Alteration of Pulmonary Oxygenation by Pulmonary Artery Occluded Pressure Measurements in Mechanically Ventilated Patients: Conclusion

Patients with coronary artery disease or with valvular heart disease seem to be candidates for the Pa02 decrease when their resting PAP was elevated, as demonstrated in Figure 3. Both inhalational and opiate anesthetic agents also affect pulmonary oxygenation and vasoreactivity, which seem to be dependent on the existing level of vascular tone. On the other hand, sympathectomy of the pulmonary vasculatures, in this case induced by cervical epidural anesthesia, is unlikely to affect the vasoreactivity to the balloon manipulation. Thus, it remains unclear whether the Pa02 decrease during the balloon inflation was caused by purely mechanical obstruction, and/or by changes in reflex responses due to either anesthetics used or the disease per se. —Ā

In addition to significant changes in blood distribution within the lungs, the mechanical obstruction of pulmonary blood flow might increase anastomotic bronchial blood flow. The importance of these factors for the changes, both a decrease or an increase in Pa02, could also be dependent on the degree of obstructed area of the pulmonary vasculature and the position of the balloon* as indicated in the present results. However, a recent study has verified that the distal tip of the PAC moves synchronously with the balloon inflation and deflation. Since we took the chest radiographs during the deflation, the importance of the influence of the obstructed area due to the presence of the PAC balloon on the changes in PaOz may need to be reexamined.
We conclude that although pulmonary arterial occlusion by the PAC balloon could not cause severe hypoxemia in the majority of anesthetized, mechanically ventilated adult patients, in some female patients and patients with cardiac and coronary artery disease, a significant decrease in Pa02 could occur during the PAOP measurements probably due to redistribution and/or maldistribution of pulmonary blood flow. Since CO is maintained during the balloon inflation, significant impairment in the oxygen delivery to the tissues is unlikely to occur. However, our results suggest that PAOP measurements may cause impairment in oxygenation in patients with reduced pulmonary vasculature and/or with compromised pulmonary oxygenation such as acute pulmonary failure.


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