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What is shock?

Shock is a life-threatening condition that occurs when different organs of the body are not getting enough blood to ensure normal function. It is a frequent cause of admission to the ICU.

  • Because blood carries the oxygen required for each organ to fulfill its role, patients in shock can experience a dramatic "shut down" of their organs;
  • Low blood pressure is a typical sign of shock;
  • Low levels of consciousness, low urine output, and cold, clammy extremities (hands and feet) are other indicators that a patient may be in shock.

What can cause shock?

Shock can be caused by different medical conditions, including:

  • Severe infections;
  • Heart problems, such as a heart attack or abnormal heart beat;
  • Bleeding;
  • Severe dehydration;
  • Allergic reactions;
  • A blood clot in the lung, known as a pulmonary embolism.

Why is the blood pressure so low?

Depending on the cause of the shock, the low blood pressure may be result from:

  • A failure of the heart to pump the blood around the body;
  • A loss of tone of the blood vessels, known as vasodilatation;
  • A combination of both of the above.

What can be done to normalize blood pressure?

Different treatments can be given to normalize the blood pressure:

  • Medications, called Vasopressors, can be used to help increase the blood pressure;
  • Treating the underlying cause of the shock, such as using antibiotics to control an infection.

What are the risks of having a low blood pressure?

If the blood pressure (or the blood flow) is not restored rapidly in a patient in shock, then different organs will stop functioning normally.

  • The brain, lungs, heart, kidneys, liver, and bowel may all be damaged by a low blood pressure;
  • Some of this damage may be reversible, but if the shock is prolonged despite aggressive treatments, some organs may never return to normal function.

What is a safe range for low blood pressure?

Blood pressure varies from minute to minute within the same patient and between patients.

In the ICU, the medical team often uses the mean arterial pressure to monitor and treat patients. The mean arterial pressure is the average pressure in a patient’s arteries during one cardiac cycle, or contraction and relaxation of the heart.

  • A mean arterial pressure equal or above 65 is usually considered normal, and is often used as a target when attempting to revive a patient back to consciousness (resuscitation) and treating the shock.

However, a target of 65 may not be right for every patient.

  • Some patients may not develop serious organ problems until the mean arterial pressure drops to 60 or even below;
  • Other patients (such as those with untreated chronic high blood pressure) may need a higher mean arterial pressure to maintain normal organ functions.

The ICU team will determine which mean arterial pressure is the most appropriate target for each patient.

What signs indicate the patient is getting better?

The return of a normal blood pressure may not necessarily mean the patient is getting better. That could simply be the result of the vasopressor medication, and the patient may still be very sick.

So the medical team looks for other signs of improvement, including:

  • Normal blood pressure even when the dose of the vasopressor has been reduced or the medication has been stopped completely;
  • Favorable response to any treatment targeting the cause of the shock. For example, successfully reopening a blocked blood vessel;
  • Improved function of different organs. For instance, increase urine output can indicate improved kidney function.

The bedside nurse and the ICU physician will be best able to tell you if any of these changes indicate a real improvement.

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Location and contact

Critical Care Medicine

Sunnybrook Health Sciences Centre
2075 Bayview Avenue, 
D-wing, 1st floor
room D1 08
Toronto, ON M4N 3M5

Phone: 416-480-4522
Fax: 416-480-4999

For information about patients admitted to Sunnybrook's Intensive Care Units, please contact the unit through the hospital switchboard at 416-480-6100