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Image: “Treatment of emergency patients by a rescue team of Malteser“ by Nallchen. License: (CC BY-SA 3.0)

Definition of Shock

The life-threatening state of shock

The relevant parameters that characterize the clinical picture of shock are arterial blood pressure, with a systolic pressure below 90 mm Hg or significantly lower than the baseline value. Moreover, an increased heart rate can be observed in most cases. The pulse is fast and thread-like. Thread-like describes a pulse that is weak, filled, quickened, difficult to palpate, and easy to suppress. The cardiac output can be decreased significantly. Furthermore, changes in the state of consciousness can be observed. Additional symptoms are as follows:

  • Decreased urinary excretion
  • Pale, cold, marbled, and cyanotic skin

Note: The cardinal symptoms of shock are: hypotension, disturbed consciousness, oliguria, and metabolic acidosis.

Definition of hypotension

  • Less than 100 mm Hg systolic blood pressure (normal = 120/80 mm Hg)
  • Common symptoms: fatigue, dizziness, occasionally fainting
  • Patients may have a fast or slow heart rate.
  • The skin is warm and not sweaty, although some patients may have cool and sweaty skin.
  • Often related to dehydration or blood loss
Normal Shock
Defense mechanisms Maintain a normal blood pressure Are overwhelmed; blood pressure decreases
Circulating components of the immune system Fight invading bacteria Are released in high concentrations and cause organs to malfunction; blood pressure drops
Blood vessels Constrict and raise blood pressure Dilate, which decreases peripheral vascular resistance and blood pressure

Types of Shocks and their Development


Image: Graphic illustration of different kinds of shock: no shock (left), neurogenic shock with dilation of the blood vessels (middle), hypovolemic shock caused by blood loss (right). By Alex. License: (CC BY-SA 3.0).

Shock is a condition with inadequate perfusion of tissue. This means that there is insufficient oxygen transport and a disturbed removal of metabolic degradation products.

There are different types of shock. However, treatment always starts with a diagnosis, which must be made fast and is, therefore, a major challenge for preclinical and medical care. There is a risk of multiple organ failure, yet other causes for signs of shock have to be considered within the scope of differential diagnoses.

Note: The phases of shock can be differentiated into three stages. The first stage is also called the compensated stage, the second one is the decompensated stage, and the third one is the irreversible stage.

Hypovolemic shock Cardiogenic shock Obstructive shock Distributive shock (septic)
Cardiac output Low Low Low Increased
Vascular resistance High High High Low (Cause: toxins → V.S.)
Mixed venous O2 saturation (Mvo2) Low Low Low Normal or high
Base deficit High High High High
PCWP Low High Low
LVEDP Low High Low
Cardiac index (normal: 2.8–4.2) Decreased Very decreased Increased

Anaphylactic Shock

Definition and etiology of anaphylactic shock

Anaphylaxis is an acute and systemic reaction that is characterized by symptoms of an allergic shock. Its course can be life threatening. Anaphylactic shock is among the most severe allergic reactions of the body.

There is no standardized definition that is used globally. In Germany, anaphylactic shock refers to an acute, pathologic reaction of the immune system in response to a chemical stimulus, which affects the whole organism. Shocks like this can occur in humans and animals.

Epidemiology and cardinal symptoms of anaphylactic shock

Symptome der Anaphylaxie

Image: Signs and symptoms of anaphylaxis. By Mikael Häggström. License: (CC0 1.0).

There are different triggers for anaphylactic shock that can hardly be determined at first glance. Additionally, triggers can also be hidden in foodstuff, which can lead to a dangerous delay of their identification, especially if rare triggers are involved.

Medications and food are identified particularly frequently as triggers, with nuts, seafood, and celery being the most common among foods. Further possible triggers are chicken eggs and insect poisons.

Anaphylactic shock may also be caused by a combination of different factors. In this case, we speak of allergen exposure. This is possible, for example, with concurrent stress after the consumption of alcohol or acute infections. Fifty-eight percent of the factors causing anaphylactic shock in children are food, approximately 24% are insect poisons, and 8% are medications. In adults, the factors causing anaphylactic shock are: approximately 16% food, 55% insect poisons, and 21% medication.

Severity levels of anaphylactic shock

Anaphylactic shock can occur in four degrees of severity.

First degree—lightest form

The patient feels light reactions that can be accompanied by dizziness and headache. Skin reactions are possible as well. This includes itching, skin redness with sensible heating of the skin, and nettle rash (generalized urticaria). This condition is not life threatening. However, it requires clarification. Prominent features are conjunctivitis and rhinitis as well as general restlessness.

Second degree

Second-degree shock includes symptoms of the first-degree form. Additionally, further signs such as tachycardia and dyspnea can be observed. Vomiting and nausea are also possible. Furthermore, the urge to defecate arises. The patient complains about dizziness.

Third degree

Symptoms of the first and second degrees are present. Characteristics of the third degree are bronchospasms with clear dyspnea; hoarseness, drowsiness, and fear are also visible. Quincke’s edema may occur, which can cause laryngeal swelling (Quincke’s edema—see below).

Fourth degree

Fourth-degree anaphylactic shock causes respiratory failure, heart failure, and circulatory arrest. Uncontrolled stool and urine excretion occur. This condition is life threatening.

Differential Diagnosis of Anaphylactic Shock: Formation of Edema

Formation of edema as similar clinical picture

Edema can occur due to anaphylactic shock. However, edema can also have a completely different trigger. Edema is classified according to their localization. They can be generalized (symmetric), localized (on one or both sides). They can also be located peripherally.

Peripheral edema is located, for example, inside the ankles but also in the lower leg. Bedridden patients can also have sacral edema.

A different classification considers the results of palpation. Pitting edema gives way when palpated, whereas non-pitting edema does not give way. Consistency, which means whether the edema is soft or hardened, is also of importance.

Quincke’s edema

Quincke’s edema, also called angioedema, occurs acutely and can last up to 3 days. It is a swelling found especially in the face (lips and eyelids) but also the hands, feet, and genital area can swell dramatically. Quincke’s edema becomes life threatening if the upper airways swell up.

Differential diagnosis of Quincke’s edema

angioneurotisches Ödem

Image: ‘Angioedema’ by BruceBlaus. License: (CC BY 3.0)

Quincke’s edema can be caused genetically and is triggered by an enzyme deficiency. This is the case in the so-called hereditary angioedema, which is, however, very rare. Another trigger can be physical stimulation. Furthermore, Quincke’s edema can be an accompanying symptom of chronic infections as well as autoimmune diseases. There is also an idiopathic type, which refers to a form of Quincke’s edema with an uncertain cause.

Reinke’s edema

Reinke Ödem

Image: ‘Reinke’s edema’ by Welleschick. License: (CC BY-SA 3.0)

Reinke’s edema is a disease of the vocal folds due to the collection of tissue fluid. It can occur unilaterally, bilaterally, or even affect the entire vocal folds. The patient notices his voice becoming lower or ‘tilting’. Talking over extended periods becomes difficult. Hoarseness can be an accompanying symptom.

Treatment of Reinke’s edema

Reinke’s edema is treated with sprays containing cortisone to reduce the swelling. Chemical fumes and other noxious influences such as smoking, which are usually the cause for Reinke’s edema, should be avoided. In severe cases, surgery may be necessary.

Perifocal Edema

Perifocal edema is located in healthy tissue surrounding the focus of disease. It occurs in the case of, for example, abscesses but also tumors and bleeding. It is also a possible complication after radiotherapy.

Pretibial edema

Pretibial edema is a collection of fluid in the subcutaneous tissue of the shinbone (tibia). Occurrences of pretibial edema are a sign of disturbed lymph circulation. Pretibial edema is easy to diagnose but it can have many causes.

Possible causes for pretibial edema

Right heart failure is a possible cause (cardiac edema). It may also be chronic venous insufficiency. Furthermore, endocrine diseases can lead to the formation of pretibial edema (myxedema) and it may also be possible to find the cause within the lymphatic system. A diagnosis is absolutely necessary because pretibial edema can be dangerous but also of harmless origin.

Hemorrhagic Shock

Definition of hemorrhagic shock

The reason for hemorrhagic shock is blood loss (hypovolemic shock), which is not necessarily visible. Possible causes are gastrointestinal bleeding, ruptures of vessels after accidents, gynecologic bleeding sources, and also tumors or chronic inflammation. Hemorrhagic shock is graded into four stages depending on the amount of blood loss.

Classes of hemorrhage

  • Class 1 hemorrhage → the patient compensates for blood loss through a sympathetic response that induces:
    • Mild tachycardia
    • Peripheral vascular constriction (capillary refill is maintained (< 2 seconds)
  • Class 2 hemorrhage → all the manifestations can be attributed to further increases in sympathetic discharge and shunting of blood from less critical vascular beds such as the skin, leading to skin vasoconstriction ⇒ skin is cold and moist
  • Class 3 hemorrhage → decompensation = hypotension (can no longer maintain the blood pressure at normal levels) despite further increases in heart rate and peripheral vascular constriction; this leads to:
    • Decreased level of consciousness
    • Further decrease in urine output due to poor cerebral and renal perfusion, respectively
  • Class 4 hemorrhage → patient appears lethargic, tachypneic, and has markedly decreased urine output. Circulatory failure and death are imminent ⇒ without therapeutic intervention.

Degrees and etiology of hemorrhagic shock

  • First degree ⇒ blood loss up to 750 mL
  • Second degree ⇒ blood loss from 750–1,500 mL
  • Third degree ⇒ blood loss of approximately 2,000 mL
  • Fourth degree ⇒ blood loss over 2,000 mL

Hemorrhagic shock of first and second degrees are also referred to as compensated shock. From third degree upward, the shock is decompensated. As soon as the blood loss exceeds 50% the condition becomes life threatening. The patient is usually unconscious and the risk of circulatory collapse is likely.

Further causes of hemorrhagic shock

Hypovolemic shock can also be a result of a loss of electrolytes, which can occur in cases of severe diarrhea. Possible reasons are severe burns as well as serious hyperthermia and insufficient intake of fluids, which, particularly among elderly people, is not uncommon.

Therapy of hemorrhagic shock

The fluid balance must be restored as soon as possible, even if the patient is in a first- or second-degree shock condition. Otherwise, severe complications can occur, even if the patient’s life has been saved. The bleeding must be stopped as soon as possible.

Signs for improvements of the condition

A number of signs indicate an improvement of the shock condition. This includes an improvement of the vital signs as well as an increase in pulse and blood pressure. However, the patient may still not be responsive.

Differential Diagnoses of Hemorrhagic Shock

Possible differential diagnoses are simple drops in blood pressure that can also lead to collapse. In this case, the condition is usually already improved by a low positioning of the head. From a differential diagnosis point of view, the drop in hemoglobin is missing in simple drops of blood pressure. Another possible cause is vasovagal syncope.

Cardiogenic Shock

Definition and etiology of cardiogenic shock

Cardiogenic shock is caused by a primary systolic failure of the heart. The skin turns pale but the cardiac output may be normal. The pulmonary capillary wedge pressure (PCWP) is increased. Arterio-venous O2 difference and total peripheral resistance (TPR) increase as well.

Reasons for cardiogenic shock can be either myocardial or mechanical. The myocardial reasons include myocardial infarction, myocarditis, cardiomyopathies, medication toxicity, and myocardial ischemia. The mechanical causes include pulmonary embolisms, artificial valve dysfunctions or diseases of the heart valves but also pericardial tamponade, intracavitary disturbances of fluid movement, or pericarditis constructiva.

Symptoms and diagnosis of cardiogenic shock

The patient is confused or has another form of disturbed consciousness. The mortality rate remains high, even if the patient is hospitalized. The blood pressure can be normal. The visible symptoms are moist and cold skin, cyanosis, tachycardia, and oliguria. Cardiogenic shock is known as the most frequent cause of death in cases of acute myocardial infarction.

Note: Up to 80% of all cardiogenic shock cases are triggered by acute myocardial ischemia.

Echocardiography and right heart catheters are used to diagnose cardiogenic shock.

Differential Diagnoses of Cardiogenic Shock

The accuracy of a cardiogenic shock diagnosis can be clarified using echocardiography and right heart catheters. In cases of circulatory–obstructive shock, which occurs due to a pulmonary embolism, a massive right ventricular load and a simultaneously good left ventricular contractility can be observed.

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