The Pump--Cardiogenic Shock

The inability of the Left Ventricle to produce adequate Stroke Volume is the most common cause of Shock. Remember that Stroke Volume is the amount of oxygenated blood pumped out of the heart during systole. In the adult, 70 ml is the average volume for each heartbeat.

Infarction of more than 40% of the Left Ventricular Muscle, Congestive Heart Failure, Cardiac Tamponade and Chest Trauma are among the many disorders that can cause this type of Shock As the Pump begins to fail, the first Swan-Ganz value to change is PCWP. Incomplete Left Ventricular emptying increases the filling pressures as incoming blood is pumped into a nearly full chamber.

Graphic--The above X-Ray illustrates Congestive Heart Failure in an adult patient (i.e., the CT ratio is > .5. Diminished stroke volume due to a nearly full chamber and a weak ventricular pumping action causes PCWP to increase.

PCWP increases to a mean value of 15 mm Hg or more. As the Left ventricular failure gets worse and blood begins to back up into the left atrium, rising pressures are transmitted to the Pulmonary Veins, the Pulmonary Capillary Bed and finally the Pulmonary Artery.

PA pressures increase to 28/16 mm Hg or beyond. As pump failure continues, the rise in pressures may transmit all the way back to the right ventricle and atrium. This situation is worsen by peripheral vascular constriction in response to Low Cardiac Output as sensed by the arterial baroreceptors. The Peripheral Vascular constriction would result in an increase in systemic Vascular resistance (SVR). Remember that the arterial baroreceptors are blood pressure receptors located on the Arch of the Aorta.

The back up of pressure from the Left Ventricle plus the increase in SVR causes blood to pool in the thorax pushing CVP values beyond the normal limit of 7 mm HG.

Review--Signs of Cardiogenic Shock--First a rise in PCWP, followed by a rise in PA, followed by a rise in CVP. The skin' color and temperature is not affected by this type of Shock.

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