Gardner, Reed M.

Thomas, Frank

English

The University of Utah: J. Willard Marriott Digital Library

OO'I0-14'11/X4/ 121 0-0Xh0$02 00/0 CRITICAl CARl Mllll<l"l Copynghl '" I 'IX4 hv The Williams & Wilkms Co. Vol. 12, No. 10 Printed tn USA. A prospective comparison of arterial catheter blood and catheter-tip cultures in critically ill patients FRANK THOMAS. MD; JAMES F. ORME, JR, MD; TERRY P. CLEMMER, MD; JOHN P. BURKE, MD; C. GREGORY ELLIOTT. MD; REED M. GARDNER, PHD To determine if a culture of blood obtained through an arterial catheter reflects culture of the catheter's tip, we studied 68 arterial catheters removed from 65 pa-tients with and without suspected catheter infections. Cultures of blood obtained before catheter removal were compared to catheter-tip cultures. The arterial catheter blood culture was neither sensitive nor highly predictive of positive catheter-tip cultures. Suspicion of catheter infection was not associated with a significantly higher rate of positive catheter-tip or blood cultures. Catheter-caused sepsis is a serious problem whose diagnosis usually requires removing the catheter to obtain its tip for culture. Catheter removal may com-promise care of the critically ill by the temporary loss of laboratory and monitoring data obtained through the catheter. To determine if cultures of blood drawn through the arterial catheter could replace catheter-tip cultures, we compared arterial catheter blood and tip culture results in patients with and without suspected catheter infection. METHODS The study included all patients admitted to the LOS Hospital's Shock-Trauma Unit from June 1981 to March 1982, in whom a radial or femoral artery cath-eter was inserted. At the time of catheter removal, physicians completed a questionnaire to identify those catheters which were removed because of suspected catheter infection. Catheter-related infection was sus-pected when the patient showed evidence of sepsis despite appropriate treatment of an identified infection, or when the source of infection was not identifiable. Before catheter removal, aseptic technique was used to withdraw 10 ml of blood through the 3-way stopcock lock of femoral artery catheters, and directly through the catheter port of radial artery catheters. Five-ml From the Shock-Trauma Unit (Drs. Thomas and Orme) and the Departments of Critical Care Medicine (Dr. Clemmer), Infectious Disease (Dr. Burke), Respiratory Therapy (Dr. Elliott), and Medical Biophysics and Computing (Dr. Gardner), LOS Hospital, University of Utah, Salt Lake City, UT. This study was supported, in part, by a grant from the LOS Hospital-Deseret Foundation. Address requests for reprints to: Dr. Frank Thomas, Shock-Trauma Unit, LOS Hospital, 325 Eighth Avenue, Salt Lake City, UT 84143. 860 aliquots of blood were added under aseptic conditions to 100 ml of tryptose phosphate broth (aerobic) and to 100 ml of brain-heart infusion broth (anaerobic). At the time of catheter removal, the protective dress-ing was removed and the insertion site was cleaned with a povidone-iodine solution and wiped dry with a sterile gauze pad. The catheter was then removed asep-tically by the research nurse, one of the authors (F.T.), or an ICU nurse. The distal 2 to 3 em of the catheter was cut ofT with sterile scissors or a scalpel blade and placed into a sterile test tube containing 2.5 ml of tryptose-phosphate broth. Arterial catheter blood cul-tures and the catheter tip were then immediately taken to the laboratory. There, a sterile, 0.01-ml calibrated loop was used to withdraw an aliquot of vortexed tryptose-phosphate broth. This aliquot was then plated on blood agar for semiquantitative culture. Ten ml of thioglycollate broth was added to the remaining tryp-tose-phosphate broth and catheter tip. All cultures were incubated at 37"C and evaluated daily for 14 days, for bacterial and fungal growth. Isolates were identified by standard bacteriologic tech-niques. All culture data were analyzed using Fischer's exact test to determine statistical difference in measured variables. RESULTS Blood and catheter-tip cultures were obtained from 68 arterial catheters inserted into 65 critically ill patients (32 males and 33 females; mean age of 54 ± 20 yr). One male underwent an additional catheter insertion, and one female underwent two additional catheter in-sertions. Eleven patients died, and 54 patients were receiving antibiotics at the time of catheter removal. Thirty-two catheters were inserted femorally, and 36 catheters were inserted radially. Catheter duration in situ was 5.8 ± 5.1 days. Fifteen catheters were removed because of suspected catheter infection. Table I shows catheter blood and tip culture results in patients with and without suspected catheter infection. Table 2 shows organisms cultured from arterial catheter blood and tip cultures. For groups lA, IB and II, all with positive blood cultures, a wide variety of organisms was ob-tained; while for group III, in which the blood culture was negative and the tip culture was positive, Staphy-Vol. 12, No. lO Thomas et a/-ARTERIAL CATHETER BLOOD AND TIP CULTURES 861 TABlE I. Culture results No. of Catheters Blood Catheter-Tip Group Culture Culture Infection Not Infection Suspected Suspected lA + + 2 I IB" + + I 0 II + 5 2 Ill + 7 3 IV 38 9 53 15 "Group IB had a different organism in blood culture and catheter-tip culture. TABlE 2. Culture results (+)Arterial Blood and (+)Catheter-Tip Organism Group lA and IB Staphylococcus aureus Candida Pseudomonas Escherichia coli and diphtheroids Group II Pseudomonas Staphylococcus epidermidis Enterococcus Klebsiella Diphtheroids Bacteroides fragilis Group Ill Staphylococcus epidermidis Staphylococcus aureus No. of Patients I a 9 • Arterial catheter blood and catheter-tip cultures yielded different organisms. lococcus epidermidis was the primary organism identi-fied. Table 3 compares the sensitivity, specificity, and predictive value of arterial blood cultures in patients with and without suspected catheter-tip infection. None of the comparisons showed arterial catheter blood cul-tures useful in predicting catheter-tip culture results. The sensitivity of blood cultures in detecting positive tip cultures was only .21 for all patients studied. Sensi-tivity did not improve (.25) in those patients suspected of having an arterial catheter infection. Similarly, arte-rial catheter blood cultures had a low predictive value in determining positive catheter tips in all patients studied (.30), and in patients suspected of catheter infection (.33). There was no significant relationship between suspicion of catheter infection and positive catheter tip or catheter blood cultures (Table 4). DISCUSSION In critically ill and immunosuppressed patients, no-socomial infection is a major complication. Approxi-mately 25,000 cannula-related septicemias occur yearly. 1 One device frequently used in the critical care setting is the arterial catheter, which provides rapid access to blood for laboratory studies and continuous physiologic monitoring of the seriously ill patient. How-ever, the use of these devices has been associated with life-threatening infection. 2- 4 Several techniques have been developed to assess catheter-related infection5• 6 ; however, all require removing the catheter for culture. Because this may compromise access to blood speci-mens and continuous hemodynamic monitoring, it would be preferable to evaluate possible infection with-out removing the catheter. Theoretically, blood cultures withdrawn through the catheter would be expected to contain any bacteria found on the tip of the catheter. However, we found that blood cultures drawn through the arterial catheter lacked sensitivity for determining positive catheter-tip cultures. These results confirm and extend the observations of Singh et al. 7 TABlE 3. Sensitivity, specificity. and predictive value of blood culture for catheter-tip culture All patients Blood+ Blood-Total Catheter infection suspected Blood+ Blood-Catheter infection not suspected Blood+ Blood-Positive catheter 3 II 14 I 3 2 8 Negative catheter 7 47 54 2 9 5 38 Sensitivity= .21 Predictive value+ = .30 Sensitivity = .25 Predictive value+ = .33 Sensitivity = .20 Predictive value+ = .29 Specificity = .87 Predictive value- = .81 Specificity = .82 Predictive value-= .75 Specificity = .88 Predictive value- = .83 862 CRITICAL CARE MEDICINE OCTOBER, 1984 TABLE 4. Suspicion of catheter infection vs. culture results Infection Infection value Suspected Not Suspected p------------·-Positive catheter-tip culture 4 10 NS Negative catheter-tip culture II 43 Positive blood culture 3 8 NS Negative blood culture 12 45 Several explanations may be responsible for this lack of correlation. Catheter-induced sepsis is generally at-tributed to either the infusion or the cannula. 1 Contam-inated infusion fluid occurs much less frequently than cannula-produced bacteremia.8 Two sources of can-nula-related infection are contamination of the catheter tip by bacteremic spread from another source of infec-tion, and the spread of a local infection down the transcutaneous cannula tract. Evidence suggests that most catheter-related septicemias are derived from the latter source. 9 This theory helps explain the decreased incidence of catheter-related sepsis with arterial versus venous catheters, because the greater distance of skin to the artery may hinder the spread of infection. In order to be detected by the catheter blood culture, bacteria from the transcutaneous tract must reach the catheter tip. This would require bacteria to move against the high-velocity flow of arterial blood and travel a considerable distance to reach the catheter tip. It is unlikely that arterial blood withdrawn through the catheter, which represents blood proximal to the cath-eter tip, reflects the cannula tract infection but rather the blood-borne spread of bacteria to the tip. However, catheter-tip cultures reflect bacteria found in the trans-cutaneous catheter tract. This could explain the high incidence of S. epidermidis recovered from catheter tips. 10 Our data support previous findings that clinical sus-picion of catheter-related infection is not predictive of catheter-tip infection. 11 Our data further show that arterial catheter blood cultures are likewise not predic-tive of catheter infection. REFERENCES I. Maki DG: Sepsis arising from extrinsic contamination of infusion and measures for control. In: Microbiologic Hazards of Infusion Therapy. Phillips I, Meers PD, D'Arcy PE (Eds). Lancaster, England, MTP Press, 1977, p 99 2. Stamm ME, Colilla JJ, Anderson RL, et al: Indwelling arterial catheters as source of nosocomial bacteremia. An outbreak caused by flavobacterium. N Eng/ J Med 1975; 292:1099 3. Weinstein RA, Emori TG, Anderson RL, et al: Pressure moni-toring devices. Overlooked source of nosocomial infection. Chest 1976; 69:338 4. Maki DG, McCormick RD, Uman SJ, et al: Septic endarteritis due to intraarterial catheters for cancer chemotherapy. Cancer 1979; 44: 1228 5. Band JD, Maki DG: Infections caused by arterial catheters used for hemodynamic monitoring. Am J Med 1979; 67:735 6. Cieri DJ, Corrads ML, Seligman SJ: Quantitative culture of intravenous catheters and other intravascular inserts. J Infect Dis 1980; 141:781 7. Singh S, Nelson N, Acosta I, et al: Catheter colonization and bacteremia with pulmonary and arterial catheters. Crit Care Med 1982; 10:763 8. Band JD, Maki DG: Safety of changing intravenous delivery systems at longer than 24-hour intervals. Ann Intern Med 1979; 91:173 9. Maki DG, Goldman DA, Rhame FS: Infection control in intra-venous therapy. Ann Intern Med 1973; 79:867 10. Penilla JC, Ross DF, Martin T, et al: Study of the incidence of intravascular catheter infection and associated septicemia in crit-ically ill patients. Crit Care Med 1983; II :21 II. Thomas F, Burke JP, Parker J, et al: The risk of infection related to radial vs. femoral sites for arterial catheterization. Crit Care Med 1983; 11:807 

Prospective Comparison of Arterial Catheter Blood and Catheter-Tip Cultures in Critically Ill Patients

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Prospective Comparison of Arterial Catheter Blood and Catheter-Tip Cultures in Critically Ill Patients

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