Roy E. Gagnon

Near infrared spectroscopy for intraoperative monitoring of the spinal cord.

Study Design. Animal model study of three healthy commercial pigs was conducted. Objective. To determine whether near infrared spectroscopic monitoring of the spinal cord is feasible, and whether changes in near infrared spectroscopy correlate with changes in blood flow to the cord or operative maneuvers. Summary of Background Data. Near infrared spectroscopy is a noninvasive continuous monitoring tool capable of measuring absolute changes in the concentration of three chromophores: oxygenated hemoglobin, deoxygenated hemoglobin, and cytochrome aa3, the terminal enzyme in the electron transfer chain and a measure of cellular energy equilibrium. Near infrared spectroscopy has been used to monitor the brain intraoperatively in multiple circumstances. The authors hypothesized that near infrared spectroscopy could be used to monitor the spinal cord’s cellular energy equilibrium during spinal surgery (i.e., that vascular compromise could be identified before irreversible damage occurred). Methods. The posterior elements of the spine were exposed, and near infrared spectroscopy optodes (fiberoptic bundles) were sutured to either the lamina or the spinous processes of T9, T10, or both and directed toward the spinal cord. Interventions included manipulation of oxygen saturation and distraction of the T9–T10 disc space. Results. With reduced oxygen delivery (lower arterial oxygen saturation and blood flow), oxygenated hemoglobin concentration decreased and deoxygenated hemoglobin concentration increased. With distraction, blood volume (oxygenated hemoglobin plus deoxygenated hemoglobin) decreased, and cytochrome aa3 became more oxidized. Changes were apparent within 1 second of the intervention beginning, and recovery to the baseline of near infrared spectroscopy occurred with relief of each intervention. Conclusions. This near infrared spectroscopy technique monitors changes in oxygenation of the spinal cord, and therefore appears capable of intraoperative warning about impending vascular compromise of the spinal cord.

Diurnal changes in the profile shape and range of motion of the back

The diurnal height change reported to occur in young adults was investigated to characterize changes in the lumbar range of motion, spinal profile, and range of motion of the back. Twelve subjects aged 18–22 years were measured using stereophotography and standard clinical examinations in the evening and after a minimum of 8 hours of complete bed rest. The average increase in height was 20 mm. Forty percent of the height increase took place in the lumbar spine without change in the depth of the lordosis, and forty percent took place in the thoracic curve with a decrease in the kyphosis. The remaining 20% of the height increase was not located, but no measurements were taken of the cervical spine. Range of motion studies revealed that lumbar flexion, as measured using the lumber flexion increment was decreased in the morning, and straight leg rales was decreased when measured clinically but not when measured photographically. Extension, rotation, and femoral stretch test were not affected. The authors conclude that stereophotogrammetry offers an accurate, noninvasive way to study spinal profiles. Further work is needed to assess and quantify the relative motion of the skin and the underlying structures.

Diurnal changes in lumbar intervertebral distance, measured using ultrasound.

Study Design This study measured the distances between the tips of the transverse processes of adjacent lumbar vertebrae (L1‐L4) in the same subjects after 1 day of normal activities and again the next morning. Objectives To determine the feasibility of directly measuring the lumbar intervertebral distance using ultrasound and to determine the magnitude of the diurnal change in the intervertebral distance. Summary of Background Data A diurnal variation in height results from, in part, a decrease in height of the intervertebral discs with loading of the spine during the day. Previous estimates of the diurnal changes in disc height have used radiologic, stereophotographic, and magnetic resonance imaging techniques. No previous study has used ultrasound imaging. Methods Ultrasound was used to measure the distance between the tips of adjacent lumbar vertebral transverse processes. Measurements were made on six occasions in each of seven subjects after 6:00 PM in the evening and again the following morning before rising. Results The distance between the tips of adjacent transverse processes could be measured, within an individual, with a reproducibility of better than ± 7.5% coefficient of variation. Reproducibility of the measurement of the total distance between L1 and L4 was better than ± 4%. The intervertebral distances between L1 and L4 were significantly greater in the morning than in the evening. The average diurnal change in the total intervertebral distance L1‐L4 was 5.3 mm. Conclusions The study confirms the feasibility of using ultrasound to directly measure changes in the distances between the lumbar vertebrae.

Comparison of 13 published cytochrome c oxidase near-infrared spectroscopy algorithms

Conflicting patterns of change in cytochrome c oxidase (Cyt a,a3) redox status have been obtained between different near-infrared spectrophotometers when making measurements during tissue ischaemia. This study identifies possible sources of error that could be the cause of the discrepancy. A single set of optical density data was repeatedly analysed using each of the absorption spectra from 13 publications. In addition, changes in Cyt a,a3 redox status were calculated from the data set using three numerical methods, five computer software routines, eight displacements in wavelength, and ten incremental changes in the value of absorption or concentration coefficients. All Cyt a,a3 absorption spectra resulted in algorithms yielding similar patterns of change, regardless of the numerical method or computer process employed (0.9996 averager2, coefficient of correlation). However, a significantly different pattern of change in Cyt a,a3 redox status, resembling that reported by Piantadosi [Piantadosi CA (1993) Methods Toxicol. 2:107–126], was obtained when either the wavelengths, and/or the absorption values were altered to simulate erroneous values. This implies that all of the present algorithms are valid (including those of Piantadosi), but that microchip encoding errors may exist in the instrument used by Piantadosi.

Effects of propofol on cerebral oxygenation during cardiopulmonary bypass in children

Purpose: Neurologic complications occur following cardiopulmonary bypass surgery. We conducted a randomized, controlled, single-blind study to determine the effect of propofol on the redox status of cytaa3, and to evaluate its potential for decreasing neurologic complications.Methods and Materials: Twenty-four children (median age: 3.3 yr; median weight: 14.4 kg) scheduled for elective cardiopulmonary bypass surgery were assigned to either the experimental group (Group P, given sufficient propofol to eliminate brain electrical activity as measured on EEG (i.e. burst suppression)) or the control group (Group C, no propofol). Near infrared spectroscopy data were collected at one-second intervals throughout the surgical procedures. Pre- and postoperative neurologic examinations were completed by a physician blinded to the group to which the patient was assigned. Change in cytochrome aa3 data at 10-min intervals (10, 20, 30, 40 min) following start of bypass were compared between groups by repeated measures analysis of variance.Results: The patterns of change in redox state of cytochrome were different between the two groups (P<0.002). The pattern of change within Group P was similar to that in hypothermic patients in Group C. There were correlations between change in cytaa3 redox status and temperature in the control subjects. There were no gross neurologic complications in either group.Conclusions: Propofol appears to stabilize the energy supply/demand equilibrium of the brain during cardiopulmonary bypass surgery and thus theoretically could reduce the incidence or severity of neurologic complications.RésuméObjectif: Des complications neurologiques peuvent survenir à la suite de circulation extracorporelle (CEC) pendant une intervention chirurgicale. Nous avons réalisé une étude randomisée, contrôlée et à l’insu, afin de déterminer l’effet du propofol sur l’état redox du cytochrome aa3 et d’évaluer sa capacité à réduire les complications neurologiques.Méthode: L’étude a porté sur 24 enfants (âge moyen: 3,3 ans; poids moyen: 14,4 kg) qui devaient subir une intervention avec CEC. Ils ont reçu, dans le groupe expérimental P, suffisamment de propofol pour éliminer l’activité électrique cérébrale comme l’indiquait l’EEG (c.-à-d. la suppression des bouffées du tracé EEG). Le second groupe, témoin (T), n’a pas reçu de propofol. Les données spectrographiques près de l’infrarouge ont été recueillies à une seconde d’intervalle tout au long de l’opération. Un examen neurologique préopératoire et postopératoire a été fait par un médecin impartial. La modification des données sur le cytochrome aa3 enregistrées à 10 min d’intervalle (10, 20, 30, 40 min) après le début de la CEC, a été comparée entre les groupes par des analyses de variance pour mesures répétées.Résultats: Les modèles de changement d’état redox du cytochrome ont été différents d’un groupe à l’autre (P<0,002). Le modèle de changement dans le groupe P a été similaire à celui qu’on a observé chez les patients hypothermiques du groupe T. On pouvait établir des corrélations entre le changement d’état du cytochrome aa3 et la température chez les sujets témoins. Aucune complication neurologique importante n’est survenue dans un groupe ou l’autre.Conclusion: Le propofol semble maintenir l’équilibre entre l’offre et la demande d’énergie cérébrale pendant une intervention chirurgicale avec circulation extracorporelle. Il pourrait ainsi réduire, en théorie, l’incidence ou la sévérité des complications neurologiques.

NIRS monitoring of brain and spinal cord — detection of adverse intraoperative events

Near infrared spectroscopy (NIRS) monitors changes in oxygenated haemoglobin (HbO2), and redox status of cytochromeaa3 (cyt) continuously and non-invasively in living tissue. We present examples where clinically relevant changes in HbO2 and/or cyt were detected in real time, allowing intervention to avert potentially harmful hypoxic-ischaemic damage to the brain and/or spinal cord. Brain monitoring: In children undergoing surgery on cardiopulmonary bypass, observations include that: atrial fibrillation (cardiac arrhythmia) lowered cerebral HbO2 concentration; concealed haemorrhage decreased cerebral HbO2 concentration; inadequate level of anaesthetic resulted in spikes of changes in volume with interventions such as suturing; circulatory arrest reduced brain HbO2 and cyt redox status; and bypass pump problems compromised cerebral blood flow. Spinal cord monitoring: In the experimental animal, we observed that NIRS detected ischaemic change immediately following aortic compression, spinal column distraction (instrumentation to separate the vertebrae), and hypoxia. In an infant requiring release of a congenitally tethered spinal cord, we observed that traction on the spinal cord of the infant resulted in decreased total haemoglobin concentration. Summary: NIRS brain monitoring probably represents the “standard of care” during cardiac surgery because adverse events can be detected and quantified. Similarly, spinal cord monitoring could reduce ischaemic spinal cord damage in spinal cord surgery and aortic aneurysm repair.

Clinical NIRS of the urinary bladder – A demonstration case report

Urinary incontinence is a common affliction among people of all ages throughout the world. There are many causes of incontinence, treatment options are determined by the cause, and current diagnostic methods require urodynamic assessment, which involves urethral and rectal catheterization, which are uncomfortable and distasteful for patients. Since clinical near infrared spectrophotometry (NIRS) is a non-invasive, rapid means of measuring tissue oxygenation status at the bedside, we examined whether NIRS could be useful as a diagnostic tool for bladder dysfunction. An adult patient attending an incontinence clinic for routine urodynamic testing also had NIRS data collection during the standard bladder filling regimen. NIRS optodes were placed on the skin of the intact abdomen over the supra pubic region. Changes in oxy and de-oxy hemoglobin concentration and changes in cytochrome c oxidase net redox status via NIRS were collected at 6 Hz. The magnitudes of change that occurred during NIRS data collection are on the order of 0.5 µmol/l and the moments of change correspond to the subjects reported sensations of bladder filling and emptying, and with conventional urodynamics. These observations suggest that NIRS may be a disruptive technology with a role to play in non-invasive evaluation of bladder dysfunction in humans.

Cerebral oxygenation during defibrillator threshold testing of implantable cardioverter defibrillators.

Background: The induction of ventricular fibrillation (VF) during defibrillator threshold testing of implantable cardioverter defibrillators (ICD) provokes global cerebral hypoperfusion and impaired oxygen delivery. Limited data are available on the neurophysiological effects of defibrillator threshold testing. Near infrared spectroscopy (NIRS) can noninvasively measure changes in specific chromophores, which reflect cerebral oxygenation at the intravascular and mitochondrial levels. We performed a prospective trial using NIRS to analyze cerebral cortical oxygenation during defibrillator threshold testing.

An inventory of Canadian anesthesiology. Human research from 1995 through 1999.

PurposeThe year 2000 provides a symbolic opportunity to assess the past initiatives in anesthesia research. As in many other fields, medical research has benefited from utilizing computerized data bases to facilitate enumerating areas of interest. We have created a baseline survey of past research in the fields of anesthesia, anesthetics, analgesia, and analgesics to highlight Canadian studies.MethodsThe survey was undertaken using the Medical Literature Analysis and Retrieval System (MEDLARS) medical literature archive for the years 1995 through 1999. The principal categories and sub-categories of MEDLARS’ anesthesia classifications were counted for 70 countries contributing to the archive.ResultsCanadian contributions ranged from 141 (1992) to 185 (1999) and represented annually 3% of the world total in the anesthesia categories. The greatest number of studies (30–38%) were about adults aged 19 to 44 yr, and there were between 4% and 14% more studies of females than males. “Pharmacology” and “therapeutic use” were the most frequent topics, lidocaine, fentanyl, and propofol were the most studied anesthetics, and non-steroidal anti-inflammatories, opium, morphine, and fentanyl were the most studied analgesics. Among the types of studies, those classified as “quality of health care” occurred most frequently (16%). Canadian trends closely follow world trends.ConclusionThe collected counts provide a comprehensive overview of research trends for the past five years.RésuméObjectifL’an 2000 fournit un prétexte symbolique pour évaluer les initiatives passées en recherche anesthésique. Comme beaucoup d’autres champs de connaissances, la recherche médicale a bénéficié des bases de données informatisées qui facilitent le recensement des champs d’intérêt. Nous avons procédé à une enquête de base sur les recherches passées en anesthésie, sur les anesthésiques, l’analgésie et les analgésiques afin de faire ressortir les études canadiennes.MéthodeL’enquête a été faite à partir des archives de la documentation médicale du Medical Literature Analysis and Retrieval System (MEDLARS) pour les années 1995 à 1999. Les principales catégories et sous-catégories des classifcations anesthésiques de MEDLARS ont été dénombrées pour 10 pays qui contribuent aux archives.RésultatsLes contributions canadiennes vont de 141 (1992) à 185 (1999) et représentent annuellement 3 % du total mondial dans les catégories anesthésiques. Le plus grand nombre (30–38%) comprenait des adultes de 19 à 44 ans; il y a eu entre 4% et 14 % plus d’études sur les femmes que sur les hommes. “La pharmacologie” et “l’usage thérapeutique” sont les sujets les plus fréquents; la lidocaïne, le fentanyl et le propofol sont les anesthésiques les plus testés; les anti-inflammatoires non stéroïdiens, l’opium, la morphine et le fentanyl sont les analgésiques les plus étudiés. Parmi les types d’études, celles qui portent sur la “qualité des soins de santé” sont les plus nombreuses (16%). Les orientations canadiennes sont celles du reste du monde.ConclusionLes dénombrements recueillis fournissent une vue d’ensemble détaillée des tendances de la recherche pour les cinq dernières années.

Unresolved Instrumentation Problems Following Clinical Trials Using Near Infrared Spectroscopy

Near infrared spectroscopy (NIRS) clinical trials conducted over a seven year period have identified instrument engineering problems related to fiber optic failure, electromagnetic interference, chromophore algorithms, and computational software. These problems have caused confusion amongst clinicians at the bedside, rejection of large volumes of data, repeated reanalysis of data, and a significant diversion of project resources away from clinical studies and into engineering solutions. This article summarizes previously published studies and presents new data which, together, emphasize the need for improvements in NIRS technology. Instrument designers need to be aware of the need for these improvements if NIRS is to serve clinicians better during research designed to rationally define clinical management protocols.