Shock is defined as a state of circulatory dysfunction in which tissue O2 delivery is less than required. If untreated, multi-organ failure and death will result. Shock is the final common pathway of numerous disease states. Shock is a life-threatening medical emergency and is one of the leading causes of death. The primary cause may lead to many other medical emergencies like hypoxia and cardiac arrest. Hypoxia is defined as lack of oxygen to the tissues. Cardiac arrest is the cessation of cardiac contractions.
Patho physiology: There are many general classifications however the following are most widely recognised:
Hypovolemic Shock:
Most common type of shock, due to insufficient circulating volume. Main cause is loss of fluid from the circulatory system e.g. bleeding, burns. Cardiogenic Shock:
Due to failure of the myocardium to pump effectively. Often due to damage of the heart muscle as a result of Myocardial Infarction. Other causes include arrhythmias, cardiomyopathy, Congestive Heart Failure and cardiac valve problems. Distributive Shock:
Some authors include septic shock, Anaphylactic and Neurogenic shock under this classification. Other authors classify them separately. As the name implies, in this type of shock, there is no blood loss but the shock is due to dilation of blood vessels.
Septic Shock:
Due to sepsis caused by an overwhelming infection leading vasodilatation e.g. infection by bacteria of the Proteus species. These release toxins which produce adverse biochemical, immunological and occasionally neurological effects. Patients usually have a history of fever, pyrexia and hyperthermia.
Anaphylactic Shock:
Caused by severe reaction to an allergen, antigen, drug or foreign protein. Release of histamine caused widespread vasodilatation.
C. Neurogenic Shock:
This is a very uncommon type of shock. It is most often seen in patients who have had extensive spinal cord injuries. The loss of autonomic and motor reflexes below the level of injury results in loss of sympathetic control. This leads to relaxation of vessel walls and peripheral dilation and hypotension.
Endocrine Shock:
Mainly due to hormone disturbances e.g. Hypothyroidism and adrenal insufficiency. Hypothyroidism is corrected with levothyroxin and adrenal insufficiency is corrected with corticosteroids. Obstructive Shock:
Obstruction of blood flow results in cardiac arrest. Examples which lead to this type of shock are Cardiac tamponade, Tension pneumothorax, Pulmonary embolism and aortic stenosis.
Signs and Symptoms:
Clinical signs are for the most part non-specific. Any one or a combination of any of the following may be present. The stage and severity of the shock will influence the signs and symptoms.
- Tachycardia: Heart rate of greater than 100 b/min in an adult patient. Some authors may describe this as a “galloping heart”.
- Hypotension - Low blood pressure, particularly decreased diastolic BP
- Oliguria: Urinary output of less than 0.5ml per kg of body weight in an adult patient.
- Changed level of Consciousness, usually a decrease in LOC
- Underlying infection / blood loss, spinal cord injury
Stages of Shock
There are three stages of shock are commonly identified. Stage I, sometimes called the compensated or non progressive stage because the symptoms may be mild or non-existent. Stage II is often called the decompensated or progressive stage. Stage III may be referred to as the irreversible stage.
Stage I. Early, Reversible and Compensatory Shock
This stage is characterized by low BP. It results in decreased perfusion, particularly to the peripheral tissues. Initial signs of shock include sinus tachycardia, peripheral vasoconstriction (blood vessels throughout the body become slightly smaller in diameter) and the renal system (kidneys) works to retain fluid in the cardiovascular system. These processes are activated to maintain and restore tissue perfusion. The end result is that blood flow to key vital organs is maintained. The key vital organs are the kidneys, brain, and heart. As a result of this compensatory mechanism the body is maintained. Consequently, the patient in this stage of shock displays very few symptoms. Proper treatment at this stage can halt progression of shock.
Stage II. Intermediate or Progressive shock
During this stage of shock the normal compensatory mechanisms begin to fail. The systems of the body are not perfused adequately any longer. The patient's symptoms may reflect this fact. Oxygen deprivation to the brain causes the patient to become confused and disoriented. Oxygen deprivation to the heart may cause chest pain. With quick and appropriate treatment, this stage of shock can be reversed.
Stage III. Refractory or Irreversible Shock
The length of time that poor perfusion has existed begins to take a permanent toll on the body's organs and tissues. The heart's functioning continues to spiral downward, and the kidneys usually shut down completely. Cells in organs and tissues throughout the body are injured and dying. The endpoint of Stage III shock is the patient's death.
Diagnosis of Shock
An accurate diagnosis of shock is essential for proper treatment and management. An accurate history and assessment of the patient's symptoms must be done before commencing treatment. Key indicators are a significant drop in blood pressure when compared with the patient's normal blood pressure. Extremely low urine output (oliguria) is usually present. Blood tests will reveal overly acidic blood pH with a low circulating concentration of carbon dioxide. Lactic acid levels will be elevated. Other tests may be performed to diagnose underlying condition. Chest x-rays, CVP, Hb, blood gases, and U&E may be performed.
Management of Shock
Management consists of supportive interventions which are geared to the underlying cause of the shock.
- Establish and maintain parenteral access. Two IV lines are preferred. Intra-osseous cannula may be needed in some patients.
- Supplemental oxygen therapy may be needed
- If the patient is in noncardiogenic shock (e.g. myocarditis, ventricular arrhythmias ), administer a colloid in 10 ml/kg boluses until BP and HR return to acceptable levels.
- If the patient has cardiogenic shock as suggested by cardiomegally, peripheral and pulmonary oedema, low voltages on ECG, and AV valvar regurgitation murmurs then the patient should be treated with inotropes, e.g. noradrenaline and with volume resuscitation.
- Dopamine at a starting dose of 5 - 10 ug/kg/min is a reasonable starting point for most situations (15 mg/kg in 50 ml D5 or NS at 1 - 2 ml/hour)
- Intubation may be needed patients with depressed consciousness where the GCS is less than 8 and it is secondary to shock
- Colloid challenge of 40 - 50 ml/kg in total
- Antibiotics may be prescribed for many patients who are suspected septic shock
- ABC: Fundamentals such as airway control, breathing and circulatory support must be addressed as a higher priority than antibiotic therapy. Ceftriaxone 100 mg/kg IV or IM is generally used because it provides good broad spectrum antibiotic coverage for most situations.
- Special cases (Neonates, immunosuppressed patients, and very old patients may require alternative or additional medications
- Neutropaenia protocols may be needed for immunocompromised patients
Prognosis
The prognosis for a patient depends on the underlying cause, nature and extent of comorbities. Septic Shock has a mortality of between 30 and 50 %. Hypovolemic, Anaphylactic and Neurogenic shocks respond well to medical interventions. The prognosis for cardiogenic shock is poor. Mortality of greater than 50 % may be expected.
Prevention
Nurses and ED physicians play an important role in the prevention of shock. Most preventable shocks are caused by dehydration during acute illnesses. The dehydration is usually secondary to severe vomiting or diarrhoea. Hence, shock can be prevented by recognizing patients who are unable to drink. Fluid replacement should be commenced as soon as possible. Other types of shocks are preventable by managing the underlying condition. Early interventions and treatments should be aimed preventing the occurrence of shock.
