Help me improve the ASA fitness classification system
November 9, 2012 10:20 AM   Subscribe

The ASA physical status classification system is used by anaesthesiologists, surgeons and epidemiologists the world over. It has a major flaw - it makes no odds whether index patients have 1 or 5 systemic diseases: only the leading/worst is counted. This has the advantage of simplicity but is potentially misleading and should be done better in the 21st century. Numbercrunchers with a biomedical background needed ...

I have often thought that one (admittedly slightly tedious) way of overcoming the major limitation of the American Society of Anesthesiologists' (ASA) Physical Status classification system, i.e. that whether your patient has 1 or 5 diseases it counts the same - would be to sum morbidity severities:

e.g. Asthma, mild (2) + HT, mild (2) + Angina, mild (2) + renal impairment, mild (2) totals 8, compared to COPD, severe and a constant threat to life (4) totals 4.

There is a certain logic to doing that, but epidemiologists would need to spend a few weekends crunching numbers to calculate adjustment factor(s) that adequately control(s) for imbalances (maybe give a 50 percent discount to all additional mild conditions or some such). And you would need to generate surgical survival curves (operator-receiver type?) to correlate with the "morbidity scores". Has anything like this been done using the ASA scheme as a starting point?
posted by kairab to Health & Fitness (4 answers total) 2 users marked this as a favorite
Unfortunately anesthesiologists use this classification or their purposes, not epidemiological purposes.

Once you've crossed the threshold of a few comorbidities, it doesn't really matter how bad it is.

It's more than likely used for insurance or billing purposes to ensure that there is an adequately trained individual in the room as opposed to just letting a CRNA take the case and the anesthesiologist monitoring everything remotely.

What you're asking is for a lot more paperwork to be done and even some calculations for no net clinical gain. Similar to the current level of pilot training, standardization in design checklists and training in the field of anesthesiology has made massive bounds in ensuring safety and limiting complications.

That is more or less why CRNAs and anesthesiology PAs are currently so successful in taking over what is a very complex and dangerous science and making it very undervalued.
posted by hobo gitano de queretaro at 10:41 AM on November 9, 2012

Maybe you're thinking something like the Charlson index and similar? It's not the greatest tool (I'm working on a replacement, actually), but if you're trying to adjust for mortality risk, it's pretty much the gold standard, and it's where the conversation starts.

I think it's possible that you could come up with your own model to use in an anesthesiology context, but getting good data for it might present a stumbling block, depending on what outcome variable you're adjusting for (e.g. all-cause 10-y mortality, etc.) MeMail me if you have any questions or would like to follow up -- I work in consulting in just this field. Good luck!
posted by un petit cadeau at 12:08 PM on November 9, 2012

Many thanks for your helpful responses, hobogitanodequeretaro and unpetitcadeau (gotta love the handles). What actually got me thinking about this is the fact that until recently, ASA 2 was defined as "well controlled" disease whereas now it has been redefined as disease of "mild" severity; correspondingly ASA 3 used to be defined as "poorly controlled" disease whereas now it has been redefined as "severe" disease.

Quite commonly, anesthesiologists see patients who have e.g. known hypertensive disease and are on multiple antihypertensives. As long as their BP is acceptable, this would have constituted "good control" and made them ASA 2 - now their disease is arguably "severe" as it requires polypharmacy, making them ASA 3. This not only impairs the comparability of future data to historical data but has manifold practical implications: For example, guidelines consider patients suitable for day-case surgery under GA or sedoanalgesia in detached units, clinics and office-type suites only if they are ASA 1 or 2 but not if they are ASA 3. This definition change could therefore have major resource implications. A more differentiated assessment tool could be helpful by facilitating a more meaningful delineation between genuinely risky patients and those who should probably be OK.
posted by kairab at 6:06 PM on November 9, 2012

I've been doodling this a bit more, and it's become apparent that multiple comorbidities each of which is well controlled or mild, even in combination are of course far less threatening than a single disease that is very advanced or severe. Hence it would make sense to not simply sum suing the ASA categories as point scores but impose a simple mathematical manipulation such as squaring the index ASA grade points, and perhaps adding additional morbidities as unsquared scores. Might do a little pilot study in my hospital to see how that works out. Still interested in hearing more about past and ongoing work in this area ...
posted by kairab at 6:48 AM on November 10, 2012

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