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    Effect of vitamin C supplements on urinary oxalate and pH in calcium stone-forming patients
    (Blackwell Publishing Inc, 2003-03-01) Baxmann, Alessandra Calábria [UNIFESP]; Mendonça, Cláudia de Oliveira Guimarães [UNIFESP]; Heilberg, Ita Pfeferman [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)
    Background. the contribution of ascorbate to urinary oxalate is controversial. the present study aimed to determine whether urinary oxalate and pH may be affected by vitamin C supplementation in calcium stone-forming patients.Methods. Forty-seven adult calcium stone-forming patients received either 1 g (N = 23) or 2 g (N = 24) of vitamin C supplement for 3 days and 20 healthy subjects received 1 g. A 24-hour urine sample was obtained both before and after vitamin C for calcium, oxalate, magnesium, citrate, sodium, potassium, and creatinine determination. the Tiselius index was used as a calcium oxalate crystallization index. A spot fasting morning urine sample was also obtained to determine the urinary pH before and after vitamin C.Results. Fasting urinary pH did not change after 1 g (5.8 +/- 0.6 vs. 5.8 +/- 0.7) or 2 g vitamin C (5.8 +/- 0.8 vs. 5.8 +/- 0.7). A significant increase in mean urinary oxalate was observed in calcium stone-forming patients receiving either 1 g (50 +/- 16 vs. 31 +/- 12 mg/24 hours) or 2 g (48+/- 21 vs. 34 +/- 12 mg/24 hours) of vitamin C and in healthy subjects (25 +/- 12 vs. 39 +/- 13 mg/24 hours). A significant increase in mean Tiselius index was observed in calcium stone-forming patients after 1 g (1.43 +/- 0.70 vs. 0.92 +/- 0.65) or 2 g vitamin C (1.61 +/- 1.05 vs. 0.99 +/- 0.55) and in healthy subjects (1.50 +/- 0.69 vs. 0.91 +/- 0.46). Ancillary analyses of spot urine obtained after vitamin C were performed in 15 control subjects in vessels with or without ethylenediaminetetraacetic acid (EDTA) with no difference in urinary oxalate between them (28 +/- 23 vs. 26 +/- 21 mg/L), suggesting that the in vitro conversion of ascorbate to oxalate did not occur.Conclusion. These data suggest that vitamin C supplementation may increase urinary oxalate excretion and the risk of calcium oxalate crystallization in calcium stone-forming patients.
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    Is a safety guidewire needed for retrograde ureteroscopy?
    (Assoc Medica Brasileira, 2017) Molina Junior, Wilson Rica; Pessoa, Rodrigo R.; da Silva, Rodrigo Donalisio; Gustafson, Diedra; Nogueira, Leticia; Meller, Alex [UNIFESP]
    Introduction: It is generally advised to have a safety guidewire (SGW) present during ureteroscopy (URS) to manage possible complications. However, it increases the strenght needed to insert and retract the endoscope during the procedure, and, currently, there is a lack of solid data supporting the need for SGW in all procedures. We reviewed the literature about SGW utilization during URS. Method: A review of the literature was conducted through April 2017 using PubMed, Ovid, and The Cochrane Library databases to identify relevant studies. The primary outcome was to report stone-free rates, feasibility, contraindications to and complications of performing intrarenal retrograde flexible and semi-rigid URS without the use of a SGW. Results: Six studies were identified and selected for this review, and overall they included 1,886 patients where either semi-rigid or flexible URS was performed without the use of a SGW for the treatment of urinary calculi disease. Only one study reported stone-free rates with or without SGW at 77.1 and 85.9%, respectively (p= 0.001). None of the studies showed increased rates of complications in the absence of SGW and one of them showed more post-endoscopic ureteral stenosis whenever SGW was routinely used. All studies recommended utilization of SGW in complicated cases, such as ureteral stones associated with significant edema, ureteral stricture, abnormal anatomy or difficult visualization. Conclusion: Our review showed a lack of relevant data supporting the use of SGW during retrograde URS. A well-designed prospective randomized trial is in order.