Central Venous Pressure (CVP) Monitoring

Central venous pressure (CVP) monitoring is a valuable tool used to assess a patient’s hemodynamic status, particularly their fluid balance and right ventricular function. It involves measuring the pressure in the vena cava, near the right atrium of the heart.

I. Indications

CVP monitoring is indicated in patients with:

• Complex fluid balance issues.
• Hemodynamic instability.
• Severe sepsis or septic shock.
• Cardiogenic shock.
• Acute respiratory distress syndrome (ARDS).
• Renal failure.
• Major surgery.
• Need for vasoactive drug administration.

II. Contraindications

CVP monitoring is contraindicated in patients with:

• Absolute contraindications:
  • Infection at the insertion site.
  • Thrombosis of the cannulated vein.
• Relative contraindications:
  • Coagulopathy.
  • Distorted anatomy.
  • Severe pulmonary disease.

III. Procedure

The procedure for CVP monitoring involves several key steps:

1. Central Venous Catheter Placement:
   • A central venous catheter is inserted into a large central vein (internal jugular, subclavian, or femoral) using either an anatomical landmark-based technique or ultrasound guidance.
   • The choice of insertion site depends on the patient’s condition, anatomical factors, and the clinician’s expertise.
   • For the purpose of this CVP monitoring lesson, we’ll assume a CVC is already in place. The procedure for CVC placement itself is covered in other lessons.
2. Preparation of the Monitoring System:
   • Gather the necessary equipment:
     • Pressure transducer.
     • Pressure tubing.
     • Continuous flush device (usually delivering saline at 3-5 mL/hr).
     • Monitor with a pressure display.
     • IV pole.
     • Sterile gloves.
     • Zeroing device.
     • Leveling device (e.g., spirit level).
   • Ensure all connections are tight to prevent leaks.
   • Flush the pressure tubing and transducer with saline to remove any air bubbles.
3. Patient Positioning:
   • Position the patient supine, if possible. If the patient cannot lie flat, the head of the bed can be elevated up to 45 degrees. Any deviation from supine should be documented, as it will affect the CVP reading.
4. Zeroing the Transducer:
   • Identify the phlebostatic axis. This is the reference point for measuring CVP, corresponding to the level of the right atrium.
     • Find the intersection of two imaginary lines: one extending from the fourth intercostal space at the sternal border, and the other extending midway between the anterior and posterior chest wall.
   • Position the transducer at the level of the phlebostatic axis.
   • Open the transducer stopcock to air and zero the monitor. This calibrates the system to atmospheric pressure, ensuring accurate readings.
5. Obtaining the CVP Measurement:
   • Turn the stopcock to connect the transducer to the patient’s CVC.
   • Observe the CVP waveform on the monitor. It typically has three positive deflections (a, c, and v waves) and two negative deflections (x and y descents).
   • Measure the CVP at the end of expiration. This minimizes the influence of respiratory variations on the reading.
   • Record the CVP value.
   • Continuously monitor the CVP, noting any trends or significant changes.
6. Maintenance of the System:
   • Maintain a continuous infusion through the flush device to prevent clotting in the catheter.
   • Check the system for air bubbles, leaks, and loose connections regularly.
   • Re-zero the transducer periodically (e.g., every shift) and whenever the patient’s position changes.
   • Change the transducer and tubing according to hospital policy (usually every 72-96 hours).
7. Interpretation of CVP Values:
   • Normal CVP values generally range from 2 to 8 mm Hg. However, the “normal” range can vary slightly depending on the patient’s clinical condition and the reference values used by the institution.
   • A low CVP (less than 2 mm Hg) may indicate hypovolemia (fluid deficit).
   • A high CVP (greater than 8 mm Hg) may indicate hypervolemia (fluid overload) or impaired right ventricular function.
   • It is crucial to interpret CVP values in the context of the patient’s overall clinical condition, including other hemodynamic parameters (e.g., heart rate, blood pressure, urine output) and physical examination findings. CVP should not be used in isolation to guide fluid management.

IV. Intravenous Considerations

Intravenous (IV) access is crucial for CVP monitoring, both for the initial CVC placement and for ongoing management.

• Establishment of IV Access: Prior to CVC insertion, establish peripheral IV access to administer fluids, sedatives, and other medications as needed.
• Fluid Administration: IV fluids are often administered to optimize the patient’s volume status, which directly affects CVP. The rate and type of fluids are determined by the patient’s underlying condition and hemodynamic status.
• Medication Administration: Many medications, such as vasopressors or inotropes, which affect CVP, are administered intravenously.
• Continuous Infusion: A continuous IV infusion, such as normal saline, is used to maintain the patency of the pressure monitoring system and prevent clotting within the CVC.

V. Scale

While there isn’t a specific scale to predict CVP values, understanding the factors that influence CVP is essential for accurate interpretation. These factors can be broadly categorized as:

• Volume Status:
  • Hypovolemia (low blood volume) decreases CVP.
  • Hypervolemia (high blood volume) increases CVP.
• Cardiac Function:
  • Right ventricular dysfunction increases CVP.
  • Increased contractility may slightly decrease CVP.
• Venous Tone:
  • Vasoconstriction increases CVP.
  • Vasodilation decreases CVP.
• Intrathoracic Pressure:
  • Positive pressure ventilation increases CVP.
  • Spontaneous breathing has less effect on CVP.
• Patient Position:
  • Supine position is the standard for measurement.
  • Changes in position affect hydrostatic pressure and thus CVP values.