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Background Transient adenosine-induced asystole is a reliable method for producing a short period of relative hypotension during surgical and endovascular procedures. Although the technique has been described in the endovascular treatment of brain arteriovenous malformations, aortic aneurysms, and posterior circulation cerebral aneurysms, little description of its use in anterior circulation aneurysms is available. Objective To assess the benefits of adenosine-induced transient asystole in complex anterior circulation aneurysms, to describe our experience in selected cases, and to provide the first experience of the use of adenosine in anterior circulation aneurysms. Methods The adenosine-induced cardiac arrest protocol allows us to titrate the duration of cardiac arrest on the basis of individual patient responses. The operative setup is the same as with all aneurysm clippings, with the addition of the placement of transcutaneous pacemakers as a precaution for prolonged bradycardia or asystole. Escalating doses of adenosine are given to determine the approximate dose that results in 30 seconds of asystole. When requested by the surgeon, the dose of adenosine is administered for definitive dissection and clipping. We present 6 cases in which this technique was used. Results The use of transient adenosine-induced asystole provided excellent circumferential visualization of the aneurysm neck and safe clip application. All patients did well neurologically and suffered no evidence of perioperative cerebral ischemia or delayed complication from the use of adenosine itself. Conclusion Transient adenosine-induced asystole is a safe and effective technique in select circumstances that may aid in safe and effective aneurysm clipping. Along with the traditional techniques of brain relaxation, skull base approaches, and temporary clipping, adenosine-induced asystole facilitates circumferential visualization of the aneurysm neck and is another technique available to cerebrovascular surgeons.

Market economies are notoriously difficult to identify in the archeological record. This is particularly true in the subtropical Maya lowlands of Mexico, Guatemala, and Belize because most utilitarian items and consumables were made of highly perishable materials. We explore the hypothesis that ancient marketplaces can be identified through analysis of chemical residues in soils from open and easily accessible spaces in and about ancient Maya cities. We compared soil chemical signatures from a credible ancient marketplace location in the specialized trade center of Chunchucmil, Yucatan, Mexico to those from a modern marketplace at Antigua, Guatemala. We found extraordinarily high concentrations of phosphorus and zinc in the soil of Chunchucmil's proposed marketplace and the same high concentrations correlate well with food preparation and vegetable sales areas at the modern marketplace. These methods hold promise in resolving the vexing question of how large ancient Maya urban populations were sustained.

Excessive blood sampling, with its inherent risks, is of growing concern among clinicians. We performed this study to measure the changes in hematocrit (Hct) during a laboratory investigation where multiple blood samples are collected. The performance of a simple mathematical model, used in clinical practice to predict Hct changes, is evaluated. Eight healthy male volunteers participated in this study. The equation Hctf = Hcti*(EBV-BL)/EBV is used to predict changes in Hct. Where Hctf and Hcti are, respectively, the final and initial Hct, EBV is the estimated blood volume and BL is the blood loss. Thirty-five pharmacokinetic samples per subject were collected totalling 314 mL of BL. The Hct decreased from 44.2% ± 2.2% to 39.9% ± 2.5% (P = 0.001). On average, model predictions tended to have a discrete tendency to underestimate the Hct changes (-0.5% points of bias). While the predictions of the Hct were very accurate in 50% of the subjects, the discrepancy of the Hct predictions was clinically significant in the other 50% of the subjects. Consistent with the model prediction, this study demonstrated a significant reduction in the Hct values in healthy subjects undergoing incremental phlebotomy. On average, the model successfully predicted the decrease in Hct. However, the inter- and intra-individual variabilities in the Hct changes are clinically significant. In clinical settings, which are not well controlled environments, the variability is likely to be greater and the clinical use of the model cannot replace the need to monitor the Hct. Les echantillons sanguins excessifs, et leurs risques inherents, preoccupent de plus en plus les cliniciens. Nous avons mesure les modifications de l’hematocrite (Hct) au cours d’une investigation en laboratoire ou de multiples echantillons sanguins sont preleves. La performance d’un modele mathematique simple, qui predit les changements de l’Hct en clinique, est evaluee. Huit hommes volontaires en sante ont participe a l’etude. L’equation Hctf = Hct*(VSE-PS)/VSE sert a predire les changements de l’Hct ou Hct et Hct sont respectivement l’Hct final et initial, VSE est le volume sanguin estime et PS est la perte sanguine. Trente-cinq echantillons pharmacocinetiques par sujet ont ete preleves pour un total de 314 mL de PS. L’Hct a diminue de 44,2 % ± 2,2 % a 39,9 % ± 2,5 % (P = 0,001). Les predictions du modele presentaient en moyenne une tendance discrete a sous-estimer les modifications de l’Hct (-0,5 % de biais). Les predictions de l’Hct ont ete tres exactes chez 50 % des sujets, mais la divergence dans les predictions etait cliniquement significative chez les autres 50 %. L’etude a demontre, conformement au modele de prediction, une reduction significative des valeurs de l’Hct chez des sujets sains qui subissent une phlebotomie incrementielle. En moyenne, le modele a pu predire la baisse de l’Hct. Cependant, les variations interindividuelles et intra-individuelles de modification de l’Hct sont cliniquement significatives. En clinique, ce qui n’est pas un environnement bien contrale, la variabilite risque d’etre plus grande et l’usage clinique du modele ne peut remplacer la necessite du moniteur d’Hct.

Background Dexmedetomidine, a highly selective alpha2-adrenoceptor agonist used for short-term sedation of mechanically ventilated patients, has minimal effect on ventilation. Methods This study compared the respiratory effect of dexmedetomidine to that of remifentanil. The authors measured and compared respiratory responses of six healthy male volunteers during (1) a stepwise target-controlled infusion of remifentanil, (2) a stepwise target-controlled infusion of dexmedetomidine, and (3) a pseudonatural sleep session. Results Compared with baseline, remifentanil infusions resulted in respiratory depression as evidenced by a decrease in respiratory rate and minute ventilation, respiratory acidosis, and apnea episodes resulting in desaturations. Remifentanil disturbed the natural pattern of breathing and flattened the distribution of ventilatory timing (inspiratory time/ventilatory cycle time). The respiratory effects of dexmedetomidine markedly contrasted with those of remifentanil. When compared with baseline, during dexmedetomidine infusions, the respiratory rate significantly increased, and the overall apnea/hypopnea index significantly decreased. The distribution of inspiratory time/ventilatory cycle time showed an increased peak. In addition, dexmedetomidine seemed to mimic some aspect of natural sleep. While the subjects were breathing a 5% CO2 mixture, hypercapnic arousal phenomena (documented by the Bispectral Index, the electroencephalogram, and sudden increase in the minute ventilation) were observed during dexmedetomidine infusions. Similar phenomena during natural sleep have been reported in the literature. Conclusions In comparison with remifentanil, dexmedetomidine infusions (1) did not result in clinically significant respiratory depression, (2) decreased rather than increased the apnea/hypopnea index, and (3) exhibited some similarity with natural sleep.

Background Dexmedetomidine is a highly selective alpha2-adrenoceptor agonist used for short-term sedation of mechanically ventilated patients. The analgesic profile of dexmedetomidine has not been fully characterized in humans. Methods This study was designed to compare the analgesic responses of six healthy male volunteers during stepwise target-controlled infusions of remifentanil and dexmedetomidine. A computer-controlled thermode was used to deliver painful heat stimuli to the volar side of the forearms of the subjects. Six sequential 5-s stimuli (ranging from 41 degrees to 50 degrees C) were delivered in random order. The recorded visual analog scale was used to fit an Emax model. Results Compared to baseline, remifentanil infusions resulted in a right shift of the sigmoid curve (increased T50, the temperature producing a visual analog scale score of 50% of the maximal effect, from 46.1 degrees C at baseline to 48.4 degrees and 49.1 degrees C during remifentanil infusions) without a change of the steepness of the curve (identical Hill coefficients gamma during baseline and remifentanil). Compared to baseline, dexmedetomidine infusions resulted in both a right shift of the sigmoid curve (increased T50 to 47.2 degrees C) and a decrease in the steepness of the curve (decreased gamma from 3.24 during baseline and remifentanil infusions to 2.45 during dexmedetomidine infusions). There was no difference in the pain responses between baseline and after recovery from remifentanil infusions (identical T50 and gamma). Conclusion As expected, dexmedetomidine is not as effective an analgesic as the opioid remifentanil. The difference in the quality of the analgesia with remifentanil may be a reflection of a different mechanism of action or a consequence of the sedative effect of dexmedetomidine.

We present a case of tongue necrosis due to intraoperative pressure injury. A laryngeal mask airway with adhesive electrodes was inserted into the oropharynx, over an endotracheal tube, to facilitate glossopharyngeal nerve monitoring during craniotomy for a cerebellopontine angle tumor. The case, mechanisms of injury, and modifications to our current practice are discussed.

Pulse oximeters may delay displaying the correct oxygen saturation during the onset of hypoxia. We investigated the desaturation response times of pulse oximeter sensors (forehead, ear and finger) during vasoconstriction due to mild hypothermia and vasodilation caused by glyceryl trinitrate. Ten healthy male volunteers were given three hypoxic challenges of 3 min duration under differing experimental conditions. Mild hypothermia increased the mean response time of finger oximeters from 130 to 215 s. Glyceryl trinitrate partly offset this effect by reducing the response time from 215 to 187 s. In contrast, the response times of the forehead and ear oximeters were unaffected by mild hypothermia, but the difference between head and finger oximeters was highly significant (p < 0.0001). The results suggest that the head oximeters provide a better monitoring site for pulse oximeters during mild hypothermia.

Dexmedetomidine, a highly selective alpha2-adrenoceptor agonist used for short-term sedation of mechanically ventilated patients, has minimal effect on ventilation.This study compared the respiratory effect of dexmedetomidine to that of remifentanil. The authors measured and compared respiratory responses of six healthy male volunteers during (1) a stepwise target-controlled infusion of remifentanil, (2) a stepwise target-controlled infusion of dexmedetomidine, and (3) a pseudonatural sleep session.Compared with baseline, remifentanil infusions resulted in respiratory depression as evidenced by a decrease in respiratory rate and minute ventilation, respiratory acidosis, and apnea episodes resulting in desaturations. Remifentanil disturbed the natural pattern of breathing and flattened the distribution of ventilatory timing (inspiratory time/ventilatory cycle time). The respiratory effects of dexmedetomidine markedly contrasted with those of remifentanil. When compared with baseline, during dexmedetomidine infusions, the respiratory rate significantly increased, and the overall apnea/hypopnea index significantly decreased. The distribution of inspiratory time/ventilatory cycle time showed an increased peak. In addition, dexmedetomidine seemed to mimic some aspect of natural sleep. While the subjects were breathing a 5% CO2 mixture, hypercapnic arousal phenomena (documented by the Bispectral Index, the electroencephalogram, and sudden increase in the minute ventilation) were observed during dexmedetomidine infusions. Similar phenomena during natural sleep have been reported in the literature.In comparison with remifentanil, dexmedetomidine infusions (1) did not result in clinically significant respiratory depression, (2) decreased rather than increased the apnea/hypopnea index, and (3) exhibited some similarity with natural sleep.

The subject of project peer review of structural design was a major topic of discussion at both the 1983 Santa Barbara Engineering Foundation conference, Building Structural Failures—Their Cause and Prevention, and the 1987 follow‐up conference in Palm Coast, Florida, Structural Failures II. The deliberations of the Palm Coast conference regarding project peer review, which are the subject of this paper, resulted in the very significant recommendation that peer review of projects over a certain threshold level be made mandatory through incorporation into code provisions or by requirements of regulating authorities, and that the cost of such reviews should be borne by the owner. Several questions remain regarding the criteria and procedures of such a review, such as the threshold limits for projects that should be subject to review, the scope of the review, the liability of the reviewer, and the timing of the review. A joint committee of the ASCE and the American Consulting Engineers Council (ACEC) is work...