Shock: Encyclopedia - Shock

Shock

In medicine, shock (hypoperfusion) is a life-threatening medical emergency characterized by inability of the circulatory system to supply enough oxygen to meet tissue requirements. Hypotension is usually, though not always, present. Without prompt medical treatment, shock usually causes death.

Shock - Types of shock

• Hypovolemic shock. The single most common cause of shock is blood volume loss, resulting from a serious wound or a severe burn leading to hypovolemic shock. This may also be referred to as haemmorhagic shock.
• Cardiogenic shock is caused by the failure of the heart to pump effectively. This can be due to damage to the heart muscle, most often from a large myocardial infarction. Other causes of cardiogenic shock include arrhythmias, or cardiac valve problems.
• Distributive shock. As in hypovolemic shock there is an insufficient volume of blood. This form of relative hypovolaemia is the result of dilation of bloodvessels. Examples of this form of shock are:
  • Septic shock is caused by overwhelming infection leading to vasodilation. It is treated by antibiotics, fluid replacement, and vasoconstrictors.
  • Acute adrenal insufficiency is not infrequently the result of discontinuing corticosteroid treatment without tapering the dosage.
  • Less commonly severe anaphylactic reactions may cause anaphylactic shock as allergens trigger widespread vasodilation and movement of fluid out of the blood into the tissues.
  • The rarest cause of shock is acute spinal cord injury leading to neurogenic shock. Neurogenic shock is caused by the sudden loss of the sympathetic nervous system signals to the smooth muscle in vessel walls. Without this constant stimulation the vessels relax resulting in a sudden decrease in peripheral vascular resistance and decreased blood pressure.
• Obstructive shock. Hereby the flow of blood is obstructed. Several conditions result in this form of shock.
  • Cardiac tamponade, in which blood in the pericardium prevents inflow of blood into the heart (venous return). Or constrictive pericarditis which has the same effect.
  • Tension pneumothorax. Through increased intrathoracic pressure bloodflow to the heart is prevented (venous return).
  • Massive pulmonary embolism is the result of a thromboembolic incident in bloodvessels of the lungs and hinders the return of blood to the heart.

Shock - Symptoms and signs

The external signs and symptoms of shock are:

• feeling of thickness, weakness, thirst;
• pallor, especially visible at the inner side of the lips when the casualty has a dark skin;
• rapid pulse (tachycardia, more than 120 beats per minute), the radial pulse is difficult to feel;
• when pressing a finger nail, it takes more than two seconds for the color to come back;
• confusion or anxiety;

Other signs can be evaluated:

• decreased urine production
• low blood pressure.

Patients with hypovolaemic or cardiogenic shock will have cold and clammy hands and feet. Septic, anaphylactic and neurogenic shock may present with warm extremities.

In fact, the shock is a drop of blood pressure (below 80 mmHg or 10.7 kPa), and the symptoms are a reaction to this state:

• as the pressure is low, the pulse is hard to feel and the nails color back slowly;
• the transport of oxygen by the blood is less efficient, so the blood is concentrated in the important organs through peripheral vasoconstriction (causing pallor), and the heart beat and breath is accelerated to increase the oxygen transport rate;
• the thirst and decreased urine production is a result of the loss of intravascular fluid; but giving fluids to drink may be more detrimental than beneficial:
  • one of the probable symptoms is loss of alertness; in such a case the patient may lose their upper airway protective reflexes. As a result, stomach contents may be regurgitated and aspirated into the lungs. The acidic stomach contents causes a severe pneumonitis and/or obstruction of ventilation to the lungs.
  • the patient may need surgery and thus anaesthesia; a full stomach is not recommended for an anaesthesia for the same reasons.

Shock - Treatment

In general shock is a medical emergency. First aid treatment includes calling for help, controlling any external bleeding and giving oxygen if it is available. CPR may be necessary if the casualty stops breathing. If the patient does not have a spinal injury, or you do not suspect a spinal injury, the rhyme "face is red, raise the head; face is pale, raise the tail" can clue you to elevate an end of the patients body, in order to increase blood flow to the deprived area.

Although this is a protection reaction, the shock itself will induce problems; the circulatory system being less efficient, the body gets "exhausted" and finally, the blood circulation and the breathing slow down and finally stop (cardiac arrest). The main way to avoid this deadly consequence is to make the blood pressure rise again with

• vessel filling with intravenous infusions;
• use of vasopressing drugs (e.g. to induce vasoconstriction);
• use of antishock pants that compress the legs and concentrate the blood in the important organs (lungs, heart, brain).
• use of blanket/s to keep the patient warm - Mylar emergency blankets are used to reflect the patient's body heat back to the patient.

Some patients, especially those with reduced levels of consciousness, require immediate intubation and mechanical ventilation.

The aim of these acts is only to allow the survival during the transportation to the hospital; they do not cure the cause of the shock. Specific treatment depends on the cause.

A compromise must be found between:

• raising the blood pressure to be able to transport "safely" (when the blood pressure is too low, any motion can lower the heart and brain perfusion, and thus cause death);
• respecting the Golden hour: when surgery is needed, it must be performed within the first hour.

This is the stay and play versus the load and go debate.

More specific:

• Cardiogenic shock: Depending on the type of myocardal infarction one can infuse fluids or inotropica. Should that not suffice an Intra aortic balloon pump can be considered or a left ventricular assist device.
• Hypovolemic shock: In case of bleeding it is necessary to immediately control the bleeding and restore the victims blood volume by giving infusions of balanced salt solutions. Blood transufions are necessary for loss of large amounts of blood (e.g. greater than 20% of blood volume), but can be avoided in smaller and slower losses. blood transfusions. Hypovolemic shock due to burns, diarrhea, vomiting, etc. is treated with infusions of electrolyte solutions that balance the nature of the fluid lost. Sodium is essential to keep the fluid infused in the extracellular and intravascular space (and prevent water intoxication and brain swelling). Metabolic acidosis (mainly due to lactic acid) accumulates as a result of poor delivery of oxygen to the tissues, and mirrors the severity of the shock. It is best treated by rapidly restoring intravascular volume and perfusion as above. Inotropic and vasoconstrictive drugs should be avoided, as they may interfere in the knowing that blood volume is returning to normal.
• Distributive shock: In sepsis the infection is treated and supportive care is given. Anaphylaxis is treated with adrenalin and corticosteroids. Adrenal insufficienty is treated with corticosteroids. In neurogenic shock because of vasodilation in the legs, one of the most suggested treatments is placing the patient in the trendelenburg position, thereby elevating the legs and shunting blood back from the periphery to the body's core. However, since bloodvessels are highly compliant, and expand as result of the increased volume locally, this technique does not work. More suitable would be the use of vasopressors.
• Obstructive shock: the only therapy consist of removing the obstruction.

Shock - Prognosis

The prognosis of shock depends on the underlying cause and the nature and extent of concurrent problems.

Hypovolemic, anaphylactic and neurogenic shock are readily treatable and respond well to medical therapy. Septic shock however, is a grave condition and with a mortality rate between 30% and 50%. The prognosis of cardiogenic shock is even worse.

Shock is said to evolve from reversible to irreversible in experimental hemorrhagic shock in certain animal species (dogs, rats, mice) that develope intense vasoconstriction of the gut. In pigs and humans this is not seen and cessation of bleeding and restoration of blood volume is usually very effective. However, prolonged hypovolemia and hypotension does carry a higher mortality due to respiratory and then cardiac arrest in swine and in humans.

See also

• future shock
• sticker shock
• shell shock

Hemmorhagic shock on eMedicine.com

Adapted from the Wikipedia article "Shock", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki