Bo Frennby

Clinically suspected pulmonary embolism: is it safe to withhold anticoagulation after a negative spiral CT?

Abstract The goal of this study was 3-month clinical outcome in non-anticoagulated patients with clinically suspected acute pulmonary embolism (PE) following a negative spiral CT. During a 6-month period 305 patients underwent spiral CT, of whom only 8 also had a lung scintigraphy. In patients with a final CT report read as not positive for acute PE, all hospital records and answers to a patient questionnaire were analyzed for episodes of venous thrombembolism (VTE). Acute PE was diagnosed at spiral CT in 61 patients (20 %). Twenty-six of the remaining 244 patients were excluded from further analysis because of (a) long-term anticoagulation due to symptomatic acute deep venous thrombosis (n = 5), clinically diagnosed acute PE (n = 2), chronic recurrent VTE (n = 4), and cardiac disorders (n = 5); and (b) a normal perfusion scintigram (n = 4) or a negative pulmonary arteriogram (n = 6). Three patients were lost to follow-up. Among the remaining 215 patients only 10 had undergone a negative lower extremity venous study. Sixteen patients (7 %) died during the follow-up period, 6 of whom underwent autopsy. Venous thrombembolism was diagnosed in three of the 215 patients (1.4 %, 95 % confidence limits: 0.5–4.0 %), one causing the patients death. Two patients had advanced thoracic malignancies and the third severe chronic obstructive pulmonary disease (84 years old). A negative spiral CT may be able to exclude clinically significant acute PE with the same accuracy as a normal lung scintigraphy or a negative pulmonary arteriography.

Contrast media as markers of GFR

Abstract.Determination of the glomerular filtration rate (GFR) is generally considered as the most important parameter of quantifying renal function. The GFR is determined as renal or plasma clearance of an ideal filtration marker which is freely filtered by the kidney, does not undergo metabolism, tubular secretion or absorption. Markers that fulfil these demands are inulin, 51Cr-EDTA, 99mTc-DTPA, labelled or unlabelled contrast media. The renal clearance of inulin is the classic reference method for estimation of the GFR. This method is however not practical for routine clinical purposes. Radionucleids have therefore been used as alternative filtration markers since the 60s. Drawbacks related to radiation exposure especially in children and pregnant women and the safety in handling radiolabelled markers have led to an increasing interest in using non-radioactive markers. The development of simple and reliable methods to determine the concentration of contrast media in plasma and urine, such as high-performance liquid chromatography (HPLC) and X-ray fluorescence analysis have made this possible. The non-ionic low osmolar contrast medium iohexol has become the most commonly used contrast medium for GFR measurements in Europe. However, other contrast media with similar pharmacokinetics may be equally suitable as GFR markers.

Does Post-angiographic Hemodialysis Reduce the Risk of Contrast-medium Nephropathy?

Objective: Several strategies have been employed to reduce the incidence of nephrotoxicity in connection with the administration of urographic contrast media. We present the results of a randomized study to explore the effect of a single hemodialysis treatment immediately after an angiographic examination. Material and Methods: The patients studied had moderately reduced renal function. Seventeen of the 32 patients had diabetic nephropathy and 15 had other renal diseases. They were randomly selected to undergo either hemodialysis or standard treatment following the angiographic examination. The glomerular filtration rate (GFR) was determined the day before and 1 week after administration of the contrast medium. All patients were hydrated and received oral calcium-channel blocking treatment before angiography. Results: Hemodialysis lowered the level of contrast medium in plasma by approximately 80%. In spite of this no significant difference in renal iohexol clearance was noted between groups treated and not treated with hemodialysis. Conclusions: The risk of a marked and sustained reduction in renal function after administration of an iodine contrast medium is low with modern angiographic techniques. Hemodialysis reduces levels of contrast media in plasma but does not reduce the incidence of contrast-medium-induced nephrotoxicity in the GFR range from 10 to 25 ml/min.

The effect of endovascular aortic stents placed across the renal arteries

OBJECTIVES To investigate renal artery patency and renal function after deployment of aortic stents covering the orifices of renal arteries. DESIGN Prospective open animal study. SETTING Department of Experimental Surgery at a university hospital. MATERIALS Twenty-three pigs were used. METHODS Ten pigs were observed for 1 h after graft-anchoring aortic stents, Gianturco (5) and Palmaz (5), were placed so that the stents covered the renal arterial orifices. In 13 pigs, Gianturco (6) and Palmaz (7) stents without grafts were placed over the renal arteries and left in situ for 7 days. Renal function and blood flow were measured by renograms, iohexol clearance and ultrasonic blood flow meter and patency was verified by angiograms. The kidneys were microscopically examined for signs of ischaemia and microemboli. RESULTS One renal artery covered by a graft-anchoring Gianturco stent occluded. The remaining renal arteries remained patent without any significant decrease in renal blood flow after stent deployment. Normal renal function and histology was maintained. CONCLUSIONS Aortic stents placed at the level of the renal arteries do not affect renal blood flow within 1 week in this experimental model. This may prove valuable in endovascular treatment of aortic aneurysms and in other procedures involving stents.

Determining 'true' glomerular filtration rate in healthy adults using infusion of inulin and comparing it with values obtained using other clearance techniques or prediction equations.

Objective. To determine ‘true’ glomerular filtration rate (GFR) in healthy adults as renal clearance following infusion of inulin, and compare that result with those obtained using other markers and clearance techniques and with estimations of GFR using creatinine-based prediction equations. Material and methods. Twenty healthy volunteers (11 females) with a median age of 27 years (range 19–36 years) received bolus doses of inulin and iohexol i.v. and 16 blood samples were taken after injection. Then, inulin and iohexol were infused to give stable plasma concentrations and blood and urine samples were collected. Residual bladder volume was estimated using ultrasound scanning. Plasma and urine concentrations of inulin and iohexol were determined using chromatography and resorcinol methods, respectively. Different methods of GFR determination were compared as well as four formulae for GFR estimation based on serum creatinine. Results. ‘True’ GFR, i.e. renal clearance of inulin during its infusion, was a median of 117 ml/min/1.73 m2 (inter-quartile range 106–129 ml/min/1.73 m2). Similar values of GFR were obtained with renal clearance of iohexol during its infusion and also with plasma (body) clearance of inulin or iohexol following bolus injections and using 16 or five plasma samples. Endogenous creatinine clearance was higher (p<0.001) than true GFR (median 23 ml/min/1.73 m2). Plasma clearance of iohexol and inulin based on their concentrations in four blood samples underestimated their renal clearance considerably. All four creatinine-based formulae markedly underestimated renal inulin clearance. Conclusions. Plasma and renal clearance of iohexol and inulin were similar in healthy adults. Underestimation of GFR was noted when plasma clearance of iohexol and inulin was based on four but not five or more blood samples. Some prediction equations underestimate true GFR to such an extent that caution must be taken when using them to evaluate normal or high GFR values.

Contact allergy to gold in patients with gold-plated intracoronary stents

An increasingly common and effective method for the treatment of atherosclerotic disease in the coronary arteries is percutaneous transluminal coronary angioplasty (PTCA) and stenting. The stents are made of different metals. An increased rate of restenosis when using gold‐plated stents has been shown. Contact allergy to gold is common in many countries. Recently, a study has shown an increased rate of contact allergy to nickel among patients with restenosis and a nickel‐containing stent. The aims of our study were to investigate whether there was an increased rate of contact allergy to gold among patients with gold‐plated stents and if this increased the risk of restenosis. 22 patients who had received a gold‐plated stent were patch tested. An age‐ and sex‐matched population of 88 patients, previously patch tested because of a suspected contact dermatitis, served as controls. In the stent group, 10/22 (45.5%) had a contact allergy to gold, in the control group 18/88 (20.5%); the difference is statistically significant (P = 0.04). There was no significant difference regarding frequency of restenosis. Our study indicates that there is a risk of sensitizing the patient when implanting a gold‐plated stent. Further studies are needed to confirm these results and to evaluate whether there is an increased risk of restenosis.

Nephrotoxicity after renal angiography using iodine and gadolinium contrast media in pigs with renal damage

Iodine contrast medium (I-CM) induced nephrotoxicity is recognized for many years and is especially frequent in patients with pre-existing renal insufficiency alone or combined with diabetes mellitus. The use of non-ionic low osmolar contrast media (LOCM) has reduced the risk of renal injury after X-ray arteriography in patients with renal impairment (1). The importance of nephrotoxicity may increase in the future, due to an anticipated higher number of examinations of elderly subjects, who often have impaired renal function. Furthermore, interventional radiology uses large doses of contrast media (CM). These risk factors make it necessary to adopt some strategies to overcome the problems with nephrotoxicity associated with CM administration in patients with renal damage, for instance the use of non-ionic LOCM (1) and adequate

Biliary excretion and biliary clearance from plasma of lohexol in normal and nephrectomized pigs.

Markers for measuring the glomerular filtration rate (GFR) are filtered from plasma through the glomeruli and should have minimal excretion or reabsorption through the renal tubules and minimal extrarenal excretion. There is an increasing use of urographic contrast media as GFR markers (1). Examples are diatrizoate or iothalamate labeled with 125I or 131I, and nonradioactive nonionic media (such as iohexol and others). GFR is measured in milliliters per minute and is the virtual plasma volume (milliliters) from which the kidneys in 1 minute completely clear (remove) a GFR marker. In the following text, the term clearance refers to “clearance from the plasma compartment.” GFR was originally measured with renal clearance technique, which required a catheter in the bladder for collection of marker in the urine in addition to measurement of the concentration of marker in the plasma. This renal clearance technique measures the clearance of a GFR marker from plasma by the kidneys alone but involves a risk of infection from the catheter in the bladder or an inaccurate urine sampling as a source of error when no catheter is used. To avoid urine sampling, GFR is often measured as the body clearance of a GFR marker from plasma (ie, the total clearance of a marker from plasma by all of the organs of the body). This latter technique requires only plasma samples but has a source of error in that all GFR markers have some extrarenal excretion and an accompanying extrarenal clearance. The body clearance of a GFR marker will thus give a falsely high measurement of GFR because it gives the sum of “true GFR” and the extrarenal clearance of the marker. If the extrarenal clearances of GFR markers were known, or could be estimated, at different levels of GFR, this extrarenal clearance could be subtracted from the body clearance of the marker to get GFR values closer to the “true GFR.” With decreasing GFR, the extrarenal excretion and extrarenal clearance of a GFR marker could theoretically either increase to compensate for loss of renal function or remain stable or even decrease. In a number of investigations in humans and animals, the body clearances and the renal clearances of various GFR markers have been measured at different levels of GFR (2–10). The results are contradictory. In humans, the level of extrarenal clearance of GFR marker has been reported to be independent of decreasing GFR (9) and to decrease with decreasing GFR (10). In pigs with normal, reduced, or absent GFR, the total extrarenal clearances of iohexol and 51Cr-EDTA decreased with decreasing GFR and were lowest in the anuric pigs (P .01) (2,4–6). The total extrarenal excretion and the accompanying total extrarenal clearance of ionic and nonionic urographic contrast media include, inter alia, biliary and intestinal excretion and clearance (11–20). It may be expected that changes in the level of biliary clearance of the media are accompanied by similar changes in their total extrarenal clearance. Contrast medium filling of the gallbladder and biliary tract is sometimes observed on plain radiographs or computed tomographic (CT) examinations of the abdomen after injection of urographic contrast media. The phenomenon seems to increase in frequency with increasing dose of contrast medium and/or decreasing GFR. We Acad Radiol 2002; 9(suppl 1):S58–S61