Al-anoud Al-jifri Medical consultant/ID 27/2/2010

1) Anaphylaxis. 2) Drug Reactions. 3) Acute Upper Airway Obstruction.

DEFINITION ◦ Is an IgE-mediated,rapidly developing,systemic allergic reaction. ◦ Anaphylactoid reactions result from the direct release of mast cell mediators. Anaphylaxis may be mild and resolve spontaneously due to endogenous production of compensatory mediators (eg, epinephrine, angiotensin II, endothelin, and others) or it may be severe and progress within minutes to respiratory or cardiovascular compromise and death. Death from anaphylaxis usually results from asphyxiation due to upper airway edema or respiratory failure due to bronchial obstruction, and less commonly, from cardiovascular collapse.

Anaphylaxis is highly likely when any ONE of the following 3 criteria is fulfilled: 1. Acute onset of an illness (minutes to several hours) with involvement of the skin, mucosal tissue, or both (eg, generalized hives, pruritus or flushing, swollen lips-tongue-uvula) AND AT LEAST ONE OF THE FOLLOWING  A. Respiratory compromise (eg, dyspnea, wheeze-bronchospasm, stridor, reduced PEF in older children and adults, hypoxemia).  B. Reduced BP or associated symptoms of end-organ dysfunction (eg, hypotonia, collapse, syncope, incontinence).

2. TWO OR MORE OF THE FOLLOWING that occur rapidly after exposure to a likely allergen for that patient (minutes to several hours): ◦ A. Involvement of the skin-mucosal tissue (eg, generalized hives, itch-flush, swollen lips-tongue-uvula) ◦ B. Respiratory compromise (eg, dyspnea, wheeze-bronchospasm, stridor, reduced PEF in older children and adults, hypoxemia) ◦ C. Reduced BP or associated symptoms (eg, hypotonia, collapse, syncope, incontinence) ◦ D. Persistent gastrointestinal symptoms (eg, crampy abdominal pain, vomiting) 3. Reduced BP after exposure to a known allergen for that patient (minutes to several hours): ◦ A. Infants and children: low systolic BP (age specific) or greater than 30 % decrease in systolic BP. ◦ B. Adults: systolic BP of less than 90 mm Hg or greater than 30 % decrease from that person's baseline.

1. Allergen triggers (IgE-dependent immunologic mechanism) o Foods, especially peanut, tree nut, seafood, finned fish, milk, egg. o Insect stings (eg, Hymenoptera venom) and insect bites. o Natural rubber latex. o Medications (eg, beta-lactam antibiotics). o Biological materials, including allergens, vaccines to prevent infectious disease, and hormones (eg, progesterone). o Food additives, including spices, insect-derived colorants (eg, carmine), and vegetable gums Inhalants (eg, horse dander). o Occupational allergens. o Inhalants (eg, horse dander).

2.Immunologic triggers (IgE-independent immunologic mechanism) o Complement system activation. o Coagulation system activation. 3.Idiopathic anaphylaxis o Auto-immune mechanism in some patients. o Mastocytosis or clonal mast cell disorders in some patients. 4.Non-immunologic triggers (direct action of mast cells and basophils) o Physical factors (eg, exercise, cold, heat, sunlight/ultraviolet radiation). o Medications (eg, opiates). o Alcohol (ethanol).

 Plasma histamine levels typically peak within minutes of the onset of anaphylaxis symptoms, and then decline to baseline by 60 minutes.  Elevated plasma histamine levels correlate with anaphylaxis symptoms and are more likely to be increased than are total serum tryptase levels.

 Serum or plasma total tryptase needs to be obtained within 3 hours of symptom onset.

 Adverse reactions to drugs are a very common problem.  Only a subset of reactions are mediated immunologically; other drug reactions may be toxic or idiosyncratic.  Many different mechanisms can account for immunologically mediated drug reactions.  These reactions can occur with relatively low doses of the drug, usually on re-exposure after an initial sensitization to the drug.

A. Beta-lactam sensitivity.  Penicillins and other beta-lactam antibiotics are commonly associated with immunologically mediated drug reactions. B. Red man's syndrome  from vancomycin consists of pruritus and flushing of the neck and face.  It can be prevented by slowing the rate of infusion and premedicating with diphenhydramine (50 mg PO) 30 minutes before the infusion.

 Mimic anaphylaxis but are not IgE mediated.  They are due to the degranulation of mast cells induced directly by the offending drug.  Drugs may cause anaphylactoid reactions include opiates and fluoroquinolones.

C. Erythema multiforme, Stevens-Johnson syndrome (SJS), and toxic epidermal necrolysis (TEN)  are all serious drug reactions that primarily involve the skin.  Erythema multiforme is characterized most typically by target lesions.  SJS and TEN manifest with varying degrees of sloughing of the epidermis and mucous membranes ( 30% in TEN).

 Focuses on the discontinuation of suspected drugs and treating any underlying infection.  Other therapeutic maneuvers are directed to symptoms and include: i. hydration to maintain fluid balance, ii. antihistamines to decrease pruritus, iii. analgesics to relieve pain, iv. and wet dressings to débride crusted erosions.  Care in a burn unit or ICU may be required.  Systemic corticosteroids are often used, but their efficacy is unproven.  Re-administration or future skin testing with the offending drug is absolutely contraindicated.

The differential diagnosis includes:  Trauma to the face and neck.  Foreign body.  Infection (croup, epiglottitis, Ludwig's angina, retropharyngeal abscess, and diphtheria).  Tumor.  Angioedema.  Laryngospasm.  Anaphylaxis.  Retained secretions.  Blockage of the upper airway by the tongue (in the unconscious patient).

 In the conscious patient:  manifestations of airway obstruction may include stridor, impaired or absent phonation, sternal or suprasternal retractions, display of the universal choking sign, and respiratory distress.  Look for urticaria, angioedema, fever, or evidence of trauma.  The unconscious patient:  may have labored breathing or apnea.  Suspect airway obstruction in a nonbreathing patient who is difficult to ventilate.

 Therapy is directed at rapid relief of obstruction to prevent cardiopulmonary arrest and anoxic brain damage.

A. Rapidly take a history, focusing on the causes just listed. B. Perform a directed physical examination, looking for airway swelling, trismus, pharyngeal obstruction, respiratory retractions, angioedema, stridor, wheezing, and grossly swollen lymph nodes and masses in the neck.  If the patient's condition is stable, perform indirect laryngoscopy or fiberoptic nasopharyngolaryngoscopy.  A careful examination is unlikely to cause acute airway obstruction in an adult.

 C. Soft-tissue radiography of the neck (posteroanterior and lateral views) is less sensitive and specific than is direct examination but may be a valuable adjunct.  Such radiography should be performed in the emergency department as a portable study, as the patient should not be left unattended.  Rapid CT of the airway with constant attendance is an alternative approach where available.  D. Treatment is aimed at the underlying disease process; observe the patient carefully and be prepared to intervene to maintain an airway. I. Partial obstruction in the awake patient with adequate ventilation

 The most likely causes are a foreign body (usually food) and angioedema.  Other causes include infection or posttraumatic hematoma.  History is usually unavailable.  One should perform the Heimlich maneuver (subdiaphragmatic abdominal thrust) repeatedly until the object is expelled from the airway or the patient becomes unconscious.