Mixing local with NaCl

[Sonny Crocket]

Our ropivicaine only comes in 1% or 0.75%. I mixed it with NaCl to get it down to 0.5% for the first time the other day.( I never mixed local with NaCl before and do tons of blocks.) Did a block that I was very satisfied on ultrasound with and it had almost no effect post op. The patient left the Pacu pain free later on after getting morphine, clonidine and Toradol.

Does mixing local with NaCl lower the pH too much and that is why my block was lousy?

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[BLADEMDA]

Local anesthetics block the function of sodium channels located in neural tissue, inhibiting depolarization and thus the transmission of nerve impulses.1 A high sodium concentration is known to antagonize the analgesic effect of local anesthetics.2 On the other hand, dextrose when injected around nervous tissue does not cause any pain on injection and does not cause any long term neurological deficit in animals or humans.3, 4 and 5 Dilution with dextrose would reduce the concentration of sodium ions and hence reduce its antagonistic effect. In the literature, only one study using dextrose as diluent to produce 0.5% ropivacaine for axillary brachial plexus block showed a reduction in the onset time for sensory blockade when compared with dilution with saline.6 Our hypothesis was that dilution of the local anesthetics with dextrose would shorten the onset time compared to saline for a supraclavicular brachial plexus block.

http://www.sciencedirect.com/science/article/pii/S0104001415001098

 

[BLADEMDA]

http://www.ncbi.nlm.nih.gov/pubmed/22467889


IMHO, diluting local anesthetics with normal saline will shorten block duration and increase the time for the block to setup.

In your situation a completely failed block was highly unlikely due to the dilution with saline.

 

[V-SWAG]

At my program we routinely mix 20ccs Ropiv 1% with 10ccs NaCl to make Ropiv 0.66%. Seems to work very well...

 

[Sonny Crocket]

Thanks for the replies. Must have been a bad block then. It's just weird that it coincided with the first time I mixed ropi with saline.

 

[Planktonmd]

All epidural and nerve block local anesthetic infusion bags are diluted from the original concentration using NS, and they usually work well!

 

[Ignatius J]

Dilute it quite often with NS and never noticed a difference. Never really thought about it, really.

 

[repititionition]

Can someone help a student: how would an NS solution lower pH (other than long-term chloremic acidosis, which I assume is not the case here)?

 

[p30doc]

Can someone help a student: how would an NS solution lower pH (other than long-term chloremic acidosis, which I assume is not the case here)?

Look at the pH listed on a bag of NS.

 

[Wiscoblue]

I think he might be asking if adding saline affects the ratio of ionized to unionized local by affecting the final pH of the mixture. It would then affect the diffusibility and fat solubility and thereby the onset and maybe the intensity of block, and eventually also the duration of block.