Paul G. Firth

Functional MRI detection of pharmacologically induced memory impairment

To examine alterations in brain activation associated with pharmacologically induced memory impairment, we used functional MRI (fMRI) to study the effects of lorazepam and scopolamine on a face–name associative encoding paradigm. Ten healthy young subjects were scanned on four occasions, 2 weeks apart; they were administered i.v. saline during two placebo-scanning sessions and then alternately administered i.v. lorazepam (1 mg) or scopolamine (0.4 mg) in a double-blind, randomized, cross-over design. Both the extent and magnitude of activation within anatomic regions of interest (ROIs) were examined to determine the reproducibility of activation in the placebo sessions and the regional specificity of the pharmacologic effects. Activation within all ROIs was consistent across the two placebo scans during the encoding of novel face–name pairs (compared with visual fixation). With the administration of either lorazepam or scopolamine, significant decreases were observed in both the extent and magnitude of activation within the hippocampal, fusiform, and inferior prefrontal ROIs, but no significant alterations in activation in the striate cortex were found. Both medications impaired performance on postscan memory measures, and significant correlations between memory performance and extent of activation were found in hippocampal and fusiform ROIs. These findings suggest that pharmacologic effects can be detected with fMRI by using a reproducible experimental paradigm and that medications that impair memory also diminish activation in specific brain regions thought to subserve complex memory processes.

The Anesthetic Considerations of Tracheobronchial Foreign Bodies in Children: A Literature Review of 12,979 Cases

Asphyxiation by an inhaled foreign body is a leading cause of accidental death among children younger than 4 years. We analyzed the recent epidemiology of foreign body aspiration and reviewed the current trends in diagnosis and management. In this article, we discuss anesthetic management of bronchoscopy to remove objects. The reviewed articles total 12,979 pediatric bronchoscopies. Most aspirated foreign bodies are organic materials (81%, confidence interval [CI] = 77%–86%), nuts and seeds being the most common. The majority of foreign bodies (88%, CI = 85%–91%) lodge in the bronchial tree, with the remainder catching in the larynx or trachea. The incidence of right-sided foreign bodies (52%, CI = 48%–55%) is higher than that of left-sided foreign bodies (33%, CI = 30%–37%). A small number of objects fragment and lodge in different parts of the airways. Only 11% (CI = 8%–16%) of the foreign bodies were radio-opaque on radiograph, with chest radiographs being normal in 17% of children (CI = 13%–22%). Although rigid bronchoscopy is the traditional diagnostic “gold standard,” the use of computerized tomography, virtual bronchoscopy, and flexible bronchoscopy is increasing. Reported mortality during bronchoscopy is 0.42%. Although asphyxia at presentation or initial emergency bronchoscopy causes some deaths, hypoxic cardiac arrest during retrieval of the object, bronchial rupture, and unspecified intraoperative complications in previously stable patients constitute the majority of in-hospital fatalities. Major complications include severe laryngeal edema or bronchospasm requiring tracheotomy or reintubation, pneumothorax, pneumomediastinum, cardiac arrest, tracheal or bronchial laceration, and hypoxic brain damage (0.96%). Aspiration of gastric contents is not reported. Preoperative assessment should determine where the aspirated foreign body has lodged, what was aspirated, and when the aspiration occurred (“what, where, when”). The choices of inhaled or IV induction, spontaneous or controlled ventilation, and inhaled or IV maintenance may be individualized to the circumstances. Although several anesthetic techniques are effective for managing children with foreign body aspiration, there is no consensus from the literature as to which technique is optimal. An induction that maintains spontaneous ventilation is commonly practiced to minimize the risk of converting a partial proximal obstruction to a complete obstruction. Controlled ventilation combined with IV drugs and paralysis allows for suitable rigid bronchoscopy conditions and a consistent level of anesthesia. Close communication between the anesthesiologist, bronchoscopist, and assistants is essential.

Sickle cell disease and anesthesia.

IN October 1902, a “peculiar anomaly in human red blood corpuscles. . .came to notice in the histologic laboratory of the Ohio State University,” Columbus, Ohio. “Examination disclosed the fact that the colored corpuscles in the sample recently drawn by (a) student from his own finger that were elliptical and not circular.” Similar erythrocyte abnormalities were reported in North African Arab subjects shortly afterwards. In November 1910 James B Herrick, M.D. (Professor Of Medicine, Rush Medical College, Chicago, Illinois; 1861–1954) published a detailed case report. This described a patient with jaundice, shortness of breath, lymphadenopathy, dark urine, leg ulcers, epigastria pain, and anemia associated with these same types of “peculiar elongated and sickle-shaped red blood corpuscles.” This classic report was the first unequivocal clinical description in Western scientific literature of sickle cell disease (SCD), a set of closely related hemoglobinopathies that have in common the inheritance of mutant hemoglobin S (fig. 1). Clinically, SCD is characterized by chronic hemolytic anemia, recurrent episodes of intermittent vasoocclusion and severe pain, progressive organ damage, and a striking variation of expression. In 1927, Hahn and Gillespie noted that the eponymous deformation or sickling of the erythrocytes was induced by deoxygenation and reversed with reoxygenation. The clinical segue was a hypothesis that vasoocclusion was triggered by delayed passage of erythrocytes through the microcirculation, leading to a “vicious cycle” of increased sickling, mechanical obstruction to flow, further sickling, vasoocclusion, and infarction. In 1955, the first major review of the anesthetic implications of SCD acknowledged the high incidence of serious and potentially fatal exacerbations of the disease after surgical procedures. The avoidance of factors said to increase erythrocyte sickling and precipitate the vicious cycle has been the traditional foundation of anesthetic management of SCD. The century after the discovery of the peculiar anomaly has seen an immense expansion in the understanding of the complex relationship between these peculiar erythrocytes and the clinical expression of the disease. This article briefly summarizes advances made in understanding of the disease pathophysiology, describes salient clinical features relevant to the anesthesiologist, and reviews data from the perioperative period, emphasizing a new anesthetic approach to this old problem.

Mortality on Mount Everest, 1921-2006: descriptive study

Objective To examine patterns of mortality among climbers on Mount Everest over an 86 year period. Design Descriptive study. Setting Climbing expeditions to Mount Everest, 1921-2006. Participants 14 138 mountaineers; 8030 climbers and 6108 sherpas. Main outcome measure Circumstances of deaths. Results The mortality rate among mountaineers above base camp was 1.3%. Deaths could be classified as involving trauma (objective hazards or falls, n=113), as non-traumatic (high altitude illness, hypothermia, or sudden death, n=52), or as a disappearance (body never found, n=27). During the spring climbing seasons from 1982 to 2006, 82.3% of deaths of climbers occurred during an attempt at reaching the summit. The death rate during all descents via standard routes was higher for climbers than for sherpas (2.7% (43/1585) v 0.4% (5/1231), P<0.001; all mountaineers 1.9%). Of 94 mountaineers who died after climbing above 8000 m, 53 (56%) died during descent from the summit, 16 (17%) after turning back, 9 (10%) during the ascent, 4 (5%) before leaving the final camp, and for 12 (13%) the stage of the summit bid was unknown. The median time to reach the summit via standard routes was earlier for survivors than for non-survivors (0900-0959 v 1300-1359, P<0.001). Profound fatigue (n=34), cognitive changes (n=21), and ataxia (n=12) were the commonest symptoms reported in non-survivors, whereas respiratory distress (n=5), headache (n=0), and nausea or vomiting (n=3) were rarely described. Conclusions Debilitating symptoms consistent with high altitude cerebral oedema commonly present during descent from the summit of Mount Everest. Profound fatigue and late times in reaching the summit are early features associated with subsequent death.

Mountain mortality: a review of deaths that occur during recreational activities in the mountains

The growing popularity of activities such as hiking, climbing, skiing and snowboarding has ensured that the number of visitors to mountain environments continues to increase. Since such areas place enormous physical demands on individuals, it is inevitable that deaths will occur. Differences in the activities, conditions and methods of calculation make meaningful mortality rates difficult to obtain. However, it is clear that the mortality rate for some mountain activities is comparable to hang gliding, parachuting, boxing and other pastimes that are traditionally viewed as dangerous. Deaths in the mountains are most commonly due to trauma, high altitude illness, cold injury, avalanche burial and sudden cardiac death. This review describes the mortality rates of those who undertake recreational activities in the mountains and examines the aetiology that lies behind them.

Intensive Care in Low-Income Countries — A Critical Need

Providing critical care may not seem to be a rational priority in low-income countries such as Uganda. But inadequate infrastructure, disease burden, and demographic characteristics, combined with the broader benefits of ICUs, make it an essential component of improved care delivery.

Continuous noninvasive cardiac output in children: is this the next generation of operating room monitors? Initial experience in 402 pediatric patients.

Electrical Cardiometry™ (EC) estimates cardiac parameters by measuring changes in thoracic electrical bioimpedance during the cardiac cycle. The ICON®, using four electrocardiogram electrodes (EKG), estimates the maximum rate of change of impedance to peak aortic blood acceleration (based on the premise that red blood cells change from random orientation during diastole (high impedance) to an aligned state during systole (low impedance)).

Age-dependency of sevoflurane-induced electroencephalogram dynamics in children

BACKGROUND General anaesthesia induces highly structured oscillations in the electroencephalogram (EEG) in adults, but the anaesthesia-induced EEG in paediatric patients is less understood. Neural circuits undergo structural and functional transformations during development that might be reflected in anaesthesia-induced EEG oscillations. We therefore investigated age-related changes in the EEG during sevoflurane general anaesthesia in paediatric patients. METHODS We analysed the EEG recorded during routine care of patients between 0 and 28 yr of age (n=54), using power spectral and coherence methods. The power spectrum quantifies the energy in the EEG at each frequency, while the coherence measures the frequency-dependent correlation or synchronization between EEG signals at different scalp locations. We characterized the EEG as a function of age and within 5 age groups: <1 yr old (n=4), 1-6 yr old (n=12), >6-14 yr old (n=14), >14-21 yr old (n=11), >21-28 yr old (n=13). RESULTS EEG power significantly increased from infancy through ∼6 yr, subsequently declining to a plateau at approximately 21 yr. Alpha (8-13 Hz) coherence, a prominent EEG feature associated with sevoflurane-induced unconsciousness in adults, is absent in patients <1 yr. CONCLUSIONS Sevoflurane-induced EEG dynamics in children vary significantly as a function of age. These age-related dynamics likely reflect ongoing development within brain circuits that are modulated by sevoflurane. These readily observed paediatric-specific EEG signatures could be used to improve brain state monitoring in children receiving general anaesthesia.

An electronic checklist improves transfer and retention of critical information at intraoperative handoff of care.

BACKGROUND:Communication failures are a significant cause of preventable medical errors, and poor-quality handoffs are associated with adverse events. We developed and implemented a simple checklist to improve communication during intraoperative transfer of patient care. METHODS:A prospective observational assessment was performed to compare relay and retention of critical patient information between the outgoing and incoming anesthesiologist before and after introduction of an electronic handoff checklist. Secondary measurements included checklist usage and clinician satisfaction. RESULTS:Sixty-nine handoffs were observed (39 with and 30 without the checklist). Significant improvements in the frequency of information relay occurred with checklist use, most notably related to administration of vasopressors and antiemetics (85% vs 44%, P = 0.008; 46% vs 15%, P = 0.015, respectively); estimated blood loss and urine output (85% vs 57%, P = 0.014; 85% vs 52%, P = 0.006, respectively); communication about potential areas of concern (92% vs 57%, P = 0.001), postoperative planning (92% vs 43%, P < 0.001), and introduction of the relieving anesthesiologist to the operating team (51% vs 3%, P < 0.001). When queried after the handoff, relieving anesthesiologists more frequently knew the antibiotic (97% vs 75%, P = 0.020), muscle relaxant (97% vs 63%, P = 0.003), and amount of fluid administered (97% vs 72%, P = 0.008) when the checklist was used. Voluntary use of the checklist occurred in 60% of the handoffs by the end of the observation period (99% control limits: 58%–75%.). Clinicians who reported using the checklist in at least two-thirds of their handoffs reported higher satisfaction with quality of communication at handoff (P = 0.003). CONCLUSIONS:An electronic checklist improved relay and retention of critical patient information and clinician communication at intraoperative handoff of care.

Transient high altitude neurological dysfunction: an origin in the temporoparietal cortex.

This case report describes three separate episodes of isolated ataxia, hallucinations of being accompanied by another person, and bilateral dressing apraxia occurring in a single individual without prior warning signs. These symptoms are attributable to disruption of vestibular processing in the temporoparietal cortex or associated limbic structures. Neurological dysfunction at high altitude is usually ascribed to high altitude cerebral edema or acute mountain sickness. However, transient neurological symptoms occur abruptly at more extreme altitudes, often following vigorous exertion, without overt altitude-induced prodromes. These symptoms may be caused by intense neuronal discharge or neuronal synchronization as a feature of epileptic discharges or cortical spreading depression. Transient high altitude neurological dysfunction should be recognized as a separate complication of extreme altitude, distinct from high altitude cerebral edema.