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BACKGROUND: Phenylephrine is a selective alpha(1) adrenergic receptor agonist that increases arterial blood pressure by peripheral vasoconstriction. However, whether phenylephrine improves the outcome of cerebral ischemia in patients with internal carotid artery disease during hemorrhagic shock is unclear. METHODS: (Experiment 1) Twenty-one adult male Sprague-Dawley rats were anesthetized with isoflurane and their lungs mechanically ventilated. After the right common carotid artery was ligated, arterial blood was withdrawn until mean arterial blood pressure (MAP) reached 30 mm Hg to induce cerebral ischemia. After MAP was maintained at 30 mm Hg for 10 min, the animals were randomly allocated to three groups (n = 7 each). In the phenylephrine group, phenylephrine was administered IV to maintain a MAP of 70 +/- 3 mm Hg for 5 min. In the saline group, an identical volume of normal physiologic saline was continuously administered for 5 min. In the control group, neither phenylephrine nor saline was administered and MAP was maintained at 30 mm Hg. At 30 min of exsanguination, the withdrawn blood was reinfused IV at a rate of 0.25 mL/min. Diffusion-weighted magnetic resonance images were serially acquired and apparent diffusion coefficient maps were created to determine the volume of cytotoxic edema. (Experiment 2) To analyze the effect of phenylephrine on the regional cerebral blood flow (rCBF) in the right middle cerebral artery territory, rCBF was measured using laser Doppler flowmetry in 15 additional rats (n = 5 each). RESULTS: (Experiment 1) At 10 min of exsanguination, there were no significant differences in the volume of cytotoxic edema among the phenylephrine (357.5 +/- 93.5 mm(3)), saline (333.5 +/- 69.6 mm(3)), and control (303.1 +/- 85.8 mm(3)) groups. Low apparent diffusion coefficient regions significantly expanded with time in the control group, whereas they started to decrease just after phenylephrine infusion and almost all had disappeared within 30 min in the phenylephrine group. The final infarction volume in the phenylephrine group (3.9 +/- 2.6 mm(3), P < 0.01) was significantly lower than that in the saline group (341.5 +/- 213.7 mm(3)) and control group (509.1 +/- 197.0 mm(3)). (Experiment 2) Although rCBF decreased to 40%-50% of the baseline at 10 min of exsanguination, phenylephrine immediately increased rCBF over the baseline level. In the saline group, rCBF increased significantly, but there was some delay compared with the phenylephrine group. CONCLUSIONS: Phenylephrine ameliorated cytotoxic edema and decreased the infarction volume in a rat model of complete unilateral carotid artery occlusion with severe hypotension. These findings suggest that phenylephrine transiently increased CBF without increasing the tonus of cerebral vasculature during hemorrhagic shock.

The purpose of this study was to examine and compare the effects of atrial natriuretic peptide and furosemide on pulmonary gas exchange, hemodynamics, extravascular lung water, and renal function in a dog model of oleic acid-induced pulmonary edema.Prospective, comparable, experimental study.Laboratory at a university hospital.Eighteen male beagle dogs were studied under mechanical ventilation with pentobarbital anesthesia.Oleic acid (0.08 mL/kg) was injected and allowed for 1 hr to achieve pulmonary edema with hypoxemia at Fio2 of 0.3. After lung injury, dogs were divided into three groups; control group (n = 6) receiving saline (2.5 mL/hr for 5 hrs), atrial natriuretic peptide group (n = 6) receiving atrial natriuretic peptide (1 microg x kg(-1) x min(-1) for 5 hrs), and furosemide group (n = 6) receiving furosemide (1 mg x kg(-1) x hr(-1) for 5 hrs).Hemodynamics, arterial blood gases, extravascular lung water, and renal function were measured hourly for 7 hrs after injury. Oleic acid increased extravascular lung water and induced hypoxemia. In the atrial natriuretic peptide group, extravascular lung water was significantly (p.05) lower and Pao2 was significantly (p.05) higher than in the control and furosemide groups, respectively. Pulmonary hypertension induced by oleic acid was attenuated by atrial natriuretic peptide infusion but not by saline or furosemide. Increased natriuresis/diuresis did not significantly differ between the atrial natriuretic peptide and the furosemide group, whereas creatinine clearance in the atrial natriuretic peptide group was significantly higher than that in the furosemide group.These findings suggest that atrial natriuretic peptide improves pulmonary gas exchange by reducing extravascular lung water and pulmonary arterial pressure, possibly independently from natriuresis/diuresis in oleic acid-induced pulmonary edema.

To elucidate the pathologic role of endothelin-1 (ET-1) in septic shock, we measured plasma ET-1 concentrations after bacterial lipopolysaccharide (LPS) administration in dogs and determined systemic, pulmonary, and renal hemodynamics and blood gas parameters with or without the nonselective ET receptor antagonist TAK-044. Plasma ET-1 concentrations increased significantly after LPS administration, which correlated positively with mean arterial pressure, mean pulmonary arterial pressure, pulmonary capillary wedge pressure, and central venous pressure. LPS infusion induced hypotension, metabolic acidosis, hypoxemia, and renal dysfunction. TAK-044 prevented LPS-induced metabolic acidosis, hypoxemia, and renal dysfunction, but not hypotension. These findings suggest that increased circulating ET-1 plays a compensatory role in the reversal of systemic vasodilatation in septic shock, but exerts deleterious effects on renal and pulmonary circulation.

The effect of mechanical ventilation with PEEP of 0, 10, and 20 cm H2O (continuous positive-pressure ventilation [CPPV]) on hepatic blood flow (HBF) and intrahepatic oxygen delivery was studied in 26 mongrel dogs anesthetized with fentanyl. Hepatic arterial and portal venous blood flow was measured by an electromagnetic flowmeter. CPPV caused a significant decrease in HBF, which was related to the PEEP level. A linear correlation was seen between HBF and cardiac output. Intrahepatic oxygen delivery decreased more than HBF and cardiac output. The reduced oxygen delivery was due mainly to the decrease in portal venous oxygen content.