The effects of dobutamine, nitroprusside, or volume expansion on cardiac output and lung water after CPPV

Pulmonary microemboli can create an ARDS-like state in dogs (high pulmonary vascular resistance, pulmonary oedema and arterial hypoxemia). CPPV can correct the hypoxemia of pulmonary microemboli but reduces cardiac output (Q) and tissue oxygenation. This paper compares the effect of improving Q by infusing volume, reducing afterload, or increasing myocardial contractility. Four groups of seven dogs were studied. All had 0.125 g . kg-1 of starch microemboli (63-74 microns) infused and then CPPV at 15 cm H2O applied. The control group had no further treatment applied. In three other groups volume (dextran) or dobutamine or nitroprusside (NTP) was infused to return Q to the level before CPPV was applied. All treatments (volume, dobutamine and NTP) improved Q and O2 transport. Only the volume group had a significant increase in pulmonary microvascular pressure, Pmv = PLA + 0.4 (PPA - PLA) from 2.53 +/- 0.27 to 3.35 +/- 0.13 kPa, p less than 0.05. Only the volume group demonstrated a significant increase in lung water above (double) the control group as measured by a double indicator dilution technique (ETVL) and post mortem lung weights. We conclude volume infusions to improve a CPPV depressed Q may increase lung water and that better treatment would be to infuse NTP or dobutamine, thus maintaining a lower Pmv and therefore lung water. As a corollary the least CPPV should be applied to maintain adequate oxygenation and create the least need for interventions to improve Q.