當護理師未依照約定提供病人護理時，違反了哪項倫理原則？

護理倫理中，忠實（Fidelity）是指履行對病人的專業承諾與義務。當護理師與病人建立照護關係，即承諾提供符合標準的照護。未能提供約定的照護，即違反了對病人的忠實原則。這與自主（Autonomy，尊重病人決定）、行善（Beneficence，做對病人有利的事）及正義（Justice，公平對待）不同，忠實強調的是「信守承諾」。

Fidelity is the ethical principle that involves keeping promises and fulfilling professional commitments to clients. When a nurse fails to provide the agreed-upon care, she violates this duty of faithfulness, which is distinct from autonomy, beneficence, or justice.