The differential effects of recombinant brain natriuretic peptide, nitroglycerine and dihydralazine on systemic oxygen delivery and gastric mucosal microvascular oxygenation in dogs.

Brain natriuretic peptide has vasodilatory properties and may thus increase splanchnic perfusion and oxygenation. We compared the effects of recombinant brain natriuretic peptide on gastric mucosal microvascular haemoglobin oxygenation (reflectance spectrophotometry) and systemic variables with those of equi-hypotensive doses of two other vasodilators (nitroglycerine and dihydralazine). Chronically instrumented, healthy dogs were randomly allocated to receive on different days, one of the three drugs (nitroglycerine and dihydralazine doses titrated to reduce mean arterial pressure by ∼20%). Brain natriuretic peptide significantly increased gastric mucosal microvascular haemoglobin oxygenation selectively, i.e. without concomitant haemodynamic effects. In contrast, the other vasodilators either did not increase gastric mucosal microvascular haemoglobin oxygenation at all (nitroglycerine), or did so only with marked increases in other systemic haemodynamic variables (dihydralazine). Our data suggest a potential role of recombinant brain natriuretic peptide selectively for increasing microvascular mucosal oxygenation. Studies are required to extend these findings to the clinical setting.

Sevoflurane and propofol anaesthesia differentially modulate the effects of epinephrine and norepinephrine on microcirculatory gastric mucosal oxygenation.

BACKGROUND: Adequate gastrointestinal mucosal oxygenation is regarded to be crucial in the prevention and therapy of critical illness. Epinephrine and norepinephrine are used for perioperative haemodynamic support. However, their per se effects on gastromucosal haemoglobin oxygenation (µHbO(2)) remain unclear. Moreover, respective effects of epinephrine and norepinephrine may be affected by the type of underlying anaesthesia. Thus, we studied the effects of epinephrine and norepinephrine during anaesthesia with sevoflurane or propofol on regional gastromucosal µHbO(2) and systemic O(2)-derived variables. METHODS: In a double-randomized cross-over study, chronically instrumented dogs (n=6 per group) were anaesthetized randomly with sevoflurane or propofol, ventilated, and then randomly received either epinephrine or norepinephrine (0, 0.05, 0.1, and 0.2 µg kg(-1) min(-1)). We measured gastromucosal µHbO(2), systemic haemodynamics, and O(2)-derived variables. RESULTS: During sevoflurane anaesthesia, norepinephrine markedly increased µHbO(2) (P<0.0001) and systemic oxygen transport (DO(2)) (P=0.0006). In contrast, epinephrine failed to increase µHbO(2), despite doubling DO(2) (P=0.0002). During propofol anaesthesia, in contrast to sevoflurane, neither epinephrine nor norepinephrine affected µHbO(2), although epinephrine, but not norepinephrine, again resulted in markedly increased DO(2) (P<0.0001). CONCLUSIONS: The effects of epinephrine and norepinephrine depended on the type of anaesthesia. In addition, regional effects (i.e. µHbO(2)) were not predictable from systemic effects (i.e. DO(2)).