The role of medication pH in choosing an IV catheter

There are a lot of factors to consider in choosing the appropriate vascular access device (VAD), including treatment regimen and duration, patient’s medical condition, vascular health and patient preference for the type and location of the VAD.^1,2 The physiochemical properties of infusates (including medication pH) also influence VAD selection because of the potential risk of phlebitis.²

In a meta-analysis, the incidence of phlebitis in medical/surgical wards with the use of peripheral VADs (PVADs) has been shown to be 31%.³ There are three primary types of phlebitis: mechanical, infectious and chemical.¹ Causes of mechanical phlebitis include insertion trauma, high catheter-to-vein ratio or the angle or insertion position of the catheter.¹ Infectious phlebitis can result from bacteria on the skin, on the catheter, in contaminated fluids/medications, or from an infection somewhere else in the body.¹

Chemical phlebitis is the result of endothelial inflammation/injury.¹ This can be caused by the infusion of irritating infusates, infusates with extremes of pH or osmolarity, inadequate haemodilution or excessive infusion rate for a short peripheral intravenous catheter (PIVC), amongst other reasons.¹

Osmolarity describes “the number of osmotically active particles in a solution.”¹ Blood plasma contains an osmolarity level of around 290 mOsm/L.⁴ Intravenous (IV) fluids that contain a higher osmotic concentration than blood cells are hypertonic;⁴ hypotonic solutions have a lower osmotic concentration than cells.⁴

More on this topic: IV fluid osmolarity: what to know for IV catheter selection

The pH of the infusate that will be administered is also an important consideration.¹ The pH of blood is maintained by buffering systems within the body between pH 7.35 and pH 7.45.⁵

Meaning of a pH value

A pH level indicates the concentration of hydrogen ions in a solution, using a logarithmic scale ranging from 0 (acidic) to 14 (alkaline).⁴ What’s neutral, what’s acidic and what’s alkaline? These are some examples: Amiodarone has a pH of 3.5–4.5; Furosemide has a pH of 8.0–9.3; sodium thiopental has a pH of 10–11.⁶

Because the pH logarythmic scale is based on the power of 10, a seemingly small change of 1 pH unit indicates an increase or decrease of 10 times the concentration of hydrogen ions in the solution.⁴

More on this topic: Irritants and vesicants: ensuring safe IV therapy

Which type of VAD? Recommendations for solutions with a high or low medication pH or irritant or vesicant solutions

In terms of medication pH, the European Recommendations for Proper Indication and Use of Peripheral venous access (ERPIUP) advise using PVADs for the short- to medium-term infusions of solutions with a pH ranging from 5 to 9.⁷ For solutions outside of this range, with pH values of less than 5 or greater than 9, there is a wide consensus in the literature that these be delivered by a central venous access device (CVAD).⁷

According to the ERPIUP Recommendations, injury to the endothelial layer of the intima can result from the infusion of irritant or vesicant solutions via a low flow system such as a peripheral vein.⁷ However, if the infusion of a vesicant drug is via a PVAD, and lasts less than 30–60 minutes, the possibility of endothelial damage is minimised.⁷

Maintaining a list to identify solutions that may potentially be associated with endothelial damage

The ERPIUP Consensus recommends that any clinical unit should have a list of peripherally incompatible drugs which may be associated with patient harm to refer to when choosing between a PVAD or CVAD for patients.⁷

The BD Vascular Access Device Assessment Decision Tree is a tool that can help in VAD selection. This one-page guide provides a decision-tree format with the aim to help identify the appropriate VAD, based on treatment pH/osmolarity, length of therapy, venous assessment and other criteria.

References