Monitoring BP during anaesthesia

RE: Monitoring BP during anaesthesia

Thomas Johnson — Tue, 28 Feb 2017 15:24:27 GMT

[quote user="Lucy Fleming"]

[quote user="Clive Ansell"]

[quote user="Clive Ansell"]Hydrogen ion [/quote]

It was a joke - haha

[/quote]

I figured! Technically correct though...

[/quote]

And could therefore be shorthand for acidosis

RE: Monitoring BP during anaesthesia

Jill Butterworth — Tue, 28 Feb 2017 11:30:44 GMT

www.capnography.com

This website has pictures of waveforms which you can print off and laminate to keep by your capnograph/anaesthetic machine for the nurses (and vets ;) ).

RE: Monitoring BP during anaesthesia

Bob Russell — Tue, 28 Feb 2017 09:36:17 GMT

We started with a dirt cheap capnograph bought on Ebay. About £100 plus more for the consumables. Lasted a couple of years (time flies closer to five years!) and convinced us that it is about the most important bit of monitoring kit (other than a good member of staff).

Was offered another second hand monitor (Datex-Ohmeda) and this has been running for a further couple of years and still going strong. I could not cope with one of the small units with a tiny screen as I like to keep half an eye on the shape of the trace!

Eventually will get a new machine (with a similarly big screen) when this one gives up the ghost.

A capnograph does not have to cost a lot and is a fantastic bit of kit. !

RE: Monitoring BP during anaesthesia

Lucy Fleming — Tue, 28 Feb 2017 08:30:07 GMT

[quote user="Clive Ansell"]

[quote user="Clive Ansell"]Hydrogen ion [/quote]

It was a joke - haha

[/quote]

I figured! Technically correct though...

RE: Monitoring BP during anaesthesia

Emily Rainbow — Tue, 28 Feb 2017 07:50:32 GMT

Brilliant answer beats. I'm going to print it and give it to my nurses, increased monitoring by doing more BP with a view to buying a capnograph is my biggest bugbear at work. Unfortunately none of my nurses have ever worked with a capnograph so don't understand the benefits!

RE: Monitoring BP during anaesthesia

Beats — Mon, 27 Feb 2017 22:52:02 GMT

[quote user="An On MRCVS"]We've just got an indirect BP monitoring kit... Can anyone provide any rough guidelines as to what SBP we should be aiming to maintain during GA, and what reading would cause alarm bells and a need for intervention?[/quote]

Hardly a daft question! Some of the confusion comes from the varying reliability and different types of equipment measuring blood pressure. What is the exact machine you have procured? I use Doppler and cuffs, so beyond that I don't have much experience. The change in a given patient can be more significant than the absolute number sometimes given the uncertainties in measurement.

[quote user="An On MRCVS"]And what should this intervention be (roughly speaking aware not one size fits all)[/quote]

I've found the following:

1) Some of my choices of drugs have changed for cases having seen the effects on blood pressure, for instance today I no longer premed thyroidectomies with acp. BY measuring BP, you become more "BP-aware".

2) While ideally anesthetic depth shouldn't be excessive anyway, low blood pressure would first make me look at the isoflurane dose and see if this could be lowered - it's amazing the effect even a reduction by 0.25% can make on occasions, and often depth can be excessive allowing more significant dose reductions. In a dental for instance, I might stop digging, reduce the isoflurane and add a local block if not already done before proceeding on again. Pre-emptively, I might consider MAC-sparing options such as use of midazolam/opioids/local-anesthetics that will have minimal effect on blood pressure and allow lower-doses of volatile to be used.

3) If the patient is at an appropriate level of anesthesia, and the isoflurane can't be lowered further (or lowering it did not increase) then I give iv fluid bolus (assuming not at risk of congestive heart failure).

4) Check not hemorrhage causing drop in BP

5) If surgery's going to be prolonged and can't be avoided, I'd get dopamine at this stage at 5-10mcg/kg/min (I have a chart, I don't start using a calculator...); ideally I'd wrap up surgery quicker.

6) I'd monitor carefully in recovery until BP normal (usually goes normal once turn iso off) and keep on O2 during recovery.

The end-point aim is tissue oxygenation, so it isn't all about the BP - but measuring it is a helpful surrogate of part of that equation.

As a practical example, today I had a geriatric terrier for enucleation with a grade 5/6, presumed mitral valve, murmur and BP reducing to 50mmHg (on Doppler) 5mins into cutting (premed midazolam/methadone, induction etomidate, maintenance iso). Minimal hemorrhage, reduced isoflurane from 2% to 1.75% to 1.5% to 1% without minimal improvements in BP over a 10 minute period up to 60mmHg, so turned it off iso and finished off quickly. Had the procedure been going badly or required more time, I might have tried to instill some local to allow longer procedure at lower iso, but by the time I'd have done that I could just finish off and turn iso off anyway. Fluid bolus might have sent into CHF. Had I not been monitoring the BP, you could of course argue things shouldn't have been any different (patient should still have been maintained on lowest iso dose required and I should still have kept anesthetic time to a minimum and carefully monitored in recovery).

I rank my monitoring tools in order of usefulness as:

1) capnograph

2) Doppler BP

3) pulse oximeter

4) ECG

RE: Monitoring BP during anaesthesia

Beats — Mon, 27 Feb 2017 22:12:43 GMT

[quote user="Anthony Todd"]Any relationship between changes in BP and respiration rate?[/quote]

excessive anesthetic depth will generally lower both, and increasing doses of volatile anesthetic (isoflurane) will also generally reduce both

beyond that, it depends a lot on other drugs used: e.g. high-dose opioids can easily tank respiration while having very little effect on blood pressure; acp causes little respiratory depression but can tank the blood pressure.

RE: Monitoring BP during anaesthesia

Clive Ansell — Mon, 27 Feb 2017 20:08:37 GMT

[quote user="Clive Ansell"]Hydrogen ion [/quote]

It was a joke - haha

RE: Monitoring BP during anaesthesia

Anthony Todd — Mon, 27 Feb 2017 19:35:20 GMT

I have a vision of the patient rising slowly and floating out the theatre window and/or exploding as the surgeon starts to cauterise the source of the H+.....

RE: Monitoring BP during anaesthesia

Lucy Fleming — Mon, 27 Feb 2017 17:50:18 GMT

[quote user="Anthony Todd"]and WTF is "H+"[/quote]

reading between the lines I think in this case it is short for haemorrhage

RE: Monitoring BP during anaesthesia

Clive Ansell — Mon, 27 Feb 2017 16:40:29 GMT

Hydrogen ion

RE: Monitoring BP during anaesthesia

Anthony Todd — Mon, 27 Feb 2017 16:04:34 GMT

Any relationship between changes in BP and respiration rate? [just wondering vis-a-vis monitoring GA]

and WTF is "H+"

RE: Monitoring BP during anaesthesia

Jill Butterworth — Mon, 27 Feb 2017 14:39:37 GMT

It's a great idea. I've found it was just the very early warning sign that they were going too deep, and just reducing the dose of gaseous anaesthetic may be all that's needed. We had one nurse who habitually kept her animals slightly too deep and she was very resistant to retraining and caused a lot of problems (one or two of the worst kind before we realised what was happening...). Anyway, we introduced the BP machine and lo and behold, she had great problems obtaining readings...

RE: Monitoring BP during anaesthesia

Tim Charlesworth — Mon, 27 Feb 2017 14:24:20 GMT

The "normal" ranges we use are a mean of 60-100mmHg, Systolic: 80-120, Diastolic: 50-90

If mean decreases to 45-60 then we would intervene - check measurement, check pulse quality (esp how easy it is to occlude pulse). Also is it bradycardic - if yes then could be too deep under GA so decrease your inhalation agent etc, if genuine then we would bolus fluids at 10ml/kg over 10 minutes. If the mean was <45mmHg then we would give 30ml/kg/bolus and the nurses would "get help" - at this level you would expect something sig wrong so check circuit valves open, no sig ongoing H+, no compression of vena cava, possible pneumothorax etc etc.

If bolus didn't work and underlying cause not known/addressable then we would then proceed with pressors (eg ephedrine),

Tim