Circulatory or hemodynamic stabilization begins with adequate intravenous access. For fluid resuscitation, large-bore peripheral lines are equally as effective as central venous access, thus peripheral venous access should be the procedure of choice if peripheral veins are available. Trendelenburg positioning does not significantly improve cardiopulmonary performance compared with the supine position. Trendelenburg positioning may also worsen pulmonary gas exchange and enhance aspiration of vomitus. If a volume challenge is felt to be urgent, rather than using the Trendelenburg position, a compromise would be to raise the patient's legs above the level of the heart with the patient supine. Central venous access will aid in assessing volume status (CVP) and monitoring Scv o2. It is a preferred route for the long-term administration of vasopressor therapy, and provides rapid access to the heart if pacemaker placement is required.
Fluid resuscitation begins with isotonic crystalloid: the amount and rate are determined by an estimate of the hemodynamic abnormalities. Most patients in shock have either an absolute or relative volume deficit. The one exception is cardiogenic shock with pulmonary edema. Fluid is given rapidly, in set quantities (e.g., 500 to 1000 mL), with reassessment of the patient after each amount. Patients with modest degrees of hypovolemia usually require about 20 mL/kg of isotonic crystalloid; much more may be required with profound volume deficits.
The colloid-versus-crystalloid resuscitation controversy remains despite evidence that there is a slight increase in mortality when colloids are used for volume replacement in critically ill patients.14 Some studies have found a lower incidence of pulmonary edema and possibly greater benefit in elderly patients with colloid resuscitation, although survival is not statistically improved.
Without invasive hemodynamic monitoring, noncardiogenic pulmonary edema may be difficult to differentiate from cardiogenic pulmonary edema in the ED. Even though the former may respond to fluids, fluids should be minimized until appropriate monitoring can be placed.
Vasopressor agents are usually used when there has been an inadequate response to volume resuscitation or when a patient has contraindications to volume infusion. Vasopressors are most effective when the vascular space is "full" and least effective when the vascular space is depleted. However, vasopressors may be necessary early in the treatment of shock, before volume resuscitation is complete, in order to prevent potentially lethal consequences of prolonged systemic arterial hypotension. This is especially important in elderly patients with significant coronary and cerebrovascular disease. Rapidly restoring the MAP to 60 mmHg or systolic pressure to 90 mmHg may avoid the coronary and cerebral complications of decreased blood flow. Vasopressor agents are based on the catecholamine molecule and have variable effects on the a- and b-adrenergic receptors (Tablei26:5).
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