Central Venous Pressure Measurement

Central venous pressure is the pressure in the superior vena cava or right atrium, measured through a central venous catheter. It reflects right atrial filling and the interaction between venous return and right heart function.

It is used as one component of haemodynamic assessment. A single value is a poor predictor of fluid responsiveness, so trends and the waveform are more informative.

Usage. It is used in intensive care, theatre, and in the assessment of shock, heart failure and fluid status.

Preparation and technique. The transducer is zeroed and levelled at the phlebostatic axis, at the fourth intercostal space in the mid-axillary line. Readings are taken at end expiration. In patients on mechanical ventilation, positive pressure raises the reading.

Reference values. The usual range is 2 to 8 mmHg, which corresponds to about 3 to 11 cm H2O.

Waveform. The a wave reflects atrial contraction, the c wave closure of the tricuspid valve, and the v wave atrial filling. The x and y descents correspond to atrial relaxation and tricuspid opening.

Contraindications and precautions. Central line insertion is avoided or modified in coagulopathy and at infected sites. Complications of insertion include pneumothorax, arterial puncture, infection and thrombosis.

Interpretation.

• A low value supports hypovolaemia.
• A high value occurs in right heart failure, tricuspid valve disease, pulmonary embolism, pulmonary hypertension, cardiac tamponade, tension pneumothorax, fluid overload and high positive end expiratory pressure.
• Large a waves occur in tricuspid stenosis and pulmonary hypertension. Cannon a waves occur in atrioventricular dissociation. Large v waves occur in tricuspid regurgitation.
• A rising value during fluid challenge with no rise in cardiac output suggests no fluid responsiveness.

Critical values and findings needing immediate action. A high central venous pressure with hypotension and distended neck veins requires immediate assessment for tamponade, tension pneumothorax and massive pulmonary embolism.

Limitations and artefacts. Incorrect transducer level, damped traces, catheter malposition and respiratory variation distort readings. Values do not reliably predict fluid responsiveness.

Follow up tests. Echocardiography, lactate, central venous oxygen saturation, cardiac output measurement, and chest X-ray to confirm catheter position.

Special groups. Mechanically ventilated patients have raised values from intrathoracic pressure. Children use values suited to age and body size.