Implanted Ports versus Peripheral Collection: A Comparison of Methods for Therapeutic Antibiotic Level Monitoring in Pediatric Patients with Cystic Fibrosis

Abstract

Category/Date Emerging Knowledge for Clinical Practice Podium Presentations focusing on the Research Agenda Priority of Pediatric Research: Chronic Illness, Presented at NAPNAP's 40th National Conference on Pediatric Health Care, March 8, 2019, New Orleans, LA. Introduction Patients receiving treatment with certain antibiotics require frequent blood sampling to establish proper dosing and maintain a therapeutic level of the medicine in the blood. It is common for patients with cystic fibrosis to receive these medications via implantable ports. While withdrawing blood specimens from the implanted port for routine laboratory tests is a common practice, nursing practice is conflicted about the safety and accuracy of drawing antibiotic levels from implanted ports. The controversy is based on concern that drawing a specimen from the implanted port's reservoir will lead to falsely elevated serum antibiotic levels and negatively impact the ability to make accurate pharmacokinetic decisions. However, the literature is inconclusive on this subject. Researchers document varying results, use different blood sampling techniques, and do not differentiate between different types of central venous access devices. Background/Significance The extent of agreement between blood samples obtained from the same vascular access device through which the medication was administered and peripheral blood samples is unknown. This project attempts to clarify agreement between peripheral samples and those obtained from a specific type of vascular access device, the implanted port, and determine the clinical significance of any such differences. If levels drawn from implanted ports are to be used in dosing decisions, there is a clear clinical imperative to determine their accuracy; accurate drug levels are needed to ensure appropriate dosage and prevent adverse events. However, the evidence must be critically appraised and balanced with the desire to reduce avoidable suffering linked to repeated venipuncture. Objectives The primary objective is to determine if there are differences between tobramycin or vancomycin levels drawn from an implantable port, compared to those drawn peripherally among pediatric patients with cystic fibrosis undergoing inpatient antibiotic therapy. The secondary objective is to determine whether antibiotic levels drawn from implantable ports lead to dosing adjustments that would not occur with current standard practice (peripheral venipuncture). Methods/Design This is a prospective single-center observational study that compares antibiotic levels drawn from an implantable port to samples drawn peripherally in pediatric cystic fibrosis patients. Study approval was granted by the Baptist Health IRB. Inclusion criteria are patients aged 18 and under, admitted to an inpatient pediatric medical floor with a diagnosis of cystic fibrosis, an implantable port, and ordered therapy of vancomycin and/or tobramycin. For each participant, we analyze paired samples obtained concurrently from their implantable port and a peripheral blood draw. Research samples drawn from the implanted port were collected using a protocol that specifies the amount of saline flushed and blood wasted prior to sample collection. Results Overall, 20% of samples collected from implantable ports would lead to dosing discrepancies when compared with samples drawn via fingerstick or venipuncture. However, forty four percent of vancomycin levels drawn from implanted ports would lead to dosing discrepancies. The correlation of port and peripheral readings is quite high (r=0.907), but this does not mean that the two can be equated. It does suggest, however, that there is a statistical relation between the two that can be used to construct an adjustment to the port level that will more closely match the peripheral level. The only significant variable influencing ratio between peripheral and port values was lumen size, with smaller lumen (6 French) leading to larger differences. Conclusion The results demonstrate poor agreement between the two methods for collecting antibiotic levels, particularly when testing for vancomycin levels. Nurse practitioners prescribing and monitoring therapy with these medications should be alert for antibiotic level values that don't match dosing regimen. In addition, NPs should understand their institution's policies and practices surrounding central line blood sampling and ensure practices reduce the potential for residual drug within the lumen if levels are currently drawn from implanted ports. For NPs discussing port placement, ensure parents and patients are aware of potential for extra needlesticks as a possibility during therapy with antibiotics that require therapeutic drug level monitoring.