Methylene Blue and Epinephrine

Abstract

Severe hypotension resulting from anaphylactic shock may be refractory to epinephrine and impair cerebral oxygenation and metabolism contributing to anaphylactic shock morbidity and mortality. Refractoriness to epinephrine could be corrected by nitric oxide pathway inhibitors such as methylene blue. To compare the systemic and regional (brain and skeletal muscle) effects of epinephrine and methylene blue given alone or in combination in a rat model of anaphylactic shock. Prospective laboratory study. University laboratory. Male Brown-Norway rats (n = 60). After sensitization and induction of anaphylactic shock by ovalbumin, animals received either vehicle (ovalbumin group) or a 3-mg/kg methylene blue bolus (methylene blue group) or epinephrine (epinephrine group) or both (methylene blue-epinephrine group). Sensitized control rats received only vehicle and no ovalbumin (control group). Mean arterial pressure, cardiac output, cerebral blood flow, skeletal muscular oxygen partial pressure, cerebral oxygen partial pressure, skeletal muscular, and cerebral interstitial lactate/pyruvate ratio were measured. Cleaved caspase 3 and hypoxia-inducible factor-1α expression were analyzed in the cerebral cortex by Western blot. Without treatment, rats died rapidly within 15 mins from a decrease in cardiac output and mean arterial pressure, whereas treated rats survived until the end of the experiment. Methylene blue alone extended survival time but without significant improvement of hemodynamic variables and tissue perfusion and did not prevent neuronal injury. Epinephrine restored partially systemic hemodynamic variables and cerebral perfusion preventing glutamate-induced excitotoxicity. Compared with epinephrine alone, the methylene blue-epinephrine association avoided neuronal excitotoxicity and had an additive effect both on hemodynamic variables and for prevention of brain ischemia. Neither treatment could significantly restore cardiac output or prevent muscular compartment ischemia and microvascular leakage. Anaphylactic shock is associated with severe impairment of cerebral blood flow despite correction of arterial hypotension. Epinephrine must still be considered as the first-line vasoconstrictive agent to treat anaphylactic shock. The epinephrine-methylene blue association was the most effective treatment to prevent cerebral ischemia and could be used in anaphylactic shock refractory to epinephrine.