Regional anesthesia in the head and neck can supplement or serve as the main anesthetic plan for a variety of surgeries. These techniques can also aid in difficult airway management.
Craniotomies provide a unique challenge in that the majority of sensory innervation is present on the scalp, with very little within the cranial vault. As such, the analgesic needs of a craniotomy are often bimodal, markedly elevated at the beginning of and at the end of a case. Scalp blocks reduce the analgesic and sedative requirements by blocking sensation to the heavily innervated scalp. Historically, scalp blocks were commonly used when earlier general anesthetic agents had deleterious perioperative effects. With the advent of safer agents such as propofol, these blocks have been employed less.
In cases that require skull immobilization, a scalp block reduces hemodynamic increases seen with pin application. Although local infiltration by the surgeon can be used as well, a scalp block has a longer duration. This preemptive blockade of a significant pain stimulus provides several benefits. It reduces the cardiovascular lability seen with abrupt stimulation. It also reduces the general anesthetic requirements during the surgery.
Furthermore, there are several types of neurosurgeries (deep brain stimulator, mass resections) that require the patient to be awake and interact with the neurosurgeon, neurologist, and anesthesiologist. The scalp block is especially useful in these patients, as it negates painful stimuli from the pins and allows the patient to wake up in a controlled fashion.
The scalp is innervated by two nerve groups: the trigeminal nerve and the cervical spinal nerves. The trigeminal nerve is responsible for the innervation of the anterior scalp and face. It has three main branches: the ophthalmic (V1), maxillary (V2), and mandibular (V3). V1 splits into the supraorbital and supratrochlear nerves. These two branches innervate the majority of the anterior scalp and forehead. The V2 and V3 components contribute the zygomaticotemporal and auriculotemporal nerves, respectively, innervating the temporal scalp.
The posterior scalp is innervated by the greater occipital nerve and to a lesser extent the lesser occipital nerve. The greater occipital nerve is derived from the posterior ramus of the second cervical nerve root. The lesser occipital nerve is derived from the ventral rami of C1 and C2.
The entire scalp can be blocked by addressing these two nerve groups. In unilateral surgical approaches, the operative side can be favored when depositing local anesthetics. If pinning is required, a bilateral block is preferred.
There are six sites (supraorbital, supratrochlear, auriculotemporal, zygomaticotemporal, and lesser and greater occipital nerves) to block on each side. Local infiltration at so many sites can be painful, and patients often require sedation. The exact level of sedation should be tailored to the patient’s desired ...