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Biomedical subjects

I R Chambers

Publications and source records attributed to I R Chambers.

At least 19 recordsLinked to original sources
PubMed2006

BrainIT: a trans-national head injury monitoring research network.

BACKGROUND: Studies of therapeutic interventions and management strategies on head injured patients are difficult to undertake. BrainIT provides validated data for analysis available to centers that contribute data to allow post-hoc analysis and hypothesis testing. METHODS: Both physiological and intensive care management data are collected. Patient identification is eliminated prior to transfer of data to a central database in Glasgow. Requests for missing/ ambiguous data are sent back to the local center. Country coordinating centers provide advice, training, and assistance to centers and manage the data validation process. RESULTS: Currently 30 centers participate in the group. Data collection started in January 2004 and 242 patients have been recruited. Data validation tools were developed to ensure data accuracy and all analysis must be undertaken on validated data. CONCLUSION: BrainIT is an open, collaborative network that has been established with primary objectives of i) creating a core data set of information, ii) standardizing the collection methodology, iii) providing data collection tools, iv) creating and populating a data base for future analysis, and v) establishing data validation methodologies. Improved standards for multi-center data collection should permit the more accurate analysis of monitoring and management studies in head injured patients.

Biomedical Research↗
PubMed2006

Variability in pupil size estimation.

BACKGROUND: The clinical estimation of pupil size and reactivity is central to the neurological assessment of patients, particularly those with or at risk of neurological damage. Health care professionals who examine pupils have differing levels of skill and training, yet their recordings are passed along the patient care pathway and can influence care decisions. The aim of this study was to determine if any statistical differences existed in the estimation of pupil size by different groups of health care professionals. METHODS: A total of 102 health care professionals working in the critical care environment were asked to estimate and record the pupil size of a series of 12 artificial eyes with varying pupil diameter and iris colour. All estimations were performed indoors under ambient lighting conditions. RESULTS: Our results established a statistically significant difference between staff groups in the estimation of pupil size. CONCLUSION: The demonstrated variability in pupil size estimation may not be clinically significant. However, it remains desirable to have consistency of measurement throughout the patient care pathway.

Analysis of Variance↗
PubMed2005

Clinical comparison of tympanic membrane displacement with invasive intracranial pressure measurements.

A non-invasive method of assessing intracranial pressure (ICP) would be of benefit to patients with abnormal cerebral pathology that could give rise to changes in ICP. In particular, it would assist the regular monitoring of hydrocephalus patients. This study evaluated a technique using tympanic membrane displacement (TMD) measurements, which has been reported to provide a reliable, non-invasive measure of ICP. A group of 135 hydrocephalus patients was studied, as well as 13 patients with benign intracranial hypertension and a control group of 77 volunteers. TMD measurements were carried out using the Marchbanks measurement system analyser and compared between the groups. In 36 patients, invasive measurements of ICP carried out at the same time were compared with the TMD values. A highly significant relationship was found between TMD and ICP but intersubject variability was high and the predictive value of the technique low. Taking the normal range of ICP to be 10-15 mmHg, the predictive limits of the regression are an order of magnitude wider than this and therefore Vm cannot be used as a surrogate for ICP. In conclusion, TMD measurements do not provide a reliable non-invasive measure of ICP in patients with shunted hydrocephalus.

Acoustic Stimulation↗
PubMed2005

The clinical application of non-invasive intracranial blood volume pulse wave monitoring.

An ultrasonic method was used to non-invasively measure intracranial blood volume (IBV) pulse waveforms. This technology has previously shown a strong association between invasively recorded ICP pulse waves and non-invasively recorded IBV pulse waves. The objective of the present study was to investigate the diagnostic value of non-invasively measured IBV pulse waves in the cases of different pathologies. A total of 75 patients were examined and these included cases of acute, chronic and stabilized hydrocephalus, spinal cord injury and terminal blood flow. These were compared to a control group of 53 healthy volunteers. The object of comparison was normalized and averaged IBV pulse waves. Pathological IBV pulse waveforms were compared with IBV pulse waveforms of the normal group using sub-wave values, the area under waveform curve and the Euclidean distance calculation. The non-invasively measured IBV pulse waveform is not significantly dependent on acoustic path, gender or age. A detectable change in IBV pulse waveform shape was observed in situations when disturbance in intracranial hydrodynamics was present, e.g. during hypoventilation tests, in cases of terminal blood flow and hydrocephaly, depicting the level of hydrocephalus activity and the patient's compensatory capabilities as well as the effect of treatment.

Adolescent↗
PubMed2005

Critical thresholds of intracranial pressure and cerebral perfusion pressure related to age in paediatric head injury.

BACKGROUND: The principal strategy for managing head injury is to reduce the frequency and severity of secondary brain insults from intracranial pressure (ICP) and cerebral perfusion pressure (CPP), and hence improve outcome. Precise critical threshold levels have not been determined in head injured children. OBJECTIVE: To create a novel pressure-time index (PTI) measuring both duration and amplitude of insult, and then employ it to determine critical insult thresholds of ICP and CPP in children. METHODS: Prospective, observational, physiologically based study from Edinburgh and Newcastle, using patient monitored blood pressure, ICP, and CPP time series data. The PTI for ICP and CPP for 81 children, using theoretical values derived from physiological norms, was varied systematically to derive critical insult thresholds which delineate Glasgow outcome scale categories. RESULTS: The PTI for CPP had a very high predictive value for outcome (receiver operating characteristic analyses: area under curve = 0.957 and 0.890 for mortality and favourable outcome, respectively) and was more predictive than for ICP. Initial physiological values most accurately predicted favourable outcome. The CPP critical threshold values determined for children aged 2-6, 7-10, and 11-15 years were 48, 54, and 58 mm Hg. respectively. CONCLUSIONS: The PTI is the first substantive paediatric index of total ICP and CPP following head injury. The insult thresholds generated are identical to age related physiological values. Management guidelines for paediatric head injuries should take account of these CPP thresholds to titrate appropriate pressor therapy.

Adolescent↗
PubMed2005

Clinical comparison of tympanic membrane displacement with invasive ICP measurements.

OBJECTIVE: Tympanic membrane displacement (TMD) measurements may be useful in the management of patients with hydrocephalus if they can be directly associated with measurements of ICP. We have compared TMD measurements using the Marchbanks Measurement System with invasive ICP monitoring. METHODS: Twenty-nine patients who were undergoing routine invasive monitoring using a Camino fibre optic ICP measurement system as part of their clinical management were studied. Simultaneous measurements of ICP and TMD in both sitting and supine positions were successfully made in thirteen patients. RESULTS: Thirty-nine pairs of readings were obtained. The invasive ICP readings varied from 1 to 36 mmHg in the supine position and from -12 to +35 mmHg sitting. Corresponding TMD values varied from 275 to +277 nL in the supine position and -133 to +466 nL sitting. Linear regression showed a significant negative relationship between the two measurements (r = -0.57, p = 0.0013). CONCLUSIONS: There is a strong negative linear association between mean TMD and invasively measured ICP and this relationship is highly significant. Nevertheless, TMD is a poor surrogate for ICP in clinical terms because the predictive limits of the linear regression are too wide. However, serial intra-patient measurements may be useful to determine changes in ICP with time.

Acoustic Impedance Tests↗
PubMed2005

Which paediatric head injured patients might benefit from decompression? Thresholds of ICP and CPP in the first six hours.

Severe head injury in childhood continues to be associated with considerable mortality and morbidity. Early surgical decompression may be beneficial and the objective of this study was to examine the relationship between age-related thresholds of mean intracranial pressure (ICP) and cerebral perfusion pressure (CPP) over the first 6 hours and age outcome in paediatric head injury patients. A total of 209 head injured children admitted to five UK hospitals were studied. Patients aged 2 to 16 years were included if they had a minimum of six hours of invasive pressure monitoring. Mean values of ICP and CPP over this period were calculated and compared to those with independent (good recovery and moderate disability) and poor outcome (severe disability, and death) for different age groups. There were 148 children with independent outcome (92 good recovery, 56 moderately disabled), and 61 with poor outcome (30 severely disabled, 31 deaths). There was a significant difference between those with independent compared to poor outcome in relation to ICP (p < 0.001) and CPP (p < 0.001). Patients were divided into three groups according to age. The sensitivity of ICP and CPP in predicting outcome was similar for all groups but the specificity differed between groups. At a CPP of 50 mmHg the specificity varied between the age groups (2 to 6 years: 0.47, 7 to 10 years: 0.28 and 11 to 16 years: 0.10) and similarly for an ICP of 25 mmHg (2 to 6 years: 0.53, 7 to 10 years: 0.44 and 11 to 16 years: 0.38). Younger children may be able to tolerate lower perfusion pressures and still have an independent outcome. Our threshold values for young children are likely to be important in the identification of patients who might benefit from new treatments such as surgical decompression.

Adolescent↗
PubMed2005

Quantification of secondary CPP insult severity in paediatric head injured patients using a pressure-time index.

This paper describes and validates a new Cumulative Pressure-Time Index (CPT) which takes into account both duration and degree of cerebral perfusion pressure (CPP) derangement and determines critical thresholds for CPP, in a paediatric head injury dataset. Sixty-six head-injured children, with invasive minute-to-minute intracranial pressure (ICP) and blood pressure monitoring, had their pre-set CPP derangement episodes (outside the normal range) identified in three childhood age-bands (2-6, 7-10, and 11-16 years) and global outcome assessed at six months post injury. The new cumulative pressure-time index more accurately predicted outcome than previously used summary measures and by varying the threshold CPP values, it was found that these physiological threshold values (< or = 48, < or = 52 and < or = 56 mmHg for 2-6, 7-10, and 11-16 years respectively) best predicted brain insult in terms of subsequent mortality and morbidity.

Adolescent↗
PubMed2004

Age-related differences in intracranial pressure and cerebral perfusion pressure in the first 6 hours of monitoring after children's head injury: association with outcome.

OBJECTIVES: Severe head injury in childhood is associated with considerable mortality and morbidity. In this study we determined age-related differences in the relationship between outcome and intracranial pressure (ICP) and cerebral perfusion pressure (CPP) in the first 6 h of monitoring in a large cohort of head-injured children. METHODS: Two hundred and thirty-five head-injured children (admitted to five UK hospitals over a 15-year period) in whom intracranial pressure monitoring was clinically indicated were studied. RESULTS: Patients were divided into three age groups (2-6, 7-10 and 11-16 years). The sensitivity of ICP and CPP were similar. Differences were found in the specificity of ICP and CPP for each group and these were more marked for CPP. For a specificity of 50% the pressures were 53, 63 and 66 mmHg for the three age groups. CONCLUSIONS: There are age-related differences in the specificity of intracranial pressure and cerebral perfusion pressure in relation to outcome. These differences may be important in the clinical management of head-injured children. Thus cerebral perfusion pressures of 53, 63 and 66 mmHg should be the minimum to strive for in these three age groups respectively.

Adolescent↗
PubMed2004

Elderly patients with severe head injury in coma from the outset--has anything changed?

Advancing age is known to be a determinant of outcome in head injury. We have sought to discover whether there has been any change in the outcome of elderly patients with severe head injury in Newcastle, where these patients have continued to be treated with maximum intervention. A review of prospectively collected data from the Newcastle Head Injury Database for the period 1990 to 2000 was carried out. All patients aged 70 years and above who had sustained a severe head injury (Glasgow Coma Score of 8 or less from the outset) were included. The Glasgow Outcome Score (GOS) was determined at 6 months. Seventy-one patients were identified. Fifty-seven (80%) died and 2 (3%) were in a vegetative state, 11 (16%) had severe disability, 1 (1%) had moderate disability and no patients made a good recovery. The natural history of this condition remains unchanged and due consideration should be given to this when evaluating interventions for elderly patients with a severe head injury.

Aged↗
PubMed2001

Intracranial pressure within a developing intracerebral haemorrhage.

We report the time course of intracranial pressure within a developing intracerebral haemorrhage. Simultaneous readings of intracranial pressure were obtained from a contralateral parenchymal monitor and ventricular fluid pressure monitor. This recording demonstrates the existence of large pressure gradients in patients with expanding mass lesions.

Accidents, Traffic↗
PubMed2001

Clinical comparison of the Spiegelberg parenchymal transducer and ventricular fluid pressure.

The Spiegelberg brain pressure catheter is a low cost implantable intracranial pressure measuring system which has the unique ability to perform regular automatic zeroing. A new version of the catheter has become available with a subdural bolt fixation to allow insertion of the device into the brain parenchyma. The accuracy of this system has been evaluated in comparison with a ventricular fluid pressure method in a series of patients to determine its accuracy and utility in the clinical environment. Hourly readings from the Spiegelberg system have been compared with those obtained using a standard pressure transducer connected to an external ventricular drain. Measurements continued while there was a clinical need for CSF drainage. Eleven patients were recruited to the study and data were recorded for periods ranging from 40 to 111 hours. A good agreement between the two systems was obtained. In 10 cases the mean difference was less than +/-1.5 mm Hg and the dynamic changes in value were contemporaneous. In one case an intracerebral haemorrhage developed around the tips of the Spiegelberg catheter and significant differences occurred between the two methods of measurement. In conclusion, the Spiegelberg parenchymal transducer provides an accurate measurement of intracranial pressure when compared with ventricular pressure. The transducer was found to be robust in the clinical environment and very popular with the nursing staff. Further studies may determine whether the complication rate of this system is comparable with other available devices.

Calibration↗
PubMed2001

Radiological features predictive of aseptic loosening in cemented Charnley femoral stems.

The radiological features of the cement mantle around total hip replacements (THRs) have been used to assess aseptic loosening. In this case-control study we investigated the risk of failure of THR as predictable by a range of such features using data from patients recruited to the Trent Regional Arthroplasty Study (TRAS). An independent radiological assessment was undertaken on Charnley THRs with aseptic loosening within five years of surgery and on a control group from the TRAS database. Chi-squared tests were used to test the probability of obtaining the observed data by chance, and odds ratios were calculated to estimate the strength of association for different features. Several features were associated with a clinically important increase (>twofold) in the risk of loosening, which was statistically significant for four features (p < 0.01). Inadequate cementation (Barrack C and D grades) was the most significant feature, with an estimated odds ratio of 9.5 (95% confidence interval 3.2 to 28.4, p < 0.0001) for failure.

Case-Control Studies↗
PubMed2001

Determination of threshold levels of cerebral perfusion pressure and intracranial pressure in severe head injury by using receiver-operating characteristic curves: an observational study in 291 patients.

OBJECT: Intracranial pressure (ICP) and cerebral perfusion pressure (CPP) are frequently monitored in severely head injured patients. To establish which one (ICP or CPP) is more predictive of outcome and to examine whether there are significant threshold levels in the determination of outcome, receiver-operating characteristic (ROC) curves were used to analyze data in a large series of head-injured patients. METHODS: Data were obtained from a total of 291 severely head injured patients (207 adults and 84 children). Outcome was categorized as either independent (good recovery or moderate disability) or poor (severely disabled, vegetative, or dead) by using the Glasgow Outcome Scale; patients were also grouped according to the Marshall computerized tomography scan classification. CONCLUSIONS: The maximum value of a 2-minute rolling average of ICP readings (defined as ICPmax) and the minimum value of the CPP readings (CPPmin) were then used to calculate the sensitivity and specificity of the ROC curves over a range of values. Using ROC curves, a threshold value for CPPmin of 55 mm Hg and for ICPmax of 35 mm Hg appear to be the best predictors in adults. For children the levels appear to be 43 to 45 mm Hg for CPPmin and 35 mm Hg for ICPmax. Higher levels of CPPmin seem important in adults with mass lesions. These CPP thresholds (45 mm Hg for children and 55 mm Hg for adults) are lower than previously predicted and may be clinically important, especially in children, in whom a lower blood pressure level is normal. Also, CPP management at higher levels may be more important in adults with mass lesions. A larger observational series would improve the accuracy of these predictions.

Adolescent↗
PubMed2000

The cause and incidence of secondary insults in severely head-injured adults and children.

The cause and incidence of reductions in cerebral perfusion pressure, and rises in intracranial pressure have been examined in a series of patients with severe head injury defined as an initial Glasgow Coma Sum of less than or equal to 8. Two-hundred-and-seven adults (aged over 16 years) and 84 children admitted to Newcastle General Hospital, who had intracranial pressure monitoring as part of their routine management, were studied. Intracranial pressure (ICP), arterial pressure and cerebral perfusion pressure (CPP) were sampled and recorded every 2 min. Patients' CT findings were classified into distinct groups using the method described by Marshall. Secondary insults were defined using the Edinburgh University Secondary Insult Grades (EUSIG) and the incidence and cause (raised ICP, reduced CPP or a combination of the two) was established. Outcome was assessed at 6 months using the Glasgow Outcome Scale. In the majority of adults with head injury it is the combination of reduced arterial pressure and raised ICP that contributes to the reduction in cerebral perfusion pressure. This was not the case for Diffuse Injury Type I. In children similar characteristics were found across each of the CT classifications. The vast majority of falls in CPP down to 60 mmHg were caused by reduced arterial pressure. Reductions below 50 mmHg were almost always due to a combination of both reduced arterial pressure and raised ICP. The results in adults were similar, but not identical, to those of the paediatric cases. Diffuse Injury Type I stood out from all the other categories as the only one where reductions in perfusion pressure were almost exclusively due to reductions in arterial pressure and not to increases in ICP. The management of these patients should ensure the adequacy of perfusion pressure by maintaining arterial pressure at a satisfactory level. These results suggest that vigilant monitoring of both intracranial pressure and arterial pressure is required to lower the incidence of secondary insults.

Adolescent↗
PubMed2000

Intracranial pressure and clinical status: assessment of two intracranial pressure transducers.

The aim of this study was to determine the in vivo accuracy and reliability of intracranial pressure (ICP) measurement using the Codman MicroSensor by comparison with the Camino ICP transducer and associated clinical and radiological information. Paired ICP readings were recorded every minute in 17 patients. A total of 56,790 validated paired measurements were obtained over a wide range of ICP values (- 16 mm Hg to 114 mm Hg). Recording periods ranged from 3 hours to 6 days (median 41 hours). In 11 patients the MicroSensor and Camino readings were in good agreement. Paired readings were within 10 mmHg for 99% of the recording time and both readings were compatible with clinical intracranial events at all times (in one case it was not possible to verify the clinical information). In six patients large differences occurred between transducer readings (> 10 mm Hg apart for 41% of the recording period). In one case, either reading could have been compatible with intracranial clinical events. In two cases, although both readings were comparable, Camino readings were more consistent with clinical and radiological findings. In three cases, the MicroSensor readings were inconsistent with the clinical condition of the patients whereas the Camino readings were compatible. These results suggest that, during routine clinical use in our department, the MicroSensor provided misleading information in 18% of our patients and thus is not sufficiently reliable for routine use in the detection of adverse clinical events.

Adolescent↗
PubMed2000

Monitoring of head injury by myotatic reflex evaluation.

OBJECTIVES: (1) To establish the feasibility of myotatic reflex measurement in patients with head injury. (2) To test the hypothesis that cerebral dysfunction after head injury causes myotatic reflex abnormalities through disordered descending control. These objectives arise from a proposal to use reflex measurements in monitoring patients with head injury. METHODS: The phasic stretch reflex of biceps brachii was elicited by a servo-positioned tendon hammer. Antagonist inhibition was evoked by vibration to the triceps. Using surface EMG, the amplitude of the unconditioned biceps reflex and percentage antagonist inhibition were measured. After standardisation in 16 normal adult subjects, the technique was applied to 36 patients with head injury across the range of severity. Objective (1) was addressed by attempting a measurement on each patient without therapeutic paralysis; three patients were also measured under partial paralysis. Objective (2) was addressed by preceding each of the 36 unparalysed measurements with an assessment of cerebral function using the Glasgow coma scale (GCS); rank correlation was employed to test a null hypothesis that GCS and reflex indices are unrelated. RESULTS: In normal subjects, unconditioned reflex amplitude exhibited a positive skew requiring logarithmic transformation. Antagonist inhibition had a prolonged time course suggesting presynaptic mechanisms; subsequent measurements were standardised at 80 ms conditioning test interval (index termed "TI(80)"). Measurements were obtained on all patients, even under therapeutic paralysis (objective (1)). The unconditioned reflex was absent in most patients with GCS less than 5; otherwise it varied little across the patient group. TI(80) fell progressively with lower GCS, although patients' individual GCS could not be inferred from single measurements. Both reflex indices correlated with GCS (p<0.01), thereby dismissing the null hypothesis (objective (2)). CONCLUSION: Cerebral dysfunction in head injury is reflected in myotatic reflex abnormalities which can be measured at the bedside. With greater reproducibility, reflex measurements may assist monitoring of patients with head injury.

Adult↗