Effect of catheter position on thermodilution cardiac output during continuous positive-pressure ventilation

PEEP may decrease regional perfusion to nondependent lung regions, thereby creating different zones of thermal dissipation in dependent and nondependent zones of the lung. Under these conditions, the measurement of cardiac output by thermodilution may, thus, be influenced by the vertical position of the pulmonary artery catheter in the lung. We investigated this hypothesis in 7 healthy, anesthetized pigs by comparing cardiac output measurements from thermistors located in dependent and nondependent lung regions at varying levels of PEEP. Our data from thermistors in these 2 positions were similar, suggesting that the measurement of cardiac output by thermodiluation is not influenced by the vertical position of the thermal sensor with respect to the left atrium.