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Retrieval Medicine & Antibiotic Therapy : Part 2

It’s no surprise that occasionally in EMS we have to transport patients to and from a dialysis facility when they are not able to be transported by other means. Rather than being frustrated that I’m not intubating someone in a ditch, or delivering a baby in an elevator, I found it interesting to investigate exactly what caused these sometimes very young patients to need hemodialysis. These short transports began my curiosity of why renal failure was very commonly a secondary issue, rather than what they originally were in the hospital for. Would this mean that maybe this was iatrogenic? Common reasons for acute renal failure (ARF) were diabetes, hypertension, periods of hypotension, infection,and prolonged administration of certain antibiotics. 57 year old Mary is a brittle diabetic and came to the hospital from a nursing home for osteomyelitis of her left middle toe. She was found to be positive for MRSA and was subsequently discharged on Vancomycin & Pip/Tazo. 18 days later she presents to the ED with dyspnea, swollen legs, decrease urine output, dry cough, and 43 lbs weight gain since her previous visit. Her creatinine was 6.8 mg/dl. Knowing she had been on antibiotics, a trough Vancomycin level was checked and found to be 74.6 ug /ml (Goal for serious infections is 10-20 ug/ml).

So, were they overdosing her Vanco?! Not necessarily... Her body wasn’t clearing the drug as the prescribing physician had expected. Essentially, we were overdosing her for not using a renal modified dose of Vancomycin. This brings up some interesting questions: How do we determine which patients need renal dosed medications? Can certain antibiotics exacerbate or cause renal failure? How does this apply to retrieval medicine? There are certain populations of patients that have specific co-morbidities that yield a higher risk of renal failure (diabetes, hypertension, etc.) However, the best way to check for efficient filtration is to look at renal function. Glomerular Filtration Rate (GFR) looks at the amount of volume the kidneys filter in an allotted time. This can be calculated by looking at the creatinine clearance (CrCl). Our muscles are constantly releasing creatinine into our plasma. If we look at how fast we clear this byproduct of muscle use, we can get an idea of renal efficiency. Typically, a female clears about 95ml/min of creatinine, compared to 120ml/min in males. The Cockcroft-Gault formula takes into consideration body mass to be as accurate as possible.

If a medication or antibiotic is not being cleared out of circulation by the kidneys, it will eventually accumulate to well above the therapeutic concentration. Special renal dosing is needed when GFR falls below a normal parameter. Here is an example of what this CrCl based dosing regimen might look like for antibiotics.

Do certain antibiotics contribute to renal failure? There is some literature to suggest that certain antibiotic agents can cause nephrotoxicity. This can either be caused by oxidative injury to the proximal renal tubular (PRT), or alterations to PRT epithelial mitochondrial function. This is obviously exacerbated when concentrations rise above the mean inhibitory concentration (MIC), How does this apply to retrieval Medicine? As was mentioned in part one of this blog, antibiotics sometimes take a mental back seat to other life sustaining infusions. I have also seen paramedics decide to “just run the antibiotics to gravity for transport.” In a patient with normal renal function, this is probably not a huge deal. However, if this patient is receiving specific renal dosing, it is important that we maintain the rate in which the creatinine clearance allows. We also may come across a bag of antibiotics that is “almost complete.” You face a dilemma of either letting it finish in their infusion set to gravity, or re-spiking the almost empty bag with your tubing (waisting some of the medication that is left in their line). A solution to this is to use a 30-50 cc syringe and a three way stop cock to draw up the remaining medication from the bag and infusion set. This can now be connected and flushed carefully to a half set that allows the pump to infuse at the same rate through the syringe. This prevents any waste of medication and efficient continuation of therapy.

I also believe it is important to cross check renal function if we transport a patient on antibiotics. We have to view patient care as a team sport. It is very possible renal function could be over looked in the hectic environment of the ED.When you have a system that cross checks each other, and allows open loop feedback, you develop one of the safest environments for a patient.






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