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In a prospective clinical trial (July 1999 to November 2000) conducted at the Small Animal Clinic of the Free University of Berlin, the incidence of vein-catheter related infections and underlying factors was evaluated in 103 dogs (mongrels dogs and dogs of 31 different breeds ; 79 males and 24 females; mean age 6.4 years) with a variety of diseases (mammary gland tumors (n=23), gastroenteritis (n=20), pyometra (n=20), polytrauma (n=20), and orthopedic diseases n=20)). In the dogs, drugs were given perioperatively or during routine treatment using a cephalic antebrachial vein and peripheral indwelling vein catheters (fluorethylenpropylencatheter, 20G, 1 In patients with orthopedic diseases, venous catheters were removed 24 hours after insertion whereas in the other patients, catheters were removed after 48 hours. Bacterial cultures of the catheter tips were done using a semiquantitative method of MAKI et al. (1977). Fourty eight hours after removal of the catheter, ultrasonography of the ipsilateral and contralateral cephalic vein was performed. Compressibility of the vein, echogenicity of the intravascular space and the venous wall were assessed and vein diameter was measured by ultrasonography.Each patient underwent a complete physical examination. A blood cell count and a blood biochemical analysis were done as well as a coagulation profile (prothrombin time, activated partial thromboplastin time, and fibrinogen and fibrinogen degradation products) in each individual dog. In the group of orthopedic patients (indwelling catheter time of 24 hours), no clinical abnormalities of the veins were found, whereas in the other patient groups (indwelling catheter time of 48 hours), 72.3% had local signs of venous inflammation. In 10.8% of those dogs, abnormalities suggesting of thrombophlebitis were observed. None of the patients with thrombophlebitis had either clinical or blood biochemical signs indicating the occurrence of septicemia.Sonography of the veins revealed vessel abnormalities in 50% (indwelling catheter time of 24 hours) and 89% of the patients (indwelling catheter time of 48 hours), respectively. After 48 hours of catheterization, catheter associated infections (> 5 colony forming units and clinical signs of thrombophlebitis) occured in 24% of dogs, however, catheter associated bacterial colonizations (> 5 colony forming units without criteria of thrombophlebitis) only in 7.2% of dogs. After 24 hours of catheterization, bacterial colonizations at the catheter tip were found in 5% of dogs in contrast o catheter associated infection that did not occur.Staphylococcus spp (n=10), Acinetobacter spp. (n=7), Bacillus cereus (n=6), and Escherichia coli (n=3) were isolated most frequently from bacterial cultures. Enteric bacteria were predominantly found in patients with inflammatory gastrointestinal disease.Catheter associated infections as well as clinical and ultrasonographic abnormalities of the veins were detected most frequently in dogs with gastroenteritis compared to the other patient groups.The prevalence of catheter-related venous alterations and infections correlated well with the duration of catheter placement and the age of the patient with patients less than one year of age showing infections, clinical, and sonographical vein abnormalities most frequently. In addition, in dogs weighing more than 35kg, clinical and ultrasonographic vein abnormalities were detected most commonly.The results of this study indicate that catheter associated infections are common in hospitalized dogs as to be seen in people. Therefore, clinical procedures and regulations for the standardized management of indwelling vein catheters in dogs should be developed such as in human medicine. The duration of the catheter indwelling time should be considered the most critical factor for catheter related infections in hospitalized dogs.