Reflexionseffizienzen der AnaConDa-50 und AnaConDa-100

In der vorliegenden Arbeit wurden die verkleinerte Version ACD50 und ACD100 in einer Laborstudie mit einer Testlunge verglichen. Drei Versuchsreihen wurden durchgeführt. In Versuchsreihe 1 wurde der Einfluss des Totraums des Reflexionsdevices ACD50 (50 mL) und ACD100 (100 mL) auf die Isoflurankonzentration in der Testlunge (Cleer) untersucht. Der Reflektor von beiden Reflexionsdevices wurde für die Versuchsreihe 1 ausgebaut und die jeweilige Isoflurankonzentration in der Testlunge (Cleer) mit unterschiedlichen Kombinationen Tidalvolumen/Infusionsrate (Kombination VT/IR) bestimmt. Cleer mit ACD50 unterscheidet sich signifikant von Cleer mit ACD100 für eine gleiche Kombination VT/IR. Unabhängig vom Reflektor beeinflusst das innere Volumen der AnaConDa das Reflexionsphänomen. Dies kann als Volumenreflexion bezeichnet werden. Die zentral in der Testlunge und ohne Reflektor gemessene Isoflurankonzentration (Cleer) unterscheidet sich von der, in Analogie zu älteren Arbeiten, kalkulierten Isoflurankonzentration auf der Respiratorseite (Closs). Dies kann neben der Volumenreflexion auch durch einen hypostatischen Effekt erklärt werden, dass das Isofluran dank seiner höheren Dichte in der Testlunge nach unten sinkt. Die Versuchsreihe 2 wurde mit unmodifizierten ACD50 und ACD100 unter Standardbedingungen (DRY, 23°C, ohne Kohlendioxid und ohne zusätzliche Luftfeuchtigkeit) durchgeführt. Unter DRY ist die Reflexionseffizienz des ACD50 für ein Isoflurandampfvolumen in der Ausatemluft Vexh. < 4 mL höher als die des ACD100. Wird dieses Isoflurandampfvolumen in der Ausatemluft überschritten, ist die Reflexionseffizienz des ACD100 überlegen. Unter DRY und im klinischen Bereich (bis 1 MAC) beträgt die Reflexionseffizienz von beiden Reflexionsdevices ca. 90 %. Ab einem bestimmten Isoflurandampfvolumen ist der Reflektor gesättigt und mehr Isofluranmoleküle gehen durch den Reflektor auf der Respiratorseite verloren. Dieses Phänomen wird „Spill-over“ genannt. Die Spill-over-Grenze oder Reflexionskapazität des ACD50 unter DRY wurde in dieser Arbeit bestimmt und entspricht einem Isoflurandampfvolumen in der Ausatemluft Vexh.max.ACD50 von 7 mL. Die Reflexionskapazität des ACD100 Vexh.max.ACD100 wurde bereits in früheren Arbeiten bestimmt und entspricht 10 mL Isoflurandampfvolumen. Die Versuchsreihe 3 wurde mit unmodifizierten ACD50 und ACD100 unter simulierten physiologischen Bedingungen durchgeführt (CLIN). Die Testlunge wurde in einem Aquarium mit warmem Wasser (37°C) zum Teil eingetaucht. Die Luftfeuchtigkeit in der Testlunge betrug mindestens 90 %. Kohlendioxid wurde in die Testlunge geleitet, sodass physiologische CO2-Konzentrationen zwischen 35 mmHg und 45 mmHg entstanden. Unter CLIN war die Reflexionseffizienz des ACD50 der Reflexionseffizienz des ACD100 unterlegen. Unter CLIN ist die Reflexionseffizienz für beide Devices schlechter als unter DRY. Offenbar beeinträchtigt die höhere Lufttemperatur die zusätzliche Luftfeuchtigkeit oder die Anwesenheit von Kohlendioxid die Reflexion von Isofluran. Der Einfluss des eingestellten Tidalvolumens auf die Reflexionseffizienz ist unter CLIN mit ACD50 größer als mit ACD100. Mit einem Tidalvolumen 300 mL wird mit ACD50 eine signifikant bessere Reflexionseffizienz erzielt (76 % bis ca. 83 %) als mit einem Tidalvolumen 500 mL (67 % bis ca. 76 %). Unter CLIN variiert die Reflexionseffizienz mit ACD100 mit Umstellung des Tidalvolumens weniger; für beide Tidalvolumina beträgt die Reflexionseffizienz 80 % bis ca. 88 %. Eine klare Grenze für ein Spill-over-Phänomen konnte in der vorliegenden Arbeit unter CLIN nicht nachgewiesen werden. Stattdessen sinkt die Reflexionseffizienz mit steigendem Isoflurandampfvolumen allmählich ab. Die Reflexionseffizienz wird durch Luftfeuchtigkeit, Körperwärme und Kohlendioxid beeinträchtigt und ist deshalb unter klinischen Bedingungen geringer als unter trockenen Laborbedingungen. Dennoch ist sie auch für die kleinere Version für mittlere Tidalvolumina bis 500 mL und im Konzentrationsbereich bis 1 MAC mit etwa 75% ausreichend hoch.Title: Reflection efficiencies of AnaConDa-50 and AnaConDa-100 In this work, we compared the small AnaConDa Version ACD50 to the ACD100 in a bench study with a test lung. Three experimental series were realized. In the first experimental series, we analyzed the influence of the internal dead-space of the reflection devices ACD50 (50 mL) and ACD100 (100 mL) on the Isoflurane concentration inside the test lung (Cleer). We removed the reflector of both reflection devices for the first experimental series. The respective isoflurane concentration inside the test lung (Cleer) was measured with different combinations of Tidal volumes/Infusion rates (VT/IR). Cleer with ACD50 is significantly different from Cleer with ACD100 for the same combination of VT/IR. The dead-space of the reflection device has, independently of the reflector, an influence on the reflection of isoflurane. This effect can be called „Volume reflection“. The isoflurane concentration Cleer in the first experimental series was measured in the center of the test lung. Cleer is different from the isoflurane concentration on the ventilator side Closs, calculated according to previous publications. Additionally to the volume reflection, a hypostatic effect can explain the difference in Cleer and Closs, since isoflurane sinks in the test lung due to its higher density compared to air. In the second experimental series, we used unmodified ACD50 and ACD100 under standard conditions (DRY, 23°C, no additional carbondioxyd or humidity). The reflection efficiency of ACD50 is higher as that of ACD100 for an isoflurane volume in the expiratory air smaller than 4 mL. The ACD100 has a higher reflection efficiency above this isoflurane volume in the expiratory air. The reflection efficiency of both devices under DRY in clinically relevant dosages (up to 1 MAC) is approximately 90%. Above a certain isoflurane volume in the expiratory air, the reflector is saturated and isoflurane molecules get lost increasingly through the reflector joining its ventilator side. This phenomenon is known as spill-over. The spill-over limit or reflection capacity of ACD50 under DRY was determined in this work and corresponds to 7 mL isoflurane volume in the expiratory air. The reflection capacity of ACD100 was already determined in a previous work and corresponds to 10 mL isoflurane volume in the expiratory air. In the third experimental series, we used unmodified ACD50 and ACD100 under simulated physiological conditions (CLIN). The test lung was partially submerged in an aquarium under warm water (37°C). The air humidity inside the test lung was higher than 90%. Physiological concentration of carbon dioxide (35 mmHg – 45 mmHg) were added inside the test lung. The reflection efficiency of ACD50 under CLIN was lower than the reflection efficiency of ACD100. The reflection efficiency of each device was lower under CLIN compared to DRY conditions. Obviously, the higher air temperature, the additional air humidity and the presence of carbondioxyd impairs the isoflurane reflection. Under CLIN, reflection efficiency of ACD50 deteriorates earlier, when tidal volume is increased, compared to ACD100. At 0.6 MAC, with ACD50, efficiency is 83% for a tidal volume of 300 mL and 74% for 500 mL; and with ACD100, it is 88% or 80% for each tidal volume. A spill-over limit under CLIN was not detected in this work. Instead, the reflection efficiency for both devices fell gradually with increasing isoflurane volume in the expired air. Reflection efficiency is influenced by humidity, body temperature and carbon dioxide and is therefore smaller under clinical compared to dry laboratory conditions. Nevertheless, even for the smaller version, efficiency is sufficient for tidal volumes up to 500 mL tidal volume and for anaesthetic concentrations up to 1 MAC, amounting to approximately 75 %.Keine

Comparison of isoflurane and propofol sedation in critically ill COVID-19 patients-a retrospective chart review

Purpose In this retrospective study, we compared inhaled sedation with isoflurane to intravenous propofol in invasively ventilated COVID-19 patients with ARDS (Acute Respiratory Distress Syndrome). Methods Charts of all 20 patients with COVID-19 ARDS admitted to the ICU of a German University Hospital during the first wave of the pandemic between 22/03/2020 and 21/04/2020 were reviewed. Among screened 333 days, isoflurane was used in 97 days, while in 187 days, propofol was used for 12 h or more. The effect and dose of these two sedatives were compared. Mixed sedation days were excluded. Results Patients’ age (median [interquartile range]) was 64 (60–68) years. They were invasively ventilated for 36 [21–50] days. End-tidal isoflurane concentrations were high (0.96 ± 0.41 Vol %); multiple linear regression yielded the ratio (isoflurane infusion rate)/(minute ventilation) as the single best predictor. Infusion rates were decreased under ECMO (3.5 ± 1.4 versus 7.1 ± 3.2 ml∙h−1; p < 0.001). In five patients, the maximum recommended dose of propofol of 4 mg∙hour−1∙kg−1ABW was exceeded on several days. On isoflurane compared to propofol days, neuro-muscular blocking agents (NMBAs) were used less frequently (11% versus 21%; p < 0.05), as were co-sedatives (7% versus 31%, p < 0.001); daily opioid doses were lower (720 [720–960] versus 1080 [720–1620] mg morphine equivalents, p < 0.001); and RASS scores indicated deeper levels of sedation (− 4.0 [− 4.0 to − 3.0] versus − 3.0 [− 3.6 to − 2.5]; p < 0.01). Conclusion Isoflurane provided sufficient sedation with less NMBAs, less polypharmacy and lower opioid doses compared to propofol. High doses of both drugs were needed in severely ill COVID-19 patients

Increasing the reflection efficiency of the Sedaconda ACD-S by heating and cooling the anaesthetic reflector: a bench study using a test lung

Background As volatile anaesthetic gases contribute to global warming, improving the efciency of their delivery can reduce their environmental impact. This can be achieved by rebreathing from a circle system, but also by anaesthetic refection with an open intensive care ventilator. We investigated whether the efciency of such a refection system could be increased by warming the refector during inspiration and cooling it during expiration (thermocycling). Methods The Sedaconda-ACD-S (Sedana Medical, Danderyd, Sweden) was connected between an intensive care ventilator and a test lung. Liquid isofurane was infused into the device at 0.5, 1.0, 2.0 and 5.0 mL/h; ventilator settings were 500 mL tidal volume, 12 bpm, 21% oxygen. Isofurane concentrations were measured inside the test lung after equilibration. Thermocycling was achieved by heating the breathing gas in the inspiratory hose to 37 °C via a heated humidifer without water. Breathing gas expired from the test lung was cooled to 14 °C before reaching the ACD-S. In the test lung, body temperature pressure saturated conditions prevailed. Isofurane concentrations and refective efciency were compared between thermocycling and control conditions. Results With thermocycling higher isofurane concentrations in the test lung were measured for all infusion rates studied. Interpolation of data showed that for achieving 0.4 (0.6) Vol% isofurane, the infusion rate can be reduced from 1.2 to 0.7 (2.0 to 1.2) mL/h or else to 56% (58%) of control. Conclusion Thermocycling of the anaesthetic gas considerably increases the efciency of the anaesthetic refector and reduces anaesthetic consumption by almost half in a test lung model. Given that cooling can be miniaturized, this method carries a potential for further saving anaesthetics in clinical practice in the operating theatre as well as for inhaled sedation in the ICU

Isoflurane promotes early spontaneous breathing in ventilated intensive care patients: A post hoc subgroup analysis of a randomized trial

Background: Spontaneous breathing is desirable in most ventilated patients. We therefore studied the influence of isoflurane versus propofol sedation on early spon taneous breathing in ventilated surgical intensive care patients and evaluated poten tial mediation by opioids and arterial carbon dioxide during the first 20 h of study sedation. Methods: We included a single-center subgroup of 66 patients, who participated in a large multi-center trial assessing efficacy and safety of isoflurane sedation, with 33 patients each randomized to isoflurane or propofol sedation. Both sedatives were titrated to a sedation depth of −4 to −1 on the Richmond Agitation Sedation Scale. The primary outcome was the fraction of time during which patients breathed spontaneously. Results: Baseline characteristics of isoflurane and propofol-sedated patients were well balanced. There were no substantive differences in management or treatment aside from sedation, and isoflurane and propofol provided nearly identical sedation depths. The mean fraction of time spent spontaneously breathing was 82% [95% CI: 69, 90] in patients sedated with isoflurane compared to 35% [95% CI: 22, 51] in those assigned to propofol: median difference: 61% [95% CI: 14, 89], p < .001. After ad justments for sufentanil dose and arterial carbon dioxide partial pressure, patients sedated with isoflurane were twice as likely to breathe spontaneously than those se dated with propofol: adjusted risk ratio: 2.2 [95%CI: 1.4, 3.3], p < .001. Conclusions: Isoflurane compared to propofol sedation promotes early spontaneous breathing in deeply sedated ventilated intensive care patients. The benefit appears to be a direct effect isoflurane rather than being mediated by opioids or arterial carbon dioxide