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In medicine, shock (hypoperfusion) is a life-threatening medical emergency characterized by inability of the body to supply enough oxygen to meet tissue requirements. Hypotension is usually, though not always, present. Without prompt medical treatment, shock usually causes death.
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.
- 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:
- 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.
- Pneumothorax. Through increased intrathoracic pressure bloodflow to the heart is prevented (venous return).
- Pulmonary embolism is the result of a thromboembolic incident in bloodvessels of the lungs and hinders the return of blood to the heart.
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 colour to come back;
- confusion or anxiety;
Other signs can be evaluated:
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 colour 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.
- The loss of liquid is medically compensated by intravenous drip and not per os (through the mouth).
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.
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 drip;
- 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:
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. This clinical distinction is generally only made retrospectively. Most cases of untreated reversible shock progress to irreversible shock within six hours due to hypoxic tissue damage.
See also
References
- Fundamental Critical Care Support, A standardized curriculum of Critical Care, by the Society of Critical Care Medicine
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