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Biomedical subjects

N Weiler

Publications and source records attributed to N Weiler.

At least 37 records · Page 2Linked to original sources
PubMed1999

Successful treatment of a patient with ARDS after pneumonectomy using high-frequency oscillatory ventilation.

High frequency oscillatory ventilation (HFOV) was used in a patient who developed the acute respiratory distress syndrome 5 days following a right pneumonectomy for bronchogenic carcinoma. When conventional pressure-controlled ventilation failed to maintain adequate oxygenation, HFOV dramatically improved oxygenation within the first few hours of therapy. Pulmonary function and gas exchange recovered during a 10-day period of HFOV. No negative side effects were observed. Early use of HFOV may be a beneficial ventilation strategy for adults with acute pulmonary failure, even in the postoperative period after lung resection.

Airway Resistance↗
PubMed1999

Computed tomography-based tracheobronchial image reconstruction allows selection of the individually appropriate double-lumen tube size.

OBJECTIVES: To determine whether individualized selection of double-lumen tubes or alternatives based on three-dimensional reconstruction of the tracheobronchial image from routine preoperative computed tomography (CT) scans leads to clinically appropriate choices. DESIGN: Prospective observational study; comparison to historic controls. SETTING: Anesthesia and radiology facilities of a university medical center. PARTICIPANTS: Forty-nine patients undergoing thoracic surgery requiring one-lung ventilation. INTERVENTIONS: Three-dimensional image reconstruction of individual tracheobronchial anatomy was performed from routine preoperative spiral CT scans as well as from scans of five left-sided and four right-sided double-lumen tubes. Results of image-based tube size selection were compared with literature recommendations. Prospectively, individualized tube selection was performed by superimposition of printed transparencies of tubes over the tracheobronchial system and was validated using bronchoscopic and clinical criteria (n = 24). MEASUREMENTS AND MAIN RESULTS: Three-dimensional reconstruction visualized individual anatomy with good accuracy and resolution. Correlations between patient morphology and tracheobronchial dimensions were weak (height versus mainstem bronchial diameters: r < 0.50). In 11 of 48 patients (23%). CT-fitted double-lumen tube sizes would have differed from a conventional height-based and gender-based selection. Individual, prospective, CT-based double-lumen tube selection was associated with (1) good fit and positioning confirmed by fiberoptic bronchoscopy, (2) adequate bronchial cuff seal volumes, (3) complete lung separation, and (4) oxygenation and ventilation parameters during one-lung ventilation similar to those with conventional size selection. In one patient, three-dimensional CT study allowed noninvasive evaluation of a tracheal stenosis precluding double-lumen tube placement. CONCLUSION: Individualized selection of double-lumen tube size using CT-based reconstructions of tracheobronchial anatomy leads to clinically appropriate choices. Risks resulting from variations in tracheobronchial morphology are recognized in advance.

Adolescent↗
PubMed1999

[Multi-rotation CT during continuous ventilation: comparison of different density areas in healthy lungs and in the ARDS lavage model].

PURPOSE: In this animal study, density ranges for CT-based quantification of ventilated lung area were determined. Healthy lungs and ARDS lungs were compared during artificial respiration. MATERIAL AND METHODS: CT-scans were performed in 5 anesthetized pigs using a dynamic multiscan CT option on a predefined transverse slice (slice thickness 1 mm; effective temporal resolution, 250 ms). During continuous CT acquisition, airway pressure was increased or decreased in a stepwise manner. In all images, areas of defined HU ranges were determined planimetrically. The lower threshold was set to -910 HE in all images. The upper threshold was varied from -800 HE to -200 HE in steps of 100 HE. RESULTS: During inspiration in healthy lungs the HU-range of -910 to -700 HU showed the largest increase in area. During inspiration in ARDS lungs the HU range from -910 to -300 HU allowed the most sensitive assessment of area changes. These findings can be explained by recruitment of atelectases (HU-range > -300 HU) and their transition to a HU range from -700 to -300 HU. CONCLUSION: Dynamic multiscan CT acquisitions are a useful method to determine changes of ventilated lung area during a respiratory cycle. Different HU-ranges are required to access volume changes in healthy lungs and in ARDS lungs.

Animals↗
PubMed1999

Analysis of intrapulmonary O(2) concentration by MR imaging of inhaled hyperpolarized helium-3.

Inhalation of hyperpolarized (3)He allows magnetic resonance imaging (MRI) of ventilated airspaces. (3)He hyperpolarization decays more rapidly when interacting with paramagnetic O(2). We describe a method for in vivo determination of intrapulmonary O(2) concentrations ([O(2)]) based on MRI analysis of the fate of measured amounts of inhaled hyperpolarized (3)He in imaged regions of the lung. Anesthetized pigs underwent controlled normoventilation in a 1.5-T MRI unit. The inspired O(2) fraction was varied to achieve different end-tidal [O(2)] fractions (FET(O(2))). With the use of a specifically designed applicator, (3)He (100 ml, 35-45% polarized) was administered at a predefined time within single tidal volumes. During subsequent inspiratory apnea, serial two-dimensional images of airways and lungs were acquired. At least once in each animal studied, the radio-frequency excitation used for imaging was doubled at constant FET(O(2)). Signal intensity measurements in regions of interest of the animals' lungs (volume range, 54-294 cm(3)), taken at two different radio-frequency excitations, permitted calculation of [O(2)] in these regions of interest. The [O(2)] fractions in the regions of interest correlated closely with FET(O(2)) (R = 0.879; P < 0.0001). O(2)-sensitive (3)He-MRI may allow noninvasive study of regional distribution of ventilation and alveolar PO(2) in the lung.

Administration, Inhalation↗
PubMed1998

Adaptive lung ventilation (ALV) during anesthesia for pulmonary surgery: automatic response to transitions to and from one-lung ventilation.

UNLABELLED: Adaptive lung ventilation is a novel closed-loop-controlled ventilation system. Based upon instantaneous breath-to-breath analyses, the ALV controller adjusts ventilation patterns automatically to momentary respiratory mechanics. Its goal is to provide a preset alveolar ventilation (V'A) and, at the same time, minimize the work of breathing. Aims of our study were (1) to investigate changes in respiratory mechanics during transition to and from one-lung ventilation (OLV), (2) to describe the automated adaptation of the ventilatory pattern. METHODS: With institutional approval and informed consent, 9 patients (33-72 y, 66-88 kg) underwent ALV during total intravenous anesthesia for pulmonary surgery. The ALV controller uses a pressure controlled ventilation mode. V'A is preset by the anesthesiologist. Flow, pressure, and CO2 are continuously measured at the DLT connector. The signals were read into a IBM compatible PC and processed using a linear one-compartment model of the lung to calculate breath-by-breath resistance (R), compliance (C), respiratory time constant (TC), serial dead space (VdS) and V'A. Based upon the results, the controller optimizes respiratory rate (RR) and tidal volume (VT) such as to achieve the preset V'A with the minimum work of breathing. In addition to V'A, only PEEP and FIO2 settings are at the anesthesiologist's discretion. All patients were ventilated using FIO2 = 1,0 and PEEP = 3 cm H2O. Parameters of respiratory mechanics, ventilation, and ABG were recorded during three 5-min periods: 10 min prior to OLV (1), 20 min after onset of OLV (II), and after chest closure (III). Data analyses used nonparametric comparisons of paired samples (Wilcoxon, Friedman) with Bonferroni's correction. Significance was assumed at p < 0.05. Values are given as medians (range). RESULTS: 20 min after onset of OLV (II), resistance had approximately doubled compared with (1), compliance had decreased from 54 (36-81) to 50 (25-70) ml/cm H2O. TC remained stable at 1.4 (0.8-2.4) vs. 1.2 (0.9)-1.6) s. Institution of OLV was followed by a reproducible response of the ALV controller. The sudden changes in respiratory mechanics caused a transient reduction in VT by 42 (8-59)%, with RR unaffected. In order to reestablish the preset V'A, the controller increased inspiratory pressure in a stepwise fashion from 18 (14-23) to 27 (19-39) cm H2O, thereby increasing VT close to baseline (7.5 (6.6-9.0) ml/kg BW vs. 7.9 (5.4-11.7) ml/kg BW). The controller was, thus, effective in maintaining V'A. The minimum PaO2 during phase II was 101 mmHg. After chest closure, respiratory mechanics had returned to baseline. CONCLUSIONS: Respiratory mechanics during transition to and from OLV are characterized by marked changes in R and C into opposite directions, leaving TC unaffected. The ALV controller manages these transitions successfully, and maintains V'A reliably without intervention by the anesthesiologist. VT during OLV was found to be consistently lower than recommended in the literature.

Adult↗
PubMed1998

Laryngeal mask airway position and the risk of gastric insufflation.

UNLABELLED: A potential risk of the laryngeal mask airway (LMA) is an incomplete mask seal causing gastric insufflation or oropharyngeal air leakage. The objective of the present study was to assess the incidence of LMA malpositions by fiberoptic laryngoscopy, and to determine their influence on gastric insufflation and oropharyngeal air leakage. One hundred eight patients were studied after the induction of anesthesia, before any surgical manipulations. After clinically satisfactory LMA placement, tidal volumes were increased stepwise until air entered the stomach, airway pressure exceeded 40 cm H2O, or air leakage from the mask seal prevented further increases in tidal volume. LMA position in relation to the laryngeal entrance was verified using a flexible bronchoscope. The overall incidence of LMA malpositions was 40% (43 of 108). Gastric air insufflation occurred in 19% (21 of 108), and in 90% (19 of 21) of these patients, the LMA was malpositioned. Oropharyngeal air leakage occurred in 42%, and was independent of LMA position. We conclude that clinically unrecognized LMA malposition is a significant risk factor for gastric air insufflation. IMPLICATIONS: Routine placement of laryngeal mask airways does not require laryngoscopy. In our study, fiberoptic verification of mask position revealed suboptimal placement in 40% of cases. Such malpositioning considerably increased the risk of gastric air insufflation.

Adult↗
PubMed1998

[A new method for imaging ventilation-distribution with 3Helium in magnetic resonance tomography].

BACKGROUND: Conventional 1H-MRI of the lung is restricted by susceptibility effects and low proton density: Recently, imaging of lung ventilation in MRI has become feasible using hyperpolarised inert gases with a spin of I = 1/2, such as 3He and 129Xe, as inhalative "contrast agents". New technical developments, preclinical and clinical application of this method are described. MATERIALS AND METHODS: With optical laser pumping high polarisation rates can be achieved, resulting in a high signal-to-noise ratio (S/N). A dedicated application system allows accurate administration of 3He boli at different time points during inspiration. Thus, dynamic ventilation imaging becomes possible. Prerequisites for this method include a dedicated coil as well as a spectroscopy option at the MRI system. Fast sequences and low flip angles are employed to comply with the relaxation of hyperpolarise 3He in vivo. RESULTS: Overall homogeneous signal intensity (SI) represents physiological conditions. Obstructive lung disease is associated with generalised or localised signal inhomogeneity. Different time constants of specific lung regions are probably responsible for this kind of inhomogeneous inspiratory distribution of ventilation. Tumours show a clear ventilation deficit, correlating with non-ventilated lung areas. CONCLUSION: 3He MRI is a promising new modality for the evaluation of ventilation distribution under different pathological conditions. This may include obstructive lung disease and assessment of ventilation distribution before and after thoracic surgery. Furthermore, evaluation of patients with acute lung failure and validation of ventilator settings in anaesthesia may be performed.

Contrast Media↗
PubMed1997

[Spiral CT and 3-D reconstruction of the tracheobronchial tree for the selection of the proper double-lumen tubes before individual lung ventilation].

PURPOSE: To assess the potential of 3-D spiral CT in the selection of adequate double-lumen tubes (DLT) for one-lung-ventilation. MATERIALS AND METHODS: 3-D spiral CT of eight different DLTs was performed with standardized acquisition parameters: section thickness 4 mm, table speed 6 mm/s, increment 3 mm and standardised thresholds, window settings and magnification zoom. The accuracy was confirmed by measuring 3-D objects on screen and original DLTs by vernier caliper. 3-D spiral CT was performed in 20 patients preoperatively with slice thickness 4-8 mm, pitch 1-1.5, increment 4-8 mm. To select the adequate DLT size the 3-D reconstructions of the patient's tracheobronchial tree and of the DLT were superimposed by templates or computer animation. The accuracy was controlled by endoscopic and clinical measurements. RESULTS: The accuracy of the 3 D spiral CT was nearly 0.1 mm. The superimposition with templates was easy and reliable. The 3-D spiral CT determined DLTs were shown to fit perfectly by clinical and endoscopic measurements in all cases. CONCLUSION: 3-D reconstructions of the tracheobronchial tree obtained from routine preoperative spiral CT scans allow for an easy and accurate individual selection of double-lumen tubes.

Adult↗
PubMed1997

Respiratory mechanics, gastric insufflation pressure, and air leakage of the laryngeal mask airway.

A potential risk of the laryngeal mask airway (LMA) is incomplete mask seal, which causes air leakage or insufflation of air into the stomach. The objective of the present study was to assess respiratory mechanics, quantify air leakage, and measure gastric air insufflation in patients ventilated via the LMA. Thirty patients were studied after induction of anesthesia but prior to any surgical manipulations. After the insertion of the LMA, patients were ventilated with increasing tidal volumes until one of the three following end points were reached: 1) gastric air insufflation, 2) airway pressure > 40 cm H2O, or 3) limitation of further increase in tidal volume by air leakage. The following variables were determined:inspired volume (VI), expired volume (VE), maximum inspiratory pressure (Pmax), airway pressure at gastric inflation (Pinfl), respiratory time constant (RC), compliance (C), resistance (R), and leakage fraction (FL). Respiratory mechanics were in the physiological range. Gastric insufflation occurred in 27% of the patients at inspiratory pressures between 19 and 33 cm H2O. Air leakage of more than 10% was evident at inspiratory pressures between 25 and 34 cm H2O. The end point of 40 cm H2O airway pressure was reached in only three patients. We conclude that the LMA is not better in preventing airway pressure transmission to the esophagus than a conventional face mask. However, a high FL is associated with reduced gastric air insufflation.

Adolescent↗
PubMed1996

[The effects of cimetidine on the pharmacodynamics of rocuronium].

UNLABELLED: Cimetidine is a commonly used H2-receptor antagonist that has been recommended for the prevention of acid aspiration syndrome and has been shown to potentiate vecuronium-induced neuromuscular block. The present study was designed to investigate the influence of a single IV dose of cimetidine on the neuromuscular effects of rocuronium, an analogue of vecuronium with a short onset time. METHODS: Twenty adults aged 18-65 years were included in the study with their informed consent and approval of the Ethics Committee. Following oxazepam premedication, 10 patients were randomly allocated to receive cimetidine 400 mg IV 30 min before anaesthesia. After fentanyl and thiopentone induction, single-twitch stimulation of the ulnar nerve was performed every 10 s. Following stabilisation of control responses, patients received rocuronium 0.6 mg/kg for intubation. Anaesthesia was maintained with enflurane < or = 0.8 vol.% (end-tidal) and 65% nitrous oxide. Onset time and recovery times to 25% and 75% of the twitch control values were recorded. RESULTS: Onset and recovery times did not differ between groups. CONCLUSIONS: The results of the present study demonstrate that cimetidine does not increase the duration of rocuronium neuromuscular blockade. Inhibition of the cytochrome P450 system or a direct effect at the neuromuscular junction have been suggested as the mechanisms of drug interaction associated with cimetidine. Impairment of hepatic microsomal drug metabolism results in a prolonged duration of action of vecuronium, which appears to be eliminated primarily via the liver. Data on the elimination pathway of rocuronium in humans are not available. The fact that cimetidine does not alter the recovery from rocuronium-induced neuromuscular block confirms a previous suggestion that rocuronium may not be eliminated principally by the liver. A direct effect of cimetidine on the neuromuscular junction could not be confirmed by this study. Therefore, cimetidine can be given as premedication without a risk of prolonged rocuronium block.

Adolescent↗
PubMed1996

[Anesthesia in endovascular treatment of aortic aneurysm. Results and perioperative risks].

UNLABELLED: Surgical treatment of aortic aneurysms carries significant cardiovascular risks. Transvascular insertion of endoluminal prostheses is a new, minimally invasive treatment for aortic aneurysms. The pathophysiology of this novel procedure, risks and benefits of different anaesthetic techniques, and typical complications need to be defined. METHODS: With their informed, written consent, 19 male patients aged 48-83 years of ASA physical status III and IV with infrarenal (n = 18) or thoracic (n = 1) aortic aneurysms underwent 23 stenting procedures under general endotracheal (n = 9), epidural (n = 8), or local anaesthesia with sedation (n = 6). Intra-anaesthetic haemodynamics, indicators of postoperative (p.o.) oxygenation and systemic inflammatory response, and perioperative complications were analysed retrospectively and compared between anaesthetic regimens. RESULTS: Groups were well matched with regard to morphometry and preoperative risk profiles (Table I). The use of pulmonary artery pressure monitoring, incidence of intraoperative hypotensive episodes, and p.o. intensive care was more frequent with general anaesthesia. Groups did not differ in total duration of anaesthesia care, incidence and duration of intraoperative hypertensive, brady-, or tachycardic periods, incidence of arterial oxygen desaturation, use of vasopressors, colloid volume replacements, or antihypertensives (Table 2). Postoperatively, all groups showed a similar, significant systemic inflammatory response, i.e., rapidly spiking temperature (p.o. evening: mean peak 38.5 +/- 1.0 degrees C). leucocytosis, and rise of acute-phase proteins without bacteraernia (Table 3). During this period, despite supplemental oxygen, pulse oximetry revealed temporary arterial desaturation in 13 of 18 patients (70%) (Table 3). In 3 patients, hyperpyrexia was associated with intermittent tachyarrhythmias (n = 3) and angina pectoris (n = 1). There was no conversion to open aortic surgery, perioperative myocardial infarction, or death. CONCLUSIONS: Regional and local anaesthesia with sedation are feasible alternatives to general endotracheal anaesthesia for minimally invasive treatment of aortic aneurysms by endovascular stenting. However, invasive monitoring and close postoperative monitoring are strongly recommended with either method. Specific perioperative risks in patients with limited cardiovascular or pulmonary reserve are introduced by the abacterial systemic inflammatory response to aortic stent implantation. Hyperpyrexia increases myocardial and whole-body oxygen consumption, and can precipitate tachyarrhythmias. Hyperfibrino-genaemia may increase the risk of postoperative arterial and venous thromboses. Close monitoring of vital parameters and prophylactic measures, including oxygen supplementation, low-dose anticoagulation, antipyretics, and fluid replacement are warranted until this syndrome resolves.

Aged↗
PubMed1996

[Adaptive lung ventilation (AVL). Evaluation of new closed loop regulated respiration algorithm for operation in the hyperextended lateral position].

The lateral decubitus position is the standard position for nephrectomies. There is a lack of data about the effects of this extreme position upon respiratory mechanics and gas exchange. In 20 patients undergoing surgery in the nephrectomy position, we compared a new closed-loop-controlled ventilation algorithm, adaptive lung ventilation (ALV), which adapts the breathing pattern automatically, to the respiratory mechanics with conventionally controlled mandatory ventilation (CMV). The aims of our study were (1) to describe positioning effects on respiratory mechanics and gas exchange, (2) to compare ventilatory parameters selected by the ALV controller with traditional settings of CMV, and (3) to assess the individual adaptation of the ventilatory parameters by the ALV controller. The respirator used was a modified Amadeus ventilator, which is controlled by an external computer and possesses an integrated lung function analyzer. In a first set of measurements, we compared parameters of respiratory mechanics and gas exchange in the horizontal supine position and 20 min after changing to the nephrectomy position. In a second set of measurements, patients were ventilated with ALV and CMV using a randomized crossover design. The CMV settings were a tidal volume of 10 ml/kg body weight, a respiratory rate of 10 breaths/min, an I:E ratio of 1:1.5, and an end-inspiratory pause of 30% of inspiratory time. With both ventilation modes F1O2 was set to 0.5 and PEEP to 3 cm H2O. During ALV a desired alveolar ventilation of 70 ml/ kg KG.min was preset. All other ventilatory parameters were determined by the ALV controller according to the instantaneously measured respiratory parameters. Positioning induced a reduction of compliance from 61.6 to 47.9 ml/cm H2O; the respiratory time constant shortened from 1.2 to 1.08 s, whereas physiological dead space increased from 158.9 to 207.5 ml. On average, the ventilatory parameters selected by the ALV controller resembled very closely those used with CMV. However, an adaptation to individual respiratory mechanics was clearly evident with ALV. In conclusion, we found that the effects of positioning for nephrectomy are minor and may give rise to problems only in patients with restrictive lung disease. The novel ALV controller automatically selects ventilatory parameters that are clinically sound and are better adapted to the respiratory mechanics of ventilated patients than the standardized settings of CMV are.

Adult↗
PubMed1996

[An innovative procedure of oxygen detection in medicine, biology, environmental research and biotechnology based on luminescence quenching].

For most (aerobic) animal organisms, oxygen is a mandatory and global substrate. The accurate measurement of oxygen is therefore of importance in the fields of medicine, biology, environmental research and biotechnology. The fact that oxygen is not readily soluble in aqueous media makes its detection more difficult. In contrast to the technique of polarography, the use of luminescence quenching by paramagnetic oxygen, does not consume the oxygen. Another problem of oxygen detection in connection with respiration is the need for very short response times. A third problem, which is associated with luminescence itself, is the fading of the dyes, which results in long-term signal instability. The last two problems can be optimally resolved by adsorbing the luminescence dye onto chromatographic materials--in particular hydrophobic material--having a very large internal surface area, and using the decay time in accordance with the Stern-Volmer equation as oxygen signal. For this, continuous evaluation of the signal is necessary. The carrier material doped with dye is incorporated in a single-grain layer. For measurements in liquids, the detector layer is protected by a black silicone membrane. Two designs are possible for the oxygen detector: (I) a special form using glass fibres, and (II) a miniature detector utilizing optoelectronic solid state technology. Both fluorescence and phosphorescence can be employed, the dye used being excited by light, obviating the need for quartz. The detector layers may be either of high sensitivity for small oxygen concentrations, or have equal sensitivity over the entire oxygen concentration range. There is an optimal figure for the specific amount of adsorbed dye. Application examples are given for respiration and for the determination of oxygen uptake by suspended cells.

Animals↗
PubMed1995

[Experiments aimed at developing an implantable and continuously functioning glucose sensors based on polarimetry].

In vitro and in vivo experiments devised with the aim of developing a permanently implantable glucose sensor based on polarimetry are described. It was found that in ultrafiltrated human blood plasma the overall optical rotation was 94% specific for glucose, and that polarisation photometry yielded a sufficiently sensitive signal for in vivo glucose detection. The three types of capillary membrane intended for implantation that we tested, revealed an in vitro response time to glucose concentration of 10 minutes; when implanted, they maintain this over a period of weeks, during which time the same glucose concentrations can be measured daily in ultrafiltrated capillary fluid as in the blood of the animals (guinea pigs). The drop in glucose concentration induced 20 minutes after a single administration of insulin can also be detected in both fluids. The experiments described indicate that the development of an implantable polarimetric glucose sensor is possible.

Animals↗
PubMed1994

The AVL-mode: a safe closed loop algorithm for ventilation during total intravenous anesthesia.

The Adaptive Lung Ventilation Controller (ALV-Controller) represents a new approach to closed loop control of ventilation. It is based on a pressure controlled ventilation mode. Adaptive lung ventilation signifies automatic breath by breath adaptation of breathing patterns to the lung mechanics of an individual patient. The specific goals are to minimize work of breathing, to maintain a preset alveolar ventilation and to prevent the occurrence of intrinsic PEEP. We ventilated 5 patients undergoing major abdominal procedures using ALV. ALV was tolerated well in all patients. Alveolar ventilation was preset between 5500 and 6500 ml/min. Serial dead space (Vds) and respiratory time constant (resistance * compliance) of the patients ranged from 104 to 164 ml and 0.74 to 1.5 s, respectively. The resulting respiratory rates ranged from 8 to 15 breaths/min, the tidal volumes from 542 to 829 ml, and the applied maximum inspiratory pressures from 15.5 to 18.9 mbar. Expiratory time was sufficient in all cases to allow complete expiration and to avoid intrinsic PEEP. I: E-relations ranged from 0.36 to 0.76. After a step change in alveolar ventilation rise times of the breathing patterns were recorded at values from 7 to 67 s. Overshoot did not reach statistic significance compared to the variations in breathing patterns which occurred during stable measuring periods. Accuracy of the controller was high (27.8 ml difference between preset and applied alveolar ventilation in the mean) and stability was sufficient for clinical purposes. The results of this preliminary study show that the breathing patterns selected by the controller were well adapted to the lung mechanics of the patients. Respiratory rates, inspiratory pressures and tidal volumes were within the clinically acceptable range in all patients.

Adult↗