Search PubMed⌕ Search

Biomedical subjects

W Schregel

Publications and source records attributed to W Schregel.

At least 37 records · Page 2Linked to original sources
PubMed1995

[Transcranial Doppler ultrasound: effects of intravenous anesthetics in neurosurgical patients].

AIM: Although adverse effects on cerebral blood flow have been reported, intravenous anaesthetic and sedative agents are often used in neurosurgical patients. Monitoring of these effects by transcranial Doppler sonography remains a questionable procedure as long as the cross-sectional area of the insonated basal cerebral arteries is unknown. This study should evaluate the effects of thiopental, propofol, midazolam and alfentanil on flow velocities and "vessel cross-sectional area" (proportional to the reflected Doppler signal power) measured by transcranial Doppler sonography. METHOD: 19 patients with severe cerebral lesions (Glasgow Coma Scale < 6) were investigated. They were hyperventilated and sedated with fentanyl and flunitrazepam. The Doppler probe was fixed to the temporal bone and focussed to the middle cerebral artery of the more severely lesioned side. Baseline values of flow velocities and vascular cross-sectional area were measured. If routine nursing procedures required a deeper degree of sedation, either thiopental 2.5 mg/kg, propofol 1 mg/kg, midazolam 0.075 mg/kg or alfentanil 0.025 mg/kg were injected intravenously over 30 s. Further measurements were made 60, 120 and 300 s after start of the injection. Mean +/- SD were calculated, statistical evaluation was performed by analysis of variance and paired t-tests using the Bonferroni correction (p < 0.05). RESULTS: The injected agents induced significant decreases of the mean value of flow velocities; the "vessel cross-sectional area" remained unaltered. In some patients paradoxical increases of v were observed. CONCLUSION: The results indicate that intravenous anaesthetic agents are not likely to influence the cross-sectional area of the major basal cerebral arteries. Therefore TCD seems to be a valid tool to monitor the effects of these agents on the cerebral circulation of neurosurgical patients. This is probably of prognostic and therapeutic value.

Adolescent↗
PubMed1994

Transcranial Doppler sonography during isoflurane/N2O anaesthesia and surgery: flow velocity, "vessel area" and "volume flow".

Transcranial Doppler sonography (TCD) constitutes an advance in noninvasive monitoring of the cerebral circulation. However, as long as the diameter and cross-sectional area of the insonated middle cerebral artery (MCA) remain unknown, the derived flow velocities (v) are not informative. It is not known how the human MCA is influenced by anaesthetic agents. However, a TCD-modification allows noninvasive determination of "vessel area" (VA) and "volume flow" (VF) in MCA by analysing the backscattered Doppler power. This investigation evaluates the effects of isoflurane (in combination with N2O and surgery) on v, VA and VF. In 14 patients (ASA I) scheduled for minor surgical or gynaecological operations, anaesthesia was induced with droperidol, alfentanil, thiopentone and vecuronium. After intubation ventilation with N2O:O2 = 3:2 was adjusted, to maintain endexpiratory carbon dioxide (FECO2) constant between 4 and 5%. Baseline values of heart rate (HR), oscillometric mean arterial pressure (MAP), and TCD variables (v, VA VF) were measured before adding 2.4% isoflurane to the inspiratory mixture. Further measurements-were made 3, 6, 10, and 20 min after starting isoflurane. Surgery commenced between the sixth and tenth minute after isoflurane application. The MAP, FECO2, and v showed only minor alterations; HR increased after 6, 10 and 20 min. Transcranial "vessel area" and "volume flow" showed increases after isoflurane inhalation. The increase of "vessel area" supports the assumption that isoflurane greater than 1 MAC dilates large human cerebral arteries, so that if flow velocities are considered alone, alterations of cerebral blood flow may easily be underestimated.

Anesthesia, Inhalation↗
PubMed1994

[Opioids, cerebral circulation and intracranial pressure].

The effects of the opioids alfentanil (A), fentanyl (F), and sufentanil (S) on cerebral blood flow (CBF) and intracranial pressure (ICP) have been discussed in several recent publications. The purpose of this review is to describe the results of studies in animals, healthy volunteers, and patients with and without intracranial diseases. Clinical relevance and mechanisms of the reported ICP and CBF increases are analysed. METHODS. Approximately 70 original articles and abstracts were retrieved by a systematic literature search using the key word list at the end of this abstract. The cited studies came from computerised database systems like Silver Platter and DIMDI, the SNACC reference list, and the bibliographies of pertinent articles and books. These studies were classified into three groups: significant increase of ICP and/or CBF; no significant or clinically relevant alterations; and significant decreases of ICP and/or CBF. RESULTS. The numerical relationship was 6:7:3 for A, 7:16:9 for F, and 5:11:8 for S. Increases of previously normal or only slightly elevated ICP were registered in some studies in connection with a decrease in mean arterial pressure (MAP). On the other hand, in patients with brain injury and elevated ICP opioids did not further increase ICP despite MAP decreases. In studies monitoring ICP and/or CBF continuously, transient and moderate increases of questionable clinical relevance became apparent a few minutes after bolus injection of opioids. Alterations of systemic and cerebral haemodynamics observed after bolus application were not registered during continuous infusion of A and S. DISCUSSION AND CONCLUSIONS. The cerebral effects of opioids are dependent on several factors, e.g., age, species, ventilation, anaesthesia before and during measurements, systemic haemodynamics, and underlying diseases. The probable mechanism of ICP increase during decreasing MAP is cerebral vasodilatation due to maintained autoregulation. With increasing severity of the cerebral lesion autoregulation is often disturbed. Therefore, ICP often remains unaltered despite MAP decreases. However, the resulting decrease in cerebral perfusion pressure makes such patients more susceptible to develop ischaemic neurological deficits. Induction of somatic rigidity or (with high doses) convulsions, exceeding the upper limit of autoregulation, histamine release, cerebral vasodilatation, increased cerebral oxygen consumption, or carbon dioxide accumulation during spontaneous breathing were discussed as mechanisms for transient ICP/CBF increases. It is concluded that opioids are often beneficial and not generally contraindicated for patients with cerebral diseases and compromised intracranial compliance. However, since negative side effects cannot be excluded, opioid effects and side effects should be monitored (MAP, ICP, cerebrovenous oxygen saturation, transcranial Doppler sonography) in patients at risk. It has to be stressed that opioids should be administered only to patients with stable haemodynamic situations and preferably in well-titrated, continuous infusions.

Alfentanil↗
PubMed1994

[Ultrasonic guided cannulation of the axillary vein in intensive care patients].

Cannulation of the axillary vein is claimed to be an effective and relatively safe access to the central venous (CV) system [2, 4, 5, 8]. However, anatomical landmarks recommended for venous location (Muskulus pectoralis minor, processus coracoideus) are probably hard to identify in the majority of intensive care (ICU) patients. This investigation evaluated unidirectional 8 MHz Doppler ultrasound (US) in locating the axillary vein. Success rates and complications of this CV access in ICU patients is analysed. METHODS. The experimental design was approved by the local ethical committee (RUB). In 50 patients from our ICU cannulation of the axillary vein was attempted; all were in need of a CV line. Other CV puncture sites (except for the subclavian vein) were associated with contraindications. Patients were placed in a 15 degrees Trendelenburg position (15 exceptions); the arm was abducted to 45 degrees [5, 8]. The course of the axillary vein was located by Doppler US and marked on the skin with a felt pen. Prior to puncture, US intensity was judged by a score ranging from 0 to 4. After skin desinfection, sterile draping, and local anaesthesia, puncture of the axillary vein was attempted. The puncture kit LeaderCath 11,515 (Vygon, Aachen, FRG) was used. When venous blood could be aspirated, the Seldinger guidewire was inserted and the definite catheter placed. The experimental design allowed up to ten punctures, slightly modified in angle and direction of the needle, if puncture of the axillary vein or guide-wire placement failed. The cannulation attempt was classified as unsuccessful in the following cases: malposition, axillary vein not encountered by the puncture needle, guide-wire placement unsuccessful, or if identification and cannulation of the vein lasted more than 20 min. The puncture attempts were evaluated in respect to success rate, time, relation of US intensity to puncture attempts and CV pressure, complications, and malposition. RESULTS. Of the 50 attempted CV catheters, 43 were placed successfully. In 2 cases the axillary vein could not be encountered by the puncture needle. Guide-wire placement did not succeed in 4 patients. One catheter was malpositioned in the ipsilateral internal jugular vein. Four inadvertent punctures of the axillary artery remained without sequelae after compression. No further puncture-related complications were observed. With high US intensity score the number of puncture attempts necessary for successful vein cannulation was lower. On the other hand, complications and puncture failure seemed to be more frequent in patients with lower US intensity scores. DISCUSSION. CV access via the axillary vein had a satisfying success rate (43/50) and proved to be a safe procedure in our ICU patients despite higher risk factors compared to a healthy population. Although ethical reasons did not allow a randomised comparison with the standard technique, location of the axillary vein by Doppler US is likely to improve cannulation results and reduce complications induced by "blind" needle probing. With a low US intensity score, the rate of successful punctures is lower and complication rates increase. In some patients, e.g., those with extended tumour operations involving the head and neck, CV access via the axillary vein may be of high clinical value.

Axillary Vein↗
PubMed1993

Transcranial Doppler monitoring during induction of anesthesia: effects of propofol, thiopental, and hyperventilation in patients with large malignant brain tumors.

Disturbed autoregulation and CO2 reactivity have been reported in patients with brain tumors. Therefore, we decided to monitor the cerebrovascular effects of anesthetic drugs and hyperventilation. Transcranial Doppler sonography (TCD) can measure noninvasively alterations of flow velocities (v) and cross-sectional vessel area (VA) in large brain arteries. Twenty-eight patients with large malignant brain tumors in the territory of the middle cerebral artery (MCA) randomly received propofol or thiopental for induction and maintenance of anesthesia. Mean arterial pressure (MAP), heart rate (HR), and TCD parameters (vMCA and VA of the tumor or nontumor side) were determined at six data points (DP). The first measurements (MAP, HR, and TCD of the nontumor side) were performed before (DP I) and 60 s after (DP II) induction of anesthesia with either 2 mg/kg propofol or 4 mg/kg thiopental. After intubation and normoventilation (50% O2 in air), 0.05-0.1 mg/kg midazolam and an alfentanil infusion (100 micrograms/kg x h) were initiated. Then MAP, HR, vMCA, and VA of the tumor side were analyzed before (DP III) and 60 s after (DP IV) either propofol (1 mg/kg) or thiopental (2 mg/kg) were given. Finally, the effects of hyperventilation on HR, MAP, vMCA, and VA (tumor side) were determined (DP V and VI). Mean +/- SD, thiopental or propofol reactivity (non-tumor and tumor side) and CO2 reactivity (tumor side) were calculated; statistical comparison between DP I and II, III and IV, and V and VI was performed by paired t tests (p < 0.05). Unpaired t tests were used to evaluate differences between groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

[Value of transcranial Doppler sonography].

Transcranial Doppler sonography (TCD) has gained increasing relevance since its introduction by Aaslid in 1982. Basal cerebral arteries are insonated with a 2-MHz ultrasound beam. The backscattered ultrasound is analyzed by Fast-Fourier transformation and permits continuous and noninvasive determination of flow velocities (v) and pulsatility index (PI). Cerebral vasospasm after subarachnoid hemorrhage is characterized by steadily increasing flow velocities and decreasing PI. Increasing cerebrovascular resistance due to hyperventilation or intracranial pressure results in high PIs. Since the diameters of basal cerebral arteries remain constant under CO2 variations, altered flow velocities indicate altered cerebral blood flow (CBF) in this situation. Thus TCD is a useful tool for analysis of CO2 reactivity, which is relevant for patients with brain injuries or carotid lesions. Intraoperatively, TCD has been used for detection of emboli during heart operations or carotid endarterectomies. Carotid cross-clamping induces proportional reductions of flow velocities and CBF; reduction of flow velocities to less than 40% of the preclamp value should result in shunt insertion. Although often pretended, constancy of basal cerebral arteries remains questionable in the perioperative period: arterial blood pressure, intracranial pressure, sympathetic tone, and vasodilating agents like nitroglycerin, halothane and isoflurane are likely to influence large cerebral arteries. Therefore intraoperative TCD results should be interpreted cautiously. TCD is a fascinating monitoring device with many advantages. It can be useful for many patients and physicians, if its limitations and the clinical situation are kept in mind. Further studies have to define the role of TCD in neuroanaesthesia.

Blood Flow Velocity↗
PubMed1992

[The effect of halothane, alfentanil and propofol on blood flow velocity, blood vessel cross section and blood volume flow in the middle cerebral artery].

Transcranial Doppler sonography (TCD) has gained in relevance for noninvasive monitoring of the cerebral circulation during the perioperative period. As long as the diameters of the investigated vessels remain unknown, however, flow velocities alone are not really informative. Exact vessel diameter determination in humans under the influence of different anesthetic drugs has not yet been performed due to ethical and methodological restrictions. A new modification of TCD allows analysis of the reflected "Doppler power", which is proportional to the cross-sectional area of the insonated vessel. METHODS. Three groups of 15-16 patients each (ASA I) were investigated after informed consent. Anesthesia was induced with droperidol, alfentanil, thiopental, and vecuronium bromide. After intubation patients were normoventilated with N2O:O2 = 3:2 and additional doses of alfentanil were injected until the transcranial ultrasound probe was fixed to the temporal bone and focused on the middle cerebral artery. Baseline values of heart rate (HR), mean arterial pressure (MAP), expiratory minute volume (EMV), end-expiratory CO2 (FeCO2), and TCD were measured. Then 1.5 vol% halothane, 25-50 micrograms/kg alfentanil, or propofol (1.5 mg/kg iv., 10 mg/kg.min) was administered. Further measurements (HR, MAP, EMV, FeCO2 and TCD) were performed at 3, 6, 10, and 20 min after the start in the halothane and propofol groups and after 3 and 6 min in the alfentanil group. The following transcranial parameters were derived from the TCD device: mean maximal flow velocity (vmmax), pulsatility index, time-averaged mean velocity (vmmen), "vessel area (VA)", and "volume flow (VF)". The mean +/- standard deviation of each parameter was calculated. Statistical evaluation was performed by paired t-tests (level of significance P less than 0.05). RESULTS. HR showed a tendency to increase after halothane and to decline after alfentanil. Alfentanil induced a short-term decline in MAP. End-expiratory minute volume and FeCO2 showed only minor alterations in all three groups. The vmmax was nearly doubled by halothane. Alfentanil induced a transitory decline in vmmax while Propofol decreased it markedly. The pulsatility index showed a decrease after halothane; alfentanil caused a short-term increase. Propofol induced a strong increase after 3 min; in the following period a return to baseline values was observed. The vmmean was increased by halothane and reduced by 32% propofol. VA was found to be unaltered by alfentanil and propofol but was more than doubled by halothane. Accordingly, the relative value for VF increased by 148% under halothane. VF appeared to decline after propofol. DISCUSSION. The described method allows only the determination of relative values: it is not possible to quantify exactly how much the VA changed. Halothane caused significant increases of VA measured in the middle cerebral artery, whereas alfentanil and propofol did not influence this parameter. This is in accordance with previous experiments in dogs in which halothane decreased the resistance of large basal cerebral arteries (LAR). LAR remained unaltered after alfentanil administration. The site of action of some anesthetic agents on cerebral vessels does not seem to be restricted to cerebral arterioles: at least for halothane, a vasodilating effect on large cerebral arteries could be demonstrated. This should be kept in mind when transcranial Doppler is applied during the perioperative period.

Alfentanil↗
PubMed1992

[An infected fistula following a peridural catheter].

An infected fistula was observed in a woman (Age: 69 years, weight: 60 kg, height: 159 cm) 14 days after insertion and 8 days after removal of a peridural catheter inserted preoperatively for postoperative analgesia after nephrectomy (carcinoma). Due to haemodynamic problems in the early postoperative period no analgetic or local anaesthetic medication was applied via the peridural catheter. After unsuccessful antibiotic and surgical treatment the women was transferred to the Neurosurgical department five weeks after nephrectomy. Magnetic resonance imaging of the lumbar region showed a fistula (Segment L2/L3) reaching the epidural space but no epidural spreading or epidural abscess. Partial laminectomy L2/L3 was performed and the fistula excised under continuous antibiotic treatment with ofloxacin. Up until 21 months after the operation no recidivation occurred. Exact details of catheter insertion and catheter treatment in the postoperative period are not available; the fact, that no bactericide [9] local anaesthetic agents were applied, might have favoured the occurrence of this infection. Infectious complications have to be taken into consideration for the indication of peridural catheters in the perioperative period.

Aged↗
PubMed1991

Entrapment of a Swan-Ganz-catheter in tricuspidal valve.

Unsuccessful pulmonary artery catheter removal is a rare but potential life-threatening complication. This was observed in a dog during investigations on cerebrovascular reactivity. Postmortem examination showed entrappment of the pulmonary artery catheter in tricuspidal valve. "Clinical" symptoms are described and therapeutic measures in the case of suspected entrappment are discussed.

Animals↗
PubMed1989

[Transcranial Doppler sonography and hemodynamics].

13 patients without cerebral or cerebrovascular diseases were investigated by transcranial Doppler sonography during Swan-Ganz catheterisation for cardiologic purposes. Massive increases of mean arterial pressure, heart rate and cardiac index were observed during exercise; flow velocities in the middle cerebral artery increased only to the same extent as the endexpiratory carbon dioxide rose. However, the pulsatility index increased significantly (p less than 0.01) although a decrease should have been expected due to carbon dioxide accumulation. These results are indicative of a functioning autoregulation independent of carbon dioxide; they are relevant for interpretation of TCD results in patients with disturbed autoregulation.

Adult↗
PubMed1989

[Current possibilities and limits of transcranial Doppler sonography as a cerebral monitoring procedure].

Transcranial Doppler Sonography (TCD) can meet some requirements for an ideal measuring device of the cerebral circulation. TCD can measure non-invasively and repeatably blood flow velocities of basal cerebral arteries. Under the assumption of constant vessel diameters can altered flow velocities reflect alterations of cerebral blood flow. TCD-measurements have been used frequently for diagnosis of cerebral vasospasm after subarachnoid hemorrhage. Furthermore TCD has been applied in cerebrovascular diseases, during operations with extracorporal circulation and in patients with increased intracranial pressure. Unchanged diameters of basal cerebral arteries have been proven only for carbon dioxide variations and some drugs; this cannot be presupposed during alterations of mean arterial or intracranial pressure. If conditions as ventilation, hemodynamics and drug therapy are kept constant, TCD may be valuable for short-term-trend-detection of cerebral blood flow and intracranial pressure.

Brain Injuries↗
PubMed1988

Hepatic drug disposition in multiple organ failure.

In 15 patients with multiple organ failure of septic etiology, some principal partial hepatic functions of drug disposition were measured by the test substances galactose, indocyanine green, theophylline and 4-methylumbelliferon. Glucuronidation was not impaired in any case, whereas flow-limited and capacity-limited drug elimination can be influenced. Drug monitoring and intense clinical observation seem necessary to improve drug therapy and the outcome of patients with multiple organ failure.

Adult↗
PubMed1988

[Transcranial Doppler sonography: halothane increases average blood flow velocity in the middle cerebral artery].

Transcranial Doppler sonography (TCD) can non-invasively measure the blood flow velocity of basal cerebral arteries, especially of the middle cerebral artery (MCA). TCD has been used for monitoring the cerebral circulation during cardiopulmonary bypass or cross-clamping of the carotid artery. To date, systemic investigation of the effects of anesthetic agents on mean blood flow velocity in the MCA (vMCA) has been neglected, although their effects on cerebral blood flow are well known. Two groups of 10 patients each with minor surgical or gynecological operations were studied using TC2-64 (EME) TCD equipment. Constant artificial ventilation with N2O:O2 = 2:1 was controlled by capnometry; capillary pCO2 ranged from 35 to 40 mmHg in both groups. In group I, patients underwent general anaesthesia with approximately 0.8 vol% halothane. vMCA, blood pressure, and heart rate were determined before and during anesthesia as well as after skin incision. Group II patients received fentanyl and droperidol. Measurements were performed at time points comparable to those in group I. Halothane caused an increase in vMCA by more than one third of the preanesthetic value (from 54.4 +/- 12.2. to 84.2 +/- 23.9 (P less than 0.01]. In group II (neuroleptanesthesia), no significant alterations of vMCA or hemodynamic parameters were observed. These results show that anesthetic agents can influence vMCA as well as cerebral blood flow. Therefore, these data should be taken into account while monitoring vMCA during operative procedures. However it has to be considered that TCD only permits measurement of blood flow velocity, while the diameter of the investigated vessel remains unknown. Clinical applications of this fascinating noninvasive monitoring device are discussed.

Adolescent↗