Final answer:
Renal clearance does not influence the peak plasma levels of local anaesthetic after an epidural injection because it is a later stage process affecting drug levels after absorption and distribution.
Step-by-step explanation:
The question asks which factor does not influence the peak plasma levels after epidural injection of a local anaesthetic. Among the options provided, hepatic clearance and renal clearance are processes that eliminate drugs from the body. While both affect the duration of a drug's action and overall drug levels in the body, they do not directly impact the concentration of drug reaching the peak plasma level after an epidural injection. It is therefore expected that renal clearance is the factor that would not influence the peak plasma levels after epidural injection because the removal of drugs by the kidneys occurs later, after the drug has already been absorbed and distributed in the systemic circulation.