rapid dust off perioperative INR management

A post on the management of Anti Coagulation Therapy (ACT) 

by 

Vitamin K Antagonist (VKA) - Warfarin

I've decided to call this the rapid Dust Off INR management procedure

because you get into the risk zone and out of the risk zone as fast and as safely possible. 

IMPORTANT NOTE: just like a real life Dust Off it is not without any risk (what is?) and comes with a need for experienced data driven handling of your INR; it is not for anyone who is not competent to do it. 
Further this process is not intended to replace what occurs when major surgery occurs in a hospital (in case that wasn't totally obvious). In a hospital situation you must submit to their care and they will manage you (which should include restoring your ACT before discharge) they will administer heparin and supply that. So, "when in Rome..." 

Background

Normally my posts are about me somehow, but this post is the work of a friend of mine who we'll call "Chuck"

About a year ago Chuck had his aortic valve replaced with a mechanical valve and began warfarin therapy. He's been an excellent manager of INR and (his words) is within range greater than 90% of the time. Yes folks that's better than clinics.

So (as eventually happens) he (like me) needed an invasive procedure where the practitioner requested that his INR be lowered to less than 1.5 for the procedure.

Now Chuck was well familiar with my perioperative management strategy for handling ACT without bridging therapy. I strongly recommend that you go over here and read about that in detail if you're not already familiar with it. The arguments and rational here depend on understanding that work.

Bridging therapy is when you 

1. cease one anticoagulant (warfarin), 
2. commence another which has a fast acting operation (heparin),
3. cease that, 
4. have the procedure
5. wait an amount of time to ensure proper coagulation has occurred (we do need this you know)
6. begin heparin and commence warfarin again
7. measure INR and cease heparin when INR is within therapeutic range

Its a pain not just because heparin is by injection, but because its often painful itself.

Rationale

People with mechanical valves require anti-coagulation therapy, and this is strictly about that specific application. Please read that again.

Chuck had read my (above mentioned) publication and felt that it could be improved upon (as indeed did I, but simply had not been sufficiently motivated to repeat it with improvements). Being a good student of his body response to warfarin (and naturally a good documenter of it) decided (emphasis), in consultation with his medical practitioner, to manage his INR down to 1.4 while not actually ceasing warfarin therapy. 

The "therapeutic window" (as its called) is the range of INR where you in your situation are at the least risk of either a clot of a bleed. This is known to be between approximately INR = 2 and INR = 4 (it depends). This information is based on this study which I recommend you read. This figure from that summarises the risk neatly with this Figure

which I have annotated to emphasise the lowest risk regions in GREEN and the highest in RED. The numbers are pretty clear, with the range 2.5 ~ 2.9 giving a statistical probablity of 2 events per 100 patient years, even moving to 4.0 ~ 4.5 is only 2.6 events per 100 patient years. That's pretty safe and that's exactly why we call it a Therapeutic Window.

So you can see that in the range of 1.5 ~1.9 is 26.6 events per patient year, which boils down to a high chance of an event within 3.8 years.

Our intention here is to do this in far less time than that, because time is the major multiplier of risk.

Method and Data presentation

Chuck took measurements at various intervals which ranged between daily and 4 times a day. This is the sort of data acquisition which you can only get if you have your own Point of Care (POC) machine.

This is the summary information:

First lets identify the annotations on the graph:

1. the procedure was on the 15th (black lines in the dose bar chart item)
2. a red line has been added between INR 2 and 1.8 to show we are now in the hazard zone

As there was more than one dosage and more than one INR reading for some of the days I have aggregated these and taken the INR as the last INR presenting on a day and the total warfarin taken in that day as an aggregate number. The fuller presentation of data is in this chart;

This is a little more complicated, but when referring to that earlier chart. I'll leave it to the reader to read the graph.

 

Observations

This method enabled a a time outside the therapeutic window of just 3 days (with the 12th and 16th back within the therapeutic window. This is by any way of looking at it an excellent result.

One of the biggest issues is running out of the "antagonism cycle" where the following parts of the quite complex coagulation cascade are interfered with:

• cofactors (II, VII, IV, X)
• protein C
• protein S

The details of which the reader should look up if interested. However the point is that not only does it take time to build the right warfarin levels after you have ceased warfarin, the INR being 1 does not tell you about the levels of warfarin, but only about the levels these various factors. 

By not dropping below INR 1.4 we have left the engine idling as it were. While this "engine" at idle does not produce significant power, it can be restarted again much faster. So we can be sure that some of this mechanism of antagonism of coagulation is still in place and by increasing dose we can restore the desired level of antagonism: we do not need to commence all this again from scratch.

The how and the specifics of the dose that's been used is a criteria for each person, to properly determine this you need to build up a knowledge of how your INR behaves with respect to changes in dose and changes in other factors (such as alcohol or foods). This is something that an experienced self manager will have because they have been managing themselves through a variety of cases. Additionally this method requires a rigorous approach to taking your warfarin and documenting your doses and INR.

If you are not managing yourself then this approach will require the INR manager to familiarise themselves with your particulars (not hard to do). However the literature would suggest that no INR clinic is in a position to do this for you (given that they frequently can't keep you in range > 70% of the time), meaning its best done by a competent self manager or an experienced INR manager. I guess that you can see why its not common and you've not read of it before.

Summary

This procedure is something that an experienced self manager of INR can do. It requires the careful management down of INR to a still slightly anti-coagulated state. This then allows surgeons and practitioners to undertake a procedure in the absence of significant ACT. This results in

• achieving the goal of the procedure and 
• minimising the time out of therapeutic range and 
• not requiring the subcutaneous injection administration of a bolus of heparin; which at the very least is uncomfortable and requires greater coordination with prescriptions and then administration of those injections

Ultimately if you are a INR self manager, and in the lowest risk category (as defined in the above mentioned prior work of mine on this), then this procedure may be of value to you. It is intended only for those who are on ACT primarily due to the placement of a mechanical aortic valve and who have no history of stroke. It is my view that this method should prove a helpful tool in the management of ACT around the inevitable invasive procedures we are more likely to have as we age.

Acknowledgements

I'd like to thank Chuck for the opportunity to work with him on this experiment and the generous sharing of his data.

I hope this is of interest to fellow valvers and I encourage you to take this and the earlier article on the Perioperative Management of INR to your medical team when next you face an invasive procedure.

Epilogue

Lastly I'd like to venture something I learned a long time ago, empirical observation trumps investigation into "the why" of how things work.

Theory is when we know why something should work, but it doesn’t.

Practice is when something works, but we don’t know why. 

Here Theory and Practice meet: Nothing works and we don’t know why." 

- Unknown

I prefer to go with using what I know works even if I'm not entirely sure why.

Adapting a leather NATO into a nice leather watch strap

I've come to find in my journey of watches that I prefer a plain simple strap, having over the last few years experimented quite a bit with many combinations.

I have a number of straps now (meaning a single piece as opposed to the "pair of straps" which are two separate parts) which makes it not only easy to change out (and thus I frequently do) but helps to keep the back of your watch that bit cleaner from skin grease, sweat and dirt.

The NATO itself as it comes makes even less sense in leather than it does in nylon because the keeper is even more pointless, adds yet more bulk and makes threading extra length even more of a mess than nylon. However it makes it easy to make a nice strap for a low price which suits your watch and makes your watch wearing experience more comfortable as well as deepen the usefulness and fashion coordination that your watch has. You may have noticed that I wear the strap on the watch buckle down, for this reason and it makes it nicer on desk work too keeping all the strap hardware off the desktop.

Back in my early watch wearing history changing a band (or indeed a bracelet) was something which required tools, tools which were much harder to get. Thus one frequently didn't.

Back to the making a leather strap from a NATO, this also means that strap changes can be simple, convenient. 

So apart from cutting off the keeper (see here), and of course trimming the band to a nice length (because you aren't really going to need that extra length for when you wear your watch outside your tactical gear or wetsuit that fits neatly in the keepers) you need to grind some of the extra thickness out from where you'll want the watch to sit.

I encourage you to think about this and perhaps buy a nylon NATO and experiment, because once you've done this its going to be pretty permanent as you'll see in this video:

So that's it ... not real hard and leaves you with a method to get a selection of straps which will suit the watch and perhaps colour match more with your clothes.

Happy Watch Wearing

Things I don't get about NATO

As it happens I love straps, but don't like NATO. Lets take a look at the things I don't get about NATO (and why I prefer just a plain strap) and there's a few:

1. the (fundamentally useless) keeper strap that adds two layers under the watch and
2. the direction of threading for wearing (common to all straps but made worse on a NATO). 

I prefer to have something neat and out of the way, not clicketty clacking into the desk (leaving marks) like this is:

Note that its also threaded buckle down and this brings with it some other benefits (which I'll get on to in a tic). 

Compare that to this, threaded the "conventional way" with buckle up and with the NATO extra useless keeper...

... causing not just two thicknesses under the watch but a bunch of extra stuff on the side where its folded in over itself. 

This is how your watch strap looks to everyone else if you thread it like (almost) everyone else.  I suppose its for people who want to be different with their dress but don't know how to tie a bow tie themselves ...

I've already covered why the keeper is pointless over here, and explained how to get rid of it, but the focus of this post is to look at the advantages of threading your single piece strap in what some would call "Grand Seiko" style (aka buckle down).

As you may have seen above it leaves the bottom of the strap clean, but the other benefit of buckle down if you're using a computer you'll often rest you hand with it tuned slightly out: where the bunch of folded strap gets in the way.

As you can see above the wrapped up extra length of the strap (designed to allow you to wear it over clothing) is now not under your wrist but up above it and out of the way. 

I used to always find wearing a watch while working on my computer (something I do for a living) annoying, and often took it off; resulting in me leaving it at work on many occasions.

Going back a few years nobody had heard of NATO straps and we all went on quietly using single straps, two piece straps (leather, fabric or nylon) and steel bracelets. Then NATO started shipping on watches standard (and wow, weren't watch makers happy to put on a $2 piece of nylon and have people clamour for it) that we see its rise on the internet on watch forums (note: most people still haven't heard of it).

The main argument for a single piece strap is that if the spring bar fails the watch is likely to fall off. As I ride bicycles and motorcycles this is actually important to me, but you can see that even if a spring bar fails the single pass strap will hold the watch 

Indeed the keeper isn't needed to keep the watch on the strap when taking the watch off ...

So just what the keeper does is a mystery to me (well aside from add to the mystery of the name). So unless you like to have conversation starters (you know, ask a bow tie wearer about that) or fulfil some fantasy of being a military spec operative then I suggest you take the punt, remove the useless bits and thread it in buckle down.

Its actually now the most comfortable watch strap I own (well I now own a few in leather too and can thread out a strap to pick one that will better go with my shirt on the day)

Indeed the earlier RAF style is to me so much more functional as a watch strap (this one inspired me into buying the SNK805)

... becuse I couldn't find that one.

Give it a go.

over paneled

Well its been a lot in planning and significant preparation and then construction but my "shed project" has finally made it to "solar shed project" status with the mounting of my 250W panel... 

...but lets perhaps go back to the start and explain the title...

In the foreground there you can see a small 10W panel which I mounted some time ago which I discussed in this blog post, and has powered my simple lighting system from a humble Gel Cell 12V battery for the last few years.

The whole idea was naturally an extension of wanting a shed for tool storage and workshop (so that I'm not working on things in the house), the construction of the shed (and a bit of history) is discussed here, but in this blog post I'll focus only on the solar aspect of it, what I did and why.

Needs Assessment

My first step was an assessment of power needs which I did with one of these plug in power meters (easily obtainable from eBay or your local hardware shop).

I have been working outside on "flatish" areas when doing things such as building, and while I make pretty extensive use of 18V lithium battery tools I do still need 240V for things, a more powerful orbital sander, drop saw, circular saw, workshop vacuum cleaner and the like.

My normal process has been to run an extension lead out the window to where I'm working, which provides an ideal point to measure exactly what I use.

So doing some work on a few occasions I made some measurements and found that the number was about 200Wh for the days work (I took a few measurements over different days). Which isn't a lot really.

Basically if I got two 50W 22Voc panels that would give me entirely sufficient power to replenish my needs. Even if I used 1000Wh on a particular day that's only 10 hours charging, meaning that the battery bank would be back up to "float charge" after 2 days ... certainly no time for sulfation to occur there. However typically such a panel would cost about $60 which is about twice what I paid for this panel and I'd need two of those! Something like this was in my view ideal and was $160 per panel.

I'd need two because I will be charging 24V (2 FLA batteries) ... however I chose to go with the one higher Voltage panel because it was so darn cheap.

Storage

As I wanted to use 1200W tools in the shed (vacuum cleaner and compressor) I didn't want high amp loads coming from the battery to the inverter (not least because high amp loads distress the cables and distort the Amp hour rating of the battery) I immediately turned to 24V as the low hanging fruit (halving the Amp draw right there).

This has a knock on effect that you don't need as many Ah out of each 12V battery and so I picked a pair of batteries which were rated at RC95 (RC is Reserve Capacity), I'll spare you the cookie fest and paste below a definition (or you can seek your own)

Reserve minutes, also called reserve capacity, is the number of minutes a fully charged battery can sustain a designated constant load (usually 25 amps) before it is fully discharged. For a 12-volt battery, that means battery voltage will have fallen to 10.5 volts.

So I reckoned that I was not going to go close to needing 90 continuous minutes of 600W (by any stretch of the imagination) and so it was settled quickly there:

• 24V 2000W (4000W peak) high frequency inverter (AU$240)
• two 12V batteries

So we have energy captured by the solar, stored in the battery charge and delivered by inverter to the power points on the bench. Conveniently the solar charge controller has USB output which allows me to charge my phone and my Bluetooth speaker there. (*point, notice the multi meter on the bench? If you're even thinking about  this topic you must have something like that or frankly your're working blind.)

I recently did a draw down test on the system (panel, battery and inverter) running my fridge during an 8 hour power outage (IE most of the day) which was enough to pull the battery bank down to 24.5V. Now while this isn't ideal (and indeed is disappointing in some ways) it shows two things

1. the system is entirely adequate for my needs
2. the use of inverters off the battery does not allow the controller system to "see" what is going on and thus not divert sufficient (actually available) power to the "load" on the system (that's a long story right there) if one was to be going into the night and needing to keep sustaining the fridge (which is about 190W)

The Panel

One of the great things (for me at least) is the market distortions occurring due to government subsidies of solar. Pretty stupidly (but sadly not atypically)  what is happening is that are getting the subsidies to put new  systems on their roof and this includes people with existing (say 10 year old) systems and the older panels are removed and sold as surplus. 

This means I got my 240W 60 cell panel for just $20 ... fuck me dead, I can't even buy a (so called) 12V 100w panel for that (and BTW they aren't actually 12V), more like $120 each, and so getting a panel which is (more or less 32V (at maximum power) is a bargain.

The specs on the panel are something you should learn well, and you need to understand Voc, Isc, Vmpp and Impp.

Anyway to get that for a few bucks is just fantastic even if in excess of my needs. Basically this means that even if on a big day I run the workshop battery down to nearly "inverter power shut off" voltages, by the end of the next day it will be fully recharged and cell plate sulfation avoided (and my battery investment maximised). This is unlikely to ever happen as I simply don't need that much power in a day and I don't use the shed power even remotely hard most days.

So, next, the solar panel needs to be on the roof, and needs to be secure there.

Mounting

The shed I have (as you may have seen) is a basic 3 x 3 meter garden shed which I've used as the basic starter (for materials) and added a steel frame and other enhancements, accordingly the roof is not a trafficable roof and I'm against drilling holes (to later leak in the rain), and further because there is nothing underneath the "Trimdek" (like any battens) to screw into I decided to flush mount the brackets and to use a modern adhesive like Sikaflex 291 (rated to 1.8MPa tensile strength or about 140PSI) to secure the brackets to the "Trimdek" which the shed is made of.

The brackets (as you can probably make out in the first picture) are 25mm square section tube (so more or less an inch by an inch foot print on the Trimdek) and are 1200mm long (covering 7 high points). I added extra "feet" to extend out either side of the square section tube to prevent any rolling when I slid the panel up and across them, as well as add more grip surface for the adhesive.

To prevent any "movement" (slippage) while the adhesive was "skinning" I used two wooden "supports"

and again (with tape) on the upper side, giving me two nice mounts for the panel you saw back at the start of this blog post)

note that I've added some vertical mounts to secure the panel to the square tube too. These are screwed (and a small blob of sikaflex applied) into the aluminium frame of the panel. The whole thing then has overall 7 good joints like this...

... at each end to hold the panel down.

Now its important to note, that Sikalfex is humidity cured, and due to the thickness of the apparent bead (being squeezed in between the metals) you need to leave it for at least a few days to cure ... which I did.

A friend came over and helped me slide it up and screw the panel onto the side mounts.

So there we have it ... job done! (I might put some covers over the end ... I might not).

what's left?

basically the final sections are to

• neatly mount the Solar Charge Controller to the wall beside the door inside the shed
• add in some fuses / circuit breakers
• add in a neat isolator for the panel (I'm intending to insert a power monitor in there now and then) which I'll do with XT-60 connectors

However right now its fully functional, and so the components for this are:

• 250W panel (32v) = $20
• MPPT solar charge controller = $40
• 2x RC95 lead acid car batteries @$90 = $180
• 2000W (4000peak) inverter = $240
• sundry wiring

Now some may be asking "why didn't you just get an electrician to wire it to the house?", well the answer is that because of the distance down to the shed (about 30 meters) it would cost something over $1200, instead of $424.38 and I'd have learned nothing new.

Win Win

PS: I've now mounted the solar charge controller, run the wires neatly, and added a circuit breaker / fuse system which of course acts as an isolator.

The top one is for the panel (I sincerely doubt I need a circuit breaker, but as it has a manual operation its a handy isolator) and the bottom one to the battery is really for (hopefully) protecting the internal fuse that's built into the SCC.