In the present study, there were no significant changes found in any cardiorespiratory parameters after the initiation of PC-IRV at an I:E ratio of 2:1. In particular, Cl, Do2, and Vo2 remained unaltered by the use of PC-IRV These results demonstrate that the improvement in oxygenation which accompanies use of PC-IRV at this I:E ratio is not associated with any deleterious effects on cardiac function or tissue oxygen delivery. Because higher I:E ratios were not utilized in this study, it is not possible to be sure that cardiorespiratory parameters would remain unchanged as the I:E ratio is further increased.
Despite the improvement in Pa02 which occurred when PC-IRV was used in our patients, there was little change in either Ca02 or Do2. This lack of alteration in Ca02 with PC-IRV was anticipated, since the patients studied had adequate oxygen saturation on conventional volume controlled ventilation, through the use of high FIo2 and PEEP, before being started on PC-IRV. Improvements in Sa02 and in Ca02 with initiation of PC-IRV therefore, were expected to be minimal. Nevertheless, the increase in Pa02 associated with use of PC-IRV may be important in the management of the patients with severe respiratory failure since it permits further decreases in FIo2 and/ or PEEP, limiting risk of barotrauma and oxygen-induced pulmonary toxicity, while allowing maintenance of Ca02 and Do2. in detail
Hemodynamic values that would affect pulmonary mechanics directly, through their effects on extravas-cular lung water or pulmonary vascular pressures, also showed no significant changes with use of PC-IRV In particular, WP, PVR, and pulmonary artery pressures did not demonstrate any alteration with PC-IRV. Starling forces, associated with formation of extravas-cular lung water and pulmonary edema, therefore, were little changed with PC-IRV, and no directly detrimental effects on pulmonary hemodynamics or fluid transport patterns would be expected to accompany PC-IRV.
Of the nine patients studied, only one showed significant hemodynamic deterioration associated with the initiation of PC-IRV There were no preexistent physiologic factors which could have served to separate this patient from the others studied. In particular, while on conventional ventilation with a PEEP 10, this patient had a Cl of 4 L/min/m2 with elevated WP (18 mm Hg) and CVP (16 mm Hg). After PC-IRV was started, Cl fell 33 percent, accompanied by decreases in WP and CVP, suggesting that decreased cardiac filling with progression down a Frank-Starling filling curve occurred. The deterioration in this patient, although it did not cause termination of the PC-IRV trial, points out that PC-IRV cannot be used indiscriminately in acute respiratory failure, and probably should not be initiated without invasive cardiorespiratory monitoring that permits close observation of Cl, Do2, and other cardiorespiratory parameters. In addition, because sedation and paralysis, required to achieve the longer inspiratory times used in PC-IRV increase the complexity of patient care, patients must be carefully selected and monitored for PC-IRV trials.
In this study, PC-IRV was associated with improvement in Pa02, decrease in peak airway pressures, and no significant overall changes in Cl, tissue oxygen metabolism (Do2, Vo2, 02Ext), or hemodynamic parameters. These results indicate that this respiratory modality may be useful in patients with severe respiratory failure, since PC-IRV may permit decreased FIo2 and Pip with no significant cardiorespiratory effects. Further studies will be necessary to define the benefits, primarily in terms of survival, associated with the use of PC-IRV
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