Hemodynamic Effects of Oxygen Therapy in Patients With Acute Exacerbations of Chronic Obstructive Pulmonary Disease: Discussion
Standard treatment of these patients includes the administration of oxygen to increase the oxygen-carrying capacity of the blood. Therefore, defining whether increasing Sa02 in these patients leads to a rise in Vo2 is of great clinical importance in order to determine if the excess oxygen supplied is actually used by the tissues. Degaute et al observed that increasing FIo2 from 0.21 to 0.28 leads, to an increase in Pa02, Pv02, and the coefficient of oxygen delivery (the inverse of the oxygen extraction ratio) and to a decrease in cardiac output. A subgroup of patients with higher Pa02 showed no changes in Do2 and a decrease in cardiac output, whereas those with more severe pulmonary impairment presented an increase in Do2, with no change in cardiac output and greater decreases in the oxygen extraction ratio. Although no Vo2 values are reported, it can be inferred from their data that Vo2 decreased in the group in which Do2 did not change (due to the decrease in the oxygen extraction ratio), and Vo2 possibly remained constant in the group in which Do2 increased, due to the coincident and more marked decrease in the oxygen extraction ratio.
Lejeune et al found in 22 patients with decompensated COPD that increasing FIo2 from 0.21 to 0.24 to 0.28 caused an increase in Sa02 and Sv02, accompanied by a drop in cardiac output. The Do2 tended to increase, and Vo2 did not change. With higher FIo2 (0.35 to 0.40), there was a significant increase in Do2, whereas Vo2 did not change. These authors concluded that tissue oxygenation improves after oxygen therapy, as shown by increases in Pv02. This finding could also reflect a lack of utilization of the oxygen supplied by increasing Sa02 and therefore does not necessarily imply a better tissue oxygenation.
Kawakami et al found in patients with stable COPD that breathing pure oxygen resulted in an increase in Pv02 and an increase in cardiac output and the coefficient of oxygen delivery (decreased oxygen extraction ratio). Nonsurvivors presented lower baseline Sv02 values compared to survivors. After the breathing of 100 percent oxygen, the Sv02 in nonsurvivors rose to a level equivalent to that of survivors. Although not reported, the rise in Sv02 should be accompanied by an increase in Do2, since the coefficient of oxygen delivery (and therefore the oxygen extraction ratio) did not change significantly. Those findings suggest that Vo2 did not change after increasing Do2.