What is the treatment for a patient in anaphylactic shock with impaired renal function (low urine output)?

Treatment of Anaphylactic Shock with Low Urine Output

Immediate intramuscular epinephrine 0.3-0.5 mg (1:1000 concentration) injected into the anterolateral thigh remains the first-line treatment for anaphylactic shock regardless of renal function, followed by aggressive IV fluid resuscitation to restore circulating volume and renal perfusion. 1, 2

Immediate Management Algorithm

First-Line Treatment (Do Not Delay)

• Administer IM epinephrine 0.01 mg/kg (maximum 0.5 mg adults) of 1:1000 solution into the anterolateral thigh immediately upon recognition 1, 3
• Position patient supine with legs elevated to improve venous return 1
• Activate emergency medical services immediately 1
• Repeat IM epinephrine every 5-15 minutes if symptoms persist or worsen 1, 4

Aggressive Fluid Resuscitation (Critical for Low Urine Output)

• Administer 1-2 liters of normal saline rapidly in adults (20 mL/kg boluses in children) 1
• Anaphylactic shock causes up to 37% loss of circulating blood volume due to capillary leak, which directly impairs renal perfusion 1, 5
• Continue fluid boluses as needed to restore blood pressure and urine output 6

Transition to IV Epinephrine (Refractory Cases Only)

Indications for IV Route

• Multiple IM doses have failed 1, 7
• Profound hypotension unresponsive to IV fluids and IM epinephrine 7
• IV line already in place and patient in extremis 2

IV Epinephrine Dosing

• Initial IV bolus: 0.05-0.1 mg (50-100 mcg) of 1:10,000 concentration, administered slowly over several minutes 2, 7
• For continuous infusion: 5-15 μg/min, titrated to blood pressure 2, 7
• Preparation: Add 1 mg (1 mL) of 1:1000 epinephrine to 250 mL D5W (concentration: 4 μg/mL) 7
• Requires continuous hemodynamic monitoring 7

Adjunctive Therapies (Second-Line Only)

Antihistamines and Steroids

• Diphenhydramine 1-2 mg/kg (25-50 mg adults) IV or IM 1
• Ranitidine 1 mg/kg IV (or cimetidine 4 mg/kg) 1
• Methylprednisolone 1-2 mg/kg/day IV every 6 hours to prevent biphasic reactions (no acute benefit) 1

Bronchospasm Management

• Albuterol 2.5-5 mg nebulized for bronchospasm resistant to epinephrine 1

Refractory Hypotension

• Dopamine 2-20 mcg/kg/min titrated to blood pressure for refractory hypotension 1, 7
• Glucagon 1-5 mg IV over 5 minutes followed by infusion at 5-15 mcg/min for patients on beta-blockers 1, 7

Special Consideration: Renal Dysfunction and Anaphylaxis

Pathophysiology

• Low urine output in anaphylactic shock results from profound hypotension and decreased renal perfusion 8
• Impaired renal function may prolong antigen exposure if the causative agent is renally cleared 8

Advanced Intervention for Refractory Cases

• In cases of refractory anaphylactic shock with anuria and acute kidney injury from renally-excreted antigens, continuous veno-venous hemodiafiltration may expedite recovery 8
• This is reserved for extreme cases unresponsive to standard resuscitation 8

Monitoring Requirements

Close Observation

• Patients in anaphylactic shock are critically ill, and cardiovascular and respiratory status can change quickly, making close monitoring imperative 2
• Minimum 4-6 hours observation in emergency department for all patients 1
• Extended observation (up to 24 hours) for severe reactions, delayed epinephrine administration, or history of biphasic reactions 1
• 17% of patients experience delayed deterioration 1

Airway Management

• When anaphylaxis produces obstructive airway edema, rapid advanced airway management is critical 2
• Emergency cricothyroidotomy or tracheostomy may be required in some cases 2

Critical Pitfalls to Avoid

• Never delay epinephrine while administering antihistamines or steroids—this is the most common fatal error 1, 9
• Do not use subcutaneous epinephrine; absorption is slower and less reliable than IM 1
• Do not administer IV epinephrine too rapidly, as this can cause lethal arrhythmias 1, 7
• Never confuse concentrations: use 1:1000 (1 mg/mL) for IM and 1:10,000 (0.1 mg/mL) for IV 1
• Do not use vasodilators like isosorbide, which worsen hypotension in anaphylactic shock 1, 5
• There are no absolute contraindications to epinephrine in anaphylaxis, even in elderly patients with cardiac disease 1
• Approximately 7-18% of patients require more than one dose of epinephrine 1