Taking blood using 'push-pull' method gets accurate results with fewer pokes

November 09, 2017

A new study by University of Pennsylvania veterinary researchers has found that blood samples collected from an intravenous catheter using a special "mixing" technique are as accurate as those collected via venipuncture, in which a needle is used to access the vein directly.

Unlike alternative techniques for drawing blood, the mixing method, better known as the "push-pull" technique, requires no "presample" to be discarded, preventing unnecessary blood loss. It also has the potential to greatly reduce the number of needle pricks a patient receives during a hospital stay, lessening pain to the patient and trauma to the blood vessel.

The research was led by Ciara A. Barr, a lecturer in Penn's School of Veterinary Medicine, who was an anesthesiology resident at the time of the study. The senior author on the work is Deborah C. Silverstein, an associate professor in the Department of Clinical Studies at Penn Vet. Their coauthors included Giacomo Gianotti, Carly E. Graffeo and Kenneth J. Drobatz, all of Penn Vet. The study was published in the Journal of the American Veterinary Medical Association.

"This method had been shown to be accurate in human populations but we wanted to confirm that that would also be the case in our veterinary population," said Barr. "This technique is really optimal for using on an anesthetized patient; it makes taking a blood sample convenient and painless."

In human medicine as well as veterinary medicine, routine blood tests are a key part of monitoring the health of patients under anesthesia or those who are critically ill. Getting an accurate reading of such measures as blood glucose, electrolytes, packed cell volume and blood gas levels can influence treatment decisions.

"The standard of care for taking a blood sample through a catheter was to either use the discard method, where we draw a presample from a catheter, discard it, then draw a real sample for submission, or the reinfusion method, in which you reinfuse the presample after taking the real sample," said Barr.

Both methods, however, are potentially problematic. The discard method can put patients at risk of anemia, as a significant amount must be discarded in order to ensure the "real" sample isn't contaminated or diluted with drugs or saline solution from the IV. Concerns with the reinfusion method include the possibility of introducing a blood clot into the patient, contaminating the drawn blood, mistaking the presample for the real sample or damaging red blood cells during the process.

In the current study, Barr, Silverstein and colleagues decided to try another option. In the push-pull technique, the presample blood volume, equivalent to three times the volume of the "dead space" in a catheter, is pulled into a syringe, and then reinfused into the patient. This process is repeated three times, all the while keeping the syringe connected to the catheter. Then a second syringe is used to take the blood for analysis. In this case no blood is discarded and the blood never leaves the closed system of the IV, minimizing the chance for contamination.

Though already validated in human medicine and particularly widely used in pediatric patients, whose blood volume is lower and who can be more fearful of needle pricks, no one had tested the technique in veterinary patients.

To do so, the Penn Vet team enrolled in their study 30 healthy pet dogs who were coming to Penn Vet's Ryan Hospital for an elective surgery. All the dogs weighed more than 10 kilograms so that a relatively large catheter could be used.

The researchers collected blood samples, using both venipuncture and the push-pull method, both prior to and after the dogs were anesthetized. The dogs were randomly assigned to be given one of two anesthesia drugs, alfaxalone or propofol.

Comparing blood levels of pH, blood gases, electrolytes and other metrics, the researchers found no clinically relevant differences between samples collected using the two different methods. The type of anesthesia didn't make a difference either.

"We saw only very small differences between the methods," Silverstein said, "but nothing that would alter clinical assessments or decisions."

The researchers would like to follow up on this work with studies in smaller animals, including cats. They'd also like to see if the push-pull method could be used on catheters that have been in place over a longer period of time.

But for now, Penn Vet clinicians are already putting it to use.

"Now that it's been rigorously tested, we've started adopting this method for our anesthetized patients here at Ryan Hospital," Barr said. "It's convenient, it's safe for our patients and it's giving us accurate results."
The study was supported by the Frankie's Friends Resident Clinical Study Grant.

University of Pennsylvania

Related Veterinary Medicine Articles from Brightsurf:

Veterinary college team IDs gene that drives ovarian cancer
scientists at the College of Veterinary Medicine have collaborated on a study that pinpoints which specific genes drive - or delay - high-grade serious ovarian carcinoma.

Graduates of family medicine residencies are likely to enter and remain in family medicine
This study provides an overview of the characteristics of physicians who completed family medicine residency training from 1994 to 2017.

Veterinary medicine: Risk factors for heatstroke in UK dogs
Dogs that are older and heavier than their breed average or that have flat faces are at higher risk of heat-related illness, according to a study in Scientific Reports.

Nuclear medicine and COVID-19: New content from The Journal of Nuclear Medicine
In one of five new COVID-19-related articles and commentaries published in the June issue of The Journal of Nuclear Medicine, Johnese Spisso discusses how the UCLA Hospital System has dealt with the pandemic.

NUS Medicine researchers can reprogramme cells to original state for regenerative medicine
Scientists from NUS Medicine have found a way to induce totipotency in embryonic cells that have already matured into pluripotency.

AAFP releases updated feline retrovirus guidelines to the veterinary community
On Thursday, January 9, the American Association of Feline Practitioners (AAFP) will release updated Feline Retrovirus Testing and Management Guidelines to the veterinary community, which will be published in the Journal of Feline Medicine and Surgery.

UK veterinary profession simply not ready for 'no deal' Brexit
The UK veterinary profession is simply not prepared for a 'No Deal' Brexit, warns the editor of Vet Record.

Gender discrimination holding women back in veterinary practice
Research by Lancaster University Management School and Open University Business School shows women face discrimination and occupy fewer places in the higher reaches of the veterinary profession, even as they begin to outnumber men in the field.

Study reveals complementary medicine use remains hidden to conventional medicine providers
Research reveals that 1 in 3 complementary medicine (CM) users do not disclose their CM use to their medical providers, posing significant direct and indirect risks of adverse effects and harm due to unsafe concurrent use of CM and conventional medicine use.

Study of traditional medicine finds high use in Sub-Saharan Africa despite modern medicine
Researchers who have undertaken the first systematic review of into the use of traditional, complementary and alternative medicines (TCAM) in Sub-Saharan Africa found its use is significant and not just because of a lack of resources or access to 'conventional medicine'.

Read More: Veterinary Medicine News and Veterinary Medicine Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.