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.

Anaphylactic shock decreases cerebral blood flow more than what would be expected from severe arterial hypotension.

The effects of acute reduction in arterial blood pressure in severe anaphylactic shock (AS) on cerebral blood flow are of paramount importance to be investigated. We studied cerebral circulation and oxygenation in a model of severe AS and compared it with a pharmacologically induced arterial hypotension of similar magnitude. Anaphylactic shock was induced by 1 mg intravenous ovalbumin (OVA) in sensitized rats. Rats were randomized to three groups: (i) no resuscitation (OVA; n = 10) (ii) intravenous volume expansion (10 mL in 10 min after OVA injection) (OVA + VE; n = 10); (iii) control hypotension (100 µg of nicardipine followed by continuous infusion of 1 mg · 100 g · h intravenously; NICAR; n = 10). Mean arterial pressure (MAP), carotid blood flow (CBF), cardiac output, cerebral cortical blood flow (CCBF; estimated by laser Doppler technique), and cerebral tissue oxygen pressure (PtiO2) were recorded over the 15 min following AS induction in all three groups. Results are expressed as mean (SD). One minute after OVA or nicardipine injection, there was a rapid and significant 50% decrease in MAP from basal values. In the OVA group, AS severely altered systemic and cerebral hemodynamics in 5 min: 93% (SD, 4%) decrease in CBF, 66% (SD, 8%) in CCBF, and 44% (SD, 8%) in PtiO2; the decrease in CBF was significantly (P < 0.05) attenuated in the OVA + VE group; however, CCBF and PtiO2 were not statistically different in the OVA versus OVA + VE groups. On the contrary, nicardipine-induced hypotension had only a limited impact on CBF, cardiac output, CCBF, and PtiO2 for a similar MAP decrease. There was a linear relation between CCBF and blood pressure in the OVA (regression slope: 0.87 [SD, 0.06]; median r = 0.81) but not in the NICAR group (regression slope: 0.23 [SD, 0.32]; median r = 0.33). Anaphylactic shock resulted in severe impairment of cerebral blood flow and oxygenation, beyond what could be expected from the level of arterial hypotension.