Predictive performance of ten equations for estimating creatinine clearance in cardiac patients. Iohexol Cooperative Study Group

Antimicrobial dosing considerations in obese adult patients

As obesity continues to increase in prevalence throughout the world, it becomes important to explore the effects that obesity has on antimicrobial disposition. Physiologic changes in obesity can alter both the volume of distribution and clearance of many commonly used antimicrobials. These changes often present challenges such as estimation of creatinine clearance to predict drug clearance. Although these physiologic changes are increasingly being characterized, few studies assessing alterations in tissue drug distribution and the effects of obesity on antimicrobial pharmacokinetics have been published. The available data are most plentiful for antibiotics that historically have included clinical therapeutic drug monitoring. These data suggest that dosing of vancomycin and aminoglycosides be based on total body weight and adjusted body weight, respectively. Obese patients may require larger doses of beta-lactams to achieve similar concentrations as those of patients who are not obese. Fluoroquinolone pharmacokinetics are variably altered by obesity, which prevents a uniform approach. Data on the pharmacokinetics of drugs that have activity against gram-positive organisms-quinupristin-dalfopristin, linezolid, and daptomycin-reveal that they are altered in the presence of obesity, but more data are needed to solidify dosing recommendations. Limited data are available on nonantibacterials. An understanding of the physiologic changes in obesity and the available literature on specific antibiotics is valuable in providing a framework for rational selection of dosages in this increasingly common population of obese patients.

Fetuin-A Is an Independent Predictor of Death after ST-Elevation Myocardial Infarction

Background: Fetuin-A inhibits inflammation and has a protective effect against myocardial ischemia. Its deficiency has been found to be associated with cardiovascular death in patients with end-stage renal failure disease. We investigated the association between plasma fetuin-A and clinical outcome after ST-elevation acute myocardial infarction (STEMI).

Methods: We measured fetuin-A in 284 consecutive patients with STEMI and correlated these data with the occurrence of death at 6 months (n = 25). We also measured fetuin-A in a control group and chose the 95th percentile as the cutoff to define abnormality.

Results: Patient mean (SD) age was 60 (14) years, and creatinine clearance was 83 (31) mL/min; 82% were men. Mean (SD) plasma fetuin-A concentrations at admission [188 (69) mg/L, P = 0.01] and at day 3 [163 (57) mg/L, P <0.0001] were lower in patients than in controls [219 (39) mg/L; 95th percentile 140 mg/L]. Fetuin-A <140 mg/L was observed in 20% of patients at admission vs 40% at day 3 (P <0.001). Fetuin-A concentrations did not correlate with peak cardiac troponin values but did correlate inversely with C-reactive protein (CRP) and NT-pro-brain natriuretic peptide (NT-proBNP). Fetuin-A <140 mg/L at admission (OR = 3.3, P = 0.03) and at day 3 (OR = 6.3, P = 0.002) was an independent correlate of death at 6 months, irrespective of NT-proBNP, CRP, or Controlled Abciximab and Device Investigation to Lower Late Angioplasty Complications (CADILLAC) risk score. Conversely, fetuin-A ≥140 mg/L was associated with an excellent survival rate [negative predictive value (NPV) = 97% overall], even in high-risk populations with CADILLAC risk score ≥6 (NPV = 90% in patients).

Conclusions: Fetuin-A is an important predictor of death at 6 months in STEMI patients independent of NT-proBNP, CRP, and CADILLAC risk score.

Outcomes of left ventricular assist device implantation as destination therapy in the post-REMATCH era: implications for patient selection

BACKGROUND

The landmark Randomized Evaluation of Mechanical Assistance for the Treatment of Congestive Heart Failure (REMATCH) trial first demonstrated that implantation of left ventricular assist devices (LVADs) as destination therapy (DT) can provide survival superior to any known medical treatment in patients with end-stage heart failure who are ineligible for transplantation. In the present study, we describe outcomes of DT in the post-REMATCH era in the United States.

METHODS AND RESULTS

The present study included 280 patients who underwent HeartMate XVE LVAD implantation between November 2001 and December 2005. A preoperative risk score for in-hospital mortality after LVAD implantation was established in 222 patients with complete data. All patients were followed up until death or December 2006. The 1-year survival after LVAD implantation was 56%. The in-hospital mortality after LVAD surgery was 27%. The main causes of death included sepsis, right heart failure, and multiorgan failure. The most important determinants of in-hospital mortality were poor nutrition, hematological abnormalities, markers of end-organ or right ventricular dysfunction, and lack of inotropic support. Stratification of DT candidates into low (n=65), medium (n=111), high (n=28), and very high (n=18) risk on the basis of the risk score calculated from these predictors corresponded with 1-year survival rates of 81%, 62%, 28%, and 11%, respectively.

CONCLUSIONS

Appropriate selection of candidates and timing of LVAD implantation are critical for improved outcomes of DT. Patients with advanced heart failure who are referred for DT before major complications of heart failure develop have the best chance of achieving an excellent 1-year survival with LVAD therapy.

Influence of morbid obesity on the single-dose pharmacokinetics of daptomycin

The present study characterized the single-dose pharmacokinetics of daptomycin dosed as 4 mg/kg of total body weight (TBW) in seven morbidly obese and seven age-, sex-, race-, and serum creatinine-matched healthy subjects. The glomerular filtration rate (GFR) was measured for both groups following a single bolus injection of [(125)I]sodium iothalamate. Noncompartmental analysis was used to determine the pharmacokinetic parameters, and these values were normalized against TBW, ideal body weight (IBW), and fat-free weight (FFW) for comparison of the two groups. All subjects enrolled in this study were female, and the mean (+/-standard deviation) body mass index was 46.2 +/- 5.5 kg/m(2) or 21.8 +/- 1.9 kg/m(2) for the morbidly obese or normal-weight group, respectively. The maximum plasma concentration and area under the concentration-time curve from dosing to 24 h were approximately 60% higher (P < 0.05) in the morbidly obese group than in the normal-weight group, and these were a function of the higher total dose received in the morbidly obese group. No differences in daptomycin volume of distribution (V), total clearance, renal clearance, or protein binding were noted between the two groups. Of TBW, FFW, or IBW, TBW provided the best correlation to V. In contrast, TBW overestimated GFR through creatinine clearance calculations using the Cockcroft-Gault equation. Use of IBW in the Cockcroft-Gault equation or use of the four-variable modification of diet in renal disease equation best estimated GFR in morbidly obese subjects. Further studies of daptomycin pharmacokinetics in morbidly obese patients with acute bacterial infections and impaired renal function are necessary to better predict appropriate dosage intervals.

Glomerular filtration rate after left renal vein division and reconstruction during infrarenal aortic aneurysm repair

OBJECTIVES

The study assessed the effect on postoperative renal function of left renal vein (LRV) division and reconstruction by direct reanastomosis or graft interposition during infrarenal abdominal aortic aneurysm (AAA) repair.

METHODS

Between January 2001 and March 2006, 1189 patients underwent elective open repair of infrarenal AAAs. LRV division was performed in 15 (1.3%) and its reconstruction in all but one (LRV group), where the LRV was occluded. Patients' glomerular filtration rates (GFRs) were retrospectively estimated through postoperative day 4 by using the Cockcroft-Gault equation and compared with the GFRs of 56 controls undergoing AAA repair without LRV division (control group) randomly identified from a prospectively compiled database in a 4:1 ratio. Post hoc 1:1 case-matched analysis was also performed. Statistical analyses were performed as appropriate.

RESULTS

Comparison of demographics and risk factors revealed no statistically significant differences between the two groups with the exception of the following: AAAs were larger in LRV group (71.4 +/- 17.1 mm vs 56.0 +/- 14.6 mm; P = .003) and preoperative GFR was lower in LRV group (65.3 +/- 19.0 mL/min/1.73 m(2) vs 82.8 +/- 22.3 mL/min/1.73 m(2); P = .009). Postoperatively, the trend of GFR with time did not differ between groups (P = .33). The variation of GFR at day 4 after surgery compared with preoperative values was not different either (5.6 +/- 12.6 mL/min/1.73 m(2) vs 1.0 +/- 15.5 mL/min/1.73 m(2); P = .67). A further 1:1 case-matched multivariate analysis of variance, matching patients and controls by AAA size and preoperative GFR, showed no difference in trend of GFR with time between groups (P = .15). Operative time was not significantly longer in LRV group (148.4 +/- 35.8 minutes vs 131.0 +/- 40.3 minutes; P = .07). No differences between groups were found for blood loss (585.7 +/- 264.2 mL vs 567.7 +/- 222.5 mL; P = .88), perioperative complications (5 vs 8; P = .12), or hospital length of stay (6.2 +/- 1.8 days vs 5.5 +/- 1.2 days; P = .10). A 6-month follow-up of renal function available in 12 patients of LRV group showed no significant decrease in GFR compared with postoperative values (70.8 +/- 24.8 mL/min/1.73 m(2) vs 69.1 +/- 23.5 mL/min/1.73 m(2); P = .86). At duplex scan, the reconstructed LRV could be insonated in nine of these 12 patients and all were patent.

CONCLUSIONS

LRV division during AAA repair was associated with larger aneurysms and preoperative subclinical renal function impairment. In these patients, LRV reconstruction was associated with the maintenance of preoperative renal functional status without significantly lengthening of operative time or increasing the complications from surgery.

Baseline renal function screening

Renal impairment at baseline (estimated glomerular filtration rate [eGFR] <60 mL/min/1.73 m(2)) is the most important risk marker to predict the risk of contrast-induced nephropathy (CIN) in patients receiving iodinated contrast media. Hence, it is important to assess renal function before administration of contrast medium to ensure that appropriate steps are taken to reduce the risk. Serum creatinine alone does not provide a reliable measure of renal function, hence the National Kidney Foundation Kidney Disease Outcome Quality Initiative (K/DOQI) recommends that clinicians should use an eGFR calculated from the serum creatinine as an index of renal function. The CIN Consensus Working Panel agreed that eGFR should be determined before contrast administration, using the abbreviated Modification of Diet in Renal Disease (MDRD) formula, recommended by K/DOQI as the preferred equation for the calculation of eGFR in adults. Where a serum creatinine measurement or eGFR is not available, a simple survey or questionnaire can be used before contrast agent administration to identify patients at higher risk for CIN compared with the general population. In emergency situations, where the benefit of very early imaging outweighs the risk of waiting, the CIN Consensus Working Panel agreed that the procedure can be performed without assessment of renal function.

Creatinine-based formulae for the estimation of glomerular filtration rate in heart transplant recipients

Chronic renal failure (CRF) is a common complication in heart transplant patients. Serum creatinine has clear limitations for the detection and estimation of glomerular filtration rate (GFR). Various creatinine-based formulae are classically used for GFR estimation, but little scientific evidence exists for such use in a heart transplant population. GFR was measured using the plasmatic clearance of the glomerular tracer (51)Cr-EDTA in 27 heart transplant patients with two measures for 22 of the patients. Forty-nine measures were thus available for analysis. The precision and accuracy (Bland and Altman analysis) of the Cockcroft, simplified Modified Diet in Renal Diseases (MDRD) and new Mayo Clinic formulae were compared. The mean GFR of the population was 39 +/- 15 mL/min/1.73 m(2). All formulae were well correlated with the GFR. With the Bland and Altman analysis, the accuracy of the MDRD formula appeared higher than that of the Cockcroft or the Mayo Clinic formulae (bias of +12 mL/min/1.73 m(2), vs. +19.9 mL/min/1.73 m(2), and +22.1 mL/min/1.73 m(2), respectively). The difference between the estimated and measured GFR was higher than 20 mL/min/1.73 m(2) in 51% and 55% cases when using the Cockcroft and the Mayo Clinic formulae respectively, whereas the difference was only noted in 14% cases when the MDRD was used. Among creatinine-based formulae, the MDRD appears the most precise and accurate for estimating the GFR in heart transplant patients. However, when the GFR must be measured with high accuracy, we recommend the use of a reference method like inulin or (51)Cr-EDTA plasma clearance techniques.

Formulas calculating creatinine clearance are inadequate for determining eligibility for Cisplatin-based chemotherapy in bladder cancer

PURPOSE

Efficacy of formulas calculating creatinine clearance (CrCl) to determine renal function eligibility (CrCl > 60 mL/min) for cisplatin-based chemotherapy has not been examined adequately in the bladder cancer population. We hypothesize these formulas may underestimate measured CrCl, and therefore the eligibility for cisplatin-based chemotherapy.

PATIENTS AND METHODS

A database of 208 patients with unresectable or metastatic bladder cancer treated on protocol at Memorial Sloan-Kettering Cancer Center (New York, NY) with cisplatin-based chemotherapy between 1983 and 1994 was examined retrospectively. The association between measured and calculated CrCl and the ability to complete three cycles (minimum therapeutic) of chemotherapy was examined.

RESULTS

Baseline measured CrCl was less than 60 mL/min in 16% compared with 12% to 44% using various formulas. Concordance between calculated and measured CrCl less than 60 mL/min was poor (range of kappa, 0.14 to 0.38). In patients older than age 65, 22% had a measured CrCl less than 60 mL/min, compared with 10% to 63% calculated using various formulas. Overall, 80% completed at least three cycles of cisplatin-based chemotherapy. The ability to complete at least three cycles was statistically significantly related with a measured CrCl more than 60 mL/min (P = .02), but not with calculated CrCl more than 60 mL/min.

CONCLUSION

Current formulas estimating CrCl tend to underestimate measured CrCl, especially in those older than 65 years. Depending on the formula used, up to 44% who actually received cisplatin-based chemotherapy based on measured CrCl would be deemed ineligible at present, potentially affecting survival outcomes. Methodology for determining CrCl and/or renal eligibility for cisplatin-based chemotherapy in patients with bladder cancer should be re-examined.

Phase I and Pharmacokinetic Study of Pemetrexed Administered Every 3 Weeks to Advanced Cancer Patients With Normal and Impaired Renal Function

Purpose

This phase I study was conducted to determine the toxicities, pharmacokinetics, and recommended doses of pemetrexed in cancer patients with normal and impaired renal function.

Patients and Methods

Patients received a 10-minute infusion of 150 to 600 mg/m2 of pemetrexed every 3 weeks. Patients were stratified for independent dose escalation by measured glomerular filtration rate (GFR) into four cohorts ranging from ≥ 80 to less than 20 mL/min. Pemetrexed plasma and urine pharmacokinetics were evaluated for the first cycle. Patients enrolled after December 1999 were supplemented with oral folic acid and intramuscular vitamin B12.

Results

Forty-seven patients were treated with 167 cycles of pemetrexed. Hematologic dose-limiting toxicities occurred in vitamin-supplemented patients (two; 15%) and nonsupplemented patients (six; 18%), and included febrile neutropenia (four patients) and grade 4 thrombocytopenia (two patients). Nonhematologic toxicities included fatigue, diarrhea, and nausea, and did not correlate with renal function. Accrual was discontinued in patients with GFR less than 30 mL/min after one patient with a GFR of 19 mL/min died as a result of treatment-related toxicities. Pemetrexed plasma clearance positively correlated with GFR (r2 = 0.736), resulting in increased drug exposures in patients with impaired renal function. With vitamin supplementation, pemetrexed 600 mg/m2 was tolerated by patients with a GFR ≥ 80 mL/min, whereas patients with a GFR of 40 to 79 mL/min tolerated a dose of 500 mg/m2.

Conclusion

Pemetrexed was well tolerated at doses of 500 mg/m2 with vitamin supplementation in patients with GFR ≥ 40 mL/min. Additional studies are needed to define appropriate dosing for renally impaired patients receiving higher dose pemetrexed with vitamin supplementation.

Peri-operative Renal Function and Outcome after Orthotopic Heart Transplantation

BACKGROUND

Renal insufficiency is an established risk factor in patients undergoing cardiovascular surgery. We sought to evaluate the relationship between renal function and outcomes after orthotopic heart transplantation (OHT).

METHODS

We conducted a retrospective review of 622 adults who underwent 628 consecutive OHTs between 1994 and 2001 at our institution. The recipients were divided into either normal (Group 1) or impaired (Group 2) pre-operative renal function. Impaired renal function was defined as creatinine clearance (CrCl) < 40 ml/min (Cockroft-Gault formula). Meanwhile, patients in Group 1 (normal) were defined by CrCl > or = 40 ml/min. The primary end points of the study were early and late mortality. The secondary end point included post-operative renal failure defined by the requirement of dialysis or renal allograft in the early post-operative period. The Kaplan-Meier method was used to determine actuarial survival.

RESULTS

Early mortality was 7% (38/531) in Group 1 and 17% (16/96) in Group 2 (p = 0.002). Similarly, the death rate per 100 patient-years was 4.8 and 8.1 for the groups, respectively (p = 0.03). Nine percent of patients in Group 1 required post-operative dialysis (49/531), whereas 32% of recipients in Group 2 required this intervention (31/96) (p < 0.001). Early mortality was 41% for patients requiring post-operative dialysis and 3% for those not requiring such intervention (p < 0.001). Early mortality after post-operative dialysis was 41% (20/49) in Group 1 and 42% (13/31) in Group 2 (p = 0.2).

CONCLUSIONS

CrCl < 40 ml/min is a useful marker for increased post-operative renal failure and mortality. Recipients who require post-operative dialysis have greatly increased mortality regardless of pre-operative CrCl. Dialysis in patients after heart transplantation carries a prohibitive risk. Dialysis as a bridge to renal transplantation may reduce this high mortality rate.

Glomerular filtration rate is a predictor of mortality after endovascular abdominal aortic aneurysm repair

OBJECTIVE

Clinically evident renal disease is a risk factor for mortality after aneurysm repair. Serum creatinine is widely used as a measure of renal function in the preoperative evaluation of patients. Unfortunately, serum creatinine concentration is influenced by muscle mass, hydration status, and glomerular filtration rate (GFR). Calculated GFR, which takes predictors of muscle mass such as age, gender, and weight into account, is a more sensitive determinant of renal function than serum creatinine. We hypothesized that GFR would more accurately predict mortality after EVAR than serum creatinine.

METHODS

We retrospectively evaluated our database of 398 patients who underwent EVAR with the AneuRx device between October 1999 and October 2004. There were 340 men and 58 women with a mean age of 73. GFR was calculated using the Cockcroft-Gault equation. The patients were divided into four quartiles by preoperative GFR: I (7 to 45), II (45 to 60), III (61 to 79), and IV (> or =80). Survival was estimated with the Kaplan-Meier method, and heterogeneity of mortality across strata was evaluated using the log-rank test. The GFR quartiles were compared with clinically accepted criteria for abnormal renal function (serum creatinine level > or =1.7).

RESULTS

Actuarial survival at 48 months was 61.5%, 70.5%, 86.0%, and 85.7% for GFR quartiles I to IV, respectively (P < .003). Thirty-day mortality was 2.2% in quartile I, 3.2% in quartile II, and 0 in quartiles III and IV (P = .03 for q1 + q2 vs q3 + q4, P < .02 for q2 vs q3 + q4). Survival curves for quartiles II to IV were statistically indistinguishable, with quartile II running tangential to the two higher quartiles after the perioperative period. Quartile I fared significantly worse than the other three quartiles for the entire follow-up period (P < .005). According to American Kidney Foundation criteria (GFR <90), 83.3% of patients had abnormal renal function compared with 16.1% with abnormal serum creatinine (>1.7) (P < .0002).

CONCLUSION

The risk of perioperative and long-term mortality in patients undergoing EVAR is more accurately stratified by using calculated GFR than serum creatinine alone. A GFR <45 is associated with decreased survival after EVAR. Perioperative mortality at a GFR of 45 to 60 is comparable with that of the lower quartile (GFR <45), but late survival is comparable with that of patients with GFR >60. The finding of increased risk of early mortality in patients in the 45 to 60 GFR range, with survivors enjoying good long-term outcome, suggests that these patients may most benefit from the use of alternative contrast agents and periprocedural renal protection techniques.

The Cockcroft-Gault formula should not be used in children

BACKGROUND

Although designed for adults, the Cockcroft-Gault formula was recently proposed for use in children > or =13 years of age.

METHODS

We compared the feasibility of the Cockcroft-Gault formula against the standard pediatric Schwartz formula and a novel cystatin C-based formula. Our patient cohort included 262 children aged 1 to 18 years with various renal pathologies, who underwent a 99-technetium diethylenetriaminepentaacetate ((99)Tc DTPA) glomerular filtration rate (GFR) renal scan. Calculations were performed in Systeme International (SI) units using published constants and recalculated constants from our patient population. Agreement was assessed using Bland and Altman analysis.

RESULTS

Published and recalculated constants for the Cockcroft-Gault formula were 1.23 and 0.96, respectively, for boys, and 1.05 and 0.90, respectively, for girls. The published and recalculated constants for the Schwartz formula were 48 and 49.9, respectively, for boys > or =13 years old, and 38 and 46.2, respectively, for all girls and for boys <13 years old. Using published constants, there was agreement between GFR and Cockcroft-Gault formula in boys > or =13 years old (average bias 5.0 +/- 23.5%) while there was an average error of -19.0%+/- 36.4% for all ages. Similarly, the average bias with Schwartz for boys > or =13 years old was -6.8 +/- 24.0% and for all patients was -12.8 +/- 24.2%. Using recalculated constants, the average bias with Cockcroft-Gault in boys > or =13 years old was -19.8 +/- 23.5% and for all patients was -38.5 +/- 35.2%. Similarly, the average bias with Schwartz for boys < or =13 years old was -1.1 +/- 24.3% and for all patients was 3.0 +/- 24.0%. The novel cystatin C-based GFR calculations showed an average error of -4.9 +/- 20.3% in the adolescent boys and 2.4 +/- 20.4% for all ages.

CONCLUSION

Cockcroft-Gault formula showed the worst agreement with GFR, regardless of using published or recalculated constants. The cystatin C-based approach resulted in the least error, and should be used for estimation of GFR.

Limitations of glomerular filtration rate equations in the renal transplant patient

This study aims to compare the performance of endogenous creatinine clearance (CL(cr)) and a number of published mathematical equations to calculate glomerular filtration rate (GFR) in renal transplant patients considering (99m)Tc DTPA isotope scan as the reference method. A total of 152 GFR were performed on 81 renal transplant patients. Accuracy of each method was measured at different percentiles. The bias and precision of all the methods were then compared. A paired t-test was used to compare the performance of each calculation to the respective GFR measured by isotope study performed on the same day. In the total population, all calculated methods correlated significantly with the isotope results. Accuracies within specific ranges of the isotope GFR were limited in all equations (agreement with isotope result </=72% at 30% accuracy range in the total group). Within the limited accuracy, Edwards' equation (K.D. Edwards and H.M. Whyte, Australas Ann Med 1959; vol. 8: p. 218) had the least bias in the total population. Bjornsson (T.D. Bjornsson, Clin Pharmacokinet 1979; vol. 4: p. 200) had the least bias in patients with GFR >/= 50 mL/min and Gates in patients with GFR < 50 mL/min. Salazar (D.E. Salazar and G.B. Corcoran, Am J Med 1988; vol. 84: p. 1053) had the least bias in patients with BMI above 30 kg/m(2) and the Davis equation (G.A. Davis and M.H. Chandler, Am J Health Syst Pharm 1996; vol. 53: p. 1028) in patients with BMI <25 kg/m(2). In all analyses, Nankivell (B.J. Nankivell, S.M. Gruenwald, R.D.M. Allen and J.R. Chapman, Transplantation 1995; vol. 59: p. 1683) overestimated GFR by more than 80% and MDRD 1 and 2 in <10% of the time. The results demonstrate the inherited limitation in the currently available equations to calculate GFR in renal transplant patients.

Detection of renal function decline in patients with diabetes and normal or elevated GFR by serial measurements of serum cystatin C concentration: results of a 4-year follow-up study

Research on early renal function decline in diabetes is hampered by lack of simple tools for detecting trends (particularly systematic decreases) in renal function over time when GFR is normal or elevated. This study sought to assess how well serum cystatin C meets that need. Thirty participants with type 2 diabetes in the Diabetic Renal Disease Study met these three eligibility criteria: GFR >20 ml/min per 1.73 m2 at baseline (based on cold iothalamate clearance), 4 yr of follow-up, and yearly measurements of iothalamate clearance and serum cystatin C. With the use of linear regression, each individual's trend in renal function over time, expressed as annual percentage change in iothalamate clearance, was determined. Serum cystatin C in mg/L was transformed to its reciprocal (100/cystatin C), and linear regression was used to determine each individual's trend over time, expressed as annual percentage change. In paired comparisons of 100/cystatin C with iothalamate clearance at each examination, the two measures were numerically similar. More important, the trends in 100/cystatin C and iothalamate clearance were strongly correlated (Spearman r = 0.77). All 20 participants with negative trends in iothalamate clearance (declining renal function) also had negative trends for 100/cystatin C. Results were discordant for only three participants. In contrast, the trends for three commonly used creatinine-based estimates of GFR compared poorly with trends in iothalamate clearance (Spearman r < 0.35). Serial measures of serum cystatin C accurately detect trends in renal function in patients with normal or elevated GFR and provide means for studying early renal function decline in diabetes.

An Analysis of the Association Between Preoperative Renal Dysfunction and Outcome in Cardiac Surgery *

STUDY OBJECTIVES

Preoperative renal dysfunction is a risk factor for adverse events in cardiac surgery. This study compared creatinine clearance (ClCr), estimated from the Cockroft and Gault formula, and plasma creatinine level as predictors of outcome after cardiac surgery.

DESIGN

Prospective, observational.

SETTING

University hospital.

PATIENTS

A total of 6,364 cardiac surgical patients.

METHODS

The measured outcomes were postoperative renal failure requiring dialysis, and mortality and major morbidity. For each outcome, two multivariable risk models were developed, using either estimated ClCr as a measure of renal function, or plasma creatinine level. Risk-adjusted odds ratios (ORs) and their 95% confidence intervals (CIs) were calculated for each outcome. Discrimination was compared using receiver operating characteristic (ROC) curves.

RESULTS

For each 10 mL/min/1.73 m(2) decrement of estimated ClCr, the ORs for renal failure requiring dialysis, mortality, and major morbidity in the whole population were 1.52 (95% CI, 1.35 to 1.67), 1.27 (95% CI, 1.19 to 1.35), and 1.18 (95% CI, 1.14 to 1.21), respectively; for each 0.2 mg/dL increment of plasma creatinine, ORs were 1.20 (95% CI, 1.15 to 1.26), 1.08 (95% CI, 1.04 to 1.13), and 1.12 (95% CI, 1.09 to 1.15), respectively. The areas under the ROC curves for prediction of renal failure requiring dialysis were 0.83 with both risk models. For prediction of mortality and major morbidity, areas under the ROC curves were 0.83 and 0.72, respectively, with the models using estimated ClCr, and 0.74 and 0.65, respectively, with the models using plasma creatinine level (p < 0.001 vs estimated ClCr for both outcomes). In patients with normal plasma creatinine levels (n = 4,603), estimated ClCr remained a significant predictor of each outcome with similar ORs, but plasma creatinine level was not a predictor of any outcome.

CONCLUSION

The risk-adjusted association between preoperative renal dysfunction and adverse events after cardiac surgery is stronger with estimated ClCr than with plasma creatinine level, particularly in patients with normal plasma creatinine levels. The routine preoperative estimation of ClCr may improve the identification of higher-risk cardiac surgical patients.

Evaluating surrogate measures of renal dysfunction after cardiac surgery

Renal insufficiency after cardiac surgery is associated with increased mortality, morbidity, and length of intensive care unit stay. A convenient surrogate measure would facilitate the evaluation of renal-protective therapies. We evaluated two measures: the 72-h change in serum creatinine (Cr) (DeltaCr(72h)) and the percentage 72-h change in calculated (Cockcroft-Gault equation) Cr clearance (%DeltaCrCl(72h)). We randomly selected 2000 individuals who underwent aortocoronary bypass, valve surgery, or both at the Toronto General Hospital between May 1999 and August 2000. The variables were analyzed with frequency histograms and normal probability plots. Their association with dialysis, mortality, and prolonged intensive care unit stay was determined by using receiver operating characteristic (ROC) curves. DeltaCr(72h) was skewed to the right, whereas %DeltaCrCl(72h) was normally distributed. ROC curve areas showed DeltaCr(72h) to be a good predictor of dialysis (0.98), death (0.83), and prolonged hospitalization (0.74). %DeltaCrCl(72h) had similar ROC curve areas for predicting dialysis (0.97), death (0.82), and prolonged hospitalization (0.74). ROC curve areas did not differ significantly with respect to mortality (P = 0.89), dialysis (P = 0.49), or prolonged hospitalization (P = 0.85). Both variables were correlated with patient-relevant outcomes. Mathematical transformation of DeltaCr(72h) to %DeltaCrCl(72h) results in a normal distribution that is amenable to parametric statistical tests. DeltaCr(72h) and %DeltaCrCl(72h) may be used as surrogate outcomes in future trials.

IMPLICATIONS

A convenient surrogate measure of renal function is needed for evaluating renal-protective therapies in cardiac surgery. We evaluated the performance of serum creatinine concentration and calculated creatinine clearance for predicting dialysis, mortality, and prolonged hospitalization. Both measures were correlated with clinical outcomes. Creatinine clearance had the advantage of a distribution suitable for parametric statistical tests.

Impact of preoperative renal dysfunction on cardiac surgery results

Results of cardiac surgery were analyzed using a database that included plasma creatinine levels in 2,214 patients, of whom 507 had preoperative renal dysfunction (creatinine clearance < 0.9 mL x s(-1) x m(-2)). Logistic regression and propensity score analyses found preoperative renal dysfunction to be an independent predictor of morbidity and mortality. Plotting preoperative creatinine clearance against morbidity and mortality revealed an exponential increase in morbidity and mortality when preoperative creatinine clearance was < 0.84 mL x s(-1) x m(-2). Patients were stratified for age, operative procedure, and comorbidity. In all stratified groups, preoperative creatinine clearance < 0.84 mL x s(-1) x m(-2) was associated with similar exponential increases in morbidity and mortality. In patients with preoperative renal dysfunction, elevated plasma creatinine levels persevered for 6 months postoperatively. Dialysis beyond postoperative day 10 was required in < 2% of patients with preoperative plasma creatinine of 160-200 micro mol x L(-1) and in 5% in those with creatinine > 200 micro mol x L(-1) (p < 0.05). Actuarial survival was significantly reduced (< 90% at 18 months postoperatively) in patients with preoperative renal dysfunction.

Principles and Clinical Application of Assessing Alterations in Renal Elimination Pathways

Drugs and metabolites are eliminated from the body by metabolism and excretion. The kidney makes the major contribution to excretion of unchanged drug and also to excretion of metabolites. Net renal excretion is a combination of three processes - glomerular filtration, tubular secretion and tubular reabsorption. Renal function has traditionally been determined by measuring plasma creatinine and estimating creatinine clearance. However, estimated creatinine clearance measures only glomerular filtration with a small contribution from active secretion. There is accumulating evidence of poor correlation between estimated creatinine clearance and renal drug clearance in different clinical settings, challenging the 'intact nephron hypothesis' and suggesting that renal drug handling pathways may not decline in parallel. Furthermore, it is evident that renal drug handling is altered to a clinically significant extent in a number of disease states, necessitating dosage adjustment not just based on filtration. These observations suggest that a re-evaluation of markers of renal function is required. Methods that measure all renal handling pathways would allow informed dosage individualisation using an understanding of renal excretion pathways and patient characteristics. Methodologies have been described to determine individually each of the renal elimination pathways. However, their simultaneous assessment has only recently been investigated. A cocktail of markers to measure simultaneously the individual renal handling pathways have now been developed, and evaluated in healthy volunteers. This review outlines the different renal elimination pathways and the possible markers that can be used for their measurement. Diseases and other physiological conditions causing altered renal drug elimination are presented, and the potential application of a cocktail of markers for the simultaneous measurement of drug handling is evaluated. Further investigation of the effects of disease processes on renal drug handling should include people with HIV infection, transplant recipients (renal and liver) and people with rheumatoid arthritis. Furthermore, changes in renal function in the elderly, the effect of sex on renal function, assessment of living kidney donors prior to transplantation and the investigation of renal drug interactions would also be potential applications. Once renal drug handling pathways are characterised in a patient population, the implications for accurate dosage individualisation can be assessed. The simultaneous measurement of renal function elimination pathways of drugs and metabolites has the potential to assist in understanding how renal function changes with different disease states or physiological conditions. In addition, it will further our understanding of fundamental aspects of the renal elimination of drugs.

Predictive performance of renal function equations for patients with chronic kidney disease and normal serum creatinine levels

Accurate renal function measurements are important for the diagnosis and treatment of kidney disease, proper medication dosing, interpretation of possible uremic symptoms, and decision-making regarding when to initiate renal replacement therapy. Because the use of highly accurate filtration markers to measure renal function has traditionally been limited by cumbersome and costly techniques and the involvement of radioactivity (among other factors), renal function is typically estimated by using specially derived prediction equations. These formulae usually use serum creatinine levels, i.e., a marker of filtration that is insensitive to mild/moderate decreases in GFR. Although attempts have been made to validate certain renal function prediction equations among patients with chronic kidney disease (CKD) with abnormal serum creatinine levels, this is the first study to specifically evaluate the predictive performance of these equations for patients with CKD and serum creatinine levels in the normal range. The results of eight prediction equations for 109 patients with CKD and serum creatinine levels of < or =1.5 mg/dl were compared with standard iohexol GFR values. The most accurate results were obtained with the Cockroft-Gault and Bjornsson equations. The most precise formulae were the Modification of Diet in Renal Disease Study equations, although they were highly biased. Even the most accurate results exhibited levels of error that made them suboptimal for clinical treatment of these patients. These results suggest that measurement of GFR with endogenous or exogenous filtration markers might be the most prudent strategy for the assessment of renal function in the CKD population with normal serum creatinine levels. Further studies are needed to confirm the generalizability of these findings for this patient subgroup.

Medications and the elderly in the critical care setting

As the elderly population in our country continues to increase, it is imperative that the bedside practitioner be keenly aware of the factors that affect pharmacokinetics and pharmacodynamics of medication administration. Refining the admission interview process to obtain accurate medication information--including alternative and OTC drugs--will help to decrease the incidence of drug interactions and ADR in the acute care setting. Appropriate monitoring of pharmacologic effects and organ function will allow the practitioner to better treat the elderly client with as few medications as possible.

Off-pump versus on-pump coronary artery bypass surgery and postoperative renal dysfunction

Renal dysfunction is a serious complication after coronary bypass surgery with cardiopulmonary bypass (CABG). Because duration of cardiopulmonary bypass (CPB) is associated with renal outcome, it has been proposed that avoidance of CPB with off-pump coronary bypass (OPCAB) may reduce perioperative renal insult. We therefore tested the hypothesis that OPCAB is associated with less postoperative renal dysfunction compared with CABG surgery. With IRB approval, we gathered data for 690 primary elective coronary bypass patients (OPCAB, 55; CABG, 635). Perioperative change in creatinine clearance (DCrCl) was calculated by using preoperative (CrPre) and peak postoperative (CrPost) serum creatinine values, and the Cockroft-Gault equation (DCrCl = CrPreCl - CrPostCl). Univariate and linear multivariate tests were used in this retrospective analysis; P: < 0.05 was considered significant. Multivariate analysis did not identify OPCAB surgery as an independent predictor of DCrCl. However, previously reported associations of PreCrCl, age, and diabetes with DCrCl were confirmed. Power analysis demonstrated an 80% power to detect a 7.0 mL/min DCrCl difference between study groups. In this retrospective study, we could not confirm that OPCAB significantly reduces perioperative renal dysfunction compared with CABG surgery. Our findings suggest that reduction of renal risk alone should not be an indication for OPCAB over CABG surgery.

IMPLICATIONS

Retrospective analysis did not identify any significant difference in perioperative change in creatinine clearance after coronary revascularization with cardiopulmonary bypass compared with off-pump coronary surgery.

The association of epsilon-aminocaproic acid with postoperative decrease in creatinine clearance in 1502 coronary bypass patients

Renal dysfunction is a common serious complication after cardiac surgery. Reports of proteinuria and hyperkalemia after cardiac surgery with epsilon-aminocaproic acid (EACA) have therefore raised concerns for renal safety. Since EACA renders these markers unreliable, we used perioperative change in creatinine clearance (DCrCl) to test the hypothesis that EACA is associated with greater reductions in creatinine clearance after heart surgery, particularly for patients with renal disease. We evaluated data from all elective primary coronary bypass patients during EACA introduction at our institution (July 1, 1991-December 31, 1992; 10 g iv bolus pre-cardiopulmonary bypass, then 1 g/h for 5 h). DCrCl was calculated using preoperative (CrPre) and postoperative peak serum creatinine values, using the Cockroft-Gault equation. Patients with CrPre > or = 133 micromol/L were also separately analyzed. Evaluated patients (n = 1502, +/-EACA; 581/905, 16 exclusions) included 233 with CrPre > or = 133 micromol/L (+/-EACA; 98/135). Multivariate analyses confirmed several known risk factors, but no association between DCrCl and EACA in all patients (P: = 0.66), and the subgroup with CrPre > or = 133 micromol/L (P: = 0.42).

IMPLICATIONS

In a large population of primary Coronary Artery Bypass Graft including a subset with preoperative renal dysfunction, there were no postoperative reductions in creatinine clearance attributable to epsilon-aminocaproic (EACA) administration. This retrospective study suggests that moderate epsilon-aminocaproic acid dosing during cardiac surgery is safe for the kidney; however, this inference is based on a single marker of renal dysfunction and requires prospective confirmation using a variety of tests of renal function.

Dosage adjustments for antibacterials in obese patients: applying clinical pharmacokinetics

Obesity is associated with physiological changes that can alter the pharmacokinetic parameters of many drugs. Vancomycin and the aminoglycosides are the only antibacterials that have been extensively investigated in the obese population. The apparent volume of distribution (Vd) and total body clearance of vancomycin are increased in obese patients and have a better correlation with total bodyweight (TBW) than with ideal bodyweight (IBW). The Vd of aminoglycosides is increased in obesity and can be estimated from an adjusted bodyweight that accounts for a fraction of the excess bodyweight (TBW - IBW). These observed changes in pharmacokinetic parameters of vancomycin and aminoglycosides in obese patients may necessitate a deviation from the commonly recommended dosages administered to non-obese individuals. There are limited data regarding the pharmacokinetics of other antibacterial classes in obese patients. The available information for cephalosporins suggests that dosages may need to be increased in obese patients in order to obtain similar serum and tissue concentrations as in non-obese patients. Additional pharmacokinetic studies of other antibacterial classes are required in this special patient population.