Mark Hilberman

The diuretic properties of dopamine in patients after open-heart operation.

Dopamine and dobutamine were administered to 12 patients who had undergone open cardiac operations. To eliminate the effects of variation in systemic blood flow upon renal function the drug infusion rates were adjusted to achieve equal cardiac outputs. Under conditions of equivalent systemic pressure and flow, dopamine (5.0 ± 1 μg · kg-1 · min-1) and dobutamine (3.5 ± 1.8 μg · kg-1 · min-1) had similar effects upon glomerular filtration rate (90 ± 29 vs. 83 ± 27 ml · min-1 · 1.73 m-2) and effective renal plasma flow (375 ± 119 vs. 357 ± 126 ml · min-1 · 1.73 m-2). However, dopamine administration resulted in a significantly greater diuresis (2.8 ± 2.7 vs. 1.0 ± 0.3 ml/min), natriuresis (0.32 ± 0.39 vs. 0.07 ± 0.10 mEq Na+/min), and kaliuresis (0.15 ± 0.06 vs. 0.10 ± 0.03 mEq K+/min) (P < 0.05). In patients with modest depression of cardiac performance and renal vasoconstriction, dopamines selective renal vasodilator effects were not evident. Furthermore, these data suggest that dopamine inhibits tubular solute reabsorption directly. Thus, the diuresis and natriuresis that frequently accompany dopamine administration may occur independently of any effects of dopamine upon renal blood flow.

Glomerular and tubular function in non-oliguric acute renal failure

Glomerular and tubular function were evaluated in 30 non-oliguric patients with increasing azotemia following open heart surgery. Fractional clearances (theta) of test solutes relative to that of inulin were determined. In 16 patients, theta dextran (radius 22 to 30 A) exceeded unity, a finding attributed to inulin backleak through necrotic tubules. These patients were classified as having acute renal failure; 14 subsequently required dialysis. In the remaining patients (N = 14), theta dextran was normal. These patients were considered to have prerenal failure; all recovered spontaneously. clearance of inulin (Cin) was lower in acute renal failure than in prerenal failure (12 +/- 2 versus 18 +/- 2 ml/min/1.73 m2; p less than 0.025). The apparent difference in glomerular filtration rate when Cin is used as an index was abolished, however, when Cin in acute renal failure was corrected for tubule backleak of inulin. In acute renal failure, fractional clearance of p-aminohippurate (theta PAH) was 7.1 +/- 1.0, and fractional excretion of potassium (FEk) was 160 +/- 18 percent. These findings strongly suggest that secretory ability in both proximal and terminal tubule augments, respectively, is preserved in acute renal failure. Compared with prerenal failure, the urine-to-plasma inulin ratio was lower (U/Pin = 10 +/- 1 versus 25 +/- 4; p less than 0.005) and FENa was higher (FENa = 5.1 +/- 1.5 versus 0.5 +/- 1.0 percent; p less than 0.01) in acute renal failure.

Effect of the intra-aortic balloon pump upon postoperative renal function in man.

Fifty-seven postoperative cardiac surgical patients receiving intra-aortic balloon pump (IABP) support were selected for detailed hemodynamic and renal function measurements on the basis of depressed cardiac and/or renal function. Eleven patients developed acute renal failure while receiving maximal IABP support and 10 during, or after withdrawal of IABP support. To define further the relationship between IABP support and renal function, 17 patients underwent simultaneous assessment of hemodynamic and renal function under varying conditions of IABP support. These studies, performed just before IABP withdrawal, demonstrated slight, clinically insignificant, improvement in hemodynamic and renal function with increased IABP support. Arterial pressure recordings, performed above and below the intra-aortic balloon in 8 patients, revealed no significant pressure gradient across the balloon whether single- or double-chambered. In addition, the balloon pulse waveform was always evident in the femoral artery. Importantly, the intra-aortic balloon did not interfere demonstrably with renal function, nor did it decrease renal perfusion pressure, in spite of its suprarenal position. Therefore, improvement in systemic perfusion from IABP support in the early postoperative period will result in improved renal perfusion.

The Renal Effects of Sodium Nitroprusside in Postoperative Cardiac Surgical Patients

Sodium nitroprusside (SNP) is frequently used to control hypertension and/or improve systemic blood flow following cardiac operations. Although SNP causes renal vasodilation when infused into isolated kidneys, the reported effects of SNP on renal vascular resistance and blood flow in intact animals and humans have varied. To define the effects of SNP in postoperative cardiac surgical patients, renal clearances and hemodynamics were measured in seven patients within 24 hours of coronary bypass grafting. Studies were delayed until patients were stabilized and had rewarmed following operation. Following baseline measurements (off SNP), SNP infusion was used to lower mean arterial pressure to 85 torr. Pulmonary wedge pressure was maintained by appropriate fluid therapy, and the measurements repeated 1 h later. SNP administration resulted in equivalent decreases in renal (−31 per cent), pulmonic (−29 per cent) and systemic (−33 per cent) vascular resistance. Notwithstanding the decrease in arterial pressure (109 ± 14 to 91 ± 9 torr, P < 0.01), renal blood flow increased by 20 per cent (653 ± 193 to 792 ± 210 ml min−1 1.73 m−2, P < 0.02), in direct proportion to the increase in cardiac index (2.5 ± 0.4 to 3.0 ± 0.31 · min−1·m−2, P <0.01). Thus, in postoperative cardiac surgical patients, SNP administration can be expected to improve renal blood flow, so long as left artrial hypotension is avoided, and the decline in systemic arterial pressure is not excessive. The improvement in renal blood flow achievable with SNP may be critical for patients with severly depressed left ventricular function in whom severe depression of renal blood flow may occur as an antecedent to acute renal failure.

90 CORRELATION OF CARDIAC HEMODYNAMICS AND BIOENERGETICS USING PHOSPHORUS NMRSPECTROSCOPY

A model for the study of cardiac phosphate metabolism in vivo is presented which provides simultaneous measurement of hemodynamic parameters and myocardial phosphate metabolites including phosphocreatine(PCr), ATP and inorganic phosphate(Pi). Anesthetized beagles were instrumented to provide: aortic, left ventricular, pulmonary artery, and pulmonary artery wedge pressures and allow cardiac output determinations by thermal dilution. Pacing wires provided control of heart rate. Spectroscopy was performed using a 1.9 Tesla large bore magnet with a one inch surface coil placed directly on the left ventricular free wall via a left thoracotomy. Cardiac gaiting provided spectrographic data at any point in the cardiac cycle. Ten animals had resting gaited studies and four had gaited studies during periods of increased myocardial demand produced with isoproterenol (2) or hypoxemia, PaO2 35-40 mmHg (2). No significant change in the ratio of PCr/Pi or PCr/ATP occurred at any point during the cardiac cycle at rest or during stress. During graded hypoxia PCr/Pi and PCr/ATP levels remained stable until a PaO2 of 20-25 mmHg at which time cardiovascular shock occurred. These preliminary data demonstrate the wide range over which the normal heart can meet its metabolic demands and suggest that similar models may provide an in vivo method for the evaluation of high energy phosphate metabolism in acquired and congenital states of cardiac dysfunction.