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Quantification of the Glomerular Filtration of the Individual Kidney by the I 131 -Renografin Renogram

1967; Radiological Society of North America; Volume: 88; Issue: 5 Linguagem: Inglês

10.1148/88.5.984

1527-1315

I. Meschan, F. C. Watts, C. Douglas Maynard, Richard L. Witcofski, Samuel N. Smith,

Hyperglycemia and glycemic control in critically ill and hospitalized patients

In previous publications from this laboratory (1–3) the following points have been established: 1. In dogs and in man, the ratio of Renografin clearance to inulin clearance by a kidney is approximately 0.9; therefore, this agent is a reasonable inulin substitute substance for the determination of glomerular filtration rate. 2. Renografin clearance by a kidney can be quantified from an I131-Renografin renogram with significant accuracy, provided the following criteria and technics are observed: a. The patient must be in a hydrated state, and a diuretic agent must be used. We have infused an isotonic solution of glucose containing one part in five of 25 per cent mannitol at a rate of approximately one drop per second for at least forty-five minutes beforehand. This infusion is continued throughout the procedure. This “equilibrating” solution also contained 5 ml of nonradioactive Renografin in 500 ml of infusate. b. There must be a urine flow from the kidneys to the bladder of at least 1.5 ml per minute, but not more than 10 ml per minute. Urine flow rates outside these limits result in inaccuracies. The urine flow must not be obstructed, and the bladder must not become so distended as to be “seen” by the kidney probe. c. The renogram curve is analyzed for its regression coefficient, beginning the analysis five minutes after the injection of the 10 microcurie dose in accordance with a single exponential formula as follows: where Y is the concentration of the Renografin at either 0 time or time t; e is the base of the natural system of logarithms; and μ is a constant coefficient. The regression coefficient is best determined by programing for a single exponential Equation 1 in a computerized technic. (We have used a 1620 IBM computer.) It can be done with reasonable accuracy from the analog values obtained from a rectilinear chart of the regression renogram curve, provided that a period of at least twenty minutes is used. It can also be calculated from the half-time of clearance (T½) by manually plotting the regression values of the renogram curve on semi-log paper and applying the formula: or, d. Substituting Equation 3 for μ, Equation 4, the clearance for each kidney can be calculated by application of the following formula: or, We have now utilized this empiric technic in 82 patients and 104 different determinations. Our present purpose is to present the statistical data relating to these studies in these 82 patients with diverse clinical conditions. Procedure The urinary bladder is emptied prior to each twenty-minute collection period. In patients who do not have a catheter in the urinary bladder, voluntary bladder emptying is assisted by applying pressure above the pubic symphysis so as to empty the bladder as completely as possible. An indwelling heparinized needle is inserted into a vein for withdrawal of blood samples.