Search PubMed⌕ Search

Biomedical subjects

D K Menon

Publications and source records attributed to D K Menon.

At least 19 recordsLinked to original sources
PubMed2006

Attitudes of anaesthetists to awareness and depth of anaesthesia monitoring in the UK.

BACKGROUND AND OBJECTIVE: Awareness with postoperative recall of intraoperative events is a rare but serious complication of general anaesthesia. This survey investigated the attitude of anaesthetists in the UK to awareness and depth of anaesthesia monitoring. METHODS: Questionnaires were sent to 4927 consultant anaesthetists in 285 hospitals in the UK in September 2004. The responses were recorded in an electronic database, summarized and compared with the results of studies performed in Australia and the USA. RESULTS: The response rate was 44%. When judged against published awareness rates, anaesthetists underestimated the incidence of awareness in their own practice (median 1: 5000). One-third of respondents have dealt with patients who have experienced intraoperative recall. The majority of anaesthetists perceived awareness as a minor problem on an 11-point scale (modal score 2, median score 3, IQR 2-5). Eighty-six percent of anaesthetists considered clinical signs unreliable but 91% felt that measurement of end-tidal anaesthetic agent concentration reduces the likelihood of awareness. The majority of anaesthetists would use a monitor at least some of the time if one was available to them. Overall, the attitudes of anaesthetists in the UK, USA and Australia are remarkably similar. CONCLUSIONS: Anaesthetists tend not to view awareness as a serious problem. Although most accept that clinical signs are unreliable indicators of awareness, few believe that monitors of anaesthetic depth should be used for routine cases.

Adult↗
PubMed2006

Changes over time in cognitive and structural profiles of head injury survivors.

Survivors of traumatic head injury often suffer chronic cognitive deficits. Considerable evidence implicates the cholinergic system in these deficits. Recently, we reported cognitive and structural abnormalities in a cohort of head injured survivors consistent with this hypothesis [see Salmond, C. H., Chatfield, D. A., Menon, D. K., Pickard, J. D., & Sahakian, B. J. (2005). Cognitive Sequelae of Head Injury: Involvement of Basal Forebrain and associated structures. Brain, 128(1), 189-200]. The stability of the cognitive and structural MRI profiles was investigated in a longitudinal study. Twenty-one survivors of moderate-severe head injury completed two comprehensive neuropsychological assessments and two structural MRI scans at least six months apart. A cohort of controls also completed these investigations. The results revealed that the cognitive and structural profiles are relatively stable from six months post-injury forward up to 3 years post-injury. Deficits in memory, attention and reaction time were found, with relative preservation of working memory, consistent with abnormalities in the cholinergic system. These findings suggest that cholinergic enhancers may be an effective treatment for cognitive deficits post-head injury in survivors up to three years post-injury.

Adolescent↗
PubMed2006

An investigation of auto-reactivity after head injury.

Murine models of CNS injury show auto-reactive T cell responses directed at myelin antigens, associated with improved neuronal survival and functional recovery. This pilot study shows, for the first time, that similar immune responses against myelin occur in human traumatic brain injury (TBI), with an expansion of lymphocytes recognising myelin basic protein observed in 40% of patients studied. "Reactive" patients did not have greater contusion volume on imaging, but were younger than the "unreactive" subgroup and tended towards a more favorable outcome. These findings are consistent with the concept of "beneficial autoimmunity".

Adult↗
PubMed2006

Decompressive craniectomy in traumatic brain injury: outcome following protocol-driven therapy.

Although decompressive craniectomy following traumatic brain injury is an option in patients with raised intracranial pressure (ICP) refractory to medical measures, its effect on clinical outcome remains unclear. The aim of this study was to evaluate the outcome of patients undergoing this procedure as part of protocol-driven therapy between 2000-2003. This was an observational study combining case note analysis and follow-up. Outcome was assessed at an interval of at least 6 months following injury using the Glasgow Outcome Scale (GOS) score and the SF-36 quality of life questionnaire. Forty-nine patients underwent decompressive craniectomy for raised and refractory ICP (41 [83.7%] bilateral craniectomy and 8 [16.3%] unilateral). Using the Glasgow Coma Scale (GCS), the presenting head injury grade was severe (GCS 3-8) in 40 (81.6%) patients, moderate (GCS 9-12) in 8 (16.3%) patients, and initially mild (GCS 13-15) in 1 (2.0%) patient. At follow-up, 30 (61.2%) patients had a favorable outcome (good recovery or moderate disability), 10 (20.48) remained severely disabled, and 9 (18.4%) died. No patients were left in a vegetative state. Overall the results demonstrated that decompressive craniectomy, when applied as part of protocol-driven therapy, yields a satisfactory rate of favorable outcome. Formal prospective randomized studies of decompressive craniectomy are now indicated.

Adolescent↗
PubMed2006

Decompressive craniectomy in traumatic brain injury: the randomized multicenter RESCUEicp study (www.RESCUEicp.com).

The RESCUEicp (Randomized Evaluation of Surgery with Craniectomy for Uncontrollable Elevation of intracranial pressure) study has been established to determine whether decompressive craniectomy has a role in the management of patients with traumatic brain injury and raised intracranial pressure that does not respond to initial treatment measures. We describe the concept of decompressive craniectomy in traumatic brain injury and the rationale and protocol of the RESCUEicp study.

Biomedical Research↗
PubMed2006

Awake insertion of the laryngeal mask airway using topical lidocaine and intravenous remifentanil.

We assessed the use of intravenous remifentanil for the insertion of the laryngeal mask airway in 10 healthy awake volunteers, a technique primarily developed to facilitate functional magnetic resonance imaging studies of anaesthesia. Each volunteer received 200 microg glycopyrronium intravenously. Topical airway anaesthesia was effected by 4 ml nebulised lidocaine 4%, followed by 12 sprays of lidocaine 10%. Remifentanil was subsequently infused to achieve an initial target effect-site concentration of 2 ng.ml(-1); increments of 1 ng.ml(-1) were allowed with the maximum effect-site concentration limited to 6 ng.ml(-1). Insertion of the laryngeal mask airway was successful on the first attempt in all cases. The median (IQR [range]) target effect-site remifentanil concentration at insertion was 2.5 (2-3 [2-4]) ng.ml(-1). All volunteers were co-operative during the procedure and only one reported discomfort. Sore throat was a complication in all volunteers. We conclude that the technique allows successful insertion of the laryngeal mask airway in healthy awake volunteers under conditions that were safe and reproducible.

Adult↗
PubMed2005

Incidence of adrenal insufficiency after severe traumatic brain injury varies according to definition used: clinical implications.

BACKGROUND: Adrenal insufficiency impacts on the haemodynamic management of patients in intensive care. Very little is known about the incidence of adrenal insufficiency in the first 10 days after traumatic brain injury. METHODS: We retrospectively reviewed the charts of 113 traumatic brain injury patients within 10 days of their injury. They all had a high-dose corticotropin stimulation test performed because of haemodynamic instability. Blood cortisol concentrations were measured at baseline, 30 and 60 min after the administration of high-dose corticotropin. The incidence of adrenal insufficiency was determined according to various definitions used in the literature. RESULTS: The baseline cortisol concentration was <414 nmol litre(-1) (15 microg dl(-1)) in 78% of patients and <690 nmol litre(-1) (25 microg dl(-1)) in all patients. The cortisol concentration did not rise above 500 nmol litre(-1) (18 microg dl(-1)) at 30 and 60 min in 49 and 22% of patients, respectively. The cortisol concentration did not rise by 250 nmol litre(-1) (9 microg dl(-1)) at 30 and 60 min in 48 and 25% of patients respectively. Primary adrenal insufficiency defined by an abnormal baseline cortisol concentration and an abnormal response to the high-dose corticotropin stimulation test was present in 13-28% of patients according to the cut-off values used. CONCLUSIONS: The incidence of adrenal insufficiency varies from 25 to 100% in the first 10 days after traumatic brain injury. The range of incidences reported illustrates the need for standardization of the definition of adrenal insufficiency. This has a direct impact on treatment. Sampling at 60 min after the high-dose corticotropin stimulation test seems to correlate better with the maximum secreting capacity of the adrenal glands.

Adolescent↗
PubMed2005

Influence of improved teaching on medical students' acquisition and retention of drug administration skills.

BACKGROUND: Drug administration error is a major problem causing substantial morbidity and mortality worldwide. Lack of education about drug administration appears to be a causative factor. We devised an online teaching module for medical students and assessed its short- and long-term efficacy. METHODS: One hundred and thirty clinical medical students were invited to undertake additional, online, teaching about drug administration. Those participating were identified and the number of web pages viewed recorded. The students' knowledge retention was tested by means of drug administration questions incorporated into routine assessments and examinations over the next 6 months. Other indices of all students' performance were recorded to correct for confounding factors. RESULTS: Just over half (52%) responded to the invitation to participate. The amount of interest they showed in the teaching module correlated positively with their performance in questions about drug administration, although the latter waned over time. Surprisingly, correcting for students' general ability and keenness revealed that the less able students were most likely to undertake the teaching module. CONCLUSIONS: Additional online teaching about drug administration improves students' knowledge of the topic but clearly requires reinforcement; however, only about half the students took up the option. Medical students must acquire these fundamental skills, and online teaching can help. Medical educators must ensure that drug administration is taught formally to all students as part of the curriculum and must understand that it may require additional teaching.

Chemistry, Pharmaceutical↗
PubMed2005

Diffusion tensor imaging in chronic head injury survivors: correlations with learning and memory indices.

Diffusion tensor imaging (DTI) provides a unique insight into the cellular integrity of the brain. While conventional magnetic resonance imaging underestimates the extent of pathology following closed head injury, diffusion-weighted imaging has been shown to more accurately delineate the extent of cerebral damage. There have only been a few case studies of DTI in chronic head injury survivors. This study used DTI to investigate changes in anisotropy and diffusivity in survivors of head injury at least 6 months after their injury. The relationship between cognition and diffusion abnormality was also investigated. The voxel-based analysis revealed significant bilateral decreases in anisotropy, in major white matter tracts and association fibers in the temporal, frontal, parietal and occipital lobes. Statistically significant increases in diffusivity were also found in widespread areas of the cortex. A significant positive correlation was found between diffusivity and impairment of learning and memory in the left posterior cingulate, left hippocampal formation and left temporal, frontal and occipital cortex. The common pattern of abnormality despite heterogeneous injury mechanism and lesion location in the group suggests that these cellular changes reflect secondary insults. The importance of diffusion abnormalities in head injury outcome is emphasized by the significant correlation between a learning and memory index and diffusivity in areas known to subserve this cognitive function.

Adolescent↗
PubMed2005

Physiological thresholds for irreversible tissue damage in contusional regions following traumatic brain injury.

Cerebral ischaemia appears to be an important mechanism of secondary neuronal injury in traumatic brain injury (TBI) and is an important predictor of outcome. To date, the thresholds of cerebral blood flow (CBF) and cerebral oxygen utilization (CMRO(2)) for irreversible tissue damage used in TBI studies have been adopted from experimental and clinical ischaemic stroke studies. Identification of irreversibly damaged tissue in the acute phase following TBI could have considerable therapeutic and prognostic implications. However, it is questionable whether stroke thresholds are applicable to TBI. Therefore, the aim of this study was to determine physiological thresholds for the development of irreversible tissue damage in contusional and pericontusional regions in TBI, and to determine the ability of such thresholds to accurately differentiate irreversibly damaged tissue. This study involved 14 patients with structural abnormalities on late-stage MRI, all of whom had been studied with (15)O PET within 72 h of TBI. Lesion regions of interest (ROI) and non-lesion ROIs were constructed on late-stage MRIs and applied to co-registered PET maps of CBF, CMRO(2) and oxygen extraction fraction (OEF). From the entire population of voxels in non-lesion ROIs, we determined thresholds for the development of irreversible tissue damage as the lower limit of the 95% confidence interval for CBF, CMRO(2) and OEF. To test the ability of a physiological variable to differentiate lesion and non-lesion tissue, we constructed probability curves, demonstrating the ability of a physiological variable to predict lesion and non-lesion outcomes. The lower limits of the 95% confidence interval for CBF, CMRO(2) and OEF in non-lesion tissue were 15.0 ml/100 ml/min, 36.7 mumol/100 ml/min and 25.9% respectively. Voxels below these values were significantly more frequent in lesion tissue (all P < 0.005, Mann-Whitney U-test). However, a significant proportion of lesion voxels had values above these thresholds, so that definition of the full extent of irreversible tissue damage would not be possible based upon single physiological thresholds. We conclude that, in TBI, the threshold of CBF below which irreversible tissue damage consistently occurs differs from the classical CBF threshold for stroke (where similar methodology is used to define such thresholds). The CMRO(2) threshold is comparable to that reported in the stroke literature. At a voxel-based level, however (and in common with ischaemic stroke), the extent of irreversible tissue damage cannot be accurately predicted by early abnormalities of any single physiological variable.

Adolescent↗
PubMed2005

Cerebral microdialysis methodology--evaluation of 20 kDa and 100 kDa catheters.

Microdialysis monitoring of cerebral metabolism is now performed in several neuro-intensive care units. Conventional microdialysis utilizes CMA70 catheters with 20 kDa molecular weight cut-off membranes enabling the measurement of small molecules such as glucose, lactate, pyruvate and glutamate. The CMA71 100 kDa molecular weight cut-off microdialysis catheter has recently been introduced to allow detection of larger molecules such as cytokines. The objective of this study was to perform in vitro and in vivo testing of the CMA71 microdialysis catheter, comparing its performance with the CMA70. In vitro comparison studies of three of each catheter using reference analyte solutions, demonstrated equivalent recovery for glucose, lactate, pyruvate and glutamate (range 94-97% for CMA70 and 88-103% for CMA71). In vivo comparison involved intracranial placement of paired CMA70 and CMA71 catheters (through the same cranial access device) in six patients with severe traumatic brain injury. Both catheters were perfused with CNS Perfusion Fluid without dextran at 0.3 microl min-1 with hourly sampling and bedside analysis on a CMA600 microdialysis analyser. The two catheters yielded equivalent results for glucose, lactate, pyruvate, glutamate and lactate/pyruvate ratio. CMA71 microdialysis catheters can, therefore, be used for routine clinical monitoring of extracellular substances, as well as for their intended research role of larger molecular weight protein sampling.

Adolescent↗
PubMed2005

Predicting the response of intracranial pressure to moderate hyperventilation.

BACKGROUND: Hyperventilation may cause brain ischaemia after traumatic brain injury. However, moderate reductions in PaCO(2) are still an option in the management of raised intracranial pressure (ICP) under some circumstances. Being able to predict the ICP-response to such an intervention would be advantageous. We investigated the ability of pre-hyperventilation ICP and cerebrospinal compensatory reserve to predict the reduction in ICP achievable with moderate hyperventilation in head injured patients. METHODS: Thirty head injured patients requiring sedation and mechanical ventilation were investigated. ICP was monitored via an intraparenchymal probe and intracranial cerebrospinal compensatory reserve was assessed using an index (R(ap)) based on the relationship between mean ICP and its pulse amplitude. Measurements were made at a constant level of PaCO(2) during a 20-minute baseline period. The patients were then subjected to an acute decrease in PaCO(2) of approximately 1 kPa and, after an equilibration period of 10 minutes, measurements were again made at a constant level of PaCO(2) for a further 20 minutes. A multiple linear regression model, incorporating baseline PaCO(2), ICP, and R(ap) was used to identify the relevant predictors of ICP reduction. FINDINGS: Baseline ICP and R(ap) were both significant predictors of ICP-reduction (p=0.02 and 0.001 respectively) with R(ap) being the more powerful parameter. CONCLUSIONS: A model based on cerebrospinal compensatory reserve and ICP can predict the achievable ICP-reduction and may potentially be used to optimise patient selection and intensity of hyperventilation.

Adult↗
PubMed2005

Glucose metabolism in traumatic brain injury: a combined microdialysis and [18F]-2-fluoro-2-deoxy-D-glucose-positron emission tomography (FDG-PET) study.

Following traumatic brain injury, as a consequence of ionic disturbances and neurochemical cascades, glucose metabolism is affected. [18F]-2-Fluoro-2-deoxy-D-glucose (FDG) Positron Emission Tomography (FDG-PET) provides a measure of global and regional cerebral metabolic rate of glucose (rCMRglc), but only during the time of the scan. Microdialysis monitors energy metabolites over extended time periods, but only in a small focal volume of the brain. Our objective in this study is to assess the association of parameters derived from these techniques when applied to patients with traumatic brain injury. Eleven sedated, ventilated patients receiving intracranial pressure monitoring and managed using Addenbrooke's Neurosciences Critical Care Unit protocols were monitored. Dialysate values for glucose, lactate, pyruvate, and glutamate, and the lactate to glucose (L/G), lactate to pyruvate (L/P) and pyruvate to glucose (P/G) ratios were determined and correlated with rCMRglc. FDG-PET scans were performed within 24 hours (five patients), or between 1 and 4 days (two patients) or after 4 days (six patients). Two patients were rescanned 4 and 7 days after their initial scan. A 20 mm region of interest (ROI) was defined on co-registered CT scan on two contiguous slices around the microdialysis catheter. Mean (+/-sd) for rCMRglc was 19.1 +/- 5.5 micromol/100 g/min, and the corresponding microdialysis values were: glucose 1.4 +/- 1.4 mmol/ L; lactate 5.3 +/- 3.6 mmol/L; pyruvate 164.1 +/- 142.3 micromol/L; glutamate 15.0 +/- 14.7 micromol/L; L/G 11.0 +/- 16.0; L/P 27.3 +/- 7.9 and P/G 381 +/- 660. There were significant relations between rCMRglc and dialysate lactate (r = 0.58, P = 0.04); pyruvate (r = 0.57, P = 0.04), L/G (r = 0.55, P = 0.05), and the P/G (r = 0.56, P = 0.05) but not between rCMRglc and dialysate glucose, L/P or glutamate in this data set. The results suggest that increases in glucose utilization as assessed by FDG-PET in these patients albeit in mainly healthy tissue are associated with increases in dialysate lactate, pyruvate, L/G and the P/G ratio perhaps indicating a general rise in metabolism rather than a shift towards non-oxidative metabolism. Further observations are required with regions of interest (microdialysis catheters positioned) adjacent to mass lesions notably contusions.

Adolescent↗
PubMed2005

Effects of moderate hyperventilation on cerebrovascular pressure-reactivity after head injury.

In volunteers, hyperventilation improves autoregulation. However, in head-injured patients, hyperventilation-induced deterioration and improvement of autoregulation have been reported. We have re-examined this question using an index of pressure reactivity. Thirty patients with severe or moderate head-injury were studied. Arterial blood pressure, cerebral perfusion pressure (CPP), and intracranial pressure (ICP) were recorded over 20 minute epochs separated by ten minutes of equilibration at baseline and during moderate (>3.5 kPa) hyperventilation. End-tidal CO2 was constant during each phase of data acquisition. Pressure reactivity was assessed using an index 'PRx' based on the response of ICP to spontaneous blood pressure changes. Hyperventilation decreased PaCO2 from 5.1 +/- 0.4 to 4.4 +/- 0.4 kPa (p < 0.0001). ICP decreased by 3.7 +/- 2.2 mmHg (p < 0.001). CPP increased by 5.9 +/- 8.2 mmHg (p < 0.001). Overall, PRx did not change significantly with hyperventilation. However, there was a significant negative correlation between baseline PRx and the change in PRx (r = -0.71, p < 0.0001). This suggests that patients with disturbed pressure-reactivity may improve, whereas patients with intact pressure reactivity remain largely unchanged. Our data suggest that the response of pressure reactivity to hyperventilation is heterogeneous. This could be due to hyperventilation-induced changes in cerebral metabolism, or the change in CPP.

Adult↗
PubMed2005

Imaging of cerebral blood flow and metabolism in brain injury in the ICU.

The heterogeneity of the initial insult and subsequent pathophysiology has made both the study of human head injury and design of randomised controlled trials exceptionally difficult. The combination of multimodality bedside monitoring and functional brain imaging positron emission tomography (PET) and magnetic resonance (MR), incorporated within a Neurosciences Critical Care Unit, provides the resource required to study critically ill patients after brain injury from initial ictus through recovery from coma and rehabilitation to final outcome. Methods to define cerebral ischemia in the context of altered cerebral oxidative metabolism have been developed, traditional therapies for intracranial hypertension re-evaluated and bedside monitors cross-validated. New modelling and analytical approaches have been developed.

Animals↗
PubMed2005

Metallic neurosurgical implants for cranial reconstruction and fixation: assessment of magnetic field interactions, heating and artefacts at 3.0 Tesla.

The objective of this study was to evaluate the magnetic resonance imaging (MRI) compatibility of metallic neurosurgical implants commonly used for cranial reconstruction and fixation, in association with a 3.0 Tesla (T) MR system. Ten metallic neurosurgical implants used for cranioplasty operations were evaluated. The implants were tested ex vivo for magnetic field interactions (translational attraction and torque), heating (using saline and gel phantoms), and artefact production [using dual echo spin echo (DSE) and gradient echo (GRE) sequences] at 3.0 Tesla. None of the implants displayed translational attraction or torque, and heating was physiologically insignificant (maximal temperature elevation was 0.5 degrees C). MR artefacts were minimal with spin echo sequences; gradient echo sequences produced much larger artefacts. The neurosurgical implants evaluated in this study should not present a risk to patients undergoing MRI in the 3.0 T MR system. Although the implants do produce susceptibility artefacts, especially with gradient echo sequences, useful imaging should still be possible.

Artifacts↗