from cardiovascular collapse.

What is the time course of anaphylaxis?

Following exposure to an allergen there is rapid onset of sign and symptoms within seconds to minutes but rarely hours followed by resolution.

At the onset of an anaphylactic episode, it is not possible to predict how severe it will become, how rapidly it will progress, and whether it will resolve promptly and completely or become biphasic or protracted, because the factors that determine the course of anaphylaxis in an individual patient are not fully understood.

Thus, early administration of epinephrine is essential to prevent the progression to life-threatening manifestations.

How long does it take for anaphylaxis to be fatal?

Death due to anaphylaxis occurs within minutes.

In a series of 164 cases of fatal anaphylaxis, the median time interval between onset of symptoms and respiratory or cardiac arrest was 5 minutes in iatrogenic anaphylaxis (usually due to anesthetics, intravenous medications, and contrast media), 15 minutes in stinging insect venom-induced anaphylaxis, and 30 minutes in food-induced anaphylaxis.

What is Biphasic anaphylaxis?

Biphasic anaphylaxis is defined as a recurrence of symptoms that develops following the apparent resolution of the initial anaphylactic episode with no additional exposure to the causative agent.

What is protracted prophylaxis?

Protracted anaphylaxis is defined as an anaphylactic reaction that lasts for hours, days, or even weeks in extreme cases.

What is delayed anaphylaxis?

Rarely, the onset of anaphylaxis will be delayed (i.e. beginning hours rather than minutes after exposure to the causative agent).

What are common causes of anaphylaxis?

In children food allergy is common and in adults medications & insect stings are common.