Shock

So, when we talk about ischemia, we’re usually talking about this lack of blood flow to a specific area of tissue. For example, with a heart attack, a coronary artery in the heart that supplies the left ventricle with blood gets blocked, so that localized area of heart tissue doesn’t get enough blood and oxygen; that damage is localized to that left ventricle. Shock is like ischemia, but on a global scale. In other words, it’s a circulatory failure of the whole body; blood flow to tissues is dangerously low, which leads to cellular injury, possibly damages multiple organs, and can even lead to multiple organ failure if not treated immediately.

Okay, so with shock, the body’s tissues aren’t getting enough oxygen via the blood, right? Normally, blood perfuses through tissue and delivers oxygen because there’s enough pressure in the circulatory system to push it through; so, blood pressure majorly affects the amount of blood perfusing through tissues.

Now, blood pressure is determined by two components: the resistance to blood flow in the blood vessels, which is affected by things like vessel length, blood viscosity, and vessel diameter; and the cardiac output, which is the volume of blood pumped by the heart through the body per minute. You can break that down into heart rate, or the number of beats per minute, multiplied by stroke volume, or the amount pumped out each beat. The stroke volume is found by taking the total volume of blood left over after contraction, which is called the end-systolic volume, and subtracting it from the total volume in the heart after filling, or the end-diastolic volume.

All right, keeping all this in mind, shock can be caused by many different things, but we can categorize the different types of shock into the three main categories with some subcategories. The first category is called hypovolemic shock. Hypo means “low,” vol refers to “volume,” and emia refers to the blood; thus, hypovolemic shock is shock induced by a low fluid volume of blood. This could be either non-hemorrhagic or haemorrhagic. Non-hemorrhagic means that the loss of fluid volume isn’t from bleeding. For example, if you were stranded in a desert and suffered severe dehydration, eventually your loss of fluid from sweating would reduce blood volume to the point that it wouldn’t be enough to supply your body’s organs, and you’d develop hypovolemic shock. Hecommorrhagic hypovolemic shock, on the other hand, is loss of blood volume through ruptured blood vessels; in other words, it’s loss of blood volume from bleeding. A loss of about 20% of your total blood volume, which is roughly one liter, can be enough to induce hypovolemic shock.