John R. Mehall

Fibrin sheath enhances central venous catheter infection

Objective To determine whether fibrin-coated central venous catheters have a higher infection rate, and spawn more septic emboli, than uncoated catheters after exposure to bacteremia. Design Animal study comparing catheter infection and blood cultures of fibrin-coated and uncoated catheters exposed to bacteremia. Setting Animal laboratory. Subjects Adult male Sprague-Dawley rats. Interventions A total of 210 rats had catheters placed with the proximal end buried subcutaneously. Rats were divided into three groups: tail vein bacterial injection on day 0 (no fibrin group) or on day 10 (fibrin group), or no injection/saline injection (control, n = 40). Bacterial injections were 1 × 108 colony forming units of either Staphylococcus epidermidis (n = 100) or Enterobacter cloacae (n = 60). Animals were killed 3 days after injection. Blood cultures were obtained via cardiac puncture, and catheters were removed via the chest. Half of the catheter was rolled onto agar and the other half was placed in trypticase soy broth. Plates and broth were incubated at 37°C for 48 hrs. The presence of >15 colonies on roll plates, or growth in broth, was accepted as a positive sign of infection. Microscopy was performed on day 20-10 catheters. Thirty animals without catheters had bacterial injections and underwent blood culture 3 days after injection. Measurements and Main Results Catheter infection with S. epidermidis occurred in 32% of roll plates and 80% of broth from the fibrin group vs. 4% and 20% from the no fibrin group (p < .01 for each). Catheter infection with E. cloacae occurred in 50% of roll plates and 80% of broth from the fibrin group vs. 0% and 12% from the no fibrin group (p < .01 for each). Positive blood cultures occurred in 47 of 68 animals from the fibrin group vs. 8 of 68 from the no fibrin group (p < .01). Microscopy showed a fibrin sheath on 20 of 20 catheters. Without catheters, 30 of 30 blood cultures were negative. Conclusion The fibrin sheath significantly enhanced catheter-related infection and persistent bacteremia.

Prospective results of a standardized algorithm based on hemodynamic status for managing pediatric solid organ injury

BACKGROUNDnControversy surrounds the need for ICU admission, prolonged bed rest, and the duration of activity restrictions for children sustaining blunt trauma. Adult literature supports management based on hemodynamic status, not CT grade.nnnSTUDY DESIGNnA 3-year prospective study of a standardized management algorithm for hemodynamically normal pediatric patients with blunt liver or spleen injury was performed. Patient selection was based on vital signs, irrespective of injury grade on CT. Patients requiring ICU admission for nonliver or nonspleen injury were excluded. Patients were admitted to a surgical ward with serial hematocrit levels. Discharge occurred 48 hours postinjury if patients had no abdominal tenderness, tolerated a regular diet, and had a stable hematocrit. Patients were allowed noncontact activity, including school, after discharge. Patients were followed up at 1 month with ultrasonographic imaging.nnnRESULTSnEighty-nine patients sustained blunt liver or spleen injury. Forty-five patients were excluded for other injuries (Glasgow Coma Scale < 13, 32 of 45); the remaining 44 patients had a mean age of 8.9 years (range 2 to 17 years), Injury Severity Score 10.6 (range 4 to 33), liver grade 2.1, and splenic injury grade 2.3. Mechanisms of injury were predominately motor vehicle collisions (59%). All patients were managed nonoperatively without transfusion; 43 of 44 patients completed the algorithm. Mean observation was 55.2 +/- 12.3 hours. One-month followup occurred in 33 of 44 patients, with one complication detected and no delayed bleeding.nnnCONCLUSIONnManagement of pediatric solid organ injury should be guided by hemodynamic status and not injury grade on CT. Hemodynamically normal children can be safely managed without intensive care monitoring, do not need prolonged hospitalization, and can resume school on discharge.

Catheter materials affect the incidence of late blood-borne catheter infection

BACKGROUNDnAdherence of bacteria and subsequent catheter-related infections (CRI) are greatly enhanced by the fibrin sheath that develops on indwelling catheters. Since the infection rate of catheters without fibrin sheaths is low and the fibrin sheath mediates bacterial adherence, catheter material is not thought to affect the incidence of late catheter-related infection.nnnMETHODSnA total of 276 rats had catheters placed in the right jugular vein with the proximal end buried subcutaneously to eliminate exit site infection. Rats were divided into two groups: silastic catheters (SC; n = 133) and polyurethane catheters (PC; n = 143). Injections of 1 x 10(8) CFU/mL of Staphylococcus epidermidis were given via the tail vein on either the day of surgery, day 0 (n = 53 SC, n = 51 PC), or on postoperative day 10 (n = 50 SC, n = 62 PC). Thirty animals from each group (SC, PC) received sterile saline injections on day 10 and served as controls. Animals were sacrificed on postinjection day 3. Catheters were removed via the chest and placed into trypticase soy broth. Broth was incubated at 37 degrees C for 48 h. Microscopy for the fibrin sheath was done on 20 randomly selected catheters (10/group). Data were compared using Fishers exact test, with p < 0.05 considered significant.nnnRESULTSnIncidence of CRI was equal prior to the formation of the fibrin sheath, while CRI was significantly higher in silastic catheters in the presence of a fibrin sheath. Without a fibrin sheath (day 0), 8/53 silastic catheters and 3/51 polyurethane catheters were infected (p = NS). With a fibrin sheath (day 10), 31/50 silastic catheters were infected versus 20/62 polyurethane catheters (p < 0.05). Control catheters were all culture negative (30/group). With light microscopy, 20/20 catheters had fibrin sheaths at day 10 with no visible difference between silastic and polyurethane catheters.nnnCONCLUSIONnCatheter material does affect the incidence of catheter-related infection even when catheters are coated with a fibrin sheath. This difference may relate to a difference in the fibrin sheath itself as it forms on different catheter materials.

Enoxaparin inhibits fibrin sheath formation and decreases central venous catheter colonization following bacteremic challenge

Objective:Inhibition of fibrin sheath formation by enoxaparin decreases catheter colonization. Fibrin-binding radioactive tracer and catheter weights quantify fibrin reduction. Design:Controlled experimental study of central venous line colonization. Setting:Animal laboratory. Subjects:Adult male Sprague-Dawley rats. Interventions:Central venous lines were introduced into right external jugular veins of 254 animals in three groups: enoxaparin, Fibrimage, and catheter weight. The enoxaparin group (n = 196) received daily enoxaparin injections (n = 97) or catheter implantation only (n = 99); 176 received tail vein injections of Staphylococcus epidermidis on postoperative day (POD) 10. Twenty rats received saline injections as a control. On POD 13, catheters were removed and incubated in broth at 37°C for 48 hrs. Turbid samples were plated. In the Fibrimage group (n = 39), 20 rats receiving enoxaparin were compared with 19 controls without enoxaparin; all received S. epidermidis injections on POD 10. Fibrimage, fibrin-binding radiolabeled tracer, was given 1 hr before catheter removal. In the weight group (n = 19), six rats received enoxaparin; 13 did not. All received injections of S. epidermidis on POD 10. Measurements and Main Results:Positive plates underwent analytic profile index testing, ensuring correlation with inoculum. Results were compared using Fisher’s exact or chi-square tests. Gamma counts were determined in the Fibrimage group. Catheter tip weights were recorded. Results from the Fibrimage and weight groups were compared using Student’s t-test. The enoxaparin group had fewer catheters colonized (17 of 77) vs. no enoxaparin (42 of 99; p < .01). Pericatheter sheaths contained less fibrin compared with controls. Fibrimage group gamma counts were significantly decreased for the enoxaparin subgroup (x = 2244 counts per minute) vs. controls (x = 3767 counts per minute; p < .0002). The weight of catheter tips treated with enoxaparin (x = 39 mg) vs. controls (x = 90 mg) was also significantly decreased (p < .0001). Conclusions:Enoxaparin decreases the amount of fibrin surrounding central venous catheters. The incidence of catheter colonization decreases when the amount of fibrin within the pericatheter sheath decreases.

Acidification of formula with citric acid is equally effective and better tolerated than acidification with hydrochloric acid.

ObjectiveTo determine whether acidification of formula with citric acid is equally protective against bacterial translocation and gut colonization but better tolerated than acidification with hydrochloric acid in neonatal rabbits. DesignPaired animal model with control. SettingAnimal laboratory. SubjectsPremature neonatal New Zealand rabbit pups. InterventionsA standard neonatal rabbit model in two versions, a bacterial challenge and a no bacterial challenge model, was used to assess bacterial translocation and gut colonization. Two hundred forty-six rabbit pups were delivered by cesarean section 1 day premature and randomly placed into two groups sorted by type of formula acidification (hydrochloric acid or citric acid). Pups were gavage fed pH 3 kitten formula every 12 hrs. Ranitidine hydrochloride at 20 mg·kg−1·day−1 was added to all formula. Bacterial challenge animals were given 1 × 10 colony-forming units/mL of Enterobacter cloacae with the third feeding. Animals in the no bacterial challenge group received no bacterial challenge. Animals were killed on day of life 3, and the liver, spleen, mesenteric lymph nodes, and cecum were sequentially harvested and cultured. Organs were qualitatively judged for growth, whereas cecal cultures were quantified as colony-forming units/gram. Stomach biopsies were performed to look for mucosal damage. Long-term tolerance was assessed in 48 pups fed formula acidified to pH 3 with either hydrochloric acid or citric acid and 20 animals fed pH 7 formula without ranitidine. Weight gain and mortality rate were followed for 14 days. Measurements and Main ResultsGut colonization and bacterial translocation to liver, spleen, and mesenteric lymph nodes were equivalent between citric acid and hydrochloric acid in both bacterial challenge and no bacterial challenge models. Long term, citric acid animals exceeded hydrochloric acid animals in daily weight gain and survival (p < .05 for both) and equaled pH 7 animals in these measurements. ConclusionAcidification of formula with citric acid is equally protective against bacteria but better tolerated than acidification with hydrochloric acid.