Intra-abdominal hypertension (IAH)

Abdominal hypertension, also known as intra-abdominal hypertension (IAH), is a condition characterised by elevated pressure within the abdominal cavity. It can lead to significant morbidity and mortality due to its impact on abdominal organs and systemic circulation.

  • Normal: Less than 5 mmHg
  • IAH: Greater than or equal to 12 mmHg (persistent)

Categories of IAH :

  • Grade I: IAP 12-15 mmHg (Mild)
  • Grade II: IAP 16-20 mmHg (Moderate)
  • Grade III: IAP 21-25 mmHg (Severe)
  • Grade IV: IAP >25 mmHg (Very Severe)

Definition

  • Intra-Abdominal Hypertension (IAH): A sustained or repeated pathological elevation of intra-abdominal pressure (IAP) equal to or greater than 12 mmHg.
  • Abdominal Compartment Syndrome (ACS): A severe form of IAH where the intra-abdominal pressure exceeds 20 mmHg and is associated with new organ dysfunction or failure.

Causes

IAH can result from a variety of conditions that increase intra-abdominal volume or decrease abdominal wall compliance:

  1. Increased Intra-Abdominal Volume:
    • Ascites: Accumulation of fluid in the abdominal cavity.
    • Hemoperitoneum: Presence of blood in the peritoneal cavity.
    • Massive fluid resuscitation: Large volumes of fluid administered intravenously, commonly seen in critical care settings.
    • Bowel distension: Due to obstruction, ileus, or infection.
  2. Decreased Abdominal Wall Compliance:
    • Obesity: Excess adipose tissue increases abdominal pressure.
    • Abdominal trauma: Injury leading to swelling and bleeding within the abdominal cavity.
    • Postoperative conditions: Abdominal surgery can reduce compliance due to pain, muscle dysfunction, or dressings.

Pathophysiology

Elevated intra-abdominal pressure can compress abdominal organs, impairing their function and leading to systemic effects:

  1. Organ Compression:
    • Kidneys: Reduced renal perfusion leading to acute kidney injury.
    • Liver: Impaired hepatic blood flow causing liver dysfunction.
    • Gut: Decreased mesenteric blood flow leading to bowel ischemia and necrosis.
  2. Systemic Effects:
    • Cardiovascular: Increased intra-thoracic pressure, reduced venous return, and cardiac output.
    • Respiratory: Diaphragmatic elevation leading to reduced lung volumes and compliance, resulting in respiratory distress.
    • Central Nervous System: Increased intracranial pressure due to impaired venous return from the brain.

Methods of Measuring Intra-Abdominal Pressure (IAP)

  1. Trans-Bladder (Intravesical) Pressure Measurement
    • Procedure:
      • A Foley catheter is inserted into the bladder.
      • The bladder is partially filled with a sterile saline solution (typically 50-100 mL).
      • A pressure transducer is connected to the catheter, and the patient is positioned supine.
      • The pressure is measured at the end of expiration to avoid fluctuations due to respiratory movements.
    • Advantages:
      • Non-invasive and relatively simple to perform.
      • Widely accepted as the standard method for IAP measurement.
    • Considerations:
      • Ensuring the bladder is not overfilled is critical, as this can affect accuracy.
  2. Trans-Gastric Pressure Measurement
    • Procedure:
      • A nasogastric tube is placed into the stomach.
      • The tube is connected to a pressure transducer.
      • Measurements are taken similarly to the trans-bladder method, ensuring the patient is in a supine position and measurements are taken at end-expiration.
    • Advantages:
      • Useful in patients where bladder catheterisation is contraindicated.
    • Considerations:
      • Less commonly used than the trans-bladder method.
      • May be less accurate due to potential complications with gastric contents.
  3. Direct Intraperitoneal Pressure Measurement
    • Procedure:
      • Performed during surgery or via a percutaneous catheter placed directly into the abdominal cavity.
      • A pressure transducer is attached directly to the catheter to measure the intra-abdominal pressure.
    • Advantages:
      • Provides a direct and highly accurate measurement of IAP.
    • Considerations:
      • Invasive and typically reserved for surgical settings.
  4. Rectal Pressure Measurement
    • Procedure:
      • A rectal catheter is inserted, and a pressure transducer is used to measure IAP.
    • Advantages:
      • Another alternative when bladder or gastric measurements are not feasible.
    • Considerations:
      • Not widely used and may have varying accuracy depending on patient condition.

Clinical Management

Management of IAH and ACS involves both medical and surgical approaches:

  1. Medical Management:
    • Fluid Management: Careful regulation of intravenous fluids to avoid over-resuscitation.
    • Diuretics: Used to reduce fluid accumulation.
    • Paracentesis: Removal of excess abdominal fluid in cases of ascites.
  2. Surgical Management:
    • Decompression Laparotomy: Emergency surgery to relieve pressure in severe cases.
    • Abdominal Wall Reconstruction: For cases where decreased abdominal compliance is due to structural issues.
  3. Supportive Care:
    • Optimising Ventilation: Mechanical ventilation adjustments to improve respiratory function.
    • Monitoring and Support: Continuous monitoring of organ function and prompt treatment of organ failure.

References