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MI p. 311
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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.
Shock refers to a failure in tissue perfusion affecting the whole body, putting tissues and organs at risk for injury and ultimately organ failure. Causes of shock are classified into three main categories with some subcategories.
First, there is hypovolemic shock which happens when dehydration or hemorrhage reduces the volume of blood in the blood vessels. Another category is cardiogenic shock, which happens when a direct injury like a heart attack or an obstruction like a pericardial effusion prevents the heart from pumping blood efficiently. The third category is distributive shock, which occurs when something like an allergic reaction or damage to the nervous system - called neurogenic shock causes the blood vessels to vasodilate and become leaky which reduces the resistance and lowers the blood pressure.
Common symptoms of shock include low blood pressure, tachycardia, cold and clammy skin, confusion and disorientation, and blue or gray skin, especially on the extremities. Shock treatment depends on the underlying cause but typically involves restoring blood flow to the vital organs through measures such as fluid resuscitation, medications, or respiratory support.
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