Blisters from Sclerotherapy on 11/17. Any advice on what could have caused this? He is monitoring for infection (Photo)

I am not certain why you got those blisters. My first thought is a reaction to tape that may have been used.  I am a bit confused though about your comment about steri strips.  I do not know why steri strips would be used for sclerotherapy, so perhaps there is  more to your case. Also, do you know what sclerosing agent was used for your sclerotherapy?  You may have had an unusual reaction to that.  I agree with keeping the blisters clean and letting the open up themselves. I would expect them to eventually heal without significant scarring.  

I would apply Plato's Dark Scar Corrector and Plato's Scar Serum on the area to prevent further scarring. Best, Dr. KaramanoukianLos Angeles

We do 5-10 sclerotherapy procedures a day and I don't see this type of a problem: blistering.This is an allergic reaction to something, like a bandage or tape.You need to use some adjunctive measures after sclerotherapy to reduce post inflammatory hyperpigmentation. it is those that don't follow such instructions immediately following sclerotherapy, starting on day1 (next day) that seem to get retained hyperpigmentation. I recommend 2 creams: Scleroquin plus and Sclerovase and also Scler-X supplement to reduce post inflammatory hyperpigmentation (see link below) as well as compression stockings for at least 2 weeks.
H Karamanoukian MD FCS
certified vein specialist from ABVLM and double board certified surgeon

This looks like a reaction to the sclerotherapy agent that was used.  There are reactions that can occur  depending on the agent used.  I would recommend using a scar cream as these blisters can open and lead to scarring.  

Blisters post sclerotherapy treatment is most unusual.  If steri-strips were used (again not usual) the blisters could have been caused by moisture under the strips. Blisters from the solution used could be due to leakage under the skin and irritation.  The blisters shown look like there may be some blood in them which would indicate post injection bleeding.  You may want to apply silvadene cream to the blisters which may aid in healing. I prefer to break the blisters when small but leaving them alone will also heal.  I would expect you to heal well from this but you should follow up with your treating MD.

I think you may be particularly sensitive to whatever sclerosant was used to treat you or the concentration may have been a bit high. No matter how good the injector, a tiny amount of sclerosant will leak out of the vein to the surrounding tissue. Normally, it causes a little swelling like a mosquito bite but in your case it has caused blisters. You can consider a lower concentration of sclerosant or different sclerosant altogether after these blisters have completely healed. Alternatively, assuming the veins feeding the spider veins have been closed, you could try laser sclerotherapy or Veinwave.