If both the central venous catheter and PiCCO arterial catheter are placed on the same side (e.g. right femoral groin) a double hump indicator curve with resulting measurement errors may occur because of a disturbed temperature signal from the "cross talk" between the venous and arterial blood streams. In other words the cold temperature can pass across to the arterial thermistor without going through the cardiopulmonary system but directly from vein to artery. This is more common in paediatric patients.
Even when using long femoral venous catheters, there is a small effect from cross talk caused by thermal migration from the catheter into the vessel.
Cross talk can be avoided if the PiCCO arterial catheter is either placed in the opposite femoral artery or in the brachial/axillary artery.
If cross talk is avoided, thermodilution measurement is possible, but the PiCCO readings for GEDI will be slightly higher than the actual volumes. This is caused by the additional volume from the point of injection to the point of detection, because the catheter for indicator injection is not placed directly before or in the right atrium. The value for ELWI will be correct, as it is calculated from the difference of two overestimated volumes.
From PiCCO2 software version V3.1 onwards the PiCCO will ask for confirmation of where both the central venous and arterial catheters are placed to ensure accurate calculation of GEDI.