What is the first step in managing a pregnant patient at 34 weeks gestation with an allergic reaction, wheezing, tachypnea, and hypoxemia?

Management of Anaphylaxis at 34 Weeks Gestation with Wheezing and Hypoxemia

Immediately administer intramuscular epinephrine 0.3 mg (1:1000 solution) into the mid-outer thigh (vastus lateralis muscle) as the first-line treatment, followed by positioning the patient in left lateral recumbent position with leg elevation and administering high-flow oxygen. 1

Immediate First Steps (Within First Minute)

Primary Intervention: Epinephrine

• Administer epinephrine 0.3 mg intramuscular (IM) in the vastus lateralis (mid-outer thigh) immediately 1
• The intramuscular route in the thigh achieves peak plasma concentrations in 8 ± 2 minutes, compared to 34 ± 14 minutes with subcutaneous deltoid injection 1
• Epinephrine is the only medication that prevents or decreases upper airway edema, treats bronchospasm, and prevents hypotension and shock through its vasoconstrictor, bronchodilator, and cardiac inotropic effects 1
• Delayed epinephrine administration is associated with poor outcomes including fatality 1

Positioning (Critical in Pregnancy ≥20 Weeks)

• Place patient in left lateral recumbent position with lower extremities elevated 1
• At 34 weeks gestation, this positioning increases maternal cardiac output by 24%, stroke volume by 35%, and ejection fraction by 11% compared to supine position 1
• This prevents aortocaval compression from the gravid uterus and improves uteroplacental blood flow 1

Airway and Oxygen Management

• Establish and maintain airway patency 1
• Administer 100% oxygen via non-rebreathing reservoir mask immediately 1
• Oxygen is mandatory for patients with hypoxemia, prolonged reactions, or those requiring multiple epinephrine doses 1
• Pregnant women at 34 weeks have 20-33% increased oxygen consumption and reduced functional residual capacity, causing rapid hypoxemia development 1
• Target oxygen saturation 94-98% 1

Secondary Management (Within First 5-10 Minutes)

Repeat Epinephrine if Needed

• Repeat epinephrine 0.3 mg IM every 5-15 minutes if respiratory distress or hypotension persists 1
• Several doses may be required for severe bronchospasm or hypotension 1

Intravenous Access and Fluid Resuscitation

• Establish IV access and administer normal saline 1-2 liters rapidly at 5-10 mL/kg in first 5 minutes 1
• Anaphylaxis causes 50% of intravascular fluid to shift into extravascular space within 10 minutes 1
• Use normal saline specifically; avoid lactated Ringer's (may contribute to metabolic acidosis) and dextrose solutions (rapidly extravasate) 1

Adjunctive Bronchodilator Therapy

• Administer inhaled albuterol (2.5 mg nebulized) for persistent bronchospasm 1
• Inhaled β2-agonists provide adjunctive therapy for wheezing but do not replace epinephrine as they cannot treat upper airway edema or shock 1

Continuous Monitoring

• Initiate continuous pulse oximetry and cardiac monitoring 1
• Monitor for biphasic reactions (can occur hours after initial resolution) 1

Additional Supportive Measures

Antihistamines and Corticosteroids (Secondary Priority)

• Administer chlorphenamine 10 mg IV (or equivalent H1-antihistamine) 1
• Administer hydrocortisone 200 mg IV 1
• Note: These medications have slow onset (≥1 hour) and do NOT treat acute anaphylaxis; they may prevent protracted or biphasic reactions 1

If Epinephrine Injections Fail

• Consider IV epinephrine infusion: 1 mg in 100 mL saline at 30-100 mL/h (5-15 mcg/min), titrated to response 1
• This requires continuous hemodynamic monitoring 1

Critical Pitfalls to Avoid

Common Errors

• Do NOT use antihistamines or inhaled bronchodilators as first-line therapy - they do not prevent fatal outcomes 1
• Do NOT delay epinephrine administration - this is the leading cause of anaphylaxis fatalities 1
• Do NOT place patient flat supine - this worsens aortocaval compression at 34 weeks gestation 1
• Do NOT use subcutaneous epinephrine - intramuscular route in thigh is significantly faster 1

Pregnancy-Specific Considerations

• Epinephrine is safe in pregnancy; maternal hypoxemia and hypotension pose greater fetal risk than epinephrine administration 1, 2
• Cesarean delivery increases anaphylaxis risk 4-fold (adjusted OR 4.19), but this patient is not in labor 2
• At 34 weeks, fetal viability is excellent; prioritize maternal stabilization first 1

Disposition

• Transfer to intensive care or high-dependency unit for minimum 24-hour observation 1
• Biphasic reactions occur in up to 20% of cases, typically within 8 hours 1
• Fetal monitoring should be initiated once maternal condition is stabilized 1