In intra-cranial neurosurgery, scalp infiltration aims to prevent systematic and cerebral hemodynamic variations, contemporary of skin incision. The potential morbidity of these hypertension-tachycardia episodes, even in patients profoundly anaesthetized, is secondary in the increase of the cerebral blood flow and in its deleterious consequences on intra-cranial pressure in these compromised patients. Several studies report sometimes different but always convergent results, leaving in the current state of the literature no doubt about the utility of skull block in craniotomy.

innervation of the scalp

The innervation of the scalp is complex, depending on several nerves.

Regional anesthesia of the scalp (skull block or infiltration) allows realizing a local anesthesia of the skin, the subcutaneous tissues and muscles, the external periosteum of the bones of the skull. The internal periosteum and the dura, innervated by nerves satellites of the meningeal vessels, are not blocked by this infiltration. However, they are considered as only little sensitive.

Several algogenic or reflexogenic events should be considered during a craniotomy: insertion of the cranial pins of the Mayfield head holder, incision of the scalp, craniotomy, and dural incision. Regional anesthesia of the scalp aims to blunt the hemodynamic reactions associated with all these events.

Literature

Hillman et al. have first reported the benefits of the scalp infiltration with 20 mL of 0,5 %, bupivacaine, showing heart rate stability and only very little variation in blood pressure during the various stages of craniotomy. Engberg et al. showed that the infiltration of the scalp with 20 mL of 0,25 % bupivacaine assured a relative stability of cerebral DavO2, witnessing the absence of rough variation of cerebral blood flow at the time of incision in patients having benefited from this infiltration of the scalp.
Positioning the 3-point Mayfield head holder, whose pointed pins are inserted through the dermis in the cranial periosteum, usually increases blood pressure.

Three different studies yield the interest of the local anesthesia of the scalp to block or to reduce this hypertensive reaction.

Levin et al. showed the efficiency of local anesthesia of the contact points of the pins of the head holder. Large infiltration of the scalp is more effective than blocking only the 3 pins of the head holder.

In children Hartley et al. showed that the infiltration of the scalp with 0,125 % bupivacaine with epinephrine (1/400.000) can prevent hemodynamic variations associated with incision.

Pinosky et al. reported finally than blocking all the nerve that innervate the scalp, including the greater and the lesser occipital nerves, the supraorbital, the supratrochlear nerve, the zygomaticotemporal nerve, the auriculotemporal nerve and the greater auricular nerves is more effective than local or large infiltrations.

The study of Bloomfield is the only one to moderate these results. He reported significant effects, but suggested these results are moderate and of a limited clinical interest. However, it does not contradict the other studies.

Epinephrine is usually added to local anesthetic solutions. It lowers bleeding at the time of incision and prolongs duration of the local anesthesia. However Phillips et al. reported a 20 % drop in systemic blood pressure in approximately 50 % of the patients when using 0,5 % lidocaine with epinephrine (1/200.000). With volumes as large as 20 mL of 0,125 % or 0,25 %, bupivacaine, blood levels are far from toxicity.

Any craniotomies should benefit from a local anesthesia of the scalp or a skull block. During evacuation of subdural hematoma under local anesthesia, the quality of the block guarantees the feasibility of the intervention.

Performance

The infiltration can be realized by the anaesthetist. However, this infiltration should be better realized by the surgeon, in an already anaesthetized patient, after skin preparation, before drapping (bupivacaine) or just before incision (lidocaine). If a Mayfield head holder is used, infiltration would be realized before its implementation, and would concern the entire scalp.

Even when a head holder is not used, regional anesthesia of the scalp is useful for surgical drainage of a chronic subdural hematoma.

All local anesthetics can be used; 0,25 % bupivacaine with epinephrine (0,125 % in children) is widely used. It allows consequent postoperative analgesia. In case of very long duration surgery, it is possible to perform another infiltration at the time of skin closure, as soon as the dura mater is closed.

There is no report on the use of ropivacaine in this indication. However, with a 0,2 %, concentration, it should be as effective as bupivacaine. Futhermore, its intrinsic vasoconstrictor effect allows to avoid epinephrine. This would be clinically relevant in patients with compromise cerebral hemodynamics, by lowering the risk of systemic hypotension.