Noninvasive differential blood flow monitoring during one-lung anesthesia

A simple, noninvasive technique which has the capability of determining differential blood flow during one-lung anesthesia, when one lung is collapsed and the other is ventilated, is described. This technique uses partial rebreathing for a 30-s interval and an incremental Fick equation to eliminate the need for measuring mixed venous gas concentrations. The method relies on the lung as a window to the pulmonary circulation. A study on mongrel dogs that validates the hypothesis that this method can accurately measure the blood flow to the ventilated lung is reported. Total flow (cardiac output), pulmonary shunt, and the pulmonary capillary blood flow (PCBF) estimate were obtained during both lung and one-lung ventilation. Correlation of the PCBF estimate with measured PCBF for the ventilated lung is 0.86 with a regression equation y=0.85x+0.74