Comparative effects of early versus delayed use of norepinephrine in resuscitated endotoxic shock.

OBJECTIVE: To assess hemodynamic, tissue oxygenation, and tissue perfusion changes by comparing traditional therapy (fluid resuscitation followed by vasopressor treatment) and alternative therapy (early vasopressor treatment) in a hyperkinetic and sedated model of endotoxic shock.

DESIGN: Prospective controlled experimental study.

SETTING: Animal research laboratory.

SUBJECTS: Male Wistar rats.

INTERVENTIONS: Rats were anesthetized, mechanically ventilated, paralyzed, and instrumented to measure mean arterial pressure, heart rate, pulse pressure variation, aortic and mesenteric blood flow, muscle and liver tissue oxygen pressure, blood gas, and lactate. Rats were randomly divided into five groups (n = 7): endotoxin alone (Endo), endotoxin plus norepinephrine (Endo/NE), endotoxin plus fluid therapy alone (ENDO/Fl), endotoxin plus fluid therapy plus late catecholamine (Endo/Fl/Late NE), and endotoxin plus fluid therapy plus simultaneous norepinephrine administration (Endo/Fl/Early NE).

MEASUREMENTS AND MAIN RESULTS: Mean arterial pressure increased to baseline values only in the catecholamine-treated group (p < .05). In ENDO/Fl, Endo/Fl/Late NE, and Endo/Fl/Early NE, aortic blood flow was maintained. Mesenteric blood flow was maintained at baseline values only in the catecholamine-treated groups. Mesenteric/aortic blood flow ratio was higher in the early catecholamine group (p < .05). Endo and ENDO/Fl were associated with a marked decrease in liver PO2, which was maintained in catecholamine-treated groups (p < .01). Plasma lactate was lower in the Endo/Fl/Early NE group. Volume resuscitation was higher in Endo and Endo/Fl/Late NE groups with 28 +/- 6 and 27 +/- 4 mL, respectively, when compared with the Endo/Fl/Early NE group (19 +/- 3 mL) (p < .05).

CONCLUSIONS: The use of norepinephrine was associated with improved mean arterial pressure, sustained aortic and mesenteric blood flow, and better tissue oxygenation when compared with fluid resuscitation alone, irrespective of time of administration. The early use of norepinephrine plus volume expansion was associated with a higher proportion of blood flow redistributed to the mesenteric area, lower lactate levels, and less infused volume. Thus, the early use of norepinephrine is safe and may decrease the need for volume resuscitation.