Tuesday, January 13, 2015

Diagnosis and management of anaphylaxis

This practice parameter document was created by a joint task force in allergy and immunology and is available as free full text (HT to Life in the Fast Lane).

For a little background here is one of my earlier posts on anaphylaxis. And now on to a few of the key points from the document:

The role of serum tryptase measurement

Although a tryptase level is not useful for emergency decision making the authors recommend it be obtained for the information it will provide later, in follow up. Keep in mind that the positive predictive value is only 69%. The reliability of the test varies depending on the source of the anaphylaxis (low sensitivity, for example, when food related) and it is time dependent.

Give IM epi as soon as the clinical diagnosis is made

---acknowledging occasional exceptions, such as when patients present late with resolved or nearly resolved symptoms.

Early fluid resuscitation when circulatory collapse is present

From the document:

Aggressive fluid resuscitation helps to counteract the significant plasma leak associated with anaphylaxis and complement parenteral epinephrine therapy. Children might require successive IV fluid boluses of 20 mL/kg and adults might require successive IV boluses of 1,000 mL to maintain blood pressure in the early stages of anaphylaxis. To overcome venous resistance, fluids administered through IO catheters should be infused under pressure using an infusion pump, pressure bag, or manual pressure.

IM epi doses can be repeated but at some point an epi drip may be necessary for unresponsive patients

5 minute intervals between IM injections are recommended, but open to variation according to clinical judgment. If clinical judgment warrants a drip, 1 mg of epi is diluted in a liter of D5W to give a 1 mcg/ml concentration. The titration range recommended is 1 mcg/min to 10 mcg/min. In more desperate situations:

In patients with actual or impending cardiovascular collapse unresponsive to an epinephrine infusion or when an epinephrine infusion is not immediately available, slow administration of a 50-μg (0.5 mL of 1:10,000) bolus of IV epinephrine might be necessary.

IO access can be used for fluid and epi infusions

Special airway considerations apply

From the document:

Upper airway edema can preclude rescue ventilation, so the merits of an awake fiberoptic intubation should be strongly weighed against the benefits and risks of rapid sequence intubation.

When selecting airway management medications, because patients with anaphylaxis requiring intubation are often hemodynamically unstable, medications should be avoided that depress blood pressure. Paralytics should be used with caution, because mask ventilation can be impossible in the setting of upper airway edema...

Nebulized epinephrine has been shown to alleviate respiratory distress associated with upper airway obstruction in childhood croup.48 The vasoconstrictive (α1) effects likely account for the decrease of upper airway edema. Similarly, and based on anecdotal experience, aerosolized epinephrine also can decrease oropharyngeal edema and make airway management less difficult in anaphylaxis.

What if hypotension is refractory to epi (including a drip) and fluid resuscitation?

Glucagon (1-5 mg over 5 minutes followed by a 5-15 mcg/min infusion) is recommended as the next step. The typical scenario here would be the patient taking beta blockers, since glucagon bypasses the beta receptor. This being said the authors acknowledge, and cite literature, that other pressors have been used successfully.

Consider ECMO if all else fails

See statement 14 from the article.

What about steroids and antihistamines?

They're fine but don't don't put them at the front of the line ahead of epi because they don't work as fast.

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