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Biomedical subjects

C Werner

Publications and source records attributed to C Werner.

At least 145 records · Page 8Linked to original sources
PubMed1995

Effects of sufentanil on cerebral hemodynamics and intracranial pressure in patients with brain injury.

BACKGROUND: The current study investigates the effects of sufentanil on cerebral blood flow velocity and intracranial pressure (ICP) in 30 patients with intracranial hypertension after severe brain trauma (Glasgow coma scale < 6). METHODS: Mechanical ventilation (FIO2 0.25-0.4) was adjusted to maintain arterial carbon dioxide tensions of 28-30 mmHg. Continuous infusion of midazolam (200 micrograms/kg/h intravenous) and fentanyl (2 micrograms/kg/h intravenous) was used for sedation. Mean arterial blood pressure (MAP, mmHg) was adjusted using norepinephrine infusion (1-5 micrograms/min). Mean blood flow velocity (Vmean, cm/s) was measured in the middle cerebral artery using a 2-MHz transcranial Doppler sonography system. ICP (mmHg) was measured using an epidural probe. After baseline measurements, a bolus of 3 micrograms/kg sufentanil was injected, and all parameters were continuously recorded for 30 min. The patients were assigned retrospectively to the following groups according to their blood pressure responses to sufentanil: group 1, MAP decrease of less than 10 mmHg, and group 2, MAP decrease of more than 10 mmHg. RESULTS: Heart rate, arterial blood gases, and esophageal temperature did not change over time in all patients. In 18 patients, MAP did not decrease after sufentanil (group 1). In 12 patients, sufentanil decreased MAP > 10 mmHg from baseline despite norepinephrine infusion (group 2). ICP was constant in patients with maintained MAP (group 1) but was significantly increased in patients with decreased MAP. Vmean did not change with sufentanil injection regardless of changes in MAP. CONCLUSIONS: The current data show that sufentanil (3 micrograms/kg intravenous) has no significant effect on middle cerebral artery blood flow velocity and ICP in patients with brain injury, intracranial hypertension, and controlled MAP. However, transient increases in ICP without changes in middle cerebral artery blood flow velocity may occur concomitant with decreases in MAP. This suggests that increases in ICP seen with sufentanil may be due to autoregulatory decreases in cerebral vascular resistance secondary to systemic hypotension.

Anesthetics, Intravenous↗
PubMed1995

Surface characterization of hemodialysis membranes based on streaming potential measurements.

Hemodialysis membranes made from cellulose (CUPROPHAN, HEMOPHAN) and sulfonated polyethersulfone (SPES) were characterized using the streaming potential technique to determine the zeta potential at their interfaces against well-defined aqueous solutions of varied pH and potassium chloride concentrations. Streaming potential measurements enable distinction between different membrane materials. In addition to parameters of the electrochemical double layer at membrane interfaces, thermodynamic characteristics of adsorption of different solved species were evaluated. For that aim a description of double layer formation as suggested by Börner and Jacobasch (in: Electrokinetic Phenomena, p. 231. Institut für Technologie der Polymere, Dresden (1989)) was applied which is based on the generally accepted model of the electrochemical double layer according to Stern (Z. Elektrochemie 30, 508 (1924)) and Grahame (Chem. Rev. 41, 441 (1947)). The membranes investigated show different surface acidic/basic and polar/nonpolar behavior. Furthermore, alterations of membrane interfaces through adsorption processes of components of biologically relevant solutions were shown to be detectable by streaming potential measurements.

Adsorption↗
PubMed1995

[Testing methods for the characterization of catheter balloons and lumina].

The present paper reports on the characterization of catheter balloons and lumina on the basis of such known parameters as residual volume, compliance, burst pressure and flow rate, with the aim of developing standards, test methods and testing equipment as well as standards. These are becoming ever more important with the coming into force of the EC directive on medical products [7] and the law governing medical products in Germany [13], which requires manufacturers to specify the properties of their products. Our testing concept is based on a commercially available machine that subjects materials to alternating extension and compression forces over the long-term, to which we added a special hydraulic module. Using the multimedia technology we achieved a real time superimposition of the volume-diameter curve on the balloon. The function of the testing device and method is demonstrated on dilatation catheters. Our initial results reveal compatibility with the requirements of the 1% accuracy class. Use of this methodology for comparative testing of catheters and quality evaluation is recommended.

Catheterization↗
PubMed1995

Neuroprotection: fact or fantasy?

Several strategies have been proposed for protecting the brain from ischaemic and hypoxic insults, based on an understanding of the pathophysiological processes involved. They include hypervolaemic haemodilution, anaesthesia, hypothermia, normoglycaemia, calcium channel blockers, adenosine modulators, NMDA- and AMPA-receptor antagonisms and lazeroids. Some have only been shown to be effective in animals and some have clinical relevance. Only hypothermia is protective in a variety of pathological states.

Anesthesia↗
PubMed1995

[Effects of analgesia and sedation on cerebrovascular circulation, cerebral blood volume, cerebral metabolism and intracranial pressure].

Cerebral blood flow autoregulation, CO2 reactivity and the pressure-volume relationship may be impaired or abolished in patients with intracranial mass lesions, brain trauma, cerebral vasospasm or increased cerebral elastance. Sedatives, analgetics, and anesthetics may induce major changes in cerebral blood flow, cerebral metabolism and intracranial pressure (ICP). The inadequate use of these drugs may aggravate the preexisting intracranial pathology and may worsen outcome. Thus it is important to understand the effects of sedatives, analgetics, and anaesthetics on intracranial hemodynamics and metabolism during physiological and pathological conditions. Hypnotics (barbiturates, etomidate, propofol), benzodiazepines, opioids (fentanyl, alfentanil, sufentanil) and alpha-2-adrenergic agonists (clonidine, dexmedetomidine) reduce cerebral blood flow. With ketamine, cerebral blood flow changes in a regionally specific fashion, with some territories showing increases and others showing decreases in cerebral blood flow. Cerebral metabolism is decreased during sedation and analgesia with hypnotics, benzodiazepines, and opioids, while infusion of ketamine produces stimulation as well as suppression of cerebral metabolism. This suggests that the changes in cerebral blood flow seen with these drugs occur secondary to their cerebral, metabolic effects. Alpha-2-adrenergic agonists produce no significant changes in cerebral metabolism. However, cerebral blood flow is decreased with clonidine or dexmedetomidine. This suggests uncoupling between cerebral metabolism and flow due to decreases in central catecholamine turnover. Hypnotics and benzodiazepines decrease ICP due to decreases in cerebral blood volume. However, these drugs may also decrease mean arterial blood pressure, which may result in a critical reduction in cerebral perfusion pressure. ICP remains unchanged with the use of opioids as long as mean arterial pressure is maintained constant. However, decreases in mean arterial pressure during infusion of opioids induce autoregulatory cerebral vasodilation, which in turn increases cerebral blood volume and ICP. Ketamine may increase ICP specifically in subjects with spontaneous ventilation. With mechanical hyperventilation and constant systemic hemodynamics, ketamine fails to increase ICP in most of the patients. Alpha-2-adrenergic agonists produce no significant changes in ICP, although there may be a transient decrease in ICP with lower doses.

Analgesics↗
PubMed1994

Effects of saline, mannitol, and furosemide on acute decreases in renal function induced by radiocontrast agents.

BACKGROUND: Injections of radiocontrast agents are a frequent cause of acute decreases in renal function, occurring most often in patients with chronic renal insufficiency and diabetes mellitus. METHODS: We prospectively studied 78 patients with chronic renal insufficiency (mean [+/- SD] serum creatinine concentration, 2.1 +/- 0.6 mg per deciliter [186 +/- 53 mumol per liter]) who underwent cardiac angiography. The patients were randomly assigned to receive 0.45 percent saline alone for 12 hours before and 12 hours after angiography, saline plus mannitol, or saline plus furosemide. The mannitol and furosemide were given just before angiography. Serum creatinine was measured before and for 48 hours after angiography, and urine was collected for 24 hours after angiography. An acute radiocontrast-induced decrease in renal function was defined as an increase in the base-line serum creatinine concentration of at least 0.5 mg per deciliter (44 mumol per liter) within 48 hours after the injection of radiocontrast agents. RESULTS: Twenty of the 78 patients (26 percent) had an increase in the serum creatinine concentration of at least 0.5 mg per deciliter after angiography. Among the 28 patients in the saline group, 3 (11 percent) had such an increase in serum creatinine, as compared with 7 of 25 in the mannitol group (28 percent) and 10 of 25 in the furosemide group (40 percent) (P = 0.05). The mean increase in serum creatinine 48 hours after angiography was significantly greater in the furosemide group (P = 0.01) than in the saline group. CONCLUSIONS: In patients with chronic renal insufficiency who are undergoing cardiac angiography, hydration with 0.45 percent saline provides better protection against acute decreases in renal function induced by radiocontrast agents than does hydration with 0.45 percent saline plus mannitol or furosemide.

Aged↗