Mark J. Cleland

An assessment of the luminance and light field characteristics of used direct laryngoscopes.

PurposeTo determine luminance and light field characteristics and the effect of residual battery potential and luminance on light colour temperature in our used Macintosh #3 and #4 fibre-light (FLB) and bulb-light (BLB) laryngoscopes.MethodsWe used a power supply to provide laryngoscopes with potentials equivalent to those most commonly measured in the handles in use in our OR. Measurements were made under controlled, constant, conditions using a Pentax digital spotmeter (luminance) or a Minolta Color III colour temperature meter (light colour). Colour measurements were made while increasing the power source potential from 2–3 volts (v) in increments of 0.1 v. Light field measurements were made with a mm increment ruler mounted on the base of the test fixture.ResultsAt 2.5 and 2.8 v respectively, the #3 FLB produced luminance values of 23.9 ± 1 1.4 and 41.7 ± 17.2 cd·m−2 (mean ± SD), and the #4 FLB produced 58.6 ±21.4 and 90.9 ± 32.2 cd·m−2. Increasing potential increased luminance values (P < 0.001) and the #4FLB produced higher luminance values (P < 0.001). BLB produced higher luminance values than did FLB across all comparisons (P < 0.001). As potentials and luminance values decreased, light temperature was reduced (P < 0.001). There were no differences in light field dimensions noted in any comparison.ConclusionFifteen percent of the BLB did not meet the minimum luminance for laryngoscopy of 100 cd·m−2, 92% of the FLB did not meet that same standard.RésuméObjectifDéterminer les caractéristiques de la luminance et du champ lumineux, ainsi que l’effet de la luminance et de l’énergie de la pile résiduels sur la thermocolorimétrie des laryngoscopes Macintosh nos 3 et 4 avec fibre optique (LFO) et ampoule (LA).MéthodeNous avons utilisé une alimentation électrique pour fournir aux laryngoscopes l’énergie équivalente à celle qui est la plus communément utilisée dans les appareils en usage dans nos salles d’opération. Les mesures ont été faites dans des conditions contrôlées et constantes à l’aide d’un photomètre digital Pentax (luminance) ou d’un thermocolorimètre Minolta Color III (couleur de la lumière). L’enregistrement des couleurs a été réalisé tout en augmentant le potentiel de la source énergétique de 2–3 volts (v) par incréments de 0,1 v. Les mesures du champ lumineux ont été obtenues avec une règle millimétrique montée sur la base de l’appareil testé.RésultatsÀ 2,5 et 2,8 v respectivement, le LFO n∘ 3 a produit une luminance de 23,9 ± I 1,4 et 41,7 ± 17,2 cd·m−2 (moyenne ± écart type), et le LFO n∘ 4 a produit une luminance de 58,6 ± 21,4 et 90,9 ± 32,2 cd·m−2. L’augmentation de potentiel énergétique a entraîné une hausse de la luminance (P < 0,001) et le LFO n∘ 4 a produit une luminance plus importante (P < 0,001). Le LA a produit des valeurs de luminance plus élevées que le LFO pour toutes les comparaisons réalisées (P < 0,001). La température lumineuse a baissé en accord avec les diminutions d’énergie et de luminance (P < 0,001). Aucune différence de dimensions des champs lumineux n’a été notée lors des comparaisons.ConclusionOn a constaté que 15% des mesures LA et 92% des LFO n’ont pu atteindre la luminance minimale nécessaire à la laryngoscopie, soit 100 cd·m−2.

Electrocardiographic “pacemaker pseudospikes” and radio frequency interference

PurposeTo present a case of apparent interference of an ECG monitor by radiofrequency interference (RFI) and to provide a bnef review of RFI issues relevant to critical care medicine.Clinical featuresA 74-yr-old woman, with an implanted pacemaker, underwent major spinal surgery. In the post-anaesthesia care unit, the cardiac monitor demonstrated graphic evidence of pacemaker malfunction but there was no apparent effect on the patient. Investigation by the hospital’s biomedical personnel led to the conclusion that RFI was being interpreted by the monitor as abnormal pacemaker activity.ConclusionWith the emergence of portable, battery-operated cominunication devices, there is an increased risk of RFI within hospitals. Antennas and repeaters are required to receive and boost the signal levels of these devices to improve signal quality. They are located throughout hospitals and may be situated near patient care areas. Patient monitors may receive these signals, misinterpret them as being patient-generated and output erroneous information. In the case described, the monitor was presented with RFI signals and interpreted them as pacemaker spikes, generating a tracing suggestive of pacemaker malfunction. Troubleshooting strategies and minimizing the potential impacts of RFI on patient monitors are discussed.RésuméObjectifPrésenter un cas d’interférence radiofréquentielle (IRF) apparue sur un moniteur ECG et passer brièvement en revue les problèmes de l’interférence radiofréquentielle en réanimation.Éléments cliniquesUne femine de 74 ans porteuse d’un pacemaker implanté subissait une chirurgie rachidienne majeure. À l’unité des soins postanesthésiques, un enregistrement du moniteur cardiaque révélait un mauvais fonctionnement du pacemaker sans effet apparent sur la patiente. Un examen du personnel biomédical de l’hôpital permettait de conclure que l’IRF était interprétée comine une activité anormale du pacemaker.ConclusionL’apparition des instruments de cominunication portables alimentés par piles augmente le risque d’IRF à l’intérieur des hôpitaux. Dans le but d’améliorer la qualité des signaux, des antennes et des répéteurs sont utilisés pour recevoir et amplifier les signaux fournis par ces appareils. Ils sont localisés dans les hôpitaux et peuvent être situés près des secteurs de soins. Les moniteurs des patients peuvent capter ces signaux, les interpréter comine s’ils étaient générés par les patients et fournir ainsi de fausses informations. Dans le cas présent, le moniteur percevait des signaux d’IRF et les interprétait comine des pointes d’ECG, générant ainsi un tracé suggestif d’un dysfonctionnement de pacemaker. Les stratégies de détection et de correction destinées à minimiser les impacts potentiels de l’IRF sur les moniteurs font l’objet de la discussion.

Influence of arrhythmias on accuracy of non-invasive blood pressure monitors

PurposeTo compare the accuracy of non-invasive blood pressure (NIBP) monitors in response to common cardiac arrhythmias.MethodsSimulated signals of normal sinus rhythm (NSR), premature ventricular contractions (PVCs), atrial fibrillation (AF) and missed beats (MB) were generated from a Cufflink™ (Dynatech Nevada) NIBP simulator. Using these signals, the Critikon 1846SX (C1846), Critikon 845xt (C845), Critikon Vital Signs (CVIT), and Hewlett Packard M1008a (HP 1008) were studied at a standard dynamic blood pressure of 120/90/80 mmHg, in order to compare monitor accuracy and signal response times.ResultsThe C845 monitors most closely estimated a simulated SBP of 120 mmHg, although SBP was greater during PVCs and AF than NSR(P < 0.05). The Critikon 1846, Critikon Vital Signs, and Hewlett Packard systematically underestimated SBP during these arrhythmias, but variability was modest, as reflected by small coefficients of variation (< 2% for SBP) with all monitor types. In general, MAP and DBP were less sensitive to the effects of these arrhythmias. Finally, missed beats prolonged signal response times with all four monitor types (P < 0.05), whereas PVCs and AF did not alter this parameter.ConclusionsThis study demonstrates the extent to which the accuracy of NIBP monitors is altered by common cardiac arrhythmias. Differences in the electromechanical characteristics of these devices may help to explain the observed similarities and discrepancies.RésuméObjectifComparer la précision de différents moniteurs de tension artérielle non effractifs (TANE), lors d’arythmies cardiaques habituelles.MéthodesDes signaux simulés de rythme sinusal normal (RSN), d’extrasystoles ventriculaires (EV), de fibrillation auriculaire (FA) et d’arrêt sinusal (AS) ont été produits à partir d’un simulateur TANE Cufflink™ (Dynatech Nevada). En nous servant de ces signaux, nous avons étudié le Critikon 1846SX (C1846), le Critikon 845xt (C845), le Critikon Vital Signs (CVIT), et le Hewlett Packard M1008a (HP1008) selon une tension artérielle dynamique standard de 120/90/80 mmHg, dans le but de comparer la précision des moniteurs et les temps de réponse.RésultatsLe moniteur C845 a fourni l’estimation la plus juste d’un tension artérielle systolique (TAS) simulée de 120 mmHg, bien que la TAS a été meilleure pendant l’EV et la FA que pendant le RSN (P < 0,05). Le Critikon 1846, le Critikon Vital Signs et le Hewlett Packard ont systématiquement sous-estimé la TAS pendant ces arythmies, mais la variabilité a été peu importante, comme l’indiquent les faibles coefficients de variation (< 2% pour la TAS) pour tous les types de moniteurs. En général, la tension artérielle moyenne (TAM) et la tension artérielle diastolique (TAD) ont été moins sensibles aux effets de ces arythmies. Finalement, l’arrêt sinusal a prolongé le temps de réponse avec les quatre types de moniteurs (P < 0,05), alors que les EV et la FA n’ont pas modifié ce paramètre.ConclusionCette étude montre jusqu’où les arythmies cardiaques courantes modifient la précision des moniteurs de pression artérielle non effractifs. Les différentes caractéristiques électromécaniques des appareils peuvent contribuer à expliquer les similarités et les écarts observés.

Contact force mapping and voltage thresholds during high-frequency stimulation of human cardiac ganglionated plexuses

AIMS The intrinsic cardiac nervous system consists of ganglionated plexuses (GPs) localized epicardially to specific regions of the left atrium (LA). The relation between voltage thresholds and endocardial contact force associated with autonomic effects during stimulation of GPs has not previously been evaluated. METHODS AND RESULTS Sixteen patients with symptomatic atrial fibrillation (AF) underwent mapping of GPs prior to radiofrequency ablation of AF. Pre-acquired computed tomographic images were merged with 3D non-fluoroscopic electroanatomic mapping of the LA. Using high-frequency stimulation (HFS), the voltage thresholds of GPs was obtained while patients received conscious sedation. At each location, the contact force measurement from the catheter was correlated with the voltage applied during HFS at 5, 10, or 15 V to obtain an autonomic effect, usually associated with asystole, or marked bradycardia. There were 192 applications of HFS, resulting in GP identification in all patients (mean 3.4 per patient, range 1-5). During HFS, an autonomic response was significantly more likely to occur at 10 V as compared with 5 V (P < 0.008). There was no significant relation between the measured contact force and the likelihood of obtaining an autonomic response. When performing HFS at 15 V, a sudden overshoot with maximal values of contact force of up to 100 g was also observed. High-frequency stimulation was well tolerated, without associated adverse events. CONCLUSION An autonomic response during HFS was significantly more likely to occur at 10 V as compared with 5 V. Although the GPs are epicardial structures, significant contact force was not required for their localization.

Effect of Applying Force to Self-Adhesive Electrodes on Transthoracic Impedance: Implications for Electrical Cardioversion.

Current guidelines disagree on the role for applying force to electrodes during electrical cardioversion (ECV) for atrial fibrillation, particularly when using self‐adhesive pads. We evaluated the impact of this practice on transthoracic impedance (TTI) with varying force and in individuals with differing body mass indices (BMI). We additionally assessed whether specific prompts could improve physicians’ ECV technique.

Left Ventricular Assist Device Outflow Graft Disconnection

Although serious complications are becoming more rare with continuous-flow left ventricular assist devices such as the Heartmate II (Thoratec Corp, Pleasanton, CA), this case series discusses 2 patients with symptoms of bleeding and syncopal ventricular tachycardia associated with an outflow graft bend relief disconnection, which can be diagnosed by simple chest roentgenography.

Association between transthoracic impedance and electrical cardioversion success with biphasic defibrillators: An analysis of 1055 shocks for atrial fibrillation and flutter

The relevance of transthoracic impedance (TTI) to electrical cardioversion (ECV) success for atrial tachyarrhythmias when using biphasic waveform defibrillators is unknown.

Sudden power loss in a HeartMate II left ventricular assist device due to intermittent pin contact with the battery: case report.

Left ventricular assist device technology has improved such that mechanical malfunction, particularly with newer generation continuous flow devices, is a relatively rare event. We present a case of sudden power loss in a HeartMate II caused by intermittent contact of the battery terminals after a clip was dropped with the battery inserted in it. The clip was replaced and the patient made a complete recovery. A new inspection and testing methodology, and amended approach to patient and caregiver training, designed to prevent future occurrences is described.