Central haemodynamics and oxygen transport during CPPV with frequencies of 16 and 8 times per minute.

During the weaning period after 18 h of mechanical ventilation following open-heart surgery, central haemodynamics, systemic oxygen transport and total oxygen consumption were assessed in a total of 11 patients receiving continuous positive pressure ventilation. Mechanical ventilatory rates of 16 and 8 times per minute were studied. Systemic arterial pressure, cardiac index, stroke volume index, left ventricular stroke work index, rate-pressure-product, and systemic oxygen transport were observed to be higher during the lower ventilatory rate. Because transmural right atrial and pulmonary capillary wedge pressures were also higher during ventilation with a frequency of eight times per minute, the lower frequency may impede venous return less. This might explain the difference found in central haemodynamics between the two ventilation frequencies.