Possibly an aphetic use of empoigner, or a verbal derivation of poin1 without a direct Latin verbal counterpart.

The sense ‘to place one’s hand on’ in A-N Med is problematic, and alternative interpretations are poindre1 (‘to prick’) or even Middle English poinen v. (‘to stitch’). The Latin source text does not have this phrase, ‘poigniez la veine’. Since the context has the patient instructed to place his hand and fingers on his nose and face, the use of the verb related to poin1 (‘fist, hand’) may make best sense. However, the attestation remains ambiguous.