Central venous catheters versus peripheral veins for sampling blood levels of commonly used drugs

Methotrexate Drug Monitoring From Central Access: Can Blood Sample Collection From Central Venous Access Replace Peripheral Venipuncture in Adults?

BACKGROUND

Intravenous high-dose methotrexate (MTX ≥ 1 g/m2) is frequently used in patients with cerebral lymphoma or other malignancies. In addition to its potent efficacy, it is known to have pronounced toxicity and life-threatening side effects. Regular-level monitoring at short and defined intervals is mandatory. This study aimed to evaluate the possibility of replacing peripheral blood sampling with blood samples from central venous catheters for therapeutic monitoring of MTX in adults.

METHODS

A total of 6 patients and 7 cycles of chemotherapy (6 females; 5 with cerebral non-Hodgkin lymphoma and 1 with osteosarcoma, median age 51 years; range 33-62 years) were included. An immunoassay was used for quantitative analysis of MTX levels. The measurement points were obtained in the time intervals of 24, 42, 48, and 72 hours, and afterward, every 24 hours until the level was below <0.1 µmol/L. After flushing with 10 mL of saline solution and discarding 10 mL of venous blood, blood was drawn from the central venous access through which MTX had previously been administered. Simultaneously, MTX levels were obtained from peripheral venipuncture.

RESULTS

Methotrexate levels from central venous access and MTX levels from peripheral venipuncture showed a significant correlation (r = 0.998; P < 0.01; n = 35). During withdrawal from the central access group, 17 values showed a lower MTX level, 10 showed a higher level, and 8 showed no difference. However, the MTX level difference was not significant (P = 0.997, linear mixed model). No increase in the dose of calcium folinate was necessary based on the collected MTX levels.

CONCLUSIONS

In adults, MTX monitoring from central venous access is not inferior to monitoring from peripheral venipuncture. Repeated venipuncture to measure MTX levels can be replaced after establishing standardized instructions for proper sampling by a central venous catheter.

Complete Blood Count Collected Via Venipuncture Versus Peripherally Inserted Central Catheter in Hematological Patients: A Comparison of 2 Methods

BACKGROUND

The use of peripherally inserted central catheters (PICCs) in cancer care is increasing over traditional central venous catheters. Nurses frequently collect blood by venipuncture when a PICC is inserted, as there is no available evidence to confirm the reliability of blood tests collected through PICCs in adults.

OBJECTIVE

The aim of this study was to assess the reliability of blood samples for complete blood count (CBC) obtained through PICCs as an alternative to venipuncture.

METHODS

A cross-sectional design was used to recruit adult hematological patients. The blood samples were collected within 5 minutes of each other by a specialist nurse. Hemoglobin, hematocrit, and platelet count were evaluated. To determine method comparison, Passing-Bablok regression, test of linearity, Pearson product-moment correlation coefficient, and Bland-Altman plots were used.

RESULTS

Thirty paired blood samples were collected in 29 hematological patients with a mean age of 66.8 years. A statistical difference was found for hemoglobin (P = .001) and hematocrit (P = .001) levels, but no clinical difference. The regression models revealed no systematic differences and no proportional differences with a linear relationship between the methods. Bland-Altman plots highlighted a good agreement between methods.

CONCLUSION

Blood samples for CBC drawn by PICCs are as reliable as those collected via venipuncture. Blood sampling via PICC could be recommended in people with hematological malignancies in needs of frequent blood tests.

IMPLICATIONS FOR PRACTICE

Sampling through a PICC provides reliable laboratory results for CBC, and it could reduce patients' discomfort and increase the safety of professionals reducing the risk of accidental percutaneous needlestick injuries.

Therapeutic antibiotic serum concentrations by two blood collection methods within the pediatric patient: A comparative effectiveness trial

Repeated venipunctures and fingersticks to confirm serum drug concentrations cause pain and dissatisfaction for pediatric patients and their families. In many organizations, the standard of care to obtain therapeutic serum drug concentrations by peripheral venipuncture or capillary fingerstick, even when the patient has an existing peripheral intravenous catheter (PIV) or central venous catheter (CVC). The primary objective of this study was to assess agreement between serum tobramycin/vancomycin concentrations collected from a CVC or PIV, versus venipuncture or fingerstick. Among hospitalized pediatric patients (age 3 months to 22 years), 36 paired blood samples were collected. Serum trough vancomycin and random tobramycin concentrations were compared between peripheral intravenous or CVC samples, and venipuncture or fingerstick samples within the same patient. A strict sampling protocol for obtaining the samples was followed, that included collection of the CVC/PIV sample before the venipuncture or fingerstick, less than 2 min between collections of samples from the different sites, and a strict volume-based flush and waste protocol. Concordant correlation coefficients demonstrated substantial agreement between CVC/PIV and venipuncture/fingerstick concentrations for vancomycin (n = 17) and tobramycin (n = 19) (Rc = 0.982 for both). Bland-Altman analyses demonstrated good overall between-method agreement within subjects and minimal bias. Consequently, using a lumen volume-based flush and waste protocol, children with indwelling catheters may not require additional venipunctures and/or fingersticks for confirmation of drug concentrations while hospitalized, improving the quality of care and patient satisfaction.

Penicillin Dried Blood Spot Assay for Use in Patients Receiving Intramuscular Benzathine Penicillin G and Other Penicillin Preparations To Prevent Rheumatic Fever

Rheumatic heart disease (RHD) remains an important global health challenge. Administration of benzathine penicillin (BPG) every 3 to 4 weeks is recommended as a secondary prophylaxis to prevent recurrent episodes of acute rheumatic fever and subsequent RHD. Following intramuscular injection, BPG is hydrolyzed to penicillin G (benzylpenicillin). However, little is known of the pharmacokinetics (PK) of BPG in pediatric populations at high risk of RHD or of the pharmacokinetic-pharmacodynamic relationship between penicillin exposure and clinically relevant outcomes. Dried blood spot (DBS) assays can facilitate PK studies in situations where frequent venous blood sampling is logistically difficult. A liquid chromatography-mass spectroscopy assay for penicillin G in plasma and DBS was developed and validated. Application of the DBS assay for PK studies was confirmed using samples from adult patients receiving penicillin as part of an infection management plan. The limit of quantification for penicillin G in DBS was 0.005 mg/liter. Penicillin G is stable in DBS for approximately 12 h at room temperature (22°C), 6 days at 4°C, and >1 month at -20°C. Plasma and DBS penicillin G concentrations for patients receiving BPG and penicillin G given via bolus doses correlated well and had comparable time-concentration profiles. There was poor correlation for patients receiving penicillin via continuous infusions, perhaps as a result of the presence of residual penicillin in the peripherally inserted central catheter, from which the plasma samples were collected. The present DBS penicillin G assay can be used as a surrogate for plasma concentrations to provide valid PK data for studies of BPG and other penicillin preparations developed to prevent rheumatic fever and RHD.

Comparing Two Methods to Obtain Blood Specimens From Pediatric Central Venous Catheters

The purpose of this study was to test agreement in blood values obtained from a discard method and a push-pull method in samples from central venous catheters in pediatric patients. The discard method causes blood loss beyond what is necessary for blood testing and increases potential for infection each time the central venous catheter is entered. Twenty-eight children ranging in age from 6 months to 12 years were enrolled in the study. A research protocol was developed to pair the 2 methods of blood collection for each sample. The Bland-Altman method was used to test agreement on each blood value for each paired sample. Of the 438 pairs of measured blood values, 420 (95.9%) fell within the limits of agreement. Nurses reported no difficulty in using the push-pull technique to obtain any samples. The push-pull method of obtaining blood specimens from pediatric central venous catheters should be considered. It can eliminate blood loss through discard and can reduce infection because it reduces the number of times a catheter is entered.

Sources of preanalytical error in pharmacokinetic analyses - focus on intravenous drug administration and collection of blood samples

INTRODUCTION

Pharmacokinetic (PK) studies for long-established drugs are generally performed outside the well-standardized settings of pharmaceutical industry trials. Instead, such studies are usually performed within daily clinical practice of hospitals.

AREAS COVERED

This article describes aspects of intravenous (i.v.) drug administration and blood sampling that contribute to potential sources of preanalytical errors for PK investigations. Parameters that bias determination of start and end time of i.v. infusions, as well as consistent rate of drug delivery, are discussed. Causes for drug loss in the infusion device, including adsorption and insufficient flushing, are outlined. The advantages and disadvantages of different blood sampling techniques are reviewed, with an emphasis on pediatric studies.

EXPERT OPINION

For PK studies that are integrated into the general hospital routine, a variety of potential sources of error exist. Potential pitfalls depend on the specific drug and trial characteristics and they must be anticipated and discussed in advance. Working procedures need to be developed that address the anticipated problems and in detail describe procedures that need compliance between bed and bench.

Comparison of central venous catheter and peripheral vein samples of antibiotics in children with cystic fibrosis

PURPOSE.: To determine if accurate serum antibiotic levels can be obtained from central venous catheters (CVCs) in pediatric patients with cystic fibrosis. DESIGN AND METHODS.: Fifty paired CVC-peripheral vancomycin or tobramycin specimens were collected within 5 min of each other following a 5-ml flush and discard. Specimen samples were randomized by first site drawn. RESULTS.: CVC-peripheral antibiotic levels were highly correlated (r =.97, p <.001), with no statistically significant difference (t = 1.18, p =.25). Bland-Altman plot analysis revealed a bias of.47, with limits of agreement ranging from -4.20 to 6.87. PRACTICE IMPLICATIONS.: Accurate antibiotic concentrations can be obtained from CVCs, reducing pediatric patient trauma and stress.

Modeling and simulation approaches to evaluate pharmacokinetic sampling contamination from central venous catheters in pediatric pharmacokinetic studies of actinomycin-D: a report from the children's oncology group

BACKGROUND

The binding of drugs to catheters can be a source variation in dosing chemotherapeutics. Drug contamination from the dosing central venous line (CVL) can impact the reporting of pharmacokinetic (PK) results and analysis. Peripheral venipuncture avoids binding complications from the CVL but dissuades patients from enrolling. Our group has developed a catheter clearing procedure to minimize the extent of contamination so that dosing and sampling from the CVL can ensue, promoting patient willingness to participate in phase I pediatric oncology trials.

OBJECTIVES

To develop a population pharmacokinetic model of actinomycin-D (AMD) in children with cancer incorporating expressions for drug contamination from PK samples obtained via indwelling CVLs and to evaluate the efficiency of a catheter clearing procedure in removing contamination as well as the impact of contamination on PK results.

METHODS

A dataset of 199 AMD plasma concentration measurements from 36 patients (age 1.6-20.3 years) was analyzed using nonlinear mixed-effects modeling. Quantitative modeling approaches, including baseline contamination model, covariate model, and catheter clearance model, were evaluated to describe catheter contamination. Monte Carlo simulations mimicking a prospective study in children with cancer were performed to assess the performance of the final model and impact of catheter contamination on PK reporting.

RESULTS

The PK of AMD was best described by a linear 3-compartment model with first-order elimination. A baseline contamination model including a contamination factor proportional to the model-predicted concentration for samples obtained from central catheters was chosen as the most parsimonious and accurate among competing models. The final model parameters were allometrically scaled to a 70 kg person. The estimated mean parameter values were 11 L/h, 5.79, 24.2, 490 L, 17.7, and 42.8 L/h for total clearance, central volume of distribution, peripheral volume 1, peripheral volume 2, inter-compartmental clearance 1, and inter-compartmental clearance 2, respectively. The proportional contamination factor was 19.3 % immediately post-drug administration and decreased at a first-order rate of 0.0932 h(-1). Simulations precisely re-estimated kinetic parameters with catheter contamination adjustment. Large uncertainty and poor estimation were observed when contamination was ignored.

CONCLUSIONS

Drug contamination from sampling catheter can impact AMD PK results and should be accounted for in the analysis. We provide a framework for evaluating catheter contamination and guidance on adjustment in the PK model.

Minimization of the preanalytical error in plasma samples for pharmacokinetic analyses and therapeutic drug monitoring--using doxorubicin as an example

BACKGROUND

There are many sources of variability in plasma samples drawn for pharmacokinetic analyses or therapeutic drug monitoring. In this article, methods are proposed on how to prevent sample dilution (Part I) and contamination effects (Part II) in plasma samples, using doxorubicin as an example.

METHODS

Experiments were performed in the laboratory setting to identify factors that could influence plasma samples in clinical practice. In part I, it was hypothesized that saline solution left in a catheter could lead to a dilution of samples drawn through this catheter. The impact of 2 different sampling techniques, the "discard method" and the "push-pull method", was examined. In part II, an infusion system was filled with a 1 mg/mL solution of doxorubicin. After rinsing the system with increasing volumes of saline solution, the drug concentration of the fluid left in the system was analyzed. Furthermore, plasma samples were drawn through the drug administration catheter, and the contamination of these samples with doxorubicin left in the catheter was measured.

RESULTS

In part I, a discard volume of plasma equal to 4 dead volumes of the sampling line was necessary to avoid dilution of a sample taken from a port or double-lumen catheter filled with saline solution ("discard method"). Pulling up and down the same volume through the catheter 5 times ("push-pull method") was proved to be an alternative with no need to discard blood. In part II, after rinsing the infusion system with a volume of saline solution corresponding to 4 dead volumes of the system and after discarding a volume of plasma corresponding to 4 sampling line volumes, the doxorubicin contamination in the samples was negligibly small.

CONCLUSIONS

Under the described conditions, the push-pull method delivered the same results as the discard method to prevent sample dilution. To avoid contamination in plasma samples, development of standardized sampling procedures seems to be essential and feasible.

A reliable and safe method of collecting blood samples from implantable central venous catheters for determination of plasma gentamicin concentrations

STUDY OBJECTIVE

To evaluate the extent of agreement between plasma gentamicin concentrations determined from samples collected by using implantable subcutaneous central venous catheters (ports) with the push-pull method and those collected by finger lancet punctures in children with febrile neutropenia.

DESIGN

Prospective, randomized study.

SETTING

University-affiliated, tertiary care hospital.

PATIENTS

Sixty-two children with cancer who had single- or double-lumen ports and who received gentamicin for treatment of febrile neutropenia between February 2008 and October 2009.

INTERVENTION

One blood sample was collected from the port by using the push-pull method at the same time one blood sample was collected by finger lancet puncture for determination of plasma gentamicin concentrations.

MEASUREMENTS AND MAIN RESULTS

Forty-four pairs of samples were available for assessment of agreement, and 43 were available for pharmacokinetic analysis. Agreement between plasma gentamicin concentrations determined from blood samples from ports and finger lancet punctures was assessed by the intraclass correlation coefficient (ICC), Bland-Altman analysis, and comparison of simulated dosage adjustments. Changes in port patency were monitored for 1 week after port sampling. Differences in simulated dosage adjustments calculated by using either the port or finger lancet puncture samples that differed by greater than 20% were considered clinically significant. Agreement between the 44 finger lancet puncture and port sample pairs was excellent (ICC 0.991, 95% confidence interval 0.984-0.995). Port plasma gentamicin concentrations were 4.7% lower than those concentrations determined in blood from finger lancet punctures. The observed limits of agreement ranged from -20.5% to 11%. Differences in dosage adjustments calculated by using port and finger lancet puncture plasma gentamicin concentrations were not clinically significant in 38 (88%) of 43 cases. No changes in port patency were observed in the week after port sampling.

CONCLUSION

The push-pull method of blood sampling is a reliable and safe option for determining plasma gentamicin concentrations in children with ports.

Central venous catheter sampling of low molecular heparin levels: an approach to increasing result reliability

BACKGROUND

The low molecular weight heparin effect in children is monitored using the anti-factor Xa level. Venipuncture is recommended; however, central venous catheter blood sampling is often necessary. Heparin infused through central venous catheters may contaminate central venous catheter blood samples, preventing reliable anti-factor Xa level measurement. Simultaneous anti-factor Xa/partial thromboplastin time measurement with central venous catheter blood sampling may predict anti-factor Xa reliability.

OBJECTIVES

To determine the prevalence of heparin contamination as measured by the partial thromboplastin time/anti-factor Xa in central venous catheter blood samples and whether careful sampling could minimize heparin contamination of anti-factor Xa levels from central venous catheter blood sampling.

METHODS

Simultaneous partial thromboplastin time/anti-factor Xa measurements from central venous catheter blood sampling determined the prevalence of heparin contamination of central venous catheter blood samples. In phase II, children receiving low molecular weight heparin had routine central venous catheter blood sampling to measure the peak anti-factor Xa and the simultaneous partial thromboplastin time. Anti-factor Xa levels with a partial thromboplastin time of >40 secs (pair 1) were identified; there was no low molecular weight heparin dose change, and the paired sample was repeated using a careful sampling technique (pair 2). Pairs 1 and 2 were compared to determine the efficiency of the sampling technique in removing heparin from the central venous catheter blood samples.

RESULTS

In phase I, 100 children had 485 paired anti-factor Xa/partial thromboplastin time central venous catheter blood samples with 29% ± 4.1% (95% confidence interval 25% to 33%) anti-factor Xa with partial thromboplastin times of >40 secs. In phase II, 43 children had 129 paired anti-factor Xa/partial thromboplastin time samples with partial thromboplastin times of >40 secs. The pair 1 mean partial thromboplastin times/anti-factor Xa levels were 109.8 secs (SD 53.1, range 34.0 to >200 secs) and 1.03 units/mL (SD 0.56, range 0.26-4.2 units/mL). Repeated partial thromboplastin times/anti-factor Xa levels (pair 2) were significantly decreased from those of pair 1 (p < .001) with means of 58.5 secs (SD 21.2, range 22-152 secs) vs. 109.8 secs (SD 53.1, range 34.0 to > 200 secs, p < .001) and 0.63 unit/mL (SD 0.30, range 0.02-1.77 units/mL) vs. 1.03 units/mL (SD 0.56, range 0.26-4.2 units/mL), respectively.

CONCLUSIONS

Measurement of the partial thromboplastin time performed in combination with that of the anti-factor Xa level can be used to assist health practitioners to identify unfractionated heparin contamination of anti-factor Xa levels drawn from central venous catheters. A careful sampling technique may minimize heparin contamination in central venous catheter blood samples.

Double-lumen central venous port catheters: simultaneous application for chemotherapy and parenteral nutrition in cancer patients

PURPOSE

This study was designed to evaluate the clinical benefit of low-profile double-lumen port catheters in patients receiving simultaneous chemotherapy and parenteral nutrition (PN). Potential advantages, complications, and the durations of simultaneous and single use of the catheter were assessed.

METHODS

At a university teaching hospital, 10 patients received a double-lumen port catheter (5 men, 5 women; mean age 61.5 ± 12 years). All port implantations were performed under ultrasonographic and fluoroscopic guidance in the radiologic interventional suite. Procedure-related immediate, early, and late complications were recorded until removal of the device, patient's death, or completion of follow-up period. Application times and durations for chemotherapy or PN were determined.

RESULTS

No immediate complications were observed. First use of the port system for chemotherapy was within 12 days (± 25 days, range 0-84 days) and within 17 hours (± 22 hours, range 0-72 hours) for PN on average. During the application of PN, no delay or interruption of chemotherapy was observed. The port catheter was used for the simultaneous application of chemotherapy and PN for a total of 1,216 hours. One port catheter was removed after 30 days due to suspected port infection.

CONCLUSION

Central venous double-lumen port systems as a therapeutic option in patients requiring chemotherapy and PN can increase safety during those simultaneous applications, while offering improved patient comfort.

Approaches to clear residual chemotherapeutics from indwelling catheters in children with cancer

OBJECTIVES

To develop a method for drug dosing and pharmacokinetic (PK) sampling in children with cancer from a single indwelling central venous catheter that minimized drug contamination.

METHODS

A benchtop system was designed to simulate dosing and clearing actinomycin-D (AMD) and vincristine (VCR) from central venous catheters. The authors evaluated the effects of flush volume, composition and pH, timed drug instillation, and number of blood-draw return cycles on residual drug concentrations. A proof-of-principle study was conducted in three pediatric patients with cancer with paired PK samples obtained by both central and peripheral catheters.

RESULTS

Nearly complete removal of drug from the catheter was obtained after five blood-draw return cycles consisting of 5 mL of whole blood. Residual concentration of AMD was 0.18 ± 0.02 ng/mL or 0.16% of the initial infusion concentration. VCR exhibited lower propensity for catheter adsorption than AMD with residual concentrations undetectable after three blood-draw return cycles. In patients in which the clearance procedure was used, higher drug concentrations were generally observed from centrally cleared samples at most time points, but differences relative to peripherally obtained samples were not statistically significant for either AMD or VCR. Two of three patients had higher exposure for AMD based on PK samples obtained from central catheters, whereas exposure for VCR was similar for both sampling catheters in all patients.

CONCLUSIONS

A reliable procedure to efficiently reduce AMD and VCR contamination during PK sampling has been established and is currently being used in a PK study being conducted by the Children's Oncology Group.

Impact of blood collection devices on clinical chemistry assays

Blood collection devices interact with blood to alter blood composition, serum, or plasma fractions and in some cases adversely affect laboratory tests. Vascular access devices may release coating substances and exert shear forces that lyse cells. Blood-dissolving tube additives can affect blood constituent stability and analytical systems. Blood tube stoppers, stopper lubricants, tube walls, surfactants, clot activators, and separator gels may add materials, adsorb blood components, or interact with protein and cellular components. Thus, collection devices can be a major source of preanalytical error in laboratory testing. Device manufacturers, laboratory test vendors, and clinical laboratory personnel must understand these interactions as potential sources of error during preanalytical laboratory testing. Although the effects of endogenous blood substances have received attention, the effects of exogenous substances on assay results have not been well described. This review will identify sources of exogenous substances in blood specimens and propose methods to minimize their impact on clinical chemistry assays.

Therapeutic drug monitoring of methotrexate on the pediatric oncology ward: can blood sampling from central venous accesses substitute for capillary finger punctures?

Intravenous methotrexate therapy with subsequent calcium folinate rescue is widely used for treatment of various neoplastic diseases, both in adults and in children. The optimization of the methotrexate dose and/or the calcium folinate rescue is based on pharmacokinetic data calculated from plasma concentrations collected after cessation of the methotrexate infusion. The aim of the present study was to evaluate the possibility of substituting capillary blood samples with blood samples drawn from central venous catheters (PORT-A-CATH) for therapeutic drug monitoring of methotrexate on the pediatric oncology ward. Nine cancer patients (4 females and 5 males; median age: 15 years; range: 5-20 years) were included. The quantitative analysis of methotrexate was carried out by fluorescence polarization immunoassay (FPIA). The concentrations of methotrexate in venous and capillary samples were closely correlated (rs = 0.98; P < 0.0001; n = 71). The venous/capillary plasma concentration ratio was 1.00 [median value; interquartile range (IQR): 0.882-1.094]; for 85% of the data points the ratio was 0.8 to 1.2, independent of drug concentration. The observed plasma concentration differences in blood samples drawn from central venous accesses and obtained from capillary blood samples in this study could have altered the calcium folinate rescue at 1 treatment occasion only. Plotting all measured methotrexate concentration time data for the individual patients during the elimination phase, on a chart including a normal elimination curve, is mandatory to enable proper handling of the subsequent rescue after high-dose methotrexate therapy. Blood sampling from the central venous access can be used only under certain circumstances for therapeutic drug monitoring of methotrexate. Carefully evaluated standardized instructions regarding rinsing, flushing, and discarding waste volumes, as well as precautions to minimize the required blood volume, are needed.

A Comparison of Peripheral and Centrally Collected Cyclosporine A Blood Levels in Pediatric Patients Undergoing Stem Cell Transplant

PURPOSE/OBJECTIVES

To measure differences in cyclosporine A (CSA) trough concentrations from blood collected as a peripheral sample and from a CSA-uncontaminated (naive) lumen of a double-lumen central line.

DESIGN

Prospective, comparative study.

SETTING

Pediatric university teaching hospital in metropolitan Australia.

SAMPLE

71 paired central and peripheral CSA blood samples from a convenience sample of 14 pediatric allogeneic stem cell transplant recipients receiving IV CSA as prophylaxis or treatment for graft-versus-host disease. Ages ranged from 2 months to 14 years, 5 months.

METHODS

Comparing blood samples collected from a peripheral site and a CSA-naive lumen of a double-lumen central line. Data were analyzed using a paired student t test and calculation of the 95% confidence interval of the concentration ratio from different sampling sites.

MAIN RESEARCH VARIABLES

Site of blood sampling and CSA trough concentrations.

FINDINGS

No significant difference existed between CSA concentration in samples collected from the different sites in children receiving intermittent infusions of CSA (p = 0.13). The 95% confidence interval of the CSA concentration ratio was 0.92 1.04.

CONCLUSIONS

When CSA is administered on an intermittent dosing schedule, comparable CSA trough concentrations can be determined from blood collected via the CSA-naive lumen of a double-lumen central line or at a peripheral sampling site.

IMPLICATIONS FOR NURSING

Pediatric allogeneic stem cell transplant recipients who require regular CSA trough concentrations no longer will require peripheral blood samples when receiving an intermittent dosing schedule.

Extent of agreement in gentamicin concentration between serum that is drawn peripherally and from central venous catheters

OBJECTIVE

At our institution, patients who receive once-daily dosing of gentamicin have serum concentrations determined 3 and 6 hours after dose administration. Patients with single-lumen central venous catheters have the 3-hour samples drawn peripherally. The objective of this study was to evaluate the extent of agreement between peripheral and central venous catheter serum gentamicin concentrations drawn 3 hours after dose administration.

METHODS

In this prospective, observational study, patients provided both a peripheral and a central blood sample for determination of serum gentamicin concentration. The order of sampling (central venous catheter versus peripheral first) was randomized. Agreement was assessed by determination of the intraclass correlation coefficient and Bland-Altman analysis. The clinically acceptable targets for the lower limit of the intraclass correlation coefficient and Bland-Altman limits of agreement were defined a priori as >0.80 and +/-6%, respectively. Differences between the theoretical dose adjustments using the central venous catheter versus the peripheral sample result were described.

RESULTS

Forty-five pairs of samples were collected: 42 from single-lumen implantable central venous catheters (ports) and 3 from peripherally inserted central venous catheters. The intraclass correlation coefficient was 0.91. However, the Bland-Altman analysis resulted in a mean percentage difference (central venous catheter versus peripheral) of -0.92% and limits of agreement of -27.9% to 26.0%. The gentamicin dose adjustment based on the central venous catheter sample result would have led to clinically significant dose adjustments in 19 (42%) cases, when compared with the peripheral sample result.

CONCLUSIONS

These results indicate a lack of agreement between peripheral and single-lumen central venous catheter samples. In particular, ports are not appropriate sites for monitoring serum gentamicin concentrations.

Elevated blood drug levels obtained from indwelling silicon catheters during oral cyclosporine A administration

Cyclosporine A (CsA) may be bound to and released from the inner surface of central venous catheters resulting in spuriously elevated blood drug levels. We observed this phenomenon in a boy transplanted because of aplastic anemia up to 9 weeks after CsA had been switched from intravenous to oral administration. In comparison to phlebotomy, simultaneous blood sampling from the double lumen catheter resulted in a greater than 10-fold, or two-fold increase in drug levels, respectively, depending on whether or not the line used for prior CsA infusion was selected. Thus, prolonged binding of CsA to the inner surface of venous catheters should also be considered during oral administration.

Blood sampling for biochemical analysis from central venous catheters: minimizing the volume of discarded blood

The purpose of the work was to establish a reliable procedure for blood sampling from central venous catheters with a minimal loss of blood. Based on previous studies of potassium measurements, the routine procedure had been to discard 12 ml of blood. In order to clear the catheter from substances from the infusion including potassium, the catheters were first flushed with 5 ml of saline. Repeated samples in fractions of 3 ml for hematological analyses (ethylenediaminetetraacetic acid plasma; seven patients), coagulation tests (citrate plasma; seven patients) and for serum measurements (eight patients) showed that a discarded volume of 3 ml corresponding to at least six times the dead-space of the catheters was sufficient after initial flushing with saline.

Accuracy of cyclosporin measurements made in capillary blood samples obtained by skin puncture

International consensus guidelines suggest that cyclosporin should be measured in whole blood. In some instances it may be advantageous to collect capillary blood, by a finger or ear prick method. However, drug concentrations in skin-puncture blood may not necessarily correlate with those measured in venous blood. This study compared cyclosporin concentrations in blood collected from the fingertip or earlobe with blood collected by standard venipuncture. Patient preference for each of the blood collection methods was also assessed. Specimens were obtained from organ transplant patients receiving cyclosporin, using each of the three methods: venipuncture, finger prick, and earlobe prick. The samples were assayed using a specific radioimmunoassay and the results were compared. In the 102 sets of samples collected, the mean difference (+/- standard deviation) in cyclosporin concentration between finger prick and venipuncture and ear prick and venipuncture was 2.6% (+/- 9.5%) and 2.7% (+/- 12.1%), respectively, while the comparable median (IQR) differences were 1.9% (-3.4% to +6.6%) and -1.1% (-2.8% to +7.2%), respectively. A high degree of correlation was observed between finger prick and venipuncture or ear prick and venipuncture or ear prick and finger prick (r2 > 0.86). Of the three methods of blood collection, finger prick was the patients' preferred method (P < 0.01). These data suggest that capillary blood collected by skin puncture is suitable for use in cyclosporin blood monitoring and acceptable to patients.