PAH extraction and estimation of plasma flow in human postischemic acute renal failure

We determined the effect of postischemic injury to the human renal allograft on p-aminohippurate (PAH) extraction (E(PAH)) and renal blood flow. We evaluated renal function in 44 allograft recipients on two occasions: 1-3 h after reperfusion (day 0) and again on postoperative day 7. On day 0 subsets underwent intraoperative determination of renal blood flow (n = 35) by Doppler flow meter and E(PAH) (n = 25) by renal venous assay. Blood flow was also determined in another subset of 16 recipients on postoperative day 7 by phase contrast-cine-magnetic resonance imaging, and E(PAH) was computed from the simultaneous PAH clearance. Glomerular filtration rate (GFR) on day 7 was used to divide subjects into recovering (n = 23) and sustained (n = 21) acute renal failure (ARF) groups, respectively. Despite profound depression of GFR in the sustained ARF group, renal plasma flow was only slightly depressed, averaging 296 +/- 162 ml. min(-1). 1.73 m(-2) on day 0 and 202 +/- 72 ml. min(-1). 1.73 m(-2) on day 7, respectively. These values did not differ from corresponding values in the recovering ARF group: 252 +/- 133 and 280 +/- 109 ml. min(-1). 1.73 m(-2), respectively. E(PAH) was profoundly depressed on day 0, averaging 18 +/- 14 and 10 +/- 7% in recovering and sustained ARF groups, respectively, vs. 86 +/- 6% in normal controls (P < 0.001). Corresponding values on day 7 remained significantly depressed at 65 +/- 20 and 11 +/- 22%, respectively. We conclude that postischemic injury to the renal allograft results in profound impairment of E(PAH) that persists for at least 7 days, even after the onset of recovery. An ensuing reduction in urinary PAH clearance results in a gross underestimate of renal plasma flow, which is close to the normal range in the initiation, maintenance, and recovery stages of this injury.