[Histonet] Cooling paraffin blocks with ice VS. Freezing Spray

joelle weaver joelleweaver <@t> hotmail.com
Sat Sep 29 07:56:49 CDT 2012

Jenny My experience and training is to use some method involving ice or at the very least a cold-retaining tray made to chill blocks. I also was taught this method in histology school , in clinical training at four quite large institutions,  and also have used some variation of an ice cooling method in every instance in my career working in clinical and research settings. There are always variations in technique from lab to lab, but freezing spray has been generally discouraged  for constant use at the microtome, since it can introduce artifact in sections if over used. ( It is pretty easy to see the effect on the face of the paraffin block, and that is not even under the microscope.) I actually almost never use freezing spray personally for regular paraffin microtomy. I  do use it when doing frozen sections on occasion, but then it is typically only for difficult specimens such as fatty breast or soft/fattty lymph nodes that need very cold temperatures. I sometimes use it to cool only the backside of paraffin blocks during embedding when I am being impatient, and I avoid spraying directly on the face, and that is about the extent it of freeze spray's uses for me.  Personally, I prefer my blocks quite cold, in fact, one thing I don't like where I currently work , is that blocks are allowed to get to room temperature after removal from the embedding cold plate. I feel that I can more efficiently get good sections when the cold temperature is maintained and uniform though the block,  rather than re-cooling a warmed  room temp. block.  Overall,  I would expect constant and direct application of the freezing spray would be more of a problem than anything involving ice,  which would "flash freeze" mostly the surface,  and not cool throughout, which is why you have to keep spraying it.  Of course, I am not talking about leaving the faced block surface on the ice for so long a time that it becomes "water-logged"- but if you are sitting at your microtome and cutting diligently, and not leaving faced pecimens just sit there, I'm not sure how this would be an issue.  In general I think the combination of ice and water benefits most specimens  ( especially GI and Liver cores, bloody stuff,  and other types-that can sometimes be brittle and delicate due to processing)-I feel that the small amount of moisture that transfers from contact with the ice aids the smoothness/ reduces brittleness of the section, reducing "shatter" artifact. I feel that I would be unable to get sections without chatter in hard/dense tissues such as uterus body, cervix, bloody specimens and others without using ice. The only exception for me, might be brain which can cut better warm.  I am sure you must be frustrated, but if this is the clear direction of your supervisor, and they are not receptive to making any changes or allowing you to use your preferred technique, and not interested in new different methods,  then  I am not sure that there would be much that you can do other than comply with their policies. I know it is hard when people are not open to new ideas and techniques . I  had have that experience and  those feelings  quite often over the years, but just try to stay postive, do the best you can.   

Joelle Weaver MAOM, HTL (ASCP) QIHC
 > Date: Fri, 28 Sep 2012 22:39:31 -0400
> From: histotech411 <@t> gmail.com
> To: histonet <@t> lists.utsouthwestern.edu
> Subject: [Histonet] Cooling paraffin blocks with ice VS. Freezing Spray
> I want to know what is your preferred method for cutting paraffin blocks in
> the microtome everyday. At work I am having issues with my supervisor
> because we have different ways of doing things like for example she doesn't
> like to use the technique where you first trim the tissue, cool it on an
> ice tray and then make a section. That is how I learned to cut in histotech
> school. Instead she just trims and cuts the blocks at 4 microns one by one
> using the same blade until it wears out and she cools the blocks only
> freezing spray.
> She doesn't like to cool the blocks on an ice tray because according to her
> is a waste of time and that is why I have to use her technique but
> unfortunately some blocks are extremely difficult to cut and I have to go
> back to my preferred  technique. I feel I get better sections without
> wrinkles when I chill and soak the blocks on ice for a couple of minutes. I
> sometimes use freeze spray when the blocks get warm but when I cool them
> with ice I don't need to use freeze spray that much. Her technique works
> but is more successful when the blocks are well processed. I have
> difficulty getting completed sections  this way and spend more time trying
> to get the perfect section. Sometimes I have my good days but other times
> is tedious using this technique. Another thing I notice is that the blades
> get worn down quicker when you use them to trim and section. I prefer two
> separate blades, one to trim and the other one to section. I feel they stay
> sharp for more time.
> She discourages the use of ice but then complains that we are running out
> of freezing spray for the frozen sections too quickly which doesn't make
> sense. It is obvious that if she encourages to use ice to cool blocks then
> we will be using less freezing spray.
> Another reason she discourages the use of ice is that some blocks are not
> meant to be chilled which is pretty understandable. I cannot cool small
> biopsies such as gastric and skin and bone because they can get too hard
> and tear off from the block so I avoid that but I prefer to cool breast and
> colon biopsies on ice because these are fatty tissue that can be tedious to
> cut even when relying only on freezing spray.
> I want to know if it's completely acceptable for me to prefer the trim,
> cool on ice and section technique and if you feel is a waste of time
> comparing it with other ways of cutting such as the one I mentioned.
> Thanks.
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