2. Actions that may be performed for the child when a Bris is performed on Shabbos:[1]

• Mila
• Periah[2]
• Metzitzah[3]
• Medical treatment to the area:[4] One may place a bandage or poultice[5] on the area of circumcision.[6] Likewise, all other medical treatments may be done to the area of circumcision.[7] Nevertheless, initially one is required to prepare all the medical treatments before Shabbos [if their preparation involves transgressing Shabbos, even Rabbinically[8]]. Thus, all ointments which require preparation are to be prepared before Shabbos.[9] If one did not prepare the medicines before Shabbos then one may do so on Shabbos with an irregularity.[10] If one is unable to prepare the medicines on Shabbos using an irregularity[11] then it is forbidden to prepare them on Shabbos [even if doing so involves only a Rabbinical transgression[12]]. It is forbidden to prepare the medicine in such a case even if this will cause the circumcision to need to be delayed until the next day.[13] If, however, the child was already circumcised then all matters may be done to treat the child, even if they could have been done before Shabbos.[14] However, if prior to the child being circumcised the medicine spilled [and it cannot be made without a Shinuiy] then it remains forbidden to be done, and the Mila is rather to be differed until after Shabbos.[15]
• Removing pieces of the foreskin after the circumcision:[16] After the circumcision it is permitted, if necessary, to cut off any remaining pieces of the foreskin if those pieces refrain the Mitzvah from being fulfilled. However, those pieces of skin which do not refrain the Mitzvah’s fulfillment, even though they are initially required to be removed, may not be cut on Shabbos once the Mohel has removed his hand from the area after the initial circumcision. Prior however to removing his hand from the area of circumcision it is permitted to fix and cut even these pieces of skin.

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[1] Admur 331:1; Michaber O.C. 331; Y.D. 266:2; See Pesakim Uteshuvos 266:1

[2] See Encyclopedia Talmudit Vol. 46 Erech Mila p. 512-514

The reason: As Periah is included within the Milah process. [Admur ibid]

[3] See Encyclopedia Talmudit Vol. 46 Erech Mila p. 514-515

The reason: It overrides the Shabbos prohibition [of causing wound] being that not doing so can lead to danger to the child. [Admur ibid]

[4] Admur 331:1; Michaber O.C. 331; Y.D. 266:3

^[5] This refers to a dressing or pad which has ointment smeared over it which is then placed on the wound

[6] The reason: Although applying a poultice was forbidden even in a case of illness that does not involve danger, here it is allowed as giving treatment to the area is considered to be a case of danger. [Admur ibid]

[7] The reason: As the area that was circumcised can become lethally dangerous if not properly treated. [Admur ibid]

[8] The reason: As one must even mix the oil and wine ointment together before Shabbos, even though doing so on Shabbos is a Rabbinical prohibition.

[9] For example, back in the day when they would place crushed cumin and wine mixed with oil on the area, then before Shabbos one would need to crush the cumin and mix the wine with oil. [Admur ibid]

[10] Thus, is they forgot to crush the cumin before Shabbos they would be allowed on Shabbos to chew it until it is crushed. Similarly, if the wine/oil mixture was not prepared before Shabbos it would have to be placed separately, one after the other, onto the area in order to do it with an irregularity. However, one would not be allowed to mix it on Shabbos. [Admur ibid; Michaber ibid] As for the reason why it is allowed to do so with an irregularity even before the circumcision, seemingly this is because a child has a status of a Choleh Sheiyn Bo Sakana towards which all Rabbinical prohibitions may be done with an irregularity.

[11] Such as one is unable to chew the cumin and must thus grind it in its normal fashion. [Admur ibid]

[12] Admur 331:7. It may not be implied from Admur 331:1 which only mentions this Halacha with regards to grinding the cumin and not regarding mixing the oil that he holds that Rabbinical prohibitions may be done, as it is always permitted to do a Rabbinical prohibition with a Shinui for the sake of one who is bedridden, and a child has the status of one who is bedridden. Vetzaruch Iyun as prior to the Milah, the child does not need this treatment, so how can it be allowed to enter the child into this situation. In any event Admur states explicitly in 331:7 that Rabbinical prohibitions may not be done if they could have been done before Shabbos.

[13] The reason: As Mila preparations that involve Shabbos transgressions do not override the Shabbos prohibitions being that they could be done before Shabbos, and it is only the Mila itself which overrides. Now although if the treatments are not given they could jeopardize the child’s life and hence indeed override Shabbos, nevertheless this is only after the fact. However initially it is forbidden to enter the child into this state of danger, hence allowing the treatment. Thus, it is forbidden to go through with the circumcision. [Admur ibid]

[14] See Admur 331:1; Michaber O.C. 331; Y.D. 266:4

Although Admur and Michaber ibid writes this case to be referring to one who did prepare the ointment before Shabbos and after the circumcision it spilled, nevertheless obviously it is not coming to exclude a case that one transgressed and did not prepare the ointment before Shabbos, as it is a matter of life and death for the child.

[15] Admur 331:1 [Only if medicine got lost after the Mila may one do it] and 7 [or it was made and got lost] [See Admur 248:5. Vetzaruch Iyun from Admur 248:6!] Michaber O.C. 331:4; Y.D. 266:4 [Only if medicine got lost after the Mila may one do it]; Shach Y.D. 266:6; Bach 266; Rambam Mila 2:8; Rif 55; Ran Shabbos 53a in name of Razah in Hamaor Shabbos 53, and Rashba Shabbos 134b; Beis Yosef 266 in name of Rif and Rambam ibid; Levush 266:4

Other opinions: Some Poskim rule that the Mila is Docheh Shabbos for the sake of making new medicine after the Mila, as the Mila is on time and is Doche Shabbos, and once the Mila is done the Chillul Shabbos is necessary for Pikuach Nefesh. [Shach ibid in name of Ran Shabbos 53a in name of Ramban Shabbos 134; See also Admur 248:5-12 that according to some opinions one may enter a ship for the need of a Mitzvah even though he will later need to be Michalel Shabbos]

[16] Admur 331:2; Michaber O.C. 331; Y.D. 266:2; See Pesakim Uteshuvos 266:2; See Encyclopedia Talmudit Vol. 46 Erech Mila p. 508-512