3 Shock Management of Shock

In thermodynamic terms, the purpose of the heart is simple enough. Its sole function is to generate useful energy (as opposed to heat, which it also generates) and then transfer that energy into the pulmonary artery and the aortic root as efficiently as possible. The useful energy transferred into the pulmonary artery from the right ventricle moves the blood through the lungs and into the left atrium and ventricle during diastole.The useful energy transferred into the aortic root from the left ventricle moves the blood throughout the body. The blood delivers nutrients (including oxygen) to metabolizing tissues, removes waste products from those tissues, carries heat from those tissues to the skin (where the heat is dissipated into the environment), and transports hormones and intermediate products of metabolism from one part of the body to another.The remaining energy in the blood pushes the blood into the right atrium and ventricle during diastole. This useful energy has two components: flow and pressure. Flow, in the case of the cardiovascular system, is cardiac output. The pressures of interest are the mean pressures in the roots of the pulmonary artery and the aorta [see Figure 1].These pressures, like all those we describe in this chapter, are expressed as being above (or occasionally below) atmospheric pressure and are measured with transducers placed at the level of the right atrium. The formula for calculating the amount of useful energy transferred into the root of the pulmonary artery from the right ventricle (per unit time—typically 1 minute) is the cardiac output multiplied by the mean pressure in the pulmonary artery.The useful energy transferred into the aortic root from the left ventricle (per unit time) is the cardiac output multiplied by the mean aortic root pressure.1-3 If the amount of useful energy transferred into the roots of the pulmonary artery and the aorta is insufficient to meet the body’s basic metabolic needs, the patient is said to be in shock. Shock can James W. Holcroft, M.D., F.A.C.S., John T. Anderson, M.D., F.A.C.S., and Matthew J. Sena, M.D.