Wilderness and Rescue Medicine 8th Edition

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Wilderness and Rescue Medicine

when the blood vessels lose muscle tone and dilate due to injury or illness. Cardiogenic shock is caused by inadequate pumping action of the heart. The basic problem caused by all three is inadequate perfusion pressure resulting in inad-

Early on, perfusion is maintained to the vital organs of the body core through this combina- tion of increased cardiac output and respiratory effort and shell/core effect. It is augmented by fluid shifting into the blood from body cells and tissues, although this compensatory mechanism is difficult to observe directly. Dizziness may occur with standing or sitting up as brain perfusion is temporarily impaired because the circulatory system is unable to compensate quickly for the effects of gravity. If you can measure blood pressure, you may observe that the compensatory mechanisms keep it near normal in the very early stages of volume loss. Because the brain is still enjoying near-normal perfusion, the patient may exhibit only mild mental status changes. This stage is called compensated volume shock. This serves to remind us that a single measure- ment of blood pressure alone is not particularly useful. It offers only an approximation of perfu- sion pressure at one place on the upper arm or leg. It does not reliably indicate low blood volume or the status of cellular oxygenation. Unless you are alert to the entire vital sign pattern for volume shock, you may miss the diagnosis until it is too late. In the long-term care situation, monitoring urine output is a good way to monitor the status of the circulatory system. Reduced blood volume will result in greatly reduced urine output as the kidneys do their part to conserve fluid. The urine that is produced will be more concentrated and appear dark yellow or brown. These are important signs to watch for when you’re concerned about the slow loss of fluid with burns, vomiting and diarrhea, and other forms of dehydration. As volume shock progresses and the compen- sation mechanisms are overwhelmed, oxygen- ation and perfusion of the brain will be further reduced resulting in more profound brain failure . The patient’s level of consciousness will decrease and the brain’s ability to control the circulatory and respiratory systems will become impaired. Cardiac output will decrease as heart muscle is deprived of oxygen. Circulatory collapse and

equate oxygenation. Volume Shock

A history of trauma sufficient to cause severe internal or external bleeding should alert you to look for evidence of volume shock. A more com- mon mechanism in the wilderness environment, however, is dehydration from diarrhea, vomiting, or sweating. Regardless of the mechanism, the problem is the same: inadequate perfusion pres- sure due to low blood volume. Severe external bleeding is usually easy to spot. But in cases where fluid loss is not so obvious, watching the body compensate may be the only way to detect the onset of volume shock from slow internal bleeding or dehydration. We observe compensation by measuring vital signs.

General Principles

Volume Shock Inadequate perfusion pressure due to loss of blood volume

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Mechanisms: • Bleeding; internal or external • Dehydration: - sweating - diarrhea and vomiting - prolonged fluid restriction - excessive urination (e.g. , polyuria in diabetes)

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As shock develops, the first vital sign changes to occur are early mental status changes and shell/ core effect in which the body shunts blood to the core where vital organs are located. The effects are observed externally as mild anxiety and cool, pale skin and mucous membranes. A little fur- ther into the pattern compensatory efforts will include an increase in pulse and respiratory rate. This accounts for the classic symptoms of shock described as cool, pale skin and rapid pulse and respiration.