Search PubMed⌕ Search

Biomedical subjects

A R Manara

Publications and source records attributed to A R Manara.

At least 19 recordsLinked to original sources
PubMed2002

Effect of propofol anaesthesia on the event-related potential mismatch negativity and the auditory-evoked potential N1.

BACKGROUND: Studies on the effects of anaesthesia on event-related potentials and long latency auditory-evoked potentials (AEP) are sparse. Both provide information on cortical processing and may have potential as monitors of awareness. We studied the effect of propofol on the event-related potential mismatch negativity (MMN) and the long-latency AEP NI. METHODS: Twenty-one patients received 1 microgram ml-1 stepped increases in the target concentration of propofol using Diprifusor until a maximum of 6 micrograms ml-1 was achieved or the patient had lost consciousness. Neurophysiological responses (MMN and N1) and the patients' level of consciousness were recorded before the administration of propofol and at a target effector site concentration of propofol of 1, 2, 3, 4, and 6 micrograms ml-1. Grand average evoked potentials were computed at baseline, before the administration of propofol (A); at the highest propofol concentration at which each patient was responsive (B); and at the concentration of propofol at which the patient became unconscious (C). RESULTS: Patients lost consciousness at different target concentrations of propofol, all being unresponsive by 4 micrograms ml-1. The response to the deviant stimuli used to elicit duration-shift MMN was significantly more negative than to the standard stimuli at A (mean difference 2.58 microV, P = 0.0011) but this difference was virtually abolished at point B, before the patients lost consciousness (mean difference 0.63 microV, P = ns). The amplitude of N1 evoked by standard stimuli was negative compared with electrical baseline at both point A (mean amplitude -3.81 microV, P < 0.001) and at point B (mean amplitude -2.2 microV, P = 0.002), but was no longer significantly different to baseline at point C (mean amplitude 0.51 microV, P = ns). The change in the mean amplitude of N1 from last awake (point B) to first unconscious (point C) was also significant (mean difference in amplitude 1.69 microV, P = 0.02). CONCLUSIONS: MMN is unlikely to be a clinically useful tool to detect awareness in surgical patients. In contrast, the loss of N1 may identify the transition from consciousness to unconsciousness and deserves further study.

Adult↗
PubMed2001

Late deaths in multiple trauma patients receiving intensive care.

We reviewed the cause and timing of death of all the patients who died within hospital following multiple trauma and admission to a multidisciplinary intensive care unit (ICU) that also acts as a tertiary referral centre for neurosurgery. The ICU database identified 101 such patients in a 3-year period and their records were reviewed retrospectively. There were 40 (39%) deaths within 24 h of admission to the ICU, 38 of which resulted from severe brain injury and two from haemorrhagic shock (HS). A further 61 (60%) deaths occurred more than 24 h after the time of admission to ICU (mean 7 days; range 2-49 days), of which 46 (75%) were due to severe brain injury. While these findings do not question the promulgated tri-modal distribution of death following trauma, they are at variance with the view that the third peak of deaths is due mainly to multiple organ failure. When severe head injury accompanies multiple trauma, it is likely to be the major determinant of late mortality. If outcome from major trauma is to be improved, then a greater emphasis needs to be placed on the prevention and optimal management of severe brain injury.

Adolescent↗
PubMed2000

Behaviour of near-infrared light in the adult human head: implications for clinical near-infrared spectroscopy.

To test theoretical assumptions supporting the use of near-infrared spectroscopy (NIRS) in clinical practice, we examined the behaviour of NIR light transmission and attenuation in the human head. Sterile probes for emitting and detecting NIR light at a fixed separation of 40 mm were placed in turn on intact skin, skull, dura and cerebral cortex of 10 patients undergoing elective neurosurgery. In the first five patients, the detecting probe was moved through successive extracerebral layers with the emitter on the skin surface. In the second five patients, the process was reversed, with the emitting probe moved and the detector in the same place on the scalp. NIR intensity was measured at each tissue interface and compared with the intensity measured at the skin surface with all layers intact. Removal of bone and dura from the light path caused a significant reduction in detected intensity. The largest mean reduction in light intensity was a 14-fold decrease with removal of bone (unadjusted P < 0.0001; paired t test). The assumptions that extracerebral tissues contribute little to attenuation of NIR light in the adult head and that most of this attenuation occurs superficially in the scalp are drawn into question by this study. We postulate that the skull and/or its interface with other layers may act as an optical 'channel', distorting the behaviour of NIR light in the human head.

Adult↗
PubMed1999

The impact of percutaneous tracheostomy on intensive care unit practice and training.

We studied the impact of introducing percutaneous tracheostomy to our intensive care unit on the incidence and timing of tracheostomy and on the implications for surgical training. The proportion of patients receiving intensive care who underwent tracheostomy doubled from a median of 8.5% to 16.8% (p < 0.01) following the introduction of the percutaneous technique with the procedure being undertaken significantly earlier during the intensive care stay. The opportunity for surgical trainees to gain experience in open surgical tracheostomy has been virtually lost. The increase in tracheostomy rate may reflect a previous under-utilisation caused by the logistic problems of transferring a critically ill patient to theatre, or alternatively a relaxation of the indications for tracheostomy caused by a perceived benefit for the patient. An increased workload may also have contributed to the rise. Surgical trainees should be encouraged to learn percutaneous techniques and training opportunities in open surgical techniques should be maximised.

Critical Care↗
PubMed1999

Cerebral near infrared spectroscopy: emitter-detector separation must be increased.

We have compared the effect of increasing optode separation (range 0.7-5.5 cm) on the sensitivity of near infrared spectroscopy (NIRS) to discrete reductions in scalp and cerebral oxygenation in 10 healthy men (mean age 32, range 26-39 yr) using multichannel NIRS. During cerebral oligaemia (a mean reduction in middle cerebral artery flow velocity of 47%) induced by a mean reduction in end-tidal PCO2 of 2.4 kPa, the decrease in oxyhaemoglobin detected by NIRS became significantly greater with increasing optode separation (P < 0.0001). In response to scalp hyperaemia induced by inflation and release of a pneumatic scalp tourniquet, increases in oxyhaemoglobin became significantly smaller with increasing optode separation (P < 0.0002). These results are consistent with theoretical models of the behaviour of NIR light in the adult head and support the concept of using multi-detector NIRS to separate intra- and extracranial NIR signal changes. However, the emitter-detector separation used by currently available cerebral oximeters is not large enough to provide optimal spatial resolution.

Adult↗
PubMed1998

Sensitivity of near infrared spectroscopy to cerebral and extra-cerebral oxygenation changes is determined by emitter-detector separation.

OBJECTIVE: To examine the effect of two emitter-detector separations (2.7 and 5.5 cm) on the detection of changes in cerebral and extra-cerebral tissue oxygenation using near infrared spectroscopy (NIRS). METHODS: Two NIR detectors were placed on the scalp 2.7 and 5.5 cm from a single NIR emitter. Changes in deoxyhaemoglobin (HHb), oxyhaemoglobin (O2Hb),oxidised cytochrome C oxidase (Cyt) and total haemoglobin (tHb) were recorded from each detector during the induction of cerebral oligaemia (transition from hypercapnia to hypocapnia) and scalp hyperaemia (following release of a scalp tourniquet). RESULTS: Cerebral oligaemia (mean decrease in middle cerebral artery blood flow velocity of 44%) induced by a mean reduction in end tidal CO2 of 18 mmHg was accompanied by a significant increase in the spectroscopic signal for HHb and a decrease in the O2Hb signal. The signal change per unit photon path length detected at 5.5 cm was significantly greater for HHb (p = 0.007) than that detected at 2.7 cm. In contrast, the increase in all chromophores detected at 5.5 cm during scalp hyperaemia was significantly less than that detected at 2.7 cm (p<0.001). CONCLUSIONS: The differing sensitivity of the proximal and distal channels to changes in cerebral and extracerebral oxygenation is compatible with theoretical models of NIR light transmission in the adult head and may provide a basis for spatially resolving these changes. The optimal emitter-detector separation for adult NIRS requires further investigation and may differ between individuals.

Adult↗
PubMed1998

Reasons for withdrawing treatment in patients receiving intensive care.

We studied the frequency with which treatment was withdrawn in intensive care patients and the primary reason for reaching the decision. The medical records of patients having had active treatment withdrawn between August 1992 and February 1996 inclusive were reviewed. Patients were classified into an imminent death group consisting of those expected to die, a qualitative group who had treatment withdrawn on quality of life considerations and a lethal conditions group who had associated disease that precluded long-term survival. There were 1745 patients admitted, of whom 338 (19.4%) died in ICU. In 220 patients death followed the withdrawal of treatment (12.6% of all ICU admissions), 203 dying on ICU (60% of ICU deaths) and a further 17 soon after discharge to a ward. The primary reason for treatment withdrawal was imminent death in 45% of patients, qualitative considerations in 50% and lethal conditions in 5%. The reason varied significantly depending on the patient's age. Treatment is withdrawn commonly in ICU, the primary reason being quality of life considerations as often as because death is the expected outcome.

APACHE↗
PubMed1998

Treatment of compulsive behaviour in eating disorders with intermittent ketamine infusions.

We have previously shown that eating disorders are a compulsive behaviour disease, characterized by frequent recall of anorexic thoughts. Evidence suggests that memory is a neocortical neuronal network, excitation of which involves the hippocampus, with recall occurring by re-excitement of the same specific network. Excitement of the hippocampus by glutamate-NMDA receptors, leading to long-term potentiation (LTP), can be blocked by ketamine. Continuous block of LTP prevents new memory formation but does not affect previous memories. Opioid antagonists prevent loss of consciousness with ketamine but do not prevent the block of LTP. We used infusions of 20 mg per hour ketamine for 10 h with 20 mg twice daily nalmefene as opioid antagonist to treat 15 patients with a long history of eating disorder, all of whom were chronic and resistant to several other forms of treatment. Nine (responders) showed prolonged remission when treated with two to nine ketamine infusions at intervals of 5 days to 3 weeks. Clinical response was associated with a significant decrease in Compulsion score: before ketamine, mean +/- SE was 44.0 +/- 2.5; after ketamine, 27.0 +/- 3.5 (t test, p = 0.0016). In six patients (non-responders) the score was: before ketamine, 42.8 +/- 3.7; after ketamine, 44.8 +/- 3.1. There was no significant response to at least five ketamine treatments, perhaps because the compulsive drive was re-established too soon after the infusion, or because the dose of opioid antagonist, nalmefene, was too low.

Adult↗
PubMed1997

Long-term outcome after percutaneous dilational tracheostomy. Endoscopic and spirometry findings.

We studied 41 patients who had previously undergone percutaneous dilational tracheostomy at least 6 months following tracheal decannulation. The patients were examined using laryngotracheoscopy and spirometry to assess the long-term anatomical and functional consequences of percutaneous dilational tracheostomy. Apart from one patient who had requested a scar revision, no patient was symptomatic. A significant (> 10%) tracheal stenosis was identified in four asymptomatic patients, two of whom also had spirometric evidence of this obstruction. These results suggest that the long-term outcome after percutaneous tracheostomy is at least as good as that following conventional surgical tracheostomy. Refinements of the percutaneous technique, such as endoscopic guidance, may further improve the results.

Adolescent↗
PubMed1996

Event-related potentials--neurophysiological tools for predicting emergence and early outcome from traumatic coma.

OBJECTIVE: To determine the prognostic value of multimodal evoked potentials (EPs) and event-related (ERPs) potentials in coma (Glasgow Coma Score <8), after severe traumatic brain injury (TBI). DESIGN: Prospective, longitudinal study of neurophysiological responses recorded during traumatic coma. SETTING: Intensive Care Unit, Frenchay Hospital, Bristol, UK. PARTICIPANTS: Fifty-four comatose TBI patients (age range 1-80 years, mean 36.4). METHODS: Neurophysiological responses were recorded from 11 scalp electrodes with earlobe reference. Conduction times were measured for brainstem auditory, flash visual and somatosensory, short-latency EPs. Peak latencies and amplitudes were determined for long-latency components of visual and auditory ERPs, generated by passive "oddball" paradigms. These neurophysiological and various clinical parameters were correlated with patient outcome using Pearson's coefficient. MAIN OUTCOME MEASURE: Three month Glasgow Outcome Scale (GOS). RESULTS AND CONCLUSION: Highly significant (P <0.001) correlations exist between long-latency ERP components and 3-month outcome. Short-latency EPs, brainstem (wave I-V) and somatosensory conduction times also correlate significantly with the GOS (P <0.01). Of the clinical measurements, pupillary response patterns, APACHE II and Glasgow Coma Scores (GCS) correlate significantly with outcome, as do the retrospective measures of duration of coma and post-traumatic amnesia (PTA) in survivors. Unfortunately, due to variance of long-latency responses, even in controls, absolute values cannot be relied upon as prognosticators. The presence of "mismatch negativity" predicted the return of consciousness (89.7% sensitivity and 100% specificity) and preceded changes in GCS. Its latency was the single best indicator of 90-day outcome from coma (r = -0.641).

Acoustic Stimulation↗
PubMed1996

The effect of suxamethonium on intracranial pressure and cerebral perfusion pressure in patients with severe head injuries following blunt trauma.

Eleven adult patients with severe head injuries caused by blunt trauma, (Glasgow Coma Score of eight or less after resuscitation), were studied while being mechanically ventilated and sedated in the intensive care unit (ICU). In a double blind randomized cross over trial each patient received a bolus of suxamethonium (1 mg kg-1) or an equal volume of saline (0.02 mL kg-1) before planned physiotherapy. Intracranial pressure (ICP) and mean arterial pressure (MAP) were measured continuously for 10 min after each injection. There were no significant changes in intracranial pressure or cerebral perfusion pressure (CPP) following the administration of suxamethonium or saline. Suxamethonium appears to be a safe drug to use on sedated persons with severe head injuries following blunt trauma.

Adolescent↗
PubMed1995

Extracerebral absorption of near infrared light influences the detection of increased cerebral oxygenation monitored by near infrared spectroscopy.

The detection of increased cerebral oxygenation secondary to cerebral hyperaemia, induced by hypercapnia has been studied in anaesthetised patients using a near infrared, reflectance mode, cerebral oxygenation monitor (Invos 3100 Somanetics, Troy, Michigan, USA). Two studies were performed, with and without a pneumatic scalp tourniquet, to distinguish between extracranial and intracranial changes in tissue oxygenation. In the control study a mean increase in end tidal CO2 of 23.1 mm Hg was accompanied by a mean increase in middle cerebral artery flow velocity of 116%. Regional cerebral oxygen saturation (rSO2) measured transcutaneously in the frontal distribution of the middle cerebral artery increased significantly from 70.5% to 74.6% (p = 0.001). During the second study with a scalp tourniquet inflated to maintain the extracranial tissues in a state of stable ischaemia a mean increase in end tidal CO2 of 22.3 mm Hg was accompanied by a mean increase in middle cerebral artery flow velocity of 121%. The change in rSO2 from 62.6% to 64.5% was not significant (p = 0.085). There was no correlation between the change in middle cerebral artery flow velocity and rSO2 in the control or scalp ischaemia group. This study shows that the Invos 3100 monitor is sensitive to tissue oxygenation but does not reliably detect changes in cerebral oxygenation as a result of profound cerebral hyperaemia. The contribution of extracerebral tissue to the attenuation of near infrared light and the lack of spatial resolution remain major problems to be overcome before this or other near infrared spectroscopy instruments can be introduced into clinical practice.

Adult↗
PubMed1994

Experience with percutaneous tracheostomy in intensive care: the technique of choice?

The technique of percutaneous tracheostomy is described, the experience of 77 such procedures in a single intensive care unit over 2 years is reported, and the literature reviewed. Percutaneous tracheostomy is a safe, effective, simple and rapid technique for intubated patients receiving intensive care. It can be carried out by non-surgeons and has several advantages over conventional tracheostomy in these patients. It may in the future prove to be the technique of choice for elective tracheostomy in other groups of patients, including those undergoing faciomaxillary procedures.

Adolescent↗
PubMed1994

Near-infrared spectroscopy in adults: effects of extracranial ischaemia and intracranial hypoxia on estimation of cerebral oxygenation.

We have studied the effects of extracranial ischaemia and intracranial hypoxia on measurement of cerebral oxygenation using near-infrared, reflectance-mode, cerebral oximetry (Invos 3100 cerebral oximeter) in healthy adult subjects. Under stable systemic conditions, scalp ischaemia induced by a pneumatic tourniquet caused an apparent reduction in mean regional cerebral oxygenation (rSO2) from mean 72 (SD 6)% to 59 (7)% (n = 8, P < 0.001). rSO2 returned to control values within 1 min of release of the tourniquet. Local scalp ischaemia induced by rapid frontalis muscle exercise caused a significant reduction (4.5 (2)% in rSO2 (n = 12, P < 0.001). The effect of systemic hypoxia on rSO2 was examined during controlled scalp ischaemia. A decrease in mean SpO2 from 98 (2)% to 66 (6)% was associated with a decrease in mean rSO2 from 57 (4)% to 41 (6)%. There was a significant correlation between the percentage reduction in rSO2 and SpO2 during hypoxia (r = 0.81, P < 0.001). We conclude that the Invos cerebral oximeter was capable of detecting tissue hypoxia deep to the scalp under carefully controlled conditions but that it also was affected significantly by changes in extracranial blood flow and oxygenation which may affect its reliability in clinical practice. Further work is necessary to define those situations in which cerebral oximetric monitoring is useful and valid.

Adult↗