OT: Question for Vet techs - BP and anesthesia

I'm curious to know how low your feline patients' BP goes while under anesthesia? I just got hold of Cali's BP readings from her dental procedure two weeks ago and I'm a little freaked out. Well, maybe a lot freaked out. The five readings they got are: 69/30; 77/35; 72/37; 85/32.

This was an hour-long procedure. I believe agents used were midazolam and hydromorphone, propofol, and isoflurane. Bupivacaine was used for a local block. She did have a catheter placed and IV fluids during the procedure, but not before or after, AFAIK.

Is what she had typical of what you've seen for a young cat's BP readings while under anesthesia, with IV fluids? She's five years old, healthy, no cardiac issues. Her potassium level has ben on the low-ish end, but is WNL.

The two references I've found both say to maintain systolic BP at or above 90, with 80 being the minimum. Call me paranoid, but I'm now wondering if any nephrons came to harm

I'm also freaked because we were considering taking Meowzi in for a dental evaluation, to see if she needs any cleaning/extractions and if it can be done safely. If this is the range of BP that's typical under anesthesia and is considered safe, even with IV fluids in the picture, there's no way I'm allowing her to be put under unless it's a matter of life-or-death. Meowzi doesn't have any nephrons to spare at all.

 

Choy Foong I remembered seeing your post but wasn't up to responding a few weeks ago. It's an important point so I dug around to find it.

A few things. FIrst off, the type of BP machine used during surgery isn't as accurate for cats and small dogs. Why use it, then? Because doing a Doppler BP (more accurate for small animals) isn't practical; with the automatic machine you can have it run every 3-5 min and it will give you some ballpark idea of the BP.

Secondly, anesthesia lowers heart rate and BP, so there is a constant "dance" going on in which we try to keep the animal properly anesthetized while maintaining a good heart rate and BP. Based on those readings, they were probably lightening up her anesthesia to try to bring her BP up (they may have also used fluid boluses) as they went along. You can't suddenly drop their anesthestic level because you'd get a cat who was starting to wake up in an unpleasant situation, so you have to slowly nudge it around to find a good balance between sedation/anesethesia and keeping the vital signs in acceptable levels.

Every animal handles anesthesia differently. Dillon's BP tanked during his dental and he is otherwise a robust cat; meanwhile most of our pacemaker implantation dogs have kept a fabulous BP during anesthesia despite frequently fainting in real life due to their heart problems. Meaning, Cali's anesthesia-BP need not be Meowzi's anesthesia BP. (All the same, I'd weigh the urgency of her dental needs against the general risk to an older cat with renal disease.)

Finally, FWIW, no one has actually proven renal damage to occur during anesthesia due to hypotension AFAIK (and I've looked). I think it's reasonable to think it does -- the kidneys depend on good perfusion, and are always 2nd class customers since the body's priority is blood flow to the brain -- but it is not a given. I personally wouldn't worry about a single short period of hypotension like Cali's, and do not think it is anywhere near a nail in a proverbial kidney-coffin ;-)

Hope this helps.

 

Very, very, very relieved to see this :smile: :smile: :smile:

I had been fine about it until I looked up the VASG site, which said to keep BP above 80. That was when I freaked out. I sent a couple of e-mails to the dentist close to a month ago, left a msg last Friday too, but never heard back from him. It's been hard not to fret.

If you're feeling up to writing some more (and I understand if you're not) - out of curiosity, and this may be a matter of personal preference, at what point would you start backing off/lowering the anesthesia level? Below 80? Or in the 60s? I'm just surprised they let her drop that low, but maybe she just tends to have lower BP under anesthesia, like your Dillon. At what level would it be dangerous i.e. to the point that you pull out all the stops, drugs etc?

And thank you so much for looking for this thread, Jess. (((hugs)))

PS -

After learning about Cali's BP, and also after dealing with the non-responsiveness of the dentist (I wonder if he's avoiding me!), I am not inclined to have Meowzi's teeth cleaned. She's been fairly stable; I don't really want to rock the boat. I think you know I've been waffling over this dental issue for the past 1+ year ohmygod_smile

 

I found this a very interesting read. I always learn something from both of you guys. thanks.

It's nice to see you posting ((((( Jess )))))

 

The anesthesia level should always be just the minimum you need to keep the animal fully anesthetized. If you get two low BP readings in a row (I'd recheck immed after getting that first low one), you can try backing off a little and rechecking both the BP and the animal's anesthesia level (how "out" they are). If you're already on a low level of anesthesia, you look to increase the fluid rate/give a fluid bolus (do a much higher fluid rate for a short period of time), etc. Persistent hypotension is rare during surgery if you are giving them fluid and heat support and keeping the anesthesia as light as possible, IME. If an animal's hypotension cannot be corrected with fluids and the anesthesia is as light as possible, they can go on IV drugs to increase BP. This rarely happens. I usually prepare for this for cardiac procedures because most of the dogs can't tolerate IV fluid boluses but I've only had to do it once. In "regular" procedures I've only used IV drugs a few times, and all those times were critical patients who one would expect to have trouble maintaining their blood pressure.

As for letting Cali get that low, it looks like her first reading was low, not that they watched her trend downwards and did nothing. Also FWIW, I too have been startled by the first reading of a low BP because the animal looks fine otherwise--this is why we monitor BP, after all, because you just can't tell. Dillon's hypotension was the same way, the first reading was 60mmHg.

 

Hi Jess,

Have you ever compared your Doppler with an oscillometric machine?

When my cats are under, my job is to monitor the BP with the Doppler - with a Cardell unit also running.

I find that the Doppler is often ~20 mmHg lower than the Cardell.

Another question...does it really matter if the limb being used is 'up' or 'down'? The tech at my friend's hospital said that she was taught that it really does make a difference if you are monitoring an up or down limb. I can see this as being a bit more significant on a horse (heavy animal with compression of the vasculature...which is why we can't leave them in lateral recumbancy as long as a cat or dog) but does it matter much in a cat?

Thanks.. oh cardio guru. :smile:

 

Hi Dr. Lisa

Hmmm I find the Cardell/oscillometric to be generally less accurate in cats. In large dogs it's a different story, I think it provides good measurements. The criticalists I work with feel that the MAP on the Cardell more closely corresponds with the Doppler, but I've found that the Doppler is often higher than the Cardell MAP. To be honest, except during anesthesia, we never use the Cardell on cats so I can't say how it is "generally"; in surgery, we're rechecking with the Doppler because the BP looks low, and indeed it is often even lower on the Doppler than the systolic reading on the Cardell.

I'm not sure what you mean -- if the animal is standing vs laterally recumbent?

 

Laterally recumbant.

 

Sorry...typing on a darn iPad...

When the patient is lat recumbent....does it matter if the cuff is on the up or down leg. I vote that it is insignificant.

 

Oh you mean if the back leg is used, if the cuff is worn above or below the hock? I find that the cat legs are so small that I usually put the cuff btwn the hock and stifle so I have plenty of room to place the probe, but in bigger dogs will frequently put it on the metatarsus. And on the front leg, I can't imagine there is a difference in scootching up the cuff a bit. I find it fits best in a certain spot (if it's too low, when you inflate it it flexes the foot and moves the probe!) but I don't think it matters if you still get a good signal.

ANyway, I agree with you that reasonable cuff placement should not be influential. I think the size of the cuff is more important. (I wish there were a 2.5 cuff easily available as I think most cats are really a 2.5 ... !)

 

Nope....I mean the 'up' leg or the 'down' leg....ie....

The 'up' leg is the right leg...front or back....on an animal in left lateral recumbency....and the 'down' leg is the left leg...front or back....on an animal in left lat recumbency.

 

Ha ha obviously I thought you meant up or down the leg, sorry. No I don't think it matters one bit if you use the recumbent limb or not.

 

Us old....ex-horse docs speak with words that use the fewest letters possible.

And...when typing on an iPad..."up" and "down" work well.

Sorry for the confusion!

 

Actually I don't know when she went that low; all I asked was what was her lowest BP. But he's an experienced dentist, so I'm going to have to believe that it was her first reading. I've asked for a copy of her surgery chart, but he never responded. Guess I'll have to give him the benefit of the doubt.

The bigger takeaway from this discussion, for me anyway, is not how low she went anymore, but that BP monitoring is a MUST during any procedure with anesthesia, because, as you say, you just can't tell. Dr Lisa drummed it into us a long time ago, but it's one thing to know BP has to be monitored, it's another thing altogether to learn how low they do actually go (and probably even lower on the Doppler, eeek!) - and she's a healthy young cat at that. (eta: just found a note that Meowzi's systolic BP avgd 100 mmHG, range 82-110, under sevo, back in 07 during her dental cleaning. Going to look around for Cali's chart to see if hers was noted during her spay 5 years ago - nope, wasn't noted).

Thanks so much, Jess. I'm printing out this thread, and bookmarking it too.

Hi Dr Lisa

Since you're all having so much fun with up or down leg and front or back leg :mrgreen: here's a question. A Lantus kitty had his BP checked by his vet a couple of weeks ago, and the readings were front leg 185/130 and back leg 70/50, said to have been taken multiple times in succession. I dismissed it as operator error - but can it be possible that such significant differences can exist? I'm inferring from Jess' response on recumbent limb that it shouldn't? The kitty has diabetes, hyperthyroidism and CKD, FYI.