I have seen many papers in which quantum measurements are assumed to be replaced by unitaries. See this quotation from [KW00] for instance:
Often we will describe quantum circuits in a high-level manner that suggests that measurements are performed at various times as the circuits are applied to some collection of qubits. In fact, as all of our circuits are assumed to be unitary, such measurements do not occur, but rather are assumed to be simulated by unitary gates as described in [AKN98].
I have read [AKN98] but it points to other papers (lemmas 1 and 4). It seems to be a standard result in quantum computing that just requires to add ancilla qubits. Could someone explain how it's done?