Library

Description / Table of Contents: Zusammenfassung Es wurden die Einwirkung des Kanzerogens 3H-3,4-Benzpyren und des Nichtkanzerogens 3H-1,2-Benzpyren auf die Schweinehaut mit Hilfe von Kryostatschnitten autoradiographisch untersucht. Es fanden sich weder im Verteilungsmuster noch in der Verweildauer signifikante Unterschiede zwischen dem Karzinogen und dem Nichtkarzinogen. Die zelligen Bestandteile (Histiocyten, Fibroblasten und Capillarendothelien) wurden stark markiert, schwach dagegen die intercelluläre Grundsubstanz und kaum die kollagenen Fasern. Die Markierung hängt mit der hauptsächlich stattfindenden Bindung an lösliche Zellbestandteile, vor allem wahrscheinlich an lösliche Proteine zusammen. Die gleich nach Karzinogenapplikation auftretende starke Silberkornbelegung nimmt nach 1–2 Tagen stark ab, die rad. akt. Substanzen sind nach 5 Tagen weitgehend aus der löslichen Gewebsfraktion verschwunden.

Description / Table of Contents: Abstract During pressure support ventilation (PSV), the timing of the breathing cycle is mainly controlled by the patient. Therefore, the delivered flow pattern during PSV might be better synchronised with the patient's demands than during volume-assisted ventilation. In several modern ventilators, inspiration is terminated when the inspiratory flow decreases to 25% of the initial peak value. However, this timing algorithm might cause premature inspiration termination if the initial peak flow is high. This could result not only in an increased risk of dyssynchronization between the patient and the ventilator, but also in reduced ventilatory support. On the other hand, a decreased peak flow might inappropriately increase the patient's inspiratory effort. The aim of our study was to evaluate the influence of the variation of the initial peak-flow rate during PSV on respiratory pattern and mechanical work of breathing. Patients. Six patients with chronic obstructive pulmonary disease (COPD) and six patients with no or minor nonobstructive lung pathology (control) were studied during PSV with different inspiratory flow rates by variations of the pressurisation time (Evita I, Drägerwerke, Lübeck, Germany). During the study period all patients were in stable circulatory conditions and in the weaning phase. Method. Patients were studied in a 45° semirecumbent position. Using the medium pressurization time (1 s) during PSV the inspiratory pressure was individually adjusted to obtain a tidal volume of about 8 ml/kg body weight. Thereafter, measurements were performed during five pressurization times (〈0.1, 0.5, 1, 1.5, 2 s defined as T 0.1, T 0.5, T 1, T 1.5 and T 2) in random order, while maintaining the pressure support setting at the ventilator. Between each measurement steady-state was attained. Positive end-exspiratory pressure (PEEP) and FIO2 were maintained at prestudy levels and remained constant during the study period. Informed consent was obtained from each patient or his next of kin. The study protocol was approved by the ethics committee of our medical faculty. Gas flow was measured at the proximal end of the endotracheal tube with a pneumotachometer (Fleisch no. 2, Fleisch, Lausanne, Switzerland) and a differential pressure transducer. Tracheal pressure (Paw) was determined in the same position with a second differential pressure transducer (Dr. Fenyves & Gut, Basel, Switzerland). Esophageal pressure (Pes) was obtained by a nasogastric balloon-catheter (Mallinckrodt, Argyle, NY, USA) connected to a further differential pressure transducer of the same type as described above. The balloon was positioned 2–3 cm above the dome of the diaphragm. The correct balloon position was verified by an occlusion test as described elsewhere. The data were sampled after A/D conversion with a frequency of 20 Hz and processed on an IBM-compatible PC. Software for data collection and processing was self-programmed using a commercially available software program (Asyst 4.0, Asyst Software Technologies, Rochester, NY, USA). Patient's inspiratory work of breathing Wpi (mJ/l) was calculated from Pes/volume plots according to the modified Campbell's diagram. Dynamic intrinsic PEEP (PEEPidyn) was obtained from esophageal pressure tracings relative to airway pressure as the deflection in Pes before the initiation of inspiratory flow Patient's additive work of breathing (Wadd) against ventilator system resistance was calculated directly from Paw/V tracings when Paw was lower than the pressure on the compliance curve. Two-way analysis of variance (ANOVA) was used for statistical analysis, followed by post hoc testing of the least significant difference between means for multiple comparisons. Probability values less than 0.05 were considered as significant. Results. COPD patients had significantly higher pressure support than control patients. With decreasing inspiratory flow, Wpi increased significantly in COPD patients. Additionally, the duct cycle (Ti/Ttot) significantly increased with decreased flow rates which resulted in a higher PEEPidyn compared to the baseline. At T 1.5 and T 2 with lower flow rates, the pre-set pressure support level was not achieved within inspiration in the COPD patients. Wadd increased significantly at T 1, T 1.5 and T 2 in COPD patients and at T 1.5 and T 2 in the control group. In one patient, premature termination of inspiration owing to high initial peak flow was corrected by adjustment of the inspiratory flow. Conclusion. Our results demonstrate that a decreased peak flow during PSV resulted in increased patient's work of breathing in COPD patients. During lower flow, the pre-set pressure support level was not attained and additional work had to be done on the ventilator system. Furthermore, the higher PEEPidyn during lower flow rates indicates a higher risk of dynamic pulmonary hyperinflation in patients with COPD. We conclude that the use of pressurization times ≥1 s to decrease inspiratory peak flow during PSV is of no benefit and should be avoided, particularly in COPD patients. However, in selected cases, slight decrease of inappropriately high peak flows might be useful for optimization of PSV setting to avoid premature termination of inspiration.

Description / Table of Contents: Summary The beneficial effects of biphasic positive airway pressure (BIPAP) ventilation in the case of long-term mechanical ventilation of patients with ARDS are well known. The aim of the present study was to compare the hemodynamic and ventilatory effects of BIPAP with synchronized intermittent mandatory ventilation combined with pressure support ventilation (S-IMV/PSV) in short-term ventilated patients after CABG surgery. After approval by the local ethics committee eighteen male patients were investigated. The patients were randomly assigned to one of two groups representing the respective ventilation mode. Hemodynamic measurements and blood gas analyses were performed during sedation with propofol, in awake patients having reached extubation criteria and after extubation. Statistical analysis of data was performed using non-parametric tests.¶   During the first set of measurements only inspiratory peak pressure was increased significantly by 20% in S-IMV/PSV ventilated patients compared to the BIPAP ventilated patients. In this study design the increased inspiratory peak pressure did not adversely affect hemodynamic parameters and blood gas analyses, as they did not vary with the ventilatory mode. After extubation the arterial oxygen partial pressure showed only a significant decrease by 19% in the S-IMV/PSV ventilated patients.¶   Our results demonstrate that both investigated ventilatory modes have comparable effects on hemodynamics when used for short-term ventilatory support in patients after cardiac surgery. The patient’s ability to breathe independently from the mechanical respiratory cycle during BIPAP ventilation improves the patient’s comfort and may reduce the risk of myocardial ischemia in the early postoperative period by minimizing the stress due to inadequate adaptation to the ventilator.