Emergency Care Textbook Professional Responders-part-8.pdf

8 Shock Key Content Pathophysiology of Shock...... Types of Shock...................... Stages of Shock....................... Care for Shock......................... 164 165 165 166 Introduction All cells of the body require oxygen. Under normal circumstances, the circulatory system carries this ox...

8 Shock Key Content Pathophysiology of Shock...... Types of Shock...................... Stages of Shock....................... Care for Shock......................... 164 165 165 166 Introduction All cells of the body require oxygen. Under normal circumstances, the circulatory system carries this oxygen to the body’s tissues. The supply of oxygen to the cells is called perfusion: If a patient has good perfusion, the patient’s tissues are receiving the oxygen they need. An injury or sudden illness can interrupt normal body functions. In cases of minor injury or illness, this interruption is brief and the body is able to quickly compensate and resume normal operation. With more severe injuries or illnesses, SHOCK Three conditions are necessary for maintaining perfusion: 1. The heart must be functioning effectively. 2. An adequate quantity of blood must be circulating in the body. 3. The blood vessels must be able to control blood flow by dilating and constricting. 163 however, the body may be unable to adjust, and the body’s tissues may stop receiving the oxygen they require. When vital organs such as the heart, lungs, brain, and kidneys do not receive oxygen-rich blood, their ability to function effectively is compromised. This triggers a series of responses that results in a combination of signs and symptoms known as shock. These responses are the body’s attempts to maintain adequate blood flow to the vital organs and prevent them from shutting down. PATHOPHYSIOLOGY OF SHOCK SHOCK Shock is a condition defined by its effects. There are many causes of shock, ranging from emotional distress to anaphylaxis, but the outcome is the same: Blood does not circulate effectively to the body’s tissues. The causes of shock can be categorized differently for different purposes, but at the foundation, shock is caused by one or more of the following problems: 164 2. The quantity of blood circulating in the body is too low. A healthy body that is not stressed can compensate for some decrease in blood volume. When a person donates blood, for example, he or she can lose 500 mL (17 oz.) of blood in 10 or 15 minutes without causing any stress to the body. To compensate for the lost volume, the body reabsorbs fluid from the kidneys, lungs, and intestines and immediately begins to manufacture new blood cells. When blood is lost due to a severe injury, however, the blood loss may be greater or more rapid, and the body’s ability to compensate may be overwhelmed. This is often referred to as hypovolemic shock. 1. The heart is not functioning effectively. When the heart is not functioning effectively, blood will not circulate properly even if the rest of the circulatory system is working normally. A patient in cardiac arrest, for example, will rapidly go into shock. This is often referred to as cardiogenic shock. 3. The blood vessels are unable to constrict effectively. Normally, blood vessels control the flow of blood to different areas of the body by constricting and dilating to change the pressure of the blood. This process ensures that blood reaches the areas of the body that need it most. Injury, illness, toxins, and infection can all cause blood vessels to lose their ability to constrict, causing a drop in blood pressure (Figure 8–1). Although the actual volume of blood in the body does not change, the capacity of the vascular system itself increases as the vessels dilate, so the same volume of blood is under lower pressure. This is often referred to as distributive shock. It may also be DILATED NORMAL Figure 8–1: Injury or illness can cause blood vessels to lose their ability to change size, causing a drop in blood volume. called relative hypovolemic shock because the volume of blood is low relative to the dilation of the vascular system. Psychogenic Shock There are many types of shock, all of which create one or more of the three conditions described above. The following examples are most common, but any condition that causes a sudden drop in blood pressure can result in shock. Psychogenic shock is a form of relative hypovolemic shock (distributive shock) that results from emotional stress. When a person receives upsetting news, for example, the body’s blood vessels can dilate, allowing blood to pool in the extremities rather than circulating throughout the body. The effect is similar to that of neurogenic shock, but the cause is psychological rather than neurological in origin. CARDIOGENIC SHOCK Septic Shock Types of Shock Cardiogenic shock is the result of a problem with the heart itself. A patient experiencing cardiac arrest, for example, will typically be in cardiogenic shock because the heart is not pumping blood through the circulatory system. OBSTRUCTIVE SHOCK Obstructive shock occurs when something physically prevents the heart from filling or emptying effectively, even if it is otherwise pumping normally. This may be caused by a pulmonary embolism, for example, or a tension pneumothorax. Septic shock is a form of relative hypovolemic shock (distributive shock) that occurs as the result of a severe infection. As the infection progresses, it releases toxins into the blood that cause the blood vessels to dilate, allowing blood to pool in the lowest parts of the body. Anaphylactic Shock Anaphylactic is a form of true hypovolemic shock that occurs as the result of an extreme allergic reaction (anaphylaxis). It increases the permeability of the body’s blood vessels, allowing fluid to leech out of the circulatory system, thereby reducing the volume of circulating blood in the vascular system. HYPOVOLEMIC SHOCK Hemorrhagic Shock Hemorrhagic shock is the most common type of true hypovolemic shock, occurring when the vascular system rapidly loses a large quantity of blood due to hemorrhaging. Neurogenic Shock Neurogenic shock is a form of relative hypovolemic shock (distributive shock) that occurs when the nervous system loses its ability to control the constriction of the body’s blood vessels, causing them to dilate. The cause is usually an injury to the brain or spine. STAGES OF SHOCK A patient in shock will go through three distinct stages: compensated, decompensated, and irreversible (see Figure 8–2). Compensated Shock When the body initially detects that perfusion is low, it attempts to restore normal circulation through a series of compensatory mechanisms. The blood vessels constrict, focusing blood towards vital organs and helping to sustain blood pressure. This reduces the amount of blood circulating to the less critical tissues in the extremities and skin, which causes the skin to become pale and cool. A patient’s capillary refill will slow during this stage of shock as less blood travels to the extremities. The heart beats more rapidly to increase blood flow. As a result, respiration must also increase so that the level of oxygen in the blood is not reduced. These changes in pulse and respiration SHOCK Hypovolemic shock is the general term for shock that results from an insufficient volume of blood circulating in the body. This is often subdivided into true hypovolemic shock, in which the body’s total blood volume is actually reduced, and relative hypovolemic shock, in which dilated blood vessels cause blood to pool in extremities rather than circulating effectively (also called distributive shock). 165 Hemodynamic State Hemodynamic State PROGRESSION OF SHOCK Heart Rate Blood Pressure (BP) Respiration Rate Level of Responsiveness (LOR) Heart Rate Blood Pressure (BP) Respiration Rate Level of Responsivness (LOR) Normal Function Compensated Shock Decompensated Shock Irreversible Shock Decompensated Shock Irreversible Shock Figure 8–2: The effects of shock over time. Normal Function Compensated Shock can often be detected during the primary assessment, but there tends to be little change in blood pressure during the compensated stage. A patient in compensated shock may or may not be sweating, depending on the cause of shock and the individual patient’s reaction to it. The patient may be apprehensive or anxious. stage, the damage to the brain, heart, and other tissues is so extensive that the patient will not survive regardless of any interventions performed. Decompensated Shock Early recognition and care for serious injuries and conditions (e.g., controlling a hemorrhage) will minimize the effects of shock (Figure 8–3). Help the patient rest comfortably in the recovery or supine position. A supine position will help increase blood flow to the patient’s vital organs, especially the brain. Elevating the patient’s feet 20 to 30 cm (8 to 12 in.) can help improve blood flow to the head and torso. The supine position with feet elevated is sometimes referred to as the Trendelenburg position or shock position. This is not indicated if the patient has experienced trauma that is putting stress on the cardiovascular system or if the patient’s systolic blood pressure is over 100 mmHg. If the body’s compensatory mechanisms are unsuccessful, the body’s tissues begin to become hypoxic. At this stage, shock becomes lifethreatening, though immediate interventions may reverse the effects. Decreased oxygen flow to the brain can cause the patient to become confused, listless, or unresponsive, and the heart and other organs begin to work less effectively. Respiration will become slow, shallow, and irregular, and the pulse will become weak and rapid. Blood pressure will drop, and the body’s temperature will decrease. Cyanosis may occur around the lips and eyes due to the prolonged lack of oxygen, and the patient’s pupils will dilate. Diaphoresis (excessive sweating) and extreme thirst are common. SHOCK Irreversible Shock 166 Without intervention, decompensated shock progresses to irreversible shock. The body’s vascular system becomes unable to maintain its internal pressure, so blood pools in the extremities, away from the vital organs. At this CARE FOR SHOCK Help the patient maintain a normal body temperature (Figure 8–4). This may involve controlling environmental factors, such as turning off air conditioning. Avoid giving the patient anything to eat or drink, even if he or she is thirsty. The patient’s condition may be severe enough to require surgery, in which case it is better to have an empty stomach. SHOCK: THE DOMINO EFFECT Although shock can have many causes, the following example shows how it can progress through a chain of cause and effect from an initial injury to the ultimate death of the patient. This is an example of hemorrhagic shock. Initial Cause 1. An injury causes a hemorrhage (severe bleeding). Compensated shock 2. T  he heart attempts to compensate by beating faster, resulting in a rapid pulse (tachycardia). This causes more blood loss. As the body’s blood volume continues to drop, the pulse becomes weaker. 3. The increased workload on the heart results in an increased oxygen demand. Therefore, respiration becomes faster (tachypnea). 4. T  o maintain circulation of blood to the vital organs, blood vessels in the arms and legs constrict, causing the skin to become pale and cool. In response to the stress, the body perspires heavily. Decompensated shock 5. S ince tissues in the extremities are now without oxygen, their cells start to die. The brain responds by restoring blood flow to the arms and legs in an attempt to balance the oxygen needs of the extremities with those of the vital organs. 6. T  he vital organs are now lacking adequate oxygen. The heart tries to compensate by beating even faster, increasing blood loss. Irreversible shock 7. W  ithout oxygen, the vital organs stop functioning effectively. As the brain tissues become hypoxic, the person becomes restless and drowsy and eventually loses responsiveness. The pulse becomes chaotic, and soon the patient enters cardiac arrest. When the heart stops, respiration stops as well. The general care you provide in any emergency will help the patient’s body adjust to the stresses imposed by the injury or illness, preventing or slowing the progression of shock. A patient presenting the signs and symptoms of shock should be rapidly transported to an advanced care facility, regardless of the cause. Because hypoxia is the underlying condition caused by shock, high-flow supplemental oxygen is indicated. Figure 8–3: Care for shock includes providing care for the ABCs. Figure 8–4: Help the patient maintain a normal body temperature. SHOCK 8. T  he body’s continuous attempt to compensate for severe blood loss eventually results in death. 167 SUMMARY TYPES OF SHOCK Type Description Septic Severe infections create poisons in the body that cause blood vessels to dilate, reducing blood pressure and causing blood to pool in extremities. Hypovolemic Relative Psychogenic True Factors such as emotional stress cause blood vessels to dilate, reducing blood pressure and causing blood to pool in extremities. Neurogenic Failure of the nervous system to control the size of blood vessels causes them to dilate; this occurs with brain or nerve injuries. Hemorrhagic Loss of blood due to internal or external hemorrhage results in reduced blood volume. Obstructive Obstruction of blood flow outside of the heart prevents it from filling or emptying effectively. Cardiogenic Failure of the heart to effectively pump blood to all parts of the body; occurs with heart attack or cardiac arrest. Anaphylactic Life-threatening allergic reaction to a substance increases blood vessel permeability, allowing fluid to move out of the circulatory system and thereby decreasing blood volume. Three Underlying Causes of Shock 1. The heart is not functioning effectively. 2. The quantity of blood circulating in the body is too low. 3. The blood vessels are unable to constrict effectively. STAGES OF SHOCK SHOCK Stage 168 Description Effects Compensated shock The body detects low perfusion and activates compensatory mechanisms. Constricted blood vessels Pale and cool skin Tachycardia Tachypnea Possible sweating Decompensated shock Compensatory mechanisms are unsuccessful: Body tissues begin to become hypoxic. Confusion, listlessness, unresponsiveness Slow, shallow, irregular respiration Rapid, weak pulse Lowered blood pressure Lowered body temperature Dilated pupils Diaphoresis (excessive sweating) and thirst Possible cyanosis Irreversible shock The body is unable to maintain blood pressure: Blood pools in extremities, away from vital organs. The brain and heart are irreversibly damaged: Death is imminent. Unresponsiveness Chaotic pulse progressing to cardiac arrest Respiratory arrest