Introduction

Hemodialysis (HD) is a therapeutic technique for removing substances from the blood, such as urea and creatinine, using diffusion and ultrafiltration methods through a hemodialysis filter. It is a specific technique, due to the patient interaction with the extracorporeal circuit, and the complexity and sophistication of the equipment used (Cowgill & Langston 1996). Heparin has been used in the HD routine to keep the patients in the extracorporeal circuit. However, there have been some reported side effects such thrombocytopenia induction (Zimmerman 2000), bleeding (Guz et al. 1995) and need to repeat the initial doses (Koch et al. 2001). Therefore, new anticoagulants classes have been studied (Hoppensteadt et al. 1997). In recent years, low molecular weight heparin (LMWH), as calcium nadroparin, appears as an alternative for anticoagulation, and has been shown in human studies to be safe and effective (Hoppensteadt et al. 2003). Bioavailability of LMWH is high, because hardly connect to the plasma proteins, allowing their use in less repetitions then heparin. Important points to make use of this anticoagulant group are longer half-life, lower incidence of thrombocytopenia and consequently decrease of the antithrombotic effects in patients at risk of bleeding (Cohen 2000). LMWH are commonly used in deep vein thrombosis prophylaxis, treatment of acute pulmonary embolism and acute coronary syndrome (Charles & Kleinschmidt 2001). Because antithrombotic effects and longer half-life it has been tested as an anticoagulation model in human HD (Reeves et al. 1999). This is the first study to describe this kind of use in veterinary patients, and it aims to study and standardize a calcium nadroparin anticoagulation model that can be used during HD sessions in dogs.

Materials and Methods

The research was conducted at the Laboratory of the Department of Experimental Medicine, Faculty of Medicine of Botucatu--UNESP, São Paulo, Brazil, with Animals Research Ethics Committee agreement. Were used seven dogs in the experiment, mixed breed, adult, male, clinically healthy, with body weight ranging from 07 to 14 kg, from the University Central Kennel. Animals were kept in individual masonry cages, provided with a removable wooden platform, with free access to water, feed and solarium, until the end of the HD sessions, being weighed before and after each session, using for this, a digital scale. On the HD day, animals remained in fasting food (12 hours) and water (2 hours) and were anesthetized using levomepromazine hydrochloride (Neozine^®--25mg/5mL--Aventis) as pre-anesthetic medication and propofol (Propovan^® 10mg/mL--Cristália) as general anesthetic. A double-lumen catheter (8 French) was held preferably in right external jugular vein (Meneses et al. 2002) and then a simple cervical chest radiograph was performed to verify catheter positioning (cranial vena cava or right atrium). Animals were accommodated in the table to initialize HD session, where they received oxygen supplementation and heat through thermal mattress (Warm Touch^®--Patient Warming System--Mallinckrodt Medical) placed on the animal and calibrated to each patient needs (30-46°C). HD proportional system (System 1000® Series--Tina--Baxter Co.) was used, the extracorporeal circuit was connected as described by Cowgill (1995), blood flow was restricted to 10mL/kg/min, and sessions had a maximum duration of 180 minutes.

We chose to use initial priming with 0.9% saline solution to avoid hypotension and hypovolemic shock (Cowgill & Langston 1996). Polysulphate membranes (0.4 m² surface area) were used. Dogs were initially anticoagulated with 125 U anti-Xa/kg/IV/bolus of calcium nadroparin (Fraxiparine^®--5700 UI AXa/0.6mL--Sanofi Synthelabo). After 90 minutes of the HD beginning 41.6 U anti-Xa/kg/IV/bolus was given to the patient. Activated coagulation time (ACT) was held in the MCA 2000^® unit (Adib Jatene/SP). Activated partial thromboplastin time (APTT) and prothrombin time (PT) were performed collecting a blood sample, by a peripheral vein, in a test tube with citrate. After that, was proceeded plasma separation (10 minutes centrifugation at 3000 rpm (805g)), and then aliquots obtained were immediately stored in polyethylene containers for storage in liquid nitrogen (-196 °C) until the clotting test realization (APTT and PT). Anti-Xa activity test was carried out according to methodology applied by the International Laboratory Biopool Spectrolyse® Heparin (Xa) kit. Variables were measured in three moments (M1, M2, M3) using t Test for paired samples (p < 0.05) (Curi 1998).

Results

The study was conducted in three stages: Pre-HD (M1), 90 minutes after HD start (M2), and 180 minutes after HD beginning (M3). The following parameters were verified: anti-Xa, TP, and TTPA TCA, expressed in seconds. On the anti-Xa test were obtained the following values: M1 (0.02 ± 0005), M2 (0.77 ± 0.33) and M3 (0.60 ± 0.24); on the PT, the figures were, respectively, in M1 (8.71 ± 0.49), M2 (10 ± 0.81) and M3 (9.86 ± 0.90); APTT values were in M1 (20.57 ± 4.03), M2 (29.28 ± 7.20) and M3 (28.86 ± 9.94); and the ACT values were M1 (88.71 ± 27.37), M2 (213.43 ± 73.65) and M3 (173.28 ± 69.97).

Discussion and Conclusions

Kleinschmidt & Charles (2001) argued that the in vitro evidence of greater sensitivity to LMWH is the Anti-Xa, however, due its high cost and the need for a specialized laboratory, its routine use in veterinary medicine becomes restricted. The test showed LMWH uniformity during HD sessions, as well as described by Kleinschmidt & Charles (2001), and proved that it was an efficient HD anticoagulation method for dogs. Guz et al. (1995) reported, in humans, similar changes as described in this paper. Results have been shown to be possible to evaluate LMWH anticoagulation using ACT. According to Guz et al. (1995), this test has the function to evaluate the intrinsic and common pathways, but has no sensitivity as TTPA. Langston et al. (1997), studying domestic cats reported that ACT was not accurate in the final value of clotting HD coagulation, a fact inconsistent with this study where the final value of ACT, was satisfactory. It is necessary to addict TTPA, TP and anti-Xa values, to confirm ACT as a good coagulation HD monitoring test. According to Mishcke & Nolte (2000), LMWH have low anti IIa activity, not changing TTPA values. At the present research small changes in TTPA values were determined, getting close to the baseline values for dogs. This was the first Brazilian research that used calcium nadroparin as HD anticoagulant in dogs, and suggest 125 U Anti Xa/kg/IV/Bolus initially, with 1⁄4 additional initial doses after 90 minutes of the session. Thus the LMWH has proved efficient as a HD anticoagulant agent in dogs, specially reserved for animals with pre-existing clotting disorders.

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