Central venous lines and Central venous pressure

Background

  • Central venous cannulation is a relatively common procedure (particularly in anaesthesia/intensive care).
    • NB It is unlikely you will be asked to insert a central venous line as a junior doctor (let alone a student).  However, you may be asked to measure CVP from a central line or assist/observe one being inserted.

Indications

  • Measurement of CVP and/or replacement of circulating volume (e.g. in patients in shock with failed fluid resuscitation)
  • Infusion of irritant drugs and total parenteral nutrition
  • Difficult peripheral access (last resort)
  • Insertion of pacing wires or pulmonary artery catheters
  • Haemofiltration/haemodialysis
  • Long-term IV treatments e.g. chemotherapy or antibiotics

A note about catheters

  • There are many different types and sizes of catheters used in different situations
    • In general- wide bore cannulae are used in resuscitation and haemofiltration (BUT increased risk of haemorrhage and air embolus during insertion and thrombosis and subsequent stenosis); whilst narrow lumen cannulae are better suited for administering vasoactive drugs
  • There are also several different sites for CVC insertion including the internal jugular vein, the subclavian vein, the femoral vein, the external jugular vein and peripheral veins (commonly the Basilic or Cephalic veins in the antecubital fossa)
    • Whilst sites vary depending on the patient and indication, in general,
      • internal jugular vein is favoured for acute vasoactive drug administration and regular CVP monitoring
      • the subclavian is favoured for resuscitation and CVP monitoring
      • the peripheral veins are favoured for prolonged therapies

Insertion

  • Central venous catheters are generally inserted using the Seldinger technique
    • 14-03-02-figura1
  • For instructions on how to insert CVCs, see here (FRCA website).
    • NB ALWAYS use aseptic technique
  • ALWAYS carry out a CXR after CVC insertion to check position.

Potential Complications

  • Haemorrhage- particularly those on warfarin/other anticoagulation or with clotting disorders
  • Occlusion- either from thrombosis or a kinked tube.  The CVC requires regular flushing to avoid haemostasis and a secure dressing to prevent tube problems.
  • Infection- redness, pain and inflammation around the site may indicate infection.  Aseptic techniques should be used when inserting catheters and clean techniques used when measuring/removing/using etc.
  • Air embolus- if a line becomes disconnected there is a risk of air embolus.  Lines should be checked regularly to avoid this.
  • Catheter displacement- occasionally catheters can fall into the right atrium and ventricle and cause arrhtyhmias which should be noted and managed ASAP.

Measuring CVP

  • Manually using a manometer
    • WIPE (wash hands, introduce self, check patient details, explain and gain consent)
    • If IV fluid is not running, ensure the CVC is patent by flushing the catheter with normal saline
    • Place the patient flat in the supine position (if possible)
    • Line up the manometer arm with the phlebostatic axis (this is the intersection between the 4th IC space and the mid-axillary line- almost at the level of the right atrium), and ensure the bubble is between the two lines of the spirit level.
    • Move the manometer scale up and down to allow the bubble to be aligned with 0 on the scale (zeroing the manometer)
    • Turn the three way tap off to the patient and open to the manometer
    • Open the IV fluids and slowly fill the manometer to a level higher than the expected CVP
      • NB Normal CVP is 3-8 cm H20 (some say 5-10cmH20) or 2-6 mmHg
    • Turn the 3-way tap on to the patient- the fluid level should fall until gravity equals the pressure.
      • If the pressure varies with patient breathing, take the lowest value.
    • Turn the tap off to the manometer.
    • Record CVP, wash hands and thank the patient,
  • Using the transducer
    • WIPE
    • The CVC will be connected to fluids under pressure- ensure that the pressure is up to 300mmHg.
    • Place the patient flat in the supine position (if possible)
    • Often there will be multiple transducer ports to choose from (commonly the white port is used for CVP measurement- BUT CHECK)
    • Tape/secure the port to the phlebostatic axis or as close as possible to the right atrium.
    • Turn the tap off to the patient and open to the air by removing the cap from the three way port.
    • Press 0 on the monitor to zero the transducer.
    • Replace the cap and turn the tap on to the patient.
    • Observe the CVP trace and level- record the CVP.

Untitled picture

Interpretation

  • NB Interpret in conjunction with presentation and other investigations
  • Raised CVP
    • Increased intrathoracic pressure
    • Impaired cardiac function (only useful for right heart evaluation)
    • Hypervolaemia
    • SVC obstruction
  • Decreased CVP
    • Hypovolaemia
    • Reduced IT pressure (e.g. inspiration)
Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s