Vital Organ Blood Flow During Deliberate Hypotension in Dogs

Increasing the inspiratory concentration of isoflurane is a commonly used technique for producing deliberate hypotension (DH) when isoflurane is used as the principal anesthetic. When an intravenous anesthetic technique is used, DH can be produced by the administration of a peripheral vasodilator, eventually in association with low concentrations of isoflurane. The aim of this investigation was to compare the effects of these two different approaches on vital organ blood flow. DH was induced in 12 mongrel dogs with two different anesthetic techniques: inhaled anesthesia with isoflurane (ISO) or an intravenous anesthetic technique combining propofol and alfentanil in combination with the α-adrenoreceptor antagonist, urapidil, and isoflurane at low end-expiratory concentrations. Mean arterial pressure (MAP) was initially decreased by 20% of its baseline and then to 50 mm Hg. Vital organ blood flows and the cerebral metabolic rate for oxygen were determined at each decrement in MAP, and after discontinuation of DH. A decrease in cardiac output was observed in the ISO group when MAP was decreased to 50 mm Hg. Cerebral blood flow was constantly and significantly higher in the ISO group. The cerebral metabolic rate for oxygen did not change compared to baseline values in both groups. At a MAP of 50 mm Hg, a decrease in renal blood flow was observed in both groups. Splanchnic blood flow remained stable in the intravenous anesthetic group in contrast to the ISO group where splanchnic blood flow decreased significantly. The combination of total intravenous anesthesia, urapidil, and low inspired concentrations of isoflurane to produce DH may be preferable to high concentrations of isoflurane, because cerebral hyperemia is avoided and splanchnic blood flow is better preserved.