Approximately 5 million central venous catheters are used per year in US alone for easy access to blood draws and infusion of medications. The ideal volume of blood to be drawn from the catheter initially prior to drawing lab samples is not known. We intend to determine what is the current practice among medical house staffs with regards to blood drawing technique in patients with central venous catheters .
A questionnaire was distributed in two university-affiliated hospitals. Data collected included which port was used to draw blood and how much volume (ml) of blood is initially drawn and if the initial blood drawn is discarded or re-injected back to the CVCs. The survey sheet was filled anonymously. Data collected were tabulated and analyzed.
A total of 95 subjects participated in the survey. Most respondents drew blood from the brown port (77%) and 12% used all the three ports. Around 45% of the respondents discarded the first 5 ml of blood and 42% discarded 10 ml. The majority discarded the initial blood drawn, curiously about 10% re-inject it into the CVC.
The brown port was the most popular of the 3 ports of the CVC used in drawing blood. More than three quarters of those surveyed drew 5 to 10ml of blood initially and discarded it.
Indications for CVCs include frequent blood drawing in hospitalized patients. Prior to obtaining blood samples from CVCs, it has been customary to withdraw blood volume to overcome the “catheter dead space” (pre-existing fluid in the catheter lumen) that may yield inaccurate results. We estimate that the volume of fluid contained in each catheter lumen (20cm length) to be about 0.2-0.4ml. Hence current practice of discarding up to 10 ml of blood for each blood draw may be wasteful. The amount of blood required to overcome “catheter dead space” has never been investigated. Minimizing blood discarded should decrease the incidence of iatrogenic anemia, decrease blood transfusions, cost and morbidity.
H. Amin, None.