Does the central venous pressure still have the authority to evaluate a patient's volume status in clinical routine?

Background

Not rarely in clinical routine it is highly difficult to evaluate the volume status of a patient. Therefore, the attending physician can revert to the following parameters in ascending order concerning their invasive character: clinical signs (e.g. inspection of mucosa, skin turgor, the filling of jugular veins, edemas of the lower extremity, auscultation of the lungs), echocardiography, various laboratory findings (e.g. packed cell volume, electrolytes, fractional excretion of sodium), central venous pressure (CVP), thermodilution and pulse contour analysis, respectively, as well as pulmonary arterial wedge pressure.

Recent data suggest that the intrathoracic blood volume index (ITBI) determined by thermodilution can be characterized as the gold standard for the evaluation of a patient's volume status. However, in clinical routine the CVP, which has been used for decades, is still the most frequently applied nonclinical parameter for volume assessment. However, this is astonishing, because CVP has hardly been tested on modern hemodynamic measurement methods.

Aim

It was therefore the aim of our prospective study to obtain predictive values for the CVP – for ITBI values in a normal range, as well as for ITBI values falling short of or exceeding the normal range. In other words: Does the CVP still have entitlement or is it more appropriate not to identify any CVP value as to identify one that might be misleading concerning the clinical situation?

Methods

In 42 patients of an internal ICU, 837 hemodynamic measurements (respectively the average of three single measurements) including CVP as well as ITBI in combination with other thermodilution parameters (such as cardiac output index [CI], stroke volume index [SVI], extravascular lung water index [EVLWI], stroke volume variation) were determined using the PiCCO^® system (Pulsion, Munich). Twenty-four of the patients were male, 18 were female; age 60.6 years (± 13.5), APACHE II score of 22.6 on average. Statistics were analysed using SAS version 6.12.

Results

CVP, 10.9 mmHg (± 5.4); ITBI, 967 ml/m² (± 170); CI, 4.14 l/m² (± 1.16); SVI, 1505 dyn s/cm⁵/m² (± 514); EVLWI, 9.2 ml/kg (± 4.03).

A total 24.25% of the patients had ITBI < 850, resulting in a positive predictive value (PPV) of CVP of 24.49% and a negative predictive value (NPV) of 75.76% with regard to volume deficit. A total 39.07% of the patients had ITBI > 1000, resulting in a PPV of CVP of 37.74% and a NPV of 59.24% with regard to overfilling. The PPV and NPV for normal ITBI values is 34.80% and 62.16%. Two hundred and fifteen of 837 (25.70%) measurements were performed under catecholamine therapy; 64 (29.77%) of them were correctly classified with CVP, significantly less than for measurements performed without catecholamine therapy (37.94% accuracy; P = 0.031, chi-square test).

Conclusions

CVP has low PPV and NPV with regard to superior methods of preload assessment such as the ITBI. This low predictive effect is even more pronounced in patients with catecholamine therapy. In summary, volume assessment based only on CVP should be a thing of the past.