Neuroprotective effects of lactate and ketone bodies in acute brain injury

The goal of neurocritical care is to prevent and reverse the pathologic cascades of secondary brain injury by optimizing cerebral blood flow, oxygen supply and substrate delivery. While glucose is an essential energetic substrate for the brain, we frequently observe a strong decrease in glucose delivery and/or a glucose metabolic dysregulation following acute brain injury. In parallel, during the last decades, lactate and ketone bodies have been identified as potential alternative fuels to provide energy to the brain, both under physiological conditions and in case of glucose shortage. They are now viewed as integral parts of brain metabolism. In addition to their energetic role, experimental evidence also supports their neuroprotective properties after acute brain injury, regulating in particular intracranial pressure control, decreasing ischemic volume, and leading to an improvement in cognitive functions as well as survival. In this review, we present preclinical and clinical evidence exploring the mechanisms underlying their neuroprotective effects and identify research priorities for promoting lactate and ketone bodies use in brain injury.

Cerebral Lactate Uptake After Half-Molar Sodium Lactate Therapy in Traumatic Brain Injury: A Brief Report

Exogenous sodium lactate has many advantages after traumatic brain injury, including intracranial pressure control and alternative energetic supply. It remains unclear, however, whether half-molar sodium lactate (HSL) is effectively incorporated in brain metabolism, which we can verify using the arteriovenous difference in lactate (AVDlac). Hence we compared the AVDlac in patients with severe traumatic brain injury receiving an equiosmolar bolus of sodium lactate or mannitol for intracranial hypertension (IH) treatment. We included 23 patients: 14 received HSL for 25 IH episodes, and nine received mannitol for 19 episodes (total of 44 IH episodes). We observed that the median variation in AVDlac was positive in the group that received HSL (Δ +0.1 [IQR -0.08-0.2] mmol/L), which suggests a net lactate uptake by the brain. On the other hand, it was negative in the group that received mannitol (Δ -0.0 [IQR -0.1 to 0.0] mmol/L), indicating a net lactate export. Finally, there were more positive AVDlac values in the group that received HSL and more negative AVDlac values in the group that received mannitol (Fisher exact p = 0.04). Our study reports the first evidence of a positive AVDlac, which corresponds to a net lactate uptake by the brain, in patients who received HSL for severe TBI. Our results constitute a bedside confirmation of the integration of lactate into the brain metabolism and pave the way for a wider dissemination of sodium lactate in the daily clinical care of patients with traumatic brain injury.

Variations in Autoregulation-Based Optimal Cerebral Perfusion Pressure Determination Using Two Integrated Neuromonitoring Platforms in a Trauma Patient

BACKGROUND

Neuromonitoring devices are often used in traumatic brain injury. The objective of this report is to raise awareness concerning variations in optimal cerebral perfusion pressure (CPPopt) determination using exploratory information provided by two neuromonitoring monitors that are part of research programs (Moberg CNS Monitor and RAUMED NeuroSmart LogO).

METHODS

We connected both monitors simultaneously to a parenchymal intracranial pressure catheter and recorded the pressure reactivity index (PRx) and the derived CPPopt estimates for a patient with a severe traumatic brain injury. These estimates were available at the bedside and were updated at each minute.

RESULTS

Using the Bland and Altman method, we found a mean variation of - 3.8 (95% confidence internal from - 8.5 to 0.9) mm Hg between the CPPopt estimates provided by the two monitors (limits of agreement from - 26.6 to 19.1 mm Hg). The PRx and CPPopt trends provided by the two monitors were similar over time, but CPPopt trends differed when PRx values were around zero. Also, almost half of the CPPopt estimates differed by more than 10 mm Hg.

CONCLUSIONS

These wide variations recorded in the same patient are worrisome and reiterate the importance of understanding and standardizing the methodology and algorithms behind commercial neuromonitoring devices prior to incorporating them in clinical use.

Preoperative fibrinogen level and blood transfusions in liver transplantation: A systematic review

BACKGROUND

Orthotopic liver transplantation (OLT) is a major surgery often associated with significant bleeding. We conducted a systematic review to explore the association between preoperative fibrinogen level and intraoperative blood products transfusion, blood loss and clinical outcomes in patients undergoing OLT.

METHODS

We included observational studies conducted in patients undergoing an OLT mostly for end-stage liver disease that reported an association between the preoperative fibrinogen level and our outcomes of interest. Our primary outcome was the intraoperative red blood cell (RBC) transfusion requirements. Our secondary outcomes were intraoperative blood loss, intraoperative transfusion of any blood product, postoperative RBC transfusion, postoperative thrombotic or hemorrhagic complications, and mortality. We used a standardized search strategy. We reported our results mostly descriptively but conducted meta-analyses using random-effect models when judged feasible.

RESULTS

We selected 24 cohort studies reporting at least one of our outcomes. We found that a high preoperative fibrinogen level was associated with fewer intraoperative RBC and other blood products transfusions, and lower blood loss. We also found a lower overall survival in patients with a higher fibrinogen level (pooled hazard ratio [95% CI] of 1.50 [1.23 to 1.84]; 5 studies, n = 1012, I2 = 48%). Only one study formally explored a fibrinogen level threshold effect. Overall, reporting was heterogeneous, and risk of bias was variable mostly because of uncontrolled confounding.

CONCLUSION

A higher preoperative fibrinogen level was associated with fewer intraoperative RBC and other blood products transfusions, lower blood loss, and higher mortality. Further studies may help clarify observed associations and inform guidelines.

Infratentorial Brain Injury Among Patients Suspected of Death by Neurologic Criteria: A Systematic Review and Meta-analysis

BACKGROUND AND OBJECTIVES

There is a paucity of data on the frequency and prognosis of infratentorial brain injury among patients suspected of death by neurologic criteria (DNC), which likely contributes to scientific uncertainty regarding the role of isolated brainstem death in DNC determination. Our aim was to synthesize the prevalence, characteristics, and evolution of infratentorial brain injury, including isolated brainstem death, among patients suspected of DNC.

METHODS

We conducted a systematic review by searching Medline, Embase, EBM Reviews, CINAHL Complete, and the gray literature from inception to March 26, 2021. We selected cohort and cross-sectional studies, case reports, and case series that included patients suspected of DNC. Two study investigators independently performed study selection, data collection, and risk of bias assessment. Our primary outcomes were the respective prevalence of infratentorial brain injury and isolated brainstem death, which we meta-analyzed using mixed-effects Bayesian hierarchical models with diffuse priors. Our secondary outcomes were the characteristics and evolution of patients with infratentorial brain injury and isolated brainstem death.

RESULTS

Twenty-one studies met the selection criteria, most of which were of moderate to high risk of bias. Among patients suspected of DNC, the prevalence of infratentorial brain injury ranged from 2% to 16% (n = 3,602, mean prevalence: 6.3%, 95% highest density interval [2.4%-14.2%]), whereas the prevalence of isolated brainstem death ranged from 1% to 4% (n = 3,692, mean prevalence: 1.5%, 95% highest density interval [0.5%-3.9%]). A total of 38 isolated brainstem death cases with data on clinical characteristics and/or evolution were included. All had infratentorial strokes. Twenty patients had EEG background activity in the α or θ frequencies, 19 had preserved cerebral blood flow, 2 had preserved supratentorial cerebral perfusion, 2 had cortical responses to visual evoked potentials, and 1 had cortical responses to somatosensory evoked potentials. At the latest follow-up, 28 had progressed to whole-brain death.

DISCUSSION

Studies with moderate to high risk of bias suggest that infratentorial brain injury is relatively uncommon among patients suspected of DNC. Isolated brainstem death is rarer and seems to carry a high risk of progression to whole-brain death. These findings require further high-quality investigation.

Attenuation of high-frequency (30-200 Hz) thalamocortical EEG rhythms as correlate of anaesthetic action: evidence from dexmedetomidine

Background

Gamma (30-80 Hz) and high-gamma (80-200 Hz) thalamocortical EEG rhythms are involved in conscious processes and are attenuated by isoflurane and propofol. To explore the hypothesis that this attenuation is a correlate of anaesthetic action, we characterized the effect dexmedetomidine, a selective adrenergic α-2 agonist with lesser hypnotic potency, on these rhythms.

Methods

We recorded local field potentials from barrel cortex and ventroposteromedial thalamic nucleus in ten previously instrumented rats to measure spectral power (30-50 Hz, 51-75 Hz, 76-125 Hz, 126-200 Hz bands) during baseline, at four dexmedetomidine plasma concentrations obtained by i.v. target-controlled infusion (1.86, 3.75, 5.63 and 7.50 ng ml -1 ), and during recovery. Thalamocortical coherence over 0.3-200 Hz was also measured.

Results

Loss of righting reflex (LORR) occurred with 5.63 ng ml -1 . Dexmedetomidine produced a linear concentration-dependent attenuation of cortical ( P <0.04) and thalamic ( P  ≤ 0.0051) log power in all bands. Slopes for cortex and thalamus were similar. The slope for dexmedetomidine on thalamic power in the 76-200 Hz range was less than half that of the other agents ( P <0.003). LORR was associated with an increase in delta band (0.3-4.0 Hz) thalamocortical coherence ( P <0.001). Increased low-frequency coherence also occurred with propofol and isoflurane.

Conclusions

Dexmedetomidine attenuates high-frequency thalamocortical rhythms, but to a lesser degree than isoflurane and propofol. The main differences between dexmedetomidine and the other anaesthetics involved thalamic rhythms, further substantiating the link between impaired thalamic function and anaesthesia. Increased delta coherence likely reflects cyclic hyperpolarization of thalamocortical networks and may be a marker for loss of consciousness.

Feasibility and Safety of Early Repeat Transradial Access Within 30 Days of Previous Coronary Angiography and Intervention

Transradial approach (TRA) is the default access site for diagnostic angiography and intervention in many centers. Repeat ipsilateral radial artery access late after index procedure has been associated with failures. It is unknown whether early (≤30 days) and very early (<24 hours) repeat radial access is technically feasible and safe. Study population consisted of consecutive patients undergoing repeat (≥2) procedures within 30 days in a high-volume TRA center. Transradial access failure and resulting femoral approach was categorized as primary (no repeat attempt) or secondary (crossover). Timing of repeat access and reasons for failure were recorded. From November 2012 to December 2014, repeat catheterization by TRA was performed twice in 573 of 626 patients (92%) (median delay 4 [2 to 9] days), 3 times in 29 of 38 (76%) patients (median delay 15 [5 to 26] days), and 4 times in 1 patient within 21 days. When repeat catheterization occurred during the first 24 hours following the index procedure, 53% and 75% of patients had second and third procedures using the same ipsilateral radial artery, respectively. Primary radial failure occurred in 5.8% for second attempt and 13% for a third attempt, whereas crossovers were noted in 2.7% and 2.6%, respectively. Main reasons for failed re-access of ipsilateral radial artery were related either to operator's reluctance to repeat attempt (primary failure) or to issues with puncture site (crossover). In a high-volume TRA center, patients who required repeat catheterization within 24 hours and within the first 30 days had the same radial artery re-accessed in the majority of cases.

Meta-Analysis of Effects of Bivalirudin Versus Heparin on Myocardial Ischemic and Bleeding Outcomes After Percutaneous Coronary Intervention

Bivalirudin is an alternative to unfractionated heparin (UFH) anticoagulation during percutaneous coronary intervention. Previously, we have reported clinical benefit on major bleeding in favor of bivalirudin compared with UFH monotherapy but inconclusive results on mortality. Controversial data have been reported in the last 2 years. We conducted an updated meta-analysis including randomized trials and observational studies, which evaluated ischemic and bleeding outcomes for bivalirudin compared with UFH-only during percutaneous coronary intervention. We included 18 observational studies and 12 randomized trials published from 2003 to 2015. Primary outcomes were major adverse cardiovascular events within 30 days including death, myocardial infarction, and urgent revascularization and stent thrombosis, major bleeding, and transfusion. Overall, we found a significant risk reduction with bivalirudin for major bleeding (odds ratio [OR] 0.59, 95% confidence interval [CI] 0.49 to 0.71, p <0.0001) and for transfusion (OR 0.79, 95% CI 0.66 to 0.95, p = 0.01) and similar risk for major adverse cardiovascular events (OR 0.98, 95% CI 0.86 to 1.12, p = 0.80). However, there was a substantial increased risk of stent thrombosis associated with bivalirudin (OR 1.52, 95% CI 1.11 to 2.08, p = 0.009). No impact on mortality was found. Meta-regression analyses on major bleeding suggested that bivalirudin was more effective than UFH at doses >60 IU/kg and independent of radial access. In conclusion, compared with UFH monotherapy, bivalirudin remains associated with less bleeding risk but higher stent thrombosis risk. Further study remains required to define its role in current antithrombotic armamentarium.

Radiation exposure in relation to the arterial access site used for diagnostic coronary angiography and percutaneous coronary intervention: a systematic review and meta-analysis

BACKGROUND

Transradial access for cardiac catheterisation results in lower bleeding and vascular complications than the traditional transfemoral access route. However, the increased radiation exposure potentially associated with transradial access is a possible drawback of this method. Whether transradial access is associated with a clinically significant increase in radiation exposure that outweighs its benefits is unclear. Our aim was therefore to compare radiation exposure between transradial access and transfemoral access for diagnostic coronary angiograms and percutaneous coronary interventions (PCI).

METHODS

We did a systematic review and meta-analysis of the scientific literature by searching the PubMed, Embase, and Cochrane Library databases with relevant terms, and cross-referencing relevant articles for randomised controlled trials (RCTs) that compared radiation parameters in relation to access site, published from Jan 1, 1989, to June 3, 2014. Three investigators independently sorted the potentially relevant studies, and two others extracted data. We focused on the primary radiation outcomes of fluoroscopy time and kerma-area product, and used meta-regression to assess the changes over time. Secondary outcomes were operator radiation exposure and procedural time. We used both fixed-effects and random-effects models with inverse variance weighting for the main analyses, and we did confirmatory analyses for observational studies.

FINDINGS

Of 1252 records identified, we obtained data from 24 published RCTs for 19 328 patients. Our primary analyses showed that transradial access was associated with a small but significant increase in fluoroscopy time for diagnostic coronary angiograms (weighted mean difference [WMD], fixed effect: 1·04 min, 95% CI 0·84-1·24; p<0·0001) and PCI (1·15 min, 95% CI 0·96-1·33; p<0·0001), compared with transfemoral access. Transradial access was also associated with higher kerma-area product for diagnostic coronary angiograms (WMD, fixed effect: 1·72 Gy·cm(2), 95% CI -0·10 to 3·55; p=0·06), and significantly higher kerma-area product for PCI (0·55 Gy·cm(2), 95% CI 0·08-1·02; p=0·02). Mean operator radiation doses for PCI with basic protection were 107 μSv (SD 110) with transradial access and 74 μSv (68) with transfemoral access; with supplementary protection, the doses decreased to 21 μSv (17) with transradial access and 46 μSv (9) with transfemoral. Meta-regression analysis showed that the overall difference in fluoroscopy time between the two procedures has decreased significantly by 75% over the past 20 years from 2 min in 1996 to about 30 s in 2014 (p<0·0001). In observational studies, differences and effect sizes remained consistent with RCTs.

INTERPRETATION

Transradial access was associated with a small but significant increase in radiation exposure in both diagnostic and interventional procedures compared with transfemoral access. Since differences in radiation exposure narrow over time, the clinical significance of this small increase is uncertain and is unlikely to outweigh the clinical benefits of transradial access.

FUNDING

None.

The Transradial Approach and Antithrombotic Therapy: Rationale and Outcomes

This article reviews antithrombotic strategies for percutaneous coronary interventions according to the access site and the current evidence with the aim of limiting ischemic complications and preventing radial artery occlusion (RAO). Prevention of RAO should be part of the quality control of any radial program. The incidence of RAO postcatheterization and interventions should be determined initially using the echo-duplex and then frequently assessed using the more cost-effective pulse oximetry technique. Any evidence of higher risk of RAO should prompt internal analysis and multidisciplinary mechanisms to be put in place.

Current issues in the identification and treatment of metabolically healthy but obese individuals

A unique subset of obese individuals who appear to be protected from the development of metabolic disturbances has been identified in the medical literature and is termed metabolically healthy but obese (MHO). Part of the issue is that there are no clear accepted criteria on the definition of MHO and the biological mechanisms to explain this phenotype are still unknown which render findings and/or conclusions difficult to interpret and making the application of this concept difficult in clinical practice. With the current definitions, the true prevalence of the MHO phenotype in the general population varies widely from approximately 3-57% of obese adults. In several prospective studies, the MHO individual has been associated with a similar risk of developing type 2 diabetes, cardiovascular disease and mortality when compared to healthy normal weight subjects; however, there is evidence to refute this concept. Furthermore, the current evidence cannot confirm that MHO subjects are permanently protected from the risk of developing metabolic disturbances associated with obesity. Currently, no standard practice guidelines for the treatment of MHO can be proposed, however, a regular surveillance of the waist circumference and cardio-metabolic risk factors such as elevated triglycerides, glycaemia, HOMA, C-reactive protein and low HDL, as well as the prevention of any further weight gain seem to represent the most prudent and sound attitude in the management of MHO subjects.

Interaction of chronic total occlusion and chronic kidney disease in patients undergoing primary percutaneous coronary intervention for acute ST-elevation myocardial infarction

Chronic total occlusion (CTO) in a non-infarct-related artery and chronic kidney failure (CKD) are associated with worse outcomes after primary percutaneous coronary intervention (PCI). The aim of this study was to investigate the interaction of CTO and CKD in patients who underwent primary PCI for acute ST-segment elevation myocardial infarction (STEMI). Patients with STEMIs with or without CKD, defined as an estimated glomerular filtration rate <60 ml/min/1.73 m(2), were categorized into those with single-vessel disease and those with multivessel disease with or without CTO. The primary outcomes were the incidence of 30-day and 1-year mortality. Among 1,873 consecutive patients with STEMIs included between 2006 and 2011, 336 (18%) had CKD. The prevalence of CTO in a non-infarct-related artery was 13% in patients with CKD compared with 7% in those without CKD (p = 0.0003). There was a significant interaction between CKD and CTO on 30-day mortality (p = 0.018) and 1-year mortality (p = 0.013). Independent predictors of late mortality in patients with CKD were previous myocardial infarction (hazard ratio [HR] 1.71, 95% confidence interval [CI] 1.01 to 2.79), age >75 years (HR 1.86, 95% CI 1.19 to 2.95), a left ventricular ejection fraction after primary PCI <40% (HR 2.20, 95% CI 1.36 to 3.63), left main culprit artery (HR 4.46, 95% CI 1.64 to 10.25), and shock (HR 7.44, 95% CI 4.56 to 12.31), but multivessel disease with CTO was not a predictor. In contrast, multivessel disease with CTO was an independent predictor of mortality in patients without CKD (HR 3.30, 95% CI 1.70 to 6.17). In conclusion, in patients with STEMIs who underwent primary PCI, with preexisting CKD, the prevalence of CTO in a non-infarct-related artery was twice as great. In these patients, the clinical impact of CTO seems to be overshadowed by the presence of CKD.

Successive transradial access for coronary procedures: experience of Quebec Heart-Lung Institute

BACKGROUND

Transradial approach (TRA) for cardiac catheterizations and interventions improves clinical outcomes compared with transfemoral access, and its use is increasing worldwide. However, there are limited data on successive use of same artery for repeat procedures.

METHODS

Between May 2010 and May 2011, all consecutive patients undergoing a repeat TRA procedure (≥2) were retrospectively identified. Success rates and reasons for failure to use ipsilateral radial artery for repeat access were identified.

RESULTS

A total of 519 patients underwent 1,420 procedures. In 480 patients (92%), right radial artery was used as initial access, and left radial artery, in 39 patients. All patients underwent ≥2 procedures; 218 patients, ≥3; 87 patients, ≥4; 39 patients, ≥5; 19 patients, ≥6; 11 patients, ≥7; and 5 patients, ≥8 procedures. Two patients had, respectively, 9 and 10 procedures. The success rate for second attempt was 93%, 81% for third, and declining to 60% for ≥8. Linear regression analysis estimated a 5% failure rate for each repeat attempt (R(2) = 0.87, P = .007). The main reason for failure was related to clinical radial artery occlusion (RAO) including absent or faint pulse, poor oximetry, and failed puncture. All patients with clinical RAO were asymptomatic. By multivariate analysis, female gender (odds ratio [OR] 3.08, 95% CI 1.78-5.39, P < .0001), prior coronary artery bypass graft (OR 5.26, 95% CI 2.67-10.42, P < .0001), and repeat radial access (OR 2.14, 95% CI 1.70-2.76, P < .0001) were independent predictors of radial access failure.

CONCLUSION

Successive TRA is both feasible and safe in most cases for up to 10 procedures. However, failure rate for TRA increases with successive procedures, primarily due to clinical RAO. Strategies to minimize the risks of chronic clinical RAO and allow repeat use of ipsilateral radial artery need to be further defined.

Early and late outcomes after primary percutaneous coronary intervention by radial or femoral approach in patients presenting in acute ST-elevation myocardial infarction and cardiogenic shock

BACKGROUND

Although radial approach is increasingly used in percutaneous coronary interventions (PCIs) including in acute myocardial infarction (MI), patients with cardiogenic shock have been excluded from comparisons with femoral approach. The aim of our study was to compare clinical outcomes in patients undergoing primary PCI with cardiogenic shock by radial and femoral approach.

METHODS AND RESULTS

From 2,663 patients presenting with ST-elevation MI in 2 large volume radial centers, we identified 197 patients (7.4%) with signs of cardiogenic shock immediately before undergoing primary PCI. Radial approach was used in 55% of cases when at least 1 radial artery was weakly palpable, either spontaneously or after intravenous noradrenaline bolus. Patients in the radial group were older (69 ± 12 vs 64 ± 12 years, P = .010), had less diabetes (13% vs 26%, P = .028), and required less often intubation prior PCI (42% vs 66%, P = .0006) or intraaortic balloon pump (36% vs 55%, P = .0096). Mortality at 1 year was 44% in the radial group and 64% in the femoral group (P = .0044). Independent predictors of late mortality included radial approach (hazard ratio [HR] 0.65, 95% CI 0.42-0.98, P = .041), the use of glycoprotein IIb-IIIa receptor inhibitors (HR 0.63, 95% CI 0.40-0.96, P = .032), baseline creatinine ≥110 μmol/L (HR 3.34, 95% CI 2.20-5.12, P < .0001), initial glycemia >200 mg/dL (HR 2.02, 95% CI 1.34-3.11, P = .0008), and age >65 years (HR 1.80, 95% CI 1.18-2.79, P = .006).

CONCLUSION

Radial approach was safe and feasible in more than half of the patients with ST-elevation MI and cardiogenic shock treated by primary PCI. After adjustment for baseline and procedural characteristics, radial approach remained associated with better survival. However, prognosis of patients undergoing primary PCI in cardiogenic shock remains poor.

Benefit of bivalirudin versus heparin after transradial and transfemoral percutaneous coronary intervention

Bivalirudin, a direct thrombin inhibitor, has been shown to reduce major bleeding and provide a better safety profile compared to unfractionated heparin (UFH) in patients undergoing percutaneous coronary intervention (PCI) through transfemoral access. Data pertaining to the clinical benefit of bivalirudin compared to UFH monotherapy in patients undergoing transradial PCI are lacking. The present study sought to compare the in-hospital net clinical adverse events, including death, myocardial infarction, target vessel revascularization, and bleeding, for these 2 antithrombotic regimens for all patients at a tertiary care, high-volume radial center. From April 2009 to February 2011, all patients treated with bivalirudin were matched by access site to those receiving UFH. The patients in the bivalirudin group (n = 125) were older (72 ± 13 years vs 66 ± 11 years; p <0.0001), more often had chronic kidney disease (51% vs 30%; p = 0.0012), and more often underwent primary PCI (30% vs 14%, p <0.0037) than the UFH-treated patients (n = 125). A radial approach was used in 71% of both groups. The baseline bleeding risk according to Mehran's score was similar in both groups (14 ± 9 vs 15 ± 8, p = 0.48). In-hospital mortality was 2% in both groups (p = 1.00). No difference in net clinical adverse events or ischemic or bleeding complications was detected between the 2 groups. Bivalirudin reduced both ischemic and bleeding events in femoral-treated patients, but no such clinical benefit was observed in the radial-treated patients. In conclusion, as periprocedural PCI bleeding avoidance strategies have become paramount to optimize the clinical benefit, the interaction between bivalirudin and radial approach deserves additional investigation.

Auditory evoked potentials

This chapter will focus on the two auditory evoked potentials (AEP) most commonly used to assess the effects of general anesthetics on the brain, the auditory middle latency response (AMLR) and the 40 Hz auditory steady-state response (40 Hz-ASSR). We will review their physiological basis, the recording methodology, the effects of general anesthetics, their ability to track changes in level of consciousness and their clinical applications. Because of space constraints, this review will be limited to human studies.

Antagonism of sevoflurane anaesthesia by physostigmine: effects on the auditory steady-state response and bispectral index

BACKGROUND

Physostigmine, a centrally acting anticholinesterase, antagonizes the hypnotic effect of propofol, as shown by the return of consciousness (response to commands) or wakefulness (spontaneous eye-opening without response to commands) and by recovery of auditory evoked potentials (40 Hz auditory steady-state response (ASSR)) and the bispectral index (BIS). We measured the effects of physostigmine on the hypnotic effect of inhaled volatile anaesthetics, using sevoflurane as the representative agent.

METHODS

Eight healthy volunteers received sevoflurane adjusted to produce loss of consciousness. Physostigmine (plus glycopyrrolate) was given while the end-tidal concentration of sevoflurane was kept constant.

RESULTS

Loss of consciousness was accompanied by a significant (P<0.02) decrease in ASSR amplitude (to 21% of awake value) and BIS (to 70% of awake value). Five subjects had return of consciousness or wakefulness after physostigmine. The others showed no behavioural change. Physostigmine caused a significant increase of the mean ASSR amplitude from 0.11 (SD 0.04) to 0.17 (0.06) microV (P<0.05). The BIS also increased, from 66 (12) to 74 (12), but the difference was not significant.

CONCLUSIONS

Physostigmine can antagonize, at least partially, the hypnotic effect of sevoflurane and changes in arousal after physostigmine are shown by ASSR measurements. However, the antagonism is not as clear or reliable as with propofol.

Propofol anesthesia and cerebral blood flow changes elicited by vibrotactile stimulation: a positron emission tomography study

We investigated the effects of the general anesthetic agent propofol on cerebral structures involved in the processing of vibrotactile information. Using positron emission tomography (PET) and the H(2)(15)O bolus technique, we measured regional distribution of cerebral blood flow (CBF) in eight healthy human volunteers. They were scanned under five different levels of propofol anesthesia. Using a computer-controlled infusion, the following plasma levels of propofol were targeted: Level W (Waking, 0 microg/ml), Level 1 (0.5 microg/ml), Level 2 (1.5 microg/ml), Level 3 (3.5 microg/ml), and Level R (Recovery). At each level of anesthesia, two 3-min scans were acquired with vibrotactile stimulation of the right forearm either on or off. The level of consciousness was evaluated before each scan by the response of the subject to a verbal command. At Level W, all volunteers were fully awake. They reported being slightly drowsy at Level 1, they had a slurred speech and slow response at Level 2, and they were not responding at all at Level 3. The following variations in regional CBF (rCBF) were observed. During the waking state (Level W), vibrotactile stimulation induced a significant rCBF increase in the left thalamus and in several cortical regions, including the left primary somatosensory cortex and the left and right secondary somatosensory cortex. During anesthesia, propofol reduced in a dose-dependent manner rCBF in the thalamus as well as in a number of visual, parietal, and prefrontal cortical regions. At Level 1 through 3, propofol also suppressed vibration-induced increases in rCBF in the primary and secondary somatosensory cortex, whereas the thalamic rCBF response was abolished only at Level 3, when volunteers lost consciousness. We conclude that propofol interferes with the processing of vibrotactile information first at the level of the cortex before attenuating its transfer through the thalamus.

Auditory steady-state response and bispectral index for assessing level of consciousness during propofol sedation and hypnosis

We assessed the effect of propofol on the auditory steady-state response (ASSR), bispectral (BIS) index, and level of consciousness in two experiments. In Experiment 1, propofol was infused in 11 subjects to obtain effect-site concentrations of 1, 2, 3, and 4 microg/mL. The ASSR and BIS index were recorded during baseline and at each concentration. The ASSR was evoked by monaural stimuli. Propofol caused a concentration-dependent decrease of the ASSR and BIS index values (r(2) = 0.76 and 0.93, respectively; P<0.0001). The prediction probability for loss of consciousness was 0.89, 0.96, and 0.94 for ASSR, BIS, and arterial blood concentration of propofol, respectively. In Experiment 2, we compared the effects of binaural versus monaural stimulus delivery on the ASSR in six subjects during awake baseline and propofol-induced unconsciousness. During baseline, the ASSR amplitude with binaural stimulation (0.47+/-0.13 microV, mean +/- SD) was significantly (P<0.002) larger than with monaural stimulation (0.35+/-0.11 microV). During unconsciousness, the amplitude was 0.09+/-0.09 microV with monaural and 0.06+/-0.04 microV with binaural stimulation (NS). The prediction probability for loss of consciousness was 0.97 (0.04 SE) for monaural and 1.00 (0.00 SE) for binaural delivery. We conclude that the ASSR and BIS index are attenuated in a concentration-dependent manner by propofol and provide a useful measure of its sedative and hypnotic effect. BIS was easier to use and slightly more sensitive. The ASSR should be recorded with binaural stimulation. The ASSR and BIS index are both useful for assessing the level of consciousness during sedation and hypnosis with propofol. However, the BIS index was simpler to use and provided a more sensitive measure of sedation.

IMPLICATIONS

We have compared two methods for predicting whether the amount of propofol given to a human subject is sufficient to cause unconsciousness, defined as failure to respond to a simple verbal command. The two methods studied are the auditory steady-state response, which measures the electrical response of the brain to sound, and the bispectral index, which is a number derived from the electroencephalogram. The results showed that both methods are very good predictors of the level of consciousness; however, bispectral was easier to use.

Physostigmine reverses propofol-induced unconsciousness and attenuation of the auditory steady state response and bispectral index in human volunteers

BACKGROUND

It is postulated that alteration of central cholinergic transmission plays an important role in the mechanism by which anesthetics produce unconsciousness. The authors investigated the effect of altering central cholinergic transmission, by physostigmine and scopolamine, on unconsciousness produced by propofol.

METHODS

Propofol was administered to American Society of Anesthesiologists physical status 1 (n = 17) volunteers with use of a computer-controlled infusion pump at increasing concentrations until unconsciousness resulted (inability to respond to verbal commands, abolition of spontaneous movement). Central nervous system function was assessed by use of the Auditory Steady State Response (ASSR) and Bispectral Index (BIS) analysis of electrooculogram. During continuous administration of propofol, reversal of unconsciousness produced by physostigmine (28 microgram/kg) and block of this reversal by scopolamine (8.6 microgram/kg) were evaluated.

RESULTS

Propofol produced unconsciousness at a plasma concentration of 3.2 +/- 0.8 (+/- SD) microgram/ml (n = 17). Unconsciousness was associated with reductions in ASSR (0.10 +/- 0.08 microV [awake baseline 0.32 +/- 0.18 microV], P < 0.001) and BIS (55.7 +/- 8.8 [awake baseline 92.4 +/- 3.9], P < 0.001). Physostigmine restored consciousness in 9 of 11 subjects, with concomitant increases in ASSR (0.38 +/- 0.17 microV, P < 0.01) and BIS (75.3 +/- 8.3, P < 0.001). In all subjects (n = 6) scopolamine blocked the physostigmine-induced reversal of unconsciousness and the increase of the ASSR and BIS (ASSR and BIS during propofol-induced unconsciousness: 0.09 +/- 0.09 microV and 58.2 +/- 7.5, respectively; ASSR and BIS after physostigmine administration: 0.08 +/- 0.06 microV and 56.8 +/- 6.7, respectively, NS).

CONCLUSIONS

These findings suggest that the unconsciousness produced by propofol is mediated at least in part via interruption of central cholinergic muscarinic transmission.

Treating obesity. Lost cause or new opportunity?

OBJECTIVE

To review therapies for treating obese patients.

QUALITY OF EVIDENCE

Advice in this paper is based mainly on the results of randomized controlled trials. Some data from smaller, more physiologic studies are included. When appropriate, advice is based on consensus.

MAIN MESSAGE

Recent medical evidence indicates that a modest weight loss (5% to 10%) can alleviate symptoms of obesity-related comorbidity. Treatment of obesity should be comprehensive and integrated into a multi-component approach and should involve both patients and their families. The main challenge of obesity is maintaining a reduced weight.

CONCLUSION

A multi-component approach to treating obesity can help make treatment less frustrating and more rewarding for patients and physicians.

Brain mechanisms of propofol-induced loss of consciousness in humans: a positron emission tomographic study

In the present study, we used positron emission tomography to investigate changes in regional cerebral blood flow (rCBF) during a general anesthetic infusion set to produce a gradual transition from the awake state to unconsciousness. Five right-handed human volunteers participated in the study. They were given propofol with a computer-controlled infusion pump to achieve three stable levels of plasma concentrations corresponding to mild sedation, deep sedation, and unconsciousness, the latter defined as unresponsiveness to verbal commands. During awake baseline and each of the three levels of sedation, two scans were acquired after injection of an H215O bolus. Global as well as regional CBF were determined and correlated with propofol concentrations. In addition, blood flow changes in the thalamus were correlated with those of the entire scanned volume to determine areas of coordinated changes. In addition to a generalized decrease in global CBF, large regional decreases in CBF occurred bilaterally in the medial thalamus, the cuneus and precuneus, and the posterior cingulate, orbitofrontal, and right angular gyri. Furthermore, a significant covariation between the thalamic and midbrain blood flow changes was observed, suggesting a close functional relationship between the two structures. We suggest that, at the concentrations attained, propofol preferentially decreases rCBF in brain regions previously implicated in the regulation of arousal, performance of associative functions, and autonomic control. Our data support the hypothesis that anesthetics induce behavioral changes via a preferential, concentration-dependent effect on specific neuronal networks rather than through a nonspecific, generalized effect on the brain.

Effect of isoflurane on the auditory steady-state response and on consciousness in human volunteers

BACKGROUND

The auditory steady state response (ASSR) is a sustained electrical response of the brain to auditory stimuli delivered at fast rates (30-50 responses/s). The aim of this study was to evaluate the effect of 0.26-0.50% isoflurane on the ASSR and on consciousness, defined as responsiveness to verbal commands.

METHODS

Ten volunteers (21-31 yr) participated. Isoflurane was administered at three stable, end-tidal concentrations: 0.26%, 0.38%, and 0.50%. The ASSR in response to 18,000 stimuli (500-Hz tonebursts, 10 ms, 82-dB, the right ear, 35-45 bursts/s) was recorded from the vertex with reference to the right mastoid. Recordings were made during baseline, at each isoflurane concentration, and during recovery.

RESULTS

The mean (SD) ASSR amplitudes were 0.32 (0.23) microV during baseline, 0.24 (0.17) microV during 0.26% isoflurane, 0.09 (0.05) microV during 0.38% isoflurane, 0.04 (0.03) microV during 0.50% isoflurane, and 0.29 (0.33) microV during recovery. The amplitude during baseline and recovery was larger than during 0.38% and 0.50% isoflurane (P < 0.001). The amplitude at 0.26% was larger than at the other concentrations (P < 0.025). The logarithm of the ASSR amplitude was related linearly to the concentration of isoflurane (r = 0.85; P < 0.0001). The prediction probability (Pk) for loss of consciousness was 0.95 for both ASSR and measured isoflurane concentration. An ASSR amplitude < 0.07 microV was always associated with unconsciousness.

CONCLUSIONS

The ASSR is attenuated in a concentration-dependent manner by isoflurane. Suppression of consciousness and maximal attenuation of ASSR occur in the same isoflurane concentration range. Profound attenuation of ASSR appears to reflect unconsciousness, defined as unresponsiveness to verbal commands.

40 Hz auditory steady-state response and EEG spectral edge frequency during sufentanil anaesthesia

PURPOSE

The auditory steady-state evoked response (ASSR) is an evoked potential which provides a sensitive measure of the effects of general anaesthetics on the brain. We used pharmacokinetic-pharmacodynamic (PK-PD) modelling to compare the effects of sufentanil on the amplitude of the ASSR with its effect on spectral edge frequency (SEF) of the electroencephalogram.

METHODS

Nine patients scheduled for elective cardiac surgery participated. Midazolam (70 micrograms.kg-1 i.m.) was given 60 min before entering the operating room. Anaesthesia was induced with 5 micrograms.kg-1 sufentanil at a rate of 0.83 microgram.kg-1.min-1. The ASSR, SEF and plasma sufentanil concentrations were measured for 30 min after induction of anaesthesia before surgery. The half-life between the central and effect site compartments (t1/2Keo), the 50% inhibitory concentration (IC50) and the slope factor (gamma) were computed.

RESULTS

The amplitude of the ASSR increased during the first three minutes of infusion of sufentanil by up to 40%. This was followed by a rapid decrease between the fourth and fifth minutes to 16% of baseline. The SEF decreased progressively during the first five minutes of infusion to 18% of baseline. Both measures subsequently showed modest recovery. The parameters gamma, IC50 and t1/2Keo for ASSR were (mean +/- SD) 6.0 +/- 3.7, 2.1 +/- 1.2 ng.ml-1 and 7.3 +/- 2.4 min. For SEF the values were 5.9 +/- 5.2, 1.4 +/- 0.7 ng.ml-1 (P < 0.05 compared with ASSR) and 6.8 +/- 2.4 min.

CONCLUSION

The sensitivity of ASSR to sufentanil is less than that of the SEF.

The role of radiologic methods in assessing body composition and related metabolic parameters

The measurement of body composition and related metabolic parameters has become an important issue in clinical nutrition. Numerous techniques to assess visceral fat, which is strongly associated with metabolic disorders, have been developed. Other techniques focus mainly on the measurement of specific body components related to metabolic disturbances. This paper reviews methods that directly assess body composition and associated metabolic parameters. The principles of these methods and their accuracy, reproducibility and safety, as well as the clinical implications of their use, are discussed. Recent studies have documented the safety and efficacy of radiologic methods of assessing visceral fat, muscle mass, and morphology to obtain body composition data related to metabolic disturbances. Because these techniques have been documented to be safe and effective, clinicians should consider using them in the evaluation and follow-up of patients with various conditions.

Temperature during cardiopulmonary bypass for coronary artery operations does not influence postoperative cognitive function: a prospective, randomized trial

OBJECTIVE

The objective was to examine the effect of temperature (28 degrees vs 36 degrees C) during cardiopulmonary bypass on postoperative cognitive functions in a prospective, double-blind, and randomized manner.

METHODS

Sixty-two patients scheduled for coronary operations were randomized to warm or cold cardiopulmonary bypass. Preoperative and postoperative (7 days) neuropsychologic evaluations were performed by an observer unaware of cardiopulmonary bypass temperature.

RESULTS

Fifty-four patients completed the study (cold bypass, n = 24; warm bypass, n = 30). Significant (p < 0.01) postoperative deterioration for tests of psychomotor coordination and verbal memory was noted in both warm and cold groups, but no differences were observed between groups.

CONCLUSION

Temperature during cardiopulmonary bypass for coronary operations does not influence postoperative cognitive function.

Ketamine increases the amplitude of the 40-Hz auditory steady-state response in humans

The auditory middle latency response (AMLR) and the 40-Hz auditory steady-state response (40-Hz ASSR) are evoked potentials which possibly arise from the same generators in the primary auditory cortex. Both responses are attenuated by most general anaesthetics. Ketamine, however, has been reported to have no effect on the AMLR. Our aim was to evaluate the effects of ketamine on the 40-Hz ASSR. Spectral analysis of the electroencephalogram (EEG) was also conducted to independently examine the effects of ketamine. Ketamine 1.5 mg kg-1 was given to 12 patients for induction of general anaesthesia. Recordings of the 40-Hz ASSR and EEG were obtained every minute from 3 min before administration of ketamine to 5 min after injection, when the study was terminated. Similar recordings were obtained in three control subjects under identical conditions except that no medication was administered. Consciousness, defined as responsiveness to verbal commands, was assessed before each recording. Ketamine caused an increase in the amplitude of the 40-Hz ASSR (P < 0.01). Using published AMLR data, we conducted a simulation experiment that suggested that the effect of ketamine on the AMLR can explain its effects on the amplitude of the 40-Hz ASSR. There was a pronounced increase in relative theta (3.9-7.9 Hz) EEG power and a decrease in relative alpha (8.0-12.8 Hz) power (P < 0.001). These changes were not observed in the control group. Ketamine produced unconsciousness until the end of the study in five patients and transient unconsciousness in five patients. Two patients did not lose consciousness after administration of ketamine. The 40-Hz ASSR and EEG revealed no consistent differences between conscious and unconscious patients. No relationship could be demonstrated between the increase in amplitude of the 40-Hz ASSR or of relative theta power (the hallmark of ketamine effect) and loss of responsiveness to commands. We conclude that ketamine, unlike other anaesthetics, increases the amplitude of the 40-Hz ASSR.

The effects of propofol on the 40-Hz auditory steady-state response and on the electroencephalogram in humans

The auditory steady-state response (ASSR) is a nearly sinusoidal electrical response of the brain to auditory stimuli delivered at fast rates. The amplitude of the response is largest for stimulus rates near 40/s, hence the label 40-Hz ASSR. We have studied the effects of propofol (1.5 mg/kg) on the 40-Hz ASSR in 14 patients. The spectral edge frequency (SEF) and median frequency (MDF) of the electroencephalogram were recorded for comparison. The study was limited to 6 min after the injection of propofol. Recordings were obtained every minute. Consciousness, defined as responsiveness to verbal command, was assessed in all patients within 1 min. Nine patients, regained consciousness before the end of the study. Propofol caused disappearance of the 40-Hz ASSR for 2 min. Th 40-Hz ASSR reappeared afterward, reaching, at the end of the study period, an amplitude of about 65% of baseline. Recovery of the 40-Hz ASSR occurred whether or not consciousness was regained during the study, but the amplitude tended to be larger in patients who had regained consciousness compared with patients still unconscious during the same recording. The SEF was reduced by 24% within 2 min and recovered more quickly than the 40-Hz ASSR, reaching 91% of baseline within 4 min. The SEF tended to be higher in patients who had regained consciousness. The MDF was reduced by 27% within 2 min, and exceeded baseline values by 25% during recovery. The MDF was not higher in patients who had regained consciousness. We conclude that propofol transiently abolishes the 40-Hz ASSR. Recovery of the 40-Hz ASSR occurs whether or not consciousness is regained, but the 40-Hz ASSR tends to be larger after the return of consciousness. An association between higher amplitude 40-Hz ASSR and the return of consciousness could not be conclusively established, perhaps because of low signal-to-noise ratio in three patients. The 40-Hz ASSR did not offer any clear advantage over the SEF in predicting the return of consciousness.

Unintentional intraoperative awareness during sufentanil anaesthesia for cardiac surgery

PURPOSE

The aim of this clinical report is to describe a case of unintentional intraoperative awareness during sufentanil anaesthesia in a patient undergoing elective aortocoronary bypass grafting.

CLINICAL FINDINGS

After premedication with morphine (5 mg) and scopolamine (0.2 mg), this 51-yr-old woman received sufentanil (10 micrograms.kg-1), midazolam (4 mg) and isoflurane (0.3-0.4% end-tidal). The patient recalled specific events and discussions which took place in the operating room during surgery. This patient's report was clear and corroborated by operating room personnel. The patient denied having felt pain, anxiety or emotional distress.

CONCLUSION

Although awareness during opioid anaesthesia has been previously described with morphine and fentanyl, as far as we know this is the first clinical report of awareness with sufentanil. Given that recent efforts of early extubation in cardiac surgery patients may involve a reduction in the amount of opioid administered, this report serves as a reminder of the ever present potential for this disturbing complication.

Comparison of the effects of enflurane/N2O on the 40-Hz auditory steady-state response versus the auditory middle-latency response

The auditory middle-latency response (AMLR) is a sequence of negative-positive waves occurring 12-50 ms after the onset of an auditory stimulus presented at rates of 10/s or less. When the rate of stimulus presentation is increased to approximately 40/s, overlapping of the AM-LRs results in a sustained, nearly sinusoidal wave, called the "40-Hz auditory steady-state response" (40-Hz ASSR). The AMLR and 40-Hz ASSR have been used to study the effects of general anesthetics on the brain. The primary aim of this investigation was to determine whether the effects of a general anesthetic, namely enflurane, on the 40-Hz ASSR can be predicted from its effects on the AMLR. A secondary aim was to examine the relationship between the level of consciousness and the 40-Hz ASSR during emergence from anesthesia. Twelve ASA class I-II women undergoing reduction mammoplasty were tested. Anesthesia was induced with fentanyl (3 micrograms/kg) and thiopental (3-5 mg/kg) intravenously and was maintained with enflurane (0.5%, 0.8%, or 1.1% end-tidal; four patients per concentration; random assignment) in N2O (66% end-tidal), along with fentanyl (1 microgram/kg as needed). The 40-Hz ASSR and AMLR were recorded before induction and during anesthesia and surgery. The 40-Hz ASSR was also recorded during emergence. The amplitude of the 40-Hz ASSR was reduced profoundly during anesthesia and surgery (P < 0.001). The attenuation was not dose-dependent, and was much more pronounced than predicted by the effects of enflurane on the AMLR. The 40-Hz ASSR during anesthesia was surprisingly large (0.09 and 0.11 microV) in two patients, both of the 1.1% enflurane group. The regaining of the ability to follow verbal commands was associated with a significant (P < 0.001) increase in the amplitude of the 40-Hz ASSR. We conclude that, although auditory neurons remain capable of responding at a slow stimulus rate during enflurane-N2O anesthesia, their ability to be driven at a faster stimulus rate is markedly curtailed. The 40-Hz ASSR may be useful for detecting unintentional intraoperative awareness because the return of consciousness is associated with a clear increase in amplitude.

Sedation with midazolam during regional anaesthesia: is there a role for flumazenil?

The aim of this study was to reassess the efficacy of flumazenil for reversal of sedation with midazolam. Twenty-four ASA I or II patients undergoing elective surgery under epidural anaesthesia participated. Following epidural block, midazolam was administered to keep the patient sleepy but still responsive to verbal commands. At the end of surgery the patients were randomly allocated to receive, in a double-blind manner, either flumazenil (0.1 mg.ml-1) or placebo. The study drug (maximum dose: 10 ml) was titrated until the patient became fully awake. Sedation was assessed with the Modified Steward Coma Scale (MSCS), the Trieger test (TT) and Critical Flicker Frequency (CFF). The assessments were done before anaesthesia (baseline), at the end of surgery immediately before administration of study drug, and serially afterwards, at 10, 30, 60, 90, 120, 150 and 180 min. Analyses of variance for repeated measures and pooled t tests were used. The duration of surgery was (mean +/- SD) 0.72 +/- 0.25 hr in the flumazenil group and 0.74 +/- 0.28 hr in the placebo group. The total dose of midazolam was 7.2 +/- 2.2 mg for the flumazenil group and 8.9 +/- 2.7 mg for the placebo group. The volume of study drug administered was 5.5 ml +/- 1.9, equivalent to 0.55 mg, for the flumazenil group and 6.7 +/- 2.2 ml for the placebo group. Critical Flicker Frequency is the only measure which revealed a difference (P < 0.005) between the flumazenil and placebo groups and this occurred only at the ten-minute assessment.(ABSTRACT TRUNCATED AT 250 WORDS)