Low-dose dopamine after kidney transplantation: assessment by Doppler ultrasound

Low-dose dopamine (LDD) is commonly used after kidney transplantation as a renoprotective agent, although the benefits of dopamine (DA) in this setting are controversial. LDD increases renal blood flow, decreases resistive index (RI) and causes diuresis in normal kidneys. We hypothesised that the vasculature of a denervated renal transplant may not respond to DA in the same way as healthy native kidneys. In a prospective, controlled study, renal blood flow velocity and vascular resistance were measured by Doppler ultrasound in recent kidney transplants (n = 20) over a range of DA doses (0-5 microg/kg/min). Main renal artery velocity was lower in kidneys with acute renal dysfunction than in those with normal function (0.60 +/- 0.31 vs. 0.81 +/- 0.24, respectively, p < 0.05). There was no demonstrable haemodynamic effect of LDD on either RI or main renal artery velocity as measured by Doppler ultrasound. Interestingly, the only significant correlation with mean RI was trough cyclosporin A level (r = 0.57, p < 0.001). Technical or timing factors cannot be used to explain the absence of DA effect, with equivalent doses capable of producing vasodilatation and reduced RI in studies of normal kidneys. In summary, these findings contrast the DA response of healthy native kidneys and may explain studies showing no clinical benefit of LDD in the early post-transplant period. These data suggest an insensitivity of recently implanted kidneys to the vasodilatory effects of LDD, that other factors such as cyclosporin A vasoconstriction may also be important, and question the rationale for routine LDD after kidney transplantation.