SHADES OF SHOCK 4

4.4 Cardiogenic shock occurs most often as result of i) Myocardial infarction (MI) ii) Tamponade (collection of blood in the pericardium due to leak from the myocardium) This shock is due to cardiac muscle being unable to maintain
adequate cardiac output from causes intrinsic to the heart
muscle such as MI, cardiomyopathy, or drug toxicity or causes
extrinsic to heart muscle such as compression i.e. tamponade,tension pneumo- thorax or pulmonary embolus (3.3).

Cardiogenic Shock
The syndrome of cardiogenic shock is defined as the inability of the heart (as a result of reduction of its pumping function) to deliver sufficient blood flow to the tissues to meet resting metabolic needs. Thus, the clinical definition of cardiogenic shock requires a low cardiac out put and evidence of tissue hypoxia in the presence of an adequate intravascular volume. -If hemodynamic monitoring is available, the diagnosis is confirmed by the combination of a low systolic blood pressure and a depressed cardiac index (<2,2 l/min/m2) in the presence of an elevated pulmonary capillary wedge pressure (>15mmHg)
-A reduced blood pressure activates the baroreceptors.
-The adrenergic response leads to an increase in heart rate, myocardial contractility, and arterial and venous vasoconstriction.
-The renin angiotensin system is activated by inadequate renal perfusion and sympathetic stimulation, leading to additional vasoconstriction and salt and water retention.
Finally, hypotension increases the secretion of antidiuretic hormone, which further increase water retention. The reduction in blood pressure in conjunction with an elevated left ventricular end diastolic pressure resulting from fluid retention and low left ventricular function reduces coronary perfusion pressure and thus myocardial oxygen delivery.
Increase in heart rate, systemic vascular resistance, and contractility all increase myocardial oxygen consumption and demand.
-The difference between myocardial oxygen demand and oxygen delivery further reduces left ventricular function and will lead to circulatory collapse.
The clinical picture of cardiogenic shock is remarkably similar to those of hypovolemic shock.
-In making the diagnosis of cardiogenic shock, history of cardiac disease may be of great value. -Physical exam demonstrates inadequate tissue perfusion with an elevated jugular venous pressure, an S3 gallop, and pulmonary edema. -A chest radiograph provides diagnostic information regarding the presence of pulmonary edema, pleural effusion, or cardiac chamber enlargement.
-Cardiac enzymes may provide evidence of acute myocardial infarction.

Arterial blood gas analysis provides information regarding the adequacy of gas exchange. Severe hypoxia in the presence of a normal chest radiograph may support the diagnosis of massive pulmonary embolus rather than a primary cardiac cause of shock.
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