lowered, the peripheral pulse may be absent. The pulse rate in hemorrhagic shock may reach 140 or higher. An exception is neurogenic shock, where the pulse rate is slowed, often below 60.
7. The blood pressure is usually lowered in moderately severe shock; the systolic pressure drops below 100 while the pulse rises above 100. The body is compensating for circulatory fluid loss by peripheral vasoconstriction. This process tends to maintain the blood pressure at nearly a normal level despite moderately severe loss of circulating blood volume. A point comes, however, when decompensation occurs, and a small additional loss will then produce an alarming and sudden fall in blood pressure.
8. There may be nausea, vomiting, and dryness of the mouth, lips, and tongue.
9. Surface veins may collapse. Veins normally visible at the front of the elbow, forearms, and the back of the hands will be hard to distinguish.
10. There are frequent complaints of thirst. Even the severely wounded may complain of thirst rather than pain.
11. The kidneys may shut down. Urine formation either ceases or becomes greatly diminished if the systolic blood pressure falls below 80 for long periods of time.
12. The person may faint from inadequate venous blood return to the heart. This may be the result of a temporary gravitational pooling of the blood associated with standing up too quickly.
This condition is also known as oligemic or hematogenic shock. The essential feature of all forms of hypovolemic shock is loss of fluid from the circulating blood volume, so that adequate circulation cannot be maintained to all parts of the body.
In cases where there is internal or external hemorrhage due to trauma (hemorrhagic shock) there is a loss of whole blood, including red blood cells. The body tends to restore the circulatory volume by supplying fluid from the body tissues. There is a resulting progressive fall in the hematocrit (ratio of red blood cells to plasma) and in the red blood cell count due to hemodilution, However, since hemodilution is not an excessively rapid process, the hematocrit is a poor indicator of acute blood loss, i.e., less than 24 hours old,
In burn shock, on the other hand, there is a progressively increased hematocrit and red blood cell count due to hemoconcentration from loss of the plasma fraction of the blood into and through the burned area.
A third form of hypovolemic shock occurs in cases of severe diarrhea and vomiting, where body fluids and electrolytes (sodium, potassium, and chloride) are lost. This also contributes to a decrease in circulating blood volume.
Neurogenic shock, sometimes called vasogenic shock, results from the disruption of autonomic nervous system control over vasoconstriction. Under normal conditions the autonomic nervous system keeps the muscles of the veins and arteries partially contracted. At the onset of most forms of shock, further constriction is signaled. However, the vascular muscles cannot maintain this contraction indefinitely. A number of factors, including increased fluid loss, central nervous system trauma, or emotional shock, can override the autonomic nervous system control. The veins and arteries immediately dilate, drastically expanding the volume of the circulatory system, with a corresponding reduction of blood pressure.
Simple fainting (syncope) is a variation of neurogenic shock. It often is the result of a temporary gravitational pooling of the blood as a person stands up. As the person falls, blood again rushes to the head, and the problem is solved. It may also be induced by fear or horror, which override the autonomic nervous system control.
Other variations of neurogenic shock that are important to the corpsman are shell shock and bomb shock. These are psychological adjustment reactions to extremely stressful wartime experiences and do not relate to the collapse of the cardiovascular system. Symptoms range from intense fear to complete dementia and are manifestations of a loss of nervous control. Care is limited to emotional support and evacuation to the care of a psychiatrist or psychologist.
Cardiogenic shock is caused by inadequate functioning of the heart, not by loss of circulating blood volume. If the heart muscle is weakened by disease or damaged by trauma or lack of oxygen, as in cases of pulmonary disease, suffocation, or