Hemodynamic Stabilization

FLUID ADMINISTRATION Correction or stabilization of hypotension and inadequate perfusion is the second goal of resuscitation. Rapid fluid administration at a rate of 0.5 L (20 mL/kg in children) of normal saline or similar isotonic crystalloid should be administered every 5 to 10 min as needed; it is not unusual for the patient to require 4 to 6 L (60 mL/kg in children) or more of crystalloid in the initial phase of resuscitation. Stabilization of the patient's mentation, blood pressure, respiration, pulse rate, skin perfusion, and central venous pressure, with urine output greater than 30 mL/h (1 mL/kg/h in pediatric patients) are useful clinical parameters in monitoring the response to fluid administration.

INOTROPIC SUPPORT If no response to the fluid infusion is noted after 3 to 4 L of fluid, or if there are signs of fluid overload (elevated central venous pressure or pulmonary edema), an infusion of dopamine can be started. If the patient has a pulmonary artery catheter in place during this resuscitation, dopamine should be added in the setting of a PCWP of 15 to 18 mmHg or if there are marked increases of the PCWP with additional fluids. Doses of dopamine often required are 5 to 20 pg/kg/min resulting in both b-adrenergic inotropic and a-adrenergic vasopressor activity. If the patient is still unresponsive above a rate of 20 pg/kg/min of dopamine infusion, norepinephrine should be started with the goal of keeping the mean blood pressure at least 60 mmHg. Although previous investigations have raised doubts concerning the efficacy of norepinephrine in these cases, recent studies have demonstrated that norepinephrine can reverse septic shock in patients unresponsive to fluid administration and dopamine. Once the blood pressure and perfusion have been stabilized by norepinephrine, the lowest dosage that maintains blood pressure should be utilized to minimize the complications of vasoconstriction. Additionally, data from the canine model has suggested the use of low-dose dopamine (1 to 4 pg/kg/min) in patients on norepinephrine results in significantly higher renal blood flow and reduced renal vascular resistance. In one series, the norepinephrine survival group approached 40 percent. Vasodilators are rarely used in the emergency department, but they have been used in the intensive care units in situations of severe myocardial depression, increased system vascular resistance, and adequate blood pressure.

HEMODYNAMIC ENDPOINTS Most authorities recommend that the optimal hematocrit should be maintained between 30 and 35 percent to maximize oxygen transport capacity. A number of studies have suggested that increased global oxygen delivery has improved survival in critically ill patients. However, a recent multicenter trial involving more than 10,000 patients in 56 intensive care units suggested that hemodynamic therapy aimed at achieving supranormal values for cardiac index, with normal values of mixed venous oxygenation, failed to reduce morbidity or mortality in critically ill patients when compared to a control group that was supported to normal cardiac index levels.

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