In the context of septic shock, blood pressure (BP) is critically low and serves as a key diagnostic criterion, indicating a severe, life-threatening condition resulting from an infection. Specifically, septic shock is characterized by significantly low blood pressure that requires intervention to maintain organ perfusion.
Key Blood Pressure Thresholds
For a patient with a suspected or documented infection, septic shock is typically defined by specific blood pressure measurements:- Systolic Blood Pressure (SBP): This is the top number in a blood pressure reading, representing the pressure when the heart beats. In septic shock, the systolic blood pressure is often 90 mm Hg or less.
- Mean Arterial Pressure (MAP): This is the average blood pressure over a single cardiac cycle and is considered a better indicator of organ perfusion than systolic pressure alone. In septic shock, the mean arterial pressure is typically 65 mm Hg or less.
These low blood pressure readings are not isolated but must be accompanied by other signs of the body's organs not receiving enough blood flow.
To summarize the BP criteria:
| Blood Pressure Type | Threshold in Septic Shock |
|---|---|
| Systolic Blood Pressure (SBP) | ≤ 90 mm Hg |
| Mean Arterial Pressure (MAP) | ≤ 65 mm Hg |
Accompanying Signs of Hypoperfusion
The low blood pressure in septic shock is dangerous because it leads to insufficient blood flow to the body's tissues and organs, a condition known as hypoperfusion. This lack of adequate blood supply can result in organ dysfunction and failure. Therefore, the definition of septic shock necessitates that low blood pressure is accompanied by clinical signs of hypoperfusion, which may include:- Oliguria: Significantly reduced urine output, indicating poor blood flow to the kidneys.
- Hyperlactemia: Elevated levels of lactic acid in the blood, a byproduct of anaerobic metabolism that occurs when cells don't get enough oxygen.
- Poor peripheral perfusion: Signs like cool, clammy skin, or a slow capillary refill time (when pressing on the nail bed, the color returns slowly), indicating reduced blood flow to the extremities.
- Altered mental status: Confusion, disorientation, or decreased responsiveness, which points to inadequate blood flow to the brain.
