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.

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

Development of innovative non-invasive neuroimaging methods and biomarkers are critical for studying brain disease. In this work, we have developed a methodology to characterize the frequency responses and spatial localization of oscillations and movements of cerebrospinal fluid (CSF) flow in the human brain. Using 7 Tesla human MRI and ultrafast echo-planar imaging (EPI), in-vivo images were obtained to capture CSF oscillations and movements. Physiological data was simultaneously collected and correlated with the 7T MR data. The primary components of CSF oscillations were identified using spectral analysis (with frequency bands identified around 0.3Hz, 1.2Hz and 2.4Hz) and were mapped spatially and temporally onto the MR image domain and temporally onto the physiological domain. The developed methodology shows a good consistency and repeatability (standard deviation of 0.052 and 0.078 for 0.3Hz and 1.2Hz bands respectively) in-vivo for potential brain dynamics and CSF flow and clearance studies.

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).

Brain connectivity under light sedation with midazolam and ketamine during task performance and the periodic experience of pain: Examining concordance between different approaches for seed-based connectivity analysis

This work focused on functional connectivity changes under midazolam and ketamine sedation during performance of a memory task, with the periodic experience of pain. To maximize ability to compare to previous and future work, we performed secondary region of interest (ROI)-to-ROI functional connectivity analyses on these data, using two granularities of scale for ROIs. These findings are compared to the results of a previous seed-to-voxel analysis methodology, employed in the primary analysis. Healthy adult volunteers participated in this randomized crossover 3 T functional MRI study under no drug, followed by subanesthetic doses of midazolam or ketamine achieving minimal sedation. Periodic painful stimulation was delivered while subjects repeatedly performed a memory-encoding task. Atlas-based and network-level ROIs were used from within Conn Toolbox (ver 18). Timing of experimental task events was regressed from the data to assess drug-induced changes in background connectivity, using ROI-to-ROI methodology. Compared to saline, ROI-to-ROI connectivity changes under ketamine did not survive correction for multiple comparisons, thus data presented is from 16 subjects in a paired analysis between saline and midazolam. In both ROI-to-ROI analyses, the predominant direction of change was towards increased connectivity under midazolam, compared to saline. These connectivity increases occurred between functionally-distinct brain areas, with a posterior-predominant spatial distribution that included many long-range connectivity changes. During performance of an experimental task that involved periodic painful stimulation, compared to saline, low-dose midazolam was associated with robust increases in functional connectivity. This finding was concordant across different seed-based analyses for midazolam, but not ketamine. The neuroimaging drug trial from which this data was drawn was pre-registered (NCT-02515890) prior to enrollment of the first subject.

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.

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.

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) to patients who received injections of buprenorphine-clonidine-dexamethasone (BCD) admixed with BPV.

DESIGN

Prospective, parallel arms, randomized, double-blind trial.

SETTING

A single Veterans hospital.

SUBJECTS

98 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 post-operative day assessed by the total pain score in 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 post-operative day one, the SF-MPQ-2 total score for the BPV-BCD group demonstrated greater pain reduction compared to the plain BPV group (mean difference 1.8 points, 95% CI 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 to 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 post-operative day one and increased knee and hip range of motion, compared to plain BPV blocks.

Accelerated brain aging in chronic low back pain

Chronic low back pain (CLBP) is a leading cause of disability and is associated with neurodegenerative changes in brain structure. These changes lead to impairments in cognitive function and are consistent with those seen in aging, suggesting an accelerated aging pattern. In this study we assessed this using machine-learning estimated brain age (BA) as a holistic metric of morphometric changes associated with aging. Structural imaging data from 31 non-depressed CLBP patients and 32 healthy controls from the Pain and Interoception Imaging Network were included. Using our previously developed algorithm, we estimated BA per individual based on grey matter density. We then conducted multivariable linear modeling for effects of group, chronological age, and their interaction on BA. We also performed two voxel-wise analyses comparing grey matter density between CLBP and control individuals and the association between gray matter density and BA. There was an interaction between CLBP and greater chronological age on BA such that the discrepancy in BA between healthy and CLBP individuals was greater for older individuals. In CLBP individuals, BA was not associated with sex, current level of pain, duration of CLBP, or mild to moderate depressive symptoms. CLBP individuals had lower cerebellar grey matter density compared to healthy individuals. Brain age was associated with lower gray matter density in numerous brain regions. CLBP was associated with greater BA, which was more profound in later life. BA as a holistic metric was sensitive to differences in gray matter density in numerous regions which eluded direct comparison between groups.

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.

Association of Preoperative Patient Frailty and Operative Stress With Postoperative Mortality

Importance

Patients with frailty have higher risk for postoperative mortality and complications; however, most research has focused on small groups of high-risk procedures. The associations among frailty, operative stress, and mortality are poorly understood.

Objective

To assess the association between frailty and mortality at varying levels of operative stress as measured by the Operative Stress Score, a novel measure created for this study.

Design, Setting, and Participants

This retrospective cohort study included veterans in the Veterans Administration Surgical Quality Improvement Program from April 1, 2010, through March 31, 2014, who underwent a noncardiac surgical procedure at Veterans Health Administration Hospitals and had information available on vital status (whether the patient was alive or deceased) at 1 year postoperatively. A Delphi consensus method was used to stratify surgical procedures into 5 categories of physiologic stress.

Exposures

Frailty as measured by the Risk Analysis Index and operative stress as measured by the Operative Stress Score.

Main Outcomes and Measures

Postoperative mortality at 30, 90, and 180 days.

Results

Of 432 828 unique patients (401 453 males [92.8%]; mean (SD) age, 61.0 [12.9] years), 36 579 (8.5%) were frail and 9113 (2.1%) were very frail. The 30-day mortality rate among patients who were frail and underwent the lowest-stress surgical procedures (eg, cystoscopy) was 1.55% (95% CI, 1.20%-1.97%) and among patients with frailty who underwent the moderate-stress surgical procedures (eg, laparoscopic cholecystectomy) was 5.13% (95% CI, 4.79%-5.48%); these rates exceeded the 1% mortality rate often used to define high-risk surgery. Among patients who were very frail, 30-day mortality rates were higher after the lowest-stress surgical procedures (10.34%; 95% CI, 7.73%-13.48%) and after the moderate-stress surgical procedures (18.74%; 95% CI, 17.72%-19.80%). For patients who were frail and very frail, mortality continued to increase at 90 and 180 days, reaching 43.00% (95% CI, 41.69%-44.32%) for very frail patients at 180 days after moderate-stress surgical procedures.

Conclusions and Relevance

We developed a novel operative stress score to quantify physiologic stress for surgical procedures. Patients who were frail and very frail had high rates of postoperative mortality across all levels of the Operative Stress Score. These findings suggest that frailty screening should be applied universally because low- and moderate-stress procedures may be high risk among patients who are frail.

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.

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.

Electronic supplementary material

The online version of this article (10.1186/s12874-019-0660-9) contains supplementary material, which is available to authorized users.

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.

Human Posterior Insula Functional Connectivity Differs Between Electrical Pain and the Resting State

The objective in this study was to directly compare MRI-based functional connectivity between conditions of rest and painful electrical nerve stimulation for key regions involved in pain processing: the anterior and posterior insula and the anterior cingulate cortex. Electric nerve stimulation, rated 7/10 for pain, was delivered to the right index finger of 14 healthy pain-free adult volunteers in four 30-sec blocks and continuously for 2 min. Functional connectivity maps obtained at rest and during both pain tasks were compared using seed time courses from the left anterior and posterior insula and anterior cingulate. Significant Pain versus Rest connectivity differences were consistently shown for the posterior insula, notably to the posterior cingulate and precuneus, while minimal and inconsistent differences were observed for the anterior insula and anterior cingulate. This study reinforces the known differences that can occur with changes in seed region selection in functional connectivity analysis. It also presents preliminary evidence that functional connectivity for the left posterior insula can potentially differentiate the presence of acute right-sided electrical pain from the nonpainful resting state.

Optimizing and Interpreting Insular Functional Connectivity Maps Obtained During Acute Experimental Pain: The Effects of Global Signal and Task Paradigm Regression

The insula is uniquely located between the temporal and parietal cortices, making it anatomically well-positioned to act as an integrating center between the sensory and affective domains for the processing of painful stimulation. This can be studied through resting-state functional connectivity (fcMRI) imaging; however, the lack of a clear methodology for the analysis of fcMRI complicates the interpretation of these data during acute pain. Detected connectivity changes may reflect actual alterations in low-frequency synchronous neuronal activity related to pain, may be due to changes in global cerebral blood flow or the superimposed task-induced neuronal activity. The primary goal of this study was to investigate the effects of global signal regression (GSR) and task paradigm regression (TPR) on the changes in functional connectivity of the left (contralateral) insula in healthy subjects at rest and during acute painful electric nerve stimulation of the right hand. The use of GSR reduced the size and statistical significance of connectivity clusters and created negative correlation coefficients for some connectivity clusters. TPR with cyclic stimulation gave task versus rest connectivity differences similar to those with a constant task, suggesting that analysis which includes TPR is more accurately reflective of low-frequency neuronal activity. Both GSR and TPR have been inconsistently applied to fcMRI analysis. Based on these results, investigators need to consider the impact GSR and TPR have on connectivity during task performance when attempting to synthesize the literature.

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.

Pain does not follow the boxcar model: temporal dynamics of the BOLD fMRI signal during constant current painful electric nerve stimulation

The temporal dynamics of the blood oxygen level-dependent (BOLD) signal, especially for painful stimulations, is not completely understood. In this study, the BOLD signal response to a long painful electrical stimulation (a continuous painful stimulation of 2 minutes) is directly compared to that of a short painful stimulation (four 30-second periods of painful stimulation interleaved with 30-second rest) in an effort to further probe the relationship between the temporal dynamics of the BOLD signal during constant-intensity pain stimulation. Time course analysis showed that both stimulation protocols produced 3 similarly timed peaks in both data sets, suggesting an early and delayed BOLD response to painful stimulation initiation, and a response related to stimulus termination. Despite the continuous stimulation, the BOLD signal returned to baseline in the 2-minute task. Even with this signal discrepancy, however, the activation maps of the 2 pain tasks differed only slightly, suggesting that the bulk of the activation is determined by the sharp rise in BOLD signal with stimulus onset. These findings imply that the BOLD signal response time course is not directly reflective of pain perception.

PERSPECTIVE

This article demonstrates that the BOLD signal for a painful stimulation contains multiple peaks and does not maintain the constant level during stimulation that is assumed in typical analysis. Although these dynamics should be accounted for in future studies because of their ability to confound results, their presence did not significantly alter the overall group maps.

Peripheral intravenous catheter infiltration: anesthesia providers do not adhere to their own ideas of best practice

STUDY OBJECTIVE

To survey anesthesia providers for their opinion on "best practice" in perioperative peripheral intravenous catheter (PIV) management, and to determine if they follow those opinions.

DESIGN

Survey instrument.

SETTING

Academic medical center.

SUBJECTS

266 United States (U.S.) anesthesia provider respondents (attending anesthesiologists, anesthesiology residents, anesthesia assistants, certified registered nurse-anesthetists and student registered nurse-anesthetists).

MEASUREMENTS

Between May 2009 and October 2010 a national survey was distributed to individuals who provide intraoperative anesthesia care to patients. Results were gathered via the SurveyMonkey database.

MAIN RESULTS

266 anesthesia providers from across the U.S. took part in the survey. The majority (70%) had less than 5 years' experience. Nearly 90% of respondents cared for a patient with an intravenous catheter infiltration at some point during their training; 7% of these patients required medical intervention. Intravenous assessment and documentation practices showed great variability. Management and documentation of PIVs was more aggressive and vigilant when respondents were asked about "best practice" than about actual management.

CONCLUSION

There is no commonly accepted standard for management and documentation of PIVs in the operating room. From our survey, what providers think is "best practice" in the management and documentation of PIVs is not what is being done.

Comparison between end-tidal CO₂ and respiration volume per time for detecting BOLD signal fluctuations during paced hyperventilation

Respiratory motion and capnometry monitoring were performed during blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI) of the brain while a series of paced hyperventilation tasks were performed that caused significant hypocapnia. Respiration volume per time (RVT) and end-tidal carbon dioxide (ETCO(2)) were determined and compared for their ability to explain BOLD contrast changes in the data. A 35% decrease in ETCO(2) was observed along with corresponding changes in RVT. A best-fit ETCO(2) response function, with an average initial peak delay time of 12 s, was empirically determined. ETCO(2) data convolved with this response function was more strongly and prevalently correlated to BOLD signal changes than RVT data convolved with the corresponding respiration response function. The results suggest that ETCO(2) better models BOLD signal fluctuations in fMRI experiments with significant transient hypocapnia. This is due to hysteresis in the ETCO(2) response when moving from hypocapnia to normocapnia, compared to moving from normocapnia to hypocapnia.

The impact of physiologic noise correction applied to functional MRI of pain at 1.5 and 3.0 T

This study quantified the impact of the well-known physiologic noise correction algorithm RETROICOR applied to a pain functional magnetic resonance imaging (FMRI) experiment at two field strengths: 1.5 and 3.0 T. In the 1.5-T acquisition, there was an 8.2% decrease in time course variance (σ) and a 227% improvement in average model fit (increase in mean R(2)(a)). In the 3.0-T acquisition, significantly greater improvements were seen: a 10.4% decrease in σ and a 240% increase in mean R(2)(a). End-tidal carbon dioxide data were also collected during scanning and used to account for low-frequency changes in cerebral blood flow; however, the impact of this correction was trivial compared to applying RETROICOR. Comparison between two implementations of RETROICOR demonstrated that oversampled physiologic data can be applied by either downsampling or modification of the timing in the RETROICOR algorithm, with equivalent results. Furthermore, there was no significant effect from manually aligning the physiologic data with corresponding image slices from an interleaved acquisition, indicating that RETROICOR accounts for timing differences between physiologic changes and MR signal changes. These findings suggest that RETROICOR correction, as it is commonly implemented, should be included as part of the data analysis for pain FMRI studies performed at 1.5 and 3.0 T.

Acute hemodynamic changes after rapid intravenous bolus dosing of dexmedetomidine in pediatric heart transplant patients undergoing routine cardiac catheterization

BACKGROUND

Dexmedetomidine is a highly selective α(2)-adrenoceptor agonist with sedative, anxiolytic, and analgesic properties that has minimal effects on respiratory drive. Its sedative and hypotensive effects are mediated via central α(2A) and imidazoline type 1 receptors while activation of peripheral α(2B)-adrenoceptors result in an increase in arterial blood pressure and systemic vascular resistance. In this randomized, prospective, clinical study, we attempted to quantify the short-term hemodynamic effects resulting from a rapid i.v. bolus administration of dexmedetomidine in pediatric cardiac transplant patients.

METHODS

Twelve patients, aged 10 years or younger, weighing ≤40 kg, presenting for routine surveillance of right and left heart cardiac catheterization after cardiac transplantation were enrolled. After an inhaled or i.v. induction, the tracheas were intubated and anesthesia was maintained with 1 minimum alveolar concentration of isoflurane in room air, fentanyl (1 μg/kg), and rocuronium (1 mg/kg). At the completion of the planned cardiac catheterization, 100% oxygen was administered. After recording a set of baseline values that included heart rate (HR), systolic blood pressure, diastolic blood pressure, central venous pressure, systolic pulmonary artery pressure, diastolic pulmonary artery pressure, pulmonary artery wedge pressure, and thermodilution-based cardiac output, a rapid i.v. dexmedetomidine bolus of either 0.25 or 0.5 μg/kg was administered over 5 seconds. The hemodynamic measurements were repeated at 1 minute and 5 minutes.

RESULTS

There were 6 patients in each group. Investigation suggested that systolic blood pressure, diastolic blood pressure, systolic pulmonary artery pressure, diastolic pulmonary artery pressure, pulmonary artery wedge pressure, and systemic vascular resistance all increased at 1 minute after rapid i.v. bolus for both doses and decreased significantly to near baseline for both doses by 5 minutes. The transient increase in pressures was more pronounced in the systemic system than in the pulmonary system. In the systemic system, there was a larger percent increase in the diastolic pressures than the systolic pressures. Cardiac output, central venous pressure, and pulmonary vascular resistance did not change significantly. HR decreased at 1 minute for both doses and was, within the 0.5 μg/kg group, the only hemodynamic variable still changed from baseline at the 5-minute time point.

CONCLUSION

Rapid i.v. bolus administration of dexmedetomidine in this small sample of children having undergone heart transplants was clinically well tolerated, although it resulted in a transient but significant increase in systemic and pulmonary pressure and a decrease in HR. In the systemic system, there is a larger percent increase in the diastolic pressures than the systolic pressures and, furthermore, these transient increases in pressures were more pronounced in the systemic system than in the pulmonary system.

Eliminating arterial injury during central venous catheterization using manometry

BACKGROUND

Unintended arterial puncture occurs in 2%-4.5% of central venous catheterizations, resulting in arterial injury in 0.1%-0.5% of patients. Routine performance of manometry during catheterization may successfully identify unintended arterial puncture and avoid arterial cannulation and injury.

METHODS

We conducted a retrospective review of all cases of central venous catheter placement during a 15-yr period after implementation of a safety program requiring mandatory use of manometry to verify venous access. Arterial injuries were defined as unintended arterial cannulations with a 7-French or larger catheter or dilator. Arterial punctures were defined as the unintended placement of an 18-gauge catheter or needle into the artery. Data were reviewed for all arterial injuries during the entire 15-yr period. In addition, data on both arterial puncture and subsequent arterial injury were evaluated during the final year of analysis.

RESULTS

A total of 9348 central venous catheters were placed during the observation period. During the full 15 yr of observation, there were no cases of arterial injury. During the final year of assessment, 511 central venous catheters were placed, with arterial punctures in 28 patients (5%). Arterial puncture was recognized without manometry in 24 cases. Arterial puncture was identified only with manometry in 4 cases, with no incidents of arterial injury.

CONCLUSIONS

Consistent use of manometry, to verify venous placement, during central venous catheterization effectively eliminated arterial injury from unintended arterial cannulation during the 15-yr assessment.

An fMRI study of semantic priming: modulation of brain activity by varying semantic distances

OBJECTIVE

Our purpose was to study the effect of semantic priming at varying semantic distances on brain activation during a lexical decision experiment, using functional magnetic resonance imaging (fMRI).

BACKGROUND

Neuroimaging studies have demonstrated decreased brain activation for primed versus unprimed stimuli in language areas due to semantic priming, suggesting facilitated semantic retrieval. However, the effect of varying semantic distances on brain activation has not been studied. Therefore we examined direct and indirect priming effects on cerebral activation to provide information regarding spread of activation in the semantic network.

METHODS

Participants were presented with closely, distantly, and unrelated word pairs during fMRI, and asked to make a lexical decision on the second word.

RESULTS

Behavioral measurements demonstrated significant priming effects for all semantic distances. Imaging results showed modulation of brain activation due to different semantic relationships in the left inferior frontal gyrus, bilateral middle frontal gyrus and anterior temporal lobe, and consisted of decreased magnitude of activation when primed stimuli were processed compared with unprimed stimuli, with the greatest effect observed for closely related words.

CONCLUSIONS

This study demonstrates graduated effects of semantic priming on fMRI in semantic but not attentional brain regions, contributing to explain how semantic knowledge is organized and retrieved. These findings support the network model for organization of the semantic lexicon.

The effects of L-dopa on the functional magnetic resonance imaging response of patients with amblyopia: a pilot study

PURPOSE

We investigated the effects of a single dose of levodopa (L-dopa) on the level and extent of visual cortex activation of subjects with amblyopia and normal subjects using blood oxygenation level-dependent functional magnetic resonance imaging (fMRI).

SUBJECTS AND METHODS

Six patients with amblyopia and 9 control patients were recruited. A baseline fMRI session was followed by a second session 90 minutes after the dose of L-dopa. Visual stimuli included vertical sinusoidal gratings with spatial frequencies of 1 and 2 cpd that were counterphased at 4 Hz. Stimuli were presented monocularly and binocularly. The fMRI response was characterized by the total volume and the average level of activation within the occipital cortex. An interocular absolute difference (IDIF) was defined in terms of said measures for between-population analysis of monocular data.

RESULTS

After the administration of L-dopa, visual acuity improved significantly ( P = 0.026) from 0.72 +/- 0.21 (mean +/- SD) to 0.64 +/- 0.24 LogMAR in the amblyopic eye, although remaining the same in the dominant eye and in the eyes of control subjects. The response to L-dopa was found to be population-specific, as indicated by a significant treatment-by-population interaction for the volume of activation IDIF ( P = 0.018) measure: subjects with amblyopia exhibited a post-treatment increase in the volume of activation IDIF whereas control subjects showed a less prominent decrease. This post-treatment increase of IDIF in subjects with amblyopia may be explained by the decrease in the volume of activation found for the amblyopic eye after L-dopa ( P = 0.038). No L-dopa-related activation changes were detected for dominant eye or binocular stimulation in the amblyopic group, and no change was detected in control subjects.

CONCLUSION

L-dopa elicits a population-specific modulation of the fMRI response, namely, a reduced total volume of activation from the amblyopic eye despite improvement in visual acuity.

Functional Magnetic Resonance Imaging Studies of Pain

Background

Several investigations into brain activation caused by pain have suggested that the multiple painful stimulations used in typical block designs may cause attenuation over time of the signal within activated areas. The effect this may have on pain investigations using multiple tasks has not been investigated. The signal decay across a task of four repeating pain stimulations and between two serial pain tasks separated by a 4-min interval was examined to determine whether signal attenuation may significantly confound pain investigations.

Methods

The characteristics of the brain activation of six subjects were determined using whole brain blood oxygenation level-dependent functional magnetic resonance imaging on a 1.5-T scanner. Tasks included both tingling and pain induced by transcutaneous electrical stimulation of the median nerve. The average group maps were analyzed by general linear modeling with corrected cluster P values of less than 0.05. The time courses of individual voxels were further investigated by analysis of variance with P values of less than 0.05.

Results

Significant differences between pain and tingling were found in the ipsilateral cerebellum, contralateral thalamus, secondary somatosensory cortex, primary somatosensory cortex, and anterior cingulate cortex. Highly significant signal decay was found to exist across each single pain task, but the signal was found to be restored after a 4-min rest period.

Conclusions

This work shows that serial pain tasks can be used for functional magnetic resonance imaging studies using electrical nerve stimulation as a stimulus, as long as sufficient time is allowed between the two tasks.