Shock

Initially, when oxygen delivery (DO2) is decreased, tissues compensate by extracting a greater percentage of delivered oxygen. Low arterial pressure triggers an adrenergic response with sympathetic-mediated vasoconstriction and often increased heart rate. Initially, vasoconstriction is selective, shunting blood to the heart and brain and away from the splanchnic circulation. Circulating beta-adrenergic amines (epinephrine, norepinephrine) also increase cardiac contractility and trigger release of

Corticosteroids enhance the effects of catecholamines. Renin stimulates volume retention and vasoconstriction. Increased glucose increases pyruvate uptake in the mitochondria which increases lactate production when there is insufficient oxygen.

Reperfusion of ischemic cells can cause further injury. As substrate is reintroduced, neutrophil activity may increase, increasing production of damaging superoxide and hydroxyl radicals. After blood flow is restored, locally concentrated inflammatory mediators may be circulated to other organs.

The combination of direct and reperfusion injury may cause MODS—the progressive dysfunction of ≥ 2 organs consequent to life-threatening illness or injury. MODS can follow any type of shock but is most common when infection is involved; organ failure is one of the defining features of septic shock Sepsis and Septic Shock Sepsis is a clinical syndrome of life-threatening organ dysfunction caused by a dysregulated response to infection. In septic shock, there is critical reduction in tissue perfusion; acute failure... read more . MODS also occurs in > 10% of patients with severe traumatic injury and is the primary cause of death in those surviving > 24 hours.

Any organ system can be affected, but the most frequent target organs are the lungs, in which increased membrane permeability leads to flooding of alveoli and further inflammation. Progressive hypoxia may be increasingly resistant to supplemental oxygen therapy. This condition is termed acute lung injury or, if severe, acute respiratory distress syndrome Acute Hypoxemic Respiratory Failure (AHRF, ARDS) Acute hypoxemic respiratory failure is defined as severe hypoxemia (PaO2 (See also Overview of Mechanical Ventilation.) Airspace filling in acute hypoxemic respiratory failure (AHRF) may result... read more (ARDS).

The kidneys are injured when renal perfusion is critically reduced, leading to acute tubular necrosis Acute Tubular Necrosis (ATN) Acute tubular necrosis (ATN) is kidney injury characterized by acute tubular cell injury and dysfunction. Common causes are hypotension or sepsis that causes renal hypoperfusion and nephrotoxic... read more and renal insufficiency manifested by oliguria and a progressive rise in serum creatinine.

In the heart, reduced coronary perfusion and increased inflammatory mediators (including tumor necrosis factor and interleukin-1) may depress contractility, worsen myocardial compliance, and down-regulate beta-receptors. These factors decrease cardiac output, further worsening both myocardial and systemic perfusion and causing a vicious circle that often culminates in death. Arrhythmias may occur.

In the gastrointestinal tract, ileus and submucosal hemorrhage can develop. Liver hypoperfusion can cause focal or extensive hepatocellular necrosis, transaminase and bilirubin elevation, and decreased production of clotting factors.

Coagulation can be impaired, including the most severe manifestation, disseminated intravascular coagulopathy Disseminated Intravascular Coagulation (DIC) Disseminated intravascular coagulation (DIC) involves abnormal, excessive generation of thrombin and fibrin in the circulating blood. During the process, increased platelet aggregation and coagulation... read more .

Hypovolemic shock is caused by a critical decrease in intravascular volume. Diminished venous return (preload) results in decreased ventricular filling and reduced stroke volume. Unless compensated for by increased heart rate, cardiac output decreases.

A common cause is bleeding (hemorrhagic shock), typically due to trauma, surgical interventions, peptic ulcer, esophageal varices, or ruptured aortic aneurysm. Bleeding may be overt (eg, hematemesis, melena) or concealed (eg, ruptured ectopic pregnancy).

Hypovolemic shock may also follow increased losses of body fluids other than blood (see table Hypovolemic Shock Caused by Body Fluid Loss Hypovolemic Shock Caused by Body Fluid Loss ).

Hypovolemic shock may be due to inadequate fluid intake (with or without increased fluid loss). Water may be unavailable, neurologic disability may impair the thirst mechanism, or physical disability may impair access.

In hospitalized patients, hypovolemia can be compounded if early signs of circulatory insufficiency are incorrectly ascribed to heart failure and fluids are withheld or diuretics are given.

Distributive shock results from a relative inadequacy of intravascular volume caused by arterial or venous vasodilation; circulating blood volume is normal. In some cases, cardiac output (and DO2) is high, but increased blood flow through arteriovenous shunts bypasses capillary beds; this bypass plus uncoupled cellular oxygen transport cause cellular hypoperfusion (shown by decreased oxygen consumption). In other situations, blood pools in venous capacitance beds and cardiac output falls.

Distributive shock may be caused by

Anaphylactic shock and septic shock often have a component of hypovolemia as well.

Cardiogenic shock Hypotension and Cardiogenic Shock Numerous complications can occur as a result of an acute coronary syndrome and increase morbidity and mortality. Complications can be roughly categorized as Electrical dysfunction (conduction... read more is a relative or absolute reduction in cardiac output due to a primary cardiac disorder. Obstructive shock is caused by mechanical factors that interfere with filling or emptying of the heart or great vessels. Causes are listed in the table Mechanisms of Cardiogenic and Obstructive Shock Mechanisms of Cardiogenic and Obstructive Shock .

Recognizing the cause of shock is more important than categorizing the type. Often, the cause is obvious or can be recognized quickly based on the history and physical examination, aided by simple testing.

Chest pain Chest Pain Chest pain is a very common complaint. Many patients are well aware that it is a warning of potential life-threatening disorders and seek evaluation for minimal symptoms. Other patients, including... read more (with or without dyspnea) suggests myocardial infarction (MI) Acute Myocardial Infarction (MI) Acute myocardial infarction is myocardial necrosis resulting from acute obstruction of a coronary artery. Symptoms include chest discomfort with or without dyspnea, nausea, and/or diaphoresis... read more , aortic dissection Aortic Dissection Aortic dissection is the surging of blood through a tear in the aortic intima with separation of the intima and media and creation of a false lumen (channel). The intimal tear may be a primary... read more , or pulmonary embolism Pulmonary Embolism (PE) Pulmonary embolism (PE) is the occlusion of pulmonary arteries by thrombi that originate elsewhere, typically in the large veins of the legs or pelvis. Risk factors for pulmonary embolism are... read more . A systolic murmur may indicate ventricular septal rupture or mitral insufficiency due to acute MI. A diastolic murmur may indicate aortic regurgitation due to aortic dissection involving the aortic root. Cardiac tamponade Cardiac Tamponade Cardiac tamponade is accumulation of blood in the pericardial sac of sufficient volume and pressure to impair cardiac filling. Patients typically have hypotension, muffled heart tones, and distended... read more is suggested by jugular venous distention, muffled heart sounds, and a paradoxical pulse. Pulmonary embolism severe enough to cause shock typically produces decreased oxygen saturation and occurs more often in special settings, including prolonged bed rest and after a surgical procedure. Tests include electrocardiography (ECG), cardiac enzyme measurement, chest x-ray, arterial blood gas (ABG) measurement, lung scan, helical CT, and echocardiography.

Abdominal or back pain or a tender abdomen suggests pancreatitis Overview of Pancreatitis Pancreatitis is classified as either acute or chronic. Acute pancreatitis is inflammation that resolves both clinically and histologically. Chronic pancreatitis is characterized by histologic... read more , ruptured abdominal aortic aneurysm Abdominal Aortic Aneurysms (AAA) Abdominal aortic diameter ≥ 3 cm typically constitutes an abdominal aortic aneurysm. The cause is multifactorial, but atherosclerosis is often involved. Most aneurysms grow slowly (~10%/year)... read more , peritonitis (eg, due to a perforated viscus), and, in women of childbearing age, ruptured ectopic pregnancy Ectopic Pregnancy Ectopic pregnancy is the implantation of a pregnancy in a site other than the endometrial lining of the uterine cavity—ie, in the fallopian tube, uterine cornua, cervix, ovary, or abdominal... read more . A pulsatile midline mass suggests ruptured abdominal aortic aneurysm. A tender adnexal mass suggests ectopic pregnancy. Testing typically includes abdominal CT (if the patient is unstable, bedside ultrasonography can be helpful), complete blood count (CBC), amylase, lipase, and, for women of childbearing age, urine pregnancy test.

Fever, chills, and focal signs of infection suggest septic shock Sepsis and Septic Shock Sepsis is a clinical syndrome of life-threatening organ dysfunction caused by a dysregulated response to infection. In septic shock, there is critical reduction in tissue perfusion; acute failure... read more , particularly in immunocompromised patients. Isolated fever, contingent on history and clinical settings, may point to heatstroke. Tests include chest x-ray; urinalysis; CBC; and cultures of wounds, blood, urine, and other relevant body fluids.

In a few patients, the cause is occult. Patients with no focal symptoms or signs indicative of cause should have ECG, cardiac enzyme measurement, chest x-ray, and ABGs. If results of these tests are normal, the most likely causes include drug overdose, occult infection (including toxic shock Toxic Shock Syndrome (TSS) Toxic shock syndrome is caused by staphylococcal or streptococcal exotoxins. Manifestations include high fever, hypotension, diffuse erythematous rash, and multiple organ dysfunction, which... read more ), anaphylaxis, and obstructive shock.

If not already done, ECG, chest x-ray, CBC, serum electrolytes, blood urea nitrogen (BUN), creatinine, prothrombin time (PT), partial thromboplastin time (PTT), liver function tests, and fibrinogen and fibrin split products are done to monitor patient status and serve as a baseline. If the patient’s volume status is difficult to determine, monitoring of central venous pressure (CVP) or pulmonary artery occlusion pressure (PAOP) may be useful. CVP < 5 mm Hg (< 7 cm water) or PAOP < 8 mm Hg may indicate hypovolemia, although CVP may be greater in hypovolemic patients with preexisting pulmonary hypertension. Rapid bedside echocardiography (done by the treating physician) to assess adequacy of cardiac filling and function is being increasingly used to assess shock and overall cardiac performance (for review, 1, 2 Diagnosis references Shock is a state of organ hypoperfusion with resultant cellular dysfunction and death. Mechanisms may involve decreased circulating volume, decreased cardiac output, and vasodilation, sometimes... read more ).

First aid involves keeping the patient warm. External hemorrhage is controlled, airway and ventilation are checked, and respiratory assistance is given if necessary. Nothing is given by mouth, and the patient’s head is turned to one side to avoid aspiration if emesis occurs.

Treatment begins simultaneously with evaluation. Supplemental oxygen by face mask is provided. If shock is severe or if ventilation is inadequate, airway intubation with mechanical ventilation Overview of Mechanical Ventilation Mechanical ventilation can be Noninvasive, involving various types of face masks Invasive, involving endotracheal intubation Selection and use of appropriate techniques require an understanding... read more is necessary. Two large (14- to 16-gauge) IV catheters are inserted into separate peripheral veins. A central venous line or an intraosseous needle Intraosseous Infusion A number of procedures are used to gain vascular access. Most patients’ needs for IV fluid and drugs can be met with a percutaneous peripheral venous catheter. If blind percutaneous placement... read more , especially in children, provides an alternative when peripheral veins cannot promptly be accessed.

Typically, a fluid challenge is given; 1 L (or 20 mL/kg in children) of 0.9% saline is infused over 15 minutes. In major hemorrhage, Ringer’s lactate is commonly used, although in major hemorrhage, use of crystalloid should be minimized in favor of transfusion of blood products Blood Products Whole blood can provide improved oxygen-carrying capacity, volume expansion, and replacement of clotting factors and was previously recommended for rapid massive blood loss. However, because... read more (red blood cells, fresh frozen plasma, and platelets in a 1:1:1 ratio) (1 Treatment references Shock is a state of organ hypoperfusion with resultant cellular dysfunction and death. Mechanisms may involve decreased circulating volume, decreased cardiac output, and vasodilation, sometimes... read more , 2 Treatment references Shock is a state of organ hypoperfusion with resultant cellular dysfunction and death. Mechanisms may involve decreased circulating volume, decreased cardiac output, and vasodilation, sometimes... read more ). Unless clinical parameters return to normal, the infusion of fluid is repeated. Smaller volumes (eg, 250 to 500 mL) are used for patients with signs of high right-sided pressure (eg, distention of neck veins) or acute myocardial infarction. A fluid challenge should probably not be done in a patient with signs of pulmonary edema. Further fluid therapy is based on the underlying condition and may require monitoring of CVP or PAOP. Bedside cardiac ultrasonography to assess contractility and vena caval respiratory variability may help determine the need for additional fluid vs the need for inotropic support.

Patients in shock are critically ill and should be admitted to an intensive care unit. Monitoring includes

Measurement of CVP, PAOP, and thermodilution cardiac output using a balloon-tipped pulmonary arterial catheter Procedure Some monitoring of critical care patients depends on direct observation and physical examination and is intermittent, with the frequency depending on the patient’s illness. Other monitoring... read more may be helpful for diagnosis and initial management of patients with shock of uncertain or mixed etiology or with severe shock, especially when accompanied by oliguria or pulmonary edema. Echocardiography (bedside or transesophageal) is a less invasive alternative. Serial measurements of arterial blood gases, hematocrit, electrolytes, serum creatinine, and blood lactate are obtained. Sublingual carbon dioxide measurement Monitoring and Testing the Critical Care Patient Some monitoring of critical care patients depends on direct observation and physical examination and is intermittent, with the frequency depending on the patient’s illness. Other monitoring... read more , if available, is a noninvasive monitor of visceral perfusion (levels increase with decreasing tissue perfusion). A well-designed flow sheet to monitor trends is helpful.

Because tissue hypoperfusion makes intramuscular absorption unreliable, all parenteral drugs are given IV. Opioids generally are avoided because they may cause vasodilation, but severe pain may be treated with morphine 0.1 mg/kg IV given over 2 minutes and repeated every 10 to 15 minutes if necessary. Although cerebral hypoperfusion may cause anxiety, sedatives or tranquilizers are not routinely given unless the patient is intubated.

After initial resuscitation, specific treatment is directed at the underlying condition. Additional supportive care is guided by the type of shock.

In hemorrhagic shock, surgical control of bleeding is the first priority. Volume replacement Intravenous Fluid Resuscitation Almost all circulatory shock states require large-volume IV fluid replacement, as does severe intravascular volume depletion (eg, due to diarrhea or heatstroke). Intravascular volume deficiency... read more accompanies rather than precedes surgical control. Blood products and crystalloid solutions are used for resuscitation; however, red blood cells, fresh frozen plasma, and platelets are being given earlier and in a ratio of 1:1:1 in patients likely to require massive transfusion Complications of massive transfusion The most common complications of transfusion are Febrile nonhemolytic reactions Chill-rigor reactions The most serious complications, which have very high mortality rates, are Acute hemolytic... read more . Failure to respond usually indicates insufficient volume administration or unrecognized ongoing hemorrhage. Vasopressors may be tried in refractory hemorrhagic shock but only after adequate blood volume has been restored and hemorrhage controlled; giving vasopressors before that can worsen outcomes.

Distributive shock with profound hypotension after initial fluid replacement with 0.9% saline may be treated with inotropic or vasopressor agents (eg, dopamine, norepinephrine—see table Inotropic and Vasoactive Catecholamines Inotropic and Vasoactive Catecholamines ). Patients with septic shock also receive broad-spectrum antibiotics Antibiotics . Patients with anaphylactic shock Anaphylaxis Anaphylaxis is an acute, potentially life-threatening, IgE-mediated allergic reaction that occurs in previously sensitized people when they are reexposed to the sensitizing antigen. Symptoms... read more unresponsive to fluid challenge (especially if accompanied by bronchoconstriction) receive epinephrine 0.05 to 0.1 mg IV, followed by epinephrine infusion of 5 mg in 500 mL 5% dextrose in water (D/W) at 10 mL/hour or 0.02 mcg/kg/minute.

In cardiogenic shock, structural disorders (eg, valvular dysfunction, septal rupture) are repaired surgically. Coronary thrombosis is treated either by percutaneous interventions Percutaneous coronary intervention (PCI) Coronary artery disease (CAD) involves impairment of blood flow through the coronary arteries, most commonly by atheromas. Clinical presentations include silent ischemia, angina pectoris, acute... read more (angioplasty, stenting), coronary artery bypass surgery Coronary artery bypass grafting (CABG) Coronary artery disease (CAD) involves impairment of blood flow through the coronary arteries, most commonly by atheromas. Clinical presentations include silent ischemia, angina pectoris, acute... read more , or thrombolysis Fibrinolytics Treatment of acute coronary syndromes (ACS) is designed to relieve distress, interrupt thrombosis, reverse ischemia, limit infarct size, reduce cardiac workload, and prevent and treat complications... read more . Tachydysrhythmia (eg, rapid atrial fibrillation, ventricular tachycardia) is slowed by cardioversion Direct Current (DC) Cardioversion-Defibrillation The need for treatment of arrhythmias depends on the symptoms and the seriousness of the arrhythmia. Treatment is directed at causes. If necessary, direct antiarrhythmic therapy, including antiarrhythmic... read more or with antiarrhythmic drugs Medications for Arrhythmias The need for treatment of arrhythmias depends on the symptoms and the seriousness of the arrhythmia. Treatment is directed at causes. If necessary, direct antiarrhythmic therapy, including antiarrhythmic... read more . Bradycardia is treated with a transcutaneous or transvenous pacemaker Cardiac Pacemakers The need for treatment of arrhythmias depends on the symptoms and the seriousness of the arrhythmia. Treatment is directed at causes. If necessary, direct antiarrhythmic therapy, including antiarrhythmic... read more ; atropine 0.5 mg IV every 5 minutes up to 4 doses may be given pending pacemaker placement. Isoproterenol (2 mg/500 mL 5% dextrose in water [D/W] at 1 to 4 mcg/minute [0.25 to 1 mL/minute]) is occasionally useful if atropine is ineffective, but it is not advised in patients with myocardial ischemia due to coronary artery disease.

Shock after acute MI is treated with volume expansion if PAOP is low or normal; 15 to 18 mm Hg is considered optimal. If a pulmonary artery catheter is not in place, cautious volume infusion (250- to 500-mL bolus of 0.9% saline) may be tried while auscultating the chest frequently for signs of fluid overload. Shock after right ventricular MI usually responds partially to volume expansion; however, vasopressor agents may be needed. Bedside cardiac ultrasonography to assess contractility and vena caval respiratory variability can help determine the need for additional fluid vs vasopressors; inotropic support is a better approach for patients with normal or above-normal filling.

If hypotension is moderate (eg, mean arterial pressure [MAP] 70 to 90 mm Hg), dobutamine infusion may be used to improve cardiac output and reduce left ventricular filling pressure. Tachycardia and arrhythmias occasionally occur during dobutamine administration, particularly at higher doses, necessitating dose reduction. Vasodilators (eg, nitroprusside, nitroglycerin), which increase venous capacitance or lower systemic vascular resistance, reduce the workload on the damaged myocardium and may increase cardiac output in patients without severe hypotension. Combination therapy (eg, dopamine or dobutamine with nitroprusside or nitroglycerin) may be particularly useful but requires close ECG and pulmonary and systemic hemodynamic monitoring.

For more serious hypotension (MAP < 70 mm Hg), norepinephrine or dopamine may be given, with a target systolic pressure of 80 to 90 mm Hg (and not > 110 mm Hg). Intra-aortic balloon counterpulsation is valuable for temporarily reversing shock in patients with acute MI. This procedure should be considered as a bridge to permit cardiac catheterization and coronary angiography before possible surgical intervention in patients with acute MI complicated by ventricular septal rupture or severe acute mitral regurgitation who require vasopressor support for > 30 minutes.

In obstructive shock, nontraumatic cardiac tamponade requires immediate pericardiocentesis Treatment Pericarditis is inflammation of the pericardium, often with fluid accumulation in the pericardial space. Pericarditis may be caused by many disorders (eg, infection, myocardial infarction, trauma... read more , which can be done at the bedside. Trauma-related cardiac tamponade requires surgical decompression and repair. Tension pneumothorax should be immediately decompressed with a catheter inserted into the 2nd intercostal space, midclavicular line; a chest tube is then inserted. Massive pulmonary embolism resulting in shock is treated with anticoagulation and thrombolysis, surgical embolectomy, or extracorporeal membrane oxygenation in select cases.