A couple of points for you good mate.
1. Dosage changes made today affect INR in about 3 days time, so this makes dosing tricky, as you are often behind the game, trying to project changes and trends, and while a particular dose change is taking effect all manner of things can happen to also conspire to change INR (like diet, level of activity, etc)..so sometimes its not a mathematical process, unfortunately, unless you subscribe to chaos theory...
2. Your surgeon has a target INR, but that does not mean he is absolutely right for all instances, as your intensivist will have the bigger and more current situation in mind, such as your wound etc... and it may be a case of the Dr weighing up things like should your INR be temporarily lower at this stage, or slightly higher at another stage... for a myriad of reasons. Your surgeon has a prescribed range of 2.2 and 3....(mmm, an interesting range?) but it would seem that another surgeon (from the same medical school) will prescribe an INR range of 2-3, and another surgeon may prescribe 2.5-3, or whatever, its not so much about exact numbers, but having a reasonable target range for your particualr situation, and sometimes that depends on lots of variables. When I asked, my suurgeon said my target is 2.4385 ...said with all seriousness initaially, then breaking out into laughter once the nurse started to write it down on my chart...Trust me, some people's INR can vary wildly from 1 to 10 (or more) in just a very short time, and they require hospitalisation and treatment to normailse things again. You may be unduely concerned about your fluctuations that aren't actually that bad at all....honestly, you are relatively young and otherwise fit, but now there are competing challenges with your clotting... avoid a clot being thrown off your heart valve, and avoiding bleeding from your chronicly infected sternal wound...your INR might "drop our of range" as you say, but its not a switch... its not a case of its ok within range, lethal just out of range....not at all, and in fact your INR changes are really quite reasonable, and aren't worth being overly concered about at this stage...it will settle down again no doubt.
3. Some medical staff, (and this doesn't excuse the lack of this Drs explanation), have brains that turn at a million miles an hour and they simply don't explain things in terms that different patients can always follow... we all have positives and negatives, and sometimes the correct medical decisions just aren't easily explained by all Drs in all instances...I'm not offering an excuse for the Dr not explainig things, its just a possible explanation. He might well have been incorrect by changing teh dose in that manner, but may have been absolutely spot on... given what he knows about yuor current condition, your current clinical course, what his expereince has been, and weighing up all the risks etc. If you are so concerned, you may be bettter off getting a second opinion rather than changing doses secretly, but be aware that the second opinion may come from a doctor who doesn't have posession of all your particualr facts...so it can be difficult I know.
4. I was lined up for an operation unrelated to my heart surgery a couple of months after my valve operation while I was still on warfarin...(fortunately it was a false alarm and I didn't end up needing the operation), but the plan was to admit me to hospital, stop my warfarin, get me onto heparin, and just prior to the surgery, reverse my heparin by giving me protamine (so I didn't bleed "like a stuck pig" during surgery), and then get me back onto heparin, and wean my off heparin and back onto warfarin when it was clear I was not bleeding. This is sometimes not an exact "cook book" approach, but it needs to be individualised depending on a range of risks, side effects, the type of surgery and so on...
5. It is risky "self dosing" with warfaarin, honestly good mate. Mind you, its a bit confusing trying to follow the sequence of your events, does "dropped" a dose mean "missed" the 8mg dose, and trying to work out when you had the debridement or if you need another debrdement, and also not knowing what other medications you were taking, and so on. Also, I'm not sure why you say your dose was "7.16mg", as thats not really the case at all, it was in fact a cycle of 7,7,7.5, and you just can't average that out as 7.16 or 7.17 or whatever. It seems to me that maybe you are trying to think like an engineer, (and I'm not being rude whatsoever, so please don't be offended... I did study engineering a long time ago), when in actual fact it is not an exact science, dosing can depend on the Drs experience, and weighing up your risks, and your circumstances...bed ridden in ICU one week, walking the wards the next week or whatever, an operation one week, maybe anotehr operation, or maybe not ...etc etc ...you just can't always apply a mathematical formula, and you don't have to be exactly with your target INR range 100% of the time...
So...without knowing all your facts, or all the medications or all the circumstances, and I say this with all encouragement and support...and with no malice or criticism whatsoever...you may be worrying about nothing...your INR range may in fact be absolutely fine...and I definately would avoid self dosing your warfarin...at this stage, given your tricky situation with an infected sternum wound....
I know that won't help much I'm sorry, but I do know that the majority of medical staff where you are are indeed first class...quirky sometimes, difficult personalities sometimes, but generally superb, and if you are concerned, just say to the particular doctor, "I'm really not so sure about that dose, honestly Doc, I don't feel really comfortable with that dose, so can I just talk this over quickly with the senior intensivist please...please don't be offended, but I know its not a exact science, but I would feel better if I could just get confirmation so I can sleep better tonight".
Actually I would be more concerned if its a Junior Registrar (ie a trainee) making the changes to doses as opposed to a Senior Intensivist...in fact I would have infinatly more confidence in the advice of a Senior Intensivist, seriously.
I had to this tactic a couple of times, with nurses and doctors ...."Excuse me nurse, but please, please don't change that setting just yet, thats my temporary pacemaker and doctor "so and so" has specifically set it with something in mind, so please, can we double check with him first before you change that, just in case"... (The upshot of that episode was a stern instruction from doctor "so and so" to the nurse involved ..DON'T YOU EVER TOUCH A TEMPORARY PACEMAKER ON MY PATIENTS IN THIS HOSPITAL AGAIN WITHOUT SPEAKING TO ME FIRST)...phew, I survived that near miss, as the temporay pacemaker was being "adjusted" because "it doesn't seem to be working"....when in fact it was keeping me alive!
Without warfarin our INR is typically somewhere between 0.7 and 1.3, or thereabouts, but it will change with hydration state, activity, diesease etc. An INR somewhere between 2 and 3 is a typcial target range to slow or manage clot formation, or more likely somewhere between 2.5 and 3, but that doesn't mean that a disaster will occcur if your INR fluctuates, especially while in hospital when you are less likely to have a car crash or some trauma that can cause a serious bleeding event...but you have a nasty wound, with who knows what stage that healing process is at, so who knows what the doctor has in mind....take care good mate, I'm sorry if I have confused you or misread your original post...soi I just re-read your post again, and givven that you have such a nasty sternal wound, and without knowing what the extent of your wound debridement was, I don't think I would have been quite as concerned about what the doctor was proposing with your warfarin dose...honestly.
But I know its different when its your body they are playing with....so I hope that ramble of mine helps you a little bit perhaps.
BTW, are you still in the same hospital? Get well soon, the surf is up and once the rain stops the surfing will be awesome...I know, maybe not in the surf for you just yet, but it won't be long before you can hang ten again. I'm into stand up paddle boarding, a little more sedate and not as much skill required as riding a short board..
