02/02/2026
CVP Monitoring: Short details
Central venous cannulae should be placed by the internal jugular or subclavian route into the SVC (not the RA), . This allows monitoring of right-sided fi lling pressures and the dynamic response to fl uid challenges, repeated central venous blood gas estimation (of no value for pO2 and pCO2 but useful for tracking changes in pH and [lactate]), and estimation of central venous oxygen saturation (ScvO2) Central venous pressure
Normal CVP is approximately 4–8 cmH2O and should refl ect both RV and LV end-diastolic pressures. Changes in circulating volume, venoconstriction or dilatation, and pulmonary vascular disease may all mean that CVP does not reflect left-sided filling pressures. In all causes of shock, myocardial filling pressures need to increase to maintain stroke volume, but to an unpredictable degree. Consequently, static measurement of CVP is of little value and it is better to measure the response to a volume challenge. Fluid challenge
• The principle is that a fl uid challenge will produce an initial rise in CVP but, when the infusion is completed, the fl uid will redistribute and the CVP will then fall, particularly in hypovolaemia • In well-fi lled patients, there will be a net increase in CVP which will be sustained
• By convention, 200 mL of colloid (500 mL of crystalloid) is given over 10–15 min, the CVP is measured before the infusion starts, immediately it is completed, and again 10–15 min later • A sustained rise in CVP above baseline of >3 cmH 2O indicates the circulation is well-fi lled
• An initial rise then a fall, or failure of the CVP to rise by 3 cmH 2O implies the circulation is empty and more fl uid should be given.
