Hypovolemic shock

The patients of hypovolemic shock present with a history of burns, trauma, bleeding, vomiting or diarrhea. Upon examination, the skin and mucosa are dry. There is orthostatic hypotension and the neck veins are collapsed.

Cardiogenic shock

In cardiogenic shock, the presenting symptoms may be chest pain, dyspnea, palpitations and dizziness. Upon physical examination, cyanosis may be seen. The pulses may also be faint and pulsus paradoxus can be present. Occasionally, a systolic murmur may be heard. Jugular venous distension may also be observed.

Distributive shock  

In septic shock, the patient may have a history of fever associated with chills and rigors. There may also be dysuria or shortness of breath depending upon the etiology. There may be a history of spinal trauma in case of neurogenic shock. Other findings suggestive of neurogenic shock include normal capillary refill time, areflexia and weakness below the level of the lesion and occasionally absent bulbocavernosus reflex.

In hypovolemic shock, the investigations that are helpful in evaluating a hemorrhagic etiology include complete blood count, prothrombin time, liver function tests, blood typing, disseminated intravascular coagulation panel. Upper and lower gastrointestinal tract endoscopy may be performed to look for hemorrhage. Abdominal imaging can also be used to visualize aortic aneurysm and other pathologies. The tests for non-hemorrhagic etiology include serum creatinine and electrolytes, serum lipase and liver function tests.

The investigations that are useful for detecting the etiology of cardiogenic shock include electrocardiography (ECG), cardiac enzymes, arterial blood gases, tox screen, lactic acid and blood urea nitrogen. The important tests for establishing the diagnosis of septic shock include complete blood count with differential, prothrombin time, lactic acid, arterial blood gases, C-reactive proteins, urinalysis and all cultures with gram stain. Abdominal imaging should be performed to look for liver abscess, peritoneal abscess, pancreatitis and intestinal obstruction.

The treatment of shock depends upon the etiology.

Hypovolemic shock

If shock is due to hemorrhage, blood is transfused into the patient. In case of dehydration, the circulating volume is restored with crystalloids or colloid solutions [5][6]. Inotropic support can also be given if required.

Cardiogenic shock

In cardiogenic shock, heart function is improved by providing inotropic support by dopamine, dobutamine or noradrenaline [7][8]. Thrombolytic therapy is given if a thrombotic etiology is suspected in myocardial infarction or if there is pulmonary embolism. Early revascularization by angioplasty or bypass surgery may be required. If there is any arrhythmia, it must be corrected.

Distributive shock 

Early fluid resuscitation is essential for a better prognosis in the cases of septic shock [9]. Broad spectrum antimicrobial therapy should promptly be started when the diagnosis of septic shock is made. Later on when culture reports are available, a better antibiotic can be administered if needed according to the causal pathogen. Inotropic agents may be used [10]. Intravenous fluids are given to achieve hemodynamic stability. Inotropic support by dopamine should be provided. If the patient has severe bradycardia, atropine may also be used.

Poor prognosis of cardiogenic shock is implied in the patients with old age and prior history of myocardial infarction. The mortality of the patients suffering from septic shock is higher at extremes of age and in immunosuppressive states (such as neutropenia, diabetes, alcoholism, renal and respiratory failure and hypogammaglobinemia). Positive blood cultures for the etiologic agents implies severe morbidity. Certain strains of bacteria (such as Pseudomonas) have a particularly high mortality. Hypovolemic shock is usually associated with a favorable prognosis if blood transfusion and intravenous fluids are promptly given.

The etiology of shock depends upon its type.

Hypovolemic shock

Hypovolemic shock is usually associated with blood loss. The etiology of the blood loss may vary. Trauma to the liver, spleen, lungs or bones (in fracture) is associated with excessive hemorrhage which may lead to hypovolemic shock [1]. 

Gastrointestinal bleeding from ulcers, polyps and tumors can also cause significant blood loss. Other causes of blood loss include the rupture of the aortic or ventricular aneurysms, ectopic pregnancy and hemorrhagic ovarian cysts. 

Hypovolemic shock can also result from non-hemorrhagic causes such as dehydration (vomiting and diarrhea) and severe burns.

Cardiogenic shock

The risk factors for the development of cardiogenic shock include the following.

• Old age
• Diabetes mellitus
• Anterior myocardial infarction
• Hypertension
• Prior history of heart failure

Cardiogenic shock can be a feature of conditions such as acute myocardial infarction, dilated cardiomyopathies, arrhythmias, valve defects, pericardial tamponade, constrictive pericarditis and aortic dissection.

Distributive shock

Distributive shock is due to abnormal distribution of blood flow causing relative hypovolemia. Septic shock is the most common cause of distributive shock.

The risk factors for the development of septic shock include the following.

• Old age (greater than 65 years)
• Immunosuppression
• Pneumonia
• Malnutrition
• Neoplastic conditions

The most common cause of septic shock in the elderly is urinary tract infection [2]. Anaphylactic shock and neurogenic shock are also common forms of distributive shock. Neurogenic shock is caused by injury of the spinal cord by fracture or displacement of the vertebra or during the administration of spinal anesthesia.

Obstructive shock

Obstructive shock occurs when an acute obstruction of the pulmonary or systemic blood flow develops as a result of congenital or acquired conditions. Possible causes are:

• Cardiac tamponade
• Tension pneumothorax
• Massive pulmonary embolism
• Pulmonary hypertension
• Hypertrophic cardiomyopathy
• Aortic stenosis

Not much epidemiological data is available regarding hypovolemic shock. The incidence of cardiogenic shock in the patients of acute myocardial infarction is 5 to 10%. Severe sepsis occurs in as many as 3 cases per 1000 population in the United States. A study of the developed regions revealed septic shock to be the most common type of shock with 57% patients [3].

The pathophysiology of shock depends upon the type.

Hypovolemic shock

Hypovolemic shock results from significantly reduced volume of blood due to which the perfusion of all the tissues can not be effectively maintained.

Cardiogenic shock

Cardiogenic shock results from the failure of the pumping function of the heart.

Distributive shock 

Septic shock results from severe sepsis and is associated with the sequestration of large volume of blood in capillaries and veins [4]. Neurogenic shock results from the vasodilation and the loss of sympathetic tone in the vessels. The blood becomes pooled in the peripheral tissues.

Obstructive shock

Obstructive shock occurs when an acute obstruction of the pulmonary or systemic blood flow develops as a result of congenital or acquired conditions.

There is no practical way to prevent hypovolemic or neurogenic shock. Cardiogenic shock can be prevented by reducing the risk factors for myocardial infarction and arrhythmias (such as avoidance of smoking, preventing obesity and avoiding the overdose of drugs that cause arrhythmias). Septic shock can be prevented if early antimicrobial therapy is started in the early stage of sepsis.

Shock is defined as a state of inadequate perfusion of the tissues of the body resulting in hypoxia and organ failure. Upon the basis of etiology and pathophysiology, shock is divided into four main categories:

• Hypovolemic shock
• Cardiogenic shock
• Distributive shock
• Obstructive shock 

Shock refers to the failure of the circulation of sufficient blood to all the tissues of the body. Shock may result from decreased volume of blood, abnormalities of the heart and nerves, and severe infection. It is an emergency condition and must be treated quickly. The treatment depends upon the cause and type of shock.

1. Clark DR. Circulatory shock: etiology and pathophysiology. Journal of the American Veterinary Medical Association. Jul 1 1979;175(1):78-81.
2. Krcmery V. [Etiology and pathogenesis of septic shock]. Vnitrni lekarstvi. Jul 1996;42(7):467-469.
3. Fisher JD, Nelson DG, Beyersdorf H, Satkowiak LJ. Clinical spectrum of shock in the pediatric emergency department. Pediatric emergency care. Sep 2010;26(9):622-625.
4. Ackerman AD, Singhi S. Pediatric infectious diseases: 2009 update for the Rogers' Textbook of Pediatric Intensive Care. Pediatric critical care medicine : a journal of the Society of Critical Care Medicine and the World Federation of Pediatric Intensive and Critical Care Societies. Jan 2010;11(1):117-123.
5. Annane D, Siami S, Jaber S, et al. Effects of fluid resuscitation with colloids vs crystalloids on mortality in critically ill patients presenting with hypovolemic shock: the CRISTAL randomized trial. JAMA : the journal of the American Medical Association. Nov 6 2013;310(17):1809-1817.
6. Kobayashi L, Costantini TW, Coimbra R. Hypovolemic shock resuscitation. The Surgical clinics of North America. Dec 2012;92(6):1403-1423.
7. Bourdarias JP, Dubourg O, Gueret P, Ferrier A, Bardet J. Inotropic agents in the treatment of cardiogenic shock. Pharmacology & therapeutics. 1983;22(1):53-79.
8. Mueller HS. Inotropic agents in the treatment of cardiogenic shock. World journal of surgery. Feb 1985;9(1):3-10.
9. Carcillo JA, Davis AL, Zaritsky A. Role of early fluid resuscitation in pediatric septic shock. JAMA : the journal of the American Medical Association. Sep 4 1991;266(9):1242-1245.
10. Oba Y, Lone NA. Mortality benefit of vasopressor and inotropic agents in septic shock: A Bayesian network meta-analysis of randomized controlled trials. Journal of critical care. Apr 26 2014.