SHOCK

SHOCK

DEFINITION:-

Shock is defined as clinical state of cardiovascular collapse characterized by an acute reduction of effective circulatory blood volume and an inadequate perfusion of cells and tissues.

CLASSIFICATION AND ETIOLOGY OF SHOCK:-

1. Hypovolemic Shock

  i. Acute hemorrhage

  ii. Dehydration from vomitings, diarrhea

  iii. Burns

  iv. Excessive use of diuretics

  v. Acute pancreatitis

2. Cardiogenic Shock

  i. Deficient emptying, e.g.

• Myocardial infarction

• Cardiomyopathies

• Rupture of the heart, ventricle or papillary muscle

• Cardiac arrhythmias

  ii. Deficient filling, e.g.

• Cardiac tamponade from hemopericardium

  iii. Obstruction to the outflow, e.g.

• Pulmonary embolism

• Ball valve thrombus

• Tension pneumothorax

• Dissecting aortic aneurysm

3. Septic Shock

  i. Gram-negative septicemia (endotoxic shock),

 e.g. infection with E. coli, Proteus, Klebsiella, Pseudomonas

and Bacteroides

  ii. Gram-positive septicemia (exotoxic shock), 

e.g. infection with streptococci, pneumococci.

4. Other types

  i. Traumatic shock

• Severe injuries

• Surgery with marked blood loss

• Obstetrical trauma

  ii. Neurogenic shock

• High cervical spinal cord injury

• Accidental high spinal anesthesia

• Severe head injury

  iii. Hypoadrenal shock

• Administration of high doses of glucocorticoids

• Secondary adrenal insuficiency (e.g. in tuberculosis, metastatic disease, bilateral adrenal hemorrhage, idiopathic adrenal atrophy)

PATHOGENESIS:-

CLINICAL FEATURES OF SHOCK:-

- Hypotension

- Cold clammy skin

- Rapid, thready pulse

- Shallow and sighing respiration

- Pale face, sunken eyes and weakness

- Uncontrolled sepsis-warm skin due to vasodilatation

- Urinary output less than 30 ml/hour

STAGES OF SHOCK:-

- An initial non-progressive phase during which reflex compensatory mechanisms are activated and perfusion of vital organs is maintained

- A progressive stage characterized by tissue hypoperfusion and onset of worsening circulatory and metabolic imbalances including acidosis

- An irreversible stage that sets in after the body has incurred cellular and tissue injury so severe that even if the hemodynamic defects are corrected, survival is not possible.

MORPHOLOGICAL CHANGES OF SHOCK:-

The morphogenic changes in shock are due to hypoxia resulting in degeneration and necrosis.

Hypoxic encephalopathy: 

Cerebral ischemia in compensated shock may produce altered state of consciousness. In prolonged shock and cardiac arrest brain suffers from severe ischemic damage with loss of cortical function, comma and a vegetative state. Dead and dying nerve cells are replaced by gliosis.

Heart in shock: 

There are two important morphogenic changes in heart in all types of shock

1. Hemorrhage and necrosis: 

There may be small and large ischemic areas or infarcts particularly located in sub-pericardial and subendocardial region.

2. Zonal lesion: 

There are opaque transverse contraction band in myocytes near intercalated disc.

Shock lung: 

Due to dual blood supply lung are not effected by hypovolemic shock but is affected by septic shock.

• Lungs become heavy and wet.

• Changes of adult respiratory distress syndrome are seen.

• The changes include congestion, interstitial and alveolar edema, lymphocyte infiltration and fibrin and platelet thrombi in microvasculature.

 Shock kidney:

• Irreversible renal injury.

• The end result is generally anuria and death.

• Tubular lesions are seen referred to as acute tubular necrosis.

 Adrenal shock:

• Adrenal shows stress syndrome.

• This includes release of aldosterone, glucocorticoid and catecholamines like adrenaline. In severe shock, adrenal hemorrhage can occur.

Liver in shock:

• Due to hypoxia vasodepression material is released which causes vasodilatation.

• Focal necrosis, fatty liver and impaired liver functions.

 Hemorrhagic gastroentropathy: 

Hyperfusion of alimentary tract.

COMPLICATIONS:-

Life threatening complications in shock are due to hypoxic cell injury which results in immune-inflammatory responses and activation of various cascades. Various complications of shock are:

- Acute respiratory distress syndrome

- Disseminated intravascular coagulation

- Acute renal failure

- Multiple organ dysfunction syndrome

  With progression of the condition, patient can develop stupor, coma and finally death.