[Histonet] Freezing Sprays in Cryostats

[Bob Richmond]

Freezing sprays for frozen sections in cryostats are deplorable, but try
and get pathologists to give them up. I think that's probably why the CAP
has been reluctant to ban them.

During my career in pathology I saw more than one case where frozen
sections were inadvertently cut on tuberculous tissue. Tuberculosis is a
disease that sneaks up on you. In Baltimore (a hotbed of the disease)
around 1970 when we did this, we'd put the cryostat (one of the basic Damon
IEC models we had then) out of action until somebody (usually the chief
resident) could bring it up to room temperature, scrub it out with alcohol,
lubricate it, and plug it back in to cool down.

The heat extractors are usually all you need. Liquid nitrogen is not a very
satisfactory freezing medium. It's better to submerge a freezing medium
liquid into liquid nitrogen (which will eventually freeze it solid,
however). Shandon used to market a freezing container called a Histobath -
is any equivalent product available today? It held the right temperature
not to freeze the liquid medium solid.

People usually use acetone or isopentane (2-methylbutane) as the freezing
medium, both highly flammable. Better is:
3M™ Novec™ Engineered Fluid HFE-7100
This product belongs to a class of fluorocarbons called
"segregated hydrofluoroethers (HFE's)"
According to various MSDS, HFE-7100 is
methyl nonafluoroisobutyl ether
C4F9-O-CH3

But try to substitute any such thing for freezing spray, and be prepared
for a hissy-fit from your senior pathologist.

I'm glad the CDC weighed in on this. I do remind them that the decision to
do a frozen section is between the surgeon and the pathologist.

Bob Richmond
Samurai Pathologist
Maryville TN