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The effect of IV fluids on microcirculation | VETgirl Veterinary CE Blog

In this VETgirl online veterinary CE blog, we interview Dr. Deborah Silverstein, associate professor in critical care at University of Pennsylvania School of Veterinary Medicine’s Department of Clinical Studies-Philadelphia on her paper published in the American Journal of Veterinary Research on  the effects of intravenous fluids on microcirculation. This study was funded by Abbott Animal Health.

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In this study, Silverstein et al assessed the microcirculatory effects of IV crystalloid fluid administration in 49 healthy, client-owned dogs that were anesthetized for routine ovariohysterectomy. Lactated Ringer'ss solution (LRS) was administered at rates of 0, 10 or 20 mL/kg/hour to anesthetized dogs. Videomicroscopy (check out the cool YouTube video below) was used to assess and record the effects of the fluid therapy on the microcirculation of the buccal mucosa.

Several parameters were evaluated in this study including:

  • Heart rate
  • Blood pressure (as measured by Doppler)
  • Oxygen saturation (as measured by pulse oximetry)
  • CRT
  • Body temperature

Several measurements of microcirculatory variables were also assessed including:

  • Total vessel desnity
  • Microcirculatory flow index
  • Proportion of perfused vessels
  • Perfused vessel density by vessel size [< 20 μm, ≥ 20 μm, and all diameters]

Parameters were measured as soon as the patient was induced, at 30 and 60 minutes afterwards, and overall. What'd this study find? Overall, this study found that those patients that received 20 mL of LRS/kg/hour had the greatest total and perfused vessel (in those vessels that were > 20 μm in diameter, which are mostly venues and arterioles).

So what do we take from it? While our healthy patients undergoing elective procedures are at low-risk for hypoperfusion under general anesthesia as compared to our critically ill patients, keep in mind that fluid losses can occur through blood loss, the respiratory tract, and through the abdominal cavity. When these fluid losses occur in the face of anesthetic drugs, there is the risk of poor perfusion. And you know a criticalist's favorite answer to every veterinary question out there: perfusion and metabolic acidosis, right?

“When we monitor a patient’s blood pressure or oxygen levels, we’re not always able to discern what is happening at the cellular level,” Silverstein said. “Sometimes there are tissues and cells that are getting a surplus of oxygen while other cells or tissues are in need of more, but our measuring the big things, like blood pressure, doesn’t tell us that. The only way we figure that out is when the patient develops organ dysfunction or new complications arise following anesthesia.”

The American Animal Hospital Association and American Association of Feline Practitioners recommend the use of IV fluids in their guidelines under even routine procedures. While it adds to the cost of surgery (well, barely), it's worth it. Based on this study, it may improve the microcirculation in our anesthetized patients!

“The larger vessels are the ones that are constricting and dilating to feed the microcirculation,” Silverstein said. “And it appears that the animals that got the highest rate of fluids in this study — which may not be the optimal rate — are the ones that seemed to have the greatest recruitment of arterioles and venules.”

For more information, check out Penn News.

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References:

1. Silverstein DC, Cozzi EM, Hopkins AS. Microcirculatory effects of intravenous fluid administration in anesthetized dogs undergoing elective ovariohysterectomy. Am J Vet Res 2014;75(9):809-817.

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