An investigation of learning during propofol sedation and anesthesia using the process dissociation procedure

BACKGROUND: Many studies have shown that patients may remember words learned during apparently adequate anesthesia. Performance on memory tests may be influenced by explicit and implicit memory. We used the process dissociation procedure to estimate implicit and explicit memory for words presented during sedation or anesthesia. METHODS: We investigated intraoperative learning in 72 women undergoing pervaginal oocyte collection during propofol and alfentanil infusion. One word list was played once before infusion, another was played 10 times during surgery. Venous blood was taken for propofol assay at the end of the intraoperative list. Behavioral measures of anesthetic depth (eyelash reflex, hand squeeze response to command) were recorded and used to adjust the dose of anesthetic where clinically appropriate. On recovery, memory was assessed using an auditory word stem completion test with inclusion and exclusion instructions. RESULTS: The mean blood propofol concentration was 2.5 microg/ml (median, 2.3 microg/ml; range, 0.7-6.1 microg/ml). Mean alfentanil dose was 2.1 mg (median, 2.0 mg; range, 1.2-3.4 mg). Comparison of target and distractor hits in the inclusion condition showed memory for preoperative words only. However, the process dissociation procedure estimates showed explicit (mean, 0.18; P < 0.001) and implicit (mean, 0.05; P < 0.05) memory for the preoperative words, and a small amount of explicit memory for the intraoperative words (mean, 0.06; 95% confidence interval, 0.01-0.10). Memory performance did not differ between the 17 patients who consistently responded to command and eyelash reflex and the 32 patients who remained unresponsive. Blood propofol concentration and alfentanil dose did not correlate with memory for the intraoperative list. CONCLUSIONS: There was no unprompted recall of surgery, but the process dissociation procedure showed memory for words presented during surgery. This memory was apparently explicit but did not correlate with the measures of depth of anesthesia used.     

Analysis of implicit memory during propofol anesthesia

OBJECTIVE: Consensus has not been achieved on the presence of unconscious memory of messages in general anesthesia for methodological reasons. Our objective was to apply a model of anesthesia that allows for clinical control of the level of hypnosis in order to evaluate the presence and characteristics of implicit memory in deep sedation with propofol. PATIENTS AND METHODS: We randomly assigned 48 consecutive patients undergoing lower limb surgery to two groups. In both groups subarachnoid anesthesia was with varying doses of propofol to maintain a level of hypnosis marked by inability to respond to orders, absence of movements and spontaneous ventilation. The experimental group listened to a recording of the words "banana" and "melon" for the semantic category of fruits and "white" and "black" for colors. The control group listened to a recording of environmental operating room noise. We recorded, among other variables, anxiety and age. Upon awakening, after the presence of conscious memory had been ruled out, we investigated implicit memory by comparing the percentage of correct answers in the two groups. RESULTS: The experimental group had a higher percentage of correct fruit names (p = 0.03). No differences were detected for colors. The youngest patients in the experimental group were correct more often about the fruits than were older members (p = 0.04) and those with greater anxiety were more often correct (p = 0.002). CONCLUSIONS: Implicit memory is preserved under hypnosis with propofol and is more likely to be present among those who are younger or experience greater anxiety. Concrete words with object references are more easily remembered than abstract words referring to perception. The semantic load of messages is relevant.     

No implicit memory for stories played during isoflurane/alfentanil/nitrous oxide anesthesia: a reading speed measurement

Implicit memory of intraoperatively presented stories was recently detected by using the reading speed paradigm during propofol-alfentanil-nitrous oxide anesthesia. Our main goal was to evaluate the reading speed test procedure under another anesthetic regimen, i.e., isoflurane combined with nitrous oxide and alfentanil-infusion. In both experiments, patients were premedicated with oral midazolam. In a previous experiment, patients postoperatively read "old" stories that had been presented during anesthesia quicker compared with "new," unpresented stories. The same study design and test material as in the previous experiment were used. One of two audio tapes with two short stories was played randomly to patients during lumbar disk surgery and to awake controls. Approximately 7 h later, a structured interview and the reading speed test were used to determine whether the participants had any explicit or implicit memories of the presented stories. The results of 30 patients and 30 controls were calculated. Whereas the control participants showed an intact explicit and implicit memory of the previously presented material, no such effect was found in the anesthetized patients. The present experiment shows that changing the main anesthetic in otherwise equal study conditions, i. e., propofol to isoflurane (end-expiratory 0.7%), implicit memory is abolished in anesthetized patients. IMPLICATIONS: We showed that implicit memory during general anesthesia can be abolished by changing the hypnotic anesthetic. Increased postoperative reading speed for stories presented during propofol-alfentanil-nitrous oxide anesthesia was shown in a previous experiment, but not in our study using isoflurane for balanced anesthesia.     

硬膜外麻醉下异丙酚联合咪达唑仑镇静对内隐记忆的影响

目的探讨术中异丙酚联合咪达唑仑镇静对内隐记忆的影响,分析内隐记忆消失的中潜伏期听觉诱发电位(MLAEP)参数界值,为临床镇静深度监测提供一项新的客观指标。方法 硬膜外麻醉下择期手术病人45例(ASA Ⅰ～Ⅱ级),随机分为异丙酚组(P)、联合用药一组(PM1)、联合用药二组(PM2)3组,每组15例。P组:异丙酚2 mg·kg-1·h-1;PM1组:异丙酚1.5 mg·kg-1·h 咪达唑仑0.03 mg·kg-1·h-1;PM2组:异丙酚1.5 mg·kg-1·h-1 咪达唑仑0.06 mg·kg-1·h-1。所有病人经异丙酚或异丙酚联合咪达唑仑镇静15 min后,让病人听录音带即内隐记忆刺激。记录入室时(T1)、行硬膜外麻醉后(T2)、静脉给药后15min(T1)、切皮后2min(T4)、内隐记忆刺激完成即刻(T5)等时点的心率(HR)、平均动脉压(MAP)、MLAEP。术后6 h进行记忆调查,测定病人的模糊辨听率。结果 异丙酚镇静Pa、Nb波潜伏期延长、波幅降低(P<0.05),但联合用药组潜伏期延长更明显、波幅降得更低(P<0.05)。所有病人外显记忆均消失;P组均存在内隐记忆,两联合用药组内隐记忆均消失。结论异丙酚和咪达唑仑联合镇静可以消除外显记忆和内隐记忆。MLAEP参数Pa、Nb波潜伏期、波幅可以作为评价术中镇静深度的客观监测指标。     

Usefulness of isoflurane in anesthesia in elective cesarean section

A series of 25 patients undergoing iterative cesarean section under general anesthesia received isoflurane at 0.75% together with a mixture of O2 and N2O at 50% for anesthetic maintenance. The inhalant agent was withdrawn when closing fascia. There was no case of regaining of consciousness during the operations. Uterine contraction was acceptable as evaluated by the surgeon at the end of the operation. Mean hematocrit value was 31.43 (SD 1.27) at 6 hours of operation. Fetal arterial gasometric values and Apgar score at 5 and 10 minutes fell within acceptable limits.     

Peroperative adenosine infusion reduces isoflurane concentrations during general anesthesia for shoulder surgery

Background: Adenosine (ADO), and stable analogs thereof, have been shown to exert antinociceptive action under experimental conditions in animals and in humans. The aim of this randomized double-blind placebo-controlled study was to evaluate if a low dose of intravenous (i.v.) ADO could reduce isoflurane requirements during joint-associated surgery, as an indication of antinociception in deep somatic pain.
Methods: Thirty-two patients, age 19–62 years, ASA I and II, scheduled for shoulder joint surgery, were assigned to receive an i.v. infusion of either adenosine, 80 μg kg^-1 min^-1, or placebo, during the surgical procedure. Anesthesia was maintained with isoflurane/N₂O/O₂ inhalation.
Results: The peroperative isoflurane concentration was significantly reduced at 50 minutes of surgery in the group receiving adenosine infusion. Also, the systolic blood pressure level was peroperatively more stable during adenosine infusion than during placebo. Other clinical parameters, such as pain, postoperative analgesic requirements and nausea, were not different between groups.
Conclusion: A peroperative infusion of a low dose of adenosine during shoulder joint surgery may reduce the peroperative isoflurane requirement.     

Spinal anesthesia for elective lumbar spine surgery

Study Objective: To evaluate a large series of elective lumbar spine surgical procedures by a single surgeon whose patients were all offered spinal anesthesia.

Design: Retrospective chart review.

Setting: Tertiary-care teaching hospital.

Measurements and Main Results: The records of all elective lumbar spine procedures between 1984 and 1995 performed by one surgeon (GRB) were obtained, and 803 were identified. Of those 803 patients, 611 accepted spinal anesthesia. Data collected included patient demographics, details of the spinal and general anesthesia, perioperative complications, and impact of the spinal anesthetic options on the outcome of spinal anesthesia. General and spinal anesthesia patients were comparable for age, gender, height, and ASA physical status. Patients who received spinal anesthesia were significantly heavier than the general anesthesia patients. Among perioperative complications, nausea and deep venous thrombosis occurred significantly more often in the general than spinal anesthesia patients. Mild hypotension and decreased heart rate (HR) were the most common hemodynamic changes with spinal anesthesia, whereas hypertension and increased HR were the result of general anesthesia. Among spinal anesthetic drugs, plain bupivacaine was associated with the lowest incidence of supplemental local anesthetic use intraoperatively compared to hyperbaric bupivacaine or hyperbaric tetracaine.

Conclusion: Spinal anesthesia is an effective alternative to general anesthesia for lumbar spine surgery and has a reduced rate of minor complications.     

Propofol and memory: a study using a process dissociation procedure and functional magnetic resonance imaging

Thirty volunteers randomly received either mild or deep propofol sedation, to assess its effect on explicit and implicit memory. Blood oxygen level‐dependent functional magnetic resonance during sedation examined brain activation by auditory word stimulus and a process dissociation procedure was performed 4 h after scanning. Explicit memory formation did not occur in either group. Implicit memories were formed during mild but not deep sedation (p = 0.04). Mild propofol sedation inhibited superior temporal gyrus activation (Z value 4.37, voxel 167). Deep propofol sedation inhibited superior temporal gyrus (Z value 4.25, voxel 351), middle temporal gyrus (Z value 4.39, voxel 351) and inferior parietal lobule (Z value 5.06, voxel 239) activation. Propofol only abolishes implicit memory during deep sedation. The superior temporal gyrus is associated with explicit memory processing, while the formation of both implicit and explicit memories is associated with superior and middle temporal gyri and inferior parietal lobule activation.     

麻醉剂量的丙泊酚对内隐记忆的影响

目的观察麻醉剂量下丙泊酚对内隐记忆及其脑电双频谱指数(BIS)的影响.方法选择42例子宫全切术的病人,随机分为三组.Ⅰ组,Ⅱ组为试验组,各11例.Ⅲ组为对照组20例.三组病人均施予腰麻硬膜外联合麻醉.试验组加用丙泊酚2mg@kg-1,维库溴铵8mg诱导行气管内插管,静脉持续泵入丙泊酚110μg@kg-1@min-1维持麻醉.采用HXD-1型多功能脑电监测仪监测BIS.BIS＞60的病人为I组,BIS＜60的病人为Ⅱ组,关腹后给予内隐记忆听刺激.术后6h测试其模糊辨听率,同时对术中的记忆情况进行调查.结果Ⅰ、Ⅱ组间脑电BIS有显著差异,分别为71.93±10.51和56.04±11.86(P＜0.05).模糊辨听率三组间无差异(P＞0.05).试验组病人无一例存在有外显记忆.结论临床剂量的丙泊酚无论BIS大于或小于60,内隐记忆不能被消除.     

Long-term hypotensive technique with nicardipine and nitroprusside during isoflurane anesthesia for spinal surgery.

Short-term infusion of nicardipine can be used to induce deliberate hypotension but may result in plasma drug accumulation. To assess long-term nicardipine administration for deliberate hypotension in 10 patients in a moderately hemodiluted state who were undergoing spinal surgery, hemodynamics and plasma nicardipine concentrations were concomitantly measured before and 20, 80, and 140 min after starting nicardipine, at drug discontinuation, and 20 and 80 min later. A dose of 6.2 +/- 0.9 mg (mean +/- SEM) of nicardipine was initially required to obtain mean arterial blood pressures at 55-60 mm Hg. Maintenance doses of nicardipine were 3-5 mg/h. The duration of nicardipine administration was 270 +/- 20 min (mean +/- SEM). Hypotension was associated with decreased systemic and pulmonary vascular resistances, increased cardiac index, and decreased arteriovenous difference in O2 contents. Only two patients required homologous blood transfusion. Plasma nicardipine concentrations peaked at 110 +/- 21 ng/mL (mean +/- SEM) and then decreased to 38 +/- 11 ng/mL (mean +/- SEM) without changes in arterial blood pressure. After vasodilator discontinuation, hypotension was observed during a mean time of 43 min (range 27-88 min) despite plasma concentrations less than 20 ng/mL. No relationship was found between plasma nicardipine concentrations and hemodynamics. These findings suggest that an increasing effect of nicardipine over time may occur during prolonged administration. Because the reasons for this hysteresis remain unclear, use of nicardipine infusion during major surgery and anesthesia requires particular caution.     

Acute pulmonary capillary leak syndrome during elective surgery under general anesthesia

A 75-year-old previously healthy man presented for elective resection of rectal cancer under general anesthesia. Six days before the operation, he had a high-grade fever, and elevated leukocyte count and C-reactive protein concentration, but this was resolved by an intravenous antibiotic. His condition was well controlled before the operation. Soon after the operation started, severe hypoxemia emerged, with low arterial pressure. Fiberoptic bronchoscopy demonstrated a massive amount of plasma-like edema fluid; the total amount of suctioned fluid was approximately 800 ml at the end of the surgery. This acute pulmonary edema appeared to be due to increased permeability rather than pulmonary congestion as indicated by chest radiography, pulmonary artery occlusion pressure, echocardiogram, and the protein-rich edema fluid. Elevated concentrations of the proinflammatory cytokines, interleukin (IL)-6 and IL-8, in both plasma and the pulmonary edema fluid, suggested a possible role of systemic and pulmonary inflammation in the development of this acute pulmonary capillary leak. According to the “two-hit” hypothesis, the bacterial infection preceding the operation may have primed the immune cells, and the following surgical stress may have then triggered rapid progression of acute respiratory distress syndrome. We should keep in mind that, especially following sepsis, sudden massive pulmonary capillary leak can occur during elective surgery, even though the patient’s condition is well controlled.     

Cerebral protection during aneurysm surgery with isoflurane anesthesia. Technical note.

A strategy for intraoperative cerebral protection is described in which intraoperative electroencephalography is used to titrate the level of inspired isoflurane given for anesthesia to obtain isoelectricity prior to temporary vessel occlusion during repair of difficult aneurysms. During temporary vessel occlusion, arterial blood pressure is maintained or increased with an inotropic or vasopressor agent. After clipping of the aneurysm, the concentration of isoflurane is reduced to allow the patient to awaken in the operating room for early postoperative neurological examination. The combination of a high concentration of isoflurane, temporary vessel occlusion, and maintenance of arterial blood pressure may be a useful protective regimen during neurovascular procedures.     

Comparison of sevoflurane/fentanyl and isoflurane/fentanyl during elective coronary artery bypass surgery

Purpose

Due to the progressive aging of the surgical population, the proportion of patients with coronary artery disease (CAD) is likely to increase. The effects of the new inhalational anaesthetic sevoflurane must be determined in patients with known CAD.

Methods

This multicentre, randomized, open-label study compared the haemodynamic and cardiovascular effects of sevoflurane and isoflurane with fentanyl in 284 ASA physical status II–IV patients undergoing elective coronary artery bypass graft (CABG).

Results

Satisfactory records were available in 272 patients, 139 sevoflurane (Group S) and 133 isoflurane (Group I). There were no differences between groups for demographic data except that more patients in Group S were taking preoperative beta-blockers (P = 0.03). The mean end-tidal MAC and MAC · hr requirements between groups were not different (Group S received 0.63 ± 0.02 MAC and 1.00 ± 0.05 MAC · hr while Group I received 0.58 ± 0.02 MAC and 0.92 ± 0.05 MAC · hr P = NS). The preCPB use of intravenous fentanyl was not different between groups. There was a similar decrease in haemodynamic variables in both groups after induction that persisted throughout the preCPB period. The incidence of preCPB myocardial ischaemia, adverse haemodynamic events and use of vasoactive drugs did not differ between groups. The incidence of postoperative myocardial infarction was 2.2% for Group S and Group I was 4.5% (P = NS). There were five postoperative deaths, one of which was attributed to a cardiac cause (Group I).

Conclusion

In patients undergoing elective CABG with low risk factors, either sevoflurane or isoflurane, combined with fentanyl, provided an acceptable preCPB haemodynamic profile and cardiac outcomes.     

Hemodynamic effects of metocurine during isoflurane anesthesia

Anesthesia was induced in 42 adults with thiopentone 3-7 mg/kg i.v. and maintained with isoflurane at a constant inspired concentration of 1-2%. After 30 min of hemodynamic stabilization with continuous muscle relaxation and an absence of surgical stimulation, each patient was randomly assigned to one of four metocurine dosage groups: I - control (n = 11); II - 0.2 mg/kg (n = 10); III - 0.3 mg/kg (n = 10); and IV - 0.4 mg/kg (n = 11). There were no significant hemodynamic changes in Groups I or II. In Groups III and IV mean arterial pressure (MAP) decreased 32% and 26% respectively, and systemic vascular resistance (SVR) decreased 42% and 36%, respectively (P less than 0.01). In Group IV, an increase of 24% in cardiac output was also significant (P less than 0.05). These results, especially in Group IV patients, stand in marked contrast to the lack of hemodynamic effects produced by metocurine during balanced anesthesia.     

Kinetics and extravascular retention of acetated ringer's solution during isoflurane or propofol anesthesia for thyroid surgery

BACKGROUND: In sheep, isoflurane causes extravascular accumulation of infused crystalloid fluid. The current study evaluates whether isoflurane has a greater tendency than propofol to cause extravascular retention in surgical patients. METHODS: Thirty patients undergoing thyroid surgery lasting for 143 +/- 32 min (mean +/- SD) received an intravenous infusion of 25 ml/kg acetated Ringer's solution over 30 min. Anesthesia was randomized to consist of isoflurane or propofol supplemented by fentanyl. The distribution and elimination of the infused fluid was estimated using volume kinetics based on the fractional dilution of blood hemoglobin over 150 min. Extravascular retention of infused fluid was taken as the difference between the model-predicted elimination and the urinary excretion. The sodium and fluid balances were measured. RESULTS: The fractional plasma dilution increased gradually to approximately 30% during the infusion and thereafter remained at 15-20%. Urinary excretion averaged 11% of the infused volume. Mean arterial pressure was 10 mmHg lower in the isoflurane group (P < 0.001). The excess fluid volumes in the central and peripheral functional body fluid spaces were virtually identical in the groups. The sum of water losses by evaporation and extravascular fluid retention amounted to 2.0 +/- 2.5 ml/min for isoflurane and 2.2 +/- 2.1 ml/min for propofol. The sodium balance refuted that major fluid shifts occurred between the extracellular and intracellular spaces. CONCLUSIONS: The amount of evaporation and extravascular retention of fluid was small during thyroid surgery, irrespective of whether anesthesia was maintained by isoflurane or propofol.     

Pulmonary gas exchange in coronary artery surgery patients during sevoflurane and isoflurane anesthesia

As the surgical population ages, the number of patients presenting with coronary artery disease and age-related loss of pulmonary recoil will increase. Although their influence on gas exchange in this population remains unknown, sevoflurane and isoflurane are used for an increasing variety of surgical procedures. We examined pulmonary gas exchange (multiple inert gas elimination technique) in 30 patients presenting for coronary artery bypass grafting. After a baseline measurement taken during midazolam anesthesia, patients were continued on sevoflurane (n = 10), isoflurane (n = 10), or midazolam (n = 10) for 20 min, then a second measurement was taken. During sevoflurane and isoflurane anesthesia, blood flow to lung areas with a low ventilation/perfusion ratio (Va/Q) was significantly increased in comparison with control. During sevoflurane anesthesia, blood flow to lung areas with a normal Va/Q ratio (76 +/- 12 versus control: 89 +/- 5, mean +/- SD) and PaO(2) (138 +/- 31 versus control: 156 +/- 35 mm Hg, mean +/- SD) were depressed, whereas an increase in Va/Q-dispersion (log SD(Q)) was observed during isoflurane anesthesia. We conclude that both sevoflurane and isoflurane alter the distribution of perfusion in the lung, but only sevoflurane significantly depresses PaO(2). IMPLICATIONS: Both sevoflurane and isoflurane modified pulmonary blood flow in patients with coronary artery disease, but only sevoflurane depresses arterial oxygenation in this population.     

Perioperative stress response in elderly patients for elective gastrectomy--the comparison between isoflurane anesthesia and sevoflurane anesthesia both combined with epidural anesthesia

The difference in stress responses between isoflurane anesthesia (I group) and sevoflurane anesthesia (S group) was studied. Twelve patients for elective gastrectomy were divided into two groups: S group, 7 patients, 78 +/- 4.3 years of age, and I group, 5 patients, 77.4 +/- 6.9 years of age. Anesthesia was induced by fentanyl, midazolam and sevoflurane or isoflurane with 100% oxygen. After laryngeal mask air way was inserted under spontaneous ventilation, anesthesia was maintained with air (3 l.min-1), oxygen (2 l.min-1), sevoflurane or isoflurane and epidural block. Vecuronium bromide was given during surgery when needed. The demographic data were not different between the two groups. During operation, it was confirmed that the responses of sympathetic nervous system (epinephrine, norepinephrine) and pituitary-adrenocortical system (ACTH, cortisol) were maintained in both groups. After operation plasma norepinephrine levels increased in both groups. Although the responses of I group tended to be stronger than that of S group, there was no significant difference between the two groups.     

Collapsibility of the upper airway during anesthesia with isoflurane

BACKGROUND: The unprotected upper airway tends to obstruct during general anesthesia, yet its mechanical properties have not been studied in detail during this condition. METHODS: To study its collapsibility, pressure-flow relationships of the upper airway were obtained at three levels of anesthesia (end-tidal isoflurane = 1.2%, 0.8%, and 0.4%) in 16 subjects while supine and spontaneously breathing on nasal continuous positive airway pressure. At each level of anesthesia, mask pressure was transiently reduced from a pressure sufficient to abolish inspiratory flow limitation (11.8 +/- 2.7 cm H(2)O) to pressures resulting in variable degrees of flow limitation. The relation between mask pressure and maximal inspiratory flow was determined, and the critical pressure at which the airway occluded was recorded. The site of collapse was determined from simultaneous measurements of nasopharyngeal, oropharyngeal, and hypopharyngeal and esophageal pressures. RESULTS: The airway remained hypotonic (minimal or absent intramuscular genioglossus electromyogram activity) throughout each study. During flow-limited breaths, inspiratory flow decreased linearly with decreasing mask pressure (r(2) = 0.86 +/- 0.17), consistent with Starling resistor behavior. At end-tidal isoflurane of 1.2%, critical pressure was 1.1 +/- 3.5 cm H O; at 0.4% it decreased to -0.2 +/- 3.6 cm H(2)O ( < 0.05), indicating decreased airway collapsibility. This decrease was associated with a decrease in end-expiratory esophageal pressure of 0.6 +/- 0.9 cm H(2)O ( < 0.05), suggesting an increased lung volume. Collapse occurred in the retropalatal region in 14 subjects and in the retrolingual region in 2 subjects, and did not change with anesthetic depth. CONCLUSIONS: Isoflurane anesthesia is associated with decreased muscle activity and increased collapsibility of the upper airway. In this state it adopts the behavior of a Starling resistor. The decreased collapsibility observed with decreasing anesthetic depth was not a consequence of neuromuscular activity, which was unchanged. Rather, it may be related to increased lung volume and its effect on airway wall longitudinal tension. The predominant site of collapse is the soft palate.     

Median nerve evoked responses and explicit memory during recovery from isoflurane/nitrous oxide anesthesia

PURPOSE: To evaluate median nerve somatosensory evoked responses during recovery from anesthesia in relation to clinical findings. METHODS: Twenty-two gynecologic patients received isoflurane in nitrous oxide for anesthesia. Midlatency somatosensory evoked responses (N20, P25, N35, P45, N50) were recorded the day before surgery (AWAKE), during steady state anesthesia (STABLE), and every five minutes after discontinuation of anesthesia until the patients were able to name a shown object correctly (RECOVERY). Next day the patients were questioned with a structured interview about their explicit memory of the immediate recovery period and classified into groups: No-MEM (no memory) and MEM (memory). Multivariate analysis of variance compared electrophysiological parameters at the different time points and between the two memory groups. RESULTS: During STABLE isoflurane/N2O anesthesia, all cortical amplitudes were reduced (P< or =0.003) and all latencies were prolonged compared with AWAKE (P<0.001). At RECOVERY the latencies N35, P45, N50 remained prolonged (P< or =0.001), while the amplitudes N20P25 and P45N50 were reduced in comparison to AWAKE (P< or =0.02). The latencies P45 (48+/-8 vs. 61+/-9 msec) and N50 (67+/-12 vs. 81+/-10 msec) were shorter in the patients of the group MEM (P< or =0.03) at RECOVERY. CONCLUSION: The reversibility of anesthetic induced changes in amplitudes and latencies of median nerve somatosensory evoked responses reflected clinical awakening during emergence from isoflurane/nitrous oxide anesthesia. In the patients who had recall for the immediate recovery period, the reversibility of anesthetic induced changes of components P45 and N50 was faster than in patients without recall.