@Caerulea It seems like a bit of a relic from times of old. Dark/metallic nails can interfere slightly with the reading an sats probe will give but In the majority of cases it doesn’t make a clinically significant difference though. The tech in the probes does seem to be better at dealing with coloured nails than it was when they were first developed. The probe can be turned to read side-side rather than front-back, or there are sats probes that can for on the ear lobe so if you’re really worried about dark nails there are options. Very long nails can be a problem for finger probes just because they never really fit that well with huge talons!
Sats are just one of many parameters that are monitored (and they’re the monitors that are most likely stop giving useful information when someone is really sick) - anaesthetists are used to putting information from multiple sources together and not depending on one monitor. The trend in the probe readings (the number and the waveform) are often more useful than a single number.
I can count on zero fingers the number of times in the last 20yrs that being able to see someone’s nail bed made a difference to any sort of decision making (and during a lap chole, as well as a lot of other operations, a patients hands are normally by their side and wrapped up under the drapes so no one can get anywhere near them). In a low resource setting where there isn’t all the rest of the whizzy tech & monitoring it may be useful to see someone’s nail beds as a guesstimate of how sick someone might be but it doesn’t tell you anything terribly specific and there’s usually other signs that will help too.
in an emergency there isn’t usually the option of doing anything about nails - we just use our common sense and if it doesn’t cause massive issues in an emergency then it shouldn’t really in an elective scenario either. Haven’t seen acetone for normal nail varnish in theatres where I work for ages but I’m sure there’s probably a (decades old) bottle somewhere.
obviously if the surgery is something hand/finger/foot/toe related then there may be good surgical reasons for ditching the nails.
the main reaction HCPs have to nice nails is jealousy because we’re not allowed them!