Does volatile sedation with sevoflurane allow spontaneous breathing during prolonged prone positioning in intubated ARDS patients? A retrospective observational feasibility trial

Anesthetic Gas Scavenging System for Gas Evacuation in the ICU

BACKGROUND

Inhaled sedation is increasing in ICUs, with active carbon filters (ACFs) commonly used for evacuating halogenated gases. However, the potential benefits of a waste anesthetic gas system (WAGS) similar to the ones used in operating rooms should be explored. To limit the suction over the flow sensor where the WAGS is connected on ICU ventilators, an anesthetic gas receiving system (AGRS) is required, constituting with the WAGS an active gas receiving and scavenging system (AGRSS). Ensuring that this whole device does not compromise the flow sensor reliability is crucial. The aim of this study was to compare various gas evacuation devices and assess the reliability of AGRSS on ICU ventilators.

METHODS

In this experimental study, pressures and flows were recorded during the ventilation of a test lung using various ventilator settings and gas evacuation methods: no device (reference condition), ACF, the WAGS alone, AGRSS (WAGS and AGRS together), and the expiratory valve connected to the medical vacuum system with the AGRS in between. Visual comparisons of the pressure and flow curves followed by a statistical analysis comparing median pressures and flows of each device to the reference were performed.

RESULTS

The test lung model demonstrated consistent comparability in pressures and flows among all devices, except for the WAGS alone, which exhibited discordance through significant overestimation or underestimation.

CONCLUSIONS

These findings indicate that using a WAGS with the AGRS system appeared to be reliable for managing gas evacuation in ICUs without compromising pressure or flow delivery. The data from this experimental trial should be confirmed with clinical studies involving human subjects. Given the increasing use of inhaled sedation in ICUs, these results support the daily application of the WAGS with the AGRS for gas evacuation, similar to its established use in anesthesiology.

Volatile anesthetics for lung- and diaphragm-protective sedation

This review explores the complex interactions between sedation and invasive ventilation and examines the potential of volatile anesthetics for lung- and diaphragm-protective sedation. In the early stages of invasive ventilation, many critically ill patients experience insufficient respiratory drive and effort, leading to compromised diaphragm function. Compared with common intravenous agents, inhaled sedation with volatile anesthetics better preserves respiratory drive, potentially helping to maintain diaphragm function during prolonged periods of invasive ventilation. In turn, higher concentrations of volatile anesthetics reduce the size of spontaneously generated tidal volumes, potentially reducing lung stress and strain and with that the risk of self-inflicted lung injury. Taken together, inhaled sedation may allow titration of respiratory drive to maintain inspiratory efforts within lung- and diaphragm-protective ranges. Particularly in patients who are expected to require prolonged invasive ventilation, in whom the restoration of adequate but safe inspiratory effort is crucial for successful weaning, inhaled sedation represents an attractive option for lung- and diaphragm-protective sedation. A technical limitation is ventilatory dead space introduced by volatile anesthetic reflectors, although this impact is minimal and comparable to ventilation with heat and moisture exchangers. Further studies are imperative for a comprehensive understanding of the specific effects of inhaled sedation on respiratory drive and effort and, ultimately, how this translates into patient-centered outcomes in critically ill patients.

Establishment and validation of intravenous anesthesia with dexmedetomidine for pigs under assisted spontaneous breathing: A preclinical model of intensive care conditions

Large animal models are frequently used to investigate new medical approaches. In most cases, animals are kept under general anesthesia and mandatory mechanical ventilation during the experiments. However, in some situations assisted spontaneous breathing is essential, e.g. when simulating conditions in a modern intensive care unit. Therefore, we established an anesthesia regime with dexmedetomidine and midazolam/ketamine in porcine models of assisted spontaneous breathing. The total intravenous anesthesia was used in lung healthy pigs, in pigs with oleic acid induced acute respiratory distress syndrome and in pigs with methacholine induced bronchopulmonary obstruction. We were able to maintain stable conditions of assisted spontaneous breathing without impairment of hemodynamic, respiratory or blood gas variables in lung healthy pigs and pigs with induced acute respiratory distress syndrome for a period of five hours and in pigs with induced bronchopulmonary obstruction for three hours. Total intravenous anesthesia containing dexmedetomidine enables stable conditions of assisted spontaneous breathing in healthy pigs, in pigs with induced acute respiratory distress syndrome and in pigs induced bronchopulmonary obstruction as models of intensive care unit conditions.

Improved understanding of the respiratory drive pathophysiology could lead to earlier spontaneous breathing in severe acute respiratory distress syndrome

Optimisation of the respiratory drive, as early as possible in the setting of severe acute respiratory distress syndrome (ARDS) and not its suppression, could be a new paradigm in the management of severe forms of ARDS. Severe ARDS is characterised by tachypnoea and hyperpnoea, a consequence of a high respiratory drive. Some patients require endotracheal intubation, controlled mechanical ventilation (CMV) and paralysis to prevent overt ventilatory failure and self-inflicted lung injury. Nevertheless, intubation, CMV and paralysis do not address per se the high respiratory drive, they only suppress it. Optimisation of the respiratory drive could be obtained by a multimodal approach that targets attenuation of fever, agitation, systemic and peripheral acidosis, inflammation, extravascular lung water and changes in carbon dioxide levels. The paradigm we present, based on pathophysiological considerations, is that as soon as these factors have been controlled, spontaneous breathing could resume because hypoxaemia is the least important input to the respiratory drive. Hypoxaemia could be handled by combining positive end-expiratory pressure (PEEP) to prevent early expiratory closure and low pressure support to minimise the work of breathing (WOB). 'Cooperative' sedation with alpha-2 agonists, supplemented with neuroleptics if required, is the pharmacological adjunct, administered immediately after intubation as the first-line sedation regimen during the multimodal approach. Given relative contraindications (hypovolaemia, auriculoventricular block, sick sinus syndrome), alpha-2 agonists can help attenuate or moderate fever, increased oxygen consumption VO2, agitation, high cardiac output, inflammation and acidosis. They may also help to preserve microcirculation, cognition and respiratory rhythm generation, thus promoting spontaneous breathing. Returning the physiology of respiratory, ventilatory, circulatory and autonomic systems to normal will support the paradigm of optimised respiratory drive favouring early spontaneous ventilation, at variance with deep sedation, extended paralysis, CMV and use of the prone position as therapeutic strategies in severe ARDS.

GLOSSARY

Glossary and Abbreviations_SDC.

Ventilatory Effects of Isoflurane Sedation via the Sedaconda ACD-S versus ACD-L: A Substudy of a Randomized Trial

Devices used to deliver inhaled sedation increase dead space ventilation. We therefore compared ventilatory effects among isoflurane sedation via the Sedaconda ACD-S (internal volume: 50 mL), isoflurane sedation via the Sedaconda ACD-L (100 mL), and propofol sedation with standard mechanical ventilation with heat and moisture exchangers (HME). This is a substudy of a randomized trial that compared inhaled isoflurane sedation via the ACD-S or ACD-L to intravenous propofol sedation in 301 intensive care patients. Data from the first 24 h after study inclusion were analyzed using linear mixed models. Primary outcome was minute ventilation. Secondary outcomes were tidal volume, respiratory rate, arterial carbon dioxide pressure, and isoflurane consumption. In total, 151 patients were randomized to propofol and 150 to isoflurane sedation; 64 patients received isoflurane via the ACD-S and 86 patients via the ACD-L. While use of the ACD-L was associated with higher minute ventilation (average difference (95% confidence interval): 1.3 (0.7, 1.8) L/min, p < 0.001), higher tidal volumes (44 (16, 72) mL, p = 0.002), higher respiratory rates (1.2 (0.1, 2.2) breaths/min, p = 0.025), and higher arterial carbon dioxide pressures (3.4 (1.2, 5.6) mmHg, p = 0.002), use of the ACD-S did not significantly affect ventilation compared to standard mechanical ventilation and sedation. Isoflurane consumption was slightly less with the ACD-L compared to the ACD-S (-0.7 (-1.3, 0.1) mL/h, p = 0.022). The Sedaconda ACD-S compared to the ACD-L is associated with reduced minute ventilation and does not significantly affect ventilation compared to a standard mechanical ventilation and sedation setting. The smaller ACD-S is therefore the device of choice to minimize impact on ventilation, especially in patients with a limited ability to compensate (e.g., COPD patients). Volatile anesthetic consumption is slightly higher with the ACD-S compared to the ACD-L.

Increased Respiratory Drive after Prolonged Isoflurane Sedation: A Retrospective Cohort Study

Low-dose isoflurane stimulates spontaneous breathing. We, therefore, tested the hypothesis that isoflurane compared to propofol sedation for at least 48 h is associated with increased respiratory drive in intensive care patients after sedation stop. All patients in our intensive care unit receiving at least 48 h of isoflurane or propofol sedation in 2019 were included. The primary outcome was increased respiratory drive over 72 h after sedation stop, defined as an arterial carbon dioxide pressure below 35 mmHg and a base excess more than −2 mmol/L. Secondary outcomes were acid–base balance and ventilatory parameters. We analyzed 64 patients, 23 patients sedated with isoflurane and 41 patients sedated with propofol. Patients sedated with isoflurane were about three times as likely to show increased respiratory drive after sedation stop than those sedated with propofol: adjusted risk ratio [95% confidence interval]: 2.9 [1.3, 6.5], p = 0.010. After sedation stop, tidal volumes were significantly greater and arterial carbon dioxide partial pressures were significantly lower, while respiratory rates did not differ in isoflurane versus propofol-sedated patients. In conclusion, prolonged isoflurane use in intensive care patients is associated with increased respiratory drive after sedation stop. Beneficial effects of isoflurane sedation on respiratory drive may, thus, extend beyond the actual period of sedation.

Inhaled sedation in the intensive care unit

Inhaled sedation with halogenated agents, such as isoflurane or sevoflurane, is now feasible in intensive care unit (ICU) patients through dedicated vaporisers and scavenging systems. Such a sedation strategy requires specific equipment and adequate training of ICU teams. Isoflurane and sevoflurane have ideal pharmacological properties that allow efficient, well-tolerated, and titratable light-to-deep sedation. In addition to their function as sedative agents, these molecules may have clinical benefits that could be especially relevant to ICU patients. Our goal was to summarise the pharmacological basis and practical aspects of inhaled ICU sedation, review the available evidence supporting inhaled sedation as a viable alternative to intravenous sedation, and discuss the remaining areas of uncertainty and future perspectives of development.

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 spontaneous breathing in ventilated surgical intensive care patients and evaluated potential 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 adjustments for sufentanil dose and arterial carbon dioxide partial pressure, patients sedated with isoflurane were twice as likely to breathe spontaneously than those sedated 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.

Intensive care nurses' experiences using volatile anaesthetics in the intensive care unit: An exploratory study

OBJECTIVE

To explore the experiences intensive care nurses have with volatile anaesthetics in the intensive care unit.

RESEARCH METHODOLOGY AND DESIGN

A qualitative exploratory and descriptive design was used. Data were collected in 2019 from individual interviews with nine intensive care nurses, who were recruited using purposive sampling. Data were analysed using systematic text condensation.

SETTING

The study was undertaken in two general intensive care units from different university hospitals in Norway where volatile anaesthetics were utilised.

FINDINGS

Three categories emerged from the data analysis: experiencing the benefits of volatile anaesthetics; coping with unfamiliarity in handling volatile anaesthetics; and meeting challenges related to volatile anaesthetics in practice.

CONCLUSION

The intensive care nurses had positive experiences related to administering volatile anaesthetics in the intensive care unit and responded positively to the prospect of using it more often. Because volatile anaesthetics were rarely used in their units, the participants felt uncertain regarding its use due to unfamiliarity. Collegial support and guidelines were perceived as pivotal in helping them cope with this uncertainty. The participants also experienced several challenges in using volatile anaesthetics in the intensive care unit, with ambient pollution being regarded as the main challenge.

Inhaled isoflurane via the anaesthetic conserving device versus propofol for sedation of invasively ventilated patients in intensive care units in Germany and Slovenia: an open-label, phase 3, randomised controlled, non-inferiority trial

BACKGROUND

Previous studies indicate that isoflurane could be useful for the sedation of patients in the intensive care unit (ICU), but prospective studies evaluating isoflurane's efficacy have been small. The aim of this study was to test whether the sedation with isoflurane was non-inferior to sedation with propofol.

METHODS

This phase 3, randomised, controlled, open-label non-inferiority trial evaluated the efficacy and safety of up to 54 h of isoflurane compared with propofol in adults (aged ≥18 years) who were invasively ventilated in ICUs in Germany (21 sites) and Slovenia (three sites). Patients were randomly assigned (1:1) to isoflurane inhalation via the Sedaconda anaesthetic conserving device (ACD; Sedana Medical AB, Danderyd, Sweden; ACD-L [dead space 100 mL] or ACD-S [dead space 50 mL]) or intravenous propofol infusion (20 mg/mL) for 48 h (range 42-54) using permuted block randomisation with a centralised electronic randomisation system. The primary endpoint was percentage of time in Richmond Agitation-Sedation Scale (RASS) range -1 to -4, assessed in eligible participants with at least 12 h sedation (the per-protocol population), five or more RASS measurements, and no major protocol violations, with a non-inferiority margin of 15%. Key secondary endpoints were opioid requirements, spontaneous breathing, time to wake-up and extubation, and adverse events. Safety was assessed in all patients who received at least one dose. The trial is complete and registered with EudraCT, 2016-004551-67.

FINDINGS

Between July 2, 2017, and Jan 12, 2020, 338 patients were enrolled and 301 (89%) were randomly assigned to isoflurane (n=150) or propofol (n=151). 146 patients (97%) in each group completed the 24-h follow-up. 146 (97%) patients in the isoflurane group and 148 (98%) of patients in the propofol group were included in the per-protocol analysis of the primary endpoint. Least-squares mean percentage of time in RASS target range was 90·7% (95% CI 86·8-94·6) for isoflurane and 91·1% (87·2-95·1) for propofol. With isoflurane sedation, opioid dose intensity was 29% lower than with propofol for the overall sedation period (0·22 [0·12-0·34] vs 0·32 [0·21-0·42] mg/kg per h morphine equivalent dose, p=0·0036) and spontaneous breathing was more frequent on day 1 (odds ratio [OR] 1·72 [1·12-2·64], generalised mixed linear model p=0·013, with estimated rates of 50% of observations with isoflurane vs 37% with propofol). Extubation times were short and median wake-up was significantly faster after isoflurane on day 2 (20 min [IQR 10-30] vs 30 min [11-120]; Cox regression p=0·0011). The most common adverse events by treatment group (isoflurane vs propofol) were: hypertension (ten [7%] of 150 vs two [1%] of 151), delirium (eight [5%] vs seven [5%]), oliguria (seven [5%] vs six [4%]), and atrial fibrillation (five [3%] vs four [3%]).

INTERPRETATION

These results support the use of isoflurane in invasively ventilated patients who have a clinical need for sedation.

FUNDING

Sedana Medical AB.

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.

Inhaled sedation with sevoflurane in critically ill children during extracorporeal membrane oxygenation

Sedation can be challenging in critically ill children. Inhaled anesthetics such as sevoflurane have proved to be useful in difficult or long-term sedation. However, its use in children out of the operating room is still limited and little is yet known about its use in patients undergoing ECMO with no previous reports in children. The objective is to assess the effectiveness and safety of sevoflurane during ECMO in two pediatric patients. Sedation was successfully achieved in both patients, and patients' contribution to breathing was possible even with deep sedation. There were not any side effects during sevoflurane treatment or after withdrawal.

Analgesia and sedation in patients with ARDS

Acute Respiratory Distress Syndrome (ARDS) is one of the most demanding conditions in an Intensive Care Unit (ICU). Management of analgesia and sedation in ARDS is particularly challenging. An expert panel was convened to produce a "state-of-the-art" article to support clinicians in the optimal management of analgesia/sedation in mechanically ventilated adults with ARDS, including those with COVID-19. Current ICU analgesia/sedation guidelines promote analgesia first and minimization of sedation, wakefulness, delirium prevention and early rehabilitation to facilitate ventilator and ICU liberation. However, these strategies cannot always be applied to patients with ARDS who sometimes require deep sedation and/or paralysis. Patients with severe ARDS may be under-represented in analgesia/sedation studies and currently recommended strategies may not be feasible. With lightened sedation, distress-related symptoms (e.g., pain and discomfort, anxiety, dyspnea) and patient-ventilator asynchrony should be systematically assessed and managed through interprofessional collaboration, prioritizing analgesia and anxiolysis. Adaptation of ventilator settings (e.g., use of a pressure-set mode, spontaneous breathing, sensitive inspiratory trigger) should be systematically considered before additional medications are administered. Managing the mechanical ventilator is of paramount importance to avoid the unnecessary use of deep sedation and/or paralysis. Therefore, applying an "ABCDEF-R" bundle (R = Respiratory-drive-control) may be beneficial in ARDS patients. Further studies are needed, especially regarding the use and long-term effects of fast-offset drugs (e.g., remifentanil, volatile anesthetics) and the electrophysiological assessment of analgesia/sedation (e.g., electroencephalogram devices, heart-rate variability, and video pupillometry). This review is particularly relevant during the COVID-19 pandemic given drug shortages and limited ICU-bed capacity.