Circulatory shock or simply shock refers to a syndrome characterized by serious reduction of tissue perfusion with a relatively or absolutely inadequate cardiac output. Lack of oxygen delivery may be due to several conditions such as hypovolemia (decrease in blood volume), bleeding diatheses, cardiac failure, neurogenic disturbances and anaphylactic response. Main changes in shock are observed in the cardiovascular, renal and central nervous systems. Initial efforts are in compensation for the reduced oxygen levels. It can be treated, but if not treated rapidly, it may lead to death in a couple of minutes. Circulatory shock is a life-threatening medical condition that occurs due to inadequate substrate for aerobic cellular respiration. In the early stages this is generally an inadequate tissue levels of oxygen. A circulatory shock should not be confused with the emotional state of shock, as the two are not related. Medical shock is a life-threatening medical emergency and one of the most common causes of death for critically ill people. Shock can have a variety of effects, all with similar outcomes, but all relate to a problem with the body's circulatory system. For example, shock may lead to hypoxemia (a lack of oxygen in arterial blood) or cardiac arrest (the heart stopping).One of the key dangers of shock is that it progresses by a positive feedback mechanism. Once shock begins, it tends to make itself worse. This is why immediate treatment of shock is critical.
CLINICAL MARKERS OF SHOCK
Brachial systolic blood pressure: <110mmHg
Sinus tachycardia: >90 beats/min
Respiratory rate: <7 or >29 breaths/min
Urine Output: <0.5cc/kg/hr
Metabolic acidemia: [HCO3]<31mEq/L or base deficit>3mEq/L
Hypoxemia: 0-50yr: <90mmHg; 51-70yr: <80mmHg; >71yo<70mmHg;
Cutaneous vasoconstriction vs. vasodilation.
Mental Changes: anxiousness, agitation, indifference, lethargy, obtundation
Causes, incidence, and risk factors
Losing about 1/5 or more of the normal amount of blood in your body causes hypovolemic shock.
Blood loss can be due to:
Bleeding from cuts
Bleeding from other injuries
Internal bleeding, such as in the gastrointestinal tract
The amount of circulating blood in your body may drop when you lose too many other body fluids, which can happen with:
TYPES OF SHOCK
- Distributive OR Vasogenic Shock
- Cardiogenic Shock
- Distributive Shock
- Neurogenic Shock
Hypovolaemic shock also known as cold shock is caused by a low blood volume resulting in decreased cardiac output.It is characterized by - Hypotension; a rapid, thready pulse; a cold, pale, clammy skin; intense thirst; rapid respiration; and restlessness.
It may be due to:
Direct loss of effective circulating blood volume leading to: A rapid, weak, thready pulse due to decreased blood flow combined with tachycardia Cool, clammy skin due to vasoconstriction and stimulation of vasoconstriction Rapid and shallow respirations due to sympathetic nervous system stimulation and acidosis Hypothermia due to decreased perfusion and evaporation of sweat Thirst and dry mouth, due to fluid depletion Cold and mottled skin (cutis marmorata), especially extremities, due to insufficient perfusion of the skin The severity of hemorrhagic shock can be graded on a 1-4 scale on the physical signs. This approximates to the effective loss of blood volume.
Hypovolemic shock is commonly subdivided into categories on the basis of cause:-
Bleeding in hemorrhage causes decline in the blood volume which decreases venous return, and cardiac output falls. In response to this heart rate increases, and with severe hemorrhage, there is always a fall in blood pressure while with moderate hemorrhage, pulse pressure is reduced but mean arterial pressure may be normal. The skin is cool and pale and may have a grayish tinge because of stasis in the capillaries and a small amount of cyanosis. Respiration is rapid, and in patients whose consciousness is not obtunded, intense thirst is a prominent symptom.
Rapid compensatory reactions
When blood volume is reduced and venous return is decreased, the arterial baroreceptors are stretched to a lesser degree and sympathetic output is increased. Even if there is no drop in mean arterial pressure, the decrease in pulse pressure decreases the rate of discharge in the arterial baroreceptors, and reflex tachycardia and vasoconstriction result. It is interesting that with more severe blood loss, tachycardia is replaced by bradycardia. With even greater hemorrhage, the heart rate rises again . The bradycardia is presumably due to unmasking a vagally mediated depressor reflex, and the response may have evolved as a mechanism for stopping further blood loss.
Long-term compensatory reactions
- Renin Angiotensin II
Low resistance or distributive shock occurs when the blood volume is normal but the capacity of the circulation is increased by marked vasodilation. It is also called "warm shock" because the skin is not cold and clammy ,as it is in hypovolemic shock.
- Neurogenic shock occurs due to anaesthesia (marked reduction in sympathetic vasomotor tone) or vasovagal syncope(pronounced increase in vasomotor tone).
- Anaphylactic shock. Anaphylaxis releases large quantities of histamine, causing increased capillary permeability and widespread dilation of arterioles and capillaries
- Septicaemic shock. Septicaemia develops due to marked vasodilation,and disseminated intravascular coagulation.Endotoxic shock is caused by endotoxins of gram-negative bacteria.
Cardiogenic shock is caused by inadequate pumping action of heart as a result of myocardial abnormalities.
It may be due to:
- Myocardial infarction
- Congestive heart failure
it is Characterized by high preload (CVP) with low CO
Signs/SXS: Dyspnea, rales, loud P2 gallop, low BP, oliguria
Monitor/findings: CXR pulm venous congestion, elevated CVP, Low CO.
Tx: CHF– diuretics & vasodilators +/- pressors. LV failure – pressors, decrease afterload, intraaortic ballon pump & ventricular assist device.
Obstructive shock is caused by inadequate cardiac output as a result of obstruction of blood flow in lung,great vessels or heart.Pulmonary embolism and cardiac tamponade are considered forms of obstructive shock.
It may be due to:
- Tension pneumothorax
- Pulmonary embolism
- Cardiac tumor
- Cardiac tamponade
TREATMENT OF SHOCK
treatment of shock aimed at correcting the cause and helping physiologic compensatory mechanism to restore and adequate level of tissue perfusion. if the primary cause of shock is blood loss, the treatment should include early and rapid transfusion of adequate amounts of compatible whole blood. in shock due to burns and other conditions in which there is hemoconcentration plasma is the treatment of choice to restore he fundamental defect, the loss of plasma. concentrated human serum albumin and other hypertonic solutions expand the blood volume by drawing fluid out of interstitial spaces. they are valuable in emergency treatment but have the disadvantage of further dehydrating the tissues of an already dehydrated patient.
Get immediate medical help. In the meantime, follow these steps:
Keep the person comfortable and warm (to avoid hypothermia). Have the person lie flat with the feet lifted about 12 inches to increase circulation. However, if the person has a head, neck, back, or leg injury, do not change the person's position unless he or she is in immediate danger. Do not give fluids by mouth. If person is having an allergic reaction, treat the allergic reaction, if you know how. If the person must be carried, try to keep him or her flat, with the head down and feet lifted. Stabilize the head and neck before moving a person with a suspected spinal injury. The goal of hospital treatment is to replace blood and fluids. An intravenous (IV) line will be put into the person's arm to allow blood or blood products to be given.
Medicines such as dopamine, dobutamine, epinephrine, and norepinephrine may be needed to increase blood pressure and the amount of blood pumped out of the heart (cardiac output).
Other methods that may be used to manage shock and monitor the response to treatment include:
Heart monitoring, including Swan-Ganz catheterization Urinary catheter to collect and monitor how much urine is produced
The first changes seen in shock is an increased cardiac output followed by a decrease in mixed venous oxygen saturation (SmvO2) as measured in the pulmonary artery via a pulmonary artery catheter. Central venous oxygen saturation (ScvO2) as measured via a central line correlates well with SmvO2 and are easier to acquire. If shock progresses anaerobic metabolism will begin to occur with an increased blood lactic acid as the result. While many laboratory tests are typically performed there is no test that either makes or excludes the diagnosis. A chest X-ray or emergency department ultrasound may be useful to determine volume state.
- review of medical physiology by William F.Ganong