Bone density and cortical structure after pediatric renal transplantation.

The impact of renal transplantation on trabecular and cortical bone mineral density (BMD) and cortical structure is unknown. We obtained quantitative computed tomography scans of the tibia in pediatric renal transplant recipients at transplantation and 3, 6, and 12 months; 58 recipients completed at least two visits. We used more than 700 reference participants to generate Z-scores for trabecular BMD, cortical BMD, section modulus (a summary measure of cortical dimensions and strength), and muscle and fat area. At baseline, compared with reference participants, renal transplant recipients had significantly lower mean section modulus and muscle area; trabecular BMD was significantly greater than reference participants only in transplant recipients younger than 13 years. After transplantation, trabecular BMD decreased significantly in association with greater glucocorticoid exposure. Cortical BMD increased significantly in association with greater glucocorticoid exposure and greater decreases in parathyroid hormone levels. Muscle and fat area both increased significantly, but section modulus did not improve. At 12 months, transplantation associated with significantly lower section modulus and greater fat area compared with reference participants. Muscle area and cortical BMD did not differ significantly between transplant recipients and reference participants. Trabecular BMD was no longer significantly elevated in younger recipients and was low in older recipients. Pediatric renal transplant associated with persistent deficits in section modulus, despite recovery of muscle, and low trabecular BMD in older recipients. Future studies should determine the implications of these data on fracture risk and identify strategies to improve bone density and structure.

Impaired renal function is associated with greater urinary strong ion differences in critically ill patients with metabolic acidosis.

PURPOSE: Urinary excretion of chloride corrects metabolic acidosis, but this may be hampered in patients with impaired renal function. We explored the effects of renal function on acid-base characteristics and urinary strong ion excretion using the Stewart approach in critically ill patients with metabolic acidosis. MATERIALS AND METHODS: We examined the plasma and urine chemistry in 65 critically ill (mixed medical and surgical) patients with metabolic acidosis. The apparent strong ion difference, effective strong ion difference, strong ion gap, and urinary simplified strong ion difference (urinary SID) were calculated. Linear regression analyses were used (1) to assess whether plasma creatinine concentrations were related to urinary SIDs values, adjusted for blood pH levels, and (2) to determine whether urinary SID values were associated with blood pH levels. RESULTS: Creatinine concentrations were positively and significantly (P < .001) associated with urinary SIDs values, adjusted for pH levels. Urinary simplified strong ion difference values were inversely and significantly (P < .001) related to pH levels. CONCLUSIONS: In critically ill patients with metabolic acidosis, impaired renal function was associated with greater urinary SIDs. Subsequently, the higher urinary SIDs values were related to lower pH levels, illustrating the importance of renal chloride excretion to correct for acidosis.

Contribution of various metabolites to the "unmeasured" anions in critically ill patients with metabolic acidosis.

OBJECTIVE: The physicochemical approach, described by Stewart to investigate the acid-base balance, includes the strong ion gap (SIG), a quantitative measure of "unmeasured" anions, which strongly correlates to the corrected anion gap. The chemical nature of these anions is for the most part unknown. We hypothesized that amino acids, uric acid, and organic acids could contribute to the SIG. DESIGN: Prospective observational study. SETTING: Intensive care department of an academic hospital. PATIENTS: Consecutive intensive care unit patients (n = 31) with metabolic acidosis, defined as a pH of < 7.35 and a base excess of < or = -5 mmol/L. INTERVENTIONS: A single arterial blood sample was collected. MEASUREMENTS: The SIG was calculated and two groups were compared: patients with SIG of < or = 2 mEq/L and patients with SIG of > or = 5 mEq/L. "Unmeasured" anions were examined by ion-exchange column chromatography, reverse-phase high-performance liquid chromatography, and gas chromatography/mass spectrometry measuring amino acids, uric acid, and organic acids, respectively. MAIN RESULTS: Comparison of patient characteristics of both SIG groups showed that age, sex, Acute Physiology and Chronic Health Evaluation II, pH, base excess, and lactate were not significantly different. Renal insufficiency and sepsis were more prevalent in the SIG > or = 5 mEq/L group (n = 12; median SIG, 8.3 mEq/L), associated with higher mortality. Concentrations of the anionic compounds aspartic acid, uric acid, succinic acid, pyroglutamic acid, p-hydroxyphenyllactic acid, and the semiquantified organic acid homovanillic acid were all statistically significantly elevated in the SIG > or = 5 mEq/L group compared with the SIG < or = 2 mEq/L group (n = 8; median SIG, 0.6 mEq/L). Overall, the averaged difference between both SIG groups in total anionic amino acids, uric acid, and organic acids concentrations contributed to the SIG for, respectively, 0.07% (5 microEq/L, p = not significant), 2.2% (169 microEq/L, p = .021), and 5.6% (430 microEq/L, p = .025). CONCLUSIONS: Amino acids, uric acid, and organic acids together accounted for only 7.9% of the SIG in intensive care unit patients with metabolic acidosis.