Table 1

The current state of knowledge on mechanisms of analgesia in fascial plane blocks

What is knownWhat is uncertain
  • Nerves run in and through fascial planes.

  • LA spreads in fascial planes and can achieve sufficiently high concentrations for neural conduction blockade.

  • LA can spread out of fascial planes into adjacent tissue compartments.

  • Neural conduction block requires only relatively small amounts of LA.

  • Different nerve fiber types have different sensitivities to LA.

  • Clinically significant blockade of nociceptive transmission can be achieved without complete sensory or motor blockade.

  • FPBs do not always result in expected patterns of cutaneous sensory blockade.

  • Pain from surgery or trauma originates from cutaneous tissues and deeper tissues, including muscle, connective tissue, and bone.

  • FPBs produce peak plasma lidocaine concentrations in the range associated with therapeutic intravenous lidocaine infusion.

  • Bupivacaine, ropivacaine, and lidocaine have broadly similar mechanisms of action and receptor interactions.

  • The degree to which cadaveric studies of injectate spread correspond to injectate spread and clinical effect in living human subjects.

  • Determinants of LA spread within and beyond fascial planes in individual patients.

  • Determinants of vascular absorption and LA plasma concentration in individual patients.

  • The exact influence of volume, concentration and mass of LA on clinical efficacy of FPBs.

  • The extent to which FPBs block nociception from deeper musculoskeletal tissues.

  • The contribution of motor nerve blockade to analgesia in certain pain syndromes.

  • If equipotent doses of intravenous bupivacaine and ropivacaine have similar systemic analgesic effects to intravenous lidocaine.

  • If the plasma concentrations of bupivacaine and ropivacaine resulting from FPBs are sufficient to produce clinically significant systemic analgesia.

  • The molecular mechanisms of LA action that are directly relevant to the clinical analgesia associated with FPBs and different pain syndromes.

  • The relative contribution of localized and systemic effects of LA to clinical analgesia in FPBs.

  • If LA additives in FPBs consistently improve clinical analgesia and whether this is primarily mediated by a local or systemic effect.

  • FPB, fascial plane block; LA, local anesthetic.