38.2.1 Medical History

If a surgical procedure is elective, a thorough pre-anesthesia evaluation is performed. Relevant information should be documented to be able to individualize perioperative anesthetic management. It is important to document the patient’s surgical history, previous anesthetic complications, medications, smoking and alcohol consumption, allergies, and previous blood transfusions. Preoperative laboratory work-up must be done, including a complete blood count, blood chemistry, urinalysis, coagulation profiles, chest X-rays, and an electrocardiogram. An anesthetic induction plan is determined by the clinical evolution of intracranial hypertension, especially if there is headache, projectile vomiting, vestibular disorders, and cranial nerve dysfunction.

38.2.2 Patient Transanesthetic Monitoring

Patient monitoring should be complete and preferably noninvasive with a precordial stethoscope, sphygmomanometer with automatic cycling, continuous electrocardioscope, pulse oximeter, capnography, glucometer, and body temperature monitor. Invasive monitoring such as cannulation of the radial or ulnar artery to measure systemic arterial pressure, a standard central line, a flotation catheter to determine cardiac output with the standard thermodilution method, cannulation of the jugular bulb, or transesophageal echocardiography should only be used in select cases. Cerebral oximetry, EEG, and transcranial Doppler may be used to provide information on blood flow, electrical activity of the brain, and metabolism; these noninvasive methods of monitoring may only be available in highly specialized hospitals and are not absolutely essential for neuroendoscopic procedures. General anesthesia decreases cerebral blood flow (CBF) and cerebral metabolism. Perhaps guided bi-spectral index is the option for noninvasive monitoring of cortico-fronto-temporal electrical activity and muscle relaxation because it is practical, and easily interpreted.7 There has always been doubt about its use in general anesthesia as an indicator of anesthetic depth; the index represents only a global and comprehensive monitoring of the patient undergoing a surgical procedure.

38.2.3 Induction of Anesthesia

Most intravenous drugs for induction of anesthesia do not affect intracranial pressure (ICP). It has always been considered that ketamine increases ICP by raising CBF and cerebral basal metabolism; however, recent reports in the literature, have found that ketamine not only does not increase ICP but it has a favorable effect on ICP 8 because it is an NMDA [N-methyl-D-aspartate] receptor antagonist. Barbiturates, propofol, etomidate, and benzodiazepines are considered to have little effect on ICP, especially if normocapnea is maintained in a patient with adequate ventilation. Pulmonary hyperventilation decreases [partial pressure of carbon dioxide in blood] PaCO₂ levels and consequently causes cerebral vasoconstriction and lowers ICP; however, this does not occur in patients with impaired autoregulation of CBF in a predictable manner. If ICP is elevated, maneuvers are recommended such as placing the patient supine with the head elevated 20º. Whether to administer osmotic or loop diuretics or hypertonic solutions will be determined by the degree of intracranial hypertension. The administration of steroids is indicated in patients with inflammatory processes; for example, neoplasms, infections, or neurocysticercosis. It is advisable to continue steroids pre-, intra-, and postoperatively to avoid adrenal insufficiency syndrome.

38.2.4 Anesthetics

Neither total general intravenous anesthesia, inhalational anesthesia, nor balance anesthesia has proven to be superior in regards to morbidity or mortality in neuroendoscopy. Emphasis should be on maintaining adequate cerebral perfusion pressure (CPP) and adequate intracerebral dynamics in the face of intracerebral pathology. The anesthesiologist should immediately correct any deviation or abnormality in vital signs, heart rhythm, or systemic blood pressure that may arise during the procedure.

Neuroendoscopy in an awake patient, even if intended to be done under local anesthesia with infiltration of the skin and scalp, is not recommended. Incision of the dura mater causes pain, hemodynamic instability, and stress, and patients will not cooperate under these conditions. If sedoanalgesia (dexmedetomidine, short half-life benzodiazepines, opioids, or propofol) is used, it may result in excessive sedation, with hypoventilation and hypoxemia, both dangerous in a patient with elevated ICP. Uncooperative, heavily sedated, or agitated patients may require rapid induction with general anesthesia to be able to control ventilation, improve oxygenation, and maintain end-tidal carbon dioxide (ET_CO2) in normocarbia. But in these circumstances, and with poor pulmonary ventilation, intubation of the trachea is highly difficult in a positioned patient with fixation of the head and covered with surgical drapes. An agitated, hypoxic patient without controlled ventilation, without an endotracheal tube, without neuromuscular relaxation, coughing or straining, with increased intrathoracic or intra-abdominal pressure, with restlessness, and struggling while the dura mater is opened, with elevated intracranial pressure, would cause encephalic tissue exposition and difficulty to control bleeding through the bur hole.

Inhaled anesthetics increase the ICP and are dose dependent: the higher the dose, the greater increase in CBF and ICP. Halotane, enflurane, and metoxiflurane are no longer in use. Isoflurane, once considered the anesthetic of choice 9 for neurosurgical procedures, is no longer the best option. Its administration in experimental models and in humans has been reported to cause neuronal damage and apoptosis; its beneficial effects of preservation of neuronal function, even in flows of 10 ml/100 g of cerebral tissue/min and low brain tissue metabolism, thus conferring brain protection, have not been able to be replicated.10 Inhaled anesthetics, such as sevoflurane 11,12,13 and desflurane,12,13 are recommended because of their low partition coefficients, which are advantageous in the rapid onset and awakening of the patient and are particularly important as to the low metabolic biodegradation suffered in the body. With the overall decline in consumption of inhaled and intravenous anesthetics, balanced general anesthesia is an additionally advantageous hemodynamic stability and ease of titration, according to the characteristics of each patient.

Total intravenous anesthesia is also a good alternative. Opioids (fentanyl, alfentanil, remifentanil, or sufentanil), nondepolarizing muscle relaxants (atracurium, cisatracurium, vecuronium, or rocuronium), and benzodiazepine, propofol, or etomidate offer great hemodynamic stability.

Depolarizing muscle relaxants (succinylcholine) are contraindicated in the presence of intracranial hypertension. Succinylcholine increases ICP. Fasciculations cause gamma afferent stimulation, which increases muscle metabolism and increases CBF.14

Bradycardia is commonly seen during neuroendoscopic procedures, especially when exploring the aqueduct or the entrance to the fourth ventricle, and can lead to asystole. It is interesting to note that this phenomenon is corrected immediately by removing the endoscope from the site, and only in few cases have anticholinergics or β adrenergic stimulants been necessary to control it.

Bradycardia is a sentinel sign that alerts the surgical team as to the area being explored. It is recommended to increase both the volume of the pulse oximeter and ECG monitors so that the surgical team and anesthesiologist may be alerted to the start of bradycardia if it occurs and so may immediately resolve it.

During neuroendoscopy, the irrigating solution should not be placed above a height of 60 cm; the external auditory canal (EAC) can be used as a reference. In the case of intracerebral hemorrhage, if the height of the irrigation solution is above 60 cm or above the EAC, or if the irrigation solution is infused under pressure, no bleeding will be observed and the irrigation solution will enter the intravascular space. The consequences could be volume overload or dilution of coagulation factors. The brain’s ability to accommodate the irrigation solution is very limited, and it is important to monitor inflow to prevent intracranial hypertension, which could lead to Cushing’s phenomenon (rise of ICP, bradypnea, and bradycardia). When there is difficulty in the passage of the irrigation solution, indicated by an increase in intracranial pressure that exceeds 60 cm H₂O, this should be corrected immediately. This can be achieved by facilitating the exit of fluid through the bur hole; it can act as an outflow valve.