Perioperative Care of the Surgical Patient: Brain





Introduction


Cancer of the central nervous system is the 10th leading cause of death in the United States. An estimated 23,820 adults and 3720 children under the age of 15 years will be diagnosed with a primary tumor of the brain or spine in 2019. Primary tumors from the lung, breast, kidney, and bladder, and melanoma, leukemia, and lymphoma frequently metastasize to the brain, creating a secondary tumor. The treatment for both primary and metastatic brain tumors includes chemotherapy, radiation therapy, and surgery.


There are many anesthetic challenges for patients undergoing craniotomy for tumor resection. Depending on the size and location of the tumor, these patients can present with baseline motor or sensory neurologic deficits as well as seizures that may be poorly controlled. Intraoperatively, craniotomy patients require tight blood pressure control and hemodynamic stability to optimize surgical exposure and minimize blood loss. At the conclusion of surgery, a smooth and rapid emergence is desirable to decrease the risk of intracranial hemorrhage and allow for an immediate assessment of the patient’s neurologic status. Postoperatively, judicious use of pain medication must be undertaken to achieve adequate pain control while minimizing associated side effects, which may mask or mimic the signs and symptoms of postoperative surgical complications.


Preoperative Assessment


Preoperative assessment of the patient scheduled for craniotomy should include a complete history and physical examination with meticulous documentation of current neurologic status and evaluation for the presence of elevated intracranial pressure (ICP). Accurate documentation of the patient’s baseline neurologic status serves as a benchmark against which postoperative neurologic status can be measured. A significant number of these patients have neurologic findings, including seizure, vision changes, focal motor or sensory deficits, speech difficulties, balance disturbances, confusion, memory lapses, and headache. Tumors involving the pituitary gland can cause endocrine disturbances including muscle weakness, cold intolerance, excessive sweating, irritability, amenorrhea, sexual dysfunction, polyuria, unintended weight change, hypertension, hyperglycemia, easy bruisability, striae, mood change, moon facies, coarsened facial features, enlargement of hands and feet, and increased body hair. A detailed description of the seizure history, including seizure type, associated symptoms, frequency, most recent occurrence, medications tried, successful medications, and recently taken antiepileptics prepares clinicians to diagnose and treat perioperative seizures. Unilateral pupillary dilatation, double or blurred vision, photophobia, oculomotor or abducens palsy, headache, altered mental status, nausea or vomiting, or papilledema on fundoscopic examination should raise concerns for elevated ICP. Patients with severely elevated ICP can present with somnolence and irregular respiration. The appearance of Cushing’s triad consisting of systemic hypertension, bradycardia, and irregular respiration heralds impending brain herniation and death ( Fig. 19.1 , Table 19.1 ). Nausea and, less frequently, vomiting are common in patients with brain tumors, and many patients are on antiemetics during the preoperative period. Multimodal prophylaxis for postoperative nausea and vomiting (PONV; described later) is indicated for all patients undergoing a craniotomy, as the procedure itself is associated with a high incidence of PONV even if preprocedure symptoms are not present.




Fig. 19.1


Relationship between intracranial pressure (ICP) and intracranial volume. Stages of ICP and intracranial volume changes: (1) The initial stage (stage 1) is characterized by high compliance and low ICP, wherein an increase in volume does not affect ICP. (2) The transition stage (stage 2) is characterized by low compliance and low ICP, wherein an increase in volume translates to a modest increase in ICP. (3) The ascending stage (stage 3) is characterized by a low compliance and high ICP, wherein a slight change in volume results in a significant increase in ICP.


Table 19.1

Signs and Symptoms of Elevated Intracranial Pressure













General Tentorial Herniation (Lateral) Tentorial Herniation (Central) Tonsillar Herniation
Headache
Vomiting
Visual disturbances
Diplopia
Cushing’s triad:
Increased systolic pressure
Widened pulse pressure
Bradycardia
Irregular breathing
Depressed consciousness
Third nerve palsy
False localizing
Ipsilateral hemiparesis
(Kernohan’s notch)
Depressed consciousness
Homonymous hemianopia
Upward gaze palsy
Deteriorating level of consciousness
Diabetes insipidus
Neck stiffness
Elevated blood pressure
Slowed pulse rate
Transient losses of vision
Retinal venous pulsation
Papilledema
Unilateral pupillary dilatation
Kernohans’s notch syndrome


Previous cancer diagnoses and treatments, including surgery, chemotherapy, and radiation therapy, are important details of the patient’s history. For patients with a primary brain tumor, a prior craniotomy, especially if recent, may make a scalp block (discussed later) unwise. If the brain tumor is metastatic from a melanoma or renal cell primary, blood loss during craniotomy can be significantly higher. Radiation to the neck can create fibrosis and scarring of the soft tissues, making both mask ventilation and direct laryngoscopy extremely difficult or impossible. Radiation to the chest can impair both cardiac and pulmonary function. Chemotherapy agents can affect cardiac, pulmonary, hematopoietic, renal, and hepatic functions. A thorough understanding of the impact of each patient’s prior chemotherapy regimen on organ function is imperative. Patients frequently use antiepileptics, antiemetics, steroids, and hypoglycemic agents. Antiepileptics should, at a minimum, be continued in the perioperative period, and often an additional dose is administered in the early intraoperative period. A multimodal prophylactic approach to PONV is advised and often includes agents from at least three different drug classes: steroids, 5-HT 3 receptor antagonists, NK-1 receptor antagonists, antihistamines, phenothiazines, and 5-HT 4 receptor agonists. The most common combination used at our institution is a steroid, a 5-HT 3 receptor antagonist, and an NK-1 receptor antagonist. Hyperglycemia secondary to steroid administration and preexisting diabetes is common and should be managed in a systematic manner using an insulin sliding scale with either subcutaneous administration or intravenous infusion of insulin. NK-1 inhibitors interfere with birth control, and alternative means of contraception are advised for 30 days following the last dose of a medication from this drug class.


The mass effect from the brain tumor and the surrounding edema is best quantified with a computed tomography (CT) scan or magnetic resonance imaging (MRI). Findings of flattened gyri, narrowed sulci, or compression of the intracranial ventricles indicate elevated ICP. Preexisting anemia (from chemotherapy) and hyperglycemia (from steroid use) are common laboratory findings. We obtain blood typing and an antibody screen on all craniotomy patients and adhere to a protocol for perioperative glucose management, with treatment indicated for glucose above 180 mg/dL.


Intraoperative Planning


When formulating an intraoperative plan of care, the anesthesiologist should consider the tumor location, surgical positioning, neuromonitoring plans, and bleeding risk. Tumors are classified as either supratentorial or infratentorial, depending on whether they lie above or below the tentorium cerebelli, respectively. In adults primary supratentorial tumors predominate and may involve eloquent areas of the brain responsible for speech generation and comprehension, or motor function. By contrast, infratentorial tumors are more common in pediatric patients and may involve the cerebellum, fourth ventricle, cerebellopontine angle, and brainstem. Due to their locations, supratentorial and infratentorial tumors may present differently.


Positioning surgical patients is often a compromise between optimal surgical exposure and what can actually be physiologically tolerated by the patient. Most craniotomies are performed with the patient in the supine, lateral, or prone positions, with the patient’s head elevated by 10–30 degrees. The semisitting or semi-Fowler’s position can offer an advantageous surgical exposure for posterior fossa tumors, although the risk of vascular air embolism (VAE) is increased. The risk of VAE and a treatment plan should be discussed with the surgeon for every patient undergoing craniotomy. Transesophageal echocardiography is the most sensitive method for detection of VAE, but it is rarely employed in craniotomies because of its expense and invasiveness, and the need for special expertise in interpreting images. Precordial Doppler is the most sensitive noninvasive method for detecting VAE and can be placed on the 2nd, 3rd, or 4th intercostal space to the right or left of the sternum, or between the right scapula and spine in prone patients. Other methods of VAE detection that are considered to be highly sensitive include a pulmonary artery catheter and transcranial Doppler, neither of which is routinely used during craniotomies. Treatment for VAE should be readily available during every craniotomy and includes bone wax to seal air entry sites at the cut bone surfaces, normal saline to flood the surgical field, the ability to place the patient in the Trendelenburg position, the application of positive end-expiratory pressure, and manual compression of the jugular veins. Special attention must be paid to the protection of the eyes from both the preoperative skin preparation solution and inadvertent pressure from personnel and equipment. Liberal application of sterile eye ointment followed by eye pads and an occlusive, waterproof cover provides corneal protection, and provider vigilance is necessary to prevent pressure injury to the eyes.


Intraoperative neuromonitoring modalities include somatosensory evoked potentials (SSEPs), motor evoked potentials (MEPs), electroencephalography (EEG), electromyography (EMG), auditory brainstem response (ABR), Hoffmann’s reflex testing (H-reflex), and cranial nerve testing, most commonly the facial nerve (CNVII). The selection of which modalities to use is determined by the neurologic pathways at risk of injury during surgery. A detailed description of neuromonitoring modalities is beyond the scope of this chapter. SSEPs and MEPs are the most common neuromonitoring modalities used during craniotomies. SSEPs monitor the integrity of the sensory pathways from the periphery to the brain by measuring both the speed and amplitude of electrical signals traveling from a peripheral sensory nerve through the dorsal root ganglia, along the posterior column of the spinal cord to the brain. MEPs monitor the integrity of the motor pathways from the brain to the periphery by measuring both the speed and amplitude of electrical signals traveling from the motor cortex through the corticospinal tracts through the anterior horn to the peripheral muscle. Both SSEPs and MEPS are commonly used in posterior spine surgery, supratentorial craniotomies, neurovascular surgery, and skull base surgery.


General Anesthesia for Asleep Craniotomy


Inhalational anesthetics and intravenous agents may be used alone or in combination to provide general endotracheal anesthesia for craniotomy surgery. Although the use of inhalational agents alone offers a simple anesthetic approach, may minimize the risk of side effects from polypharmacy, and provide a reliable measure of anesthetic depth, inhalational agents can adversely affect central nervous system physiology. All volatile anesthetics to varying degrees increase cerebral blood flow (CBF), decrease cerebral metabolic rate (CMR), and inhibit or even abolish cerebral autoregulation. Cerebral vasodilation that results from the uncoupling of CBF from CMR can increase ICP in the closed cranium or compromise surgical exposure in an open cranium. While the vasodilatory and ICP effects can be mitigated or even reversed with hypocapnia in a normal brain, eliminating this response may not be possible when intracranial pathology is present. , Volatile anesthetics also adversely affect intraoperative neuromonitoring of SSEPs, visual evoked potentials (VEPs), and MEPs by increasing cortical latency and decreasing cortical amplitude in a dose-dependent manner. However, volatiles have minimal effects on brainstem potentials, and thus the use of inhalational agents during brainstem monitoring is acceptable.


Total intravenous anesthesia (TIVA) may be clinically indicated for specific craniotomy cases. Given the extreme sensitivity of MEPs to volatile anesthetics, TIVA should be used when neuromonitoring involves MEPs. Additionally, when elevated ICP is of particular concern, TIVA is preferred because inhalational agents can adversely affect ICP. Although ICP may not be an issue in an open cranium, the vasodilatory effects of volatile anesthetics may compromise surgical exposure; therefore if the surgical field is suboptimal, TIVA should be considered.


A combined technique that utilizes both inhalational and intravenous anesthetics offers significant advantages. Although the vasodilatory effects of volatile anesthetics can adversely affect ICP, surgical exposure, and neuromonitoring signals, these effects are usually dose-dependent. For most craniotomy cases, the use of volatile anesthetics at doses of 0.5 MAC or less supplemented with intravenous anesthetics may be acceptable.


Intravenous anesthetics and adjuncts have advantages and disadvantages when used in craniotomy. Propofol is the most commonly used intravenous anesthetic in the setting of a combined general anesthetic technique and is the primary anesthetic for TIVA. Unlike volatile anesthetics, propofol decreases both CBF and CMR without inducing cerebral vasodilation; the result is overall ICP reduction. However, propofol may lower mean arterial pressure (MAP), potentially compromising cerebral perfusion pressure (CPP) and increasing the risk of ischemic injury during craniotomy. Studies have shown that propofol anesthesia, regardless of dose, causes lower jugular bulb oxygen saturation when compared to sevoflurane-nitrous oxide or isoflurane-nitrous oxide anesthesia. Improper titration of propofol intraoperatively may contribute to prolonged emergence and postoperative sedation.


Intravenous opioid infusions are commonly used during craniotomy. While administration of opioids provides intraoperative and postoperative analgesia that may facilitate a smooth emergence, their use can delay wake-up, contribute to postoperative sedation, and interfere with an accurate and timely neurologic assessment. To avoid these side effects of longer-acting opioids, remifentanil, an ultrashort-acting opioid, is advantageous for use during craniotomy. Remifentanil does not provide any postoperative analgesia and may cause postoperative rebound hyperalgesia. According to a literature review that included 21 studies assessing intraoperative remifentanil use and acute or chronic postoperative pain, less than half of the studies found a higher postoperative analgesic requirement in patients who received remifentanil, and only four studies showed a potential association between remifentanil and chronic pain. Remifentanil use with volatile agents was associated with increased pain levels postoperatively compared to its use with TIVA or in a combined inhalation and intravenous technique. The incidence of hyperalgesia with intraoperative remifentanil use may be a function of dose, with higher infusion rates and cumulative doses posing a greater risk.


Lidocaine infusions have been shown to be beneficial in enhanced recovery protocols as adjunct medications. Lidocaine is potentially neuroprotective since it prevents sodium influx, which is the first step in the ischemic cascade, and blocks specific apoptotic cell death pathways to reduce postnecrotic injury. However, local anesthetic toxicity that can induce seizures is a potential risk, while the sedative effects of lidocaine may delay emergence and hinder rapid neurologic assessment postoperatively.


Dexmedetomidine is a selective α 2 -adrenergic agonist with anesthetic and analgesic properties. Dexmedetomidine-induced sedation results from indirect upregulation of gamma-aminobutyric acid (GABA) activity in the central nervous system through decreased noradrenergic neuron activity, while its pain-relieving properties are a result of its effects at the spinal cord level and supraspinal sites. Unlike most other sedatives and opioids, dexmedetomidine does not cause respiratory depression. It also does not reduce the latency or amplitude of the intraoperative neuromonitoring signals. Given these advantages and the synergistic effect of dexmedetomidine with various anesthetics, dexmedetomidine may be used as an adjuvant to standard general anesthesia, thereby decreasing the dose requirements of other anesthetics and analgesics that adversely affect intraoperative neuromonitoring. The side effects of dexmedetomidine include hypotension and bradycardia; therefore its use may not be appropriate in patients with significant cardiac disease or hemodynamic compromise.


Ketamine is an N -methyl-d-aspartate (NMDA) antagonist that is effective in reducing pain both intraoperatively and postoperatively. For craniotomy utilizing neuromonitoring, ketamine enhances SSEPs by increasing the amplitude, but not latency, of these recordings while minimally affecting MEPs. Because ketamine also activates certain cortical areas of the brain, the frequency on EEG is increased, resulting in a higher reading on Bispectral Index (BIS) monitoring. This cerebral stimulatory effect activates subcortical seizure activity in patients with seizure disorders. Furthermore, ketamine increases CBF and CMR, thereby negatively impacting ICP and potentially compromising the surgical exposure. For these reasons, ketamine should be avoided in patients with uncontrolled seizures or elevated ICP. Although ketamine can have psychogenic side effects, the use of subanesthetic doses will mitigate this risk while still providing effective postoperative analgesia. ,


Awake Craniotomy


Introduction


Tumor resection is a balance between extensive tumor removal and the preservation of brain function. The use of preoperative functional MRI, neuronavigation, fluorescent dyes, intraoperative magnetic resonance imaging (iMRI), and intraoperative stimulation mapping (ISM) helps delineate tumors from the functional brain. In awake craniotomy, the patient participates in ISM and neuropsychologic testing during tumor resection. Some centers use both iMRI and ISM to improve resection and minimize functional impairment.


Indications


The awake technique is the gold standard for tumor resection near “eloquent areas” of the brain. , “Eloquent areas” of the brain if injured lead to motor, sensory, vision, hearing, speech, or language processing deficits. Anatomically, “eloquent areas” of the brain include the primary motor cortex (precentral gyrus), primary sensory cortex (postcentral gyrus), primary visual cortex, primary auditory cortex, left posterior inferior frontal gyrus (Broca’s area), and left posterior superior temporal gyrus (Wernicke’s area). Tumors in or near the primary motor cortex, primary sensory cortex, or speech areas are often resected under awake conditions. Tumor location is the primary driver for choosing an awake craniotomy technique. During the awake portion of the craniotomy, patient participation in neurocognitive testing assists the surgeon in identifying functional areas of the brain, facilitating a more complete resection of the tumor while preserving brain function. A meta-analysis of 90 published reports of glioma resection with and without ISM concluded that glioma resections using ISM are associated with fewer late severe neurologic deficits and more extensive resection, and they involve eloquent locations more frequently.


Preoperative assessment by an anesthesiologist should occur at least 1 day prior to the planned surgery. A thorough preoperative evaluation and discussion between the anesthesiologist assigned to the case and the patient is strongly recommended to build rapport and trust, document preexisting neurologic deficits, prepare the patient for the surgical events, and appropriately set patient expectations. The discussion must include expected intraoperative body positioning, the possibility of unpleasant sensations (e.g., hip or shoulder pain, dry mouth, headache during resection, nausea, unfamiliar noises from surgical equipment), the tunnel-like view the patient will have due to surgical draping, strategies used to keep the patient as comfortable as possible, and the possibility that an awake technique may be abandoned if safety becomes compromised. The anesthesiologist must assess patient motivation, temperament, ability to cooperate and communicate, and preexisting comorbidities when considering the awake technique. Patients who are claustrophobic, severely anxious, or diagnosed with a psychiatric illness may not be able to stay calm and cooperate during the awake portion of the case. Patients with substantial speech impairment or expressive aphasia may not have a consistent baseline during preoperative testing, making intraoperative testing less reliable. A patient with a difficult airway or sleep apnea poses significant challenges for adequate oxygenation and ventilation.


Techniques


There are two well-described anesthetic techniques for awake craniotomy: asleep-awake-asleep and monitored anesthesia care. The primary differences between the two techniques involve anesthetic management prior to the intraoperative neuropsychologic testing. The asleep-awake-asleep technique includes induction of anesthesia, placement of a supraglottic airway, controlled ventilation during craniectomy and dural opening, awakening, and removal of the supraglottic airway followed by neuropsychologic testing. The advantages of the asleep-awake-asleep technique include a rest period for the patient prior to awake testing and tumor resection, control of ventilation to avoid hypoventilation and brain swelling, and reliable pain control during surgical opening. The monitored anesthesia care technique includes minimal sedation prior to surgical opening with the advantage of avoiding an abrupt, potentially tumultuous transition from fully anesthetized to fully awake. The MAC technique by definition includes spontaneous ventilation, which can lead to hypoventilation, increased CBF, and brain swelling. A third technique, the awake-awake-awake technique, relies on medical hypnosis to avoid all sedation.


Premedications


The choice of premedications should focus on preventing nausea, decreasing the risk of aspiration, and providing analgesia. A common regimen includes oral acetaminophen and aprepitant, and intravenous famotidine. Although transdermal scopolamine is an effective antiemetic, the side effects of mydriasis, blurred vision, and dry mouth are not well suited for patients undergoing awake craniotomy. We avoid administering benzodiazepines to decrease the likelihood of delayed awakening and delirium. However, if the monitored anesthesia care technique is planned, midazolam is commonly administered.


Preinduction


Awake positioning is critical for the success of awake craniotomy. Surgeons should place the patient in the position required for surgery. Significant effort is required to ensure maximum patient comfort in the surgical position prior to induction. Specific areas of concern include the position of the head, neck, and dependent shoulder and hip. The use of Mayfield pins, a three-pin head fixation system, is very common. Although rigid head fixation occurs after induction, the anticipated surgical position of the head and neck should be mimicked during preinduction positioning. Although head position is primarily determined by the required surgical exposure, the patient’s gaze direction must allow for participation in neuropsychologic testing. The neck position must allow for effective mask ventilation, insertion of a supraglottic airway, and airway rescue with a video-assisted bronchoscope. Reducing the pressure on the dependent shoulder and hip improves patient comfort, tolerance, and participation in testing. We use a combination of gel rolls, pillows, and foam padding to place the patient in a comfortable “sloppy lateral” position.


Induction


For the asleep-awake-asleep technique, intravenous induction with fentanyl 0.5–1 µg/kg, lidocaine 1.5 mg/kg, and propofol 1.5–2 mg/kg is standard. Following successful mask ventilation with the head and neck in the surgical position, rocuronium 0.6 mg/kg can be administered but this is not mandatory. Soon after induction, infusion of propofol 25–100 µg/kg/min and remifentanil 0.01–0.1 µg/kg/min are started. For younger or more anxious patients, the addition of dexmedetomidine 0.1–0.5 µg/kg/h is useful. Volatile anesthetic can be used if the end-tidal concentration is kept under 0.5 MAC. A supraglottic airway with a port for a gastric tube is placed, and the ability to provide adequate minute ventilation is verified. The inability to maintain an adequate seal or to provide tidal volumes of 4–6 mL/kg at peak inspiratory pressure <20 cmH 2 O indicates a poor fit or malposition of the supraglottic airway and will lead to hypoventilation. This problem must be addressed before proceeding with the surgery. The gastric tube should be advanced to a depth indicative of intragastric placement. If oral premedications have been administered, suctioning of the gastric tube is delayed until just before waking up. Following placement of the supraglottic airway, the eyes should be protected with tape to ensure complete closure. An eye lubricant is not used to preserve the clear vision needed for ISM.


For the monitored anesthesia care technique, sedation is initiated with infusions of remifentanil 0.01–0.1 µg/kg/min and either propofol 25–100 µg/kg/min or dexmedetomidine 0.1–0.5 µg/kg/h. The patient’s nose can be sprayed with lidocaine and a soft nasal trumpet coated with viscous lidocaine inserted into the most patent nostril. Supplemental oxygen is supplied by attaching the anesthesia circuit to the nasal trumpet.


Regardless of the anesthetic technique, a bilateral scalp block is performed and includes injection of ropivacaine 0.5% with epinephrine 1:200,000 at the supratrochlear, supraorbital, zygomaticotemporal, auriculotemporal, lesser occipital, and greater occipital nerves. A scalp block provides analgesia for both Mayfield pin placement and skin incision. Many surgeons inject additional local anesthetics with epinephrine along the planned incision site.


Head Fixation


The three-pin Mayfield head fixation system is widely used in craniotomies. Shen et al. describe an awake craniotomy protocol used at Stoney Brook that eliminates the need for rigid head fixation using a frameless Brainlab skull-mounted array for stereotactic navigation. The authors describe the use of a soft foam pillow instead of rigid fixation and improved patient comfort and easier access to the airway for the anesthesiologist as advantages.


Access and Monitoring


A second peripheral intravenous line, an arterial catheter, a Foley catheter, and, if available, a BIS monitor should be placed. The intravenous lines and arterial catheter should be placed on the arm ipsilateral to the surgery so that sensory and motor testing on the contralateral side are unimpeded by invasive lines.


Intraoperative Management


Following line and catheter placement, surgeons use neuronavigation, and the patient is prepped and draped. The surgical drapes must be secured in a way that allows a clear visual connection between the patient’s eyes and the anesthesiologist and neuropsychologic testing team. The use of surgical drapes containing clear panels allows room light to illuminate the patient’s face. A small microphone is secured close to the patient’s mouth to facilitate patient-to-surgeon communication.


After the dura is opened, the surgeon will request that the patient be awoken. Intravenous ondansetron should be administered, and a dose of intravenous acetaminophen can be considered. The anesthesiologist discontinues all anesthetic infusions and volatile agents. If a BIS monitor is being used, the anesthesiologist can use the BIS as a rough guide for when the patient is nearing an awake state. If rocuronium has been administered, the response to a train of four should be measured. Reversal of muscle relaxant is indicated if the response is anything less than 4/4 without fade. The patient can be placed on pressure support to elicit spontaneous respiration. The anesthesiologist is positioned in direct line of sight with the patient and should firmly hold each of the patient’s hands. The anesthesiologist should begin talking to the patient well before there is objective evidence of the awakened state. Use of a reassuring, repetitive phrase to the patient helps to orient the patient as to where they are for example, “You are in the operating room. Surgery is going well. Don’t move. Stay very still. It is time to wake up, just like we talked about. Open your eyes. Squeeze my hands.” When the patient is breathing spontaneously with adequate minute ventilation and following commands, the supraglottic airway can be removed. Typically, patients take an additional 5–10 min after airway removal to be able to participate in testing. During this time period, blood pressure often rises and requires treatment to maintain a systolic blood pressure (SBP) of <140 mmHg. Patients may report discomfort that should be promptly addressed with minor repositioning, massage, or a low-dose infusion of remifentanil. Anxiety can be alleviated in most cases with a low-dose infusion of dexmedetomidine. Small ice chips are immensely helpful in treating dry mouth, and patients are grateful for the “treat.” When the patient is fully awake, testing can begin and may include object naming, sentence completion, action naming, simple math problems, motor tasks, and sensory identification. We have a neuropsychology team in the operating room to conduct the testing. The advantages of having such a team include quantifiable measurement, precise identification of deficit (e.g., syntax error versus hesitancy versus speech arrest), potentially shorter surgical times, and more frequent gross total resection. , Additionally, when a neuropsychology team conducts intraoperative testing the anesthesia team can focus on the physical and mental well being of the patient. As the awake time period extends, patients often become fatigued and increasingly notice the discomfort of positioning. The challenges for the patient in enduring through a long awake period cannot be overstated. Throughout the awake period, the anesthesiologist attends to the patient’s needs, provides reassurance, addresses pain issues, and communicates with the surgical team regarding the patient’s ability to continue in the awake state. At the completion of the resection, the surgeon will inform the anesthesiologist that the patient may “go back to sleep.” The anesthesiologist may decide to induce general anesthesia, reinsert the supraglottic airway, and resume controlled ventilation. Alternatively, the anesthesiologist may decide to sedate the patient and allow spontaneous respiration without an airway throughout the closing period. Factors influencing the anesthesiologist’s decision include the adequacy of the patient’s natural airway, hemodynamic status, anticipated length of closure, and need for additional intraoperative imaging.


Intraoperative Challenges


The intraoperative management plan must consider several common events. Intraoperative seizure is an emergency situation during awake craniotomy and must be managed immediately. Seizures increase cerebral oxygen demand and can cause uncontrolled movement, leading to patient injury. Uncontrolled movement of the head from a seizure can lead to scalp laceration at the pin sites or dislodgement of the head from the head fixation. Ice cold saline placed on the brain by the surgeon during seizures often stops the activity. If this intervention is unsuccessful, propofol is often effective; however, propofol depresses respiration and can lead to patient apnea. Mask ventilation or emergency placement of a supraglottic airway may be necessary; hence positioning is important at the beginning of the case to enable mask ventilation of the patient in the surgical position.


Most patients undergoing awake craniotomy have some level of anxiety, and some patients, upon awakening, develop severe anxiety and simply cannot tolerate the demands of the situation. Low-dose dexmedetomidine can be immensely effective in controlling anxiety. If this intervention fails, and the patient’s anxiety makes useful testing nearly impossible, the patient should be returned to an anesthetized state. This scenario should be discussed with every patient scheduled for awake craniotomy.


Many centers use iMRI in combination with the awake craniotomy technique. The use of iMRI usually includes a preincision iMRI, mapping and resection under awake conditions, postresection iMRI with contrast, additional resection if needed, and closure. The use of iMRI precludes the use of a BIS monitor or Foley catheter containing a temperature probe. iMRI following initial resection can be performed with the patient sedated and spontaneously breathing without an artificial airway or after insertion of a supraglottic airway. The significant distance between the anesthesia team and the patient undergoing the iMRI can create a tenuous situation if the patient is sedated without a supraglottic airway. Airway obstruction, respiratory depression, and inadequate sedation leading to movement or anxiety can create a dangerous situation for the patient, and we routinely reinsert the laryngeal mask airway (LMA) and control ventilation for the postresection iMRI.


Intraoperative Considerations and Management


Induction of anesthesia should focus on adequate mask ventilation to avoid hypercarbia and oxygen desaturation. Induction medications should be titrated to avoid large variations in blood pressure during intubation, which can adversely affect ICP and CPP. Succinylcholine has the potential to increase ICP and is best avoided, if possible, in patients undergoing craniotomy. However, if succinylcholine is clinically indicated, pretreatment with a defasciculating dose of a nondepolarizing muscle relaxant blunts the ICP effect.


Vascular Access and Monitoring


Vascular access for patients undergoing craniotomy is dictated by the anticipated blood loss. For the majority of cases, it is sufficient to have two intravenous (IV) lines, preferably with one being a large-bore IV line. If the semisitting position is planned, blood loss is expected to be significant or peripheral access is difficult or impossible, placement of a central venous catheter (CVC) should be strongly considered. Otherwise, a CVC is not necessary. If a CVC is needed, placement in the subclavian vein is preferred over either the internal jugular or femoral veins due to the potential for compromised cerebral venous drainage and infection, respectively.


For intraoperative monitoring, beat-to-beat blood pressure measurements using an arterial line are routine. An arterial line also provides ease of access to blood samples when intraoperative and postoperative laboratory studies are needed. Craniotomy patients benefit from meticulous blood pressure control and hemodynamic stability to minimize fluctuations in CBF that may contribute to changes in ICP or cerebral ischemia. Therefore avoidance of both hypotension and hypertension is important. Arterial hypotension, defined as SBP less than 90 mmHg or MAP less than 70 mmHg, may decrease cerebral perfusion and increase the risk of intracranial ischemic injury. Consequences of arterial hypertension, defined as SBP greater than 140 mmHg or MAP greater than 110 mmHg, include risk of surgical bleeding and increased CBF that may contribute to brain tissue swelling. In treating aberrant blood pressure, consider using vasopressors or antihypertensive medications that are short acting, since surgical stimulation may vary widely during craniotomy. Generally, noxious stimuli are more prevalent during skin incision and closure, bone flap removal and replacement, and dural opening and closure than during the time of tumor resection when stimulation is usually minimal. However, if tumor resection involves areas adjacent to intracranial blood vessels or the dura, elevations in blood pressure and heart rate may occur. Given this dynamic surgical environment, short-acting agents allow the provider to adjust the treatment administered to meet the patient’s ever-changing needs. Rhythm disturbances may occur during craniotomy, which warrants vigilant monitoring. Most notably, asystole and bradycardia resulting from surgically induced vagus nerve stimulation or trigeminal cardiac reflex during craniotomy have been reported in the literature; treatment is with cessation of the stimulus. If local anesthetics are used, toxicity may occur that could induce both rhythm disturbances and hemodynamic instability. The treatment for local anesthetic toxicity is administration of intralipid and supportive care until the baseline cardiac rhythm and blood pressure are restored.


Measuring the depth of anesthesia using noninvasive tools such as the BIS brain monitor system should be considered when TIVA is used. However, care must be taken to avoid encroaching on the surgical field when placing the BIS electrode sensor on the patient’s forehead.


Hyperthermia in the setting of an impaired brain or one at increased risk of injury is associated with poor outcome and higher mortality. Additionally, hyperthermia, regardless of severity or duration, can cause both neurologic and cognitive impairment that may persist even after normothermia is established. Mechanistically, hyperthermia negatively impacts the cell structure and function of neurons and can exacerbate neuronal injury resulting from other processes such as ischemia. , Intraoperative hyperthermia usually results from aggressive patient warming and thus can be avoided by carefully monitoring core temperature and discontinuing active warming and/or removing excessive blankets and drapes when indicated. Ideally, core body temperature for patients undergoing craniotomy should be maintained between 36°C and 37°C.


Head Pinning and Surgical Positioning


A scalp block (discussed later) or infiltration of the pin sites with local anesthetic can dramatically decrease the hemodynamic response to placement of the head fixation pins. If the use of a local anesthetic adjuvant is not possible, pretreatment with propofol, an opioid, nicardipine, and/or esmolol should be administered to control the blood pressure and heart rate during the placement of head pins. Regardless of the drug class used to control the response to the head pins, short-acting agents provide adequate depth without the risk of prolonged hypotension.


Surgical positioning concerns specific to craniotomy include head positioning to optimize surgical exposure and use of the semisitting position. For craniotomy patients positioned horizontally, either supine or in the lateral position, head rotation should be limited to avoid compromising the patient’s airway or impeding cerebral venous drainage. As discussed above, the semisitting position is used for surgeries involving tumors in the posterior fossa and cervical region. In addition to providing the neurosurgeon better access to these tumors, the semisitting position facilitates cerebral venous and cerebral spinal fluid (CSF) drainage; consequently, surgical exposure is improved, especially for deeper structures. Anesthetic advantages of the semisitting position include better access to the patient’s airway, better access for neuromonitoring, and in the case of a cardiopulmonary event easier access to perform chest compressions. The primary risks of the semisitting position are intraoperative VAE, paradoxical air embolism, and hypotension.


The most vulnerable time for VAE occurrence is from skin incision to dural opening. From a surgical standpoint, preventative measures for VAE include applying bone wax along the borders of the intact bone when the bone flap is removed, intermittently irrigating the surgical field, and avoiding dural retraction. Signs of VAE include a millwheel murmur from the Doppler, decline in end-tidal carbon dioxide, and potentially a decline in blood pressure. If VAE is suspected, the immediate goals are prevention of further entrainment of air, identification of the source of the air, maintenance of hemodynamic stability, and repair of open vessels. Placing the patient’s bed into the steep Trendelenburg position, initiating positive end-expiratory pressure, and manually compressing the jugular veins increase intracranial venous pressure and prevent the ongoing aspiration of air. If present, the CVC should be used to aspirate any air bubbles that may be present. If hemodynamic compromise occurs, supportive care with fluids and positive inotropic agents should be employed.


Brain Relaxation and Optimizing Surgical Exposure


Intraoperative brain relaxation, defined as the volume of brain tissue relative to the intracranial space in an open cranium, is an important determinant of surgical exposure and overall operating conditions. A variety of strategies may be employed to achieve brain relaxation, a state in which the intracranial tissue is soft, lacks swelling, and the ratio of tissue content to cranial volume is optimized. These strategies include hyperventilation, administration of a hyperosmolar treatment along with judicious use of fluids, placing the patient in the reverse Trendelenburg position, administration of a steroid, and minimizing or eliminating the use of volatile anesthetics.


Hyperventilation results in hypocapnia-induced cerebral vasoconstriction, which decreases cerebral blood volume (CBV) and helps to curtail tissue swelling. Because the reduction in CBV is associated with reduced CBF, the risk of ischemia-induced brain injury may be increased with hyperventilation. Current recommendations are to use hyperventilation only when there is a clinical indication and only as a temporizing measure when brain swelling is present. , Other side effects of hyperventilation include respiratory alkalosis and potential hypokalemia. Therefore, in the setting of hyperventilation, arterial blood gas (ABG) tests should be performed periodically to monitor the partial pressure of carbon dioxide (Pco 2 ), pH, and potassium level. If utilizing hyperventilation, the lowest recommended arterial Pco 2 value to target is 30 mmHg; below this threshold, the risks of hyperventilation may outweigh its benefits.


Administration of a hyperosmolar fluid, such as mannitol or hypertonic saline, also aids in brain relaxation. Hyperosmolar agents create an osmotic gradient that displaces free water from brain tissue to the intravascular space, effectively reducing brain tissue edema. However, in the setting of intracranial hypertension, hyperosmolar therapy may cause normal tissue to contract and exacerbate any midline shift or herniation. Risks specifically associated with the use of mannitol include severe diuresis, renal dysfunction, electrolyte disturbances, and transient changes in preload, afterload, and cardiac output. Fortunately, these side effects are self-limiting in patients with preserved cardiac and renal function. If there is a disruption in the blood-brain barrier, mannitol may worsen cerebral edema and thus should be avoided in these patients. Potential adverse effects of hypertonic saline include hypernatremia, hypokalemia, central pontine myelinolysis, and pulmonary edema. , , In addition to utilizing hyperosmolar treatments, limiting the use of hypotonic fluids can help minimize brain swelling. Although furosemide has traditionally been used to facilitate brain relaxation, recent studies have not demonstrated its efficacy in reducing cerebral edema either alone or in conjunction with hyperosmolar fluids. ,


When feasible, placing the patient in reverse Trendelenburg position can facilitate brain relaxation. In this head-up tilt position, the effect of gravity will translocate cerebral spinal fluid from the intracranial space to the extracranial subarachnoid space and enhance cerebral venous drainage to effectively reduce CBV; as a result, the intracranial tissue volume will be reduced. The risks associated with reverse Trendelenburg include systemic hypotension, cerebral hypoperfusion, VAE, and pneumocephalus. , , Limiting the head-up tilt position to 30 degrees or less can reduce ICP and minimize cerebral edema without affecting brain perfusion. , ,


Administration of glucocorticoids in patients undergoing intracranial tumor resection has become a standard practice to reduce vasogenic edema from tumor-associated disruption of the blood-brain barrier, primarily affecting the white matter. Although the exact mechanism is not known, the effectiveness of glucocorticoids in facilitating brain relaxation is well established. The risks of steroid treatment include hyperglycemia and potential immunosuppression that may negatively impact the patient’s postoperative outcome and cancer prognosis. , ,


As discussed above, TIVA, consisting primarily of propofol, reduces ICP through its effect on CBF and CBV compared to volatile anesthetics. This reduction in ICP may translate to improved brain relaxation in the open cranium during craniotomy. Despite the generally accepted premise that TIVA has favorable effects on brain swelling, findings from clinical studies on anesthetic techniques and brain relaxation have not demonstrated a distinct advantage of one anesthetic agent over any other. , Because inhalational anesthetics have a dose-dependent effect on cerebral vasodilation, intravenous anesthetics may confer benefit as an adjunct to limit the dose of the volatile agent to <0.5 MAC.


Emergence From Anesthesia


Emergence from anesthesia is a critical period in which there is a greater chance of intracranial hemorrhage. To reduce this risk, meticulous blood pressure control is crucial, since both hypertension and tachycardia usually occur as the patient awakens. Although these hemodynamic derangements may be brief in duration, they are often severe enough to necessitate treatment. Incremental doses of a short-acting antihypertensive and beta blockers, such as nicardipine and esmolol, respectively, can be used to rapidly treat hypertension and tachycardia while minimizing the risk of prolonged hypotension. For patients with a history of severe hypertension that is refractory to treatment, a continuous infusion of nicardipine may be required and should be titrated to effect. Persistent hypertension that is observed after the extubation of the patient should be treated with a longer-acting antihypertensive medication. The desirable blood pressure and heart rate parameters outside of which the patient will require treatment should be determined based on the patient’s baseline preoperative values, comorbidities, and surgical determinants.


An intracranial bleed may also be caused by elevated ICP from coughing or retching during emergence due to endotracheal tube-induced stimulation. Patients with increased airway sensitivity (e.g., smokers and asthmatic patients) or in whom there is an increased risk of surgical bleeding should be considered for either deep extubation or LMA exchange. Deep extubation can decrease the risk of coughing, retching, and bronchospasm, but also has its own risks. Contraindications to deep extubation include known increased risk for aspiration, suspected or proven difficult mask ventilation or intubation, and risk of pneumocephalus if positive pressure mask ventilation is required. Deep extubation leaves the patient at some risk for aspiration because the endotracheal tube is removed before full airway reflexes have returned. Laryngospasm after deep extubation is common and can occur as the patient passes through stage two of anesthesia. Intraoperative fluid administration can cause airway edema, making deep extubation unwise.


An alternative to deep extubation is LMA exchange to facilitate smooth emergence. Similar to deep extubation, LMA exchange requires removal of the endotracheal tube, while the patient is still fully anesthetized. However, after the patient is extubated, an LMA is placed, and the patient can be mechanically ventilated during emergence from anesthesia. The LMA is subsequently removed once the patient meets the extubation criteria. Because LMA is less invasive and better tolerated in most patients than an endotracheal tube, its use may alleviate coughing and retching that might otherwise occur. The main advantage of this technique over deep extubation is the presence of a secured airway. However, it is important to recognize that deep extubation is still required, thus presenting the same risks—aspiration, laryngospasm, and hypoxia. Additionally, there is a potential that the LMA may not seat appropriately to allow adequate ventilation, in which case reintubation with an endotracheal tube is needed.


In addition to a smooth emergence, rapid wake-up from anesthesia is desirable in patients undergoing craniotomy. Intraoperatively, anesthetics and analgesics should be titrated to ensure that patients are awake and alert after extubation, allowing for adequate assessment of the neurologic status. Prolonged sedation from anesthesia can mimic the signs and symptoms of surgical complications and is problematic. While prolonged sedation will resolve with time, the delay in treatment for neurosurgical complications may be life threatening.


Scalp Block


As discussed above, patients undergoing craniotomy present a unique challenge in anesthetic management wherein tight regulation of blood pressure and heart rate is balanced with the need for rapid and smooth emergence. To address such challenges, the use of a regional block, termed a scalp block, can be incorporated in the anesthetic care plan as part of a multimodal approach to perioperative pain control in patients undergoing supratentorial craniotomy. A scalp block selectively targets up to 12 sensory nerves (6 on each side) innervating the forehead and scalp. These include the supraorbital, supratrochlear, zygomaticotemporal, auriculotemporal, greater occipital, and lesser occipital nerves ( Fig. 19.2 ).


Jun 26, 2022 | Posted by in ANESTHESIA | Comments Off on Perioperative Care of the Surgical Patient: Brain

Full access? Get Clinical Tree

Get Clinical Tree app for offline access