Continuous Positive Airway Pressure With And Without High-Frequency Ventilation - Hemodynamics, Oxygenation, And Endocrine Response

After 18 h of mechanical ventilation following open heart surgery, central hemodynamics, systemic oxygen delivery (DO2), and oxygen consumption were assessed in ten consecutive patients receiving continuous positive airway pressure (CPAP) therapy. Plasma vasopressin, norepinephrine, and epinephrine levels were analyzed. While maintaining the mean airway pressure, two CPAP methods were studied: a demand CPAP with continuous flow without (CPAP) and one with high-frequency ventilation (CPAP-HFV). The frequency used during CPAP-HFV was 300 cycle/min. The spontaneous ventilatory rate was found to be equal during CPAP and CPAP-HFV. The cardiac and stroke volume indices were slightly higher (p less than .05) during CPAP-HFV, which accounted for the finding that DO2 was also slightly higher (p less than .05) during CPAP-HFV. The epinephrine and norepinephrine levels did not differ, whereas the vasopressin level was somewhat higher during CPAP-HFV, which might indicate a higher level of vigilance. It is concluded that cardiac output was slightly higher during CPAP-HFV compared to that during CPAP. This may be due to an effect of the oscillations on circulation or to differences in the level of vigilance.