Use of xenon as a sedative for patients receiving critical care

TIVA versus Inhalational Agents for Pediatric Cardiac Intensive Care

The field of pediatric intensive care has come a long way, especially with the recognition that adequate sedation and analgesia form an imperative cornerstone of patient management. With various drugs available for the same, the debate continues as to which is the better: total intravenous anesthesia (TIVA) or inhalational agents. While each have their own advantages and disadvantages, in the present era of balance toward the IV agents, we should not forget the edge our volatile agents (VAs) might have in special scenarios. And ultimately as anesthesiologists, let us not forget that be it knob and dial, or syringe and plunger, our aim is to put pain to sleep and awaken a new faith to breathe.

Better haemodynamic stability under xenon anaesthesia than under isoflurane anaesthesia during partial nephrectomy - a secondary analysis of a randomised controlled trial

Background

Renal dysfunction following intraoperative arterial hypotension is mainly caused by an insufficient renal blood flow. It is associated with higher mortality and morbidity rates. We hypothesised that the intraoperative haemodynamics are more stable during xenon anaesthesia than during isoflurane anaesthesia in patients undergoing partial nephrectomy.

Methods

We performed a secondary analysis of the haemodynamic variables collected during the randomised, single-blinded, single-centre PaNeX study, which analysed the postoperative renal function in 46 patients who underwent partial nephrectomy. The patients received either xenon or isoflurane anaesthesia with 1:1 allocation ratio. We analysed the duration of the intraoperative systolic blood pressure decrease by > 40% from baseline values and the cumulative duration of a mean arterial blood pressure (MAP) of < 65 mmHg as primary outcomes. The secondary outcomes were related to other blood pressure thresholds, the amount of administered norepinephrine, and the analysis of confounding factors on the haemodynamic stability.

Results

The periods of an MAP of < 65 mmHg were significantly shorter in the xenon group than in the isoflurane group. The medians [interquartile range] were 0 [0–10.0] and 25.0 [10.0–47.5] minutes, for the xenon and isoflurane group, respectively (P = 0.002). However, the cumulative duration of a systolic blood pressure decrease by > 40% did not significantly differ between the groups (P = 0.51). The periods with a systolic blood pressure decrease by 20% from baseline, MAP decrease to values < 60 mmHg, and the need for norepinephrine, as well as the cumulative dose of norepinephrine were significantly shorter and lower, respectively, in the xenon group. The confounding factors, such as demographic data, surgical technique, or anaesthesia data, were similar in the two groups.

Conclusion

The patients undergoing xenon anaesthesia showed a better haemodynamic stability, which might be attributed to the xenon properties. The indirect effect of xenon anaesthesia might be of importance for the preservation of renal function during renal surgery and needs further elaboration.

Trial registration

ClinicalTrials.gov: NCT01839084. Registered 24 April 2013.

Electronic supplementary material

The online version of this article (10.1186/s12871-019-0799-2) contains supplementary material, which is available to authorized users.

Development of a hybrid CFD-PBPK model to predict the transport of xenon gas around a human respiratory system to systemic regions

Administering incorrect doses of conventional anesthetic agents through the pulmonary route can cause potential health risks such as blood coagulation, platelet dysfunction, and deteriorating organ function. As an alternative, xenon can minimize the impact on the cardiovascular system and provide the neuroprotective effect, hemodynamic stability, and fast recovery. However, the inhalation pattern still needs to be carefully monitored and controlled to avoid health risks caused by over administering xenon to patients during unconsciousness. Thus, high-resolution lung absorption and whole-body translocation data are critically needed to fully understand how to administer the gas and coordinate with the patient to accurately control the dose. Clinical studies are not able to provide accurate dosimetry data due to their limited operational flexibility and imaging resolution. Therefore, a computational fluid dynamics (CFD) model was employed in this study to simulate the transport and absorption of the inhaled xenon which is connected with a physiologically based pharmacokinetic (PBPK) model to predict the translocation into the systemic regions. To study the effects of different breathing patterns on xenon transport dynamics in the human body, a realistic breathing waveform and two steady-state flow rates with inhalation durations of 2 and 1.5 seconds were selected. For the realistic breathing cycle, the inhalation-exhalation periods are defined for a human at rest and the other two cases have a fixed volumetric flow rate of 15 L/min. As the two latter cases only simulate the inspiratory phase, a 1-second holding time was applied to represent the missing periods of the full breathing time. Simulations were performed in a subject-specific human upper airway configuration from mouth to G6. Numerical results show that with the accurate lung uptake predictions obtained from the CFD model, the hybrid CFD-PBPK model with TRANSIT compartments generates more precise and breath-specific trends compared to simple PBPK models. Numerical results demonstrate that breathing pattern can significantly influence the xenon uptake in the human body, which can be utilized as a critical factor to be coordinated by clinicians to achieve the optimized xenon dose. Furthermore, parametric analyses were performed for the influence of breathing patterns on local airflow distributions, gas species translocations, and lung elimination mechanisms followed by species diffusion into the systemic regions.

Xenon: An Emerging Neuroprotectant With Potential Application for Cardiac Arrest Care

Xenon is an inert, highly polarizable noble gas with demonstrated safety and application in general anesthesia for over 50 years. A potent inhibitor of the N-methyl-D-aspartate subtype of glutamate receptors, xenon has a well-documented ameliorating effect on excitotoxic neuronal injury in numerous cellular and animal models of hypoxic-ischemic brain injury. The most important determinant of overall survival and morbidity in out-of-hospital cardiac arrest is the severity of neurological injury. The only approved neuroprotective strategy in this setting is mild therapeutic hypothermia, which has demonstrated significant, albeit modest, improvements in mortality. The combination therapy of therapeutic hypothermia and xenon in porcine models of cardiac arrest has shown a greater improvement in functional outcomes than either intervention alone, thereby prompting the study of combination therapy in randomized clinical trials. The treatment of postarrest patients with xenon and mild hypothermia is safe and demonstrates favorable cardiovascular features, including a reduced heart rate, a reduction in troponin elevations, and a decreased need for vasopressors. Combination therapy is superior in protecting white matter integrity than hypothermia alone, but did not significantly impact neurological outcomes at 6-month follow-up. Despite an abundance of preclinical evidence supporting xenon's neuroprotective properties, its translational potential in postcardiac arrest care is indeterminate due to a lack of adequately-powered studies.

Xenon Combined With Hypothermia in Perinatal Hypoxic-Ischemic Encephalopathy: A Noble Gas, a Noble Mission

Perinatal hypoxia-ischemia is a major cause of neonatal morbidity. It generates primary neuronal damage of the neonatal brain and later secondary damage when reperfusion of the ischemic brain tissue causes a surge of oxygen free radicals and inflammation. This post-hypoxic-ischemic brain damage is a leading cause of motor and intellectual disabilities in survivors. Research worldwide has focused on mitigating this injury. Mild or moderate hypothermia is the standard treatment in many centers. However, its benefit is modest and the search for combinatorial effective neuroprotectants continues. This review focuses on xenon as one such agent. The use of mild to moderate hypothermia is reviewed first. Then promising results on the use of xenon to potentiate the effect of hypothermia in in vitro and in vivo animal experiments are discussed. In the first feasibility study on human neonates, researchers found a significant benefit of using 50% xenon for 18 hours in addition to 72 hours of hypothermia. Yet, this additional benefit of xenon was lacking in a larger cohort study, potentially because xenon was used beyond six hours of birth. The future of using xenon is promising, but further clinical studies are awaited to confirm the feasibility of its routine use and its optimal timing, concentration, and duration, for human neonatal hypoxia-ischemia.

Neuroprotection and neurotoxicity in the developing brain: an update on the effects of dexmedetomidine and xenon

Growing and consistent preclinical evidence, combined with early clinical epidemiological observations, suggest potentially neurotoxic effects of commonly used anesthetic agents in the developing brain. This has prompted the FDA to issue a safety warning for all sedatives and anesthetics approved for use in children under three years of age. Recent studies have identified dexmedetomidine, the potent α2-adrenoceptor agonist, and xenon, the noble gas, as effective anesthetic adjuvants that are both less neurotoxic to the developing brain, and also possess neuroprotective properties in neonatal and other settings of acute ongoing neurologic injury. Dexmedetomidine and xenon are effective anesthetic adjuvants that appear to be less neurotoxic than other existing agents and have the potential to be neuroprotective in the neonatal and pediatric settings. Although results from recent clinical trials and case reports have indicated the neuroprotective potential of xenon and dexmedetomidine, additional randomized clinical trials corroborating these studies are necessary. By reviewing both the existing preclinical and clinical evidence on the neuroprotective effects of dexmedetomidine and xenon, we hope to provide insight into the potential clinical efficacy of these agents in the management of pediatric surgical patients.

Survival after long-term isoflurane sedation as opposed to intravenous sedation in critically ill surgical patients: Retrospective analysis

BACKGROUND

Isoflurane has shown better control of intensive care sedation than propofol or midazolam and seems to be a useful alternative. However, its effect on survival remains unclear.

OBJECTIVE

The objective of this study is to compare mortality after sedation with either isoflurane or propofol/midazolam.

DESIGN

A retrospective analysis of data in a hospital database for a cohort of consecutive patients.

SETTING

Sixteen-bed interdisciplinary surgical ICU of a German university hospital.

PATIENTS

Consecutive cohort of 369 critically ill surgical patients defined within the database of the hospital information system. All patients were continuously ventilated and sedated for more than 96 h between 1 January 2005 and 31 December 2010. After excluding 169 patients (93 >79 years old, 10 <40 years old, 46 mixed sedation, 20 lost to follow-up), 200 patients were studied, 72 after isoflurane and 128 after propofol/midazolam.

INTERVENTIONS

Sedation with isoflurane using the AnaConDa system compared with intravenous sedation with propofol or midazolam.

MAIN OUTCOME MEASURES

Hospital mortality (primary) and 365-day mortality (secondary) were compared with the Kaplan-Meier analysis and a log-rank test. Adjusted odds ratios (ORs) [with 95% confidence interval (95% CI)] were calculated by logistic regression analyses to determine the risk of death after isoflurane sedation.

RESULTS

After sedation with isoflurane, the in-hospital mortality and 365-day mortality were significantly lower than after propofol/midazolam sedation: 40 versus 63% (P = 0.005) and 50 versus 70% (P = 0.013), respectively. After adjustment for potential confounders (coronary heart disease, chronic obstructive pulmonary disease, acute renal failure, creatinine, age and Simplified Acute Physiology Score II), patients after isoflurane were at a lower risk of death during their hospital stay (OR 0.35; 95% CI 0.18 to 0.68, P = 0.002) and within the first 365 days (OR 0.41; 95% CI 0.21 to 0.81, P = 0.010).

CONCLUSION

Compared with propofol/midazolam sedation, long-term sedation with isoflurane seems to be well tolerated in this group of critically ill patients after surgery.

Evidence and consensus based guideline for the management of delirium, analgesia, and sedation in intensive care medicine. Revision 2015 (DAS-Guideline 2015) - short version

In 2010, under the guidance of the DGAI (German Society of Anaesthesiology and Intensive Care Medicine) and DIVI (German Interdisciplinary Association for Intensive Care and Emergency Medicine), twelve German medical societies published the “Evidence- and Consensus-based Guidelines on the Management of Analgesia, Sedation and Delirium in Intensive Care”. Since then, several new studies and publications have considerably increased the body of evidence, including the new recommendations from the American College of Critical Care Medicine (ACCM) in conjunction with Society of Critical Care Medicine (SCCM) and American Society of Health-System Pharmacists (ASHP) from 2013. For this update, a major restructuring and extension of the guidelines were needed in order to cover new aspects of treatment, such as sleep and anxiety management. The literature was systematically searched and evaluated using the criteria of the Oxford Center of Evidence Based Medicine. The body of evidence used to formulate these recommendations was reviewed and approved by representatives of 17 national societies. Three grades of recommendation were used as follows: Grade “A” (strong recommendation), Grade “B” (recommendation) and Grade “0” (open recommendation). The result is a comprehensive, interdisciplinary, evidence and consensus-based set of level 3 guidelines. This publication was designed for all ICU professionals, and takes into account all critically ill patient populations. It represents a guide to symptom-oriented prevention, diagnosis, and treatment of delirium, anxiety, stress, and protocol-based analgesia, sedation, and sleep-management in intensive care medicine.

Xenon Blocks Neuronal Injury Associated with Decompression

Despite state-of-the-art hyperbaric oxygen (HBO) treatment, about 30% of patients suffering neurologic decompression sickness (DCS) exhibit incomplete recovery. Since the mechanisms of neurologic DCS involve ischemic processes which result in excitotoxicity, it is likely that HBO in combination with an anti-excitotoxic treatment would improve the outcome in patients being treated for DCS. Therefore, in the present study, we investigated the effect of the noble gas xenon in an ex vivo model of neurologic DCS. Xenon has been shown to provide neuroprotection in multiple models of acute ischemic insults. Fast decompression compared to slow decompression induced an increase in lactate dehydrogenase (LDH), a well-known marker of sub-lethal cell injury. Post-decompression administration of xenon blocked the increase in LDH release induced by fast decompression. These data suggest that xenon could be an efficient additional treatment to HBO for the treatment of neurologic DCS.

Safety and feasibility of xenon as an adjuvant to sevoflurane anaesthesia in children undergoing interventional or diagnostic cardiac catheterization: study protocol for a randomised controlled trial

BACKGROUND

Xenon has minimal haemodynamic side effects when compared to volatile or intravenous anaesthetics. Moreover, in in vitro and in animal experiments, xenon has been demonstrated to convey cardio- and neuroprotective effects. Neuroprotection could be advantageous in paediatric anaesthesia as there is growing concern, based on both laboratory studies and retrospective human clinical studies, that anaesthetics may trigger an injury in the developing brain, resulting in long-lasting neurodevelopmental consequences. Furthermore, xenon-mediated neuroprotection could help to prevent emergence delirium/agitation. Altogether, the beneficial haemodynamic profile combined with its putative organ-protective properties could render xenon an attractive option for anaesthesia of children undergoing cardiac catheterization.

METHODS/DESIGN

In a phase-II, mono-centre, prospective, single-blind, randomised, controlled study, we will test the hypothesis that the administration of 50% xenon as an adjuvant to general anaesthesia with sevoflurane in children undergoing elective cardiac catheterization is safe and feasible. Secondary aims include the evaluation of haemodynamic parameters during and after the procedure, emergence characteristics, and the analysis of peri-operative neuro-cognitive function. A total of 40 children ages 4 to 12 years will be recruited and randomised into two study groups, receiving either a combination of sevoflurane and xenon or sevoflurane alone.

DISCUSSION

Children undergoing diagnostic or interventional cardiac catheterization are a vulnerable patient population, one particularly at risk for intra-procedural haemodynamic instability. Xenon provides remarkable haemodynamic stability and potentially has cardio- and neuroprotective properties. Unfortunately, evidence is scarce on the use of xenon in the paediatric population. Our pilot study will therefore deliver important data required for prospective future clinical trials.

TRIAL REGISTRATION

EudraCT: 2014-002510-23 (5 September 2014).

Radiation dose and image quality in K-edge subtraction computed tomography of lung in vivo

K-edge subtraction computed tomography (KES-CT) allows simultaneous imaging of both structural features and regional distribution of contrast elements inside an organ. Using this technique, regional lung ventilation and blood volume distributions can be measured experimentally in vivo. In order for this imaging technology to be applicable in humans, it is crucial to minimize exposure to ionizing radiation with little compromise in image quality. The goal of this study was to assess the changes in signal-to-noise ratio (SNR) of KES-CT lung images as a function of radiation dose. The experiments were performed in anesthetized and ventilated rabbits using inhaled xenon gas in O2 at two concentrations: 20% and 70%. Radiation dose, defined as air kerma (Ka), was measured free-in-air and in a 16 cm polymethyl methacrylate phantom with a cylindrical ionization chamber. The dose free-in-air was varied from 2.7 mGy to 8.0 Gy. SNR in the images of xenon in air spaces was above the Rose criterion (SNR > 5) when Ka was over 400 mGy with 20% xenon, and over 40 mGy with 70% xenon. Although in human thorax attenuation is higher, based on these findings it is estimated that, by optimizing the imaging sequence and reconstruction algorithms, the radiation dose could be further reduced to clinically acceptable levels.

Feasibility and cardiac safety of inhaled xenon in combination with therapeutic hypothermia following out-of-hospital cardiac arrest

OBJECTIVES

Preclinical studies reveal the neuroprotective properties of xenon, especially when combined with hypothermia. The purpose of this study was to investigate the feasibility and cardiac safety of inhaled xenon treatment combined with therapeutic hypothermia in out-of-hospital cardiac arrest patients.

DESIGN

An open controlled and randomized single-centre clinical drug trial (clinicaltrials.gov NCT00879892).

SETTING

A multipurpose ICU in university hospital.

PATIENTS

Thirty-six adult out-of-hospital cardiac arrest patients (18-80 years old) with ventricular fibrillation or pulseless ventricular tachycardia as initial cardiac rhythm.

INTERVENTIONS

Patients were randomly assigned to receive either mild therapeutic hypothermia treatment with target temperature of 33°C (mild therapeutic hypothermia group, n=18) alone or in combination with xenon by inhalation, to achieve a target concentration of at least 40% (Xenon+mild therapeutic hypothermia group, n=18) for 24 hours. Thirty-three patients were evaluable (mild therapeutic hypothermia group, n=17; Xenon+mild therapeutic hypothermia group, n=16).

MEASUREMENTS AND MAIN RESULTS

Patients were treated and monitored according to the Utstein protocol. The release of troponin-T was determined at arrival to hospital and at 24, 48, and 72 hours after out-of-hospital cardiac arrest. The median end-tidal xenon concentration was 47% and duration of the xenon inhalation was 25.5 hours. The frequency of serious adverse events, including inhospital mortality, status epilepticus, and acute kidney injury, was similar in both groups and there were no unexpected serious adverse reactions to xenon during hospital stay. In addition, xenon did not induce significant conduction, repolarization, or rhythm abnormalities. Median dose of norepinephrine during hypothermia was lower in xenon-treated patients (mild therapeutic hypothermia group=5.30 mg vs Xenon+mild therapeutic hypothermia group=2.95 mg, p=0.06). Heart rate was significantly lower in Xenon+mild therapeutic hypothermia patients during hypothermia (p=0.04). Postarrival incremental change in troponin-T at 72 hours was significantly less in the Xenon+mild therapeutic hypothermia group (p=0.04).

CONCLUSIONS

Xenon treatment in combination with hypothermia is feasible and has favorable cardiac features in survivors of out-of-hospital cardiac arrest.

XENON in medical area: emphasis on neuroprotection in hypoxia and anesthesia

Xenon is a medical gas capable of establishing neuroprotection, inducing anesthesia as well as serving in modern laser technology and nuclear medicine as a contrast agent. In spite of its high cost, its lack of side effects, safe cardiovascular and organoprotective profile and effective neuroprotective role after hypoxic-ischemic injury (HI) favor its applications in clinics. Xenon performs its anesthetic and neuroprotective functions through binding to glycine site of glutamatergic N-methyl-D-aspartate (NMDA) receptor competitively and blocking it. This blockage inhibits the overstimulation of NMDA receptors, thus preventing their following downstream calcium accumulating cascades. Xenon is also used in combination therapies together with hypothermia or sevoflurane. The neuroprotective effects of xenon and hypothermia cooperate synergistically whether they are applied synchronously or asynchronously. Distinguishing properties of Xenon promise for innovations in medical gas field once further studies are fulfilled and Xenon’s high cost is overcome.

Worsening respiratory function in mechanically ventilated intensive care patients: feasibility and value of xenon-enhanced dual energy CT

OBJECTIVES

To evaluate the feasibility and incremental diagnostic value of xenon-enhanced dual-energy CT in mechanically ventilated intensive care patients with worsening respiratory function.

METHODS

The study was performed in 13 mechanically ventilated patients with severe pulmonary conditions (acute respiratory distress syndrome (ARDS), n=5; status post lung transplantation, n=5; other, n=3) and declining respiratory function. CT scans were performed using a dual-source CT scanner at an expiratory xenon concentration of 30%. Both ventilation images (Xe-DECT) and standard CT images were reconstructed from a single CT scan. Findings were recorded for Xe-DECT and standard CT images separately. Ventilation defects on xenon images were matched to morphological findings on standard CT images and incremental diagnostic information of xenon ventilation images was recorded if present.

RESULTS

Mean xenon consumption was 2.95 l per patient. No adverse events occurred under xenon inhalation. In the visual CT analysis, the Xe-DECT ventilation defects matched with pathologic changes in lung parenchyma seen in the standard CT images in all patients. Xe-DECT provided additional diagnostic findings in 4/13 patients. These included preserved ventilation despite early pneumonia (n=1), more confident discrimination between a large bulla and pneumothorax (n=1), detection of an airway-to-pneumothorax fistula (n=1) and exclusion of a suspected airway-to-mediastinum fistula (n=1). In all 4 patients, the additional findings had a substantial impact on patients' management.

CONCLUSIONS

Xenon-enhanced DECT is safely feasible and can add relevant diagnostic information in mechanically ventilated intensive care patients with worsening respiratory function.

Prothrombolytic action of normobaric oxygen given alone or in combination with recombinant tissue-plasminogen activator in a rat model of thromboembolic stroke

The potential benefit of 100 vol% normobaric oxygen (NBO) for the treatment of acute ischemic stroke patients is still a matter of debate. To advance this critical question, we studied the effects of intraischemic normobaric oxygen alone or in combination with recombinant tissue-plasminogen activator (rtPA) on cerebral blood flow and ischemic brain damage and swelling in a clinically relevant rat model of thromboembolic stroke. We show that NBO provides neuroprotection by achieving cerebral blood flow restoration equivalent to 0.9 mg/kg rtPA through probable direct interaction and facilitation of the fibrinolytic properties of endogenous tPA. In contrast, combined NBO and rtPA has no neuroprotective effect on ischemic brain damage despite producing cerebral blood flow restoration. These results 1) by providing a new mechanism of action of NBO highlight together with previous findings the way by which intraischemic NBO shows beneficial action; 2) suggest that NBO could be an efficient primary care therapeutic intervention for patients eligible for rtPA therapy; 3) indicate that NBO could be an interesting alternative for patients not eligible for rtPA therapy; and 4) caution the use of NBO in combination with rtPA in acute stroke patients.

Assessing the depth of hypnosis of xenon anaesthesia with the EEG

Xenon was approved as an inhaled anaesthetic in Germany in 2005 and in other countries of the European Union in 2007. Owing to its low blood/gas partition coefficient, xenons effects on the central nervous system show a fast onset and offset and, even after long xenon anaesthetics, the wake-up times are very short. The aim of this study was to examine which electroencephalogram (EEG) stages are reached during xenon application and whether these stages can be identified by an automatic EEG classification. Therefore, EEG recordings were performed during xenon anaesthetics (EEG monitor: Narcotrend®). A total of 300 EEG epochs were assessed visually with regard to the EEG stages. These epochs were also classified automatically by the EEG monitor Narcotrend® using multivariate algorithms. There was a high correlation between visual and automatic classification (Spearman's rank correlation coefficient r=0.957, prediction probability Pk=0.949). Furthermore, it was observed that very deep stages of hypnosis were reached which are characterised by EEG activity in the low frequency range (delta waves). The burst suppression pattern was not seen. In deep hypnosis, in contrast to the xenon EEG, the propofol EEG was characterised by a marked superimposed higher frequency activity. To ensure an optimised dosage for the single patient, anaesthetic machines for xenon should be combined with EEG monitoring. To date, only a few anaesthetic machines for xenon are available. Because of the high price of xenon, new and further developments of machines focus on optimizing xenon consumption.

Analgesia and sedation after pediatric cardiac surgery

In recent years, the importance of appropriate intra-operative anesthesia and analgesia during cardiac surgery has become recognized as a factor in postoperative recovery. This includes the early perioperative management of the neonate undergoing radical surgery and more recently the care surrounding fast-track and ultra fast-track surgery. However, outside these areas, relatively little attention has focused on postoperative sedation and analgesia within the pediatric intensive care unit (PICU). This reflects perceived priorities of the primary disease process over the supporting structure of PICU, with a generic approach to sedation and analgesia that can result in additional morbidities and delayed recovery. Management of the marginal patient requires optimisation of not only cardiac and other attendant pathophysiology, but also every aspect of supportive care. Individualized sedation and analgesia strategies, starting in the operating theater and continuing through to hospital discharge, need to be regarded as an important aspect of perioperative care, to speed the process of recovery.

[Functioning of the anaesthetic conserving device: aspects to consider for use in inhalational sedation]

The new anaesthetic conserving device (ACD) allows the use of isoflurane and sevoflurane without classical anaesthesia workstations. Volatile anaesthetic exhaled by the patient is absorbed by a reflector and released to the patient during the next inspiration. Liquid anaesthetic is delivered via a syringe pump. Currently the use of the ACD is spreading among European intensive care units (ICU). This article focuses on the functioning of the device and on particularities which are important to consider. The ACD constantly reflects 90% of the exhaled anaesthetic back to the patient, but if one exhaled breath contains more than 10 ml of anaesthetic vapour (e.g. >1 vol% in 1,000 ml), the capacity of the reflector will be exceeded and relatively more anaesthetic will be lost to the patient. This spill over decreases efficiency but it also contributes to safety as very high concentrations are averted. Compared to classical anaesthesia systems the ACD used in conjunction with ICU ventilators offers advantages in the ICU setting: investment costs are low, carbon dioxide absorbent is not needed, breathing comfort is higher, anaesthetic consumption is low (equal to an anaesthesia circuit with a fresh gas flow of approximately 1 l/min) and anaesthetic concentrations can be controlled very quickly (increased by small boluses and decreased by removal of the ACD). On the other hand, case costs are higher (single patient use) and a dead space of 100 ml is added. There are pitfalls: by a process called auto-pumping, expansion of bubbles inside the syringe may lead to uncontrolled anaesthetic delivery. Auto-pumping is provoked by high positioning of the syringe pump, heat and prior cooling of the liquid anaesthetic. Inherent to the device is an early inspiratory concentration peak and an end-inspiratory dip which may mislead commonly used gas monitors. Workplace concentrations can be minimized by proper handling, a sufficient turnover of room air is important and gas from the expiration port of the ventilator should be scavenged. Inhalational compared to intravenous ICU sedation offers the advantages of better control of the sedation level, online drug monitoring, no accumulation in patients with renal or hepatic insufficiency and bronchodilation. With a lowered opioid dose spontaneous breathing and intestinal motility are well preserved. A clinical algorithm for the care of patients with respiratory insufficiency including inhalational sedation is proposed. Inhalational sedation with isoflurane has been widely used for more than 20 years in many countries and even for periods of up to several weeks. In the German S3 guidelines for the management of analgesia, sedation and delirium in intensive care (Martin et al. 2010), inhalational sedation is mentioned as an alternative sedation method for patients ventilated via an endotracheal tube or a tracheal cannula. Nevertheless, isoflurane is not officially licensed for ICU sedation and its use is under the responsibility of the prescribing physician.

Sedation management in Australian and New Zealand intensive care units: doctors' and nurses' practices and opinions

OBJECTIVE

To explore the use of sedatives and analgesics, tools for scoring level of sedation, sedation and pain protocols, and daily interruptions in sedation in Australian and New Zealand intensive care units and to examine doctors' and nurses' opinions about the sedation management of critically ill patients.

METHODS

A cross-sectional Internet-based survey design was used. In total, 2146 members of professional critical care organizations in Australia and New Zealand were e-mailed the survey during a 4-month period in 2006 through 2007.

RESULTS

Of 348 members (16% response rate) who accessed the survey, 246 (71%) completed all sections. Morphine, fentanyl, midazolam, and propofol were the most commonly used medicines. Newer medicines, such as dexmedetomidine and remifentanil, and inhalant medications, such as nitrous oxide and isoflurane, were rarely used by most respondents. Respondents used protocols to manage sedatives (54%) and analgesics (51%), and sedation assessment tools were regularly used by 72%. A total of 62% reported daily interruption of sedation; 23% used daily interruption for more than 75% of patients. A disparity was evident between respondents' opinions on how deeply patients were usually sedated in practice and how deeply patients should ideally be sedated.

CONCLUSIONS

Newer medications are used much less than are traditional sedatives and analgesics. Sedation protocols are increasingly used in Australasia, despite equivocal evidence supporting their use. Similarly, daily interruption of sedation is common in management of patients receiving mechanical ventilation. Research is needed to explore contextual and personal factors that may affect sedation management.

Evidence and consensus-based German guidelines for the management of analgesia, sedation and delirium in intensive care--short version

Targeted monitoring of analgesia, sedation and delirium, as well as their appropriate management in critically ill patients is a standard of care in intensive care medicine. With the undisputed advantages of goal-oriented therapy established, there was a need to develop our own guidelines on analgesia and sedation in intensive care in Germany and these were published as 2(nd) Generation Guidelines in 2005. Through the dissemination of these guidelines in 2006, use of monitoring was shown to have improved from 8 to 51% and the use of protocol-based approaches increased to 46% (from 21%). Between 2006-2009, the existing guidelines from the DGAI (Deutsche Gesellschaft für Anästhesiologie und Intensivmedizin) and DIVI (Deutsche Interdisziplinäre Vereinigung für Intensiv- und Notfallmedizin) were developed into 3(rd) Generation Guidelines for the securing and optimization of quality of analgesia, sedation and delirium management in the intensive care unit (ICU). In collaboration with another 10 professional societies, the literature has been reviewed using the criteria of the Oxford Center of Evidence Based Medicine. Using data from 671 reference works, text, diagrams and recommendations were drawn up. In the recommendations, Grade "A" (very strong recommendation), Grade "B" (strong recommendation) and Grade "0" (open recommendation) were agreed. As a result of this process we now have an interdisciplinary and consensus-based set of 3(rd) Generation Guidelines that take into account all critically illness patient populations. The use of protocols for analgesia, sedation and treatment of delirium are repeatedly demonstrated. These guidelines offer treatment recommendations for the ICU team. The implementation of scores and protocols into routine ICU practice is necessary for their success.

Therapeutic antioxidant medical gas

Medical gases are pharmaceutical gaseous molecules which offer solutions to medical needs and include traditional gases, such as oxygen and nitrous oxide, as well as gases with recently discovered roles as biological messenger molecules, such as carbon monoxide, nitric oxide and hydrogen sulphide. Medical gas therapy is a relatively unexplored field of medicine; however, a recent increasing in the number of publications on medical gas therapies clearly indicate that there are significant opportunities for use of gases as therapeutic tools for a variety of disease conditions. In this article, we review the recent advances in research on medical gases with antioxidant properties and discuss their clinical applications and therapeutic properties.

Xenon alters right ventricular function

BACKGROUND

In contrast to other volatile anesthetics, xenon produces less cardiovascular depression with fewer fluctuations of various hemodynamic parameters, but reduces cardiac output (CO) in vivo. Besides an increase in left ventricular afterload and reduction of heart rate, an impairment of the right ventricular function might be an additional pathophysiological mechanism for the reduction of CO. Therefore, we used an animal model to study the effects of xenon as a supplemental anesthetic on right ventricular function, especially right ventricular afterload.

METHODS

Right ventricular function was monitored with a volumetric pulmonary artery catheter in 11 pigs during general anesthesia with thiopental. Six animals received additional 70% (volume) xenon (equivalent to 0.55 MAC minimum alveolar concentration). Parameters for systolic function, afterload, and preload were calculated at baseline and during 50 min of xenon application, and in a corresponding control group. Significant differences were detected by multivariate analyses of variance for repeated measures.

RESULTS

Xenon reduced CO on average by 30% and increased pulmonary arterial elastance by 60%, which led to a reduction of the right ventricular ejection fraction by 25%. Whereas right ventricular preload remained stable, maximal slope of pulmonary artery pressure and the right ventricular elastance increased. No effect on the ratio of stroke work and end-diastolic volume was found.

CONCLUSION

The reduction in CO during xenon anesthesia was partly due to an impairment of the right ventricular function, mainly caused by an increased afterload, without an impairment of systolic ventricular function.

A cryogenic machine for selective recovery of xenon from breathing system waste gases

BACKGROUND

Xenon has many characteristics that make it very attractive as an anesthetic and therapeutic drug. Unfortunately, the supply of xenon is fixed, and therefore reclamation and recovery from even the most efficient breathing circuits is desirable. We built and evaluated a cryogenic device to recover xenon from waste anesthetic gases.

METHODS

Xenon was selectively frozen to -139.2 degrees C from test gas mixtures at ambient pressure (STP). The machine ran on standard 240 V 13 A electrical current without refrigerants that required replenishing, e.g., liquid nitrogen. A wide range of xenon/oxygen mixtures were processed over a range of freezing chamber temperatures. Efflux gas and thawed reclaimed xenon were collected separately. Xenon purity and yield (fraction recovered) were measured and calculated on each occasion.

RESULTS

Gas was processed at 300 mL/min, and the operating temperature was -139.2 (0.096) degrees C [Mean (sd)]. Purity and yield were >90% and >70% for gas mixtures containing > or =20% xenon, increasing to >95% and >85%, respectively, with an input gas xenon fraction > or =40%. Efficiency improved linearly with reducing temperature.

CONCLUSIONS

Xenon of high purity (>90%) and yield (>70%) for such a machine was recovered from all gas mixtures containing > or =20% xenon. The operating temperature of the freezing chamber is a major influence on the efficiency of recovery.

Economic evaluation of sustained sedation/analgesia in the intensive care unit

Lorazepam, midazolam, propofol and opioids are the primary agents that are used for sustained sedation and analgesia of critically ill patients. The choice of agent depends on safety profiles, expected outcomes, cost, patient characteristics and clinical experience. Few studies have comparatively evaluated the sedatives in terms of cost. Many factors, aside from drug costs, influence the total cost of sedation in the intensive care unit. This article reviews the cost parameters of intensive care unit sedation that are specific to the characteristics of commonly used sedatives and analgesics, evaluates economic studies and cost models, summarises alternative methods of sedation and analgesia, and provides practical recommendations for methods of cost containment, including daily sedation interruption, sedation monitoring and protocol implementation.

Xenon measurement in breathing systems: a comparison of ultrasonic and thermal conductivity methods

Xenon is an anaesthetic and possibly neuroprotective gas that is impossible to measure using conventional anaesthetic gas analysers. We compared the performance of two commissioned xenon analysers using ultrasonic and thermal conductivity principles against a reference method of laser refractometry. An experimental gas circuit was constructed and xenon concentrations compared over a range of 0-100% in oxygen. Eighty-two paired measurements were made comparing the experimental methods with laser refractometry. The ultrasonic method displayed good agreement with laser refractometry, with a mean difference of - 0.74% and two standard deviation limits of agreement of + 1.08% to - 2.56%. The agreement between laser refractometry and thermal conductivity was poor, the mean difference being - 5.37%, with two standard deviation limits of agreement of + 0.6% to - 11.3%. The ultrasonic method for measuring xenon concentrations can be used in breathing circuits. The thermal conductivity instrument may need further development.

Inhalational anaesthetics in the ICU: theory and practice of inhalational sedation in the ICU, economics, risk-benefit

ICU sedation poses many problems. The action and side-effects of intravenous drugs in the severely ill patient population of an ICU are difficult to control. The incidence of post-traumatic stress disorder after long-term sedation is high. The recent focus on propofol infusion syndrome entails restrictions in the use of this drug. On the other hand, volatile anaesthetics very selectively suppress consciousness but leave many autonomic functions intact. In the absence of perception and disturbed information processing the number of adverse experiences should be lower, leading to a better psychological outcome. Respiration and intestinal motility are not depressed, facilitating modern therapeutic concepts such as early enteral feeding and augmentation of spontaneous breathing. Awakening after inhalational ICU sedation is quick and predictable, extubation can be planned and organized, and the time during which the patient needs very close observation will be short. Technological advances have greatly simplified the application of inhalational anaesthetics. New anaesthesia ventilators offer ventilatory modes and high flow generation comparable to ICU ventilators. However, they are not yet licensed for stand-alone use. The introduction of a volatile anaesthetic reflection filter for the first time enables the concept of inhalational sedation to be performed with very little effort by many ICUs. This 'anaesthetic conserving device' (AnaConDa) is connected between the patient and a normal ICU ventilator, and it retains 90% of the volatile anaesthetic inside the patient just like a heat and moisture exchanger. In this chapter possible advantages of the new concept and the choice of the inhalational agent are discussed. The technical prerequisites are explained, and the practice and pitfalls of inhalational ICU sedation in general and when using the AnaConDa are described in detail.

Xenon: from stranger to guardian

PURPOSE OF REVIEW

Xenon anaesthesia has recently been evaluated in large-scale clinical trials that have demonstrated xenon's safe and effective clinical profile. Despite the relatively high cost of xenon anaesthesia, xenon has clear clinical advantages over other current anaesthetics.

RECENT FINDINGS

Xenon possesses distinct neuroprotective and cardioprotective properties in addition to a favourable pharmacokinetic profile and analgesic effects. In addition, xenon exerts preconditioning effects in the heart and may offer postoperative, as well as intraoperative, cardio and neuroprotection.

SUMMARY

Further clinical trials are required to evaluate the role that xenon can play in the perioperative period.

Cardiovascular effects of xenon and nitrous oxide in patients during fentanyl-midazolam anaesthesia*

Xenon anaesthesia appears to have minimal haemodynamic effects. The purpose of this randomised prospective study was to compare the cardiovascular effects of xenon and nitrous oxide in patients with known ischaemic heart disease. In 20 patients who were due to undergo coronary artery bypass graft surgery, 30 min following induction of anaesthesia with fentanyl 30 microg x kg(-1) and midazolam 0.1 mg x kg(-1) but prior to the start of surgery, xenon or nitrous oxide 60% was administered for 15 min. The results showed that xenon caused a minimal decrease in the mean arterial pressure (from 81 (7) to 75 (8) mmHg, mean (SD)), but did not affect the systolic function of the left ventricle, as demonstrated by unchanged left ventricular stroke work index (LVSWI) and the fractional area change of the left ventricle (FAC) derived from transoesophageal echocardiography (TOE). However, in contrast, nitrous oxide was found to decrease the mean arterial pressure (from 81 (8) to 69 (7) mmHg), the LVSWI, and the FAC. The cardiac index, central venous and pulmonary artery occlusion pressures, systemic and pulmonary vascular resistances, and the TOE-derived E/A ratio through the mitral valve were unchanged by xenon or nitrous oxide. We conclude that xenon provides improved haemodynamic stability compared with nitrous oxide, conserving the left ventricular systolic function.

Nitrogen Diffusion into Closed Anesthesia Systems

OBJECTIVE

In order to reduce losses of gases through plastic components and to reduce nitrogen accummulation during closed system anaesthesia we investigated either 10 sets of anaesthetic tubing made of silicon as used in standard clinical practice and 10 sets made of latex, which are not used anymore due to concerns about latex allergies. The results were compared to each one set made of conventional industrial rubber.

METHODS

Anaesthetic tubings were connected to ventilators with low fresh gas losses, suitable for closed system anaesthesia. For nitrogen measurements, a mass spectrometer was used. The fresh gas flow was set to exceed losses by leakages and the amount of gases, extracted from the system by the mass spectrometer.

RESULTS

Highest accumulation of nitrogen was found using tubings made of silicone.

CONCLUSION

If closed anaesthetic systems in the future will be used in intensive care therapy or in case of long lasting procedures in which closed system anaesthesia is proceeded, materials other than silicone should be investigated to avoid regular purging of system and consecutive losses of gas mixtures.

Xenon: elemental anaesthesia in clinical practice

The 'noble' gases have been known to have anaesthetic properties for 50 years yet only recently has their application become a clinical reality. In this review we describe the preclinical and clinical studies that have led to a resurgence of interest in the use of the element xenon as an anaesthetic. Furthermore, we highlight specific areas where xenon demonstrates advantages over other anaesthetics, including safety, beneficial pharmacokinetics, cardiovascular stability, analgesia and neuroprotection.