Can variable practice habits and injection port dead-volume put patients at risk?

Abstract

Injection ports used to administer medications and draw blood samples have inherent dead-volume. This volume can potentially lead to inadvertent drug administration, contribute to erroneous laboratory values by dilution of blood samples, and increase the risk of vascular air embolism. We sought to characterize provider practice in management of intravenous (IV) and arterial lines and measure dead-volumes of various injection ports. A survey was circulated to anesthesiology physicians and nurses to determine practice habits when administering medications and drawing blood samples. Dead-volume of one and four-way injection ports was determined by injecting methylene blue to simulate medication administration or blood sample aspiration and using absorption spectroscopy to measure sample concentration. Among the 65 survey respondents, most (64.52%) increase mainstream flow rate to flush medication given by a 1-way injection port. When using 4-way stopcocks, 56.45% flush through the same injection site. To obtain a sample from an arterial line, 67.74% draw back blood and collect the sample from the same 4-way stopcock; 32.26% use a different stopcock. Mean (SD) dead-volume in microliters ranged from 0.1 (0.0) to 5.6 (1.0) in 1-way injection ports and from 54.1 (2.8) to 126.5 (8.3) in 4-way injection ports. The practices of our providers when giving medications and drawing blood samples are variable. The dead-volume associated with injection ports used at our institution may be clinically significant, increasing errors in medication delivery and laboratory analysis.

Appendices

Appendix 1

1.1 Provider survey

Question 1. When administering a medication through a one-way injection port on an IV line, do you typically flush the medication in:

• By flushing through the same injection port as the medication was given through?

• By increasing the flow rate of the IV line?

Question 2. When administering a medication through the side-port of a 4-way stopcock, do you typically flush the medication in by flushing through:

• The same injection site as the medication was given?

• A different injection site or increasing the flow rate of the IV line?

Question 3. When you draw a blood sample from an arterial line, do you typically draw back on the line and remove the blood sample from:

• The same 4-way stopcock?

• A different 4-way stopcock (e.g., one closer to the patient)?

Question 4. After drawing a blood sample from an arterial line, do you flush out and remove the residual blood from the side port from where you drew the sample? (Yes or No)

Question 5. Do you remain committed to using a single injection port to administer all medications throughout a case? (Yes or No)

Appendix 2: calibration curves and calculation of dead-volume

2.1 Calibration curve set-up

On the day of experiments, calibration curves were set-up by serially diluting stock methylene blue 10 times by a factor of 2 with Plasmalyte-A. Each standard sample dilution was aliquoted on the spectrometric well plates to generate three replicates for spectrometric analysis at a wavelength of 608 nm. The three measures were averaged to determine standard sample absorption. The calculated dilution factors were plotted as a function of measured absorptions. The linear portion of the curve was used to calculate the equation of a line of best fit (Fig. 3).

Fig. 3

Example of calibration curve used to calculate dead-volume

2.2 Calculation of dead-volume

Each collected experimental sample was plated to generate three replicates and the three absorption measurements were averaged to yield the absorption for the given experimental sample. The three experimental runs for each stopcock or injection port were then averaged to yield a final absorption value. Dead-volume was calculated by determining an experimental sample’s dilution based on the calibration’s equation of a line. The sample’s dilution was then multiplied by the volume of the collected sample to yield the calculated dead-volume. Using this approach, it was not necessary to determine the concentration of stock methylene blue. In the simulations of drug administration (Fig. 1), two sequential 5 mL samples were collected when evacuating methylene blue. In this case, dead-volumes were calculated separately for the sequential samples and then added to calculate the total dead-volume.