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Emergence From Anesthesia
Introduction
Multiple historical factors may be related directly or indirectly with the emergence from anesthesia. William Harvey’s statement in Exercitatio anatomica de motu cordis et sanguinis in animalibus ( On the Movement of the Heart and Blood in Animals ) regarding the blood circulating around the body (1628) took down Galenic dogma (130 BC) about blood circulatory mechanism and created the basis of physiological and pharmacological principles. In 1846, William T. Morton performed the first successful administration of anesthesia but little was known about emergence from anesthesia and patients’ reaction after ether administration. Prior to this successful experience, Morton tried couple of times to anesthetize a patient with unexpected reactions: agitation and disorganized speech.
Cerebral autoregulation and physiological adaptation in the immediate postoperative period are linked to intraoperative efforts to maintain homeostasis. Induced hypocapnia, use of osmotic fluids, and placement of drains are examples of perioperative variables with an important impact in outcomes during the emergence from anesthesia.
An increasing body of evidence regarding anesthesia management supports different techniques based on physicians and institutions’ preferences such as total intravenous anesthesia (TIVA), balanced anesthesia, local anesthesia, or use of adjuvants and their combinations.
Postoperative stress response during extubation may entail increased catecholamine response, oxygen consumption (VO 2 ), blood pressure, and heart rate due to laryngeal stimulation, although other mechanisms are described. Variations in metabolism, hemodynamic parameters, cerebral blood flow (CBF), and intracranial pressure may be developed as a result of shivering or pain with consequent impairment in patients’ outcomes.
Neurological examination should be carried out in the operating room during emergence to identify a potential neurological deficit or emergence delirium. Some patients undergoing complex procedures involving eloquent areas of the brain may be suitable for a planned delay in emergence from anesthesia, avoiding life-threatening complications such as intracranial hemorrhage (ICH), respiratory impairment, and aspiration due to unprotected airway.
Neurophysiological Response During Emergence in Neurosurgical Patients
Several physiological changes take place during the emergence from anesthesia including metabolic variations and those affecting brain homeostasis. Even with slightly normal PaCO 2 levels, bicarbonate levels in the cerebrospinal fluid (CSF) may decrease significantly. Therefore, consequent pH reduction in brain perivascular areas will lead to vasodilation and hyperemia.
Apparently, these events occur regardless of the anesthetic agent used during maintenance. Bruder et al. reported a significant increment of 60% from baseline in CBF velocity during extubation and within the first hour after neurosurgery, with no relation found between these values and the surgery or anesthesia techniques.
Increased catecholamine blood levels have been reported after neurological surgery. However, this condition by itself may interfere with the CBF only in the presence of a defective blood–brain barrier or when autoregulation is compromised. Different options are available to treat catecholamine hemodynamic effects such as β-blocker use (e.g., esmolol) and hypothermia prevention.
On the other hand, sympathetic activation may play a crucial role on the central nervous system (CNS) responses during emergence from anesthesia. Reuptake inhibition of dopamine and norepinephrine by methylphenidate administration will trigger several mechanisms within the CNS leading to a faster recovery after isoflurane and propofol exposure.
Surgery and anesthesia may also increase the incidence of emesis during the emergence. The “emesis center” includes the area postrema (AP), nucleus tractus solitarius, and the dorsal motor nucleus of the vagus nerve. No less than 17 neurotransmitters exert their action on this center throughout the interaction with several receptors such as dopamine, substance P/neurokinin-1, cannabinoid, histamine, among others. The aforementioned responses may be generated during extubation as a result of the autonomic nervous system activation.
Specific Perioperative Considerations
Diagnosis of potential postoperative complications may be delayed due to a slow return to consciousness making neurological examination difficult to perform after neurosurgery. Postanesthesia arousal is a variable considered when assessing anesthesia quality. Preoperative neurologic status, location and size of the lesion, and anesthesia technique are some of the variables interfering with the early postoperative recovery of cognition, hemodynamics, and nociception during emergence.
Surgical Site and Lesion Location
Brain herniation, ischemia, and poor surgical field are the expected consequences of increased intracranial volume. These events have been associated with delayed arousal after intracranial surgery. Predictive factors for delayed postsurgical emergence are the following: mass effect of space-occupying lesion (over 30 mm size), cerebral structures shifting from midline >3 mm with perilesional edema, and prolonged retraction pressure needed to expose the surgical field during tumor resection.
Anesthetic Techniques
Definitive criteria for quality of recovery related to the anesthesia technique during neurosurgical procedures have not been established. However, a targeted and neurological evaluation is performed at the end of surgery to assess outcomes.
The Short Orientation Memory Concentration Test (SOMCT) and the Aldrete score are commonly used when comparing the time and quality of recovery of patients undergoing supratentorial craniotomy, either under balanced or TIVA technique.
TIVA based on propofol–remifentanil has shown slightly shorter extubation time, faster return to consciousness, and faster recovery in comparison with balanced anesthesia. However, most of the studies have demonstrated no statistical significance in quality of recovery among patients either when TIVA or balanced anesthesia was performed.
The NeuroMorfeo Study was carried out in 411 patients reporting no difference in time after extubation to achieve an Aldrete score ≥9 between both balanced and TIVA groups. Hemodynamics and brain surgical conditions were also similar among groups. Nevertheless, a reduced endocrine response to surgical stress was linked to propofol/remifentanil combination.
Balanced Anesthesia
Desflurane provides shorter extubation and recovery time than sevoflurane in patients undergoing craniotomy under balanced anesthesia. Magni et al. compared the effects of sevoflurane (1.5–2%) and desflurane (6–7%) on emergence analyzing the data collected from 120 neurosurgical patients. No significant difference was found regarding the time for emergence (12.2 ± 4.9 min versus 10.8 ± 7.2 min), recorded as the time when eye opening occurred since the inhaled agent administration was suspended. On the other hand, the sevoflurane group needed more time for tracheal extubation in contrast to the desflurane group (18.2 ± 2.3 min versus 11.3 ± 3.9 min). Similarly, the time of recovery (defined in this study as the time that patients’ consciousness allowed them to repeat their name and date of birth) was longer in the sevoflurane group (12.4 ± 7.7 min versus 1.3 ± 3.9 min). The characteristic of the surgical field, such as state of the brain tissue and the intracranial pressure (ICP) and postoperative cognitive function are also comparable between both inhaled anesthetics during supratentorial surgeries. Cognitive impairment commonly occurs in both groups within the first 15 min after extubation or after Aldrete score was ≥9, usually returning to baseline during the next 30 min.
Moreover, when compared with opioids such as fentanyl, alfentanil, and sufentanil in combination with isoflurane showed no clinical relevance regarding the time for obtaining a satisfactory neurological evaluation after surgery.
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