Over the years, I have been a part of many discussions related to drawing blood samples from umbilical lines. There are various factors of concern.
· Amount/frequency of blood draws
· Speed of blood draw
· Amount of flush used/type of flush
· Blood clearance/waste and related practices
A previous blog addressed accessing central lines via ports with attention to avoiding infections. This blog will address blood clearance and related practices as well as speed of blood draws/returns and flushing.
Schulz et al (2003) reports a study in which withdrawal of blood from a high-positioned umbilical arterial catheter over 20 seconds resulted in decreased cerebral oxygenation. The population studied was infants with a mean gestational age of 30 weeks and mean birth weight of 1170 grams. This was shown not to happen when the blood was withdrawn over 40 seconds. The volume withdrawn was consistent over the specified time period. This drop in cerebral oxygenation lasted for 2.5 minutes. In this study, reinfusion was not found to have the same effect.
In another study by Roll et al (2005), a standard volume of blood was withdrawn over 40 second and 80 second time periods. They found cerebral oxygenation was significantly decreased during aspiration, re-injection of draw-up volume and flushing with saline over both time periods. This decrease lasted for 5 minutes after the end of the procedure. These changes in cerebral oxygenation were only limited by decreasing the volume of blood drawn, not by extending the time over which it was drawn. This study was also performed using high-positioned umbilical arterial catheters.
In light of this information, one might desire to limit blood volumes drawn. While amounts drawn for lab studies are usually minimized to the extent possible, what about clearance volumes? Davies, Mehr & Morley (2000) studied this issue. Using a catheter and stopcock arrangement with a dead space of 0.6 ml, they investigated the amount of blood needed for draw-back in order to avoid sample contamination. They found that a volume of 1.6 ml was the minimum clearance volume needed to avoid sample contamination. Roll et al studied a sample volume of 1.7 and 0.2 ml with a clearance volume of 1.6 ml. They found cerebral oxygenation changes in both cases, but less so in the case of the lower volume (1.7 ml).
Another variable for consideration is the UAC tip position as alluded to earlier. A study by Lott, Conner and Phillips (1996) showed an alteration in cerebral blood flow velocity with a high-positioned line and less so with a low positioned line. However, the significant risks of low-placed lines doesn’t make that a viable option for mitigating the effects on cerebral blood flow. A Cochrane Review (Barrington, 1999) of complications related to high vs low umbilical arterial catheters shows more complications and need for replacement of low lying umbilical catheters than with high placed catheters. This document was reviewed and found to be up-to-date in 2009. There was no increase in intraventricular hemorrhage related to high placement. Presumably, the decrease and subsequent increase in cerebral blood flow and oxygenation would increase the risk for both periventricular leukomalacia and intraventricular hemorrhage. So, while there is a change in cerebral oxygenation as measured by NIRS, is there a clinical effect from that change? There are, of course, many considerations about other factors that may affect the cerebral blood flow and oxygenation besides the blood draw from the umbilical catheter.
Huning, Horsch and Roll (2007) also studied blood withdrawal from umbilical venous catheters, searching for a safe alternative to umbilical arterial blood draw. They found that the effect of blood draw from a UVC was similar regarding cerebral blood flow and cerebral oxygenation as blood sampling for an umbilical arterial catheter.
So, what take-away practice points can be obtained from the studies cited here? Perhaps more questions than answers remain. First, is the clearance volume of 1.6 the proper volume for your own umbilical line set up? The Davies et al study in 2000 used a traditional “open” system which has been replaced in most units with a closed blood draw system of some sort. Basically, they found that a volume more than twice the dead space was required to avoid contamination. For some systems, this would mean quite a large draw-back volume when compared to total blood volume in extremely low birth weight infants.
One of the studies mentioned earlier found that cerebral oxygenation was impacted utilizing a 40 second withdrawal and another found that it was not. Both studies were small, with one having 48 infants in the study and the other having 20 infants in the study with 30 blood draw procedures studied. After evaluating the available evidence, utilizing a quality improvement model, one group implemented a practice of limiting speed of blood withdrawal and infusion to be no faster than 1 ml/30 seconds. Volume was not addressed in this project.
So, while this information is helpful and certainly something that can increase our awareness, further studies are needed. In addition, no study has addressed blood draws from peripheral arterial catheters. How might those be the same or different? And, even if safer from a standpoint of cerebral oxygenation and blood flow, various other factors make them less favorable, in some circumstances, as a blood sampling port.
Barrington KJ. Umbilical artery catheters in the newborn: effects of position of the catheter tip. Cochrane Database of Systematic Reviews 1999, Issue 1. Art. No.: CD000505. DOI: 10.1002/14651858.CD000505
Davies mW, Mehr S, Morley CJ. The effect of draw-up volume on the accuracy of electrolyte measurements from neonatal arterial lines. Journal Paediatr Child Health. 2000; 36:122-124.
Gordon M, Bartruff L, Gordon S, Lofgren M, Widness JA. How fast is too fast?: A practice change in umbilical arterial catheter blood sampling using the Iowa Model of Evidence-Based Practice. Advances in Neonatal Care. 2008; 8(4):198-207
Huning BM, Horsch S, Roll C. Blood sampling via umbilical vein catheters decreases cerebral oxygenation and blood volume in preterm infants. Acta Paediatr. 2007;96(11):1617-1621.
Roll C, Huning B, Kaunicke M, Krug J, Horsch S. Umbilical artery catheter blood sampllng volume and velocity: Impact on cerebral blood volume and oxygenation in very-low-birthweight infants. Acta Paediatrica. 2006; 95:68-73.
Schulz G, Keller E, Haensse D, Arlettaz R, Bucher HU, Fauchere J-C. Slow blood sampling from an umbilical artery catheter prevents a decrease in cerebral oxygenation in the preterm newborn. Pediatrics. 2003;111(1):e73-e76.