I have been searching for articles that support the practice of using central venous catheters when the drug pH or osmolarity is out of the accepted range. I can find no studies or articles that give me the science behind the practice. In order to have more influence over the physician I need this evidence. Please help.
This is based on animal studies from the 1990's that demonstrated the extreme ranges of both solution pH and osmolarity increased the rates of thrombophlebitis. Those studies are:
1. Kuwahara T, Asanami S, Kawauchi Y, Kubo S. Experimental infusion phlebitis: Tolerance pH of peripheral veins. Journal of Toxicology Science. 1999;24(2):113-121.
2. Kuwahara T, Asanami S, Kubo S. Experimental infusion phlebitis: Tolerance osmolality of peripheral venous endothelial cells. Nutrition. 1998;14(6):496-501.
3. Kuwahara T, Asanami S, Tamura T, Kubo S. Dilution is effective in reducing infusion phlebitis in peripheral parenteral nutrition: An experimental study in rabbits. Nutrition. 1998;14(2):186-190.
Also, go to the very first message I posted on this blog about changing physician's perceptions of infusing Vancomycin.
There are numerous other articles on outcomes of short peripheral catheters that have documented high rates of superficial phlebitis attributed to the irritation of many drugs.
The risk vs benefits of inserting a CVC must be assessed for each patient. When the irritating drug will be required for a very short period, it might not be feasible to insert a CVC. Or if the patient has other risk factors for CVC-related complications, you may be forced to infuse irritating drugs through a short peripheral catheter. When this happens, it becomes nursing responsibility to ensure the following:
1. always use the smallest gauge catheter (e.g. 24 g) in the largest vein possible. This promotes hemodilution in the same manner as the CVC does, although the actual vein diameters and amount of blood flow is much smaller.
2. always avoid areas of joint flexion (e.g. hand, wrist, antecubital fossa) as many solutions with extremes of pH and osmolarity are also vesicant medications that will cause tissue damage if they leak from the vein. Areas of joint flexion have an increased risk of infiltration/extravasation injury.
3. use a manufactured catheter stabilization device to prevent catheter motion inside the vein, a factor that increases mechanical phlebitis.
4. reduce osmolarity by more dilution of the medication if the patient's medical status will allow for the additional fluid. Dilution will not alter drug pH however.
5. frequently assess the site using the OPAL method
O-observe the site condition
P-palpate for induration or other complaints from the patient
A-aspirate for a blood return
L-listen for all patient complaints and do not try to explain away any pain as something that is common with a specific drug.
I wish you success with your efforts to educate physicians, nurses, any other key personnel about this important issue.
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4 comments:
You mention the pH of the fluid will not change despite any dilution. I don't think that is true and do you have any information to support this? It just doesn't seem reasonable to state that. Thanks
Yes, it is true. Marc Stranz, RPh, is frequently giving presentations at INS and AVA conferences about this. Dilution changes the osmolarity but not the pH. Marc published on this in a past issue of JAVA:
Stranz M. Adjusting pH and osmolarity levels to fit standards an practices. Journal of Vascular Access Devices. 2002;7(3):12-18.
This article can be located on CINAHL or Ingenta.com.
When a drug is mixed with another drug or solution and there is incompatibility, there will be a precipitate formed. This develops because the pH has changed. So any crystal formation you may see in a syringe, fluid container, IV tubing or catheter is probably related to a radical change in the pH of one or more of the drugs in contact with each other. But when all drugs and solutions are compatible with each other, there is no change in the pH of the drug. So regardless of how a drug is diluted, if the pH is above 9 or below 5, it will lead to phlebitis and if possible should be given through a central venous catheter.
It's a while since I studied chemistry in school but I can't see how the pH won't change on dilution. pH is a measure of hydrogen ion concentration and it would seem strange for the concentration of hydrogen ions to remain the same when diluted. If one took a litre of hydrochloric acid and tipped it into a lake, one wouldn't expect the lake to become strongly acidic.
I can understand your confusion and I apologize for taking so long to reply to your post.
All medications are prepared by the manufacturer to be as close to normal serum pH as possible. However this is not always possible due to the drug itself. The goal is to ensure drug stability and the longest possible shelf life. Trying to adjust the pH of a specific medication could easily result in a drug precipitate which will either prevent the drug from being useful after infusion, cause a catheter lumen occlusion, and/or become lodged in the small capillaries of the lungs and diminish the lung's ability to properly function.
For this reason, pharmacist and nurses must follow the drug manufacturer's instructions for the correct type and volume of dilution for all IV medications. Going outside of these instructions could easily render the drug unstable and produce the drug precipitate. Dextrose 5% in water or 0.9% sodium chloride are the common solutions used for diluting medications. Neither of these solutions contains carbonic acid or hydroxide, therefore the pH is not altered and the pH of the final solution is determined by the drug and not the diluting solution.
Drug stability is the primary concern and altering the pH of the solution is not an acceptable method for mitigating the negative impact of pH extremes on the vein wall. The acceptable method is to infuse drugs below 5 and above 9 into veins with greater hemodilution. In other words, these drugs should be infused through a central venous catheter because of the larger vein diameter and greater blood flow to rapidly dilute the drug with blood.
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