Shock may be defined in physiological as well as practical terms. Practically speaking the cardiovascular system in shock is no longer able to deliver a blood volume sufficient to vital functions. In physiological terms, due to cardiovascular insufficiency oxygen transport is no longer adequate to support cellular respiration.
Shock is best treated if recognized early in its course. This requires attention to the early signs of shock. The early signs of shock include anxiety, restlessness, and agitation. A patient who appears non-compliant or difficult to examine due to these three signs may be in early shock and in need of urgent acls support. It is also important to remember that in early shock, blood pressure may be normal because especially in younger patients, vasoconstriction compensates and hypotension appears late in the process. Tachycardia is a more sensitive indicator of shock and is manifest with a 12-15 percent or more blood volume deficit. However it can also be misleading because in certain types of shock a tachycardia may also be suppressed. This may be due to vagal response or certain medications on board. Examining the patient for orthostatic changes in pulse and blood pressure also serves as a sensitive indicator of early shock.
In general however a patient with unexplained anxiety, agitation, restlessness, with tachycardia or hypotension often exhibiting pallor, cool clammy skin, poor capillary refill, poor urine output, and change in mental status may be presumed to be in shock until proven otherwise. It is better to go forward with the presumed diagnosis of shock than to temporize until the condition worsens. This is because early diagnosis of the cause of shock is important for effective treatment.
The condition known as shock can have several causes. There is a particular presentation common to all forms of shock because the final common pathway of the various causes of shock is cardiovascular decompensation, poor delivery of blood and its oxygen passenger to the tissue level. This poor delivery can be the result of impaired pump function, decreased blood volume, loss of vascular tone.
The first general cause of shock, impaired pump function, pertains to the region of the heart. Cardiogenic shock - In cardiogenic shock the heart is damaged perhaps due to a myocardiopathy, a disease of the heart muscle, or an ischemic infarction and is unable to maintain an adequate cardiac output. The pump mechanism may be damaged in other ways in cardiogenic shock. The heart valves may be diseased, cardiac tamponade or restrictive pericarditis may impair the pumping action of the heart. Whatever the abnormality the heart, for all intents and purposes, is unable to pump adequate volumes of blood. In the emergency setting this cause of shock must be recognized and measures taken. One should look for chest pain, age and history of heart disease, absence of other causes, pulmonary edema, abnormal heart sounds, neck vein distention in an effort to diagnose cardiogenic shock. A tension pneumothorax, cardiac tamponade, or massive pulmonary embolism can all impair the pump mechanism of the heart by preventing adequate filling of the heart. This is known as obstructive shock. An arrhythmia such as a bradycardia or tachycardia can also present as shock by decreasing the efficiency of the heart.
The second general cause of shock, a decrease in blood volume, is known as hypovolemic shock. This form of shock or impaired tissue perfusion and oxygenation can be due to external blood loss from a penetrating wound, or internal blood loss due to blunt trauma into the thorax, abdomen, cranium in children, or hip fractures in adults. Leaking aortic aneurysms should be kept in mind when dealing with sighs of hypovolemic shock especially in middle aged and elderly adults. A ruptured ectopic pregnancy is a common cause of shock in a female patient of child-bearing age. In addition to loss of whole blood as described, shock can also occur in the presence of profound dehydration and fluid loss. This may occur with vomiting and/or diarrhea, and burns.
The third category of shock, loss of vascular tone, is due to loss of systemic vascular resistance which is essential to maintaining a blood pressure. The term distributive shock refers to this cause and includes septic shock, anaphylactic shock, neurogenic shock, shock due to vasodilator drugs, and acute adrenal insufficiency. In these conditions the blood volume while not in itself depleted is distributed inefficiently due to poor vascular tone. Neurogenic shock - decreased systemic vascular resistance may be found in neurogenic shock. Neurogenic shock is due to the loss of vascular tone which occurs when the spinal cord is injured. The peripheral arteriovenous system no longer constricts normally making the patient relatively hypovolemic. To a certain extent this can be treated by fluid therapy. This is a form of shock which often does not present with tachycardia because the damage interrupts sympathetic nerve stimulation of both the heart and vasculature. Septic shock - Impaired vascular tone also occurs in septic shock. Bacteria produce toxins which cause widespread vascular dilatation and loss of fluid into the tissues. The heart may still be pumping adequately in septic shock and still be unable to support an adequate blood pressure. There may be signs of sepsis or bacteremia in septic shock such as skin mottling, hot dry skin, petechial or hemorrhagic rash, source of infection such as an abcess, and fever. Another cause of shock due to loss of vascular tone is ingestion of certain medications and poisons especially vasodilator drugs. This form of shock can be recognized on the basis of history, and blood studies. Anaphylactic Shock - a dramatic allergic reaction that causes shock is anaphylaxsis. Tachycardia and hypotension are signs of anaphylaxis. And the patient may have a history of recent use of medications or bee, or wasp sting.
All patients who present in shock are treated with attention to the A,B,C's of ACLS protocol and ATLS in suspected trauma. It is important to properly position the patient, apply cardiac and oxygen saturation monitors and administer oxygen, perform routine laboratory studies, ekg and chest xray, monitor blood pressure, and urine output. The airway must be immediately evaluated and secured, breathing facilitated by positioning and adjunctive measures if necessary, and circulation and the general cause of shock assessed with the purpose of initiating appropriate fluid therapy.
Cardiogenic shock - cardiogenic shock is caused by the failure of the pumping mechanism of the heart. In cardiogenic shock treatment rests on the correct diagnosis of the pump failure, fluids must be used very carefully to offset the development of pulmonary edema. Medications such as norepinephrine, dopamine, and dobutamine may be used to increase cardiac output and effect systemic vascular resistance. Pulmonary edema which often occurs in cardiogenic shock requires the use of diuretics such as Furosemide (Lasix).
Cardiac Valvular disease - There are four one-way valves in the heart. These are the aortic, pulmonic, mitral and tricuspid. If these are damaged by disease the pump mechanism of the heart will be seriously impaired. This form of shock requires surgical intervention.
Cardiac tamponade - When fluid fills the closed sac around the heart called the pericardium, the heart can't expand and fill adequately in diastole with a resultant decrease in cardiac output. This can be due to trauma as well as some medical conditions. Pericardiocentesis must be performed to remove some of the fluid if the patient is in shock due to percardial tamponade.
Tension pneumothorax - In tension pneumothorax there is a collapsed lung and leakage of air into the pleural cavity which presses the lung and mediastinum over to one side. This mediastinal compression can impair the pump mechanism and cause shock. There may be decreased breath sounds on the affected side, and tracheal deviation to the opposite side. Treatment is thoracentesis with a 20 guage needle and withdrawal of 50 cc's of air with a syringe, and insertion of a chest tube which usually gives prompt reversal of symptoms.
Massive pulmonary embolism - A blood clot may travel to the lung from another part of the body. If large enough it may impede the flow of blood from the lung to the heart and this presents as shock. Treatment often requires surgical intervention.
Cardiac arrhythmias - Arrhythmias which cause shock are the profound bradycardias and rapid tachycardias. Bradycardias may require pacing and tachycardias in patients with unstable symptoms and signs such as those of shock require dc cardioversion.
Hypovolemic shock - Bleeding internal and external, and other forms of hypovolemic shock may be considered together in discussing initial treatment. ATLS protocol calls for attention to ABC's, compression of visible bleeding sites, two large bore cannulas and rapid iv infusion of crystalloids and packed red blood cells as indicated, In addition a search must be made for internal bleeding with chest xray, pelvic xray in suspected pelvic fracture, and peritoneal lavage. Ruptured ectopic pregnancy, leaking aortic aneurysm, splenic rupture all require urgent surgical intervention. In fluid loss due to vomiting and/or diarrhea attention to electrolyte and acid-base status is also important.
Burns - patients with extensive burns require aggressive fluid management according to various replacement protocols.
Neurogenic shock - this is due to a relative hypovolemia secondary to peripheral vascular vasodilatation. It is managed by fluid administration and pressors if needed.
Septic shock - septic shock is treated by fluid management, use of pressors and of course broad spectrum antibiotics after initial septic work-up.
Anaphylactic shock - epinephrine, antihistamines, and corticosteroids as well as administration of fluids are essential to the treatment of this devastating form of shock.
Fluid third spacing-internal shifts of large volumes of fluid from the blood vessels into the tissues. Acute Pancreatitis is an example of fluid third spacing. In acute pancreatitis, the pancreas, a digestive gland located near the stomach and duodenum becomes swollen and hemorrhagic. If severe, enough fluid is third-spaced, that is, leaked into the soft tissues, to cause a form of shock termed refractory hemorrhagic shock. Ascites which is a buildup of fluid in the abdominal cavity is another example of third spacing of fluid. In bowel obstruction large shock producing volumes of fluid may third space into the bowel lumen.
In shock poor tissue perfusion leads to metabolic defects such as metabolic acidosis. These defects serve to worsen the condition rapidly as time passes. In addition certain organs such as the kidney, and lung can tolerate shock for limited periods of time. Shock can lead to renal shutdown and to "shock lung". Of course when the brain and heart are deprived of oxygen there are serious consequences.
It is obvious that shock with its many causes and expressions is very common. One should always have a high index of suspicion for shock whenever its early signs and symptoms present. Protect the patient from the downward spiral of shock by early diagnosis and treatment according to ACLS and ATLS protocols and prompt consultation.