These are the Rebbe's letters to individuals about their own situations. Throughout, the Rebbe instructed people to consult an expert doctor and follow his guidance; anyone facing a medical question should do the same.
The Rebbe's guidance to people facing surgery:
Before an irreversible procedure, get more than one expert opinion. The Rebbe repeatedly advised consulting two specialists, or several, before deciding on surgery; this is rooted in both Torah and reason (IK 1383, 5829, 5960, 6756, 7889). The level of the advisers matters; for serious cases, a joint consultation of top specialists (IK 5762).
Don't rush into surgery when it is not urgent. First try every other possible treatment, and be open to alternatives (IK 1737, 1895, 5654, 8111, 10832). Irreversible procedures should be undertaken only when truly necessary, after exhausting the alternatives (IK 6429). Consider both the physical and the emotional sides (IK 7713). Where surgery is medically appropriate, it may be preferable to other treatments (IK 8547). Timing can also be considered, such as waiting until after the summer heat (IK 1781).
Consult a rav on the halachic side before certain procedures, including procedures that may affect fertility, and arrange that the surgery is carried out in accordance with halachah. Where possible, avoid scheduling close to Shabbos or during the Nine Days (IK 1411, 2842, 7633, 8547, 10190, 10267).
Prepare spiritually: give tzedakah before the surgery, pray, strengthen Torah study and mitzvos, and think positively and trust in Hashem, since healing comes from Hashem through the doctor (IK 675, 712, 1383, 1451, 7034).