Venipuncture versus central venous access: a comparison of methotrexate levels in pediatric leukemia patients

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.

A Comparison of Antibiotic Serum Concentrations Drawn Simultaneously from Peripherally Inserted Central Catheters and Peripheral Veins in Children with Respiratory Infection

The purpose of the study was to evaluate serum concentration of antibiotics drawn from a peripherally inserted central catheter (PICC) compared with a peripheral venipuncture. This prospective comparative study included patients with ages 1month to 21years admitted with a respiratory infection requiring IV vancomycin or IV tobramycin via a newly placed PICC. The difference between the antibiotic levels from the venipuncture and PICC samples was statistically significant for both the peak and trough levels. However, the difference in values was not enough to impact antibiotic dosing and therefore was not clinically significant.

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.

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.

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.

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.

Occurrence and impact of unanticipated variation in intravenous methotrexate dosing

BACKGROUND

Studies using direct measurement suggest that the doses of up to 65% of drug infusions are outside industry standards. These preparation-associated errors occur despite routine safety procedures. As of April 5, 2006, the clinical impact of these errors had not been evaluated.

OBJECTIVE

To measure the occurrence and associated clinical outcomes of variations in intravenous methotrexate dosing.

METHODS

A prospective observational study was performed on 47 methotrexate infusions of 800 mg/m2 that were administered to 19 children with acute lymphoblastic leukemia. Serum methotrexate concentrations were measured at the end of the infusions, which were administered over 24 hours. The total methotrexate dose was determined by direct measurement of the concentration and the volume of each infusion.

RESULTS

Dosing errors greater than or equal to 10% occurred in 11 (23%) infusions and ranged from -61% to 55% of the ideal dose. Repeated measures regression analysis found the measured total methotrexate dose was not significantly associated with the serum methotrexate concentration (p = 0.58) or with clinical toxicities. The methotrexate dose administered over the last hours of infusion (p = 0.006) and the serum creatinine level at diagnosis (p = 0.05) were the most significant predictors of the methotrexate concentration. High methotrexate concentrations were significantly associated with increased hepatic aminotransferase levels; however, the degree of elevation was of limited clinical relevance.

CONCLUSIONS

While unexpected errors in drug dosing are more common than is suggested by other methods, the clinical impact observed in this model of methotrexate infusion was not demonstrably greater than medication errors described by other methods. Subsequent studies in this model of dosing error will require larger sample sizes, and other drugs should be evaluated.

Health care implications and space allocation of research published in nursing journals

PURPOSE

To examine how research is disseminated through nursing journals and to examine characteristics of published research.

DESIGN

A cross-sectional descriptive survey was conducted with manuscripts from 78 nursing journals that publish research.

METHOD

The final issue for 1999 was examined. Pairs of independent raters content-analyzed all research manuscripts.

DISCUSSION

Research studies comprised 241 (42.9%) of the manuscripts and 51.4% of the journal space. Many empirical studies omitted validity and reliability. Few manuscripts reported the date for completion of data collection, and fewer than one third contained the length of time from acceptance to publication.

CONCLUSIONS

Enhanced instrumentation reporting, shorter time from data collection to publication, and an increase in journal space devoted to research might enable nurses to make more cutting-edge clinical decisions.