The Gemara says that four have to say Hagomel:
To what level of danger must one be subjected to qualify for #3? For instance, anesthesia is a routine procedure that still carries a significant risk of not waking up. Would one who undergoes anesthesia need to bentch Gomel?
www.shut-halacha.co.il reports a Teshuva from Rav Avigdor Nebenzahl which says:
מי שעבר ניתוח בהרדמה כללית צריך לברך הגומל, כיון שהרדמה כללית הנה סכנה.
Someone who underwent surgery with a total anesthetic should say Hagomel since a total anesthetic is a danger.
Yeshiva.org's article on Birkas Hagomel distinguishes between the views of the Shulchan Oruch and the Rema. This is a short summary:
SA: someone who is so sick that he stays in bed for 3 days says Hagomel.
Rema: someone whose life has been in danger to the extent that the Shabbos could be desecrated for him, says Hagomel. This applies even where there has been the smallest risk of danger to life.
Rav Eliezer Waldenberg (Tzitz Eliezer 12:18) requires Hagomel for any operation however minor (e.g. surgery for the eye, fracture or hemorrhoids) because there are always possibilities of complications and danger. Operations with an anesthetic also require Hagomel.
Sefardim and some Ashkenazim follow the SA; most Ashkenazim follow the Rema.
Here is a Ma’aseh Rav showing that R. Hayyim Joseph David Azulai recited this blessing after recovering from an illness which does not seem to have been particularly dangerous or life-threatening, but merely very uncomfortable. In his diary entry for June 14th, 1776 he writes:
Friday, Shelah: some of the community leaders came to see me concerning ‘our secret’ and I was sullen and annoyed. That morning I was unable to get out of bed. I suffered from vomiting and diarrhoea and fever; and I was in distress all day long.
(Cymerman translation)
In the entry for the following say he continues describing his illness:
Saturday, the holy Sabbath: we prayed the evening service at home. And I ate a little. In the morning I forced myself, though suffering greatly, to go to the Synagogue. And by dint of great effort I managed to eat two meals, just a small amount; and the vomit and diarrhoea continued.
(Cymerman translation)
Again, the next day:
Sunday, Qorah: I was in distress all day through my illness.
(Cymerman translation)
And the next day:
Monday, Qorah: I went to the Synagogue in great pain. And they kept on begging me to take a doctor; I had declined [till now] for various reasons. [But now] there had come from Livorno S. Moses Cohen, grandson of Hakham Rabbi Eliezer Ha-Cohen. He showed me his family genealogy - attested to by the old rabbis of Aram Tsovah [=Lebanon], and among whose archives it was found - going back to OMR Samuel Ha-Cohen of the Beth Din of the RaSHBA in Barcelona: and this doctor gave me a medicine three times and the vomiting ceased. On that same day, the g’vir S. Hakham Rabbi Samuel Hai Cohen came from Mantua to visit me and he invited me to his house in Mantua.
(Cymerman translation)
The next day:
Wednesday: the doctor gave me rabarbaro [= rhubarb] and the ‘exiting’ ceased. I ate [just] a little meat and toasted bread soaked in wine, ‘for the hand had failed’ and I had no strength. Later I went by Calesso to take a walk round the walls with my good friends the brothers [sic] S. Minervi and his grandsons ytv.
(Cymerman translation)
And finally:
Thursday: I went to the Synagogue and recited the benediction Hagomel [... who deals bountifully] etc.’ Praise t.L.f.H.i.g.f.H.k.e.f.e.
(Cymerman translation)
