Ian A. Herrick

Propofol sedation during awake craniotomy for seizures: patient-controlled administration versus neurolept analgesia.

This prospective study evaluated the safety and efficacy of patient-controlled sedation (PCS) using propofol during awake seizure surgery performed under bupivacaine scalp blocks. Thirty-seven patients were randomized to receive either propofol PCS combined with a basal infusion of propofol (n = 20) or neurolept analgesia using an initial bolus dose of fentanyl and droperidol followed by a fentanyl infusion (n = 17). Both groups received supplemental fentanyl and dimenhydrinate for intraoperative pain and nausea, respectively. Comparisons were made between groups for sedation, memory, and cognitive function, patient satisfaction, and incidence of complications. Levels of intraoperative sedation and patient satisfaction were similar between groups. Memory and cognitive function were well preserved in both groups. The incidence of transient episodes of ventilatory rate depression (<8 bpm) was more frequent among the propofol patients (5 vs 0, P = 0.04), particularly after supplemental doses of opioid. Intraoperative seizures were more common among the neurolept patients (7 vs 0, P = 0.002). PCS using propofol represents an effective alternative to neurolept analgesia during awake seizure surgery performed in a monitored care environment. (Anesth Analg 1997;84:1285-91)

Propofol sedation during awake craniotomy for seizures: electrocorticographic and epileptogenic effects.

This prospective study evaluated the effects of propofol sedation on the incidence of intraoperative seizures and the adequacy of electrocorticographic (ECoG) recordings during awake craniotomy performed for the management of refractory epilepsy.Thirty patients scheduled for temporal or frontal lobectomy for epilepsy under bupivacaine scalp block were randomized to receive patient-controlled propofol sedation (PCS) combined with a basal infusion of propofol (n = 15) or neurolept analgesia using an initial bolus dose of fentanyl (0.7 micro g/kg) and droperidol (0.04 mg/kg) followed by a fentanyl infusion (n = 15). Propofol administration was suspended 15 min before ECoG recording in the PCS group. The occurrence of inappropriate intraoperative seizures was noted and, based on blind review, the adequacy of ECoG recordings was compared. A higher incidence of intraoperative seizures was noted among the neurolept patients (6 vs 0, P = 0.008). Intraoperatively, ECoG recordings were adequate to proceed with resection in both groups. Evidence of low spike activity on ECoG did not correlate with the type of sedation administered. Higher frequency background ECoG activity was noted among patients who received propofol, but this did not interfere with ECoG interpretation. The use of propofol sedation does not appear to interfere with ECoG during epilepsy surgery, provided administration is suspended at least 15 min before recording. (Anesth Analg 1997;84:1280-4)

Postoperative cognitive impairment in the elderly : Choice of patient-controlled analgesia opioid

This study evaluated the safety and cognitive impact of patient‐controlled analgesia with fentanyl compared to patient‐controlled analgesia with morphine among elderly postoperative patients. In addition, two screening tests for cognitive impairment, the Mini Mental Status Exam and the Short Portable Mental Status Questionnaire, were compared. Ninety‐six elderly patients were randomly allocated to receive patient‐controlled analgesia with either fentanyl or morphine following hip or knee arthroplasty. Patients were evaluated postoperatively for clinical confusion, cognitive function test results, adequacy of analgesia, drug use and complications. Fentanyl produced less depression in postoperative cognitive function compared to morphine. The incidence of clinical confusion was not statistically different between groups (4.3% for fentanyl versus 14.3% for morphine). Fentanyl patients used more opioid based on a dose ratio of 100:1 suggesting that this dose ratio is inadequate. The incidence of urinary retention was lower in the fentanyl group. A poor agreement between the two tests of cognitive impairment mandates caution when peri‐operative cognitive function is compared using different tests.

Postobstructive pulmonary edema following anesthesia

Pulmonary edema developing after the relief of upper airway obstruction has been reported in association with a diversity of etiologic factors, including hanging, strangulation, tumors, foreign bodies, goiter, and laryngospasm. Since 1977, 18 cases of adults with postobstructive pulmonary edema associated with anesthesia have been reported. A case is presented of a healthy 20-year-old male who developed pulmonary edema following two episodes of acute upper airway obstruction associated with general anesthesia. Postanesthetic laryngospasm has been implicated as the most frequent cause of this syndrome in adults. Risk factors for the development of upper airway obstruction have been identified in the majority of these cases. A heightened awareness among anesthesiologists of this poorly recognized and hence often perplexing syndrome may help reduce the occurrence and facilitate the treatment of this potential complication of perioperative airway management.

Sedative doses of remifentanil have minimal effect on ECoG spike activity during awake epilepsy surgery.

The use of remifentanil for sedation during awake epilepsy surgery has been described in a case report. However, little information is available regarding the effect of remifentanil on the quality of intraoperative electrocorticography (ECoG). This study was designed to investigate the effect of sedative doses of remifentanil on ECoG interictal spike activity among patients undergoing awake anterior temporal lobectomy for refractory epilepsy. Ten adult patients were studied prospectively. After baseline EcoG recordings were obtained, remifentanil was administered as a continuous infusion at 0.1 &mgr;g/kg/min and the ECoG recorded continuously for 15 minutes. Recordings obtained before and during the administration of remifentanil were compared with respect to spike frequency and location. A trend toward a small decrease in spike frequency was observed as patients became increasingly somnolescent and background ECoG activity slowed. The difference was not statistically significant. Blood pressure and heart rate were not adversely affected by the administration of remifentanil. Respiratory rates decreased in all patients (mean decrease, 8 breaths/min) and one patient transiently developed a respiratory rate of 4 breaths per minute that elicited a decrease in the rate of remifentanil administration. Remifentanil administered at sedation doses does not adversely affect intraoperatively recorded interictal spike activity. Further investigation of the use of this drug during awake epilepsy surgery is warranted.

EFFECTS OF FENTANYL, SUFENTANIL, AND ALFENTANIL ON BRAIN RETRACTOR PRESSURE

Sufentanil and alfentanil have been reported to increase cerebral blood flow and intracranial pressure. Agents producing these effects may adversely affect the relationship between brain retractors and underlying cerebral tissues during craniotomy, potentially predisposing the patient to brain retractor injury. The effects of fentanyl, sufentanil, alfentanil, and a placebo (saline) on brain retractor pressure were therefore evaluated prospectively in 24 adults undergoing elective craniotomy. None of these narcotics significantly affected brain retractor pressure. Each significantly and similarly decreased arterial pressure and cerebral perfusion pressure. If these narcotics are administered in doses that avoid adverse hemodynamic changes that could compromise cerebral tissues indirectly, each of the narcotics studied appears safe for intraoperative administration once the cranium is open.

Brain areas that influence general anesthesia

This document reviews the literature on local brain manipulation of general anesthesia in animals, focusing on behavioral and electrographic effects related to hypnosis or loss of consciousness. Local inactivation or lesion of wake-active areas, such as locus coeruleus, dorsal raphe, pedunculopontine tegmental nucleus, perifornical area, tuberomammillary nucleus, ventral tegmental area and basal forebrain, enhanced general anesthesia. Anesthesia enhancement was shown as a delayed emergence (recovery of righting reflex) from anesthesia or a decrease in the minimal alveolar concentration that induced loss of righting. Local activation of various wake-active areas, including pontis oralis and centromedial thalamus, promoted behavioral or electrographic arousal during maintained anesthesia and facilitated emergence. Lesion of the sleep-active ventrolateral preoptic area resulted in increased wakefulness and decreased isoflurane sensitivity, but only for 6 days after lesion. Inactivation of any structure within limbic circuits involving the medial septum, hippocampus, nucleus accumbens, ventral pallidum, and ventral tegmental area, amygdala, entorhinal and piriform cortex delayed emergence from anesthesia, and often reduced anesthetic-induced behavioral excitation. In summary, the concept that anesthesia works on the sleep-wake system has received strong support from studies that inactivated/lesioned or activated wake-active areas, and weak support from studies that lesioned sleep-active areas. In addition to the conventional wake-sleep areas, limbic structures such as the medial septum, hippocampus and prefrontal cortex are also involved in the behavioral response to general anesthesia. We suggest that hypnosis during general anesthesia may result from disrupting the wake-active neuronal activities in multiple areas and suppressing an atropine-resistant cortical activation associated with movements.

Effect of varying intravenous patient-controlled analgesia dose and lockout interval while maintaining a constant hourly maximum dose

STUDY OBJECTIVE To investigate the effect on the use of intravenous patient-controlled analgesia (PCA) of varying the dose (D) and lockout interval (LI) while keeping the hourly maximum dose constant. DESIGN Randomized, prospective study. SETTING Teaching hospital. PATIENTS 75 patients scheduled to receive PCA morphine following abdominal surgery. INTERVENTIONS Postoperatively, patients were randomly assigned to receive PCA morphine with the following parameters: D = 1 mg, LI = 6 min (Group 1-6), D = 1.5 mg, LI = 9 min (Group 1.5-9), or D = 2 mg, LI = 12 min (Group 2-12), so that each group could receive a maximum hourly dose or 10 mg. Inadequate analgesia was managed by increasing the dose and lockout interval, while excessive sedation or respiratory rate less than 10 breaths/min resulted in decreasing the dose and lockout interval. MEASUREMENTS AND MAIN RESULTS Patients were assessed for pain [visual analog scale (VAS), verbal rating scale (VRS)] and side effects at 1, 2, 4, and 24 hours. The number of doses administered, missed attempts, and morphine used for the first 24 hours was recorded by automatic printout from the PCA machine. There was no difference in the total 24-hour morphine consumption, analgesia, or incidence of side effects among the three groups at any of the measurement times. Two patients, one each in the 1.5-9 and 2-12 groups, required naloxone for respiratory depression. The number of PCA injections, attempts, missed attempts, and the incidence of dosage adjustment were all significantly higher for the 1-6 group (p < 0.05). CONCLUSION The use of 1.0 mg with a 6-minute lockout may represent appropriate dose titration because this group obtained equivalent analgesia, morphine use, and side effects as the two larger dose and lockout groups. However, the increased number of PCA attempts and missed attempts may reflect lower satisfaction with PCA therapy.

Lesion of cholinergic neurons in nucleus basalis enhances response to general anesthetics.

Acetylcholine in the brain has been associated with consciousness and general anesthesia effects. We tested the hypothesis that the integrity of the nucleus basalis magnocellularis (NBM) affects the response to general anesthetics. Cholinergic neurons in NBM were selectively lesioned by bilateral infusion of 192IgG-saporin in adult, male Long-Evans rats, and control rats were infused with saline. Depletion of choline-acetyltransferase (ChAT)-immunoreactive cells in the NBM and decrease in optical density of acetylcholinesterase (AChE) staining in the frontal and visual cortices confirmed a significant decrease in NBM cholinergic neurons in lesioned as compared to control rats. AChE staining in the hippocampus and ChAT-positive neurons in the medial septum-vertical limb of the diagonal band were not different between lesioned and control rats. When a general anesthetic was administered, lesioned compared to control rats showed significantly longer duration of loss of righting reflex (LORR) after propofol (5 or 10mg/kg i.v.), pentobarbital (20 or 40 mg/kg i.p.) but not halothane (2%). However, the behavioral excitation, as indicated by horizontal movements, induced by halothane was reduced in lesioned as compared to control rats. Reversible inactivation of NBM with GABA(A) receptor agonist muscimol increased slow waves in the neocortex during awake immobility, and prolonged the duration of LORR and loss of tail-pinch response after propofol, pentobarbital and halothane. In summary, lesion of NBM cholinergic neurons or inactivation of the NBM prolonged the LORR response to general anesthetic drugs.

Patient-controlled sedation using propofol during interventional neuroradiologic procedures.

Patient-controlled sedation (PCS) using propofol has been reported to provide safe and effective sedation during a variety of procedures performed under regional or local anesthesia. In a prospective, randomized fashion, this study evaluated propofol PCS compared to anesthesiologist-administered midazolam-fentanyl sedation during interventional neuroradiologic (INR) procedures. Nineteen patients undergoing 24 INR procedures received propofol PCS (PCS dose, 0.5 mg/kg; lockout interval, 3 min) or anesthesiologist-administered midazolam-fentanyl sedation. Study parameters included discomfort, sedation and anxiety visual analogue scores (VAS), cognitive function, patient satisfaction, and complications. No difference was found between the two sedation techniques with respect to the levels of sedation and anxiolysis. Cognitive function was well preserved in both groups. Patient satisfaction was similarly high in both groups. Complications were similar between groups. These included ventilatory depression (two patients in each group) and excessive sedation (two patients in each group). Three patients in the propofol group became excessively restless, resulting in brief interruptions during the respective procedures. Propofol PCS offers a safe sedation technique during INR procedures with a sedation and anxiolysis profile that was not distinguishable from anesthesiologist-administered midazolam-fentanyl sedation.