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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: Abstract In clinical practice, the administration of supplementary albumin often depends on the measured plasma concentration of total protein (TPC). A TPC of less than 5 g/dl is generally accepted as an indication for albumin therapy, assuming an albumin concentration of less than 2.5 g/dl. However, a physiological relation between TPC and albumin cannot be expected in critically ill patients, and thus, measurement of TPC may be misleading as an indicator for the use of albumin. Therefore, we investigated the sensitivity and specificity of TPC testing for diagnosing hypoalbuminaemia requiring treatment. Methods. In this prospective study, 210 consecutive patients were included. Protein electrophoresis was performed three times a week; the second electrophoresis was selected for evaluation. Applied statistical analysis revealed the number of positive total protein tests indicating hypalbuminaemia requiring treatment (sensitivity) and the number of negative with tolerably reduced albumin concentrations (specificity). Results. Of the investigated patients, 27.6% had normal TPCs between 6.2 and 8.0 g/dl. In 81.9% of cases an albumin concentration below 3.5 g/dl was found, while 43 patients had a concentration below 2.5 g/dl. The sensitivity and specificity of TPC measurement for the diagnosis of clinically relevant hypoalbuminaemia (albumin concentration 〈2.5 g/dl) was calculated at different cutoff points for total protein. With a TPC of 6.0 g/dl, the sensitivity was 0.96 and the specificity 0.44. With a cutoff point of 5.0 g/dl, the sensitivity was reduced to 0.65 and specificity increased to 0.86. Finally, with a TPC of 4.0 g/dl sensitivity was 0.25 and specificity almost 1. Conclusions. Depending on the cutoff point for TPC, a relevant albumin requirement would frequently not be detected. In other cases, a need for albumin would be assumed from a reduced TPC even though the albumin concentration still exceeded 2.5 g/dl. Therefore, determination of TPC is not a suitable indicator of the need for albumin replacement. As a result, we suggest routine determination of albumin concentrations instead of TPC.

Description / Table of Contents: Summary There is evidence that diastolic function is a major determinant of overall cardiac performance. Intraoperative use of transesophageal echocardiography (TEE) enables Doppler measurement of mitral inflow pattern (E/A ratio). The E/A ratio is suggested to be a reliable index of changes in myocardial relaxation. In the present study we compared the time course of the E/A ratio and the time constant of myocardial relaxation (τ) assessed by direct left ventricular pressure recordings in patients before and after cardiopulmonary bypass (CPB). After ethical approval, 12 patients undergoing CABG surgery were studied. Measurements of the E/A ratio and τ were performed after induction of anesthesia (I), immediately prior to CPB with the pericardium open (II), 5 min after CPB (III), and after sternal closure (IV). Time constant of myocardial relaxation was calculated as the reciprocal value of the slope of the left ventricular dP/dt and left ventricular pressure plot. The E/A ratio was significantly decreased at the end of surgery (IV). In contrast, τ was increased immediately after CPB, but decreased after sternal closure (IV). Cardiac index and heart rate both increased after CPB.¶ The results of the present study demonstrate that diastolic dysfunction occurred immediately after CPB, as indicated by an increase in the time constant of myocardial relaxation. However, τ improved rapidly to pre-CPB values. The E/A ratio alone failed to detect the initial post-CPB alteration in left ventricular relaxation.

Description / Table of Contents: Zusammenfassung An 16 druckunterstützt beatmeten Patienten, davon acht mit chronisch obstruktiver Lungenerkrankung (COPD) und acht ohne obstruktive Lungenkrankheiten wurde der Einfluß eines PEEP von 5 cmH2O und einer Druckunterstützung von 5 und 10 cmH2O auf die mechanische Atemarbeit und andere atemmechanische Meßgrößen untersucht. Sowohl durch PEEP wie auch durch Druckunterstützung konnte die Atemarbeit gesenkt werden. Die Kombination beider Maßnahmen wirkte additiv. Ein PEEP von 5 cm H2O und eine Druckunterstützung von 10 cmH2O senkte die Atemarbeit im Durchschnitt um mehr als 50% in beiden Patientengruppen. Ohne Druckunterstützung leistet der Patienten mehr als 20% seiner gesamten Atemarbeit auf Widerstände des Beatmungssystems (z.B. Gasflußanlieferung, Triggermechanismus etc.). Durch 10 cmH2O Druckunterstützung war dieser Atemarbeitsanteil nahezu kompensiert und zu vernachlässigen. Ein bestehender intrinsischer PEEP bei COPD-Patienten erhöhte die Atemarbeit und wurde durch Applikation eines externen PEEP vermindert. Die Höhe der Atemarbeit war in unserer Untersuchung interindividuell sehr unterschiedlich. Daher erscheint uns eine individuelle Anpassung von PEEP und Druckunterstützung anhand der gemessenen Atemarbeit sinnvoll.

Description / Table of Contents: Zusammenfassung Perioperative pulmonale Komplikationen treten bei Patienten mit vorbestehenden Lungenerkrankungen viel häufiger auf als bei lungengesunden Patienten. Häufigste perioperative respiratorische Komplikationen sind Reduktion der Lungenvolumina, Pneumonie und Bronchospastik. Bei der Identifikation von pulmonalen Risikopatienten stellen Anamnese und klinische Untersuchung die wichtigsten Instrumente dar. Wichtigste pulmonale Risikofaktoren sind chronische Lungenerkrankung, Oberbauch- und Thoraxoperation, Adipositas und Rauchen. Häufigste vorbestehende respiratorische Erkrankungen sind chronisch obstruktive Lungenerkrankungen (COPD und Asthma), während restriktive Lungenerkrankungen eher selten sind. Das Risiko einer pulmonalen Komplikation kann reduziert werden, wenn Genese und Ausprägung der Lungenfunktionsstörung bekannt sind und entweder präoperativ, spätestens aber postoperativ eine adäquate Therapie eingeleitet wird bzw. ein entsprechend geeignetes Anästhesieverfahren und optimale Anästhetika gewählt werden.