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Biomedical subjects

A I Maas

Publications and source records attributed to A I Maas.

At least 19 recordsLinked to original sources
PubMed2001

Neuroprotective agents in traumatic brain injury.

The role of neuroprotection in traumatic brain injury (TBI) is reviewed. Basic research and experimental investigations have identified many different compounds with potential neuroprotective effect. However, none of the Phase III trials performed in TBI have been successful in convincingly demonstrating efficacy in the overall population. A common misconception is that consequently these agents are ineffective. The negative results as reported in the overall population may in part be caused by specific aspects of the head injury population as well as by aspects of clinical trial design and analysis. The heterogeneity of the TBI population causes specific problems, such as a risk of imbalances between placebo and treated groups but also causes problems when a possible treatment effect is evaluated in relation to the prognostic effect present. Trials of neuroprotective agents should be targeted first of all to a population in which the mechanism at which the agent is directed is likely to be present and secondly to a population in which the chances of demonstrating efficacy are realistic, e.g., to patients with an intermediate prognosis. The possibilities for concomitant or sequential administration of different neuroprotective agents at different times deserve consideration. The potential for neuroprotection in TBI remains high and we should not be discouraged by recent failures obtained up until now. Rather, prior to initiating new trials, careful consideration of experimental evidence is required in order to optimise chances for mechanistic targeting and lessons learned from previous experience need to be taken to heart in the design of future studies.

Animals↗
PubMed2000

CO2 reactivity and brain oxygen pressure monitoring in severe head injury.

OBJECTIVE: To investigate the effect of hyperventilation on cerebral oxygenation after severe head injury. DESIGN: A prospective, observational study. SETTING: Neurointensive care unit at a university hospital. PATIENTS: A total of 90 patients with severe head injury (Glasgow Coma Scale score < or =8), in whom continuous monitoring of brain tissue oxygen pressure (PbrO2) was performed as a measure of cerebral oxygenation. INTERVENTIONS: Arterial PCO2 was decreased each day over a 5-day period for 15 mins by increasing minute volume on the ventilator setting to 20% above baseline. Arterial blood gas analysis was performed before and after changing ventilator settings. Multimodality monitoring, including PbrO2, was performed in all patients. Absolute and relative PbrO2/PaCO2 reactivity was calculated. Outcome at 6 months was evaluated according to the Glasgow Outcome Scale. MEASUREMENTS AND MAIN RESULTS: Effective hyperventilation, defined by a decrease of PaCO2 > or =2 torr (0.27 kPa), was obtained in 218 (84%) of 272 tests performed. Baseline PaCO2 averaged 32.3 +/- 4.5 torr (4.31 +/- 0.60 kPa). Average reduction in PaCO2 was 3.8 +/- 1.7 torr (0.51 +/- 0.23 kPa). PbrO2 decreased by 2.8 +/- 3.7 torr (0.37 +/- 0.49 kPa; p < .001) from a baseline value of 26.5 +/- 11.6 torr (3.53 +/- 1.55 kPa). PbrO2/PaCO2 reactivity was low on day 1 (0.8 +/- 2.3 torr [0.11 +/- 0.31 kPa]), increasing on subsequent days to 6.1 +/- 4.4 torr (0.81 +/- 0.59 kPa) on day 5. PbrO2/PaCO2 reactivity on days 1 and 2 was not related to outcome. In later phases in patients with unfavorable outcome, relative reactivity was increased more markedly, reaching statistical significance on day 5. CONCLUSIONS: Increased hyperventilation causes a significant reduction in PbrO2, providing further evidence for possible increased risk of secondary ischemic damage during hyperventilation. The low PbrO2/PaCO2 reactivity on day 1 indicates the decreased responsiveness of cerebral microvascular vessels to PaCO2 changes, caused by generalized vascular narrowing. The increasing PbrO2/PaCO2 reactivity from days 2 to 5 suggests that the risk of compromising cerebral oxygenation by hyperventilation may increase over time.

Adolescent↗
PubMed2000

Brain oxygen tension in severe head injury.

OBJECTIVE: Ensuring adequate cerebral oxygenation and perfusion is of fundamental importance in the treatment of patients with acute cerebral disorders. Online continuous monitoring of brain oxygenation is possible with a parenchymal microelectrode that measures local brain oxygen tension. The ultimate question is whether therapeutic approaches can be targeted on the basis of such monitoring. Before this question can be addressed, the technique requires validation in the clinical setting. The frequency of occurrence of low values and its relation to outcome need to be established. METHODS: One hundred one comatose head-injured patients (Glasgow Coma Scale score < or = 8) were studied. Local brain oxygen tension probes were inserted in an undamaged part of the frontal region. Patients were treated in conformance with the European Brain Injury Consortium guidelines. Outcome at 6 months was determined by Glasgow Outcome Scale score. RESULTS: Early brain tissue hypoxia was frequently observed, despite aggressive treatment for intracranial pressure and cerebral perfusion pressure. Values lower than 15 mm Hg, for a duration longer than 30 minutes, were observed in 57 patients. Values lower than 10 mm Hg in 42 patients, and lower than 5 mm Hg in 22 patients, were observed during the first 24 hours. Depth and duration of tissue hypoxia were related to outcome and proved to be an independent predictor of unfavorable outcome and death. CONCLUSION: Monitoring the partial oxygen pressure of local brain tissue is a safe and reliable method for regulating cerebral oxygenation. Because brain tissue hypoxia occurs frequently and is significantly related to poor outcome, future efforts should be aimed at the treatment of brain tissue hypoxia. The effects of such brain hypoxia-targeted treatment need to be established in a multicenter study.

Adolescent↗
PubMed1999

The prognostic importance of the volume of traumatic epidural and subdural haematomas revisited.

The size of a traumatic intracranial haematoma at the moment of diagnosis can be impressive. Haematoma thickness is an inaccurate estimator of haematoma volume, and association with patient outcome is controversial. In this study computerized volumetry of offline digitized CT scans was used to relate haematoma volume with both patient characteristics on admission and at the six months outcome. This retrospective study covered the time period 1981/1990. Ninety eight patients operated upon for an epidural haematoma and 91 patients operated upon for an acute subdural haematoma were analyzed. The relative importance of clinical data, CT scan parameters, and calculated haematoma volumes was determined by multivariate analysis. Volume of the haematoma did not correlate with preoperative neurological condition or the six months outcome in either group, and consequently is not of additional prognostic value.

Acute Disease↗
PubMed1998

Brain parenchyma/pO2 catheter interface: a histopathological study in the rat.

Local cerebral oxygenation can be monitored continuously using an intraparenchymal Clark-type pO2 sensitive catheter. Measured values of brain tissue pO2 (PbrO2) not only depend on the clinically interesting balance between oxygen offer and demand, but also on catheter properties and characteristics of the probe tissue interface. Microdamage surrounding pO2-sensitive needles, inserted into various tissues, has been reported; we evaluated histologic changes at the probe tissue interface after insertion of pO2 probes, suitable for clinical use, in the rat brain. The effect of insertion of the probe itself (mechanical damage), the application of micropotential during the measurements, and the effect of time was evaluated using digital image analysis of H&E-stained histological slices. Surrounding the probe tract, a zone of edema with an average radius of 126.8 microm was seen; microhemorrhages with an average surface area of 56.2 x 10(3) microm2 were observed in nearly all cases. The area of edema and the presence of microhemorrhages were not influenced by performed measurements or by time. Intraventricular blood was observed in 10 of 19 rats studied. Measured low PbrO2 values were related to the presence of a microhemorrhage in either probe tract or ventricles. Tissue damage due to the measurements is negligible, and the amount of edema itself does not influence the accuracy or response time of the pO2 probe. Low PbrO2 readings, however, could be caused by local microhemorrhages, undetectable on CT or MRI.

Analysis of Variance↗
PubMed1998

A multicenter trial on the efficacy of using tirilazad mesylate in cases of head injury.

OBJECT: The authors prospectively studied the efficacy of tirilazad mesylate, a novel aminosteroid, in humans with head injuries. METHODS: A cohort of 1120 head-injured patients received at least one dose of study medication (tirilazad or placebo). Eighty-five percent (957) of the patients had suffered a severe head injury (Glasgow Coma Scale [GCS] score 4-8) and 15% (163) had sustained a moderate head injury (GCS score 9-12). Six-month outcomes for the tirilazad- and placebo-treated groups for the Glasgow Outcome Scale categories of both good recovery and death showed no significant difference (good recovery in the tirilazad-treated group was 39% compared with the placebo group in which it was 42% [p=0.461]; death in the tirilazad-treated group occurred in 26% of patients compared with the placebo group, in which it occurred in 25% [p=0.750]). Subgroup analysis suggested that tirilazad mesylate may be effective in reducing mortality rates in males suffering from severe head injury with accompanying traumatic subarachnoid hemorrhage (death in the tirilazad-treated group occurred in 34% of patients; in the placebo group it occurred in 43% [p=0.026]). No significant differences in frequency or types of serious adverse events were shown between the treatment and placebo groups. CONCLUSIONS: Striking problems with imbalance concerning basic prognostic variables were observed in spite of the large population studied. These imbalances concerned pretreatment hypotension, pretreatment hypoxia, and the incidence of epidural hematomas. In future trials of pharmacological therapy for severe head injury, serious consideration must be given to alternative randomization strategies. Given the heterogeneous nature of head injury and the identification of populations that do relatively well with standard therapy, target populations with a higher risk for mortality and morbidity may be more suitable for clinical trials of such agents.

Adult↗
PubMed1997

EBIC-guidelines for management of severe head injury in adults. European Brain Injury Consortium.

Guidelines for the management of severe head injury in adults as evolved by the European Brain Injury Consortium are presented and discussed. The importance of preventing and treating secondary insults is emphasized and the principles on which treatment is based are reviewed. Guidelines presented are of a pragmatic nature, based on consensus and expert opinion, covering the treatment from accident site to intensive care unit. Specific aspects pertaining to the conduct of clinical trials in head injury are highlighted. The adopted approach is further discussed in relation to other approaches to the development of guidelines, such as evidence based analysis.

Adult↗
PubMed1996

Continuous monitoring of partial pressure of brain tissue oxygen in patients with severe head injury.

Ischemia is one of the major factors causing secondary brain damage after severe head injury. We have investigated the value of continuous partial pressure of brain tissue oxygen (PbrO2) monitoring as a parameter for cerebral oxygenation in 22 patients with severe head injury (Glasgow Coma Scale score, < or = 8). Jugular bulb oxygenation, intracranial pressure, and cerebral perfusion pressure were simultaneously recorded. O2 and CO2 reactivity tests were performed daily to evaluate oxygen autoregulatory mechanisms. PbrO2 monitoring was started an average of 7.0 hours after trauma with a mean duration of 74.3 hours. No complications were seen, and the calibration of the catheters after measurement showed a zero drift of 1.2 +/- 0.8 mm Hg and a sensitivity drift of 9.7 +/- 5.3%. In 86% of patients, PbrO2 was < 20 mm Hg in the acute phase. Mean PbrO2 significantly increased during the first 24 hours after injury. Two distinct patterns of change of PbrO2 over time were noted. The first pattern was characterized by normal stable levels after 24 hours, and the second was characterized by transiently elevated levels of PbrO2 during the second and third days. PbrO2 values < or = 5 mm Hg within 24 hours after trauma negatively correlated with outcome. O2 reactivity was significantly lower in patients with good outcomes. CO2 reactivity showed no constant pattern of change over time and was not correlated with outcome. Increased hyperventilation was shown to decrease PbrO2 in some patients. Accurate detection of the moment of cerebral death was possible on the basis of the PbrO2 measurements. The correlation between PbrO2 and other parameters, such as intracranial pressure and cerebral perfusion pressure, was weak. We conclude that PbrO2 monitoring is a safe and clinically applicable method in patients with severe head injury. The early occurrence of ischemia after head injury can be monitored on a continuous basis. Deficiency of oxygen autoregulatory mechanisms can be demonstrated, and their occurrence is inversely related to outcome. For practical clinical use, the method seemed to be superior to jugular oximetry.

Adolescent↗
PubMed1993

Monitoring cerebral oxygenation: experimental studies and preliminary clinical results of continuous monitoring of cerebrospinal fluid and brain tissue oxygen tension.

Cerebral ischaemia is considered to be the central mechanism leading to secondary brain damage in patients with severe head injury. It would therefore seem appropriate to monitor cerebral oxygenation in these patients. The possibilities of continuous monitoring of brain tissue and CSF oxygen tension as parameters for cerebral oxygenation were evaluated. In experimental studies the influence of changed oxygen offer and decreased cerebral perfusion pressure on CSF and brain tissue pO2 were investigated. Fast changes in CSF pO2 were observed in response to decreasing oxygen offer. Slower changes were noted in response to hypo- and hyperventilation. An autoregulatory mechanism regulating CSF pO2 is postulated. Reducing cerebral perfusion pressure decreased both brain tissue and CSF pO2, but in the reperfusion phase after complete ischaemia a dissociation occurred between brain tissue and CSF pO2, CSF pO2 being restored, but brain tissue pO2 remaining low or even decreasing further. From these studies it is concluded that both CSF pO2 and brain tissue pO2 reflect changes in cerebral oxygenation caused by changes in oxygen offer as well as by changes in cerebral blood flow. Brain tissue pO2 is also sensitive to oxygen demand from the tissue. Preliminary studies of continuous monitoring of brain tissue pO2 in patients with severe head injury are reported.

Animals↗
PubMed1990

[Carpal tunnel syndrome].

The results of operative treatment of 117 patients with carpal tunnel syndrome (CTS) are reported. CTS occurred four to five times more frequently in women than in men. It occurred predominantly in the age group 40 to 60 years. Information on the results of operative treatment and residual complaints were obtained by written inquiry (response: 117/126 = 93%). All patients who were dissatisfied or still had complaints were seen in the outpatient department. The duration of follow-up averaged 15 months: 75% of all patients reported good results. In 89% of the patients the preoperative complaints had disappeared. Dissatisfaction with the operative result was often caused by factors not related to the carpal tunnel syndrome. Factors favouring good results were typical complaints, defined as nocturnal paraesthesias on the volar aspect of the hand and abnormal nerve conduction studies. The results obtained with operation under local anaesthesia in the outpatient department are equivalent to those reported of patients operated in the clinical setting. One-third of the patients felt able to return to work or to resume full normal daily activities within 6 weeks, and 2/3 of the patients within 3 months of the operation.

Adult↗
PubMed1987

Fontanelle pressure monitoring in infants with the Rotterdam Teletransducer: a reliable technique.

Intracranial Pressure (ICP) monitoring is important in patients at risk for raised ICP. In infants non-invasive methods for measuring ICP are to be preferred, and hence Anterior Fontanelle Pressure (AFP) measurements have been employed. So far, techniques used were not reliable since application of a transducer to the fontanelle generally influences the recorded pressure value. For the purpose of non-ambiguous ICP recording the Rotterdam Teletransducer was fitted in a special light weight skill adaptor, provided with a special fixation frame. With this adaptor the transducer can be set and maintained at accurate depth in the fontanelle according to the pressure depth curve. The plateau in the pressure depth curve represents actual ICP. The development of this reliable and reproducible technique is discussed. The results of instantaneous and continuous monitoring of AFP in 70 children with- and without neurological diseases are presented.

Brain Diseases↗
PubMed1986

Intracerebral malignant schwannoma.

A case of highly malignant primary intracerebral schwannoma is presented in a boy aged 15 years. The histological, ultrastructural and immunocytochemical properties were consistent with a partly epithelioid schwannoma. All reports so far published of 18 intracerebral schwannomas were of benign tumors, one case was semi-malignant. As far as we know, this is the first report of a highly malignant intracerebral schwannoma.

Adolescent↗
PubMed1986

The Rotterdam Teletransducer: state of the device.

The developments of a telemetric device for monitoring intracranial pressure, the Rotterdam Teletransducer, are described. The major problem in telemetric pressure sensing devices consists of diffusion of water into the transducer, resulting in unpredictable zero drift. Therefore, special attention was paid to bonding techniques for sealing the transducer. The results of improved epoxy sealing, active metal brazing and glass bonding are described. In vitro tests showed transducers sealed with epoxy resin to be stable for two months. Using the more complicated techniques of glass bonding and active metal brazing, hermetic seals could be achieved with stable transducers for over one year. In vivo functioning of the Rotterdam Teletransducer was tested in acute and chronic animal experiments. The in vivo results corresponded to those obtained in the in vitro experiments. Regression analysis between epidural and ventricular fluid pressure showed a one to one ratio. Results of clinical application of the device in 22 patients are described. Accurate depth setting of the transducer on the dura, according to the pressure depth curve, was shown to be essential. The device has also been used with success for non-invasive fontanelle pressure measurements in infants. The depth positioning of the transducer on the fontanelle according to a pressure depth curve is described.

Animals↗
PubMed1985

The Rotterdam Teletransducer: state of the device.

The development of a telemetric device for monitoring intracranial pressure, the Rotterdam Teletransducer, is described. Special attention was paid to bonding techniques for sealing the transducer. The results of improved epoxy sealing, active metal brazing and glass bonding are reported. In vitro tests showed transducers sealed with epoxy resin to be stable for two months. Using the more complicated techniques of glass bonding and active metal brazing, hermetic seals could be achieved with stable transducers for over one year. In vivo functioning of the Rotterdam Teletransducer was tested in acute and chronic animal experiments and the results corresponded to those obtained in the in vitro experiments. Regression analysis between epidural and ventricular fluid pressure showed a one to one ratio. Results of clinical application of the device in 22 patients are also described. Accurate depth setting of the transducer on the dura, according to the pressure depth curve, was shown to be essential. The device has also been used with success for non-invasive fontanelle pressure measurements in infants.

Animals↗
PubMed1984

Non-invasive intracranial pressure monitoring. A technique for reproducible fontanelle pressure measurements.

Anterior fontanelle pressure was measured in 14 infants. A technique is described for preforming reproducible measurements utilising the Rotterdam Teletransducer. One gradually increasing the dept of the transducer relative to the fontanelle a characteristic pressure depth curve is obtained. The importance of positioning the transducer according to the pressure depth curve is described.

Humans↗
PubMed1983

Agreement between physicians on assessment of outcome following severe head injury.

This study describes inter-observer agreement between physicians and consistency of one observer on repeated scoring in the assessment of outcome 6 to 12 months after severe head injury. Observer agreement is expressed by Kappa, taking chance agreement into account. The study was conducted in "live" and "non-live" situations, using five- and eight-category outcome scales. Kappa values were considerably higher when the five-category scale was used. However, even with the five-category scale, disagreement was considerable, and the results indicate that accurate predictions of the quality of survival will be difficult to attain. Observer agreement should be taken into account in prognosis studies, and when different therapeutic regimens are evaluated on the basis of outcome.

Brain Injuries↗