It is known that measurement of the intrathoracic blood volume (ITBV) is a more accurate estimate of cardiac preload than pressure measurements using central venous or pulmonary artery occlusion pressures. There is evidence to suggest that therapy to reduce extravascular lung water may improve outcome in the critically ill patient. The PiCCO^® monitoring system (Pulsion Medical Systems, Munich, Germany) provides an estimate of the ITBV, extravascular lung water (EVLW) and cardiac output (CO) via a thermodilution system. We hypothesised that the use of continuous veno-venous haemofiltration (CVVH) during these measurements could affect the PiCCO^® system and give inaccurate results.

Twenty-six patients (aged 20–81 years) were studied. Patients were hypotensive, required haemodynamic monitoring and were receiving CVVH for either renal failure or sepsis. Three measurements of CO, ITBV and EVLW were recorded on and off CVVH. The measurements were indexed for body surface area and the mean of each set of three values recorded. Data were normally distributed and analysed by paired t tests.

Performing PiCCO^® measurements with CVVH running underestimates CO, underestimates ITBV and overestimates EVLW. These measurement errors could result in wrong therapeutic decisions in the management of shocked patients. PiCCO^® measurements should be made with CVVH temporarily switched.