Treatment

In the prehospital setting, the medical control physician should consider directing the patient suspected to be in cardiogenic shock to a facility that has an intraaortic balloon pump, 24-h emergency percutaneous transluminal coronary angioplasty (PTCA), and emergent coronary artery bypass graft (CABG) capabilities.

In both the prehospital and emergency department setting, monitoring should begin immediately: oxygen, intravenous access, cardiac monitor, and continuous pulse oximetry. When detected, hypoxia, hypovolemia, rhythm disturbances, electrolyte abnormalities, and acid-base alterations should be corrected. In the setting of an AMI, aspirin should be given unless the patient is allergic or has an absolute contraindication. Pain control can be attempted judiciously using intravenous nitroglycerin or morphine sulfate with attentive concern for maintaining the systemic blood pressure. In the absence of evidence for pulmonary edema, careful boluses of normal saline (100-250 mL) should be administered. As noted earlier, some patients with AMI and hypotension have a degree of relative or absolute volume deficiency and benefit from fluid administration. In a RV infarct with hypotension, fluid support is the first action. Oral tracheal intubation is often necessary to maintain oxygenation and ventilation, but the change to positive-pressure ventilation may further decrease preload and cardiac output. Alternatively, continuous positive airway pressure can be used in selected patients with a reduction in the need for intubation and a trend toward decreased mortality. 9

In the absence of profound hypotension, dobutamine is a mainstay of initial pharmacologic treatment.1 H This sympathomimetic agent improves myocardial contractility and augments diastolic coronary blood flow without inducing excessive tachycardia. Usually, cardiac output increases and LV filling pressures decrease. Infusions should be started at 2.5 to 5.0 pg/kg per minute, titrating at 2.5 pg/kg per minute increments to achieve the desired effect. Increases should be stopped at 15 pg/kg per minute. With profound hypotension (systolic pressure <70 mmHg), dopamine is preferred, either as a single agent or in combination with dobutamine. Dopamine is started at 2.5 to 5.0 pg/kg per minute and titrated to desired effect. The lowest possible dose of dopamine should be used because this agent can produce excessive tachycardia, increase myocardial oxygen demands, and induce arrhythmias. When shock persists despite use of these agents, mechanical inotropic support with an intraaortic balloon pump is required.1 ,13

The intraaortic balloon pump can temporarily stabilize the hemodynamics in cardiogenic shock. «I3 It decreases afterload and augments diastolic pressure and coronary perfusion, resulting in decreased myocardial work. It is only temporizing and does not improve survival without successful revascularization of the culprit coronary artery or surgical correction of an acute mechanical catastrophe.1314 If a patient requires transfer for surgical therapy, the balloon pump can be used to support the patient during transport.

Limiting infarction size with reperfusion is the key to successful therapy of cardiogenic shock. Although early use of fibrinolytic therapy in AMI has been shown to markedly decrease morbidity and mortality, once cardiogenic shock has developed, the mortality rate remains high, at about 75 percent. One reason for the high mortality despite the use of fibrinolytics is that documented clot lysis in the infarct-related artery and reperfusion in cases of cardiogenic shock is only 40 to 50 percent with these agents. Another reason is that shock combined with the existence of multivessel disease limits the effectiveness of these agents. Thus, while fibrinolytic agents are successful in preventing cardiogenic shock in AMI, they have much less benefit once shock has developed.

A number of nonrandomized trials have reported relatively good mortality rates as low as 30 percent with primary PTCA in conjunction with balloon pump support for patients in cardiogenic shock. Although these results await confirmation by randomized trials, PTCA, if available within 60 minutes, appears to be the reperfusion modality of choice for patients who present with or develop cardiogenic shock in the emergency department. 513 Conversely, in hospitals without PCTA immediately available, fibrinolytics should be administered as soon as possible.

Emergent CABG also has been reported to decrease mortality in cardiogenic shock. However, the extensive surgical and medical resources required, as well as the operative risk for these seriously ill patients, have limited its use. For patients who develop a mechanical complication of infarction (e.g., ventricular septal rupture or acute mitral insufficiency) with cardiogenic shock, temporary inotropic support with the intraaortic balloon pump followed by early surgical repair produces the best outcome.

Acute RV failure leading to cardiogenic shock may occur with RV infarction. Although attempts to reverse hypotension should begin with rapid infusion of normal saline, dobutamine should be started if no improvement is observed after 1 L. As with LV infarction, early reperfusion is essential.

Acute mitral valve insufficiency accounts for about 8 percent of cases of cardiogenic shock and can be suspected at the bedside in the face of sudden hypotension, pulmonary edema, and a holosystolic apical murmur. Hemodynamic support can be initiated with dobutamine and nitroprusside to support contractility and provide afterload reduction to promote forward systemic blood flow. The intraaortic balloon pump is also beneficial for temporary support. Acute septal rupture accounts for about 4 percent of cases of cardiogenic shock and is treated with dobutamine, nitroprusside, and the intraaortic balloon pump. Confirmatory evidence for these emergent conditions with two-dimensional echocardiography should be sought concomitant with emergency notification of the cardiac surgical team.

Clearly, not all patients may benefit from aggressive care. The decision to perform or withhold therapies should be made in light of the patient's desires and wishes. Factors that may influence the decision to pursue aggressive therapy include advanced age, diminished functional status, and comorbid conditions.

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