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Meg Surg Ch. 67 Shock
Terms in this set (38)
What is shock?
a syndrome characterized by decreased tissue perfusion and impaired cellular metabolism. This results in an imbalance between the supply of and demand for oxygen and nutrients. The exchange of oxygen and nutrients at the cellular level is essential to life.
what happens when cells experience hypo-perfusion?
When cells experience hypoperfusion, the demand for oxygen and nutrients exceeds the supply at the microcirculatory level.
What are the 4 main categories of shock?
cardiogenic, hypovolemic, distributive, and obstructive
When does hypovolemic shock occur?
Hypovolemic shock occurs after a loss of intravascular fluid volume. The volume is inadequate to fill the vascular space.
What are the 2 types of volume loss?
may be either an absolute or a relative volume loss.
What is absolute hypovolemia?
Absolute hypovolemia results when fluid is lost through hemorrhage, gastrointestinal (GI) loss (e.g., vomiting, diarrhea), fistula drainage, diabetes insipidus, or diuresis.
What is relative hypovolemia?
In relative hypovolemia, fluid volume moves out of the vascular space into the extravascular space (e.g., intracavitary space). This type of fluid shift is called third spacing.
What is one example of relative volume loss?
One example of relative volume loss is leakage of fluid from the vascular space to the interstitial space from increased capillary permeability, as seen in burns
What does a reduction on intravascular volume results in?
a decreased venous return to the heart, decreased preload, decreased stroke volume, and decreased CO. A cascade of events results in decreased tissue perfusion and impaired cellular metabolism, the hallmarks of shock
What does the patients response to acute volume loss depend on?
depends on a number of factors, including extent of injury, age, and general state of health. However, the clinical presentation of hypovolemic shock is consistent. An overall assessment of physiologic reserves may indicate the patient's ability to compensate.
How much loss can a patient compensate for?
A patient may compensate for a loss of up to 15% of the total blood volume (approximately 750 mL). Further loss of volume (15% to 30%) results in a sympathetic nervous system (SNS)-mediated response.
What does the SNS-mediated response result in?
results in an increase in heart rate, CO, and respiratory rate and depth. The stroke volume, central venous pressure (CVP), and PAWP are decreased because of the decreased circulating blood volume.
What do patients show during hypovolemic shock?
The patient may appear anxious, and urine output begins to decrease.
If hypovolemia is corrected by crystalloid fluid replacement at a certain time what happens?
If hypovolemia is corrected by crystalloid fluid replacement at this time, tissue dysfunction is generally reversible.
What happens if volume loss is greater than 30%?
If volume loss is greater than 30%, compensatory mechanisms may begin to fail and immediate replacement with blood products should be started. Loss of autoregulation in the microcirculation and irreversible tissue destruction occur with loss of more than 40% of the total blood volume.
What does it mean when RBC, HCT, and Hemoglobin are reduced?
This happens when: Hemorrhagic shock after fluid resuscitation when fluids other than blood are used.
What does it mean when RBC count, hemocrit and hemoglobin are increased?
Nonhemorrhagic shock caused by actual hypovolemia and hemoconcentration.
Why would RBC count, hematocrit and hemoglobin be normal?
Remains within normal limits in shock because of relative hypovolemia and pump failure and in hemorrhagic shock before fluid resuscitation.
What is the most important clinical manifestation in neurogenic shock?
hypotension (from the massive vasodilation) and bradycardia (from unopposed parasympathetic stimulation). The patient may not be able to regulate body temperature.
What is the pathophysiology of hypovolemic shock?
decreased circulating volume-> decreased venous return-> decreased stroke volume-> decreased cardiac output-> decreased oxygen supply -> cellular oxygen supply-> decreased tissue perfusion and then impaired cellular metabolism
What is spinal sock?
Spinal shock is a transient condition that is present after an acute spinal cord injury
What is anaphylactic shock?
Anaphylactic shock is an acute, life-threatening hypersensitivity (allergic) reaction to a sensitizing substance (e.g., drug, chemical, vaccine, food, insect venom). The reaction quickly causes massive vasodilation, release of vasoactive mediators, and an increase in capillary permeability. As capillary permeability increases, fluid leaks from the vascular space into the interstitial space.
What is sepsis?
a systemic inflammatory response to a documented or suspected infection
What is septic sock?
is the presence of sepsis with hypotension despite adequate fluid resuscitation, along with inadequate tissue perfusion resulting in tissue hypoxia.
How is shock categorized?
into three clinically apparent but overlapping stages: compensatory stage, progressive stage, and irreversible stage
What is the compensatory stage?
the body activates neural, hormonal, and biochemical compensatory mechanisms in an attempt to overcome the increasing consequences of anaerobic metabolism and to maintain homeostasis. The patient's clinical presentation begins to reflect the body's responses to the imbalance in oxygen supply and demand.
What is one of the classic signs of sock?
One of the classic signs of shock is a drop in blood pressure (BP), which occurs because of a decrease in CO and a narrowing of the pulse pressure. The baroreceptors in the carotid and aortic bodies immediately respond by activating the SNS.
What does the SNS do when it is activated by the baroreceptor response?
The SNS stimulates vasoconstriction and the release of the potent vasoconstrictors epinephrine and norepinephrine. Blood flow to the most essential (vital) organs, the heart and brain, is maintained, while blood flow to the nonvital organs, such as kidneys, GI tract, skin, and lungs, is diverted or shunted.
How does the myocardium respond to the SNS simulation?
The myocardium responds to the SNS stimulation and the increase in oxygen demand by increasing the heart rate and contractility. However, increased contractility increases myocardial oxygen consumption. The coronary arteries dilate inan attempt to meet the increased oxygen demands of the myocardium.
What happens to the lung when the body is in shock?
Shunting blood away from the lungs has an important clinical effect in the patient in shock. Decreased blood flow to the lungs increases the patient's physiologic dead space.
What is physiologic dead space?
Physiologic dead space is the anatomic dead space (the amount of air that will not reach gas-exchanging units) and any inspired air that cannot participate in gas exchange.
What is the clinical result of an increase in dead space ventilation?
The clinical result of an increase in dead space ventilation is a ventilation-perfusion mismatch. Some areas of the lungs that are participating in ventilation will not be perfused because of the decreased blood flow to the lungs. Arterial oxygen levels will decrease, and the patient will have a compensatory increase in the rate and depth of respirations
What happens to the GI tract as a result of shunting of the blood from other organ systems?
The shunting of blood from other organ systems also results in clinically important changes. The decrease in blood flow to the GI tract results in impaired motility and a slowing of peristalsis. This increases the risk for the development of a paralytic ileus.
What happens to the skin as a result of decreased blood flow?
Decreased blood flow to the skin results in the patient feeling cool and clammy.
What is an exception to the cool and clammy skin?
The exception is the patient in early septic shock who may feel warm and flushed because of a hyperdynamic state.
What happens to decreased blood flow to the kidneys?
Decreased blood flow to the kidneys activates the renin-angiotensin system. Renin stimulates angiotensinogen to produce angiotensin I, which is then converted to angiotensin II. Angiotensin II is a potent vasoconstrictor that causes both arterial and venous vasoconstriction. The net result is an increase in venous return to the heart and an increase inBP.
What does angiotensin II also stimulate?
Angiotensin II also stimulates the adrenal cortex to release aldosterone. This results in sodium and water reabsorption and potassium excretion by the kidneys. The increase in sodium reabsorption raises the serum osmolality and stimulates the release of antidiuretic hormone (ADH) from the posterior pituitary gland.
What does ADH do?
increases water reabsorption by the kidneys, thus further increasing blood volume. The increase in total circulating volume results in an increase in CO and BP.
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