This is the first in a series of posts, that will go over the five types of shock. Covering the basics of pathophysiology, presenting signs and symptoms, and the course of treatment. Before we can understand the various types of shock, we must first have a foundation on which to build. What follows is a review of anatomy, physiology, and the general pathophysiology of shock.
Shock is a serious life threatening medical emergency, and can be caused by several conditions.No mater what the cause , the end result will be Hypoperfusion of the cells (Shock) and if uncorrected, death. The cells of the body require a constant supply of Oxygen and other nutrients, as well as a content removal of Carbon dioxide, and other waist products in order to functions efficiently and maintain Homeostasis. For normal perfusion to occur, three systems must be intact: The pump (the heart) The pipes (the blood vessels) and The fluid ( the blood ).
The pump is what “pushes” the oxygenated blood from the lungs, and circulates it to the cells, tissues and organs of the body, where oxygen and other nutrients are exchanged for carbon dioxide and other waist products, which are then carried back to the lungs and other organ systems (such as the liver and kidneys) to be removed. If the pump is too slow, as in Bradycardia, or pumps too fast or inefficiently as in Supra-ventricular tachycardia or other arrhythmias, or if the pump is not strong enough to circulate the blood effectively, hypoperfusion may occur.
The pipes are what carries the blood to the cells and tissues of the body. If there is a obstruction in the pipe as in a Thrombus or Embolism. Blood flow and thus perfusion beyond the point of occlusion will decrease. If the integrity of the pipe is lost either through Trauma, a ruptured Aneurysm or increased vascular permeability resulting in a decrease of circulating volume, there will be less blood available to transport nutrients and waist. Also, excessive vasodilatation can lower blood pressure resulting in hypoperfusion.
The fluid is what holds and transports the nutrients and waist products. The blood contains erythrocytes (Red blood cells) which have a protein called Hemoglobin. Oxygen molecules attach them selfs to the hemoglobin so that they may be carried throughout the body. In the lungs deoxygenated blood travels through the capillaries surrounding the alveoli. Through the proses of diffusion, oxygen which is at a higher concentration in the alveoli, crosses the alveoli-capillary membrane into the blood where there is a lesser concentration of oxygen. At the same time, carbon dioxide which is at a higher concentration in the blood, crosses the capillary-alveoli membrane into the alveoli, where it is removed during exhalation. The oxygen molecules bind to the hemoglobin and is transported throughout the body. The blood enters capillaries within the tissue where again through diffusion oxygen is exchanged from the blood to the tissue, and carbon dioxide form the tissue to the blood. The blood, now deoxygnated returns the the lungs where the process repeats it self.
If there is a decrease in circulating volume as with blood loss and or dehydration, there will be less blood to transport nutrients and waist products. Also conditions effecting the red blood cell and its hemoglobin such as anemia and carbon monoxide poisoning can decrease the amount of oxygen that can be transported to the tissues, resulting in hypoperfusion. As you can see, a malfunction in any one of the systems can result in shock.
During hypoferfusion the cells become ischemic and switch from a Aerobic metabolism ( with oxygen ) to a Anaerobic metabolism ( without oxygen ). The primary energy source for the cell is glucose. In a Aerobic metabolism glucose is broken down ( Glycolysis ) which produces pyruvic acid which is further broken down into carbon dioxide, water, and energy (ATP). However during hypoperfusion the cell switches to an Anaerobic metabolism (without oxygen) where only the first stage of glycolysis is possible. This produces very little energy and with out oxygen pyruvic acid can not be broken down, and instead is converted into lactic acid which accumulates in the cell, lowering the cellular pH. The acidosis reduces the ability of hemoglobin to transport oxygen which compounds the problem. The lower intracellular pH causes the membranes of the lysosomes and other organelles to rupture releasing enzymes that damage the Sodium-Potassium pump which causes an influx of sodium and fluid, which causes cellular edema, which causes the cell to rupture releasing the lysosomal enzymes, lactic acid, hydrogen and other cellular contents into the interstitial and intravenous space causing further acidosis.
The body has various ways of compensating during shock. However if the cause of the shock is not corrected the compensatory mechanisms will become overwhelmed and fail, causing death. A decrease in blood pressure is detected by the Baroreceptors which activates systems to reestablish normal blood pressure. The sympathetic nervous system stimulates the adrenal glands to secrete epinephrine and nor-epinephrine which causes an increase in heart rate and contractile strength, as well as vasoconstiction all of which increase blood pressure.
In the kidneys, the detection of low blood pressure stimulates the Renin-Angiotensin-Aldosterone system. The enzyme renin is released by the kidneys. Renin acts on a plasma protein called angiotensin, which is converted into angiotensin I. Angiotensin I is converted into angiotensin II in the lungs by angiotensin converting enzyme (ACE). Angiotensin II is a potent vasoconstrictor which increases peripheral vascular resistants which increases blood pressure. Angiotensin II also stimulates the sympathetic response, and stimulates the pituitary glands secretion of antidiuretic hormone (ADH) which causes the kidneys to retain electrolytes and fluid. The hormone Aldosterone which is secreted by the adrenal cortex also stimulates the kidneys to reabsorb sodium potassium and water, increases the intravascular volume. As the blood pressure slowly decreases, so does the intravascular osmotic pressure, which causes fluid to shift from the interstitial space and the intracellular space, into the intravascular space to increase the circulating volume.
Respirations increase both in rate and depth. This increases the amount of oxygen available, and attempts to eliminate the build up of toxins from the anaerobic metabolism. If there is blood loss due to hemorrhage, the damaged blood vessels constrict slowing the amount of blood flow and the clotting and coagulation cascade begins. If the conditions causing shock are too serious, or progress too rapidly, the body will be unable to keep up with the demands and move into a state of decompensation.
The heart rate and respirations will increase dramatically. The skin will be very pale cool and diaphoretic. Peripheral pulses will be weak or absent. Urine out put will low or almost none. Level of conciseness will decease from agitated to unresponsive, and the body moves into irreversible shock. At this point the blood pressure is so low the heart and brain become hypoperfused. The hypoxic heart will tire quickly, possibly becoming arrhythmical before failing. The Vasomotor, cardiac, and respiratory centers of the brain will become ischemic and die causing the cessation of compensatory efforts. The blood will begin to pool and coagulate in the capillaries. Because of the loss of vasomotor control from the brain and the low blood pH, capillaries become permeable and the pre and post capillary sphincters relax causing wash out sending microemboli and toxins into the tissues and systemic circulation, and the body dies. Once the body moves into the late stages of decompensation and irreversible shock, resuscitation and survivability are extremely low.
Now that we have all that taken care of, we can move in to the various types of shock, and what to do about them. Remember that for a patient experiencing shock, the best treatment is always safe and efficient transport to an appropriate facility.
In part two, the basic pathophysiology, signs and symptoms, and treatment of Cardiogenic Shock. <—- Read Here
