PIKKU'AḤ NEFESH (Heb. פִּקּוּחַ נֶפֶשׁ; "regard for human life"), the rabbinical term applied to the duty to save human life in a situation in which it is imperiled. The danger to life may be due to a grave state of illness or other direct peril (sakkanat nefashot), or indirectly, to a condition of health which, though not serious, might deteriorate and consequently imperil life (safek sakkanat nefashot). Pikku'aḥ nefesh is a biblical injunction derived from the verse "Neither shalt thou stand idly by the blood of thy neighbor" (Lev. 19:16), and according to the Talmud it supersedes even the Sabbath laws (pikku'aḥ nefesh doḥeh et ha-Shabbat; Yoma 85a). One should be more particular about matters concerning danger to health and life than about ritual observances (Ḥul 10a). The strict rules of hygiene codified in the Shulḥan Arukh center around the principle of pikku'aḥ nefesh (yd 116). The rabbis interpreted the verse "Ye shall therefore keep my statutes and my ordinances which if a man do he shall live by them" (Lev. 18:5), that man shall "live" by these commandments, and not die as a result of observing them (Yoma 85b; Sanh. 74a).
The Talmud (bm 62a) discusses the problem of an individual faced with the choice of saving his own life or that of his companion, and mentions the example of two men in a desert with a supply of water sufficient for one only. Although *Ben Peturah advocated that neither should attempt to save his own life at the expense of the other but that both share the water, R. *Akiva, whose opinion prevailed, ruled that one should save one's own life and not share the water. Only when faced with a choice between death and committing idolatry, unlawful sexual intercourse, or murder is martyrdom to be preferred (Sanh. 74a–b). One must also sacrifice one's life rather than submit to what may be taken for a renunciation of faith through the violation of any religious law in public (Sanh. 74a–b; Sh. Ar., yd 157). In all other cases, the rule of pikku'aḥ nefesh takes precedence (Sanh. 74a–b; Maim., Iggeretha-Shemad 3).
The rule that one may profane one Sabbath in order to save the life of a person and enable him subsequently to observe many others (Yoma 85b) is inferred by the rabbis from the verse "The children of Israel shall keep the Sabbath to observe the Sabbath" (Ex. 31:16). Thus, on the Sabbath (or a festival), every type of medical treatment must be accorded to a dangerously ill person, to the extent of even putting out the light to help him sleep (Shab. 2:5; Sh. Ar., oḤ 278). Equal efforts must be made even where there is only a possibility of danger to life (safek sakkanat nefashot, Yoma 8:6; ibid. 84b). Only in cases of minor illnesses or physical discomforts should violations of the Sabbath be kept to the minimum; if possible a non-Jew should perform these duties (Sh. Ar., oḤ 328:17). In all other instances, the medical treatment should be administered by a Jew, and those who are assiduous in their help, comfort, and work for the sick on the Sabbath, are deemed worthy of the highest praise (ibid., 328:12–13). If a dangerously ill person is in need of food on the Sabbath, one should slaughter animals and prepare them according to the dietary laws, rather than feed him ritually forbidden food (ibid., 328:14). If, however, it is deemed necessary for the recovery of the patient that he eat forbidden food, he is allowed to do so (ibid., 328). A woman in confinement is considered dangerously ill for a period of three days after delivery. Should one of these days be a Sabbath, everything possible must be done to ease her pain and lessen her discomfort, including the kindling of a fire to warm her (Maim. Yad, Shabbat 2:13–14; Sh. Ar., oḤ 330:1, 4–6). A sick person is forbidden to fast on the *Day of Atonement if it is thought that this would seriously endanger his recovery. Moreover, even a healthy person seized by a fit of "ravenous hunger" which causes faintness (bulmos), must be fed on the Day of Atonement with whatever food is available (including ritually forbidden food (Sh. Ar., oḤ 618:9)) until he recovers (Yoma 8:6; Sh. Ar., oḤ 618).
Eisenstein, Dinim, 291, 342–3.