A ruptured abdominal aneurysm is a surgical emergency often accompanied by serious hypotension and vascular collapse before surgery and massive fluid shifts with renal failure after surgery. In this case, all the hemodynamic parameters indicate inadequate intravascular volume, and the patient is therefore suffering from hypovolemic shock. The low urine output indicates poor renal perfusion, while the high urine-specific gravity indicates adequate renal function with compensatory free-water conservation. The administration of a vasopressor agent would ceainly raise the blood pressure, but it would do so by increasing peripheral vascular resistance and thereby fuher decrease tissue perfusion. The deleterious effects of shock would be increased. A vasodilating agent to lower the systemic vascular resistance would lead to profound hypotension and possibly complete vascular collapse because of pooling of an already depleted vascular volume. This patient's blood pressure is critically dependent on an elevated systemic vascular resistance. A diuretic would exacerbate the patient's existing volume depletion. To properly treat this patient, rapid fluid infusion and expansion of the intravascular volume must be undeaken. This can be easily done with lactated Ringer solution or blood (or both) until improvements in such parameters as the PCWP, urine output, and blood pressure are noted.