In a bahuvrīhi samāsa a Participle in a kta preceded by a preposition, standing as the first member of the compound has optionally acute accent (udātta) on the last syllable.,
Thus प्रधौत꣡मुखः or प्रधौतमुखः꣡ 6.2.169, or प्र꣡धौतमुखः 6.2.49 and 6.2.1 प्रक्षालित꣡पादः or प्र꣡क्षालितपादः ॥ When the word मुखः means (mouth) then by 6.2.167 which is an optional rule, the accent falls on the last syllable खः ॥ When the other alternative is taken or when it does not mean (mouth) then by 6.2.49 the acute falls on प्र, which accent is retained 6.2.1. Why do we say \a Nishtha\? Observe प्रसवकमुखः which is acute in the middle by the krit accent being retained after प्र 6.2.139. Why do we say 'preceded by a preposition'? Observe शुष्कमुखम् which has acute on the first by 6.1.206.,