Plasma-Lyte 148

Hartmanns has been around since the 1930s; Plasma-Lyte was patented first in 1982. So, by that comparison, it's the hot new thing.

In contrast to Hartmanns solution, Plasma-Lyte contains sodium acetate and sodium gluconate instead of sodium lactate.

Unlike Hartmann's it has yet to percolate into every critical care department. There is some contention that something with so much bicarbonate precursor in it will likely result in alkalosis, which is not always useful. And thus conceptually it is no better than dirty old normal saline, which cases acidosis. I suppose department heads are disinclined to be charged $21.92 per litre of unwanted alkalosis.

Contents and properties of Plasma-Lyte 148

As with Hartmann’s, the ultimate goal of infusing something other than sodium chloride is alkalinization. On one hand, you don’t get hyperchloraemic acidosis; on the other you get to metabolise all that acetate and gluconate ultimately into CO2 and water, which consumes a hydrogen ion. One often forgets that this process has real nutritional dividends. One litre of plasma-Lyte 148 contains 66 kilojoules (15.7calories).

 In order to understand the influence of intravenous fluids on acid-base balance one can refer to this excellent resource from www.ccmtutorials.com; or to TJ Morgan’s definitive article.

Baxter have this PI data sheet for their product, as well as this information document - subtle differences existed between them, and in particular the latter disagrees with the former as to the pH of Plasmalyte. One reports an exact pH of 7.4, whereas the other reports a range of 4.5-6.0.

Having received correspondence from a kind Baxter representative (Thanks Anne!), I am compelled to formally state that the pH of Plasma-Lyte is actually closer to 7.4 at body temperature. Baxter, it seems, are quite keen to prevent any misconceptions about the acidity of their product, and would like to assure the public that it is not delivered into the vein at a corrosive pH of 4.5.

So where did the pH range of 4.5-6.0 come from?  An excellent article by Benjamin Reddi (2013) sheds some light on the issue. Even distilled water has a pH of around 5.6 when exposed to the atmosphere, owing to the inevitable absorption of atmospheric CO2. One must also take into account the (complex) influence of dissolved salts on the solubility of CO2 and activity of H3O+ions.  The slow degradation of PVC packaging liberates acidic diethylhexyl phthalate, and autoclaving of PVC releases acetic and formic acid; the net effect is a difference in the pH of saline packaged in PVC (4.6) and in glass (5.71). Reddi does not explore the pH of Plasmalyte specifically, but the implications are obvious. And, to satisfy the Baxter people, it is important to assert at this point that the abstract concept of in vitro pH has nothing to do with the acid-base effects of Plasmalyte 148, which are laudably alkalinising and which are celebrated gloriously in a chapter dedicated to that purpose.

References

From MIMS online, via CIAP; using Baxter Full PI data sheets. Those PI documents are word for word what you will find on the bags.  Additionally, the anaesthesiauk website has this page, with a summary of the relevant details. To find out more about the pH of intravenous solutions, you could pay JAMA for this article.

Also;

Thomas J Morgan, Clinical review: The meaning of acid–base abnormalities in the
intensive care unit – effects of fluid administration
Critical Care 2005, 9:204-211 (DOI 10.1186/cc2946)

Reddi, Benjamin AJ. "Why is saline so acidic (and does it really matter?)." International journal of medical sciences 10.6 (2013): 747. - Thanks to Mike Purvis-Smith for finding this for me and putting to rest the question of in vitro fluid pH