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1274 PART 11: Special Problems in Critical Care

Endogenous compensatory to distinguish anaphylaxis from a vasovagal reaction. However, brady-
mechanisms cardia has also been described during anaphylaxis. It can occur second-
Epinephrine ary to increased vagal reactivity mediated through unmyelinated vagal
C-fibers which are activated by ischemia. Brown et al studied 21 adults
with history of systemic insect sting allergy who were challenged with
Norepinephrine stings in controlled settings. Eighteen individuals developed systemic
Adrenal Endothelin reactions. Hypotension accompanied by bradycardia developed in two
individuals. Allergic reactions can trigger not only anginal episodes,
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Angiotensin II Ganglion but also acute myocardial infarction. This was first reported in the
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Kidney American Heart Journal in 1950 with a case of a prolonged allergic reac-
Endothelium tion to penicillin. In 1991, Kounis and Zavras described the Kounis
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syndrome as chest pain during an anaphylactic reaction. The chest
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Angiotensin I
pain can present as classical angina pectoris. Myocardial infarction with
normal coronary arteries can occur due to this phenomenon. 111-113 The
Kounis syndrome has been divided into two subtypes. In type I, chest
pain occurs without coronary artery disease during an acute allergic
FIGURE 128-2. Compensatory mechanisms activated during anaphylaxis. reaction in patients without predisposing factors for coronary artery
disease. These cases have a normal myocardial perfusion scan and
normal coronary angiogram. These cases are thought to be due to
114
115
pulmonary edema fluid and the low pulmonary artery wedge pressures endothelial dysfunction or microvascular angina. In type II there is
indicate that the pulmonary edema in anaphylaxis is noncardiogenic and preexisting coronary artery disease. 113,114 This syndrome has been mostly
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likely due to increased microvascular permeability. 101,102 reported in adults but can be seen in children as well. The clinical pre-
sentation of KS includes a mixture of symptoms and signs of an allergic
CLINICAL PRESENTATION reaction and acute coronary syndrome, with chest pain, dyspnea, faint-
ness, nausea, vomiting, syncope, pruritus, urticaria, diaphoresis, pallor,
The signs and symptoms of anaphylaxis are summarized in Table 128-5. palpitations, hypotension, bradycardia. Respiratory complaints, for
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This table is based on a compilation of 1865 patients and includes example, wheeze, dyspnea, stridor, and rhinitis are seen in 40% to 60%
patients with idiopathic anaphylaxis, exercise-induced anaphylaxis, and of cases. Arterial blood gas abnormalities usually consist of a fall in P O 2
other causes of anaphylaxis. Cutaneous manifestations are most com- and P CO 2 early in the course. If severe respiratory difficulty supervenes,
20
mon and occur in more than 90% of cases. The cutaneous symptoms the hypoxia worsens and an elevation of P CO 2 may occur, along with
20
include urticaria, angioedema, flushing, and pruritus. Over 90% of a fall in pH that is probably due to a combination of carbon dioxide
adults experience cutaneous manifestations. However, the incidence of retention and metabolic acidosis. Other unusual presentations include
cutaneous manifestations in children may be lower. 103,104 Cardiovascular syncope which can occur alone or associated with seizures. Syncope
symptoms, for example, dizziness, syncope, arrhythmia, and hypoten- has been reported with anaphylaxis resulting from insect sting, fire ant,
sion occur in about 30% to 35% of cases. Severe episodes characterized and mastocytosis. Profound anaphylaxis with hypotension can result
10
by rapid cardiovascular collapse and shock can occur without cutaneous in fibrinolysis and disseminated intravascular coagulation. Tranexamic
manifestations. 105,106 In fact, in a series of 27 severe episodes, only 70% acid can rapidly reverse the coagulopathy. 118
of patients with circulatory and/or cardiovascular collapse had cutane- Symptoms of anaphylaxis usually begin within 5 to 30 minutes when
ous manifestations. Reflex tachycardia occurs commonly secondary to antigen has been administered by injection. With ingestion, they usu-
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hypovolemia during anaphylaxis. This is a useful differentiating feature ally occur within the first 2 hours after ingestion but can be delayed for
several hours. There is believed to be a direct correlation between the
immediacy of onset of symptoms and the severity of a given attack: the
more rapid the onset, the more severe the episode.
TABLE 128-5 Signs and Symptoms of Anaphylaxis 1 Anaphylactic events can occur in three clinical patterns. They may
Signs and Symptoms Percent a be acute followed by rapid resolution with or without therapy. They can
be prolonged and protracted, lasting hours and in rare instances days.
Cutaneous In the case of protracted events, there are usually several remissions
Urticaria and angioedema 85-90 followed by exacerbations. Finally they can be characterized by a resolu-
Flushing 45-55 tion in manifestations followed by a recurrence even in the absence of
Pruritus without rash 2-5 further antigen exposure. The latter type is called a “biphasic” response.
Respiratory Biphasic anaphylaxis occurs in 1% to 23% of episodes of anaphylaxis.
Dyspnea, wheeze 45-50 Symptoms may recur hours (most within 10 hours) after apparent
Upper airway angioedema 50-60 resolution of the initial phase. Risk factors for biphasic reactions include
history of a previous biphasic reaction, the nature of the antigen (foods
Rhinitis 15-20
are more likely to cause biphasic events than other allergens), a failure to
Dizziness, syncope, hypotension 30-35 administer corticosteroids, a delay in epinephrine administration, and
Abdominal inadequate epinephrine dosing.
Nausea, vomiting, diarrhea, cramping pain 25-30 It is also important to consider that signs and symptoms of anaphy-
Miscellaneous laxis can vary according to the clinical setting in which the event occurs.
Headache 5-8 In perioperative anaphylaxis, cutaneous symptoms are less common
compared to hemodynamic collapse. The diagnostic challenge in the
Substernal pain 4-6 intensive care unit is that many of the signs and symptoms of anaphy-
Seizure 1-2 laxis are not uncommon among critically ill patients. Often the only
a On the basis of a compilation of 1865 patients. Percentages are approximations. diagnostic clue is a skin rash as part of this general constellation of
Reproduced with permission from Lieberman P, Kemp S, Oppenheimer J, et al. The diagnosis and management symptoms. Allergic reactions presenting without cutaneous symptoms
of anaphylaxis: an updated practice parameter. J Allergy Clin Immunol. March 2005;115(3 suppl 2):S483-S523. in ventilated and sedated patients may mimic other diagnoses.

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