Patients with diseases of the central nervous system (CNS) may require diagnostic, therapeutic as well as a surgical intervention under anesthesia. The pharmacodynamic effects of anesthetic agents are mediated through their action on various proteins in the CNS. These agents may cause long-term neurological sequelae in patients with underlying pathology of CNS. The patients with CNS disorders may have cognitive, sensory, motor, and autonomic deficit that make preoperative assessment difficult and in addition make intraoperative and postoperative care challenging. This chapter highlights salient anesthetic considerations of common CNS disorders.
Avoid dopaminergic drugs like metoclopramide as premedication. Prokinetic agents such as cisapride or domperidone do not interact with dopaminergic receptors and are an acceptable alternative to metoclopramide.
Opioids like alfentanil and fentanyl can cause exacerbation of muscle rigidity, while morphine has a dose-related effect on dyskinesia (dyskinesia decreases at low dose and increases at a higher dose).
Loss of memory and cognitive dysfunction makes the patient disoriented, uncooperative, confused, and at times violent. Besides, the clinical history and examination may remain incomplete, and obtaining consent is difficult.
The dose of intravenous (IV) anesthetics and minimum alveolar concentration (MAC) of inhaled anesthetics should be kept low and titrated to achieve an adequate balance between the anesthetic effect and the harmful effects.
Postoperative cognitive dysfunction (POCD) and delirium are possible consequences of anesthetic agents interacting with acetylcholine receptors (AChRs) to produce inhibition of central cholinergic transmission already impaired by age-related changes.
The burden of epilepsy in the general population ranges from 0.5 to 1.0%. Epilepsy is the paroxysmal, abnormal cerebral electrical discharge associated with a clinical change. It can be either generalized or focal.
All of the commonly used anticonvulsants cause enzyme induction in the liver. This can lead to markedly reduced duration of activity of the aminosteroidal muscle relaxants, particularly those which are excreted via the liver (vecuronium and pancuronium).
The neurological deficit should be evaluated and documented during the preoperative evaluation. The risk of perioperative stroke and exacerbation of neurological deficit should be explained to patients, and consent for the same must be obtained.
On the other hand, local anesthesia or sedation provides smooth hemodynamics and allows intraprocedural clinical neurological evaluation. However, it has
disadvantages like lack of airway protection, continued patient movement, uncontrolled pain and agitation, and prolonged procedure time.
Apart from standard American Society of Anesthesiologists (ASA) monitoring, invasive arterial blood pressure, central venous pressure, urine output, and neuromuscular monitoring on the unaffected side may be required.
Cerebral electrophysiological monitoring and transcranial Doppler (TCD) are restricted to patients at high-risk repeat stroke. Cerebral oximetry is useful to detect ischemia during high-risk cardiac or major vascular surgery and surgeries in the beach chair position.
Avoid hypotension as it can reduce the focal cerebral blood flow and predispose the patient to postoperative stroke. Intraoperative blood pressure should be maintained at baseline or slightly elevated levels.