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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. more...

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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.

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.

Read more at Wikipedia.org


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Effects of autotransfusion on microvascular perfusion using passive leg-raising in patients with septic shock
From CHEST, 10/1/05 by Peter E. Spronk

PURPOSE: Passive leg raising (PLR) can be used effectively to treat hypotension associated with hypovolemia. Shock is associated with impairment of microvascular flow. We investigated the microvascular response to PLR in patients with shock.

METHODS: Patients who were admitted to the ICU with septic shock (defined by MAP<60 mm Hg and sepsis according to standard criteria) were assessed for sublingual microvascular perfusion by orthogonal polarization spectral (UPS) imaging before and 1 minute after PLR (45 degrees upward). Perfusion was estimated using a semi-quantitative microvascular flow index (MH) in small (diameter 10-25 [micro]m), medium (25-50 [micro]m), and large-sized (50-100 [micro]m) capillaries (0=no flow; 1=sludging (0-0,5 mm/s), 2=moderate flow (0,5-1,0 mm/s), 3=high flow (1,0-3,0 mm/s)).

RESULTS: Ten patients (2 female, 8 male; mean age 67 years) participated in this study. Mean APACHE-II score was 23 (range 13-33). Mean lactate levels were 3.5 mmol/l. MAP and CVP inceased after PLR (table). Microvascular flow increased in parallel in most patients, i.e. flow increased predominantly in small microvessels, while flow in the larger microvessels remained relatively preserved. In 4 patients, microvascular flow hardly improved after PLR. Also, after infusion of fluids until CVP was above 10, in 3 of those 4 patients flow had still not normalized. After giving 0,5 mg nitroglycerin iv as described before, flow normalized in all cases.

CONCLUSION: Changes in sublingual microvascular perfusion after PLR reflect the recruitment of blood from the venous leg pool in shock patients. Microvascular flow improves by volume infusion in most cases. Some patients may require additional infusion of nitroglycerin to actively open the microvascular system.

CLINICAL IMPLICATIONS: UPS imaging may be a valuable bed-side tool for assessing optimal fluid resuscitation.

DISCLOSURE: Peter Spronk, None.

Peter E. Spronk PhD * Daniel F. Faber MD Johannes H. Rommes PhD Gelre Hospitals (Lukas site), Apeldoorn, Netherlands

COPYRIGHT 2005 American College of Chest Physicians
COPYRIGHT 2005 Gale Group

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