Effects of Increased Tissue Pressure on Organ Perfusion
Increased tissue pressure directly impairs organ perfusion by reducing the effective perfusion pressure, which is calculated as the difference between mean arterial pressure and tissue pressure. 1
Understanding Tissue Pressure and Perfusion Pressure
Organ perfusion is determined by the effective perfusion pressure, which is influenced by three key factors:
- Mean arterial pressure (MAP): The inflow pressure for most organs and the main determinant of organ perfusion 1
- Venous outflow pressure: Affects blood flow out of the organ 1
- Extravascular/tissue pressure: Pressure exerted on vessels from surrounding tissue compartments 1
The relationship can be expressed as:
- Effective perfusion pressure = Mean arterial pressure - (Venous pressure + Tissue pressure) 1
Mechanisms of Impaired Perfusion with Increased Tissue Pressure
Increased tissue pressure negatively impacts organ perfusion through several mechanisms:
- Direct vessel compression: Elevated extravascular pressure compresses blood vessels, particularly capillaries and venules, reducing their diameter and increasing resistance to flow 1
- Reduced pressure gradient: Decreases the effective perfusion pressure driving blood through the tissue 1
- Impaired microcirculation: Compromises oxygen and nutrient delivery to cells 2
- Venous congestion: Can occur when outflow is impeded, further increasing tissue pressure in a vicious cycle 1
Clinical Scenarios with Increased Tissue Pressure
Several clinical conditions involve increased tissue pressure affecting organ perfusion:
- Compartment syndromes: Elevated pressure within fascial compartments compromises tissue perfusion 1
- Intraabdominal hypertension: At pressures of 20 mmHg, portal venous flow and hepatic arterial flow are reduced by 35% and 55%, respectively 1
- Intracranial hypertension: Reduces cerebral perfusion pressure 1
- Surgical positioning: Steep Trendelenburg position increases organ outflow pressure 1
- Gas insufflation: Peritoneal or thoracic gas insufflation during surgery increases compartment pressure 1
Clinical Management Considerations
When managing patients with increased tissue pressure:
- Adjust MAP targets: Increase mean arterial pressure targets when venous or compartment pressures are elevated 1
- Compensate for compartment pressure: If compartment pressure is 15 mmHg and target perfusion pressure is 65 mmHg, maintain MAP >80 mmHg 1
- Monitor tissue oxygenation: Consider using tissue oxygen tension monitoring as an early indicator of compromised perfusion 3, 4
- Decompress when necessary: Surgical decompression may be required in severe compartment syndromes 1
- Fluid management: Appropriate fluid resuscitation helps enhance visceral perfusion in conditions like mesenteric ischemia 1
Organ-Specific Considerations
Different organs have varying sensitivity to increased tissue pressure:
- Kidneys: Particularly sensitive to decreased perfusion pressure; elevated intraabdominal pressure promotes splanchnic venous congestion and impairs renal function 1
- Intestines: Vulnerable to ischemia when mesenteric perfusion pressure decreases, as in intraabdominal hypertension 1
- Brain: Intracranial pressure directly opposes cerebral perfusion pressure 1
- Skin and subcutaneous tissues: Often the first to show signs of compromised perfusion with increased tissue pressure 4
Monitoring Approaches
To assess the impact of increased tissue pressure on organ perfusion:
- Direct pressure measurement: When possible, measure compartment pressures directly 1
- Tissue oxygen tension: Subcutaneous oxygen tension (PsqO2) is a sensitive indicator of compromised tissue perfusion 4
- Lactate levels: Elevated lactate suggests inadequate tissue perfusion 1
- Organ-specific function tests: Monitor for signs of organ dysfunction (e.g., decreased urine output for kidneys) 1
- Tissue perfusion pressure (TPP): A newer concept defined as the difference between mean arterial pressure and critical closing pressure, which may provide additional information about perfusion adequacy 5