Epinephrine, compared with arginine vasopressin, is associated with similar haemodynamic effects but significantly improved brain oxygenation in the early phase of anaphylactic shock in rats: An experimental study.

Background: In contrast to other types of shock, anaphylactic shock decreases cerebral blood flow more than would be expected from severe arterial hypotension, thus potentially affecting survival through brain ischaemia/hypoxia. We hypothesised that epinephrine (EPI) used as a first-line treatment of anaphylactic shock and arginine vasopressin (AVP) proposed in case of EPI refractoriness may have different effects on brain oxygenation.

Objectives: To compare the effect of EPI and AVP on brain oxygenation under similar macro-haemodynamic target values in an anaphylactic shock model.

Design: Prospective laboratory study.

Setting: University laboratory.

Animals: Male brown Norway rats (n = 27).

Interventions: Twenty-seven rats were sensitised with ovalbumin (OVA). Twenty rats had anaphylactic shock induced with OVA and were resuscitated with either 0.9% saline (OVA group), EPI (EPI group) or AVP (AVP group). Sensitised control rats received only 0.9% saline and no OVA (CON group).

Main Outcome Measures: Mean arterial pressure (MAP), carotid artery blood flow (CaBF), cerebral cortical blood flow (CBF) and hippocampal oxygen partial pressure (PtiO2) were recorded.

Results: All rats in the OVA group died within 15 min. EPI and AVP restored comparable levels of MAP, carotid artery blood flow and CBF, and extended survival time. EPI was associated with biologically relevant and significantly (P < 0.05) higher PtiO2 values (nadir values at 20 min: 25.0 ± 2.2 mmHg) compared with the AVP group (14.9 ± 2.0 mmHg). The slopes of the correlations of MAP vs. PtiO2 and CBF were significantly steeper with AVP (more pressure dependence) compared with EPI. By the end of the experiment, hippocampal PtiO2 values between the EPI (24.1 ± 2.1 mmHg) and the AVP (20.8 ± 2.0 mmHg) groups were similar.

Conclusion: At early, but not at late time points, resuscitation of anaphylactic shock with EPI or AVP to similar MAP and CBF endpoints resulted in hippocampal PtiO2 being significantly higher after EPI. In addition, the PtiO2 after EPI always remained above the threshold for brain hypoxia, whereas PtiO2 after AVP was below the hypoxic threshold most of the time. Because of this early brain hypoxia, AVP may not be the drug of first choice for resuscitation of anaphylactic shock.