Bispectral Index Changes Following Boluses of Commonly Used Intravenous Medications During Volatile Anesthesia Identified From Retrospective Data.

BACKGROUND: Although patients are commonly monitored for depth of anesthesia, it is unclear to what extent administration of intravenous anesthetic medications may affect calculated bispectral (BIS) index values under general anesthesia. METHODS: In a retrospective analysis of electronic anesthesia records from an academic medical center, we examined BIS index changes associated with 14 different intravenous medications, as administered in routine practice, during volatile-based anesthesia using a novel screening approach. Discrete-time windows were identified in which only a single drug bolus was administered, and subsequent changes in the BIS index, concentration of volatile anesthetic, and arterial pressure were analyzed. Our primary outcome was change in BIS index, following drug administration. Adjusted 95% confidence intervals were compared to predetermined thresholds for clinical significance. Secondary sensitivity analyses examined the same outcomes, with available data separated according to differences in baseline volatile anesthetic concentrations, doses of the administered medications, and length of time window. RESULTS: The study cohort was comprised of data from 20,170 distinct cases, 54.7% of patients were men, with a median age of 55. In the primary analysis, ketamine at a median dose of 20 mg was associated with a median (confidence limits) increase in BIS index of 3.8 (2.5-5.0). Midazolam (median dose 2 mg) was associated with a median decrease in BIS index of 3.0 (1.5-4.5). Neither of these drug administrations occurred during time periods associated with changes in volatile anesthetic concentration. Analysis for dexmedetomidine was confounded by concomitant decreases in volatile anesthetic concentration. No other medication analyzed, including propofol and common opioids, was associated with a significant change in BIS index. Secondary analyses revealed that similar BIS index changes occurred when midazolam and ketamine were administered at different volatile anesthetic concentrations and different doses, and these changes persisted 11 to 20 minutes postadministration. CONCLUSIONS: Modest, but persistent changes in BIS index occurred following doses of ketamine (increase) and midazolam (decrease) during periods of stable volatile anesthetic administration.

Neutral auditory words immediately followed by painful electric shock may show reduced next-day recollection.

In this study, we investigated the effect of experimentally delivered acute pain on memory. Twenty-five participants participated in experimental sessions on consecutive days. The first session involved a categorization task to encourage memory encoding. There were two conditions, presented in randomized order, in which participants listened to a series of words, which were repeated three times. In one condition, one-third of the word items were immediately followed by a painful electrical shock. This word-shock pairing was consistent across repetition and the pain-paired items were presented unpredictably. In the other condition, all word items were not associated with pain. Response times over these repeated presentations were assessed for differences. Explicit memory was tested the following day, employing a Remember-Know assessment of word recognition, with no shocks employed. We found evidence that recollection may be reduced for pain-paired words, as the proportion of correct Remember responses (out of total correct responses) was significantly lower. There were no significant reductions in memory for non-pain items that followed painful stimulation after a period of several seconds. Consistent with the experience of pain consuming working memory resources, we theorize that painful shocks interrupt memory encoding for the immediately preceding experimental items, due to a shift in attention away from the word item.

Realising the potential of functional imaging to reveal brain changes after anaesthesia and surgery.

We highlight the ability of functional brain imaging to detect changes in human brain function, even when changes are not seen in cognitive testing. These imaging changes are plausible as they correlate with known activity changes in carriers of APOE4, a genetic variant associated with increased risk for Alzheimer's disease. However, to realise the potential of functional imaging for perioperative neurocognitive disorders, collaborations similar to the Alzheimer's Disease Neuroimaging Initiative (ADNI) with open data sharing will be required. For the practicing anaesthesiologist, we believe that postoperative cognitive issues are important topics to discuss during the informed consent process.

Day-One Pain Reductions After Hip and Knee Replacement When Buprenorphine-Clonidine-Dexamethasone Is Added to Bupivacaine Nerve/Plexus Blocks: A Randomized Clinical Trial.

OBJECTIVE: To compare pain outcome reports of patients undergoing hip or knee replacement who received single-injection nerve/plexus blocks with plain bupivacaine (BPV) with those of patients who received injections of buprenorphine-clonidine-dexamethasone (BCD) admixed with BPV. DESIGN: Prospective, parallel-arm, randomized, double-blind trial. SETTING: A single veterans' hospital. SUBJECTS: Ninety-eight veterans scheduled for total hip or knee replacement surgery with spinal as the primary anesthetic. METHODS: Participants were randomized to BPV-BCD or plain BPV groups. They underwent nerve/plexus blocks in the L2-L4 and L4-S3 distributions in advance of joint replacement surgery. The primary outcome was change in pain from baseline during the postoperative day, as assessed by the total pain score on the short-form McGill Pain Questionnaire-v2 (SF-MPQ-2). Secondary outcomes were pain during movement, pain interference, range of motion, mobility, and quality of recovery. RESULTS: On postoperative day one, the SF-MPQ-2 total score for the BPV-BCD group demonstrated greater pain reduction than that of the plain BPV group (mean difference 1.8 points, 95% confidence interval 0.6 to 3.0, P = 0.003). The BPV-BCD group also had larger reductions in pain during movement in the surgical joint and less pain interference, along with increased range of hip and knee flexion, compared with the plain BPV group. Outcomes of mobility and quality of recovery were not different between groups. CONCLUSIONS: Preoperative BPV-BCD blocks in the L2-L4 and L4-S3 nerve distributions for hip and knee replacements led to less pain on postoperative day one and increased knee and hip range of motion, compared with plain BPV blocks. TRIAL REGISTRATION: ClinicalTrials.gov ID NCT02891798.

Comparison of test-retest reliability of BOLD and pCASL fMRI in a two-center study.

BACKGROUND: The establishment of test-retest reliability and reproducibility (TRR) is an important part of validating any research tool, including functional magnetic resonance imaging (fMRI). The primary objective of this study is to investigate the reliability of pseudo-Continuous Arterial Spin Labeling (pCASL) and Blood Oxygen Level Dependent (BOLD) fMRI data acquired across two different scanners in a sample of healthy adults. While single site/single scanner studies have shown acceptable repeatability, TRR of both in a practical multisite study occurring in two facilities spread out across the country with weeks to months between scans is critically needed. METHODS: Ten subjects were imaged with similar 3 T MRI scanners at the University of Pittsburgh and Massachusetts General Hospital. Finger-tapping and Resting-state data were acquired for both techniques. Analysis of the resting state data for functional connectivity was performed with the Functional Connectivity Toolbox, while analysis of the finger tapping data was accomplished with FSL. pCASL Blood flow data was generated using AST Toolbox. Activated areas and networks were identified via pre-defined atlases and dual-regression techniques. Analysis for TRR was conducted by comparing pCASL and BOLD images in terms of Intraclass correlation coefficients, Dice Similarity Coefficients, and repeated measures ANOVA. RESULTS: Both BOLD and pCASL scans showed strong activation and correlation between the two locations for the finger tapping tasks. Functional connectivity analyses identified elements of the default mode network in all resting scans at both locations. Multivariate repeated measures ANOVA showed significant variability between subjects, but no significant variability for location. Global CBF was very similar between the two scanning locations, and repeated measures ANOVA showed no significant differences between the two scanning locations. CONCLUSIONS: The results of this study show that when similar scanner hardware and software is coupled with identical data analysis protocols, consistent and reproducible functional brain images can be acquired across sites. The variability seen in the activation maps is greater for pCASL versus BOLD images, as expected, however groups maps are remarkably similar despite the low number of subjects. This demonstrates that multi-site fMRI studies of task-based and resting state brain activity is feasible.

Midazolam and Ketamine Produce Distinct Neural Changes in Memory, Pain, and Fear Networks during Pain.

BACKGROUND: Despite the well-known clinical effects of midazolam and ketamine, including sedation and memory impairment, the neural mechanisms of these distinct drugs in humans are incompletely understood. The authors hypothesized that both drugs would decrease recollection memory, task-related brain activity, and long-range connectivity between components of the brain systems for memory encoding, pain processing, and fear learning. METHODS: In this randomized within-subject crossover study of 26 healthy adults, the authors used behavioral measures and functional magnetic resonance imaging to study these two anesthetics, at sedative doses, in an experimental memory paradigm using periodic pain. The primary outcome, recollection memory performance, was quantified with d' (a difference of z scores between successful recognition versus false identifications). Secondary outcomes were familiarity memory performance, serial task response times, task-related brain responses, and underlying brain connectivity from 17 preselected anatomical seed regions. All measures were determined under saline and steady-state concentrations of the drugs. RESULTS: Recollection memory was reduced under midazolam (median [95% CI], d' = 0.73 [0.43 to 1.02]) compared with saline (d' = 1.78 [1.61 to 1.96]) and ketamine (d' = 1.55 [1.12 to 1.97]; P < 0.0001). Task-related brain activity was detected under saline in areas involved in memory, pain, and fear, particularly the hippocampus, insula, and amygdala. Compared with saline, midazolam increased functional connectivity to 20 brain areas and decreased to 8, from seed regions in the precuneus, posterior cingulate, and left insula. Compared with saline, ketamine decreased connectivity to 17 brain areas and increased to 2, from 8 seed regions including the hippocampus, parahippocampus, amygdala, and anterior and primary somatosensory cortex. CONCLUSIONS: Painful stimulation during light sedation with midazolam, but not ketamine, can be accompanied by increased coherence in brain connectivity, even though details are less likely to be recollected as explicit memories.

Extended Perineural Analgesia After Hip and Knee Replacement When Buprenorphine-Clonidine-Dexamethasone Is Added to Bupivacaine: Preliminary Report from a Randomized Clinical Trial.

OBJECTIVE: We tested the hypothesis that buprenorphine-clonidine-dexamethasone (BCD) extends perineural analgesia compared with plain bupivacaine (BPV) nerve blocks used for hip and knee replacement surgery. DESIGN: Prospective, parallel-arms, randomized, double-blind trial. SETTING: A single veterans' hospital. SUBJECTS: Seventy-eight veterans scheduled for total hip or knee replacement with plans for spinal as the primary anesthetic. METHODS: Participants underwent nerve/plexus blocks at L2-L4 and L4-S3 in advance of hip or knee joint replacement surgery. Patients were randomized to receive BPV-BCD or plain BPV in a 4:1 allocation ratio. Patients answered four block duration questions (listed below). Time differences between treatments were analyzed using the t test. RESULTS: Significant (P < 0.001) prolongation of the time parameters was reported by patients after the BPV-BCD blocks (N = 62) vs plain BPV (N = 16). The time until start of postoperative pain was 26 vs 11 hours (mean difference = 15 hours, 95% CI = 8 to 21). The time until no pain relief from the blocks was 32 vs 15 hours (mean difference = 17 hours, 95% CI = 10 to 24). The time until the numbness wore off was 37 vs 21 hours (mean difference = 16 hours, 95% CI = 8 to 23). The time until the worst postoperative pain was 39 vs 20 hours (mean difference = 19 hours, 95% CI = 11 to 27). CONCLUSIONS: BPV-BCD provided 26-39 hours of perineural analgesia in the L2-L4 and L4-S3 nerve distributions after hip/knee replacement surgery, compared with 11-21 hours for plain BPV.

Retrospective analysis of cases of intraoperative awareness in a large multi-hospital health system reported in the early postoperative period.

BACKGROUND: Awareness with recall under general anesthesia remains a rare but important issue that warrants further study. METHODS: We present a series of seven cases of awareness that were identified from provider-reported adverse event data from the electronic anesthesia records of 647,000 general anesthetics. RESULTS: The low number of identified cases suggests an under-reporting bias. Themes that emerge from this small series can serve as important reminders to anesthesia providers to ensure delivery of an adequate anesthetic for each patient. Commonalities between a majority of our identified anesthetic awareness cases include: obesity, use of total intravenous anesthesia, use of neuromuscular blockade, and either a lack of processed electroencephalogram (EEG) monitoring or documented high depth of consciousness index values. An interesting phenomenon was observed in one case, where adequately-dosed anesthesia was delivered without technical issue, processed EEG monitoring was employed, and the index value suggested an adequate depth of consciousness throughout the case. CONCLUSIONS: Provider-reported adverse event data in the immediate post-operative period are likely insensitive for detecting cases of intraoperative awareness. Though causation cannot firmly be established from our data, themes identified in this series of cases of awareness with recall under general anesthesia provide important reminders for anesthesia providers to maintain vigilance in monitoring depth and dose of anesthesia, particularly with total intravenous anesthesia.

The triple variable index combines information generated over time from common monitoring variables to identify patients expressing distinct patterns of intraoperative physiology.

BACKGROUND: Mean arterial pressure (MAP), bispectral index (BIS), and minimum alveolar concentration (MAC) represent valuable, yet dynamic intraoperative monitoring variables. They provide information related to poor outcomes when considered together, however their collective behavior across time has not been characterized. METHODS: We have developed the Triple Variable Index (TVI), a composite variable representing the sum of z-scores from MAP, BIS, and MAC values that occur together during surgery. We generated a TVI expression profile, defined as the sequential TVI values expressed across time, for each surgery where concurrent MAP, BIS, and MAC monitoring occurred in an adult patient (≥18 years) at the University of Pittsburgh Medical Center between January and July 2014 (n = 5296). Patterns of TVI expression were identified using k-means clustering and compared across numerous patient, procedure, and outcome characteristics. TVI and the triple low state were compared as prediction models for 30-day postoperative mortality. RESULTS: The median frequency MAP, BIS, and MAC were recorded was one measurement every 3, 5, and 5 min. Three expression patterns were identified: elevated, mixed, and depressed. The elevated pattern displayed the highest average MAP, BIS, and MAC values (86.5 mmHg, 45.3, and 0.98, respectively), while the depressed pattern displayed the lowest values (76.6 mmHg, 38.0, 0.66). Patterns (elevated, mixed, depressed) were distinct across the following characteristics: average patient age (52, 53, 54 years), American Society of Anesthesiologists Physical Status 4 (6.7, 16.1, 27.3%) and 5 (0.1, 0.6, 1.6%) categories, cardiac (2.2, 6.5, 16.1%) and emergent (5.8, 10.5, 12.8%) surgery, cardiopulmonary bypass use (0.3, 2.6, 9.8%), intraoperative medication administration including etomidate (3.0, 7.3, 12.6%), hydromorphone (47.6, 26.3, 25.2%), ketamine (11.2, 4.6, 3.0%), dexmedetomidine (18.4, 16.6, 13.6%), phenylephrine (74.0, 74.8, 83.0), epinephrine (2.0, 6.0, 18.0%), norepinephrine (2.4, 7.5, 21.2%), vasopressin (3.4, 7.6, 21.0%), succinylcholine (74.0, 69.0, 61.9%), intraoperative hypotension (28.8, 33.0, 52.3%) and the triple low state (9.4, 30.3, 80.0%) exposure, and 30-day postoperative mortality (0.8, 2.7, 5.6%). TVI was a better predictor of patients that died or survived in the 30 days following surgery compared to cumulative triple low state exposure (AUC 0.68 versus 0.62, p < 0.05). CONCLUSIONS: Surgeries that share similar patterns of TVI expression display distinct patient, procedure, and outcome characteristics.

Memory for non-painful auditory items is influenced by whether they are experienced in a context involving painful electrical stimulation.

In this study, we sought to examine the effect of experimentally induced somatic pain on memory. Subjects heard a series of words and made categorization decisions in two different conditions. One condition included painful shocks administered just after presentation of some of the words; the other condition involved no shocks. For the condition that included painful stimulations, every other word was followed by a shock, and subjects were informed to expect this pattern. Word lists were repeated three times within each condition in randomized order, with different category judgments but consistent pain-word pairings. After a brief delay, recognition memory was assessed. Non-pain words from the pain condition were less strongly encoded than non-pain words from the completely pain-free condition. Recognition of pain-paired words was not significantly different than either subgroup of non-pain words. An important accompanying finding is that response times to repeated experimental items were slower for non-pain words from the pain condition, compared to non-pain words from the completely pain-free condition. This demonstrates that the effect of pain on memory may generalize to non-pain items experienced in the same experimental context.

Updated Retrospective Single-Center Comparative Analysis of Peripheral Nerve Block Complications Using Landmark Peripheral Nerve Stimulation Versus Ultrasound Guidance as a Primary Means of Nerve Localization.

OBJECTIVES: The purpose of this study was to perform an updated analysis of complications associated with upper and lower extremity peripheral nerve blocks (PNBs) performed with ultrasound (US) guidance versus the landmark approach. METHODS: We conducted a single-center retrospective cohort analysis to compare the incidence of PNB complications between the techniques. The primary outcome was local anesthetic systemic toxicity (LAST), whereas the secondary outcomes included short- and long-term nerve injuries. The current query included cases performed between 2012 and 2015. A combined analysis included data extending to 2006. The Statistical examination relied on the χ2 test. RESULTS: During this 4-year period, we performed 7789 US-guided and 498 landmark-guided blocks with no statistically significant difference in the incidence of nerve injury or LAST between the groups. Our 10-year analysis, however, revealed a significant increase (P < .01) in the rate of LAST with the landmark technique: 7 of 5932 versus 0 of 16,858 cases. The combined data also revealed a significant increase (P < .01) in short-term injuries associated with the landmark approach (30 of 5932 versus 33 of 16,858) but no significant difference in the incidence of long-term injuries. CONCLUSIONS: Our analysis supports a conclusion that the use of US guidance during PNBs leads to a significant reduction in the incidence of LAST, adding to growing evidence from similar investigations. The impact of US on the incidence of nerve injuries remains unclear, considering that the nature of transient deficits is thought to be multifactorial, and the frequency of lasting injuries did not differ significantly in this study.

GlideScope Use improves intubation success rates: an observational study using propensity score matching.

BACKGROUND: Rigid video laryngoscopes are popular alternatives to direct laryngoscopy for intubation, but further large scale prospective studies comparing these devices to direct laryngoscopy in routine anesthesiology practice are needed. We hypothesized that the first pass success rate with one particular video laryngoscope, the GlideScope, would be higher than the success rate with direct laryngoscopy. METHODS: 3831 total intubation attempts were tracked in an observational study comparing first-pass success rate using a Macintosh or Miller-style laryngoscope with the GlideScope. Propensity scoring was then used to select 626 subjects matched between the two groups based on their morphologic traits. RESULTS: Comparing the GlideScope and direct laryngoscopy groups suggested that intubation would be more difficult in the GlideScope group based on the Mallampati class, cervical range of motion, mouth opening, dentition, weight, and past intubation history. Thus, a propensity score based on these factors was used to balance the groups into two 313 patient cohorts. Direct laryngoscopy was successful in 80.8% on the first-pass intubation attempt, while the GlideScope was successful in 93.6% (p <0.001; risk difference of 0.128 with a 95% CI of 0.0771 - 0.181). CONCLUSION: A greater first-attempt success rate was found when using the GlideScope versus direct laryngoscopy. In addition, the GlideScope was found to be 99% successful for intubation after initial failure of direct laryngoscopy, helping to reduce the incidence of failed intubation.

Characterization of pulsations in the brain and cerebrospinal fluid using ultra-high field magnetic resonance imaging.

The development of innovative non-invasive neuroimaging methods and biomarkers is critical for studying brain disease. Imaging of cerebrospinal fluid (CSF) pulsatility may inform the brain fluid dynamics involved in clearance of cerebral metabolic waste. In this work, we developed a methodology to characterize the frequency and spatial localization of whole brain CSF pulsations in humans. Using 7 Tesla (T) human magnetic resonance imaging (MRI) and ultrafast echo-planar imaging (EPI), in-vivo images were obtained to capture pulsations of the CSF signal. Physiological data were simultaneously collected and compared with the 7 T MR data. The primary components of signal pulsations were identified using spectral analysis, with the most evident frequency bands identified around 0.3, 1.2, and 2.4 Hz. These pulsations were mapped spatially and temporally onto the MR image domain and temporally onto the physiological measures of electrocardiogram and respiration. We identified peaks in CSF pulsations that were distinct from peaks in grey matter and white matter regions. This methodology may provide novel in vivo biomarkers of disrupted brain fluid dynamics.

Validity of the Modified Defense and Veterans Pain Rating Scale Supplemented With Items Germane to Total Joint Replacement: Secondary Analysis From a Randomized Trial.

INTRODUCTION: Valid measures of pain are helpful to adjust treatment plans in real time after total joint replacement (TJR). We enhanced the existing Defense and Veterans Pain Rating Scale (DVPRS) with items related to pain at rest and movement, in specific reference to operative and nonoperative joints, creating the TJR-DVPRS. This manuscript is presented to validate the modified survey instrument. The aims of this psychometric study were to evaluate (1) the latent structure of the TJR-DVPRS, (2) the relationships among the pain dimensions represented on the TJR-DVPRS and the reference-standard Short-Form McGill Pain Questionnaire (version 2, SF-MPQ-2), and (3) the responsiveness of these two measures before and after TJR. MATERIALS AND METHODS: This report involves a secondary analysis of pain surveys from 135 veterans undergoing TJR at one center who participated in a randomized trial. The study was approved by the institutional review boards from participating institutions. The TJR-DVPRS and SF-MPQ-2 were completed preoperatively, during postoperative day 1, and 6 weeks post-surgery. Standard psychometric evaluations included correlations, principal component analysis, and internal consistency of survey items and subscales, using preoperative baseline data as a frame of reference. Responsiveness analysis included assessing both effect size and thresholds of clinically important change for survey subscales using data from all three time points. RESULTS: Two reliable subscales were identified for the TJR-DVPRS, one including items about pain intensity and interference related to the operative joint (Cronbach's α = .809) and the other including two pain items on the nonoperative joint. Combining the subscales indicated a two-factor solution: The first valid factor entailed the four subscales of the SF-MPQ-2 and the TJR-DVPRS operative joint subscales, indicating that these subscales validly represent the same pain dimension. The second valid factor entailed the TJR-DVPRS subscale addressing the nonoperative joint. Responsiveness analysis following accepted psychometric methods demonstrated significant decreases in pain from the preoperative period to 6 weeks postoperatively for all subscales. The TJR-DVPRS and SF-MPQ-2 subscales were similarly responsive, except for the SF-MPQ-2 neuropathic and TJR-DVPRS nonoperative joint subscales, which were minimally responsive during the preoperative to 6-week period. CONCLUSIONS: The TJR-DVPRS is valid for use among veterans undergoing TJR and poses significantly less respondent burden than does the SF-MPQ-2. The brevity and ease of use of the TJR-DVPRS make it a practical tool for use during surgical recovery to monitor pain intensity at rest and with movement in the operative joint, and to assess pain interference with activity, sleep, and mood. The TJR-DVPRS is at least as responsive as the SF-MPQ-2, but the SF-MPQ-2 neuropathic and TJR-DVPRS nonoperative joint subscales were minimally responsive. Limitations of this study include the small sample size, under-representation of women (which would be expected in the veteran population), and using only veterans. Future validations studies should include civilians and active military TJR patients.

Assessing Common Content and Responsiveness of the QoR-15 and the SF-8 in the Context of Recovery from Regional Anesthesia for Joint Replacement.

PURPOSE: There is no consensus regarding how best to measure postoperative quality of recovery after anesthesia/surgery (e.g., using 24-hour survey instruments) in veterans or active military. Our goals were to (1) describe health-related quality-of-life (HRQoL) and recovery across time in veterans, (2) examine the commonality between the quality of recovery (QoR-15) and short-form (SF) surveys (including the SF-8, 24-hour version), and (3) examine the responsiveness of these surveys. MATERIALS AND METHODS: This study was approved by the Institutional Review Boards from the University of Pittsburgh, the VA Pittsburgh, and the Human Research Protection Office of the Department of Defense. Secondary analyses of data were executed based on a randomized trial dataset of knee/hip arthroplasty patients, the study having recruited 135 total veterans. QoR-15 and HRQoL SF surveys were completed and self-reported before surgery (pre-op), on postoperative day 2 (PO-D2), and 6 weeks postoperatively. Descriptive statistics were used to examine scores across time. Common content was examined using Pearson's r. Responsiveness was examined using distribution-based methods. RESULTS: Average veteran age was 67 year, 89% were male, 88% white, and average body mass index was 33 kg∙m-2. QoR-15 scores declined from pre-op to PO-D2 but were higher than pre-op at 6 weeks. SF physical component summary (PCS) scores were low both pre-op and PO-D2, but were elevated over baseline at 6 weeks. SF mental component summary (MCS) scores declined from baseline to PO-D2 but were higher than pre-op at 6 weeks. Associations of the QoR-15 total score and PCS/MCS were medium/large and statistically significant at P ≤ .01. Both instruments were responsive to changes. CONCLUSION: QoR-15 and SF-8 have high content commonality and performed similarly in veterans across time. SF-8 has added benefits of (1) brevity, (2) assessment of physical and mental health components, and (3) being normed to the general population. The SF-8, if used without the QoR-15 in tandem in future study of anesthesia-related outcomes, would need to be supplemented by separate questions addressing postoperative nausea/vomiting (a frequent outcome after anesthesia that is relevant to same-day and next-day mobilization after elective joint replacement surgery).