Is EVLW displayed correctly in a patient following pneumonectomy or when parts of the lungs are not perfused?
Generally, EVLW is only measured in the parts of the lungs that are perfused. In the case of a pneumonectomy, there will be discrepancies in the Intrathoracic Blood Volume (ITBV) and Extravascular Lung Water (EVLW), but the values for Cardiac Output as well as GEDV are correct. To estimate the error in EVLW measurement post pneumonectomy we have to go in the formulas: Generally: ITTV = CO x Mtt ITTV = Intrathoracic Thermal Volume, “needle to needle volume” PBV = CO x Dst PBV = Pulmonary Blood Volume, biggest “mixing chamber” GEDV = ITTV – PBV ITBV = GEDV x 1.25 empiric determination for normal lungs EVLW = ITTV – ITBV Post pneumonectomy: ITTV post pneumonectomy will decrease, but measured correctly PBV post pneumonectomy will decrease, but measured correctly GEDV = ITTV – PBV will be calculated correctly ITBV = GEDV x 1.25 factor 1.25 is valid for 2 lungs, post pneumonectomy this factor is assumed to be smaller ITBV will be overestimated post pneumonectomy EVLW = ITTV – ITBV overestima
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